| /*! |
| Types and routines specific to lazy DFAs. |
| |
| This module is the home of [`hybrid::dfa::DFA`](DFA). |
| |
| This module also contains a [`hybrid::dfa::Builder`](Builder) and a |
| [`hybrid::dfa::Config`](Config) for configuring and building a lazy DFA. |
| */ |
| |
| use core::{iter, mem::size_of}; |
| |
| use alloc::vec::Vec; |
| |
| use crate::{ |
| hybrid::{ |
| error::{BuildError, CacheError, StartError}, |
| id::{LazyStateID, LazyStateIDError}, |
| search, |
| }, |
| nfa::thompson, |
| util::{ |
| alphabet::{self, ByteClasses, ByteSet}, |
| determinize::{self, State, StateBuilderEmpty, StateBuilderNFA}, |
| empty, |
| prefilter::Prefilter, |
| primitives::{PatternID, StateID as NFAStateID}, |
| search::{ |
| Anchored, HalfMatch, Input, MatchError, MatchKind, PatternSet, |
| }, |
| sparse_set::SparseSets, |
| start::{self, Start, StartByteMap}, |
| }, |
| }; |
| |
| /// The minimum number of states that a lazy DFA's cache size must support. |
| /// |
| /// This is checked at time of construction to ensure that at least some small |
| /// number of states can fit in the given capacity allotment. If we can't fit |
| /// at least this number of states, then the thinking is that it's pretty |
| /// senseless to use the lazy DFA. More to the point, parts of the code do |
| /// assume that the cache can fit at least some small number of states. |
| const MIN_STATES: usize = SENTINEL_STATES + 2; |
| |
| /// The number of "sentinel" states that get added to every lazy DFA. |
| /// |
| /// These are special states indicating status conditions of a search: unknown, |
| /// dead and quit. These states in particular also use zero NFA states, so |
| /// their memory usage is quite small. This is relevant for computing the |
| /// minimum memory needed for a lazy DFA cache. |
| const SENTINEL_STATES: usize = 3; |
| |
| /// A hybrid NFA/DFA (also called a "lazy DFA") for regex searching. |
| /// |
| /// A lazy DFA is a DFA that builds itself at search time. It otherwise has |
| /// very similar characteristics as a [`dense::DFA`](crate::dfa::dense::DFA). |
| /// Indeed, both support precisely the same regex features with precisely the |
| /// same semantics. |
| /// |
| /// Where as a `dense::DFA` must be completely built to handle any input before |
| /// it may be used for search, a lazy DFA starts off effectively empty. During |
| /// a search, a lazy DFA will build itself depending on whether it has already |
| /// computed the next transition or not. If it has, then it looks a lot like |
| /// a `dense::DFA` internally: it does a very fast table based access to find |
| /// the next transition. Otherwise, if the state hasn't been computed, then it |
| /// does determinization _for that specific transition_ to compute the next DFA |
| /// state. |
| /// |
| /// The main selling point of a lazy DFA is that, in practice, it has |
| /// the performance profile of a `dense::DFA` without the weakness of it |
| /// taking worst case exponential time to build. Indeed, for each byte of |
| /// input, the lazy DFA will construct as most one new DFA state. Thus, a |
| /// lazy DFA achieves worst case `O(mn)` time for regex search (where `m ~ |
| /// pattern.len()` and `n ~ haystack.len()`). |
| /// |
| /// The main downsides of a lazy DFA are: |
| /// |
| /// 1. It requires mutable "cache" space during search. This is where the |
| /// transition table, among other things, is stored. |
| /// 2. In pathological cases (e.g., if the cache is too small), it will run |
| /// out of room and either require a bigger cache capacity or will repeatedly |
| /// clear the cache and thus repeatedly regenerate DFA states. Overall, this |
| /// will tend to be slower than a typical NFA simulation. |
| /// |
| /// # Capabilities |
| /// |
| /// Like a `dense::DFA`, a single lazy DFA fundamentally supports the following |
| /// operations: |
| /// |
| /// 1. Detection of a match. |
| /// 2. Location of the end of a match. |
| /// 3. In the case of a lazy DFA with multiple patterns, which pattern matched |
| /// is reported as well. |
| /// |
| /// A notable absence from the above list of capabilities is the location of |
| /// the *start* of a match. In order to provide both the start and end of |
| /// a match, *two* lazy DFAs are required. This functionality is provided by a |
| /// [`Regex`](crate::hybrid::regex::Regex). |
| /// |
| /// # Example |
| /// |
| /// This shows how to build a lazy DFA with the default configuration and |
| /// execute a search. Notice how, in contrast to a `dense::DFA`, we must create |
| /// a cache and pass it to our search routine. |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// let dfa = DFA::new("foo[0-9]+")?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let expected = Some(HalfMatch::must(0, 8)); |
| /// assert_eq!(expected, dfa.try_search_fwd( |
| /// &mut cache, &Input::new("foo12345"))?, |
| /// ); |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[derive(Clone, Debug)] |
| pub struct DFA { |
| config: Config, |
| nfa: thompson::NFA, |
| stride2: usize, |
| start_map: StartByteMap, |
| classes: ByteClasses, |
| quitset: ByteSet, |
| cache_capacity: usize, |
| } |
| |
| impl DFA { |
| /// Parse the given regular expression using a default configuration and |
| /// return the corresponding lazy DFA. |
| /// |
| /// If you want a non-default configuration, then use the [`Builder`] to |
| /// set your own configuration. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// let dfa = DFA::new("foo[0-9]+bar")?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let expected = HalfMatch::must(0, 11); |
| /// assert_eq!( |
| /// Some(expected), |
| /// dfa.try_search_fwd(&mut cache, &Input::new("foo12345bar"))?, |
| /// ); |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[cfg(feature = "syntax")] |
| pub fn new(pattern: &str) -> Result<DFA, BuildError> { |
| DFA::builder().build(pattern) |
| } |
| |
| /// Parse the given regular expressions using a default configuration and |
| /// return the corresponding lazy multi-DFA. |
| /// |
| /// If you want a non-default configuration, then use the [`Builder`] to |
| /// set your own configuration. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// let dfa = DFA::new_many(&["[0-9]+", "[a-z]+"])?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let expected = HalfMatch::must(1, 3); |
| /// assert_eq!( |
| /// Some(expected), |
| /// dfa.try_search_fwd(&mut cache, &Input::new("foo12345bar"))?, |
| /// ); |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[cfg(feature = "syntax")] |
| pub fn new_many<P: AsRef<str>>(patterns: &[P]) -> Result<DFA, BuildError> { |
| DFA::builder().build_many(patterns) |
| } |
| |
| /// Create a new lazy DFA that matches every input. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// let dfa = DFA::always_match()?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let expected = HalfMatch::must(0, 0); |
| /// assert_eq!(Some(expected), dfa.try_search_fwd( |
| /// &mut cache, &Input::new(""))?, |
| /// ); |
| /// assert_eq!(Some(expected), dfa.try_search_fwd( |
| /// &mut cache, &Input::new("foo"))?, |
| /// ); |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn always_match() -> Result<DFA, BuildError> { |
| let nfa = thompson::NFA::always_match(); |
| Builder::new().build_from_nfa(nfa) |
| } |
| |
| /// Create a new lazy DFA that never matches any input. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, Input}; |
| /// |
| /// let dfa = DFA::never_match()?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// assert_eq!(None, dfa.try_search_fwd(&mut cache, &Input::new(""))?); |
| /// assert_eq!(None, dfa.try_search_fwd(&mut cache, &Input::new("foo"))?); |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn never_match() -> Result<DFA, BuildError> { |
| let nfa = thompson::NFA::never_match(); |
| Builder::new().build_from_nfa(nfa) |
| } |
| |
| /// Return a default configuration for a `DFA`. |
| /// |
| /// This is a convenience routine to avoid needing to import the [`Config`] |
| /// type when customizing the construction of a lazy DFA. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to build a lazy DFA that heuristically supports |
| /// Unicode word boundaries. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, MatchError, Input}; |
| /// |
| /// let re = DFA::builder() |
| /// .configure(DFA::config().unicode_word_boundary(true)) |
| /// .build(r"\b\w+\b")?; |
| /// let mut cache = re.create_cache(); |
| /// |
| /// // Since our haystack is all ASCII, the DFA search sees then and knows |
| /// // it is legal to interpret Unicode word boundaries as ASCII word |
| /// // boundaries. |
| /// let input = Input::new("!!foo!!"); |
| /// let expected = HalfMatch::must(0, 5); |
| /// assert_eq!(Some(expected), re.try_search_fwd(&mut cache, &input)?); |
| /// |
| /// // But if our haystack contains non-ASCII, then the search will fail |
| /// // with an error. |
| /// let input = Input::new("!!βββ!!"); |
| /// let expected = MatchError::quit(b'\xCE', 2); |
| /// assert_eq!(Err(expected), re.try_search_fwd(&mut cache, &input)); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn config() -> Config { |
| Config::new() |
| } |
| |
| /// Return a builder for configuring the construction of a `Regex`. |
| /// |
| /// This is a convenience routine to avoid needing to import the |
| /// [`Builder`] type in common cases. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to use the builder to disable UTF-8 mode |
| /// everywhere for lazy DFAs. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{hybrid::dfa::DFA, util::syntax, HalfMatch, Input}; |
| /// |
| /// let re = DFA::builder() |
| /// .syntax(syntax::Config::new().utf8(false)) |
| /// .build(r"foo(?-u:[^b])ar.*")?; |
| /// let mut cache = re.create_cache(); |
| /// |
| /// let input = Input::new(b"\xFEfoo\xFFarzz\xE2\x98\xFF\n"); |
| /// let expected = Some(HalfMatch::must(0, 9)); |
| /// let got = re.try_search_fwd(&mut cache, &input)?; |
| /// assert_eq!(expected, got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn builder() -> Builder { |
| Builder::new() |
| } |
| |
| /// Create a new cache for this lazy DFA. |
| /// |
| /// The cache returned should only be used for searches for this |
| /// lazy DFA. If you want to reuse the cache for another DFA, then |
| /// you must call [`Cache::reset`] with that DFA (or, equivalently, |
| /// [`DFA::reset_cache`]). |
| pub fn create_cache(&self) -> Cache { |
| Cache::new(self) |
| } |
| |
| /// Reset the given cache such that it can be used for searching with the |
| /// this lazy DFA (and only this DFA). |
| /// |
| /// A cache reset permits reusing memory already allocated in this cache |
| /// with a different lazy DFA. |
| /// |
| /// Resetting a cache sets its "clear count" to 0. This is relevant if the |
| /// lazy DFA has been configured to "give up" after it has cleared the |
| /// cache a certain number of times. |
| /// |
| /// Any lazy state ID generated by the cache prior to resetting it is |
| /// invalid after the reset. |
| /// |
| /// # Example |
| /// |
| /// This shows how to re-purpose a cache for use with a different DFA. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// let dfa1 = DFA::new(r"\w")?; |
| /// let dfa2 = DFA::new(r"\W")?; |
| /// |
| /// let mut cache = dfa1.create_cache(); |
| /// assert_eq!( |
| /// Some(HalfMatch::must(0, 2)), |
| /// dfa1.try_search_fwd(&mut cache, &Input::new("Δ"))?, |
| /// ); |
| /// |
| /// // Using 'cache' with dfa2 is not allowed. It may result in panics or |
| /// // incorrect results. In order to re-purpose the cache, we must reset |
| /// // it with the DFA we'd like to use it with. |
| /// // |
| /// // Similarly, after this reset, using the cache with 'dfa1' is also not |
| /// // allowed. |
| /// dfa2.reset_cache(&mut cache); |
| /// assert_eq!( |
| /// Some(HalfMatch::must(0, 3)), |
| /// dfa2.try_search_fwd(&mut cache, &Input::new("☃"))?, |
| /// ); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn reset_cache(&self, cache: &mut Cache) { |
| Lazy::new(self, cache).reset_cache() |
| } |
| |
| /// Returns the total number of patterns compiled into this lazy DFA. |
| /// |
| /// In the case of a DFA that contains no patterns, this returns `0`. |
| /// |
| /// # Example |
| /// |
| /// This example shows the pattern length for a DFA that never matches: |
| /// |
| /// ``` |
| /// use regex_automata::hybrid::dfa::DFA; |
| /// |
| /// let dfa = DFA::never_match()?; |
| /// assert_eq!(dfa.pattern_len(), 0); |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// And another example for a DFA that matches at every position: |
| /// |
| /// ``` |
| /// use regex_automata::hybrid::dfa::DFA; |
| /// |
| /// let dfa = DFA::always_match()?; |
| /// assert_eq!(dfa.pattern_len(), 1); |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// And finally, a DFA that was constructed from multiple patterns: |
| /// |
| /// ``` |
| /// use regex_automata::hybrid::dfa::DFA; |
| /// |
| /// let dfa = DFA::new_many(&["[0-9]+", "[a-z]+", "[A-Z]+"])?; |
| /// assert_eq!(dfa.pattern_len(), 3); |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn pattern_len(&self) -> usize { |
| self.nfa.pattern_len() |
| } |
| |
| /// Returns the equivalence classes that make up the alphabet for this DFA. |
| /// |
| /// Unless [`Config::byte_classes`] was disabled, it is possible that |
| /// multiple distinct bytes are grouped into the same equivalence class |
| /// if it is impossible for them to discriminate between a match and a |
| /// non-match. This has the effect of reducing the overall alphabet size |
| /// and in turn potentially substantially reducing the size of the DFA's |
| /// transition table. |
| /// |
| /// The downside of using equivalence classes like this is that every state |
| /// transition will automatically use this map to convert an arbitrary |
| /// byte to its corresponding equivalence class. In practice this has a |
| /// negligible impact on performance. |
| pub fn byte_classes(&self) -> &ByteClasses { |
| &self.classes |
| } |
| |
| /// Returns this lazy DFA's configuration. |
| pub fn get_config(&self) -> &Config { |
| &self.config |
| } |
| |
| /// Returns a reference to the underlying NFA. |
| pub fn get_nfa(&self) -> &thompson::NFA { |
| &self.nfa |
| } |
| |
| /// Returns the stride, as a base-2 exponent, required for these |
| /// equivalence classes. |
| /// |
| /// The stride is always the smallest power of 2 that is greater than or |
| /// equal to the alphabet length. This is done so that converting between |
| /// state IDs and indices can be done with shifts alone, which is much |
| /// faster than integer division. |
| fn stride2(&self) -> usize { |
| self.stride2 |
| } |
| |
| /// Returns the total stride for every state in this lazy DFA. This |
| /// corresponds to the total number of transitions used by each state in |
| /// this DFA's transition table. |
| fn stride(&self) -> usize { |
| 1 << self.stride2() |
| } |
| |
| /// Returns the memory usage, in bytes, of this lazy DFA. |
| /// |
| /// This does **not** include the stack size used up by this lazy DFA. To |
| /// compute that, use `std::mem::size_of::<DFA>()`. This also does not |
| /// include the size of the `Cache` used. |
| /// |
| /// This also does not include any heap memory used by the NFA inside of |
| /// this hybrid NFA/DFA. This is because the NFA's ownership is shared, and |
| /// thus not owned by this hybrid NFA/DFA. More practically, several regex |
| /// engines in this crate embed an NFA, and reporting the NFA's memory |
| /// usage in all of them would likely result in reporting higher heap |
| /// memory than is actually used. |
| pub fn memory_usage(&self) -> usize { |
| // The only thing that uses heap memory in a DFA is the NFA. But the |
| // NFA has shared ownership, so reporting its memory as part of the |
| // hybrid DFA is likely to lead to double-counting the NFA memory |
| // somehow. In particular, this DFA does not really own an NFA, so |
| // including it in the DFA's memory usage doesn't seem semantically |
| // correct. |
| 0 |
| } |
| } |
| |
| impl DFA { |
| /// Executes a forward search and returns the end position of the leftmost |
| /// match that is found. If no match exists, then `None` is returned. |
| /// |
| /// In particular, this method continues searching even after it enters |
| /// a match state. The search only terminates once it has reached the |
| /// end of the input or when it has entered a dead or quit state. Upon |
| /// termination, the position of the last byte seen while still in a match |
| /// state is returned. |
| /// |
| /// # Errors |
| /// |
| /// This routine errors if the search could not complete. This can occur |
| /// in a number of circumstances: |
| /// |
| /// * The configuration of the lazy DFA may permit it to "quit" the search. |
| /// For example, setting quit bytes or enabling heuristic support for |
| /// Unicode word boundaries. The default configuration does not enable any |
| /// option that could result in the lazy DFA quitting. |
| /// * The configuration of the lazy DFA may also permit it to "give up" |
| /// on a search if it makes ineffective use of its transition table |
| /// cache. The default configuration does not enable this by default, |
| /// although it is typically a good idea to. |
| /// * When the provided `Input` configuration is not supported. For |
| /// example, by providing an unsupported anchor mode. |
| /// |
| /// When a search returns an error, callers cannot know whether a match |
| /// exists or not. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to run a basic search. |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// let dfa = DFA::new("foo[0-9]+")?; |
| /// let mut cache = dfa.create_cache(); |
| /// let expected = HalfMatch::must(0, 8); |
| /// assert_eq!(Some(expected), dfa.try_search_fwd( |
| /// &mut cache, &Input::new("foo12345"))?, |
| /// ); |
| /// |
| /// // Even though a match is found after reading the first byte (`a`), |
| /// // the leftmost first match semantics demand that we find the earliest |
| /// // match that prefers earlier parts of the pattern over later parts. |
| /// let dfa = DFA::new("abc|a")?; |
| /// let mut cache = dfa.create_cache(); |
| /// let expected = HalfMatch::must(0, 3); |
| /// assert_eq!(Some(expected), dfa.try_search_fwd( |
| /// &mut cache, &Input::new("abc"))?, |
| /// ); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// # Example: specific pattern search |
| /// |
| /// This example shows how to build a lazy multi-DFA that permits searching |
| /// for specific patterns. |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// Anchored, HalfMatch, PatternID, Input, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().starts_for_each_pattern(true)) |
| /// .build_many(&["[a-z0-9]{6}", "[a-z][a-z0-9]{5}"])?; |
| /// let mut cache = dfa.create_cache(); |
| /// let haystack = "foo123"; |
| /// |
| /// // Since we are using the default leftmost-first match and both |
| /// // patterns match at the same starting position, only the first pattern |
| /// // will be returned in this case when doing a search for any of the |
| /// // patterns. |
| /// let expected = Some(HalfMatch::must(0, 6)); |
| /// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?; |
| /// assert_eq!(expected, got); |
| /// |
| /// // But if we want to check whether some other pattern matches, then we |
| /// // can provide its pattern ID. |
| /// let expected = Some(HalfMatch::must(1, 6)); |
| /// let input = Input::new(haystack) |
| /// .anchored(Anchored::Pattern(PatternID::must(1))); |
| /// let got = dfa.try_search_fwd(&mut cache, &input)?; |
| /// assert_eq!(expected, got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// # Example: specifying the bounds of a search |
| /// |
| /// This example shows how providing the bounds of a search can produce |
| /// different results than simply sub-slicing the haystack. |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// // N.B. We disable Unicode here so that we use a simple ASCII word |
| /// // boundary. Alternatively, we could enable heuristic support for |
| /// // Unicode word boundaries since our haystack is pure ASCII. |
| /// let dfa = DFA::new(r"(?-u)\b[0-9]{3}\b")?; |
| /// let mut cache = dfa.create_cache(); |
| /// let haystack = "foo123bar"; |
| /// |
| /// // Since we sub-slice the haystack, the search doesn't know about the |
| /// // larger context and assumes that `123` is surrounded by word |
| /// // boundaries. And of course, the match position is reported relative |
| /// // to the sub-slice as well, which means we get `3` instead of `6`. |
| /// let expected = Some(HalfMatch::must(0, 3)); |
| /// let got = dfa.try_search_fwd( |
| /// &mut cache, |
| /// &Input::new(&haystack[3..6]), |
| /// )?; |
| /// assert_eq!(expected, got); |
| /// |
| /// // But if we provide the bounds of the search within the context of the |
| /// // entire haystack, then the search can take the surrounding context |
| /// // into account. (And if we did find a match, it would be reported |
| /// // as a valid offset into `haystack` instead of its sub-slice.) |
| /// let expected = None; |
| /// let got = dfa.try_search_fwd( |
| /// &mut cache, |
| /// &Input::new(haystack).range(3..6), |
| /// )?; |
| /// assert_eq!(expected, got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[inline] |
| pub fn try_search_fwd( |
| &self, |
| cache: &mut Cache, |
| input: &Input<'_>, |
| ) -> Result<Option<HalfMatch>, MatchError> { |
| let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); |
| let hm = match search::find_fwd(self, cache, input)? { |
| None => return Ok(None), |
| Some(hm) if !utf8empty => return Ok(Some(hm)), |
| Some(hm) => hm, |
| }; |
| // We get to this point when we know our DFA can match the empty string |
| // AND when UTF-8 mode is enabled. In this case, we skip any matches |
| // whose offset splits a codepoint. Such a match is necessarily a |
| // zero-width match, because UTF-8 mode requires the underlying NFA |
| // to be built such that all non-empty matches span valid UTF-8. |
| // Therefore, any match that ends in the middle of a codepoint cannot |
| // be part of a span of valid UTF-8 and thus must be an empty match. |
| // In such cases, we skip it, so as not to report matches that split a |
| // codepoint. |
| // |
| // Note that this is not a checked assumption. Callers *can* provide an |
| // NFA with UTF-8 mode enabled but produces non-empty matches that span |
| // invalid UTF-8. But doing so is documented to result in unspecified |
| // behavior. |
| empty::skip_splits_fwd(input, hm, hm.offset(), |input| { |
| let got = search::find_fwd(self, cache, input)?; |
| Ok(got.map(|hm| (hm, hm.offset()))) |
| }) |
| } |
| |
| /// Executes a reverse search and returns the start of the position of the |
| /// leftmost match that is found. If no match exists, then `None` is |
| /// returned. |
| /// |
| /// # Errors |
| /// |
| /// This routine errors if the search could not complete. This can occur |
| /// in a number of circumstances: |
| /// |
| /// * The configuration of the lazy DFA may permit it to "quit" the search. |
| /// For example, setting quit bytes or enabling heuristic support for |
| /// Unicode word boundaries. The default configuration does not enable any |
| /// option that could result in the lazy DFA quitting. |
| /// * The configuration of the lazy DFA may also permit it to "give up" |
| /// on a search if it makes ineffective use of its transition table |
| /// cache. The default configuration does not enable this by default, |
| /// although it is typically a good idea to. |
| /// * When the provided `Input` configuration is not supported. For |
| /// example, by providing an unsupported anchor mode. |
| /// |
| /// When a search returns an error, callers cannot know whether a match |
| /// exists or not. |
| /// |
| /// # Example |
| /// |
| /// This routine is principally useful when used in |
| /// conjunction with the |
| /// [`nfa::thompson::Config::reverse`](crate::nfa::thompson::Config::reverse) |
| /// configuration. In general, it's unlikely to be correct to use both |
| /// `try_search_fwd` and `try_search_rev` with the same DFA since any |
| /// particular DFA will only support searching in one direction with |
| /// respect to the pattern. |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// nfa::thompson, |
| /// hybrid::dfa::DFA, |
| /// HalfMatch, Input, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .thompson(thompson::Config::new().reverse(true)) |
| /// .build("foo[0-9]+")?; |
| /// let mut cache = dfa.create_cache(); |
| /// let expected = HalfMatch::must(0, 0); |
| /// assert_eq!( |
| /// Some(expected), |
| /// dfa.try_search_rev(&mut cache, &Input::new("foo12345"))?, |
| /// ); |
| /// |
| /// // Even though a match is found after reading the last byte (`c`), |
| /// // the leftmost first match semantics demand that we find the earliest |
| /// // match that prefers earlier parts of the pattern over latter parts. |
| /// let dfa = DFA::builder() |
| /// .thompson(thompson::Config::new().reverse(true)) |
| /// .build("abc|c")?; |
| /// let mut cache = dfa.create_cache(); |
| /// let expected = HalfMatch::must(0, 0); |
| /// assert_eq!(Some(expected), dfa.try_search_rev( |
| /// &mut cache, &Input::new("abc"))?, |
| /// ); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// # Example: UTF-8 mode |
| /// |
| /// This examples demonstrates that UTF-8 mode applies to reverse |
| /// DFAs. When UTF-8 mode is enabled in the underlying NFA, then all |
| /// matches reported must correspond to valid UTF-8 spans. This includes |
| /// prohibiting zero-width matches that split a codepoint. |
| /// |
| /// UTF-8 mode is enabled by default. Notice below how the only zero-width |
| /// matches reported are those at UTF-8 boundaries: |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// nfa::thompson, |
| /// HalfMatch, Input, MatchKind, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .thompson(thompson::Config::new().reverse(true)) |
| /// .build(r"")?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// // Run the reverse DFA to collect all matches. |
| /// let mut input = Input::new("☃"); |
| /// let mut matches = vec![]; |
| /// loop { |
| /// match dfa.try_search_rev(&mut cache, &input)? { |
| /// None => break, |
| /// Some(hm) => { |
| /// matches.push(hm); |
| /// if hm.offset() == 0 || input.end() == 0 { |
| /// break; |
| /// } else if hm.offset() < input.end() { |
| /// input.set_end(hm.offset()); |
| /// } else { |
| /// // This is only necessary to handle zero-width |
| /// // matches, which of course occur in this example. |
| /// // Without this, the search would never advance |
| /// // backwards beyond the initial match. |
| /// input.set_end(input.end() - 1); |
| /// } |
| /// } |
| /// } |
| /// } |
| /// |
| /// // No matches split a codepoint. |
| /// let expected = vec![ |
| /// HalfMatch::must(0, 3), |
| /// HalfMatch::must(0, 0), |
| /// ]; |
| /// assert_eq!(expected, matches); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// Now let's look at the same example, but with UTF-8 mode on the |
| /// underlying NFA disabled: |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// nfa::thompson, |
| /// HalfMatch, Input, MatchKind, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .thompson(thompson::Config::new().reverse(true).utf8(false)) |
| /// .build(r"")?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// // Run the reverse DFA to collect all matches. |
| /// let mut input = Input::new("☃"); |
| /// let mut matches = vec![]; |
| /// loop { |
| /// match dfa.try_search_rev(&mut cache, &input)? { |
| /// None => break, |
| /// Some(hm) => { |
| /// matches.push(hm); |
| /// if hm.offset() == 0 || input.end() == 0 { |
| /// break; |
| /// } else if hm.offset() < input.end() { |
| /// input.set_end(hm.offset()); |
| /// } else { |
| /// // This is only necessary to handle zero-width |
| /// // matches, which of course occur in this example. |
| /// // Without this, the search would never advance |
| /// // backwards beyond the initial match. |
| /// input.set_end(input.end() - 1); |
| /// } |
| /// } |
| /// } |
| /// } |
| /// |
| /// // No matches split a codepoint. |
| /// let expected = vec![ |
| /// HalfMatch::must(0, 3), |
| /// HalfMatch::must(0, 2), |
| /// HalfMatch::must(0, 1), |
| /// HalfMatch::must(0, 0), |
| /// ]; |
| /// assert_eq!(expected, matches); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[inline] |
| pub fn try_search_rev( |
| &self, |
| cache: &mut Cache, |
| input: &Input<'_>, |
| ) -> Result<Option<HalfMatch>, MatchError> { |
| let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); |
| let hm = match search::find_rev(self, cache, input)? { |
| None => return Ok(None), |
| Some(hm) if !utf8empty => return Ok(Some(hm)), |
| Some(hm) => hm, |
| }; |
| empty::skip_splits_rev(input, hm, hm.offset(), |input| { |
| let got = search::find_rev(self, cache, input)?; |
| Ok(got.map(|hm| (hm, hm.offset()))) |
| }) |
| } |
| |
| /// Executes an overlapping forward search and returns the end position of |
| /// matches as they are found. If no match exists, then `None` is returned. |
| /// |
| /// This routine is principally only useful when searching for multiple |
| /// patterns on inputs where multiple patterns may match the same regions |
| /// of text. In particular, callers must preserve the automaton's search |
| /// state from prior calls so that the implementation knows where the last |
| /// match occurred. |
| /// |
| /// When using this routine to implement an iterator of overlapping |
| /// matches, the `start` of the search should remain invariant throughout |
| /// iteration. The `OverlappingState` given to the search will keep track |
| /// of the current position of the search. (This is because multiple |
| /// matches may be reported at the same position, so only the search |
| /// implementation itself knows when to advance the position.) |
| /// |
| /// If for some reason you want the search to forget about its previous |
| /// state and restart the search at a particular position, then setting the |
| /// state to [`OverlappingState::start`] will accomplish that. |
| /// |
| /// # Errors |
| /// |
| /// This routine errors if the search could not complete. This can occur |
| /// in a number of circumstances: |
| /// |
| /// * The configuration of the lazy DFA may permit it to "quit" the search. |
| /// For example, setting quit bytes or enabling heuristic support for |
| /// Unicode word boundaries. The default configuration does not enable any |
| /// option that could result in the lazy DFA quitting. |
| /// * The configuration of the lazy DFA may also permit it to "give up" |
| /// on a search if it makes ineffective use of its transition table |
| /// cache. The default configuration does not enable this by default, |
| /// although it is typically a good idea to. |
| /// * When the provided `Input` configuration is not supported. For |
| /// example, by providing an unsupported anchor mode. |
| /// |
| /// When a search returns an error, callers cannot know whether a match |
| /// exists or not. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to run a basic overlapping search. Notice |
| /// that we build the automaton with a `MatchKind::All` configuration. |
| /// Overlapping searches are unlikely to work as one would expect when |
| /// using the default `MatchKind::LeftmostFirst` match semantics, since |
| /// leftmost-first matching is fundamentally incompatible with overlapping |
| /// searches. Namely, overlapping searches need to report matches as they |
| /// are seen, where as leftmost-first searches will continue searching even |
| /// after a match has been observed in order to find the conventional end |
| /// position of the match. More concretely, leftmost-first searches use |
| /// dead states to terminate a search after a specific match can no longer |
| /// be extended. Overlapping searches instead do the opposite by continuing |
| /// the search to find totally new matches (potentially of other patterns). |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{ |
| /// hybrid::dfa::{DFA, OverlappingState}, |
| /// HalfMatch, Input, MatchKind, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().match_kind(MatchKind::All)) |
| /// .build_many(&[r"\w+$", r"\S+$"])?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let haystack = "@foo"; |
| /// let mut state = OverlappingState::start(); |
| /// |
| /// let expected = Some(HalfMatch::must(1, 4)); |
| /// dfa.try_search_overlapping_fwd( |
| /// &mut cache, &Input::new(haystack), &mut state, |
| /// )?; |
| /// assert_eq!(expected, state.get_match()); |
| /// |
| /// // The first pattern also matches at the same position, so re-running |
| /// // the search will yield another match. Notice also that the first |
| /// // pattern is returned after the second. This is because the second |
| /// // pattern begins its match before the first, is therefore an earlier |
| /// // match and is thus reported first. |
| /// let expected = Some(HalfMatch::must(0, 4)); |
| /// dfa.try_search_overlapping_fwd( |
| /// &mut cache, &Input::new(haystack), &mut state, |
| /// )?; |
| /// assert_eq!(expected, state.get_match()); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[inline] |
| pub fn try_search_overlapping_fwd( |
| &self, |
| cache: &mut Cache, |
| input: &Input<'_>, |
| state: &mut OverlappingState, |
| ) -> Result<(), MatchError> { |
| let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); |
| search::find_overlapping_fwd(self, cache, input, state)?; |
| match state.get_match() { |
| None => Ok(()), |
| Some(_) if !utf8empty => Ok(()), |
| Some(_) => skip_empty_utf8_splits_overlapping( |
| input, |
| state, |
| |input, state| { |
| search::find_overlapping_fwd(self, cache, input, state) |
| }, |
| ), |
| } |
| } |
| |
| /// Executes a reverse overlapping search and returns the start of the |
| /// position of the leftmost match that is found. If no match exists, then |
| /// `None` is returned. |
| /// |
| /// When using this routine to implement an iterator of overlapping |
| /// matches, the `start` of the search should remain invariant throughout |
| /// iteration. The `OverlappingState` given to the search will keep track |
| /// of the current position of the search. (This is because multiple |
| /// matches may be reported at the same position, so only the search |
| /// implementation itself knows when to advance the position.) |
| /// |
| /// If for some reason you want the search to forget about its previous |
| /// state and restart the search at a particular position, then setting the |
| /// state to [`OverlappingState::start`] will accomplish that. |
| /// |
| /// # Errors |
| /// |
| /// This routine errors if the search could not complete. This can occur |
| /// in a number of circumstances: |
| /// |
| /// * The configuration of the lazy DFA may permit it to "quit" the search. |
| /// For example, setting quit bytes or enabling heuristic support for |
| /// Unicode word boundaries. The default configuration does not enable any |
| /// option that could result in the lazy DFA quitting. |
| /// * The configuration of the lazy DFA may also permit it to "give up" |
| /// on a search if it makes ineffective use of its transition table |
| /// cache. The default configuration does not enable this by default, |
| /// although it is typically a good idea to. |
| /// * When the provided `Input` configuration is not supported. For |
| /// example, by providing an unsupported anchor mode. |
| /// |
| /// When a search returns an error, callers cannot know whether a match |
| /// exists or not. |
| /// |
| /// # Example: UTF-8 mode |
| /// |
| /// This examples demonstrates that UTF-8 mode applies to reverse |
| /// DFAs. When UTF-8 mode is enabled in the underlying NFA, then all |
| /// matches reported must correspond to valid UTF-8 spans. This includes |
| /// prohibiting zero-width matches that split a codepoint. |
| /// |
| /// UTF-8 mode is enabled by default. Notice below how the only zero-width |
| /// matches reported are those at UTF-8 boundaries: |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::{DFA, OverlappingState}, |
| /// nfa::thompson, |
| /// HalfMatch, Input, MatchKind, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().match_kind(MatchKind::All)) |
| /// .thompson(thompson::Config::new().reverse(true)) |
| /// .build_many(&[r"", r"☃"])?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// // Run the reverse DFA to collect all matches. |
| /// let input = Input::new("☃"); |
| /// let mut state = OverlappingState::start(); |
| /// let mut matches = vec![]; |
| /// loop { |
| /// dfa.try_search_overlapping_rev(&mut cache, &input, &mut state)?; |
| /// match state.get_match() { |
| /// None => break, |
| /// Some(hm) => matches.push(hm), |
| /// } |
| /// } |
| /// |
| /// // No matches split a codepoint. |
| /// let expected = vec![ |
| /// HalfMatch::must(0, 3), |
| /// HalfMatch::must(1, 0), |
| /// HalfMatch::must(0, 0), |
| /// ]; |
| /// assert_eq!(expected, matches); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// Now let's look at the same example, but with UTF-8 mode on the |
| /// underlying NFA disabled: |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::{DFA, OverlappingState}, |
| /// nfa::thompson, |
| /// HalfMatch, Input, MatchKind, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().match_kind(MatchKind::All)) |
| /// .thompson(thompson::Config::new().reverse(true).utf8(false)) |
| /// .build_many(&[r"", r"☃"])?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// // Run the reverse DFA to collect all matches. |
| /// let input = Input::new("☃"); |
| /// let mut state = OverlappingState::start(); |
| /// let mut matches = vec![]; |
| /// loop { |
| /// dfa.try_search_overlapping_rev(&mut cache, &input, &mut state)?; |
| /// match state.get_match() { |
| /// None => break, |
| /// Some(hm) => matches.push(hm), |
| /// } |
| /// } |
| /// |
| /// // Now *all* positions match, even within a codepoint, |
| /// // because we lifted the requirement that matches |
| /// // correspond to valid UTF-8 spans. |
| /// let expected = vec![ |
| /// HalfMatch::must(0, 3), |
| /// HalfMatch::must(0, 2), |
| /// HalfMatch::must(0, 1), |
| /// HalfMatch::must(1, 0), |
| /// HalfMatch::must(0, 0), |
| /// ]; |
| /// assert_eq!(expected, matches); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[inline] |
| pub fn try_search_overlapping_rev( |
| &self, |
| cache: &mut Cache, |
| input: &Input<'_>, |
| state: &mut OverlappingState, |
| ) -> Result<(), MatchError> { |
| let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); |
| search::find_overlapping_rev(self, cache, input, state)?; |
| match state.get_match() { |
| None => Ok(()), |
| Some(_) if !utf8empty => Ok(()), |
| Some(_) => skip_empty_utf8_splits_overlapping( |
| input, |
| state, |
| |input, state| { |
| search::find_overlapping_rev(self, cache, input, state) |
| }, |
| ), |
| } |
| } |
| |
| /// Writes the set of patterns that match anywhere in the given search |
| /// configuration to `patset`. If multiple patterns match at the same |
| /// position and the underlying DFA supports overlapping matches, then all |
| /// matching patterns are written to the given set. |
| /// |
| /// Unless all of the patterns in this DFA are anchored, then generally |
| /// speaking, this will visit every byte in the haystack. |
| /// |
| /// This search routine *does not* clear the pattern set. This gives some |
| /// flexibility to the caller (e.g., running multiple searches with the |
| /// same pattern set), but does make the API bug-prone if you're reusing |
| /// the same pattern set for multiple searches but intended them to be |
| /// independent. |
| /// |
| /// If a pattern ID matched but the given `PatternSet` does not have |
| /// sufficient capacity to store it, then it is not inserted and silently |
| /// dropped. |
| /// |
| /// # Errors |
| /// |
| /// This routine errors if the search could not complete. This can occur |
| /// in a number of circumstances: |
| /// |
| /// * The configuration of the lazy DFA may permit it to "quit" the search. |
| /// For example, setting quit bytes or enabling heuristic support for |
| /// Unicode word boundaries. The default configuration does not enable any |
| /// option that could result in the lazy DFA quitting. |
| /// * The configuration of the lazy DFA may also permit it to "give up" |
| /// on a search if it makes ineffective use of its transition table |
| /// cache. The default configuration does not enable this by default, |
| /// although it is typically a good idea to. |
| /// * When the provided `Input` configuration is not supported. For |
| /// example, by providing an unsupported anchor mode. |
| /// |
| /// When a search returns an error, callers cannot know whether a match |
| /// exists or not. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to find all matching patterns in a haystack, |
| /// even when some patterns match at the same position as other patterns. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// Input, MatchKind, PatternSet, |
| /// }; |
| /// |
| /// let patterns = &[ |
| /// r"\w+", r"\d+", r"\pL+", r"foo", r"bar", r"barfoo", r"foobar", |
| /// ]; |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().match_kind(MatchKind::All)) |
| /// .build_many(patterns)?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let input = Input::new("foobar"); |
| /// let mut patset = PatternSet::new(dfa.pattern_len()); |
| /// dfa.try_which_overlapping_matches(&mut cache, &input, &mut patset)?; |
| /// let expected = vec![0, 2, 3, 4, 6]; |
| /// let got: Vec<usize> = patset.iter().map(|p| p.as_usize()).collect(); |
| /// assert_eq!(expected, got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[inline] |
| pub fn try_which_overlapping_matches( |
| &self, |
| cache: &mut Cache, |
| input: &Input<'_>, |
| patset: &mut PatternSet, |
| ) -> Result<(), MatchError> { |
| let mut state = OverlappingState::start(); |
| while let Some(m) = { |
| self.try_search_overlapping_fwd(cache, input, &mut state)?; |
| state.get_match() |
| } { |
| let _ = patset.try_insert(m.pattern()); |
| // There's nothing left to find, so we can stop. Or the caller |
| // asked us to. |
| if patset.is_full() || input.get_earliest() { |
| break; |
| } |
| } |
| Ok(()) |
| } |
| } |
| |
| impl DFA { |
| /// Transitions from the current state to the next state, given the next |
| /// byte of input. |
| /// |
| /// The given cache is used to either reuse pre-computed state |
| /// transitions, or to store this newly computed transition for future |
| /// reuse. Thus, this routine guarantees that it will never return a state |
| /// ID that has an "unknown" tag. |
| /// |
| /// # State identifier validity |
| /// |
| /// The only valid value for `current` is the lazy state ID returned |
| /// by the most recent call to `next_state`, `next_state_untagged`, |
| /// `next_state_untagged_unchecked`, `start_state_forward` or |
| /// `state_state_reverse` for the given `cache`. Any state ID returned from |
| /// prior calls to these routines (with the same `cache`) is considered |
| /// invalid (even if it gives an appearance of working). State IDs returned |
| /// from _any_ prior call for different `cache` values are also always |
| /// invalid. |
| /// |
| /// The returned ID is always a valid ID when `current` refers to a valid |
| /// ID. Moreover, this routine is defined for all possible values of |
| /// `input`. |
| /// |
| /// These validity rules are not checked, even in debug mode. Callers are |
| /// required to uphold these rules themselves. |
| /// |
| /// Violating these state ID validity rules will not sacrifice memory |
| /// safety, but _may_ produce an incorrect result or a panic. |
| /// |
| /// # Panics |
| /// |
| /// If the given ID does not refer to a valid state, then this routine |
| /// may panic but it also may not panic and instead return an invalid or |
| /// incorrect ID. |
| /// |
| /// # Example |
| /// |
| /// This shows a simplistic example for walking a lazy DFA for a given |
| /// haystack by using the `next_state` method. |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, Input}; |
| /// |
| /// let dfa = DFA::new(r"[a-z]+r")?; |
| /// let mut cache = dfa.create_cache(); |
| /// let haystack = "bar".as_bytes(); |
| /// |
| /// // The start state is determined by inspecting the position and the |
| /// // initial bytes of the haystack. |
| /// let mut sid = dfa.start_state_forward( |
| /// &mut cache, &Input::new(haystack), |
| /// )?; |
| /// // Walk all the bytes in the haystack. |
| /// for &b in haystack { |
| /// sid = dfa.next_state(&mut cache, sid, b)?; |
| /// } |
| /// // Matches are always delayed by 1 byte, so we must explicitly walk the |
| /// // special "EOI" transition at the end of the search. |
| /// sid = dfa.next_eoi_state(&mut cache, sid)?; |
| /// assert!(sid.is_match()); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[inline] |
| pub fn next_state( |
| &self, |
| cache: &mut Cache, |
| current: LazyStateID, |
| input: u8, |
| ) -> Result<LazyStateID, CacheError> { |
| let class = usize::from(self.classes.get(input)); |
| let offset = current.as_usize_untagged() + class; |
| let sid = cache.trans[offset]; |
| if !sid.is_unknown() { |
| return Ok(sid); |
| } |
| let unit = alphabet::Unit::u8(input); |
| Lazy::new(self, cache).cache_next_state(current, unit) |
| } |
| |
| /// Transitions from the current state to the next state, given the next |
| /// byte of input and a state ID that is not tagged. |
| /// |
| /// The only reason to use this routine is performance. In particular, the |
| /// `next_state` method needs to do some additional checks, among them is |
| /// to account for identifiers to states that are not yet computed. In |
| /// such a case, the transition is computed on the fly. However, if it is |
| /// known that the `current` state ID is untagged, then these checks can be |
| /// omitted. |
| /// |
| /// Since this routine does not compute states on the fly, it does not |
| /// modify the cache and thus cannot return an error. Consequently, `cache` |
| /// does not need to be mutable and it is possible for this routine to |
| /// return a state ID corresponding to the special "unknown" state. In |
| /// this case, it is the caller's responsibility to use the prior state |
| /// ID and `input` with `next_state` in order to force the computation of |
| /// the unknown transition. Otherwise, trying to use the "unknown" state |
| /// ID will just result in transitioning back to itself, and thus never |
| /// terminating. (This is technically a special exemption to the state ID |
| /// validity rules, but is permissible since this routine is guarateed to |
| /// never mutate the given `cache`, and thus the identifier is guaranteed |
| /// to remain valid.) |
| /// |
| /// See [`LazyStateID`] for more details on what it means for a state ID |
| /// to be tagged. Also, see |
| /// [`next_state_untagged_unchecked`](DFA::next_state_untagged_unchecked) |
| /// for this same idea, but with bounds checks forcefully elided. |
| /// |
| /// # State identifier validity |
| /// |
| /// The only valid value for `current` is an **untagged** lazy |
| /// state ID returned by the most recent call to `next_state`, |
| /// `next_state_untagged`, `next_state_untagged_unchecked`, |
| /// `start_state_forward` or `state_state_reverse` for the given `cache`. |
| /// Any state ID returned from prior calls to these routines (with the |
| /// same `cache`) is considered invalid (even if it gives an appearance |
| /// of working). State IDs returned from _any_ prior call for different |
| /// `cache` values are also always invalid. |
| /// |
| /// The returned ID is always a valid ID when `current` refers to a valid |
| /// ID, although it may be tagged. Moreover, this routine is defined for |
| /// all possible values of `input`. |
| /// |
| /// Not all validity rules are checked, even in debug mode. Callers are |
| /// required to uphold these rules themselves. |
| /// |
| /// Violating these state ID validity rules will not sacrifice memory |
| /// safety, but _may_ produce an incorrect result or a panic. |
| /// |
| /// # Panics |
| /// |
| /// If the given ID does not refer to a valid state, then this routine |
| /// may panic but it also may not panic and instead return an invalid or |
| /// incorrect ID. |
| /// |
| /// # Example |
| /// |
| /// This shows a simplistic example for walking a lazy DFA for a given |
| /// haystack by using the `next_state_untagged` method where possible. |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, Input}; |
| /// |
| /// let dfa = DFA::new(r"[a-z]+r")?; |
| /// let mut cache = dfa.create_cache(); |
| /// let haystack = "bar".as_bytes(); |
| /// |
| /// // The start state is determined by inspecting the position and the |
| /// // initial bytes of the haystack. |
| /// let mut sid = dfa.start_state_forward( |
| /// &mut cache, &Input::new(haystack), |
| /// )?; |
| /// // Walk all the bytes in the haystack. |
| /// let mut at = 0; |
| /// while at < haystack.len() { |
| /// if sid.is_tagged() { |
| /// sid = dfa.next_state(&mut cache, sid, haystack[at])?; |
| /// } else { |
| /// let mut prev_sid = sid; |
| /// // We attempt to chew through as much as we can while moving |
| /// // through untagged state IDs. Thus, the transition function |
| /// // does less work on average per byte. (Unrolling this loop |
| /// // may help even more.) |
| /// while at < haystack.len() { |
| /// prev_sid = sid; |
| /// sid = dfa.next_state_untagged( |
| /// &mut cache, sid, haystack[at], |
| /// ); |
| /// at += 1; |
| /// if sid.is_tagged() { |
| /// break; |
| /// } |
| /// } |
| /// // We must ensure that we never proceed to the next iteration |
| /// // with an unknown state ID. If we don't account for this |
| /// // case, then search isn't guaranteed to terminate since all |
| /// // transitions on unknown states loop back to itself. |
| /// if sid.is_unknown() { |
| /// sid = dfa.next_state( |
| /// &mut cache, prev_sid, haystack[at - 1], |
| /// )?; |
| /// } |
| /// } |
| /// } |
| /// // Matches are always delayed by 1 byte, so we must explicitly walk the |
| /// // special "EOI" transition at the end of the search. |
| /// sid = dfa.next_eoi_state(&mut cache, sid)?; |
| /// assert!(sid.is_match()); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[inline] |
| pub fn next_state_untagged( |
| &self, |
| cache: &Cache, |
| current: LazyStateID, |
| input: u8, |
| ) -> LazyStateID { |
| debug_assert!(!current.is_tagged()); |
| let class = usize::from(self.classes.get(input)); |
| let offset = current.as_usize_unchecked() + class; |
| cache.trans[offset] |
| } |
| |
| /// Transitions from the current state to the next state, eliding bounds |
| /// checks, given the next byte of input and a state ID that is not tagged. |
| /// |
| /// The only reason to use this routine is performance. In particular, the |
| /// `next_state` method needs to do some additional checks, among them is |
| /// to account for identifiers to states that are not yet computed. In |
| /// such a case, the transition is computed on the fly. However, if it is |
| /// known that the `current` state ID is untagged, then these checks can be |
| /// omitted. |
| /// |
| /// Since this routine does not compute states on the fly, it does not |
| /// modify the cache and thus cannot return an error. Consequently, `cache` |
| /// does not need to be mutable and it is possible for this routine to |
| /// return a state ID corresponding to the special "unknown" state. In |
| /// this case, it is the caller's responsibility to use the prior state |
| /// ID and `input` with `next_state` in order to force the computation of |
| /// the unknown transition. Otherwise, trying to use the "unknown" state |
| /// ID will just result in transitioning back to itself, and thus never |
| /// terminating. (This is technically a special exemption to the state ID |
| /// validity rules, but is permissible since this routine is guarateed to |
| /// never mutate the given `cache`, and thus the identifier is guaranteed |
| /// to remain valid.) |
| /// |
| /// See [`LazyStateID`] for more details on what it means for a state ID |
| /// to be tagged. Also, see |
| /// [`next_state_untagged`](DFA::next_state_untagged) |
| /// for this same idea, but with memory safety guaranteed by retaining |
| /// bounds checks. |
| /// |
| /// # State identifier validity |
| /// |
| /// The only valid value for `current` is an **untagged** lazy |
| /// state ID returned by the most recent call to `next_state`, |
| /// `next_state_untagged`, `next_state_untagged_unchecked`, |
| /// `start_state_forward` or `state_state_reverse` for the given `cache`. |
| /// Any state ID returned from prior calls to these routines (with the |
| /// same `cache`) is considered invalid (even if it gives an appearance |
| /// of working). State IDs returned from _any_ prior call for different |
| /// `cache` values are also always invalid. |
| /// |
| /// The returned ID is always a valid ID when `current` refers to a valid |
| /// ID, although it may be tagged. Moreover, this routine is defined for |
| /// all possible values of `input`. |
| /// |
| /// Not all validity rules are checked, even in debug mode. Callers are |
| /// required to uphold these rules themselves. |
| /// |
| /// Violating these state ID validity rules will not sacrifice memory |
| /// safety, but _may_ produce an incorrect result or a panic. |
| /// |
| /// # Safety |
| /// |
| /// Callers of this method must guarantee that `current` refers to a valid |
| /// state ID according to the rules described above. If `current` is not a |
| /// valid state ID for this automaton, then calling this routine may result |
| /// in undefined behavior. |
| /// |
| /// If `current` is valid, then the ID returned is valid for all possible |
| /// values of `input`. |
| #[inline] |
| pub unsafe fn next_state_untagged_unchecked( |
| &self, |
| cache: &Cache, |
| current: LazyStateID, |
| input: u8, |
| ) -> LazyStateID { |
| debug_assert!(!current.is_tagged()); |
| let class = usize::from(self.classes.get(input)); |
| let offset = current.as_usize_unchecked() + class; |
| *cache.trans.get_unchecked(offset) |
| } |
| |
| /// Transitions from the current state to the next state for the special |
| /// EOI symbol. |
| /// |
| /// The given cache is used to either reuse pre-computed state |
| /// transitions, or to store this newly computed transition for future |
| /// reuse. Thus, this routine guarantees that it will never return a state |
| /// ID that has an "unknown" tag. |
| /// |
| /// This routine must be called at the end of every search in a correct |
| /// implementation of search. Namely, lazy DFAs in this crate delay matches |
| /// by one byte in order to support look-around operators. Thus, after |
| /// reaching the end of a haystack, a search implementation must follow one |
| /// last EOI transition. |
| /// |
| /// It is best to think of EOI as an additional symbol in the alphabet of a |
| /// DFA that is distinct from every other symbol. That is, the alphabet of |
| /// lazy DFAs in this crate has a logical size of 257 instead of 256, where |
| /// 256 corresponds to every possible inhabitant of `u8`. (In practice, the |
| /// physical alphabet size may be smaller because of alphabet compression |
| /// via equivalence classes, but EOI is always represented somehow in the |
| /// alphabet.) |
| /// |
| /// # State identifier validity |
| /// |
| /// The only valid value for `current` is the lazy state ID returned |
| /// by the most recent call to `next_state`, `next_state_untagged`, |
| /// `next_state_untagged_unchecked`, `start_state_forward` or |
| /// `state_state_reverse` for the given `cache`. Any state ID returned from |
| /// prior calls to these routines (with the same `cache`) is considered |
| /// invalid (even if it gives an appearance of working). State IDs returned |
| /// from _any_ prior call for different `cache` values are also always |
| /// invalid. |
| /// |
| /// The returned ID is always a valid ID when `current` refers to a valid |
| /// ID. |
| /// |
| /// These validity rules are not checked, even in debug mode. Callers are |
| /// required to uphold these rules themselves. |
| /// |
| /// Violating these state ID validity rules will not sacrifice memory |
| /// safety, but _may_ produce an incorrect result or a panic. |
| /// |
| /// # Panics |
| /// |
| /// If the given ID does not refer to a valid state, then this routine |
| /// may panic but it also may not panic and instead return an invalid or |
| /// incorrect ID. |
| /// |
| /// # Example |
| /// |
| /// This shows a simplistic example for walking a DFA for a given haystack, |
| /// and then finishing the search with the final EOI transition. |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, Input}; |
| /// |
| /// let dfa = DFA::new(r"[a-z]+r")?; |
| /// let mut cache = dfa.create_cache(); |
| /// let haystack = "bar".as_bytes(); |
| /// |
| /// // The start state is determined by inspecting the position and the |
| /// // initial bytes of the haystack. |
| /// let mut sid = dfa.start_state_forward( |
| /// &mut cache, &Input::new(haystack), |
| /// )?; |
| /// // Walk all the bytes in the haystack. |
| /// for &b in haystack { |
| /// sid = dfa.next_state(&mut cache, sid, b)?; |
| /// } |
| /// // Matches are always delayed by 1 byte, so we must explicitly walk |
| /// // the special "EOI" transition at the end of the search. Without this |
| /// // final transition, the assert below will fail since the DFA will not |
| /// // have entered a match state yet! |
| /// sid = dfa.next_eoi_state(&mut cache, sid)?; |
| /// assert!(sid.is_match()); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[inline] |
| pub fn next_eoi_state( |
| &self, |
| cache: &mut Cache, |
| current: LazyStateID, |
| ) -> Result<LazyStateID, CacheError> { |
| let eoi = self.classes.eoi().as_usize(); |
| let offset = current.as_usize_untagged() + eoi; |
| let sid = cache.trans[offset]; |
| if !sid.is_unknown() { |
| return Ok(sid); |
| } |
| let unit = self.classes.eoi(); |
| Lazy::new(self, cache).cache_next_state(current, unit) |
| } |
| |
| /// Return the ID of the start state for this lazy DFA for the given |
| /// starting configuration. |
| /// |
| /// Unlike typical DFA implementations, the start state for DFAs in this |
| /// crate is dependent on a few different factors: |
| /// |
| /// * The [`Anchored`] mode of the search. Unanchored, anchored and |
| /// anchored searches for a specific [`PatternID`] all use different start |
| /// states. |
| /// * Whether a "look-behind" byte exists. For example, the `^` anchor |
| /// matches if and only if there is no look-behind byte. |
| /// * The specific value of that look-behind byte. For example, a `(?m:^)` |
| /// assertion only matches when there is either no look-behind byte, or |
| /// when the look-behind byte is a line terminator. |
| /// |
| /// The [starting configuration](start::Config) provides the above |
| /// information. |
| /// |
| /// This routine can be used for either forward or reverse searches. |
| /// Although, as a convenience, if you have an [`Input`], then it |
| /// may be more succinct to use [`DFA::start_state_forward`] or |
| /// [`DFA::start_state_reverse`]. Note, for example, that the convenience |
| /// routines return a [`MatchError`] on failure where as this routine |
| /// returns a [`StartError`]. |
| /// |
| /// # Errors |
| /// |
| /// This may return a [`StartError`] if the search needs to give up when |
| /// determining the start state (for example, if it sees a "quit" byte |
| /// or if the cache has become inefficient). This can also return an |
| /// error if the given configuration contains an unsupported [`Anchored`] |
| /// configuration. |
| #[cfg_attr(feature = "perf-inline", inline(always))] |
| pub fn start_state( |
| &self, |
| cache: &mut Cache, |
| config: &start::Config, |
| ) -> Result<LazyStateID, StartError> { |
| let lazy = LazyRef::new(self, cache); |
| let anchored = config.get_anchored(); |
| let start = match config.get_look_behind() { |
| None => Start::Text, |
| Some(byte) => { |
| if !self.quitset.is_empty() && self.quitset.contains(byte) { |
| return Err(StartError::quit(byte)); |
| } |
| self.start_map.get(byte) |
| } |
| }; |
| let start_id = lazy.get_cached_start_id(anchored, start)?; |
| if !start_id.is_unknown() { |
| return Ok(start_id); |
| } |
| Lazy::new(self, cache).cache_start_group(anchored, start) |
| } |
| |
| /// Return the ID of the start state for this lazy DFA when executing a |
| /// forward search. |
| /// |
| /// This is a convenience routine for calling [`DFA::start_state`] that |
| /// converts the given [`Input`] to a [start configuration](start::Config). |
| /// Additionally, if an error occurs, it is converted from a [`StartError`] |
| /// to a [`MatchError`] using the offset information in the given |
| /// [`Input`]. |
| /// |
| /// # Errors |
| /// |
| /// This may return a [`MatchError`] if the search needs to give up when |
| /// determining the start state (for example, if it sees a "quit" byte or |
| /// if the cache has become inefficient). This can also return an error if |
| /// the given `Input` contains an unsupported [`Anchored`] configuration. |
| #[cfg_attr(feature = "perf-inline", inline(always))] |
| pub fn start_state_forward( |
| &self, |
| cache: &mut Cache, |
| input: &Input<'_>, |
| ) -> Result<LazyStateID, MatchError> { |
| let config = start::Config::from_input_forward(input); |
| self.start_state(cache, &config).map_err(|err| match err { |
| StartError::Cache { .. } => MatchError::gave_up(input.start()), |
| StartError::Quit { byte } => { |
| let offset = input |
| .start() |
| .checked_sub(1) |
| .expect("no quit in start without look-behind"); |
| MatchError::quit(byte, offset) |
| } |
| StartError::UnsupportedAnchored { mode } => { |
| MatchError::unsupported_anchored(mode) |
| } |
| }) |
| } |
| |
| /// Return the ID of the start state for this lazy DFA when executing a |
| /// reverse search. |
| /// |
| /// This is a convenience routine for calling [`DFA::start_state`] that |
| /// converts the given [`Input`] to a [start configuration](start::Config). |
| /// Additionally, if an error occurs, it is converted from a [`StartError`] |
| /// to a [`MatchError`] using the offset information in the given |
| /// [`Input`]. |
| /// |
| /// # Errors |
| /// |
| /// This may return a [`MatchError`] if the search needs to give up when |
| /// determining the start state (for example, if it sees a "quit" byte or |
| /// if the cache has become inefficient). This can also return an error if |
| /// the given `Input` contains an unsupported [`Anchored`] configuration. |
| #[cfg_attr(feature = "perf-inline", inline(always))] |
| pub fn start_state_reverse( |
| &self, |
| cache: &mut Cache, |
| input: &Input<'_>, |
| ) -> Result<LazyStateID, MatchError> { |
| let config = start::Config::from_input_reverse(input); |
| self.start_state(cache, &config).map_err(|err| match err { |
| StartError::Cache { .. } => MatchError::gave_up(input.end()), |
| StartError::Quit { byte } => { |
| let offset = input.end(); |
| MatchError::quit(byte, offset) |
| } |
| StartError::UnsupportedAnchored { mode } => { |
| MatchError::unsupported_anchored(mode) |
| } |
| }) |
| } |
| |
| /// Returns the total number of patterns that match in this state. |
| /// |
| /// If the lazy DFA was compiled with one pattern, then this must |
| /// necessarily always return `1` for all match states. |
| /// |
| /// A lazy DFA guarantees that [`DFA::match_pattern`] can be called with |
| /// indices up to (but not including) the length returned by this routine |
| /// without panicking. |
| /// |
| /// # Panics |
| /// |
| /// If the given state is not a match state, then this may either panic |
| /// or return an incorrect result. |
| /// |
| /// # Example |
| /// |
| /// This example shows a simple instance of implementing overlapping |
| /// matches. In particular, it shows not only how to determine how many |
| /// patterns have matched in a particular state, but also how to access |
| /// which specific patterns have matched. |
| /// |
| /// Notice that we must use [`MatchKind::All`] when building the DFA. If we |
| /// used [`MatchKind::LeftmostFirst`] instead, then the DFA would not be |
| /// constructed in a way that supports overlapping matches. (It would only |
| /// report a single pattern that matches at any particular point in time.) |
| /// |
| /// Another thing to take note of is the patterns used and the order in |
| /// which the pattern IDs are reported. In the example below, pattern `3` |
| /// is yielded first. Why? Because it corresponds to the match that |
| /// appears first. Namely, the `@` symbol is part of `\S+` but not part |
| /// of any of the other patterns. Since the `\S+` pattern has a match that |
| /// starts to the left of any other pattern, its ID is returned before any |
| /// other. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{hybrid::dfa::DFA, Input, MatchKind}; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().match_kind(MatchKind::All)) |
| /// .build_many(&[ |
| /// r"\w+", r"[a-z]+", r"[A-Z]+", r"\S+", |
| /// ])?; |
| /// let mut cache = dfa.create_cache(); |
| /// let haystack = "@bar".as_bytes(); |
| /// |
| /// // The start state is determined by inspecting the position and the |
| /// // initial bytes of the haystack. |
| /// let mut sid = dfa.start_state_forward( |
| /// &mut cache, &Input::new(haystack), |
| /// )?; |
| /// // Walk all the bytes in the haystack. |
| /// for &b in haystack { |
| /// sid = dfa.next_state(&mut cache, sid, b)?; |
| /// } |
| /// sid = dfa.next_eoi_state(&mut cache, sid)?; |
| /// |
| /// assert!(sid.is_match()); |
| /// assert_eq!(dfa.match_len(&mut cache, sid), 3); |
| /// // The following calls are guaranteed to not panic since `match_len` |
| /// // returned `3` above. |
| /// assert_eq!(dfa.match_pattern(&mut cache, sid, 0).as_usize(), 3); |
| /// assert_eq!(dfa.match_pattern(&mut cache, sid, 1).as_usize(), 0); |
| /// assert_eq!(dfa.match_pattern(&mut cache, sid, 2).as_usize(), 1); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[inline] |
| pub fn match_len(&self, cache: &Cache, id: LazyStateID) -> usize { |
| assert!(id.is_match()); |
| LazyRef::new(self, cache).get_cached_state(id).match_len() |
| } |
| |
| /// Returns the pattern ID corresponding to the given match index in the |
| /// given state. |
| /// |
| /// See [`DFA::match_len`] for an example of how to use this method |
| /// correctly. Note that if you know your lazy DFA is configured with a |
| /// single pattern, then this routine is never necessary since it will |
| /// always return a pattern ID of `0` for an index of `0` when `id` |
| /// corresponds to a match state. |
| /// |
| /// Typically, this routine is used when implementing an overlapping |
| /// search, as the example for `DFA::match_len` does. |
| /// |
| /// # Panics |
| /// |
| /// If the state ID is not a match state or if the match index is out |
| /// of bounds for the given state, then this routine may either panic |
| /// or produce an incorrect result. If the state ID is correct and the |
| /// match index is correct, then this routine always produces a valid |
| /// `PatternID`. |
| #[inline] |
| pub fn match_pattern( |
| &self, |
| cache: &Cache, |
| id: LazyStateID, |
| match_index: usize, |
| ) -> PatternID { |
| // This is an optimization for the very common case of a DFA with a |
| // single pattern. This conditional avoids a somewhat more costly path |
| // that finds the pattern ID from the corresponding `State`, which |
| // requires a bit of slicing/pointer-chasing. This optimization tends |
| // to only matter when matches are frequent. |
| if self.pattern_len() == 1 { |
| return PatternID::ZERO; |
| } |
| LazyRef::new(self, cache) |
| .get_cached_state(id) |
| .match_pattern(match_index) |
| } |
| } |
| |
| /// A cache represents a partially computed DFA. |
| /// |
| /// A cache is the key component that differentiates a classical DFA and a |
| /// hybrid NFA/DFA (also called a "lazy DFA"). Where a classical DFA builds a |
| /// complete transition table that can handle all possible inputs, a hybrid |
| /// NFA/DFA starts with an empty transition table and builds only the parts |
| /// required during search. The parts that are built are stored in a cache. For |
| /// this reason, a cache is a required parameter for nearly every operation on |
| /// a [`DFA`]. |
| /// |
| /// Caches can be created from their corresponding DFA via |
| /// [`DFA::create_cache`]. A cache can only be used with either the DFA that |
| /// created it, or the DFA that was most recently used to reset it with |
| /// [`Cache::reset`]. Using a cache with any other DFA may result in panics |
| /// or incorrect results. |
| #[derive(Clone, Debug)] |
| pub struct Cache { |
| // N.B. If you're looking to understand how determinization works, it |
| // is probably simpler to first grok src/dfa/determinize.rs, since that |
| // doesn't have the "laziness" component. |
| /// The transition table. |
| /// |
| /// Given a `current` LazyStateID and an `input` byte, the next state can |
| /// be computed via `trans[untagged(current) + equiv_class(input)]`. Notice |
| /// that no multiplication is used. That's because state identifiers are |
| /// "premultiplied." |
| /// |
| /// Note that the next state may be the "unknown" state. In this case, the |
| /// next state is not known and determinization for `current` on `input` |
| /// must be performed. |
| trans: Vec<LazyStateID>, |
| /// The starting states for this DFA. |
| /// |
| /// These are computed lazily. Initially, these are all set to "unknown" |
| /// lazy state IDs. |
| /// |
| /// When 'starts_for_each_pattern' is disabled (the default), then the size |
| /// of this is constrained to the possible starting configurations based |
| /// on the search parameters. (At time of writing, that's 4.) However, |
| /// when starting states for each pattern is enabled, then there are N |
| /// additional groups of starting states, where each group reflects the |
| /// different possible configurations and N is the number of patterns. |
| starts: Vec<LazyStateID>, |
| /// A sequence of NFA/DFA powerset states that have been computed for this |
| /// lazy DFA. This sequence is indexable by untagged LazyStateIDs. (Every |
| /// tagged LazyStateID can be used to index this sequence by converting it |
| /// to its untagged form.) |
| states: Vec<State>, |
| /// A map from states to their corresponding IDs. This map may be accessed |
| /// via the raw byte representation of a state, which means that a `State` |
| /// does not need to be allocated to determine whether it already exists |
| /// in this map. Indeed, the existence of such a state is what determines |
| /// whether we allocate a new `State` or not. |
| /// |
| /// The higher level idea here is that we do just enough determinization |
| /// for a state to check whether we've already computed it. If we have, |
| /// then we can save a little (albeit not much) work. The real savings is |
| /// in memory usage. If we never checked for trivially duplicate states, |
| /// then our memory usage would explode to unreasonable levels. |
| states_to_id: StateMap, |
| /// Sparse sets used to track which NFA states have been visited during |
| /// various traversals. |
| sparses: SparseSets, |
| /// Scratch space for traversing the NFA graph. (We use space on the heap |
| /// instead of the call stack.) |
| stack: Vec<NFAStateID>, |
| /// Scratch space for building a NFA/DFA powerset state. This is used to |
| /// help amortize allocation since not every powerset state generated is |
| /// added to the cache. In particular, if it already exists in the cache, |
| /// then there is no need to allocate a new `State` for it. |
| scratch_state_builder: StateBuilderEmpty, |
| /// A simple abstraction for handling the saving of at most a single state |
| /// across a cache clearing. This is required for correctness. Namely, if |
| /// adding a new state after clearing the cache fails, then the caller |
| /// must retain the ability to continue using the state ID given. The |
| /// state corresponding to the state ID is what we preserve across cache |
| /// clearings. |
| state_saver: StateSaver, |
| /// The memory usage, in bytes, used by 'states' and 'states_to_id'. We |
| /// track this as new states are added since states use a variable amount |
| /// of heap. Tracking this as we add states makes it possible to compute |
| /// the total amount of memory used by the determinizer in constant time. |
| memory_usage_state: usize, |
| /// The number of times the cache has been cleared. When a minimum cache |
| /// clear count is set, then the cache will return an error instead of |
| /// clearing the cache if the count has been exceeded. |
| clear_count: usize, |
| /// The total number of bytes searched since the last time this cache was |
| /// cleared, not including the current search. |
| /// |
| /// This can be added to the length of the current search to get the true |
| /// total number of bytes searched. |
| /// |
| /// This is generally only non-zero when the |
| /// `Cache::search_{start,update,finish}` APIs are used to track search |
| /// progress. |
| bytes_searched: usize, |
| /// The progress of the current search. |
| /// |
| /// This is only non-`None` when callers utlize the `Cache::search_start`, |
| /// `Cache::search_update` and `Cache::search_finish` APIs. |
| /// |
| /// The purpose of recording search progress is to be able to make a |
| /// determination about the efficiency of the cache. Namely, by keeping |
| /// track of the |
| progress: Option<SearchProgress>, |
| } |
| |
| impl Cache { |
| /// Create a new cache for the given lazy DFA. |
| /// |
| /// The cache returned should only be used for searches for the given DFA. |
| /// If you want to reuse the cache for another DFA, then you must call |
| /// [`Cache::reset`] with that DFA. |
| pub fn new(dfa: &DFA) -> Cache { |
| let mut cache = Cache { |
| trans: alloc::vec![], |
| starts: alloc::vec![], |
| states: alloc::vec![], |
| states_to_id: StateMap::new(), |
| sparses: SparseSets::new(dfa.get_nfa().states().len()), |
| stack: alloc::vec![], |
| scratch_state_builder: StateBuilderEmpty::new(), |
| state_saver: StateSaver::none(), |
| memory_usage_state: 0, |
| clear_count: 0, |
| bytes_searched: 0, |
| progress: None, |
| }; |
| debug!("pre-init lazy DFA cache size: {}", cache.memory_usage()); |
| Lazy { dfa, cache: &mut cache }.init_cache(); |
| debug!("post-init lazy DFA cache size: {}", cache.memory_usage()); |
| cache |
| } |
| |
| /// Reset this cache such that it can be used for searching with the given |
| /// lazy DFA (and only that DFA). |
| /// |
| /// A cache reset permits reusing memory already allocated in this cache |
| /// with a different lazy DFA. |
| /// |
| /// Resetting a cache sets its "clear count" to 0. This is relevant if the |
| /// lazy DFA has been configured to "give up" after it has cleared the |
| /// cache a certain number of times. |
| /// |
| /// Any lazy state ID generated by the cache prior to resetting it is |
| /// invalid after the reset. |
| /// |
| /// # Example |
| /// |
| /// This shows how to re-purpose a cache for use with a different DFA. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// let dfa1 = DFA::new(r"\w")?; |
| /// let dfa2 = DFA::new(r"\W")?; |
| /// |
| /// let mut cache = dfa1.create_cache(); |
| /// assert_eq!( |
| /// Some(HalfMatch::must(0, 2)), |
| /// dfa1.try_search_fwd(&mut cache, &Input::new("Δ"))?, |
| /// ); |
| /// |
| /// // Using 'cache' with dfa2 is not allowed. It may result in panics or |
| /// // incorrect results. In order to re-purpose the cache, we must reset |
| /// // it with the DFA we'd like to use it with. |
| /// // |
| /// // Similarly, after this reset, using the cache with 'dfa1' is also not |
| /// // allowed. |
| /// cache.reset(&dfa2); |
| /// assert_eq!( |
| /// Some(HalfMatch::must(0, 3)), |
| /// dfa2.try_search_fwd(&mut cache, &Input::new("☃"))?, |
| /// ); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn reset(&mut self, dfa: &DFA) { |
| Lazy::new(dfa, self).reset_cache() |
| } |
| |
| /// Initializes a new search starting at the given position. |
| /// |
| /// If a previous search was unfinished, then it is finished automatically |
| /// and a new search is begun. |
| /// |
| /// Note that keeping track of search progress is _not necessary_ |
| /// for correct implementations of search using a lazy DFA. Keeping |
| /// track of search progress is only necessary if you want the |
| /// [`Config::minimum_bytes_per_state`] configuration knob to work. |
| #[inline] |
| pub fn search_start(&mut self, at: usize) { |
| // If a previous search wasn't marked as finished, then finish it |
| // now automatically. |
| if let Some(p) = self.progress.take() { |
| self.bytes_searched += p.len(); |
| } |
| self.progress = Some(SearchProgress { start: at, at }); |
| } |
| |
| /// Updates the current search to indicate that it has search to the |
| /// current position. |
| /// |
| /// No special care needs to be taken for reverse searches. Namely, the |
| /// position given may be _less than_ the starting position of the search. |
| /// |
| /// # Panics |
| /// |
| /// This panics if no search has been started by [`Cache::search_start`]. |
| #[inline] |
| pub fn search_update(&mut self, at: usize) { |
| let p = |
| self.progress.as_mut().expect("no in-progress search to update"); |
| p.at = at; |
| } |
| |
| /// Indicates that a search has finished at the given position. |
| /// |
| /// # Panics |
| /// |
| /// This panics if no search has been started by [`Cache::search_start`]. |
| #[inline] |
| pub fn search_finish(&mut self, at: usize) { |
| let mut p = |
| self.progress.take().expect("no in-progress search to finish"); |
| p.at = at; |
| self.bytes_searched += p.len(); |
| } |
| |
| /// Returns the total number of bytes that have been searched since this |
| /// cache was last cleared. |
| /// |
| /// This is useful for determining the efficiency of the cache. For |
| /// example, the lazy DFA uses this value in conjunction with the |
| /// [`Config::minimum_bytes_per_state`] knob to help determine whether it |
| /// should quit searching. |
| /// |
| /// This always returns `0` if search progress isn't being tracked. Note |
| /// that the lazy DFA search routines in this crate always track search |
| /// progress. |
| pub fn search_total_len(&self) -> usize { |
| self.bytes_searched + self.progress.as_ref().map_or(0, |p| p.len()) |
| } |
| |
| /// Returns the total number of times this cache has been cleared since it |
| /// was either created or last reset. |
| /// |
| /// This is useful for informational purposes or if you want to change |
| /// search strategies based on the number of times the cache has been |
| /// cleared. |
| pub fn clear_count(&self) -> usize { |
| self.clear_count |
| } |
| |
| /// Returns the heap memory usage, in bytes, of this cache. |
| /// |
| /// This does **not** include the stack size used up by this cache. To |
| /// compute that, use `std::mem::size_of::<Cache>()`. |
| pub fn memory_usage(&self) -> usize { |
| const ID_SIZE: usize = size_of::<LazyStateID>(); |
| const STATE_SIZE: usize = size_of::<State>(); |
| |
| // NOTE: If you make changes to the below, then |
| // 'minimum_cache_capacity' should be updated correspondingly. |
| |
| self.trans.len() * ID_SIZE |
| + self.starts.len() * ID_SIZE |
| + self.states.len() * STATE_SIZE |
| // Maps likely use more memory than this, but it's probably close. |
| + self.states_to_id.len() * (STATE_SIZE + ID_SIZE) |
| + self.sparses.memory_usage() |
| + self.stack.capacity() * ID_SIZE |
| + self.scratch_state_builder.capacity() |
| // Heap memory used by 'State' in both 'states' and 'states_to_id'. |
| + self.memory_usage_state |
| } |
| } |
| |
| /// Keeps track of the progress of the current search. |
| /// |
| /// This is updated via the `Cache::search_{start,update,finish}` APIs to |
| /// record how many bytes have been searched. This permits computing a |
| /// heuristic that represents the efficiency of a cache, and thus helps inform |
| /// whether the lazy DFA should give up or not. |
| #[derive(Clone, Debug)] |
| struct SearchProgress { |
| start: usize, |
| at: usize, |
| } |
| |
| impl SearchProgress { |
| /// Returns the length, in bytes, of this search so far. |
| /// |
| /// This automatically handles the case of a reverse search, where `at` |
| /// is likely to be less than `start`. |
| fn len(&self) -> usize { |
| if self.start <= self.at { |
| self.at - self.start |
| } else { |
| self.start - self.at |
| } |
| } |
| } |
| |
| /// A map from states to state identifiers. When using std, we use a standard |
| /// hashmap, since it's a bit faster for this use case. (Other maps, like |
| /// one's based on FNV, have not yet been benchmarked.) |
| /// |
| /// The main purpose of this map is to reuse states where possible. This won't |
| /// fully minimize the DFA, but it works well in a lot of cases. |
| #[cfg(feature = "std")] |
| type StateMap = std::collections::HashMap<State, LazyStateID>; |
| #[cfg(not(feature = "std"))] |
| type StateMap = alloc::collections::BTreeMap<State, LazyStateID>; |
| |
| /// A type that groups methods that require the base NFA/DFA and writable |
| /// access to the cache. |
| #[derive(Debug)] |
| struct Lazy<'i, 'c> { |
| dfa: &'i DFA, |
| cache: &'c mut Cache, |
| } |
| |
| impl<'i, 'c> Lazy<'i, 'c> { |
| /// Creates a new 'Lazy' wrapper for a DFA and its corresponding cache. |
| fn new(dfa: &'i DFA, cache: &'c mut Cache) -> Lazy<'i, 'c> { |
| Lazy { dfa, cache } |
| } |
| |
| /// Return an immutable view by downgrading a writable cache to a read-only |
| /// cache. |
| fn as_ref<'a>(&'a self) -> LazyRef<'i, 'a> { |
| LazyRef::new(self.dfa, self.cache) |
| } |
| |
| /// This is marked as 'inline(never)' to avoid bloating methods on 'DFA' |
| /// like 'next_state' and 'next_eoi_state' that are called in critical |
| /// areas. The idea is to let the optimizer focus on the other areas of |
| /// those methods as the hot path. |
| /// |
| /// Here's an example that justifies 'inline(never)' |
| /// |
| /// ```ignore |
| /// regex-cli find match hybrid \ |
| /// --cache-capacity 100000000 \ |
| /// -p '\pL{100}' |
| /// all-codepoints-utf8-100x |
| /// ``` |
| /// |
| /// Where 'all-codepoints-utf8-100x' is the UTF-8 encoding of every |
| /// codepoint, in sequence, repeated 100 times. |
| /// |
| /// With 'inline(never)' hyperfine reports 1.1s per run. With |
| /// 'inline(always)', hyperfine reports 1.23s. So that's a 10% improvement. |
| #[cold] |
| #[inline(never)] |
| fn cache_next_state( |
| &mut self, |
| mut current: LazyStateID, |
| unit: alphabet::Unit, |
| ) -> Result<LazyStateID, CacheError> { |
| let stride2 = self.dfa.stride2(); |
| let empty_builder = self.get_state_builder(); |
| let builder = determinize::next( |
| self.dfa.get_nfa(), |
| self.dfa.get_config().get_match_kind(), |
| &mut self.cache.sparses, |
| &mut self.cache.stack, |
| &self.cache.states[current.as_usize_untagged() >> stride2], |
| unit, |
| empty_builder, |
| ); |
| let save_state = !self.as_ref().state_builder_fits_in_cache(&builder); |
| if save_state { |
| self.save_state(current); |
| } |
| let next = self.add_builder_state(builder, |sid| sid)?; |
| if save_state { |
| current = self.saved_state_id(); |
| } |
| // This is the payoff. The next time 'next_state' is called with this |
| // state and alphabet unit, it will find this transition and avoid |
| // having to re-determinize this transition. |
| self.set_transition(current, unit, next); |
| Ok(next) |
| } |
| |
| /// Compute and cache the starting state for the given pattern ID (if |
| /// present) and the starting configuration. |
| /// |
| /// This panics if a pattern ID is given and the DFA isn't configured to |
| /// build anchored start states for each pattern. |
| /// |
| /// This will never return an unknown lazy state ID. |
| /// |
| /// If caching this state would otherwise result in a cache that has been |
| /// cleared too many times, then an error is returned. |
| #[cold] |
| #[inline(never)] |
| fn cache_start_group( |
| &mut self, |
| anchored: Anchored, |
| start: Start, |
| ) -> Result<LazyStateID, StartError> { |
| let nfa_start_id = match anchored { |
| Anchored::No => self.dfa.get_nfa().start_unanchored(), |
| Anchored::Yes => self.dfa.get_nfa().start_anchored(), |
| Anchored::Pattern(pid) => { |
| if !self.dfa.get_config().get_starts_for_each_pattern() { |
| return Err(StartError::unsupported_anchored(anchored)); |
| } |
| match self.dfa.get_nfa().start_pattern(pid) { |
| None => return Ok(self.as_ref().dead_id()), |
| Some(sid) => sid, |
| } |
| } |
| }; |
| |
| let id = self |
| .cache_start_one(nfa_start_id, start) |
| .map_err(StartError::cache)?; |
| self.set_start_state(anchored, start, id); |
| Ok(id) |
| } |
| |
| /// Compute and cache the starting state for the given NFA state ID and the |
| /// starting configuration. The NFA state ID might be one of the following: |
| /// |
| /// 1) An unanchored start state to match any pattern. |
| /// 2) An anchored start state to match any pattern. |
| /// 3) An anchored start state for a particular pattern. |
| /// |
| /// This will never return an unknown lazy state ID. |
| /// |
| /// If caching this state would otherwise result in a cache that has been |
| /// cleared too many times, then an error is returned. |
| fn cache_start_one( |
| &mut self, |
| nfa_start_id: NFAStateID, |
| start: Start, |
| ) -> Result<LazyStateID, CacheError> { |
| let mut builder_matches = self.get_state_builder().into_matches(); |
| determinize::set_lookbehind_from_start( |
| self.dfa.get_nfa(), |
| &start, |
| &mut builder_matches, |
| ); |
| self.cache.sparses.set1.clear(); |
| determinize::epsilon_closure( |
| self.dfa.get_nfa(), |
| nfa_start_id, |
| builder_matches.look_have(), |
| &mut self.cache.stack, |
| &mut self.cache.sparses.set1, |
| ); |
| let mut builder = builder_matches.into_nfa(); |
| determinize::add_nfa_states( |
| &self.dfa.get_nfa(), |
| &self.cache.sparses.set1, |
| &mut builder, |
| ); |
| let tag_starts = self.dfa.get_config().get_specialize_start_states(); |
| self.add_builder_state(builder, |id| { |
| if tag_starts { |
| id.to_start() |
| } else { |
| id |
| } |
| }) |
| } |
| |
| /// Either add the given builder state to this cache, or return an ID to an |
| /// equivalent state already in this cache. |
| /// |
| /// In the case where no equivalent state exists, the idmap function given |
| /// may be used to transform the identifier allocated. This is useful if |
| /// the caller needs to tag the ID with additional information. |
| /// |
| /// This will never return an unknown lazy state ID. |
| /// |
| /// If caching this state would otherwise result in a cache that has been |
| /// cleared too many times, then an error is returned. |
| fn add_builder_state( |
| &mut self, |
| builder: StateBuilderNFA, |
| idmap: impl Fn(LazyStateID) -> LazyStateID, |
| ) -> Result<LazyStateID, CacheError> { |
| if let Some(&cached_id) = |
| self.cache.states_to_id.get(builder.as_bytes()) |
| { |
| // Since we have a cached state, put the constructed state's |
| // memory back into our scratch space, so that it can be reused. |
| self.put_state_builder(builder); |
| return Ok(cached_id); |
| } |
| let result = self.add_state(builder.to_state(), idmap); |
| self.put_state_builder(builder); |
| result |
| } |
| |
| /// Allocate a new state ID and add the given state to this cache. |
| /// |
| /// The idmap function given may be used to transform the identifier |
| /// allocated. This is useful if the caller needs to tag the ID with |
| /// additional information. |
| /// |
| /// This will never return an unknown lazy state ID. |
| /// |
| /// If caching this state would otherwise result in a cache that has been |
| /// cleared too many times, then an error is returned. |
| fn add_state( |
| &mut self, |
| state: State, |
| idmap: impl Fn(LazyStateID) -> LazyStateID, |
| ) -> Result<LazyStateID, CacheError> { |
| if !self.as_ref().state_fits_in_cache(&state) { |
| self.try_clear_cache()?; |
| } |
| // It's important for this to come second, since the above may clear |
| // the cache. If we clear the cache after ID generation, then the ID |
| // is likely bunk since it would have been generated based on a larger |
| // transition table. |
| let mut id = idmap(self.next_state_id()?); |
| if state.is_match() { |
| id = id.to_match(); |
| } |
| // Add room in the transition table. Since this is a fresh state, all |
| // of its transitions are unknown. |
| self.cache.trans.extend( |
| iter::repeat(self.as_ref().unknown_id()).take(self.dfa.stride()), |
| ); |
| // When we add a sentinel state, we never want to set any quit |
| // transitions. Technically, this is harmless, since sentinel states |
| // have all of their transitions set to loop back to themselves. But |
| // when creating sentinel states before the quit sentinel state, |
| // this will try to call 'set_transition' on a state ID that doesn't |
| // actually exist yet, which isn't allowed. So we just skip doing so |
| // entirely. |
| if !self.dfa.quitset.is_empty() && !self.as_ref().is_sentinel(id) { |
| let quit_id = self.as_ref().quit_id(); |
| for b in self.dfa.quitset.iter() { |
| self.set_transition(id, alphabet::Unit::u8(b), quit_id); |
| } |
| } |
| self.cache.memory_usage_state += state.memory_usage(); |
| self.cache.states.push(state.clone()); |
| self.cache.states_to_id.insert(state, id); |
| Ok(id) |
| } |
| |
| /// Allocate a new state ID. |
| /// |
| /// This will never return an unknown lazy state ID. |
| /// |
| /// If caching this state would otherwise result in a cache that has been |
| /// cleared too many times, then an error is returned. |
| fn next_state_id(&mut self) -> Result<LazyStateID, CacheError> { |
| let sid = match LazyStateID::new(self.cache.trans.len()) { |
| Ok(sid) => sid, |
| Err(_) => { |
| self.try_clear_cache()?; |
| // This has to pass since we check that ID capacity at |
| // construction time can fit at least MIN_STATES states. |
| LazyStateID::new(self.cache.trans.len()).unwrap() |
| } |
| }; |
| Ok(sid) |
| } |
| |
| /// Attempt to clear the cache used by this lazy DFA. |
| /// |
| /// If clearing the cache exceeds the minimum number of required cache |
| /// clearings, then this will return a cache error. In this case, |
| /// callers should bubble this up as the cache can't be used until it is |
| /// reset. Implementations of search should convert this error into a |
| /// [`MatchError::gave_up`]. |
| /// |
| /// If 'self.state_saver' is set to save a state, then this state is |
| /// persisted through cache clearing. Otherwise, the cache is returned to |
| /// its state after initialization with two exceptions: its clear count |
| /// is incremented and some of its memory likely has additional capacity. |
| /// That is, clearing a cache does _not_ release memory. |
| /// |
| /// Otherwise, any lazy state ID generated by the cache prior to resetting |
| /// it is invalid after the reset. |
| fn try_clear_cache(&mut self) -> Result<(), CacheError> { |
| let c = self.dfa.get_config(); |
| if let Some(min_count) = c.get_minimum_cache_clear_count() { |
| if self.cache.clear_count >= min_count { |
| if let Some(min_bytes_per) = c.get_minimum_bytes_per_state() { |
| let len = self.cache.search_total_len(); |
| let min_bytes = |
| min_bytes_per.saturating_mul(self.cache.states.len()); |
| // If we've searched 0 bytes then probably something has |
| // gone wrong and the lazy DFA search implementation isn't |
| // correctly updating the search progress state. |
| if len == 0 { |
| trace!( |
| "number of bytes searched is 0, but \ |
| a minimum bytes per state searched ({}) is \ |
| enabled, maybe Cache::search_update \ |
| is not being used?", |
| min_bytes_per, |
| ); |
| } |
| if len < min_bytes { |
| trace!( |
| "lazy DFA cache has been cleared {} times, \ |
| which exceeds the limit of {}, \ |
| AND its bytes searched per state is less \ |
| than the configured minimum of {}, \ |
| therefore lazy DFA is giving up \ |
| (bytes searched since cache clear = {}, \ |
| number of states = {})", |
| self.cache.clear_count, |
| min_count, |
| min_bytes_per, |
| len, |
| self.cache.states.len(), |
| ); |
| return Err(CacheError::bad_efficiency()); |
| } else { |
| trace!( |
| "lazy DFA cache has been cleared {} times, \ |
| which exceeds the limit of {}, \ |
| AND its bytes searched per state is greater \ |
| than the configured minimum of {}, \ |
| therefore lazy DFA is continuing! \ |
| (bytes searched since cache clear = {}, \ |
| number of states = {})", |
| self.cache.clear_count, |
| min_count, |
| min_bytes_per, |
| len, |
| self.cache.states.len(), |
| ); |
| } |
| } else { |
| trace!( |
| "lazy DFA cache has been cleared {} times, \ |
| which exceeds the limit of {}, \ |
| since there is no configured bytes per state \ |
| minimum, lazy DFA is giving up", |
| self.cache.clear_count, |
| min_count, |
| ); |
| return Err(CacheError::too_many_cache_clears()); |
| } |
| } |
| } |
| self.clear_cache(); |
| Ok(()) |
| } |
| |
| /// Clears _and_ resets the cache. Resetting the cache means that no |
| /// states are persisted and the clear count is reset to 0. No heap memory |
| /// is released. |
| /// |
| /// Note that the caller may reset a cache with a different DFA than what |
| /// it was created from. In which case, the cache can now be used with the |
| /// new DFA (and not the old DFA). |
| fn reset_cache(&mut self) { |
| self.cache.state_saver = StateSaver::none(); |
| self.clear_cache(); |
| // If a new DFA is used, it might have a different number of NFA |
| // states, so we need to make sure our sparse sets have the appropriate |
| // size. |
| self.cache.sparses.resize(self.dfa.get_nfa().states().len()); |
| self.cache.clear_count = 0; |
| self.cache.progress = None; |
| } |
| |
| /// Clear the cache used by this lazy DFA. |
| /// |
| /// If 'self.state_saver' is set to save a state, then this state is |
| /// persisted through cache clearing. Otherwise, the cache is returned to |
| /// its state after initialization with two exceptions: its clear count |
| /// is incremented and some of its memory likely has additional capacity. |
| /// That is, clearing a cache does _not_ release memory. |
| /// |
| /// Otherwise, any lazy state ID generated by the cache prior to resetting |
| /// it is invalid after the reset. |
| fn clear_cache(&mut self) { |
| self.cache.trans.clear(); |
| self.cache.starts.clear(); |
| self.cache.states.clear(); |
| self.cache.states_to_id.clear(); |
| self.cache.memory_usage_state = 0; |
| self.cache.clear_count += 1; |
| self.cache.bytes_searched = 0; |
| if let Some(ref mut progress) = self.cache.progress { |
| progress.start = progress.at; |
| } |
| trace!( |
| "lazy DFA cache has been cleared (count: {})", |
| self.cache.clear_count |
| ); |
| self.init_cache(); |
| // If the state we want to save is one of the sentinel |
| // (unknown/dead/quit) states, then 'init_cache' adds those back, and |
| // their identifier values remains invariant. So there's no need to add |
| // it again. (And indeed, doing so would be incorrect!) |
| if let Some((old_id, state)) = self.cache.state_saver.take_to_save() { |
| // If the state is one of the special sentinel states, then it is |
| // automatically added by cache initialization and its ID always |
| // remains the same. With that said, this should never occur since |
| // the sentinel states are all loop states back to themselves. So |
| // we should never be in a position where we're attempting to save |
| // a sentinel state since we never compute transitions out of a |
| // sentinel state. |
| assert!( |
| !self.as_ref().is_sentinel(old_id), |
| "cannot save sentinel state" |
| ); |
| let new_id = self |
| .add_state(state, |id| { |
| if old_id.is_start() { |
| // We don't need to consult the |
| // 'specialize_start_states' config knob here, because |
| // if it's disabled, old_id.is_start() will never |
| // return true. |
| id.to_start() |
| } else { |
| id |
| } |
| }) |
| // The unwrap here is OK because lazy DFA creation ensures that |
| // we have room in the cache to add MIN_STATES states. Since |
| // 'init_cache' above adds 3, this adds a 4th. |
| .expect("adding one state after cache clear must work"); |
| self.cache.state_saver = StateSaver::Saved(new_id); |
| } |
| } |
| |
| /// Initialize this cache from emptiness to a place where it can be used |
| /// for search. |
| /// |
| /// This is called both at cache creation time and after the cache has been |
| /// cleared. |
| /// |
| /// Primarily, this adds the three sentinel states and allocates some |
| /// initial memory. |
| fn init_cache(&mut self) { |
| // Why multiply by 2 here? Because we make room for both the unanchored |
| // and anchored start states. Unanchored is first and then anchored. |
| let mut starts_len = Start::len().checked_mul(2).unwrap(); |
| // ... but if we also want start states for every pattern, we make room |
| // for that too. |
| if self.dfa.get_config().get_starts_for_each_pattern() { |
| starts_len += Start::len() * self.dfa.pattern_len(); |
| } |
| self.cache |
| .starts |
| .extend(iter::repeat(self.as_ref().unknown_id()).take(starts_len)); |
| // This is the set of NFA states that corresponds to each of our three |
| // sentinel states: the empty set. |
| let dead = State::dead(); |
| // This sets up some states that we use as sentinels that are present |
| // in every DFA. While it would be technically possible to implement |
| // this DFA without explicitly putting these states in the transition |
| // table, this is convenient to do to make `next_state` correct for all |
| // valid state IDs without needing explicit conditionals to special |
| // case these sentinel states. |
| // |
| // All three of these states are "dead" states. That is, all of |
| // them transition only to themselves. So once you enter one of |
| // these states, it's impossible to leave them. Thus, any correct |
| // search routine must explicitly check for these state types. (Sans |
| // `unknown`, since that is only used internally to represent missing |
| // states.) |
| let unk_id = |
| self.add_state(dead.clone(), |id| id.to_unknown()).unwrap(); |
| let dead_id = self.add_state(dead.clone(), |id| id.to_dead()).unwrap(); |
| let quit_id = self.add_state(dead.clone(), |id| id.to_quit()).unwrap(); |
| assert_eq!(unk_id, self.as_ref().unknown_id()); |
| assert_eq!(dead_id, self.as_ref().dead_id()); |
| assert_eq!(quit_id, self.as_ref().quit_id()); |
| // The idea here is that if you start in an unknown/dead/quit state and |
| // try to transition on them, then you should end up where you started. |
| self.set_all_transitions(unk_id, unk_id); |
| self.set_all_transitions(dead_id, dead_id); |
| self.set_all_transitions(quit_id, quit_id); |
| // All of these states are technically equivalent from the FSM |
| // perspective, so putting all three of them in the cache isn't |
| // possible. (They are distinct merely because we use their |
| // identifiers as sentinels to mean something, as indicated by the |
| // names.) Moreover, we wouldn't want to do that. Unknown and quit |
| // states are special in that they are artificial constructions |
| // this implementation. But dead states are a natural part of |
| // determinization. When you reach a point in the NFA where you cannot |
| // go anywhere else, a dead state will naturally arise and we MUST |
| // reuse the canonical dead state that we've created here. Why? Because |
| // it is the state ID that tells the search routine whether a state is |
| // dead or not, and thus, whether to stop the search. Having a bunch of |
| // distinct dead states would be quite wasteful! |
| self.cache.states_to_id.insert(dead, dead_id); |
| } |
| |
| /// Save the state corresponding to the ID given such that the state |
| /// persists through a cache clearing. |
| /// |
| /// While the state may persist, the ID may not. In order to discover the |
| /// new state ID, one must call 'saved_state_id' after a cache clearing. |
| fn save_state(&mut self, id: LazyStateID) { |
| let state = self.as_ref().get_cached_state(id).clone(); |
| self.cache.state_saver = StateSaver::ToSave { id, state }; |
| } |
| |
| /// Returns the updated lazy state ID for a state that was persisted |
| /// through a cache clearing. |
| /// |
| /// It is only correct to call this routine when both a state has been |
| /// saved and the cache has just been cleared. Otherwise, this panics. |
| fn saved_state_id(&mut self) -> LazyStateID { |
| self.cache |
| .state_saver |
| .take_saved() |
| .expect("state saver does not have saved state ID") |
| } |
| |
| /// Set all transitions on the state 'from' to 'to'. |
| fn set_all_transitions(&mut self, from: LazyStateID, to: LazyStateID) { |
| for unit in self.dfa.classes.representatives(..) { |
| self.set_transition(from, unit, to); |
| } |
| } |
| |
| /// Set the transition on 'from' for 'unit' to 'to'. |
| /// |
| /// This panics if either 'from' or 'to' is invalid. |
| /// |
| /// All unit values are OK. |
| fn set_transition( |
| &mut self, |
| from: LazyStateID, |
| unit: alphabet::Unit, |
| to: LazyStateID, |
| ) { |
| assert!(self.as_ref().is_valid(from), "invalid 'from' id: {:?}", from); |
| assert!(self.as_ref().is_valid(to), "invalid 'to' id: {:?}", to); |
| let offset = |
| from.as_usize_untagged() + self.dfa.classes.get_by_unit(unit); |
| self.cache.trans[offset] = to; |
| } |
| |
| /// Set the start ID for the given pattern ID (if given) and starting |
| /// configuration to the ID given. |
| /// |
| /// This panics if 'id' is not valid or if a pattern ID is given and |
| /// 'starts_for_each_pattern' is not enabled. |
| fn set_start_state( |
| &mut self, |
| anchored: Anchored, |
| start: Start, |
| id: LazyStateID, |
| ) { |
| assert!(self.as_ref().is_valid(id)); |
| let start_index = start.as_usize(); |
| let index = match anchored { |
| Anchored::No => start_index, |
| Anchored::Yes => Start::len() + start_index, |
| Anchored::Pattern(pid) => { |
| assert!( |
| self.dfa.get_config().get_starts_for_each_pattern(), |
| "attempted to search for a specific pattern \ |
| without enabling starts_for_each_pattern", |
| ); |
| let pid = pid.as_usize(); |
| (2 * Start::len()) + (Start::len() * pid) + start_index |
| } |
| }; |
| self.cache.starts[index] = id; |
| } |
| |
| /// Returns a state builder from this DFA that might have existing |
| /// capacity. This helps avoid allocs in cases where a state is built that |
| /// turns out to already be cached. |
| /// |
| /// Callers must put the state builder back with 'put_state_builder', |
| /// otherwise the allocation reuse won't work. |
| fn get_state_builder(&mut self) -> StateBuilderEmpty { |
| core::mem::replace( |
| &mut self.cache.scratch_state_builder, |
| StateBuilderEmpty::new(), |
| ) |
| } |
| |
| /// Puts the given state builder back into this DFA for reuse. |
| /// |
| /// Note that building a 'State' from a builder always creates a new alloc, |
| /// so callers should always put the builder back. |
| fn put_state_builder(&mut self, builder: StateBuilderNFA) { |
| let _ = core::mem::replace( |
| &mut self.cache.scratch_state_builder, |
| builder.clear(), |
| ); |
| } |
| } |
| |
| /// A type that groups methods that require the base NFA/DFA and read-only |
| /// access to the cache. |
| #[derive(Debug)] |
| struct LazyRef<'i, 'c> { |
| dfa: &'i DFA, |
| cache: &'c Cache, |
| } |
| |
| impl<'i, 'c> LazyRef<'i, 'c> { |
| /// Creates a new 'Lazy' wrapper for a DFA and its corresponding cache. |
| fn new(dfa: &'i DFA, cache: &'c Cache) -> LazyRef<'i, 'c> { |
| LazyRef { dfa, cache } |
| } |
| |
| /// Return the ID of the start state for the given configuration. |
| /// |
| /// If the start state has not yet been computed, then this returns an |
| /// unknown lazy state ID. |
| #[cfg_attr(feature = "perf-inline", inline(always))] |
| fn get_cached_start_id( |
| &self, |
| anchored: Anchored, |
| start: Start, |
| ) -> Result<LazyStateID, StartError> { |
| let start_index = start.as_usize(); |
| let index = match anchored { |
| Anchored::No => start_index, |
| Anchored::Yes => Start::len() + start_index, |
| Anchored::Pattern(pid) => { |
| if !self.dfa.get_config().get_starts_for_each_pattern() { |
| return Err(StartError::unsupported_anchored(anchored)); |
| } |
| if pid.as_usize() >= self.dfa.pattern_len() { |
| return Ok(self.dead_id()); |
| } |
| (2 * Start::len()) |
| + (Start::len() * pid.as_usize()) |
| + start_index |
| } |
| }; |
| Ok(self.cache.starts[index]) |
| } |
| |
| /// Return the cached NFA/DFA powerset state for the given ID. |
| /// |
| /// This panics if the given ID does not address a valid state. |
| fn get_cached_state(&self, sid: LazyStateID) -> &State { |
| let index = sid.as_usize_untagged() >> self.dfa.stride2(); |
| &self.cache.states[index] |
| } |
| |
| /// Returns true if and only if the given ID corresponds to a "sentinel" |
| /// state. |
| /// |
| /// A sentinel state is a state that signifies a special condition of |
| /// search, and where every transition maps back to itself. See LazyStateID |
| /// for more details. Note that start and match states are _not_ sentinels |
| /// since they may otherwise be real states with non-trivial transitions. |
| /// The purposes of sentinel states is purely to indicate something. Their |
| /// transitions are not meant to be followed. |
| fn is_sentinel(&self, id: LazyStateID) -> bool { |
| id == self.unknown_id() || id == self.dead_id() || id == self.quit_id() |
| } |
| |
| /// Returns the ID of the unknown state for this lazy DFA. |
| fn unknown_id(&self) -> LazyStateID { |
| // This unwrap is OK since 0 is always a valid state ID. |
| LazyStateID::new(0).unwrap().to_unknown() |
| } |
| |
| /// Returns the ID of the dead state for this lazy DFA. |
| fn dead_id(&self) -> LazyStateID { |
| // This unwrap is OK since the maximum value here is 1 * 512 = 512, |
| // which is <= 2047 (the maximum state ID on 16-bit systems). Where |
| // 512 is the worst case for our equivalence classes (every byte is a |
| // distinct class). |
| LazyStateID::new(1 << self.dfa.stride2()).unwrap().to_dead() |
| } |
| |
| /// Returns the ID of the quit state for this lazy DFA. |
| fn quit_id(&self) -> LazyStateID { |
| // This unwrap is OK since the maximum value here is 2 * 512 = 1024, |
| // which is <= 2047 (the maximum state ID on 16-bit systems). Where |
| // 512 is the worst case for our equivalence classes (every byte is a |
| // distinct class). |
| LazyStateID::new(2 << self.dfa.stride2()).unwrap().to_quit() |
| } |
| |
| /// Returns true if and only if the given ID is valid. |
| /// |
| /// An ID is valid if it is both a valid index into the transition table |
| /// and is a multiple of the DFA's stride. |
| fn is_valid(&self, id: LazyStateID) -> bool { |
| let id = id.as_usize_untagged(); |
| id < self.cache.trans.len() && id % self.dfa.stride() == 0 |
| } |
| |
| /// Returns true if adding the state given would fit in this cache. |
| fn state_fits_in_cache(&self, state: &State) -> bool { |
| let needed = self.cache.memory_usage() |
| + self.memory_usage_for_one_more_state(state.memory_usage()); |
| trace!( |
| "lazy DFA cache capacity check: {:?} ?<=? {:?}", |
| needed, |
| self.dfa.cache_capacity |
| ); |
| needed <= self.dfa.cache_capacity |
| } |
| |
| /// Returns true if adding the state to be built by the given builder would |
| /// fit in this cache. |
| fn state_builder_fits_in_cache(&self, state: &StateBuilderNFA) -> bool { |
| let needed = self.cache.memory_usage() |
| + self.memory_usage_for_one_more_state(state.as_bytes().len()); |
| needed <= self.dfa.cache_capacity |
| } |
| |
| /// Returns the additional memory usage, in bytes, required to add one more |
| /// state to this cache. The given size should be the heap size, in bytes, |
| /// that would be used by the new state being added. |
| fn memory_usage_for_one_more_state( |
| &self, |
| state_heap_size: usize, |
| ) -> usize { |
| const ID_SIZE: usize = size_of::<LazyStateID>(); |
| const STATE_SIZE: usize = size_of::<State>(); |
| |
| self.dfa.stride() * ID_SIZE // additional space needed in trans table |
| + STATE_SIZE // space in cache.states |
| + (STATE_SIZE + ID_SIZE) // space in cache.states_to_id |
| + state_heap_size // heap memory used by state itself |
| } |
| } |
| |
| /// A simple type that encapsulates the saving of a state ID through a cache |
| /// clearing. |
| /// |
| /// A state ID can be marked for saving with ToSave, while a state ID can be |
| /// saved itself with Saved. |
| #[derive(Clone, Debug)] |
| enum StateSaver { |
| /// An empty state saver. In this case, no states (other than the special |
| /// sentinel states) are preserved after clearing the cache. |
| None, |
| /// An ID of a state (and the state itself) that should be preserved after |
| /// the lazy DFA's cache has been cleared. After clearing, the updated ID |
| /// is stored in 'Saved' since it may have changed. |
| ToSave { id: LazyStateID, state: State }, |
| /// An ID that of a state that has been persisted through a lazy DFA |
| /// cache clearing. The ID recorded here corresponds to an ID that was |
| /// once marked as ToSave. The IDs are likely not equivalent even though |
| /// the states they point to are. |
| Saved(LazyStateID), |
| } |
| |
| impl StateSaver { |
| /// Create an empty state saver. |
| fn none() -> StateSaver { |
| StateSaver::None |
| } |
| |
| /// Replace this state saver with an empty saver, and if this saver is a |
| /// request to save a state, return that request. |
| fn take_to_save(&mut self) -> Option<(LazyStateID, State)> { |
| match core::mem::replace(self, StateSaver::None) { |
| StateSaver::None | StateSaver::Saved(_) => None, |
| StateSaver::ToSave { id, state } => Some((id, state)), |
| } |
| } |
| |
| /// Replace this state saver with an empty saver, and if this saver is a |
| /// saved state (or a request to save a state), return that state's ID. |
| /// |
| /// The idea here is that a request to save a state isn't necessarily |
| /// honored because it might not be needed. e.g., Some higher level code |
| /// might request a state to be saved on the off chance that the cache gets |
| /// cleared when a new state is added at a lower level. But if that new |
| /// state is never added, then the cache is never cleared and the state and |
| /// its ID remain unchanged. |
| fn take_saved(&mut self) -> Option<LazyStateID> { |
| match core::mem::replace(self, StateSaver::None) { |
| StateSaver::None => None, |
| StateSaver::Saved(id) | StateSaver::ToSave { id, .. } => Some(id), |
| } |
| } |
| } |
| |
| /// The configuration used for building a lazy DFA. |
| /// |
| /// As a convenience, [`DFA::config`] is an alias for [`Config::new`]. The |
| /// advantage of the former is that it often lets you avoid importing the |
| /// `Config` type directly. |
| /// |
| /// A lazy DFA configuration is a simple data object that is typically used |
| /// with [`Builder::configure`]. |
| /// |
| /// The default configuration guarantees that a search will never return a |
| /// "gave up" or "quit" error, although it is possible for a search to fail |
| /// if [`Config::starts_for_each_pattern`] wasn't enabled (which it is not by |
| /// default) and an [`Anchored::Pattern`] mode is requested via [`Input`]. |
| #[derive(Clone, Debug, Default)] |
| pub struct Config { |
| // As with other configuration types in this crate, we put all our knobs |
| // in options so that we can distinguish between "default" and "not set." |
| // This makes it possible to easily combine multiple configurations |
| // without default values overwriting explicitly specified values. See the |
| // 'overwrite' method. |
| // |
| // For docs on the fields below, see the corresponding method setters. |
| match_kind: Option<MatchKind>, |
| pre: Option<Option<Prefilter>>, |
| starts_for_each_pattern: Option<bool>, |
| byte_classes: Option<bool>, |
| unicode_word_boundary: Option<bool>, |
| quitset: Option<ByteSet>, |
| specialize_start_states: Option<bool>, |
| cache_capacity: Option<usize>, |
| skip_cache_capacity_check: Option<bool>, |
| minimum_cache_clear_count: Option<Option<usize>>, |
| minimum_bytes_per_state: Option<Option<usize>>, |
| } |
| |
| impl Config { |
| /// Return a new default lazy DFA builder configuration. |
| pub fn new() -> Config { |
| Config::default() |
| } |
| |
| /// Set the desired match semantics. |
| /// |
| /// The default is [`MatchKind::LeftmostFirst`], which corresponds to the |
| /// match semantics of Perl-like regex engines. That is, when multiple |
| /// patterns would match at the same leftmost position, the pattern that |
| /// appears first in the concrete syntax is chosen. |
| /// |
| /// Currently, the only other kind of match semantics supported is |
| /// [`MatchKind::All`]. This corresponds to classical DFA construction |
| /// where all possible matches are added to the lazy DFA. |
| /// |
| /// Typically, `All` is used when one wants to execute an overlapping |
| /// search and `LeftmostFirst` otherwise. In particular, it rarely makes |
| /// sense to use `All` with the various "leftmost" find routines, since the |
| /// leftmost routines depend on the `LeftmostFirst` automata construction |
| /// strategy. Specifically, `LeftmostFirst` adds dead states to the |
| /// lazy DFA as a way to terminate the search and report a match. |
| /// `LeftmostFirst` also supports non-greedy matches using this strategy |
| /// where as `All` does not. |
| /// |
| /// # Example: overlapping search |
| /// |
| /// This example shows the typical use of `MatchKind::All`, which is to |
| /// report overlapping matches. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{ |
| /// hybrid::dfa::{DFA, OverlappingState}, |
| /// HalfMatch, Input, MatchKind, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().match_kind(MatchKind::All)) |
| /// .build_many(&[r"\w+$", r"\S+$"])?; |
| /// let mut cache = dfa.create_cache(); |
| /// let haystack = "@foo"; |
| /// let mut state = OverlappingState::start(); |
| /// |
| /// let expected = Some(HalfMatch::must(1, 4)); |
| /// dfa.try_search_overlapping_fwd( |
| /// &mut cache, &Input::new(haystack), &mut state, |
| /// )?; |
| /// assert_eq!(expected, state.get_match()); |
| /// |
| /// // The first pattern also matches at the same position, so re-running |
| /// // the search will yield another match. Notice also that the first |
| /// // pattern is returned after the second. This is because the second |
| /// // pattern begins its match before the first, is therefore an earlier |
| /// // match and is thus reported first. |
| /// let expected = Some(HalfMatch::must(0, 4)); |
| /// dfa.try_search_overlapping_fwd( |
| /// &mut cache, &Input::new(haystack), &mut state, |
| /// )?; |
| /// assert_eq!(expected, state.get_match()); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// # Example: reverse automaton to find start of match |
| /// |
| /// Another example for using `MatchKind::All` is for constructing a |
| /// reverse automaton to find the start of a match. `All` semantics are |
| /// used for this in order to find the longest possible match, which |
| /// corresponds to the leftmost starting position. |
| /// |
| /// Note that if you need the starting position then |
| /// [`hybrid::regex::Regex`](crate::hybrid::regex::Regex) will handle this |
| /// for you, so it's usually not necessary to do this yourself. |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// nfa::thompson::NFA, |
| /// Anchored, HalfMatch, Input, MatchKind, |
| /// }; |
| /// |
| /// let input = Input::new("123foobar456"); |
| /// let pattern = r"[a-z]+r"; |
| /// |
| /// let dfa_fwd = DFA::new(pattern)?; |
| /// let dfa_rev = DFA::builder() |
| /// .thompson(NFA::config().reverse(true)) |
| /// .configure(DFA::config().match_kind(MatchKind::All)) |
| /// .build(pattern)?; |
| /// let mut cache_fwd = dfa_fwd.create_cache(); |
| /// let mut cache_rev = dfa_rev.create_cache(); |
| /// |
| /// let expected_fwd = HalfMatch::must(0, 9); |
| /// let expected_rev = HalfMatch::must(0, 3); |
| /// let got_fwd = dfa_fwd.try_search_fwd(&mut cache_fwd, &input)?.unwrap(); |
| /// // Here we don't specify the pattern to search for since there's only |
| /// // one pattern and we're doing a leftmost search. But if this were an |
| /// // overlapping search, you'd need to specify the pattern that matched |
| /// // in the forward direction. (Otherwise, you might wind up finding the |
| /// // starting position of a match of some other pattern.) That in turn |
| /// // requires building the reverse automaton with starts_for_each_pattern |
| /// // enabled. |
| /// let input = input |
| /// .clone() |
| /// .range(..got_fwd.offset()) |
| /// .anchored(Anchored::Yes); |
| /// let got_rev = dfa_rev.try_search_rev(&mut cache_rev, &input)?.unwrap(); |
| /// assert_eq!(expected_fwd, got_fwd); |
| /// assert_eq!(expected_rev, got_rev); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn match_kind(mut self, kind: MatchKind) -> Config { |
| self.match_kind = Some(kind); |
| self |
| } |
| |
| /// Set a prefilter to be used whenever a start state is entered. |
| /// |
| /// A [`Prefilter`] in this context is meant to accelerate searches by |
| /// looking for literal prefixes that every match for the corresponding |
| /// pattern (or patterns) must start with. Once a prefilter produces a |
| /// match, the underlying search routine continues on to try and confirm |
| /// the match. |
| /// |
| /// Be warned that setting a prefilter does not guarantee that the search |
| /// will be faster. While it's usually a good bet, if the prefilter |
| /// produces a lot of false positive candidates (i.e., positions matched |
| /// by the prefilter but not by the regex), then the overall result can |
| /// be slower than if you had just executed the regex engine without any |
| /// prefilters. |
| /// |
| /// Note that unless [`Config::specialize_start_states`] has been |
| /// explicitly set, then setting this will also enable (when `pre` is |
| /// `Some`) or disable (when `pre` is `None`) start state specialization. |
| /// This occurs because without start state specialization, a prefilter |
| /// is likely to be less effective. And without a prefilter, start state |
| /// specialization is usually pointless. |
| /// |
| /// By default no prefilter is set. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// util::prefilter::Prefilter, |
| /// Input, HalfMatch, MatchKind, |
| /// }; |
| /// |
| /// let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "bar"]); |
| /// let re = DFA::builder() |
| /// .configure(DFA::config().prefilter(pre)) |
| /// .build(r"(foo|bar)[a-z]+")?; |
| /// let mut cache = re.create_cache(); |
| /// let input = Input::new("foo1 barfox bar"); |
| /// assert_eq!( |
| /// Some(HalfMatch::must(0, 11)), |
| /// re.try_search_fwd(&mut cache, &input)?, |
| /// ); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// Be warned though that an incorrect prefilter can lead to incorrect |
| /// results! |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// util::prefilter::Prefilter, |
| /// Input, HalfMatch, MatchKind, |
| /// }; |
| /// |
| /// let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "car"]); |
| /// let re = DFA::builder() |
| /// .configure(DFA::config().prefilter(pre)) |
| /// .build(r"(foo|bar)[a-z]+")?; |
| /// let mut cache = re.create_cache(); |
| /// let input = Input::new("foo1 barfox bar"); |
| /// assert_eq!( |
| /// // No match reported even though there clearly is one! |
| /// None, |
| /// re.try_search_fwd(&mut cache, &input)?, |
| /// ); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn prefilter(mut self, pre: Option<Prefilter>) -> Config { |
| self.pre = Some(pre); |
| if self.specialize_start_states.is_none() { |
| self.specialize_start_states = |
| Some(self.get_prefilter().is_some()); |
| } |
| self |
| } |
| |
| /// Whether to compile a separate start state for each pattern in the |
| /// lazy DFA. |
| /// |
| /// When enabled, a separate **anchored** start state is added for each |
| /// pattern in the lazy DFA. When this start state is used, then the DFA |
| /// will only search for matches for the pattern specified, even if there |
| /// are other patterns in the DFA. |
| /// |
| /// The main downside of this option is that it can potentially increase |
| /// the size of the DFA and/or increase the time it takes to build the |
| /// DFA at search time. However, since this is configuration for a lazy |
| /// DFA, these states aren't actually built unless they're used. Enabling |
| /// this isn't necessarily free, however, as it may result in higher cache |
| /// usage. |
| /// |
| /// There are a few reasons one might want to enable this (it's disabled |
| /// by default): |
| /// |
| /// 1. When looking for the start of an overlapping match (using a reverse |
| /// DFA), doing it correctly requires starting the reverse search using the |
| /// starting state of the pattern that matched in the forward direction. |
| /// Indeed, when building a [`Regex`](crate::hybrid::regex::Regex), it |
| /// will automatically enable this option when building the reverse DFA |
| /// internally. |
| /// 2. When you want to use a DFA with multiple patterns to both search |
| /// for matches of any pattern or to search for anchored matches of one |
| /// particular pattern while using the same DFA. (Otherwise, you would need |
| /// to compile a new DFA for each pattern.) |
| /// |
| /// By default this is disabled. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to use this option to permit the same lazy DFA |
| /// to run both general searches for any pattern and anchored searches for |
| /// a specific pattern. |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// Anchored, HalfMatch, Input, PatternID, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().starts_for_each_pattern(true)) |
| /// .build_many(&[r"[a-z0-9]{6}", r"[a-z][a-z0-9]{5}"])?; |
| /// let mut cache = dfa.create_cache(); |
| /// let haystack = "bar foo123"; |
| /// |
| /// // Here's a normal unanchored search that looks for any pattern. |
| /// let expected = HalfMatch::must(0, 10); |
| /// let input = Input::new(haystack); |
| /// assert_eq!(Some(expected), dfa.try_search_fwd(&mut cache, &input)?); |
| /// // We can also do a normal anchored search for any pattern. Since it's |
| /// // an anchored search, we position the start of the search where we |
| /// // know the match will begin. |
| /// let expected = HalfMatch::must(0, 10); |
| /// let input = Input::new(haystack).range(4..); |
| /// assert_eq!(Some(expected), dfa.try_search_fwd(&mut cache, &input)?); |
| /// // Since we compiled anchored start states for each pattern, we can |
| /// // also look for matches of other patterns explicitly, even if a |
| /// // different pattern would have normally matched. |
| /// let expected = HalfMatch::must(1, 10); |
| /// let input = Input::new(haystack) |
| /// .range(4..) |
| /// .anchored(Anchored::Pattern(PatternID::must(1))); |
| /// assert_eq!(Some(expected), dfa.try_search_fwd(&mut cache, &input)?); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn starts_for_each_pattern(mut self, yes: bool) -> Config { |
| self.starts_for_each_pattern = Some(yes); |
| self |
| } |
| |
| /// Whether to attempt to shrink the size of the lazy DFA's alphabet or |
| /// not. |
| /// |
| /// This option is enabled by default and should never be disabled unless |
| /// one is debugging the lazy DFA. |
| /// |
| /// When enabled, the lazy DFA will use a map from all possible bytes |
| /// to their corresponding equivalence class. Each equivalence class |
| /// represents a set of bytes that does not discriminate between a match |
| /// and a non-match in the DFA. For example, the pattern `[ab]+` has at |
| /// least two equivalence classes: a set containing `a` and `b` and a set |
| /// containing every byte except for `a` and `b`. `a` and `b` are in the |
| /// same equivalence classes because they never discriminate between a |
| /// match and a non-match. |
| /// |
| /// The advantage of this map is that the size of the transition table |
| /// can be reduced drastically from `#states * 256 * sizeof(LazyStateID)` |
| /// to `#states * k * sizeof(LazyStateID)` where `k` is the number of |
| /// equivalence classes (rounded up to the nearest power of 2). As a |
| /// result, total space usage can decrease substantially. Moreover, since a |
| /// smaller alphabet is used, DFA compilation during search becomes faster |
| /// as well since it will potentially be able to reuse a single transition |
| /// for multiple bytes. |
| /// |
| /// **WARNING:** This is only useful for debugging lazy DFAs. Disabling |
| /// this does not yield any speed advantages. Namely, even when this is |
| /// disabled, a byte class map is still used while searching. The only |
| /// difference is that every byte will be forced into its own distinct |
| /// equivalence class. This is useful for debugging the actual generated |
| /// transitions because it lets one see the transitions defined on actual |
| /// bytes instead of the equivalence classes. |
| pub fn byte_classes(mut self, yes: bool) -> Config { |
| self.byte_classes = Some(yes); |
| self |
| } |
| |
| /// Heuristically enable Unicode word boundaries. |
| /// |
| /// When set, this will attempt to implement Unicode word boundaries as if |
| /// they were ASCII word boundaries. This only works when the search input |
| /// is ASCII only. If a non-ASCII byte is observed while searching, then a |
| /// [`MatchError::quit`] error is returned. |
| /// |
| /// A possible alternative to enabling this option is to simply use an |
| /// ASCII word boundary, e.g., via `(?-u:\b)`. The main reason to use this |
| /// option is if you absolutely need Unicode support. This option lets one |
| /// use a fast search implementation (a DFA) for some potentially very |
| /// common cases, while providing the option to fall back to some other |
| /// regex engine to handle the general case when an error is returned. |
| /// |
| /// If the pattern provided has no Unicode word boundary in it, then this |
| /// option has no effect. (That is, quitting on a non-ASCII byte only |
| /// occurs when this option is enabled _and_ a Unicode word boundary is |
| /// present in the pattern.) |
| /// |
| /// This is almost equivalent to setting all non-ASCII bytes to be quit |
| /// bytes. The only difference is that this will cause non-ASCII bytes to |
| /// be quit bytes _only_ when a Unicode word boundary is present in the |
| /// pattern. |
| /// |
| /// When enabling this option, callers _must_ be prepared to |
| /// handle a [`MatchError`] error during search. When using a |
| /// [`Regex`](crate::hybrid::regex::Regex), this corresponds to using the |
| /// `try_` suite of methods. Alternatively, if callers can guarantee that |
| /// their input is ASCII only, then a [`MatchError::quit`] error will never |
| /// be returned while searching. |
| /// |
| /// This is disabled by default. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to heuristically enable Unicode word boundaries |
| /// in a pattern. It also shows what happens when a search comes across a |
| /// non-ASCII byte. |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// HalfMatch, Input, MatchError, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().unicode_word_boundary(true)) |
| /// .build(r"\b[0-9]+\b")?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// // The match occurs before the search ever observes the snowman |
| /// // character, so no error occurs. |
| /// let haystack = "foo 123 ☃"; |
| /// let expected = Some(HalfMatch::must(0, 7)); |
| /// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?; |
| /// assert_eq!(expected, got); |
| /// |
| /// // Notice that this search fails, even though the snowman character |
| /// // occurs after the ending match offset. This is because search |
| /// // routines read one byte past the end of the search to account for |
| /// // look-around, and indeed, this is required here to determine whether |
| /// // the trailing \b matches. |
| /// let haystack = "foo 123 ☃"; |
| /// let expected = MatchError::quit(0xE2, 8); |
| /// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack)); |
| /// assert_eq!(Err(expected), got); |
| /// |
| /// // Another example is executing a search where the span of the haystack |
| /// // we specify is all ASCII, but there is non-ASCII just before it. This |
| /// // correctly also reports an error. |
| /// let input = Input::new("β123").range(2..); |
| /// let expected = MatchError::quit(0xB2, 1); |
| /// let got = dfa.try_search_fwd(&mut cache, &input); |
| /// assert_eq!(Err(expected), got); |
| /// |
| /// // And similarly for the trailing word boundary. |
| /// let input = Input::new("123β").range(..3); |
| /// let expected = MatchError::quit(0xCE, 3); |
| /// let got = dfa.try_search_fwd(&mut cache, &input); |
| /// assert_eq!(Err(expected), got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn unicode_word_boundary(mut self, yes: bool) -> Config { |
| // We have a separate option for this instead of just setting the |
| // appropriate quit bytes here because we don't want to set quit bytes |
| // for every regex. We only want to set them when the regex contains a |
| // Unicode word boundary. |
| self.unicode_word_boundary = Some(yes); |
| self |
| } |
| |
| /// Add a "quit" byte to the lazy DFA. |
| /// |
| /// When a quit byte is seen during search time, then search will return a |
| /// [`MatchError::quit`] error indicating the offset at which the search |
| /// stopped. |
| /// |
| /// A quit byte will always overrule any other aspects of a regex. For |
| /// example, if the `x` byte is added as a quit byte and the regex `\w` is |
| /// used, then observing `x` will cause the search to quit immediately |
| /// despite the fact that `x` is in the `\w` class. |
| /// |
| /// This mechanism is primarily useful for heuristically enabling certain |
| /// features like Unicode word boundaries in a DFA. Namely, if the input |
| /// to search is ASCII, then a Unicode word boundary can be implemented |
| /// via an ASCII word boundary with no change in semantics. Thus, a DFA |
| /// can attempt to match a Unicode word boundary but give up as soon as it |
| /// observes a non-ASCII byte. Indeed, if callers set all non-ASCII bytes |
| /// to be quit bytes, then Unicode word boundaries will be permitted when |
| /// building lazy DFAs. Of course, callers should enable |
| /// [`Config::unicode_word_boundary`] if they want this behavior instead. |
| /// (The advantage being that non-ASCII quit bytes will only be added if a |
| /// Unicode word boundary is in the pattern.) |
| /// |
| /// When enabling this option, callers _must_ be prepared to |
| /// handle a [`MatchError`] error during search. When using a |
| /// [`Regex`](crate::hybrid::regex::Regex), this corresponds to using the |
| /// `try_` suite of methods. |
| /// |
| /// By default, there are no quit bytes set. |
| /// |
| /// # Panics |
| /// |
| /// This panics if heuristic Unicode word boundaries are enabled and any |
| /// non-ASCII byte is removed from the set of quit bytes. Namely, enabling |
| /// Unicode word boundaries requires setting every non-ASCII byte to a quit |
| /// byte. So if the caller attempts to undo any of that, then this will |
| /// panic. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to cause a search to terminate if it sees a |
| /// `\n` byte. This could be useful if, for example, you wanted to prevent |
| /// a user supplied pattern from matching across a line boundary. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{hybrid::dfa::DFA, MatchError, Input}; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().quit(b'\n', true)) |
| /// .build(r"foo\p{any}+bar")?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let haystack = "foo\nbar"; |
| /// // Normally this would produce a match, since \p{any} contains '\n'. |
| /// // But since we instructed the automaton to enter a quit state if a |
| /// // '\n' is observed, this produces a match error instead. |
| /// let expected = MatchError::quit(b'\n', 3); |
| /// let got = dfa.try_search_fwd( |
| /// &mut cache, |
| /// &Input::new(haystack), |
| /// ).unwrap_err(); |
| /// assert_eq!(expected, got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn quit(mut self, byte: u8, yes: bool) -> Config { |
| if self.get_unicode_word_boundary() && !byte.is_ascii() && !yes { |
| panic!( |
| "cannot set non-ASCII byte to be non-quit when \ |
| Unicode word boundaries are enabled" |
| ); |
| } |
| if self.quitset.is_none() { |
| self.quitset = Some(ByteSet::empty()); |
| } |
| if yes { |
| self.quitset.as_mut().unwrap().add(byte); |
| } else { |
| self.quitset.as_mut().unwrap().remove(byte); |
| } |
| self |
| } |
| |
| /// Enable specializing start states in the lazy DFA. |
| /// |
| /// When start states are specialized, an implementor of a search routine |
| /// using a lazy DFA can tell when the search has entered a starting state. |
| /// When start states aren't specialized, then it is impossible to know |
| /// whether the search has entered a start state. |
| /// |
| /// Ideally, this option wouldn't need to exist and we could always |
| /// specialize start states. The problem is that start states can be quite |
| /// active. This in turn means that an efficient search routine is likely |
| /// to ping-pong between a heavily optimized hot loop that handles most |
| /// states and to a less optimized specialized handling of start states. |
| /// This causes branches to get heavily mispredicted and overall can |
| /// materially decrease throughput. Therefore, specializing start states |
| /// should only be enabled when it is needed. |
| /// |
| /// Knowing whether a search is in a start state is typically useful when a |
| /// prefilter is active for the search. A prefilter is typically only run |
| /// when in a start state and a prefilter can greatly accelerate a search. |
| /// Therefore, the possible cost of specializing start states is worth it |
| /// in this case. Otherwise, if you have no prefilter, there is likely no |
| /// reason to specialize start states. |
| /// |
| /// This is disabled by default, but note that it is automatically |
| /// enabled (or disabled) if [`Config::prefilter`] is set. Namely, unless |
| /// `specialize_start_states` has already been set, [`Config::prefilter`] |
| /// will automatically enable or disable it based on whether a prefilter |
| /// is present or not, respectively. This is done because a prefilter's |
| /// effectiveness is rooted in being executed whenever the DFA is in a |
| /// start state, and that's only possible to do when they are specialized. |
| /// |
| /// Note that it is plausibly reasonable to _disable_ this option |
| /// explicitly while _enabling_ a prefilter. In that case, a prefilter |
| /// will still be run at the beginning of a search, but never again. This |
| /// in theory could strike a good balance if you're in a situation where a |
| /// prefilter is likely to produce many false positive candidates. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to enable start state specialization and then |
| /// shows how to check whether a state is a start state or not. |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, MatchError, Input}; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().specialize_start_states(true)) |
| /// .build(r"[a-z]+")?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let haystack = "123 foobar 4567".as_bytes(); |
| /// let sid = dfa.start_state_forward(&mut cache, &Input::new(haystack))?; |
| /// // The ID returned by 'start_state_forward' will always be tagged as |
| /// // a start state when start state specialization is enabled. |
| /// assert!(sid.is_tagged()); |
| /// assert!(sid.is_start()); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| /// |
| /// Compare the above with the default lazy DFA configuration where |
| /// start states are _not_ specialized. In this case, the start state |
| /// is not tagged and `sid.is_start()` returns false. |
| /// |
| /// ``` |
| /// use regex_automata::{hybrid::dfa::DFA, MatchError, Input}; |
| /// |
| /// let dfa = DFA::new(r"[a-z]+")?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let haystack = "123 foobar 4567".as_bytes(); |
| /// let sid = dfa.start_state_forward(&mut cache, &Input::new(haystack))?; |
| /// // Start states are not tagged in the default configuration! |
| /// assert!(!sid.is_tagged()); |
| /// assert!(!sid.is_start()); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn specialize_start_states(mut self, yes: bool) -> Config { |
| self.specialize_start_states = Some(yes); |
| self |
| } |
| |
| /// Sets the maximum amount of heap memory, in bytes, to allocate to the |
| /// cache for use during a lazy DFA search. If the lazy DFA would otherwise |
| /// use more heap memory, then, depending on other configuration knobs, |
| /// either stop the search and return an error or clear the cache and |
| /// continue the search. |
| /// |
| /// The default cache capacity is some "reasonable" number that will |
| /// accommodate most regular expressions. You may find that if you need |
| /// to build a large DFA then it may be necessary to increase the cache |
| /// capacity. |
| /// |
| /// Note that while building a lazy DFA will do a "minimum" check to ensure |
| /// the capacity is big enough, this is more or less about correctness. |
| /// If the cache is bigger than the minimum but still "too small," then the |
| /// lazy DFA could wind up spending a lot of time clearing the cache and |
| /// recomputing transitions, thus negating the performance benefits of a |
| /// lazy DFA. Thus, setting the cache capacity is mostly an experimental |
| /// endeavor. For most common patterns, however, the default should be |
| /// sufficient. |
| /// |
| /// For more details on how the lazy DFA's cache is used, see the |
| /// documentation for [`Cache`]. |
| /// |
| /// # Example |
| /// |
| /// This example shows what happens if the configured cache capacity is |
| /// too small. In such cases, one can override the cache capacity to make |
| /// it bigger. Alternatively, one might want to use less memory by setting |
| /// a smaller cache capacity. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// let pattern = r"\p{L}{1000}"; |
| /// |
| /// // The default cache capacity is likely too small to deal with regexes |
| /// // that are very large. Large repetitions of large Unicode character |
| /// // classes are a common way to make very large regexes. |
| /// let _ = DFA::new(pattern).unwrap_err(); |
| /// // Bump up the capacity to something bigger. |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().cache_capacity(100 * (1<<20))) // 100 MB |
| /// .build(pattern)?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let haystack = "ͰͲͶͿΆΈΉΊΌΎΏΑΒΓΔΕΖΗΘΙ".repeat(50); |
| /// let expected = Some(HalfMatch::must(0, 2000)); |
| /// let got = dfa.try_search_fwd(&mut cache, &Input::new(&haystack))?; |
| /// assert_eq!(expected, got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn cache_capacity(mut self, bytes: usize) -> Config { |
| self.cache_capacity = Some(bytes); |
| self |
| } |
| |
| /// Configures construction of a lazy DFA to use the minimum cache capacity |
| /// if the configured capacity is otherwise too small for the provided NFA. |
| /// |
| /// This is useful if you never want lazy DFA construction to fail because |
| /// of a capacity that is too small. |
| /// |
| /// In general, this option is typically not a good idea. In particular, |
| /// while a minimum cache capacity does permit the lazy DFA to function |
| /// where it otherwise couldn't, it's plausible that it may not function |
| /// well if it's constantly running out of room. In that case, the speed |
| /// advantages of the lazy DFA may be negated. On the other hand, the |
| /// "minimum" cache capacity computed may not be completely accurate and |
| /// could actually be bigger than what is really necessary. Therefore, it |
| /// is plausible that using the minimum cache capacity could still result |
| /// in very good performance. |
| /// |
| /// This is disabled by default. |
| /// |
| /// # Example |
| /// |
| /// This example shows what happens if the configured cache capacity is |
| /// too small. In such cases, one could override the capacity explicitly. |
| /// An alternative, demonstrated here, let's us force construction to use |
| /// the minimum cache capacity if the configured capacity is otherwise |
| /// too small. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; |
| /// |
| /// let pattern = r"\p{L}{1000}"; |
| /// |
| /// // The default cache capacity is likely too small to deal with regexes |
| /// // that are very large. Large repetitions of large Unicode character |
| /// // classes are a common way to make very large regexes. |
| /// let _ = DFA::new(pattern).unwrap_err(); |
| /// // Configure construction such it automatically selects the minimum |
| /// // cache capacity if it would otherwise be too small. |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().skip_cache_capacity_check(true)) |
| /// .build(pattern)?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let haystack = "ͰͲͶͿΆΈΉΊΌΎΏΑΒΓΔΕΖΗΘΙ".repeat(50); |
| /// let expected = Some(HalfMatch::must(0, 2000)); |
| /// let got = dfa.try_search_fwd(&mut cache, &Input::new(&haystack))?; |
| /// assert_eq!(expected, got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn skip_cache_capacity_check(mut self, yes: bool) -> Config { |
| self.skip_cache_capacity_check = Some(yes); |
| self |
| } |
| |
| /// Configure a lazy DFA search to quit after a certain number of cache |
| /// clearings. |
| /// |
| /// When a minimum is set, then a lazy DFA search will *possibly* "give |
| /// up" after the minimum number of cache clearings has occurred. This is |
| /// typically useful in scenarios where callers want to detect whether the |
| /// lazy DFA search is "efficient" or not. If the cache is cleared too many |
| /// times, this is a good indicator that it is not efficient, and thus, the |
| /// caller may wish to use some other regex engine. |
| /// |
| /// Note that the number of times a cache is cleared is a property of |
| /// the cache itself. Thus, if a cache is used in a subsequent search |
| /// with a similarly configured lazy DFA, then it could cause the |
| /// search to "give up" if the cache needed to be cleared, depending |
| /// on its internal count and configured minimum. The cache clear |
| /// count can only be reset to `0` via [`DFA::reset_cache`] (or |
| /// [`Regex::reset_cache`](crate::hybrid::regex::Regex::reset_cache) if |
| /// you're using the `Regex` API). |
| /// |
| /// By default, no minimum is configured. Thus, a lazy DFA search will |
| /// never give up due to cache clearings. If you do set this option, you |
| /// might consider also setting [`Config::minimum_bytes_per_state`] in |
| /// order for the lazy DFA to take efficiency into account before giving |
| /// up. |
| /// |
| /// # Example |
| /// |
| /// This example uses a somewhat pathological configuration to demonstrate |
| /// the _possible_ behavior of cache clearing and how it might result |
| /// in a search that returns an error. |
| /// |
| /// It is important to note that the precise mechanics of how and when |
| /// a cache gets cleared is an implementation detail. |
| /// |
| /// ``` |
| /// # if cfg!(miri) { return Ok(()); } // miri takes too long |
| /// use regex_automata::{hybrid::dfa::DFA, Input, MatchError, MatchErrorKind}; |
| /// |
| /// // This is a carefully chosen regex. The idea is to pick one |
| /// // that requires some decent number of states (hence the bounded |
| /// // repetition). But we specifically choose to create a class with an |
| /// // ASCII letter and a non-ASCII letter so that we can check that no new |
| /// // states are created once the cache is full. Namely, if we fill up the |
| /// // cache on a haystack of 'a's, then in order to match one 'β', a new |
| /// // state will need to be created since a 'β' is encoded with multiple |
| /// // bytes. Since there's no room for this state, the search should quit |
| /// // at the very first position. |
| /// let pattern = r"[aβ]{100}"; |
| /// let dfa = DFA::builder() |
| /// .configure( |
| /// // Configure it so that we have the minimum cache capacity |
| /// // possible. And that if any clearings occur, the search quits. |
| /// DFA::config() |
| /// .skip_cache_capacity_check(true) |
| /// .cache_capacity(0) |
| /// .minimum_cache_clear_count(Some(0)), |
| /// ) |
| /// .build(pattern)?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// // Our search will give up before reaching the end! |
| /// let haystack = "a".repeat(101).into_bytes(); |
| /// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack)); |
| /// assert!(matches!( |
| /// *result.unwrap_err().kind(), |
| /// MatchErrorKind::GaveUp { .. }, |
| /// )); |
| /// |
| /// // Now that we know the cache is full, if we search a haystack that we |
| /// // know will require creating at least one new state, it should not |
| /// // be able to make much progress. |
| /// let haystack = "β".repeat(101).into_bytes(); |
| /// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack)); |
| /// assert!(matches!( |
| /// *result.unwrap_err().kind(), |
| /// MatchErrorKind::GaveUp { .. }, |
| /// )); |
| /// |
| /// // If we reset the cache, then we should be able to create more states |
| /// // and make more progress with searching for betas. |
| /// cache.reset(&dfa); |
| /// let haystack = "β".repeat(101).into_bytes(); |
| /// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack)); |
| /// assert!(matches!( |
| /// *result.unwrap_err().kind(), |
| /// MatchErrorKind::GaveUp { .. }, |
| /// )); |
| /// |
| /// // ... switching back to ASCII still makes progress since it just needs |
| /// // to set transitions on existing states! |
| /// let haystack = "a".repeat(101).into_bytes(); |
| /// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack)); |
| /// assert!(matches!( |
| /// *result.unwrap_err().kind(), |
| /// MatchErrorKind::GaveUp { .. }, |
| /// )); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn minimum_cache_clear_count(mut self, min: Option<usize>) -> Config { |
| self.minimum_cache_clear_count = Some(min); |
| self |
| } |
| |
| /// Configure a lazy DFA search to quit only when its efficiency drops |
| /// below the given minimum. |
| /// |
| /// The efficiency of the cache is determined by the number of DFA states |
| /// compiled per byte of haystack searched. For example, if the efficiency |
| /// is 2, then it means the lazy DFA is creating a new DFA state after |
| /// searching approximately 2 bytes in a haystack. Generally speaking, 2 |
| /// is quite bad and it's likely that even a slower regex engine like the |
| /// [`PikeVM`](crate::nfa::thompson::pikevm::PikeVM) would be faster. |
| /// |
| /// This has no effect if [`Config::minimum_cache_clear_count`] is not set. |
| /// Namely, this option only kicks in when the cache has been cleared more |
| /// than the minimum number. If no minimum is set, then the cache is simply |
| /// cleared whenever it fills up and it is impossible for the lazy DFA to |
| /// quit due to ineffective use of the cache. |
| /// |
| /// In general, if one is setting [`Config::minimum_cache_clear_count`], |
| /// then one should probably also set this knob as well. The reason is |
| /// that the absolute number of times the cache is cleared is generally |
| /// not a great predictor of efficiency. For example, if a new DFA state |
| /// is created for every 1,000 bytes searched, then it wouldn't be hard |
| /// for the cache to get cleared more than `N` times and then cause the |
| /// lazy DFA to quit. But a new DFA state every 1,000 bytes is likely quite |
| /// good from a performance perspective, and it's likely that the lazy |
| /// DFA should continue searching, even if it requires clearing the cache |
| /// occasionally. |
| /// |
| /// Finally, note that if you're implementing your own lazy DFA search |
| /// routine and also want this efficiency check to work correctly, then |
| /// you'll need to use the following routines to record search progress: |
| /// |
| /// * Call [`Cache::search_start`] at the beginning of every search. |
| /// * Call [`Cache::search_update`] whenever [`DFA::next_state`] is |
| /// called. |
| /// * Call [`Cache::search_finish`] before completing a search. (It is |
| /// not strictly necessary to call this when an error is returned, as |
| /// `Cache::search_start` will automatically finish the previous search |
| /// for you. But calling it where possible before returning helps improve |
| /// the accuracy of how many bytes have actually been searched.) |
| pub fn minimum_bytes_per_state(mut self, min: Option<usize>) -> Config { |
| self.minimum_bytes_per_state = Some(min); |
| self |
| } |
| |
| /// Returns the match semantics set in this configuration. |
| pub fn get_match_kind(&self) -> MatchKind { |
| self.match_kind.unwrap_or(MatchKind::LeftmostFirst) |
| } |
| |
| /// Returns the prefilter set in this configuration, if one at all. |
| pub fn get_prefilter(&self) -> Option<&Prefilter> { |
| self.pre.as_ref().unwrap_or(&None).as_ref() |
| } |
| |
| /// Returns whether this configuration has enabled anchored starting states |
| /// for every pattern in the DFA. |
| pub fn get_starts_for_each_pattern(&self) -> bool { |
| self.starts_for_each_pattern.unwrap_or(false) |
| } |
| |
| /// Returns whether this configuration has enabled byte classes or not. |
| /// This is typically a debugging oriented option, as disabling it confers |
| /// no speed benefit. |
| pub fn get_byte_classes(&self) -> bool { |
| self.byte_classes.unwrap_or(true) |
| } |
| |
| /// Returns whether this configuration has enabled heuristic Unicode word |
| /// boundary support. When enabled, it is possible for a search to return |
| /// an error. |
| pub fn get_unicode_word_boundary(&self) -> bool { |
| self.unicode_word_boundary.unwrap_or(false) |
| } |
| |
| /// Returns whether this configuration will instruct the lazy DFA to enter |
| /// a quit state whenever the given byte is seen during a search. When at |
| /// least one byte has this enabled, it is possible for a search to return |
| /// an error. |
| pub fn get_quit(&self, byte: u8) -> bool { |
| self.quitset.map_or(false, |q| q.contains(byte)) |
| } |
| |
| /// Returns whether this configuration will instruct the lazy DFA to |
| /// "specialize" start states. When enabled, the lazy DFA will tag start |
| /// states so that search routines using the lazy DFA can detect when |
| /// it's in a start state and do some kind of optimization (like run a |
| /// prefilter). |
| pub fn get_specialize_start_states(&self) -> bool { |
| self.specialize_start_states.unwrap_or(false) |
| } |
| |
| /// Returns the cache capacity set on this configuration. |
| pub fn get_cache_capacity(&self) -> usize { |
| self.cache_capacity.unwrap_or(2 * (1 << 20)) |
| } |
| |
| /// Returns whether the cache capacity check should be skipped. |
| pub fn get_skip_cache_capacity_check(&self) -> bool { |
| self.skip_cache_capacity_check.unwrap_or(false) |
| } |
| |
| /// Returns, if set, the minimum number of times the cache must be cleared |
| /// before a lazy DFA search can give up. When no minimum is set, then a |
| /// search will never quit and will always clear the cache whenever it |
| /// fills up. |
| pub fn get_minimum_cache_clear_count(&self) -> Option<usize> { |
| self.minimum_cache_clear_count.unwrap_or(None) |
| } |
| |
| /// Returns, if set, the minimum number of bytes per state that need to be |
| /// processed in order for the lazy DFA to keep going. If the minimum falls |
| /// below this number (and the cache has been cleared a minimum number of |
| /// times), then the lazy DFA will return a "gave up" error. |
| pub fn get_minimum_bytes_per_state(&self) -> Option<usize> { |
| self.minimum_bytes_per_state.unwrap_or(None) |
| } |
| |
| /// Returns the minimum lazy DFA cache capacity required for the given NFA. |
| /// |
| /// The cache capacity required for a particular NFA may change without |
| /// notice. Callers should not rely on it being stable. |
| /// |
| /// This is useful for informational purposes, but can also be useful for |
| /// other reasons. For example, if one wants to check the minimum cache |
| /// capacity themselves or if one wants to set the capacity based on the |
| /// minimum. |
| /// |
| /// This may return an error if this configuration does not support all of |
| /// the instructions used in the given NFA. For example, if the NFA has a |
| /// Unicode word boundary but this configuration does not enable heuristic |
| /// support for Unicode word boundaries. |
| pub fn get_minimum_cache_capacity( |
| &self, |
| nfa: &thompson::NFA, |
| ) -> Result<usize, BuildError> { |
| let quitset = self.quit_set_from_nfa(nfa)?; |
| let classes = self.byte_classes_from_nfa(nfa, &quitset); |
| let starts = self.get_starts_for_each_pattern(); |
| Ok(minimum_cache_capacity(nfa, &classes, starts)) |
| } |
| |
| /// Returns the byte class map used during search from the given NFA. |
| /// |
| /// If byte classes are disabled on this configuration, then a map is |
| /// returned that puts each byte in its own equivalent class. |
| fn byte_classes_from_nfa( |
| &self, |
| nfa: &thompson::NFA, |
| quit: &ByteSet, |
| ) -> ByteClasses { |
| if !self.get_byte_classes() { |
| // The lazy DFA will always use the equivalence class map, but |
| // enabling this option is useful for debugging. Namely, this will |
| // cause all transitions to be defined over their actual bytes |
| // instead of an opaque equivalence class identifier. The former is |
| // much easier to grok as a human. |
| ByteClasses::singletons() |
| } else { |
| let mut set = nfa.byte_class_set().clone(); |
| // It is important to distinguish any "quit" bytes from all other |
| // bytes. Otherwise, a non-quit byte may end up in the same class |
| // as a quit byte, and thus cause the DFA stop when it shouldn't. |
| // |
| // Test case: |
| // |
| // regex-cli find match hybrid --unicode-word-boundary \ |
| // -p '^#' -p '\b10\.55\.182\.100\b' -y @conn.json.1000x.log |
| if !quit.is_empty() { |
| set.add_set(&quit); |
| } |
| set.byte_classes() |
| } |
| } |
| |
| /// Return the quit set for this configuration and the given NFA. |
| /// |
| /// This may return an error if the NFA is incompatible with this |
| /// configuration's quit set. For example, if the NFA has a Unicode word |
| /// boundary and the quit set doesn't include non-ASCII bytes. |
| fn quit_set_from_nfa( |
| &self, |
| nfa: &thompson::NFA, |
| ) -> Result<ByteSet, BuildError> { |
| let mut quit = self.quitset.unwrap_or(ByteSet::empty()); |
| if nfa.look_set_any().contains_word_unicode() { |
| if self.get_unicode_word_boundary() { |
| for b in 0x80..=0xFF { |
| quit.add(b); |
| } |
| } else { |
| // If heuristic support for Unicode word boundaries wasn't |
| // enabled, then we can still check if our quit set is correct. |
| // If the caller set their quit bytes in a way that causes the |
| // DFA to quit on at least all non-ASCII bytes, then that's all |
| // we need for heuristic support to work. |
| if !quit.contains_range(0x80, 0xFF) { |
| return Err( |
| BuildError::unsupported_dfa_word_boundary_unicode(), |
| ); |
| } |
| } |
| } |
| Ok(quit) |
| } |
| |
| /// Overwrite the default configuration such that the options in `o` are |
| /// always used. If an option in `o` is not set, then the corresponding |
| /// option in `self` is used. If it's not set in `self` either, then it |
| /// remains not set. |
| fn overwrite(&self, o: Config) -> Config { |
| Config { |
| match_kind: o.match_kind.or(self.match_kind), |
| pre: o.pre.or_else(|| self.pre.clone()), |
| starts_for_each_pattern: o |
| .starts_for_each_pattern |
| .or(self.starts_for_each_pattern), |
| byte_classes: o.byte_classes.or(self.byte_classes), |
| unicode_word_boundary: o |
| .unicode_word_boundary |
| .or(self.unicode_word_boundary), |
| quitset: o.quitset.or(self.quitset), |
| specialize_start_states: o |
| .specialize_start_states |
| .or(self.specialize_start_states), |
| cache_capacity: o.cache_capacity.or(self.cache_capacity), |
| skip_cache_capacity_check: o |
| .skip_cache_capacity_check |
| .or(self.skip_cache_capacity_check), |
| minimum_cache_clear_count: o |
| .minimum_cache_clear_count |
| .or(self.minimum_cache_clear_count), |
| minimum_bytes_per_state: o |
| .minimum_bytes_per_state |
| .or(self.minimum_bytes_per_state), |
| } |
| } |
| } |
| |
| /// A builder for constructing a lazy deterministic finite automaton from |
| /// regular expressions. |
| /// |
| /// As a convenience, [`DFA::builder`] is an alias for [`Builder::new`]. The |
| /// advantage of the former is that it often lets you avoid importing the |
| /// `Builder` type directly. |
| /// |
| /// This builder provides two main things: |
| /// |
| /// 1. It provides a few different `build` routines for actually constructing |
| /// a DFA from different kinds of inputs. The most convenient is |
| /// [`Builder::build`], which builds a DFA directly from a pattern string. The |
| /// most flexible is [`Builder::build_from_nfa`], which builds a DFA straight |
| /// from an NFA. |
| /// 2. The builder permits configuring a number of things. |
| /// [`Builder::configure`] is used with [`Config`] to configure aspects of |
| /// the DFA and the construction process itself. [`Builder::syntax`] and |
| /// [`Builder::thompson`] permit configuring the regex parser and Thompson NFA |
| /// construction, respectively. The syntax and thompson configurations only |
| /// apply when building from a pattern string. |
| /// |
| /// This builder always constructs a *single* lazy DFA. As such, this builder |
| /// can only be used to construct regexes that either detect the presence |
| /// of a match or find the end location of a match. A single DFA cannot |
| /// produce both the start and end of a match. For that information, use a |
| /// [`Regex`](crate::hybrid::regex::Regex), which can be similarly configured |
| /// using [`regex::Builder`](crate::hybrid::regex::Builder). The main reason |
| /// to use a DFA directly is if the end location of a match is enough for your |
| /// use case. Namely, a `Regex` will construct two lazy DFAs instead of one, |
| /// since a second reverse DFA is needed to find the start of a match. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to build a lazy DFA that uses a tiny cache capacity |
| /// and completely disables Unicode. That is: |
| /// |
| /// * Things such as `\w`, `.` and `\b` are no longer Unicode-aware. `\w` |
| /// and `\b` are ASCII-only while `.` matches any byte except for `\n` |
| /// (instead of any UTF-8 encoding of a Unicode scalar value except for |
| /// `\n`). Things that are Unicode only, such as `\pL`, are not allowed. |
| /// * The pattern itself is permitted to match invalid UTF-8. For example, |
| /// things like `[^a]` that match any byte except for `a` are permitted. |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// nfa::thompson, |
| /// util::syntax, |
| /// HalfMatch, Input, |
| /// }; |
| /// |
| /// let dfa = DFA::builder() |
| /// .configure(DFA::config().cache_capacity(5_000)) |
| /// .thompson(thompson::Config::new().utf8(false)) |
| /// .syntax(syntax::Config::new().unicode(false).utf8(false)) |
| /// .build(r"foo[^b]ar.*")?; |
| /// let mut cache = dfa.create_cache(); |
| /// |
| /// let haystack = b"\xFEfoo\xFFar\xE2\x98\xFF\n"; |
| /// let expected = Some(HalfMatch::must(0, 10)); |
| /// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?; |
| /// assert_eq!(expected, got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| #[derive(Clone, Debug)] |
| pub struct Builder { |
| config: Config, |
| #[cfg(feature = "syntax")] |
| thompson: thompson::Compiler, |
| } |
| |
| impl Builder { |
| /// Create a new lazy DFA builder with the default configuration. |
| pub fn new() -> Builder { |
| Builder { |
| config: Config::default(), |
| #[cfg(feature = "syntax")] |
| thompson: thompson::Compiler::new(), |
| } |
| } |
| |
| /// Build a lazy DFA from the given pattern. |
| /// |
| /// If there was a problem parsing or compiling the pattern, then an error |
| /// is returned. |
| #[cfg(feature = "syntax")] |
| pub fn build(&self, pattern: &str) -> Result<DFA, BuildError> { |
| self.build_many(&[pattern]) |
| } |
| |
| /// Build a lazy DFA from the given patterns. |
| /// |
| /// When matches are returned, the pattern ID corresponds to the index of |
| /// the pattern in the slice given. |
| #[cfg(feature = "syntax")] |
| pub fn build_many<P: AsRef<str>>( |
| &self, |
| patterns: &[P], |
| ) -> Result<DFA, BuildError> { |
| let nfa = self |
| .thompson |
| .clone() |
| // We can always forcefully disable captures because DFAs do not |
| // support them. |
| .configure( |
| thompson::Config::new() |
| .which_captures(thompson::WhichCaptures::None), |
| ) |
| .build_many(patterns) |
| .map_err(BuildError::nfa)?; |
| self.build_from_nfa(nfa) |
| } |
| |
| /// Build a DFA from the given NFA. |
| /// |
| /// Note that this requires owning a `thompson::NFA`. While this may force |
| /// you to clone the NFA, such a clone is not a deep clone. Namely, NFAs |
| /// are defined internally to support shared ownership such that cloning is |
| /// very cheap. |
| /// |
| /// # Example |
| /// |
| /// This example shows how to build a lazy DFA if you already have an NFA |
| /// in hand. |
| /// |
| /// ``` |
| /// use regex_automata::{ |
| /// hybrid::dfa::DFA, |
| /// nfa::thompson, |
| /// HalfMatch, Input, |
| /// }; |
| /// |
| /// let haystack = "foo123bar"; |
| /// |
| /// // This shows how to set non-default options for building an NFA. |
| /// let nfa = thompson::Compiler::new() |
| /// .configure(thompson::Config::new().shrink(true)) |
| /// .build(r"[0-9]+")?; |
| /// let dfa = DFA::builder().build_from_nfa(nfa)?; |
| /// let mut cache = dfa.create_cache(); |
| /// let expected = Some(HalfMatch::must(0, 6)); |
| /// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?; |
| /// assert_eq!(expected, got); |
| /// |
| /// # Ok::<(), Box<dyn std::error::Error>>(()) |
| /// ``` |
| pub fn build_from_nfa( |
| &self, |
| nfa: thompson::NFA, |
| ) -> Result<DFA, BuildError> { |
| let quitset = self.config.quit_set_from_nfa(&nfa)?; |
| let classes = self.config.byte_classes_from_nfa(&nfa, &quitset); |
| // Check that we can fit at least a few states into our cache, |
| // otherwise it's pretty senseless to use the lazy DFA. This does have |
| // a possible failure mode though. This assumes the maximum size of a |
| // state in powerset space (so, the total number of NFA states), which |
| // may never actually materialize, and could be quite a bit larger |
| // than the actual biggest state. If this turns out to be a problem, |
| // we could expose a knob that disables this check. But if so, we have |
| // to be careful not to panic in other areas of the code (the cache |
| // clearing and init code) that tend to assume some minimum useful |
| // cache capacity. |
| let min_cache = minimum_cache_capacity( |
| &nfa, |
| &classes, |
| self.config.get_starts_for_each_pattern(), |
| ); |
| let mut cache_capacity = self.config.get_cache_capacity(); |
| if cache_capacity < min_cache { |
| // When the caller has asked us to skip the cache capacity check, |
| // then we simply force the cache capacity to its minimum amount |
| // and mush on. |
| if self.config.get_skip_cache_capacity_check() { |
| debug!( |
| "given capacity ({}) is too small, \ |
| since skip_cache_capacity_check is enabled, \ |
| setting cache capacity to minimum ({})", |
| cache_capacity, min_cache, |
| ); |
| cache_capacity = min_cache; |
| } else { |
| return Err(BuildError::insufficient_cache_capacity( |
| min_cache, |
| cache_capacity, |
| )); |
| } |
| } |
| // We also need to check that we can fit at least some small number |
| // of states in our state ID space. This is unlikely to trigger in |
| // >=32-bit systems, but 16-bit systems have a pretty small state ID |
| // space since a number of bits are used up as sentinels. |
| if let Err(err) = minimum_lazy_state_id(&classes) { |
| return Err(BuildError::insufficient_state_id_capacity(err)); |
| } |
| let stride2 = classes.stride2(); |
| let start_map = StartByteMap::new(nfa.look_matcher()); |
| Ok(DFA { |
| config: self.config.clone(), |
| nfa, |
| stride2, |
| start_map, |
| classes, |
| quitset, |
| cache_capacity, |
| }) |
| } |
| |
| /// Apply the given lazy DFA configuration options to this builder. |
| pub fn configure(&mut self, config: Config) -> &mut Builder { |
| self.config = self.config.overwrite(config); |
| self |
| } |
| |
| /// Set the syntax configuration for this builder using |
| /// [`syntax::Config`](crate::util::syntax::Config). |
| /// |
| /// This permits setting things like case insensitivity, Unicode and multi |
| /// line mode. |
| /// |
| /// These settings only apply when constructing a lazy DFA directly from a |
| /// pattern. |
| #[cfg(feature = "syntax")] |
| pub fn syntax( |
| &mut self, |
| config: crate::util::syntax::Config, |
| ) -> &mut Builder { |
| self.thompson.syntax(config); |
| self |
| } |
| |
| /// Set the Thompson NFA configuration for this builder using |
| /// [`nfa::thompson::Config`](crate::nfa::thompson::Config). |
| /// |
| /// This permits setting things like whether the DFA should match the regex |
| /// in reverse or if additional time should be spent shrinking the size of |
| /// the NFA. |
| /// |
| /// These settings only apply when constructing a DFA directly from a |
| /// pattern. |
| #[cfg(feature = "syntax")] |
| pub fn thompson(&mut self, config: thompson::Config) -> &mut Builder { |
| self.thompson.configure(config); |
| self |
| } |
| } |
| |
| /// Represents the current state of an overlapping search. |
| /// |
| /// This is used for overlapping searches since they need to know something |
| /// about the previous search. For example, when multiple patterns match at the |
| /// same position, this state tracks the last reported pattern so that the next |
| /// search knows whether to report another matching pattern or continue with |
| /// the search at the next position. Additionally, it also tracks which state |
| /// the last search call terminated in. |
| /// |
| /// This type provides little introspection capabilities. The only thing a |
| /// caller can do is construct it and pass it around to permit search routines |
| /// to use it to track state, and also ask whether a match has been found. |
| /// |
| /// Callers should always provide a fresh state constructed via |
| /// [`OverlappingState::start`] when starting a new search. Reusing state from |
| /// a previous search may result in incorrect results. |
| #[derive(Clone, Debug, Eq, PartialEq)] |
| pub struct OverlappingState { |
| /// The match reported by the most recent overlapping search to use this |
| /// state. |
| /// |
| /// If a search does not find any matches, then it is expected to clear |
| /// this value. |
| pub(crate) mat: Option<HalfMatch>, |
| /// The state ID of the state at which the search was in when the call |
| /// terminated. When this is a match state, `last_match` must be set to a |
| /// non-None value. |
| /// |
| /// A `None` value indicates the start state of the corresponding |
| /// automaton. We cannot use the actual ID, since any one automaton may |
| /// have many start states, and which one is in use depends on several |
| /// search-time factors. |
| pub(crate) id: Option<LazyStateID>, |
| /// The position of the search. |
| /// |
| /// When `id` is None (i.e., we are starting a search), this is set to |
| /// the beginning of the search as given by the caller regardless of its |
| /// current value. Subsequent calls to an overlapping search pick up at |
| /// this offset. |
| pub(crate) at: usize, |
| /// The index into the matching patterns of the next match to report if the |
| /// current state is a match state. Note that this may be 1 greater than |
| /// the total number of matches to report for the current match state. (In |
| /// which case, no more matches should be reported at the current position |
| /// and the search should advance to the next position.) |
| pub(crate) next_match_index: Option<usize>, |
| /// This is set to true when a reverse overlapping search has entered its |
| /// EOI transitions. |
| /// |
| /// This isn't used in a forward search because it knows to stop once the |
| /// position exceeds the end of the search range. In a reverse search, |
| /// since we use unsigned offsets, we don't "know" once we've gone past |
| /// `0`. So the only way to detect it is with this extra flag. The reverse |
| /// overlapping search knows to terminate specifically after it has |
| /// reported all matches after following the EOI transition. |
| pub(crate) rev_eoi: bool, |
| } |
| |
| impl OverlappingState { |
| /// Create a new overlapping state that begins at the start state of any |
| /// automaton. |
| pub fn start() -> OverlappingState { |
| OverlappingState { |
| mat: None, |
| id: None, |
| at: 0, |
| next_match_index: None, |
| rev_eoi: false, |
| } |
| } |
| |
| /// Return the match result of the most recent search to execute with this |
| /// state. |
| /// |
| /// A searches will clear this result automatically, such that if no |
| /// match is found, this will correctly report `None`. |
| pub fn get_match(&self) -> Option<HalfMatch> { |
| self.mat |
| } |
| } |
| |
| /// Runs the given overlapping `search` function (forwards or backwards) until |
| /// a match is found whose offset does not split a codepoint. |
| /// |
| /// This is *not* always correct to call. It should only be called when the |
| /// underlying NFA has UTF-8 mode enabled *and* it can produce zero-width |
| /// matches. Calling this when both of those things aren't true might result |
| /// in legitimate matches getting skipped. |
| #[cold] |
| #[inline(never)] |
| fn skip_empty_utf8_splits_overlapping<F>( |
| input: &Input<'_>, |
| state: &mut OverlappingState, |
| mut search: F, |
| ) -> Result<(), MatchError> |
| where |
| F: FnMut(&Input<'_>, &mut OverlappingState) -> Result<(), MatchError>, |
| { |
| // Note that this routine works for forwards and reverse searches |
| // even though there's no code here to handle those cases. That's |
| // because overlapping searches drive themselves to completion via |
| // `OverlappingState`. So all we have to do is push it until no matches are |
| // found. |
| |
| let mut hm = match state.get_match() { |
| None => return Ok(()), |
| Some(hm) => hm, |
| }; |
| if input.get_anchored().is_anchored() { |
| if !input.is_char_boundary(hm.offset()) { |
| state.mat = None; |
| } |
| return Ok(()); |
| } |
| while !input.is_char_boundary(hm.offset()) { |
| search(input, state)?; |
| hm = match state.get_match() { |
| None => return Ok(()), |
| Some(hm) => hm, |
| }; |
| } |
| Ok(()) |
| } |
| |
| /// Based on the minimum number of states required for a useful lazy DFA cache, |
| /// this returns the minimum lazy state ID that must be representable. |
| /// |
| /// It's not likely for this to have any impact 32-bit systems (or higher), but |
| /// on 16-bit systems, the lazy state ID space is quite constrained and thus |
| /// may be insufficient if our MIN_STATES value is (for some reason) too high. |
| fn minimum_lazy_state_id( |
| classes: &ByteClasses, |
| ) -> Result<LazyStateID, LazyStateIDError> { |
| let stride = 1 << classes.stride2(); |
| let min_state_index = MIN_STATES.checked_sub(1).unwrap(); |
| LazyStateID::new(min_state_index * stride) |
| } |
| |
| /// Based on the minimum number of states required for a useful lazy DFA cache, |
| /// this returns a heuristic minimum number of bytes of heap space required. |
| /// |
| /// This is a "heuristic" because the minimum it returns is likely bigger than |
| /// the true minimum. Namely, it assumes that each powerset NFA/DFA state uses |
| /// the maximum number of NFA states (all of them). This is likely bigger |
| /// than what is required in practice. Computing the true minimum effectively |
| /// requires determinization, which is probably too much work to do for a |
| /// simple check like this. |
| /// |
| /// One of the issues with this approach IMO is that it requires that this |
| /// be in sync with the calculation above for computing how much heap memory |
| /// the DFA cache uses. If we get it wrong, it's possible for example for the |
| /// minimum to be smaller than the computed heap memory, and thus, it may be |
| /// the case that we can't add the required minimum number of states. That in |
| /// turn will make lazy DFA panic because we assume that we can add at least a |
| /// minimum number of states. |
| /// |
| /// Another approach would be to always allow the minimum number of states to |
| /// be added to the lazy DFA cache, even if it exceeds the configured cache |
| /// limit. This does mean that the limit isn't really a limit in all cases, |
| /// which is unfortunate. But it does at least guarantee that the lazy DFA can |
| /// always make progress, even if it is slow. (This approach is very similar to |
| /// enabling the 'skip_cache_capacity_check' config knob, except it wouldn't |
| /// rely on cache size calculation. Instead, it would just always permit a |
| /// minimum number of states to be added.) |
| fn minimum_cache_capacity( |
| nfa: &thompson::NFA, |
| classes: &ByteClasses, |
| starts_for_each_pattern: bool, |
| ) -> usize { |
| const ID_SIZE: usize = size_of::<LazyStateID>(); |
| const STATE_SIZE: usize = size_of::<State>(); |
| |
| let stride = 1 << classes.stride2(); |
| let states_len = nfa.states().len(); |
| let sparses = 2 * states_len * NFAStateID::SIZE; |
| let trans = MIN_STATES * stride * ID_SIZE; |
| |
| let mut starts = Start::len() * ID_SIZE; |
| if starts_for_each_pattern { |
| starts += (Start::len() * nfa.pattern_len()) * ID_SIZE; |
| } |
| |
| // The min number of states HAS to be at least 4: we have 3 sentinel states |
| // and then we need space for one more when we save a state after clearing |
| // the cache. We also need space for one more, otherwise we get stuck in a |
| // loop where we try to add a 5th state, which gets rejected, which clears |
| // the cache, which adds back a saved state (4th total state) which then |
| // tries to add the 5th state again. |
| assert!(MIN_STATES >= 5, "minimum number of states has to be at least 5"); |
| // The minimum number of non-sentinel states. We consider this separately |
| // because sentinel states are much smaller in that they contain no NFA |
| // states. Given our aggressive calculation here, it's worth being more |
| // precise with the number of states we need. |
| let non_sentinel = MIN_STATES.checked_sub(SENTINEL_STATES).unwrap(); |
| |
| // Every `State` has 5 bytes for flags, 4 bytes (max) for the number of |
| // patterns, followed by 32-bit encodings of patterns and then delta |
| // varint encodings of NFA state IDs. We use the worst case (which isn't |
| // technically possible) of 5 bytes for each NFA state ID. |
| // |
| // HOWEVER, three of the states needed by a lazy DFA are just the sentinel |
| // unknown, dead and quit states. Those states have a known size and it is |
| // small. |
| let dead_state_size = State::dead().memory_usage(); |
| let max_state_size = 5 + 4 + (nfa.pattern_len() * 4) + (states_len * 5); |
| let states = (SENTINEL_STATES * (STATE_SIZE + dead_state_size)) |
| + (non_sentinel * (STATE_SIZE + max_state_size)); |
| // NOTE: We don't double count heap memory used by State for this map since |
| // we use reference counting to avoid doubling memory usage. (This tends to |
| // be where most memory is allocated in the cache.) |
| let states_to_sid = (MIN_STATES * STATE_SIZE) + (MIN_STATES * ID_SIZE); |
| let stack = states_len * NFAStateID::SIZE; |
| let scratch_state_builder = max_state_size; |
| |
| trans |
| + starts |
| + states |
| + states_to_sid |
| + sparses |
| + stack |
| + scratch_state_builder |
| } |
| |
| #[cfg(all(test, feature = "syntax"))] |
| mod tests { |
| use super::*; |
| |
| // Tests that we handle heuristic Unicode word boundary support in reverse |
| // DFAs in the specific case of contextual searches. |
| // |
| // I wrote this test when I discovered a bug in how heuristic word |
| // boundaries were handled. Namely, that the starting state selection |
| // didn't consider the DFA's quit byte set when looking at the byte |
| // immediately before the start of the search (or immediately after the |
| // end of the search in the case of a reverse search). As a result, it was |
| // possible for '\bfoo\b' to match 'β123' because the trailing \xB2 byte |
| // in the 'β' codepoint would be treated as a non-word character. But of |
| // course, this search should trigger the DFA to quit, since there is a |
| // non-ASCII byte in consideration. |
| // |
| // Thus, I fixed 'start_state_{forward,reverse}' to check the quit byte set |
| // if it wasn't empty. The forward case is tested in the doc test for the |
| // Config::unicode_word_boundary API. We test the reverse case here, which |
| // is sufficiently niche that it doesn't really belong in a doc test. |
| #[test] |
| fn heuristic_unicode_reverse() { |
| let dfa = DFA::builder() |
| .configure(DFA::config().unicode_word_boundary(true)) |
| .thompson(thompson::Config::new().reverse(true)) |
| .build(r"\b[0-9]+\b") |
| .unwrap(); |
| let mut cache = dfa.create_cache(); |
| |
| let input = Input::new("β123").range(2..); |
| let expected = MatchError::quit(0xB2, 1); |
| let got = dfa.try_search_rev(&mut cache, &input); |
| assert_eq!(Err(expected), got); |
| |
| let input = Input::new("123β").range(..3); |
| let expected = MatchError::quit(0xCE, 3); |
| let got = dfa.try_search_rev(&mut cache, &input); |
| assert_eq!(Err(expected), got); |
| } |
| } |