| //! [`super::usefulness`] explains most of what is happening in this file. As explained there, |
| //! values and patterns are made from constructors applied to fields. This file defines a |
| //! `Constructor` enum, a `Fields` struct, and various operations to manipulate them and convert |
| //! them from/to patterns. |
| //! |
| //! There's one idea that is not detailed in [`super::usefulness`] because the details are not |
| //! needed there: _constructor splitting_. |
| //! |
| //! # Constructor splitting |
| //! |
| //! The idea is as follows: given a constructor `c` and a matrix, we want to specialize in turn |
| //! with all the value constructors that are covered by `c`, and compute usefulness for each. |
| //! Instead of listing all those constructors (which is intractable), we group those value |
| //! constructors together as much as possible. Example: |
| //! |
| //! ``` |
| //! match (0, false) { |
| //! (0 ..=100, true) => {} // `p_1` |
| //! (50..=150, false) => {} // `p_2` |
| //! (0 ..=200, _) => {} // `q` |
| //! } |
| //! ``` |
| //! |
| //! The naive approach would try all numbers in the range `0..=200`. But we can be a lot more |
| //! clever: `0` and `1` for example will match the exact same rows, and return equivalent |
| //! witnesses. In fact all of `0..50` would. We can thus restrict our exploration to 4 |
| //! constructors: `0..50`, `50..=100`, `101..=150` and `151..=200`. That is enough and infinitely |
| //! more tractable. |
| //! |
| //! We capture this idea in a function `split(p_1 ... p_n, c)` which returns a list of constructors |
| //! `c'` covered by `c`. Given such a `c'`, we require that all value ctors `c''` covered by `c'` |
| //! return an equivalent set of witnesses after specializing and computing usefulness. |
| //! In the example above, witnesses for specializing by `c''` covered by `0..50` will only differ |
| //! in their first element. |
| //! |
| //! We usually also ask that the `c'` together cover all of the original `c`. However we allow |
| //! skipping some constructors as long as it doesn't change whether the resulting list of witnesses |
| //! is empty of not. We use this in the wildcard `_` case. |
| //! |
| //! Splitting is implemented in the [`Constructor::split`] function. We don't do splitting for |
| //! or-patterns; instead we just try the alternatives one-by-one. For details on splitting |
| //! wildcards, see [`SplitWildcard`]; for integer ranges, see [`SplitIntRange`]. |
| |
| use std::{ |
| cell::Cell, |
| cmp::{max, min}, |
| iter::once, |
| ops::RangeInclusive, |
| }; |
| |
| use hir_def::{EnumVariantId, HasModule, LocalFieldId, VariantId}; |
| use smallvec::{smallvec, SmallVec}; |
| use stdx::never; |
| |
| use crate::{ |
| infer::normalize, inhabitedness::is_enum_variant_uninhabited_from, AdtId, Interner, Scalar, Ty, |
| TyExt, TyKind, |
| }; |
| |
| use super::{ |
| is_box, |
| usefulness::{helper::Captures, MatchCheckCtx, PatCtxt}, |
| FieldPat, Pat, PatKind, |
| }; |
| |
| use self::Constructor::*; |
| |
| /// Recursively expand this pattern into its subpatterns. Only useful for or-patterns. |
| fn expand_or_pat(pat: &Pat) -> Vec<&Pat> { |
| fn expand<'p>(pat: &'p Pat, vec: &mut Vec<&'p Pat>) { |
| if let PatKind::Or { pats } = pat.kind.as_ref() { |
| for pat in pats { |
| expand(pat, vec); |
| } |
| } else { |
| vec.push(pat) |
| } |
| } |
| |
| let mut pats = Vec::new(); |
| expand(pat, &mut pats); |
| pats |
| } |
| |
| /// [Constructor] uses this in unimplemented variants. |
| /// It allows porting match expressions from upstream algorithm without losing semantics. |
| #[derive(Copy, Clone, Debug, PartialEq, Eq)] |
| pub(super) enum Void {} |
| |
| /// An inclusive interval, used for precise integer exhaustiveness checking. |
| /// `IntRange`s always store a contiguous range. This means that values are |
| /// encoded such that `0` encodes the minimum value for the integer, |
| /// regardless of the signedness. |
| /// For example, the pattern `-128..=127i8` is encoded as `0..=255`. |
| /// This makes comparisons and arithmetic on interval endpoints much more |
| /// straightforward. See `signed_bias` for details. |
| /// |
| /// `IntRange` is never used to encode an empty range or a "range" that wraps |
| /// around the (offset) space: i.e., `range.lo <= range.hi`. |
| #[derive(Clone, Debug, PartialEq, Eq)] |
| pub(super) struct IntRange { |
| range: RangeInclusive<u128>, |
| } |
| |
| impl IntRange { |
| #[inline] |
| fn is_integral(ty: &Ty) -> bool { |
| matches!( |
| ty.kind(Interner), |
| TyKind::Scalar(Scalar::Char | Scalar::Int(_) | Scalar::Uint(_) | Scalar::Bool) |
| ) |
| } |
| |
| fn is_singleton(&self) -> bool { |
| self.range.start() == self.range.end() |
| } |
| |
| fn boundaries(&self) -> (u128, u128) { |
| (*self.range.start(), *self.range.end()) |
| } |
| |
| #[inline] |
| fn from_bool(value: bool) -> IntRange { |
| let val = value as u128; |
| IntRange { range: val..=val } |
| } |
| |
| #[inline] |
| fn from_range(lo: u128, hi: u128, scalar_ty: Scalar) -> IntRange { |
| match scalar_ty { |
| Scalar::Bool => IntRange { range: lo..=hi }, |
| _ => unimplemented!(), |
| } |
| } |
| |
| fn is_subrange(&self, other: &Self) -> bool { |
| other.range.start() <= self.range.start() && self.range.end() <= other.range.end() |
| } |
| |
| fn intersection(&self, other: &Self) -> Option<Self> { |
| let (lo, hi) = self.boundaries(); |
| let (other_lo, other_hi) = other.boundaries(); |
| if lo <= other_hi && other_lo <= hi { |
| Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi) }) |
| } else { |
| None |
| } |
| } |
| |
| fn to_pat(&self, _cx: &MatchCheckCtx<'_, '_>, ty: Ty) -> Pat { |
| match ty.kind(Interner) { |
| TyKind::Scalar(Scalar::Bool) => { |
| let kind = match self.boundaries() { |
| (0, 0) => PatKind::LiteralBool { value: false }, |
| (1, 1) => PatKind::LiteralBool { value: true }, |
| (0, 1) => PatKind::Wild, |
| (lo, hi) => { |
| never!("bad range for bool pattern: {}..={}", lo, hi); |
| PatKind::Wild |
| } |
| }; |
| Pat { ty, kind: kind.into() } |
| } |
| _ => unimplemented!(), |
| } |
| } |
| |
| /// See `Constructor::is_covered_by` |
| fn is_covered_by(&self, other: &Self) -> bool { |
| if self.intersection(other).is_some() { |
| // Constructor splitting should ensure that all intersections we encounter are actually |
| // inclusions. |
| assert!(self.is_subrange(other)); |
| true |
| } else { |
| false |
| } |
| } |
| } |
| |
| /// Represents a border between 2 integers. Because the intervals spanning borders must be able to |
| /// cover every integer, we need to be able to represent 2^128 + 1 such borders. |
| #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)] |
| enum IntBorder { |
| JustBefore(u128), |
| AfterMax, |
| } |
| |
| /// A range of integers that is partitioned into disjoint subranges. This does constructor |
| /// splitting for integer ranges as explained at the top of the file. |
| /// |
| /// This is fed multiple ranges, and returns an output that covers the input, but is split so that |
| /// the only intersections between an output range and a seen range are inclusions. No output range |
| /// straddles the boundary of one of the inputs. |
| /// |
| /// The following input: |
| /// ``` |
| /// |-------------------------| // `self` |
| /// |------| |----------| |----| |
| /// |-------| |-------| |
| /// ``` |
| /// would be iterated over as follows: |
| /// ``` |
| /// ||---|--||-|---|---|---|--| |
| /// ``` |
| #[derive(Debug, Clone)] |
| struct SplitIntRange { |
| /// The range we are splitting |
| range: IntRange, |
| /// The borders of ranges we have seen. They are all contained within `range`. This is kept |
| /// sorted. |
| borders: Vec<IntBorder>, |
| } |
| |
| impl SplitIntRange { |
| fn new(range: IntRange) -> Self { |
| SplitIntRange { range, borders: Vec::new() } |
| } |
| |
| /// Internal use |
| fn to_borders(r: IntRange) -> [IntBorder; 2] { |
| use IntBorder::*; |
| let (lo, hi) = r.boundaries(); |
| let lo = JustBefore(lo); |
| let hi = match hi.checked_add(1) { |
| Some(m) => JustBefore(m), |
| None => AfterMax, |
| }; |
| [lo, hi] |
| } |
| |
| /// Add ranges relative to which we split. |
| fn split(&mut self, ranges: impl Iterator<Item = IntRange>) { |
| let this_range = &self.range; |
| let included_ranges = ranges.filter_map(|r| this_range.intersection(&r)); |
| let included_borders = included_ranges.flat_map(|r| { |
| let borders = Self::to_borders(r); |
| once(borders[0]).chain(once(borders[1])) |
| }); |
| self.borders.extend(included_borders); |
| self.borders.sort_unstable(); |
| } |
| |
| /// Iterate over the contained ranges. |
| fn iter(&self) -> impl Iterator<Item = IntRange> + '_ { |
| use IntBorder::*; |
| |
| let self_range = Self::to_borders(self.range.clone()); |
| // Start with the start of the range. |
| let mut prev_border = self_range[0]; |
| self.borders |
| .iter() |
| .copied() |
| // End with the end of the range. |
| .chain(once(self_range[1])) |
| // List pairs of adjacent borders. |
| .map(move |border| { |
| let ret = (prev_border, border); |
| prev_border = border; |
| ret |
| }) |
| // Skip duplicates. |
| .filter(|(prev_border, border)| prev_border != border) |
| // Finally, convert to ranges. |
| .map(|(prev_border, border)| { |
| let range = match (prev_border, border) { |
| (JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1), |
| (JustBefore(n), AfterMax) => n..=u128::MAX, |
| _ => unreachable!(), // Ruled out by the sorting and filtering we did |
| }; |
| IntRange { range } |
| }) |
| } |
| } |
| |
| /// A constructor for array and slice patterns. |
| #[derive(Copy, Clone, Debug, PartialEq, Eq)] |
| pub(super) struct Slice { |
| _unimplemented: Void, |
| } |
| |
| impl Slice { |
| fn arity(self) -> usize { |
| match self._unimplemented {} |
| } |
| |
| /// See `Constructor::is_covered_by` |
| fn is_covered_by(self, _other: Self) -> bool { |
| match self._unimplemented {} |
| } |
| } |
| |
| /// A value can be decomposed into a constructor applied to some fields. This struct represents |
| /// the constructor. See also `Fields`. |
| /// |
| /// `pat_constructor` retrieves the constructor corresponding to a pattern. |
| /// `specialize_constructor` returns the list of fields corresponding to a pattern, given a |
| /// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and |
| /// `Fields`. |
| #[allow(dead_code)] |
| #[derive(Clone, Debug, PartialEq)] |
| pub(super) enum Constructor { |
| /// The constructor for patterns that have a single constructor, like tuples, struct patterns |
| /// and fixed-length arrays. |
| Single, |
| /// Enum variants. |
| Variant(EnumVariantId), |
| /// Ranges of integer literal values (`2`, `2..=5` or `2..5`). |
| IntRange(IntRange), |
| /// Ranges of floating-point literal values (`2.0..=5.2`). |
| FloatRange(Void), |
| /// String literals. Strings are not quite the same as `&[u8]` so we treat them separately. |
| Str(Void), |
| /// Array and slice patterns. |
| Slice(Slice), |
| /// Constants that must not be matched structurally. They are treated as black |
| /// boxes for the purposes of exhaustiveness: we must not inspect them, and they |
| /// don't count towards making a match exhaustive. |
| Opaque, |
| /// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used |
| /// for those types for which we cannot list constructors explicitly, like `f64` and `str`. |
| NonExhaustive, |
| /// Stands for constructors that are not seen in the matrix, as explained in the documentation |
| /// for [`SplitWildcard`]. The carried `bool` is used for the `non_exhaustive_omitted_patterns` |
| /// lint. |
| Missing { nonexhaustive_enum_missing_real_variants: bool }, |
| /// Wildcard pattern. |
| Wildcard, |
| /// Or-pattern. |
| Or, |
| } |
| |
| impl Constructor { |
| pub(super) fn is_wildcard(&self) -> bool { |
| matches!(self, Wildcard) |
| } |
| |
| pub(super) fn is_non_exhaustive(&self) -> bool { |
| matches!(self, NonExhaustive) |
| } |
| |
| fn as_int_range(&self) -> Option<&IntRange> { |
| match self { |
| IntRange(range) => Some(range), |
| _ => None, |
| } |
| } |
| |
| fn as_slice(&self) -> Option<Slice> { |
| match self { |
| Slice(slice) => Some(*slice), |
| _ => None, |
| } |
| } |
| |
| pub(super) fn is_unstable_variant(&self, _pcx: PatCtxt<'_, '_>) -> bool { |
| false //FIXME: implement this |
| } |
| |
| pub(super) fn is_doc_hidden_variant(&self, _pcx: PatCtxt<'_, '_>) -> bool { |
| false //FIXME: implement this |
| } |
| |
| fn variant_id_for_adt(&self, adt: hir_def::AdtId) -> VariantId { |
| match *self { |
| Variant(id) => id.into(), |
| Single => { |
| assert!(!matches!(adt, hir_def::AdtId::EnumId(_))); |
| match adt { |
| hir_def::AdtId::EnumId(_) => unreachable!(), |
| hir_def::AdtId::StructId(id) => id.into(), |
| hir_def::AdtId::UnionId(id) => id.into(), |
| } |
| } |
| _ => panic!("bad constructor {self:?} for adt {adt:?}"), |
| } |
| } |
| |
| /// The number of fields for this constructor. This must be kept in sync with |
| /// `Fields::wildcards`. |
| pub(super) fn arity(&self, pcx: PatCtxt<'_, '_>) -> usize { |
| match self { |
| Single | Variant(_) => match *pcx.ty.kind(Interner) { |
| TyKind::Tuple(arity, ..) => arity, |
| TyKind::Ref(..) => 1, |
| TyKind::Adt(adt, ..) => { |
| if is_box(pcx.cx.db, adt.0) { |
| // The only legal patterns of type `Box` (outside `std`) are `_` and box |
| // patterns. If we're here we can assume this is a box pattern. |
| 1 |
| } else { |
| let variant = self.variant_id_for_adt(adt.0); |
| Fields::list_variant_nonhidden_fields(pcx.cx, pcx.ty, variant).count() |
| } |
| } |
| _ => { |
| never!("Unexpected type for `Single` constructor: {:?}", pcx.ty); |
| 0 |
| } |
| }, |
| Slice(slice) => slice.arity(), |
| Str(..) |
| | FloatRange(..) |
| | IntRange(..) |
| | NonExhaustive |
| | Opaque |
| | Missing { .. } |
| | Wildcard => 0, |
| Or => { |
| never!("The `Or` constructor doesn't have a fixed arity"); |
| 0 |
| } |
| } |
| } |
| |
| /// Some constructors (namely `Wildcard`, `IntRange` and `Slice`) actually stand for a set of actual |
| /// constructors (like variants, integers or fixed-sized slices). When specializing for these |
| /// constructors, we want to be specialising for the actual underlying constructors. |
| /// Naively, we would simply return the list of constructors they correspond to. We instead are |
| /// more clever: if there are constructors that we know will behave the same wrt the current |
| /// matrix, we keep them grouped. For example, all slices of a sufficiently large length |
| /// will either be all useful or all non-useful with a given matrix. |
| /// |
| /// See the branches for details on how the splitting is done. |
| /// |
| /// This function may discard some irrelevant constructors if this preserves behavior and |
| /// diagnostics. Eg. for the `_` case, we ignore the constructors already present in the |
| /// matrix, unless all of them are. |
| pub(super) fn split<'a>( |
| &self, |
| pcx: PatCtxt<'_, '_>, |
| ctors: impl Iterator<Item = &'a Constructor> + Clone, |
| ) -> SmallVec<[Self; 1]> { |
| match self { |
| Wildcard => { |
| let mut split_wildcard = SplitWildcard::new(pcx); |
| split_wildcard.split(pcx, ctors); |
| split_wildcard.into_ctors(pcx) |
| } |
| // Fast-track if the range is trivial. In particular, we don't do the overlapping |
| // ranges check. |
| IntRange(ctor_range) if !ctor_range.is_singleton() => { |
| let mut split_range = SplitIntRange::new(ctor_range.clone()); |
| let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range()); |
| split_range.split(int_ranges.cloned()); |
| split_range.iter().map(IntRange).collect() |
| } |
| Slice(slice) => match slice._unimplemented {}, |
| // Any other constructor can be used unchanged. |
| _ => smallvec![self.clone()], |
| } |
| } |
| |
| /// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`. |
| /// For the simple cases, this is simply checking for equality. For the "grouped" constructors, |
| /// this checks for inclusion. |
| // We inline because this has a single call site in `Matrix::specialize_constructor`. |
| #[inline] |
| pub(super) fn is_covered_by(&self, _pcx: PatCtxt<'_, '_>, other: &Self) -> bool { |
| // This must be kept in sync with `is_covered_by_any`. |
| match (self, other) { |
| // Wildcards cover anything |
| (_, Wildcard) => true, |
| // The missing ctors are not covered by anything in the matrix except wildcards. |
| (Missing { .. } | Wildcard, _) => false, |
| |
| (Single, Single) => true, |
| (Variant(self_id), Variant(other_id)) => self_id == other_id, |
| |
| (IntRange(self_range), IntRange(other_range)) => self_range.is_covered_by(other_range), |
| (FloatRange(void), FloatRange(..)) => match *void {}, |
| (Str(void), Str(..)) => match *void {}, |
| (Slice(self_slice), Slice(other_slice)) => self_slice.is_covered_by(*other_slice), |
| |
| // We are trying to inspect an opaque constant. Thus we skip the row. |
| (Opaque, _) | (_, Opaque) => false, |
| // Only a wildcard pattern can match the special extra constructor. |
| (NonExhaustive, _) => false, |
| |
| _ => { |
| never!("trying to compare incompatible constructors {:?} and {:?}", self, other); |
| // Continue with 'whatever is covered' supposed to result in false no-error diagnostic. |
| true |
| } |
| } |
| } |
| |
| /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is |
| /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is |
| /// assumed to have been split from a wildcard. |
| fn is_covered_by_any(&self, _pcx: PatCtxt<'_, '_>, used_ctors: &[Constructor]) -> bool { |
| if used_ctors.is_empty() { |
| return false; |
| } |
| |
| // This must be kept in sync with `is_covered_by`. |
| match self { |
| // If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s. |
| Single => !used_ctors.is_empty(), |
| Variant(_) => used_ctors.iter().any(|c| c == self), |
| IntRange(range) => used_ctors |
| .iter() |
| .filter_map(|c| c.as_int_range()) |
| .any(|other| range.is_covered_by(other)), |
| Slice(slice) => used_ctors |
| .iter() |
| .filter_map(|c| c.as_slice()) |
| .any(|other| slice.is_covered_by(other)), |
| // This constructor is never covered by anything else |
| NonExhaustive => false, |
| Str(..) | FloatRange(..) | Opaque | Missing { .. } | Wildcard | Or => { |
| never!("found unexpected ctor in all_ctors: {:?}", self); |
| true |
| } |
| } |
| } |
| } |
| |
| /// A wildcard constructor that we split relative to the constructors in the matrix, as explained |
| /// at the top of the file. |
| /// |
| /// A constructor that is not present in the matrix rows will only be covered by the rows that have |
| /// wildcards. Thus we can group all of those constructors together; we call them "missing |
| /// constructors". Splitting a wildcard would therefore list all present constructors individually |
| /// (or grouped if they are integers or slices), and then all missing constructors together as a |
| /// group. |
| /// |
| /// However we can go further: since any constructor will match the wildcard rows, and having more |
| /// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors |
| /// and only try the missing ones. |
| /// This will not preserve the whole list of witnesses, but will preserve whether the list is empty |
| /// or not. In fact this is quite natural from the point of view of diagnostics too. This is done |
| /// in `to_ctors`: in some cases we only return `Missing`. |
| #[derive(Debug)] |
| pub(super) struct SplitWildcard { |
| /// Constructors seen in the matrix. |
| matrix_ctors: Vec<Constructor>, |
| /// All the constructors for this type |
| all_ctors: SmallVec<[Constructor; 1]>, |
| } |
| |
| impl SplitWildcard { |
| pub(super) fn new(pcx: PatCtxt<'_, '_>) -> Self { |
| let cx = pcx.cx; |
| let make_range = |start, end, scalar| IntRange(IntRange::from_range(start, end, scalar)); |
| |
| // Unhandled types are treated as non-exhaustive. Being explicit here instead of falling |
| // to catchall arm to ease further implementation. |
| let unhandled = || smallvec![NonExhaustive]; |
| |
| // This determines the set of all possible constructors for the type `pcx.ty`. For numbers, |
| // arrays and slices we use ranges and variable-length slices when appropriate. |
| // |
| // If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that |
| // are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the |
| // returned list of constructors. |
| // Invariant: this is empty if and only if the type is uninhabited (as determined by |
| // `cx.is_uninhabited()`). |
| let all_ctors = match pcx.ty.kind(Interner) { |
| TyKind::Scalar(Scalar::Bool) => smallvec![make_range(0, 1, Scalar::Bool)], |
| // TyKind::Array(..) if ... => unhandled(), |
| TyKind::Array(..) | TyKind::Slice(..) => unhandled(), |
| TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), subst) => { |
| let enum_data = cx.db.enum_data(*enum_id); |
| |
| // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an |
| // additional "unknown" constructor. |
| // There is no point in enumerating all possible variants, because the user can't |
| // actually match against them all themselves. So we always return only the fictitious |
| // constructor. |
| // E.g., in an example like: |
| // |
| // ``` |
| // let err: io::ErrorKind = ...; |
| // match err { |
| // io::ErrorKind::NotFound => {}, |
| // } |
| // ``` |
| // |
| // we don't want to show every possible IO error, but instead have only `_` as the |
| // witness. |
| let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(pcx.ty); |
| |
| let is_exhaustive_pat_feature = cx.feature_exhaustive_patterns(); |
| |
| // If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it |
| // as though it had an "unknown" constructor to avoid exposing its emptiness. The |
| // exception is if the pattern is at the top level, because we want empty matches to be |
| // considered exhaustive. |
| let is_secretly_empty = enum_data.variants.is_empty() |
| && !is_exhaustive_pat_feature |
| && !pcx.is_top_level; |
| |
| let mut ctors: SmallVec<[_; 1]> = enum_data |
| .variants |
| .iter() |
| .map(|(local_id, _)| EnumVariantId { parent: *enum_id, local_id }) |
| .filter(|&variant| { |
| // If `exhaustive_patterns` is enabled, we exclude variants known to be |
| // uninhabited. |
| let is_uninhabited = is_exhaustive_pat_feature |
| && is_enum_variant_uninhabited_from(variant, subst, cx.module, cx.db); |
| !is_uninhabited |
| }) |
| .map(Variant) |
| .collect(); |
| |
| if is_secretly_empty || is_declared_nonexhaustive { |
| ctors.push(NonExhaustive); |
| } |
| ctors |
| } |
| TyKind::Scalar(Scalar::Char) => unhandled(), |
| TyKind::Scalar(Scalar::Int(..) | Scalar::Uint(..)) => unhandled(), |
| TyKind::Never if !cx.feature_exhaustive_patterns() && !pcx.is_top_level => { |
| smallvec![NonExhaustive] |
| } |
| TyKind::Never => SmallVec::new(), |
| _ if cx.is_uninhabited(pcx.ty) => SmallVec::new(), |
| TyKind::Adt(..) | TyKind::Tuple(..) | TyKind::Ref(..) => smallvec![Single], |
| // This type is one for which we cannot list constructors, like `str` or `f64`. |
| _ => smallvec![NonExhaustive], |
| }; |
| |
| SplitWildcard { matrix_ctors: Vec::new(), all_ctors } |
| } |
| |
| /// Pass a set of constructors relative to which to split this one. Don't call twice, it won't |
| /// do what you want. |
| pub(super) fn split<'a>( |
| &mut self, |
| pcx: PatCtxt<'_, '_>, |
| ctors: impl Iterator<Item = &'a Constructor> + Clone, |
| ) { |
| // Since `all_ctors` never contains wildcards, this won't recurse further. |
| self.all_ctors = |
| self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect(); |
| self.matrix_ctors = ctors.filter(|c| !c.is_wildcard()).cloned().collect(); |
| } |
| |
| /// Whether there are any value constructors for this type that are not present in the matrix. |
| fn any_missing(&self, pcx: PatCtxt<'_, '_>) -> bool { |
| self.iter_missing(pcx).next().is_some() |
| } |
| |
| /// Iterate over the constructors for this type that are not present in the matrix. |
| pub(super) fn iter_missing<'a, 'p>( |
| &'a self, |
| pcx: PatCtxt<'a, 'p>, |
| ) -> impl Iterator<Item = &'a Constructor> + Captures<'p> { |
| self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors)) |
| } |
| |
| /// Return the set of constructors resulting from splitting the wildcard. As explained at the |
| /// top of the file, if any constructors are missing we can ignore the present ones. |
| fn into_ctors(self, pcx: PatCtxt<'_, '_>) -> SmallVec<[Constructor; 1]> { |
| if self.any_missing(pcx) { |
| // Some constructors are missing, thus we can specialize with the special `Missing` |
| // constructor, which stands for those constructors that are not seen in the matrix, |
| // and matches the same rows as any of them (namely the wildcard rows). See the top of |
| // the file for details. |
| // However, when all constructors are missing we can also specialize with the full |
| // `Wildcard` constructor. The difference will depend on what we want in diagnostics. |
| |
| // If some constructors are missing, we typically want to report those constructors, |
| // e.g.: |
| // ``` |
| // enum Direction { N, S, E, W } |
| // let Direction::N = ...; |
| // ``` |
| // we can report 3 witnesses: `S`, `E`, and `W`. |
| // |
| // However, if the user didn't actually specify a constructor |
| // in this arm, e.g., in |
| // ``` |
| // let x: (Direction, Direction, bool) = ...; |
| // let (_, _, false) = x; |
| // ``` |
| // we don't want to show all 16 possible witnesses `(<direction-1>, <direction-2>, |
| // true)` - we are satisfied with `(_, _, true)`. So if all constructors are missing we |
| // prefer to report just a wildcard `_`. |
| // |
| // The exception is: if we are at the top-level, for example in an empty match, we |
| // sometimes prefer reporting the list of constructors instead of just `_`. |
| let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty); |
| let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing { |
| if pcx.is_non_exhaustive { |
| Missing { |
| nonexhaustive_enum_missing_real_variants: self |
| .iter_missing(pcx) |
| .any(|c| !(c.is_non_exhaustive() || c.is_unstable_variant(pcx))), |
| } |
| } else { |
| Missing { nonexhaustive_enum_missing_real_variants: false } |
| } |
| } else { |
| Wildcard |
| }; |
| return smallvec![ctor]; |
| } |
| |
| // All the constructors are present in the matrix, so we just go through them all. |
| self.all_ctors |
| } |
| } |
| |
| /// A value can be decomposed into a constructor applied to some fields. This struct represents |
| /// those fields, generalized to allow patterns in each field. See also `Constructor`. |
| /// |
| /// This is constructed for a constructor using [`Fields::wildcards()`]. The idea is that |
| /// [`Fields::wildcards()`] constructs a list of fields where all entries are wildcards, and then |
| /// given a pattern we fill some of the fields with its subpatterns. |
| /// In the following example `Fields::wildcards` returns `[_, _, _, _]`. Then in |
| /// `extract_pattern_arguments` we fill some of the entries, and the result is |
| /// `[Some(0), _, _, _]`. |
| /// ```rust |
| /// let x: [Option<u8>; 4] = foo(); |
| /// match x { |
| /// [Some(0), ..] => {} |
| /// } |
| /// ``` |
| /// |
| /// Note that the number of fields of a constructor may not match the fields declared in the |
| /// original struct/variant. This happens if a private or `non_exhaustive` field is uninhabited, |
| /// because the code mustn't observe that it is uninhabited. In that case that field is not |
| /// included in `fields`. For that reason, when you have a `mir::Field` you must use |
| /// `index_with_declared_idx`. |
| #[derive(Clone, Copy)] |
| pub(super) struct Fields<'p> { |
| fields: &'p [DeconstructedPat<'p>], |
| } |
| |
| impl<'p> Fields<'p> { |
| fn empty() -> Self { |
| Fields { fields: &[] } |
| } |
| |
| fn singleton(cx: &MatchCheckCtx<'_, 'p>, field: DeconstructedPat<'p>) -> Self { |
| let field = cx.pattern_arena.alloc(field); |
| Fields { fields: std::slice::from_ref(field) } |
| } |
| |
| pub(super) fn from_iter( |
| cx: &MatchCheckCtx<'_, 'p>, |
| fields: impl IntoIterator<Item = DeconstructedPat<'p>>, |
| ) -> Self { |
| let fields: &[_] = cx.pattern_arena.alloc_extend(fields); |
| Fields { fields } |
| } |
| |
| fn wildcards_from_tys(cx: &MatchCheckCtx<'_, 'p>, tys: impl IntoIterator<Item = Ty>) -> Self { |
| Fields::from_iter(cx, tys.into_iter().map(DeconstructedPat::wildcard)) |
| } |
| |
| // In the cases of either a `#[non_exhaustive]` field list or a non-public field, we hide |
| // uninhabited fields in order not to reveal the uninhabitedness of the whole variant. |
| // This lists the fields we keep along with their types. |
| fn list_variant_nonhidden_fields<'a>( |
| cx: &'a MatchCheckCtx<'a, 'p>, |
| ty: &'a Ty, |
| variant: VariantId, |
| ) -> impl Iterator<Item = (LocalFieldId, Ty)> + Captures<'a> + Captures<'p> { |
| let (adt, substs) = ty.as_adt().unwrap(); |
| |
| let adt_is_local = variant.module(cx.db.upcast()).krate() == cx.module.krate(); |
| // Whether we must not match the fields of this variant exhaustively. |
| let is_non_exhaustive = is_field_list_non_exhaustive(variant, cx) && !adt_is_local; |
| |
| let visibility = cx.db.field_visibilities(variant); |
| let field_ty = cx.db.field_types(variant); |
| let fields_len = variant.variant_data(cx.db.upcast()).fields().len() as u32; |
| |
| (0..fields_len).map(|idx| LocalFieldId::from_raw(idx.into())).filter_map(move |fid| { |
| let ty = field_ty[fid].clone().substitute(Interner, substs); |
| let ty = normalize(cx.db, cx.db.trait_environment_for_body(cx.body), ty); |
| let is_visible = matches!(adt, hir_def::AdtId::EnumId(..)) |
| || visibility[fid].is_visible_from(cx.db.upcast(), cx.module); |
| let is_uninhabited = cx.is_uninhabited(&ty); |
| |
| if is_uninhabited && (!is_visible || is_non_exhaustive) { |
| None |
| } else { |
| Some((fid, ty)) |
| } |
| }) |
| } |
| |
| /// Creates a new list of wildcard fields for a given constructor. The result must have a |
| /// length of `constructor.arity()`. |
| pub(crate) fn wildcards( |
| cx: &MatchCheckCtx<'_, 'p>, |
| ty: &Ty, |
| constructor: &Constructor, |
| ) -> Self { |
| let ret = match constructor { |
| Single | Variant(_) => match ty.kind(Interner) { |
| TyKind::Tuple(_, substs) => { |
| let tys = substs.iter(Interner).map(|ty| ty.assert_ty_ref(Interner)); |
| Fields::wildcards_from_tys(cx, tys.cloned()) |
| } |
| TyKind::Ref(.., rty) => Fields::wildcards_from_tys(cx, once(rty.clone())), |
| &TyKind::Adt(AdtId(adt), ref substs) => { |
| if is_box(cx.db, adt) { |
| // The only legal patterns of type `Box` (outside `std`) are `_` and box |
| // patterns. If we're here we can assume this is a box pattern. |
| let subst_ty = substs.at(Interner, 0).assert_ty_ref(Interner).clone(); |
| Fields::wildcards_from_tys(cx, once(subst_ty)) |
| } else { |
| let variant = constructor.variant_id_for_adt(adt); |
| let tys = Fields::list_variant_nonhidden_fields(cx, ty, variant) |
| .map(|(_, ty)| ty); |
| Fields::wildcards_from_tys(cx, tys) |
| } |
| } |
| ty_kind => { |
| never!("Unexpected type for `Single` constructor: {:?}", ty_kind); |
| Fields::wildcards_from_tys(cx, once(ty.clone())) |
| } |
| }, |
| Slice(slice) => match slice._unimplemented {}, |
| Str(..) |
| | FloatRange(..) |
| | IntRange(..) |
| | NonExhaustive |
| | Opaque |
| | Missing { .. } |
| | Wildcard => Fields::empty(), |
| Or => { |
| never!("called `Fields::wildcards` on an `Or` ctor"); |
| Fields::empty() |
| } |
| }; |
| ret |
| } |
| |
| /// Returns the list of patterns. |
| pub(super) fn iter_patterns<'a>( |
| &'a self, |
| ) -> impl Iterator<Item = &'p DeconstructedPat<'p>> + Captures<'a> { |
| self.fields.iter() |
| } |
| } |
| |
| /// Values and patterns can be represented as a constructor applied to some fields. This represents |
| /// a pattern in this form. |
| /// This also keeps track of whether the pattern has been found reachable during analysis. For this |
| /// reason we should be careful not to clone patterns for which we care about that. Use |
| /// `clone_and_forget_reachability` if you're sure. |
| pub(crate) struct DeconstructedPat<'p> { |
| ctor: Constructor, |
| fields: Fields<'p>, |
| ty: Ty, |
| reachable: Cell<bool>, |
| } |
| |
| impl<'p> DeconstructedPat<'p> { |
| pub(super) fn wildcard(ty: Ty) -> Self { |
| Self::new(Wildcard, Fields::empty(), ty) |
| } |
| |
| pub(super) fn new(ctor: Constructor, fields: Fields<'p>, ty: Ty) -> Self { |
| DeconstructedPat { ctor, fields, ty, reachable: Cell::new(false) } |
| } |
| |
| /// Construct a pattern that matches everything that starts with this constructor. |
| /// For example, if `ctor` is a `Constructor::Variant` for `Option::Some`, we get the pattern |
| /// `Some(_)`. |
| pub(super) fn wild_from_ctor(pcx: PatCtxt<'_, 'p>, ctor: Constructor) -> Self { |
| let fields = Fields::wildcards(pcx.cx, pcx.ty, &ctor); |
| DeconstructedPat::new(ctor, fields, pcx.ty.clone()) |
| } |
| |
| /// Clone this value. This method emphasizes that cloning loses reachability information and |
| /// should be done carefully. |
| pub(super) fn clone_and_forget_reachability(&self) -> Self { |
| DeconstructedPat::new(self.ctor.clone(), self.fields, self.ty.clone()) |
| } |
| |
| pub(crate) fn from_pat(cx: &MatchCheckCtx<'_, 'p>, pat: &Pat) -> Self { |
| let mkpat = |pat| DeconstructedPat::from_pat(cx, pat); |
| let ctor; |
| let fields; |
| match pat.kind.as_ref() { |
| PatKind::Binding { subpattern: Some(subpat), .. } => return mkpat(subpat), |
| PatKind::Binding { subpattern: None, .. } | PatKind::Wild => { |
| ctor = Wildcard; |
| fields = Fields::empty(); |
| } |
| PatKind::Deref { subpattern } => { |
| ctor = Single; |
| fields = Fields::singleton(cx, mkpat(subpattern)); |
| } |
| PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => { |
| match pat.ty.kind(Interner) { |
| TyKind::Tuple(_, substs) => { |
| ctor = Single; |
| let mut wilds: SmallVec<[_; 2]> = substs |
| .iter(Interner) |
| .map(|arg| arg.assert_ty_ref(Interner).clone()) |
| .map(DeconstructedPat::wildcard) |
| .collect(); |
| for pat in subpatterns { |
| let idx: u32 = pat.field.into_raw().into(); |
| wilds[idx as usize] = mkpat(&pat.pattern); |
| } |
| fields = Fields::from_iter(cx, wilds) |
| } |
| TyKind::Adt(adt, substs) if is_box(cx.db, adt.0) => { |
| // The only legal patterns of type `Box` (outside `std`) are `_` and box |
| // patterns. If we're here we can assume this is a box pattern. |
| // FIXME(Nadrieril): A `Box` can in theory be matched either with `Box(_, |
| // _)` or a box pattern. As a hack to avoid an ICE with the former, we |
| // ignore other fields than the first one. This will trigger an error later |
| // anyway. |
| // See https://github.com/rust-lang/rust/issues/82772 , |
| // explanation: https://github.com/rust-lang/rust/pull/82789#issuecomment-796921977 |
| // The problem is that we can't know from the type whether we'll match |
| // normally or through box-patterns. We'll have to figure out a proper |
| // solution when we introduce generalized deref patterns. Also need to |
| // prevent mixing of those two options. |
| let pat = |
| subpatterns.iter().find(|pat| pat.field.into_raw() == 0u32.into()); |
| let field = if let Some(pat) = pat { |
| mkpat(&pat.pattern) |
| } else { |
| let ty = substs.at(Interner, 0).assert_ty_ref(Interner).clone(); |
| DeconstructedPat::wildcard(ty) |
| }; |
| ctor = Single; |
| fields = Fields::singleton(cx, field) |
| } |
| &TyKind::Adt(adt, _) => { |
| ctor = match pat.kind.as_ref() { |
| PatKind::Leaf { .. } => Single, |
| PatKind::Variant { enum_variant, .. } => Variant(*enum_variant), |
| _ => { |
| never!(); |
| Wildcard |
| } |
| }; |
| let variant = ctor.variant_id_for_adt(adt.0); |
| let fields_len = variant.variant_data(cx.db.upcast()).fields().len(); |
| // For each field in the variant, we store the relevant index into `self.fields` if any. |
| let mut field_id_to_id: Vec<Option<usize>> = vec![None; fields_len]; |
| let tys = Fields::list_variant_nonhidden_fields(cx, &pat.ty, variant) |
| .enumerate() |
| .map(|(i, (fid, ty))| { |
| let field_idx: u32 = fid.into_raw().into(); |
| field_id_to_id[field_idx as usize] = Some(i); |
| ty |
| }); |
| let mut wilds: SmallVec<[_; 2]> = |
| tys.map(DeconstructedPat::wildcard).collect(); |
| for pat in subpatterns { |
| let field_idx: u32 = pat.field.into_raw().into(); |
| if let Some(i) = field_id_to_id[field_idx as usize] { |
| wilds[i] = mkpat(&pat.pattern); |
| } |
| } |
| fields = Fields::from_iter(cx, wilds); |
| } |
| _ => { |
| never!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, &pat.ty); |
| ctor = Wildcard; |
| fields = Fields::empty(); |
| } |
| } |
| } |
| &PatKind::LiteralBool { value } => { |
| ctor = IntRange(IntRange::from_bool(value)); |
| fields = Fields::empty(); |
| } |
| PatKind::Or { .. } => { |
| ctor = Or; |
| let pats: SmallVec<[_; 2]> = expand_or_pat(pat).into_iter().map(mkpat).collect(); |
| fields = Fields::from_iter(cx, pats) |
| } |
| } |
| DeconstructedPat::new(ctor, fields, pat.ty.clone()) |
| } |
| |
| pub(crate) fn to_pat(&self, cx: &MatchCheckCtx<'_, 'p>) -> Pat { |
| let mut subpatterns = self.iter_fields().map(|p| p.to_pat(cx)); |
| let pat = match &self.ctor { |
| Single | Variant(_) => match self.ty.kind(Interner) { |
| TyKind::Tuple(..) => PatKind::Leaf { |
| subpatterns: subpatterns |
| .zip(0u32..) |
| .map(|(p, i)| FieldPat { |
| field: LocalFieldId::from_raw(i.into()), |
| pattern: p, |
| }) |
| .collect(), |
| }, |
| TyKind::Adt(adt, _) if is_box(cx.db, adt.0) => { |
| // Without `box_patterns`, the only legal pattern of type `Box` is `_` (outside |
| // of `std`). So this branch is only reachable when the feature is enabled and |
| // the pattern is a box pattern. |
| PatKind::Deref { subpattern: subpatterns.next().unwrap() } |
| } |
| TyKind::Adt(adt, substs) => { |
| let variant = self.ctor.variant_id_for_adt(adt.0); |
| let subpatterns = Fields::list_variant_nonhidden_fields(cx, self.ty(), variant) |
| .zip(subpatterns) |
| .map(|((field, _ty), pattern)| FieldPat { field, pattern }) |
| .collect(); |
| |
| if let VariantId::EnumVariantId(enum_variant) = variant { |
| PatKind::Variant { substs: substs.clone(), enum_variant, subpatterns } |
| } else { |
| PatKind::Leaf { subpatterns } |
| } |
| } |
| // Note: given the expansion of `&str` patterns done in `expand_pattern`, we should |
| // be careful to reconstruct the correct constant pattern here. However a string |
| // literal pattern will never be reported as a non-exhaustiveness witness, so we |
| // ignore this issue. |
| TyKind::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() }, |
| _ => { |
| never!("unexpected ctor for type {:?} {:?}", self.ctor, self.ty); |
| PatKind::Wild |
| } |
| }, |
| &Slice(slice) => match slice._unimplemented {}, |
| &Str(void) => match void {}, |
| &FloatRange(void) => match void {}, |
| IntRange(range) => return range.to_pat(cx, self.ty.clone()), |
| Wildcard | NonExhaustive => PatKind::Wild, |
| Missing { .. } => { |
| never!( |
| "trying to convert a `Missing` constructor into a `Pat`; this is a bug, \ |
| `Missing` should have been processed in `apply_constructors`" |
| ); |
| PatKind::Wild |
| } |
| Opaque | Or => { |
| never!("can't convert to pattern: {:?}", self.ctor); |
| PatKind::Wild |
| } |
| }; |
| Pat { ty: self.ty.clone(), kind: Box::new(pat) } |
| } |
| |
| pub(super) fn is_or_pat(&self) -> bool { |
| matches!(self.ctor, Or) |
| } |
| |
| pub(super) fn ctor(&self) -> &Constructor { |
| &self.ctor |
| } |
| |
| pub(super) fn ty(&self) -> &Ty { |
| &self.ty |
| } |
| |
| pub(super) fn iter_fields<'a>(&'a self) -> impl Iterator<Item = &'p DeconstructedPat<'p>> + 'a { |
| self.fields.iter_patterns() |
| } |
| |
| /// Specialize this pattern with a constructor. |
| /// `other_ctor` can be different from `self.ctor`, but must be covered by it. |
| pub(super) fn specialize<'a>( |
| &'a self, |
| cx: &MatchCheckCtx<'_, 'p>, |
| other_ctor: &Constructor, |
| ) -> SmallVec<[&'p DeconstructedPat<'p>; 2]> { |
| match (&self.ctor, other_ctor) { |
| (Wildcard, _) => { |
| // We return a wildcard for each field of `other_ctor`. |
| Fields::wildcards(cx, &self.ty, other_ctor).iter_patterns().collect() |
| } |
| (Slice(self_slice), Slice(other_slice)) |
| if self_slice.arity() != other_slice.arity() => |
| { |
| match self_slice._unimplemented {} |
| } |
| _ => self.fields.iter_patterns().collect(), |
| } |
| } |
| |
| /// We keep track for each pattern if it was ever reachable during the analysis. This is used |
| /// with `unreachable_spans` to report unreachable subpatterns arising from or patterns. |
| pub(super) fn set_reachable(&self) { |
| self.reachable.set(true) |
| } |
| pub(super) fn is_reachable(&self) -> bool { |
| self.reachable.get() |
| } |
| } |
| |
| fn is_field_list_non_exhaustive(variant_id: VariantId, cx: &MatchCheckCtx<'_, '_>) -> bool { |
| let attr_def_id = match variant_id { |
| VariantId::EnumVariantId(id) => id.into(), |
| VariantId::StructId(id) => id.into(), |
| VariantId::UnionId(id) => id.into(), |
| }; |
| cx.db.attrs(attr_def_id).by_key("non_exhaustive").exists() |
| } |
