src/tools/clippy/clippy_lints/src/checked_conversions.rs - toolchain/rustc - Git at Google

 //! lint on manually implemented checked conversions that could be transformed into `try_from`

 use if_chain::if_chain;
 use rustc::hir::*;
 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
 use rustc::{declare_lint_pass, declare_tool_lint};
 use rustc_errors::Applicability;
 use syntax::ast::LitKind;

 use crate::utils::{snippet_with_applicability, span_lint_and_sugg, SpanlessEq};

 declare_clippy_lint! {
     /// **What it does:** Checks for explicit bounds checking when casting.
     ///
     /// **Why is this bad?** Reduces the readability of statements & is error prone.
     ///
     /// **Known problems:** None.
     ///
     /// **Example:**
     /// ```rust
     /// # let foo: u32 = 5;
     /// # let _ =
     /// foo <= i32::max_value() as u32
     /// # ;
     /// ```
     ///
     /// Could be written:
     ///
     /// ```rust
     /// # let _ =
     /// i32::try_from(foo).is_ok()
     /// # ;
     /// ```
     pub CHECKED_CONVERSIONS,
     pedantic,
     "`try_from` could replace manual bounds checking when casting"
 }

 declare_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);

 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CheckedConversions {
     fn check_expr(&mut self, cx: &LateContext<'_, '_>, item: &Expr) {
         let result = if_chain! {
             if !in_external_macro(cx.sess(), item.span);
             if let ExprKind::Binary(op, ref left, ref right) = &item.node;

             then {
                 match op.node {
                     BinOpKind::Ge | BinOpKind::Le => single_check(item),
                     BinOpKind::And => double_check(cx, left, right),
                     _ => None,
                 }
             } else {
                 None
             }
         };

         if_chain! {
             if let Some(cv) = result;
             if let Some(to_type) = cv.to_type;

             then {
                 let mut applicability = Applicability::MachineApplicable;
                 let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut
                                 applicability);
                 span_lint_and_sugg(
                     cx,
                     CHECKED_CONVERSIONS,
                     item.span,
                     "Checked cast can be simplified.",
                     "try",
                     format!("{}::try_from({}).is_ok()",
                             to_type,
                             snippet),
                     applicability
                 );
             }
         }
     }
 }

 /// Searches for a single check from unsigned to _ is done
 /// todo: check for case signed -> larger unsigned == only x >= 0
 fn single_check(expr: &Expr) -> Option<Conversion<'_>> {
     check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
 }

 /// Searches for a combination of upper & lower bound checks
 fn double_check<'a>(cx: &LateContext<'_, '_>, left: &'a Expr, right: &'a Expr) -> Option<Conversion<'a>> {
     let upper_lower = |l, r| {
         let upper = check_upper_bound(l);
         let lower = check_lower_bound(r);

         transpose(upper, lower).and_then(|(l, r)| l.combine(r, cx))
     };

     upper_lower(left, right).or_else(|| upper_lower(right, left))
 }

 /// Contains the result of a tried conversion check
 #[derive(Clone, Debug)]
 struct Conversion<'a> {
     cvt: ConversionType,
     expr_to_cast: &'a Expr,
     to_type: Option<&'a str>,
 }

 /// The kind of conversion that is checked
 #[derive(Copy, Clone, Debug, PartialEq)]
 enum ConversionType {
     SignedToUnsigned,
     SignedToSigned,
     FromUnsigned,
 }

 impl<'a> Conversion<'a> {
     /// Combine multiple conversions if the are compatible
     pub fn combine(self, other: Self, cx: &LateContext<'_, '_>) -> Option<Conversion<'a>> {
         if self.is_compatible(&other, cx) {
             // Prefer a Conversion that contains a type-constraint
             Some(if self.to_type.is_some() { self } else { other })
         } else {
             None
         }
     }

     /// Checks if two conversions are compatible
     /// same type of conversion, same 'castee' and same 'to type'
     pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_, '_>) -> bool {
         (self.cvt == other.cvt)
             && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
             && (self.has_compatible_to_type(other))
     }

     /// Checks if the to-type is the same (if there is a type constraint)
     fn has_compatible_to_type(&self, other: &Self) -> bool {
         transpose(self.to_type.as_ref(), other.to_type.as_ref()).map_or(true, |(l, r)| l == r)
     }

     /// Try to construct a new conversion if the conversion type is valid
     fn try_new(expr_to_cast: &'a Expr, from_type: &str, to_type: &'a str) -> Option<Conversion<'a>> {
         ConversionType::try_new(from_type, to_type).map(|cvt| Conversion {
             cvt,
             expr_to_cast,
             to_type: Some(to_type),
         })
     }

     /// Construct a new conversion without type constraint
     fn new_any(expr_to_cast: &'a Expr) -> Conversion<'a> {
         Conversion {
             cvt: ConversionType::SignedToUnsigned,
             expr_to_cast,
             to_type: None,
         }
     }
 }

 impl ConversionType {
     /// Creates a conversion type if the type is allowed & conversion is valid
     fn try_new(from: &str, to: &str) -> Option<Self> {
         if UINTS.contains(&from) {
             Some(ConversionType::FromUnsigned)
         } else if SINTS.contains(&from) {
             if UINTS.contains(&to) {
                 Some(ConversionType::SignedToUnsigned)
             } else if SINTS.contains(&to) {
                 Some(ConversionType::SignedToSigned)
             } else {
                 None
             }
         } else {
             None
         }
     }
 }

 /// Check for `expr <= (to_type::max_value() as from_type)`
 fn check_upper_bound(expr: &Expr) -> Option<Conversion<'_>> {
     if_chain! {
          if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node;
          if let Some((candidate, check)) = normalize_le_ge(op, left, right);
          if let Some((from, to)) = get_types_from_cast(check, MAX_VALUE, INTS);

          then {
              Conversion::try_new(candidate, from, to)
          } else {
             None
         }
     }
 }

 /// Check for `expr >= 0|(to_type::min_value() as from_type)`
 fn check_lower_bound(expr: &Expr) -> Option<Conversion<'_>> {
     fn check_function<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
         (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
     }

     // First of we need a binary containing the expression & the cast
     if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node {
         normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
     } else {
         None
     }
 }

 /// Check for `expr >= 0`
 fn check_lower_bound_zero<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
     if_chain! {
         if let ExprKind::Lit(ref lit) = &check.node;
         if let LitKind::Int(0, _) = &lit.node;

         then {
             Some(Conversion::new_any(candidate))
         } else {
             None
         }
     }
 }

 /// Check for `expr >= (to_type::min_value() as from_type)`
 fn check_lower_bound_min<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
     if let Some((from, to)) = get_types_from_cast(check, MIN_VALUE, SINTS) {
         Conversion::try_new(candidate, from, to)
     } else {
         None
     }
 }

 /// Tries to extract the from- and to-type from a cast expression
 fn get_types_from_cast<'a>(expr: &'a Expr, func: &'a str, types: &'a [&str]) -> Option<(&'a str, &'a str)> {
     // `to_type::maxmin_value() as from_type`
     let call_from_cast: Option<(&Expr, &str)> = if_chain! {
         // to_type::maxmin_value(), from_type
         if let ExprKind::Cast(ref limit, ref from_type) = &expr.node;
         if let TyKind::Path(ref from_type_path) = &from_type.node;
         if let Some(from_sym) = int_ty_to_sym(from_type_path);

         then {
             Some((limit, from_sym))
         } else {
             None
         }
     };

     // `from_type::from(to_type::maxmin_value())`
     let limit_from: Option<(&Expr, &str)> = call_from_cast.or_else(|| {
         if_chain! {
             // `from_type::from, to_type::maxmin_value()`
             if let ExprKind::Call(ref from_func, ref args) = &expr.node;
             // `to_type::maxmin_value()`
             if args.len() == 1;
             if let limit = &args[0];
             // `from_type::from`
             if let ExprKind::Path(ref path) = &from_func.node;
             if let Some(from_sym) = get_implementing_type(path, INTS, FROM);

             then {
                 Some((limit, from_sym))
             } else {
                 None
             }
         }
     });

     if let Some((limit, from_type)) = limit_from {
         if_chain! {
             if let ExprKind::Call(ref fun_name, _) = &limit.node;
             // `to_type, maxmin_value`
             if let ExprKind::Path(ref path) = &fun_name.node;
             // `to_type`
             if let Some(to_type) = get_implementing_type(path, types, func);

             then {
                 Some((from_type, to_type))
             } else {
                 None
             }
         }
     } else {
         None
     }
 }

 /// Gets the type which implements the called function
 fn get_implementing_type<'a>(path: &QPath, candidates: &'a [&str], function: &str) -> Option<&'a str> {
     if_chain! {
         if let QPath::TypeRelative(ref ty, ref path) = &path;
         if path.ident.name.as_str() == function;
         if let TyKind::Path(QPath::Resolved(None, ref tp)) = &ty.node;
         if let [int] = &*tp.segments;
         let name = &int.ident.name.as_str();

         then {
             candidates.iter().find(|c| name == *c).cloned()
         } else {
             None
         }
     }
 }

 /// Gets the type as a string, if it is a supported integer
 fn int_ty_to_sym(path: &QPath) -> Option<&str> {
     if_chain! {
         if let QPath::Resolved(_, ref path) = *path;
         if let [ty] = &*path.segments;
         let name = &ty.ident.name.as_str();

         then {
             INTS.iter().find(|c| name == *c).cloned()
         } else {
             None
         }
     }
 }

 /// (Option<T>, Option<U>) -> Option<(T, U)>
 fn transpose<T, U>(lhs: Option<T>, rhs: Option<U>) -> Option<(T, U)> {
     match (lhs, rhs) {
         (Some(l), Some(r)) => Some((l, r)),
         _ => None,
     }
 }

 /// Will return the expressions as if they were expr1 <= expr2
 fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr, right: &'a Expr) -> Option<(&'a Expr, &'a Expr)> {
     match op.node {
         BinOpKind::Le => Some((left, right)),
         BinOpKind::Ge => Some((right, left)),
         _ => None,
     }
 }

 // Constants
 const FROM: &str = "from";
 const MAX_VALUE: &str = "max_value";
 const MIN_VALUE: &str = "min_value";

 const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
 const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
 const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];
	//! lint on manually implemented checked conversions that could be transformed into `try_from`

	use if_chain::if_chain;
	use rustc::hir::*;
	use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
	use rustc::{declare_lint_pass, declare_tool_lint};
	use rustc_errors::Applicability;
	use syntax::ast::LitKind;

	use crate::utils::{snippet_with_applicability, span_lint_and_sugg, SpanlessEq};

	declare_clippy_lint! {
	/// What it does: Checks for explicit bounds checking when casting.
	///
	/// Why is this bad? Reduces the readability of statements & is error prone.
	///
	/// Known problems: None.
	///
	/// Example:
	/// ```rust
	/// # let foo: u32 = 5;
	/// # let _ =
	/// foo <= i32::max_value() as u32
	/// # ;
	/// ```
	///
	/// Could be written:
	///
	/// ```rust
	/// # let _ =
	/// i32::try_from(foo).is_ok()
	/// # ;
	/// ```
	pub CHECKED_CONVERSIONS,
	pedantic,
	"`try_from` could replace manual bounds checking when casting"
	}

	declare_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);

	impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CheckedConversions {
	fn check_expr(&mut self, cx: &LateContext<'_, '_>, item: &Expr) {
	let result = if_chain! {
	if !in_external_macro(cx.sess(), item.span);
	if let ExprKind::Binary(op, ref left, ref right) = &item.node;

	then {
	match op.node {
	BinOpKind::Ge \| BinOpKind::Le => single_check(item),
	BinOpKind::And => double_check(cx, left, right),
	_ => None,
	}
	} else {
	None
	}
	};

	if_chain! {
	if let Some(cv) = result;
	if let Some(to_type) = cv.to_type;

	then {
	let mut applicability = Applicability::MachineApplicable;
	let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut
	applicability);
	span_lint_and_sugg(
	cx,
	CHECKED_CONVERSIONS,
	item.span,
	"Checked cast can be simplified.",
	"try",
	format!("{}::try_from({}).is_ok()",
	to_type,
	snippet),
	applicability
	);
	}
	}
	}
	}

	/// Searches for a single check from unsigned to _ is done
	/// todo: check for case signed -> larger unsigned == only x >= 0
	fn single_check(expr: &Expr) -> Option<Conversion<'_>> {
	check_upper_bound(expr).filter(\|cv\| cv.cvt == ConversionType::FromUnsigned)
	}

	/// Searches for a combination of upper & lower bound checks
	fn double_check<'a>(cx: &LateContext<'_, '_>, left: &'a Expr, right: &'a Expr) -> Option<Conversion<'a>> {
	let upper_lower = \|l, r\| {
	let upper = check_upper_bound(l);
	let lower = check_lower_bound(r);

	transpose(upper, lower).and_then(\|(l, r)\| l.combine(r, cx))
	};

	upper_lower(left, right).or_else(\|\| upper_lower(right, left))
	}

	/// Contains the result of a tried conversion check
	#[derive(Clone, Debug)]
	struct Conversion<'a> {
	cvt: ConversionType,
	expr_to_cast: &'a Expr,
	to_type: Option<&'a str>,
	}

	/// The kind of conversion that is checked
	#[derive(Copy, Clone, Debug, PartialEq)]
	enum ConversionType {
	SignedToUnsigned,
	SignedToSigned,
	FromUnsigned,
	}

	impl<'a> Conversion<'a> {
	/// Combine multiple conversions if the are compatible
	pub fn combine(self, other: Self, cx: &LateContext<'_, '_>) -> Option<Conversion<'a>> {
	if self.is_compatible(&other, cx) {
	// Prefer a Conversion that contains a type-constraint
	Some(if self.to_type.is_some() { self } else { other })
	} else {
	None
	}
	}

	/// Checks if two conversions are compatible
	/// same type of conversion, same 'castee' and same 'to type'
	pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_, '_>) -> bool {
	(self.cvt == other.cvt)
	&& (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
	&& (self.has_compatible_to_type(other))
	}

	/// Checks if the to-type is the same (if there is a type constraint)
	fn has_compatible_to_type(&self, other: &Self) -> bool {
	transpose(self.to_type.as_ref(), other.to_type.as_ref()).map_or(true, \|(l, r)\| l == r)
	}

	/// Try to construct a new conversion if the conversion type is valid
	fn try_new(expr_to_cast: &'a Expr, from_type: &str, to_type: &'a str) -> Option<Conversion<'a>> {
	ConversionType::try_new(from_type, to_type).map(\|cvt\| Conversion {
	cvt,
	expr_to_cast,
	to_type: Some(to_type),
	})
	}

	/// Construct a new conversion without type constraint
	fn new_any(expr_to_cast: &'a Expr) -> Conversion<'a> {
	Conversion {
	cvt: ConversionType::SignedToUnsigned,
	expr_to_cast,
	to_type: None,
	}
	}
	}

	impl ConversionType {
	/// Creates a conversion type if the type is allowed & conversion is valid
	fn try_new(from: &str, to: &str) -> Option<Self> {
	if UINTS.contains(&from) {
	Some(ConversionType::FromUnsigned)
	} else if SINTS.contains(&from) {
	if UINTS.contains(&to) {
	Some(ConversionType::SignedToUnsigned)
	} else if SINTS.contains(&to) {
	Some(ConversionType::SignedToSigned)
	} else {
	None
	}
	} else {
	None
	}
	}
	}

	/// Check for `expr <= (to_type::max_value() as from_type)`
	fn check_upper_bound(expr: &Expr) -> Option<Conversion<'_>> {
	if_chain! {
	if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node;
	if let Some((candidate, check)) = normalize_le_ge(op, left, right);
	if let Some((from, to)) = get_types_from_cast(check, MAX_VALUE, INTS);

	then {
	Conversion::try_new(candidate, from, to)
	} else {
	None
	}
	}
	}

	/// Check for `expr >= 0\|(to_type::min_value() as from_type)`
	fn check_lower_bound(expr: &Expr) -> Option<Conversion<'_>> {
	fn check_function<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
	(check_lower_bound_zero(candidate, check)).or_else(\|\| (check_lower_bound_min(candidate, check)))
	}

	// First of we need a binary containing the expression & the cast
	if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node {
	normalize_le_ge(op, right, left).and_then(\|(l, r)\| check_function(l, r))
	} else {
	None
	}
	}

	/// Check for `expr >= 0`
	fn check_lower_bound_zero<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
	if_chain! {
	if let ExprKind::Lit(ref lit) = &check.node;
	if let LitKind::Int(0, _) = &lit.node;

	then {
	Some(Conversion::new_any(candidate))
	} else {
	None
	}
	}
	}

	/// Check for `expr >= (to_type::min_value() as from_type)`
	fn check_lower_bound_min<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
	if let Some((from, to)) = get_types_from_cast(check, MIN_VALUE, SINTS) {
	Conversion::try_new(candidate, from, to)
	} else {
	None
	}
	}

	/// Tries to extract the from- and to-type from a cast expression
	fn get_types_from_cast<'a>(expr: &'a Expr, func: &'a str, types: &'a [&str]) -> Option<(&'a str, &'a str)> {
	// `to_type::maxmin_value() as from_type`
	let call_from_cast: Option<(&Expr, &str)> = if_chain! {
	// to_type::maxmin_value(), from_type
	if let ExprKind::Cast(ref limit, ref from_type) = &expr.node;
	if let TyKind::Path(ref from_type_path) = &from_type.node;
	if let Some(from_sym) = int_ty_to_sym(from_type_path);

	then {
	Some((limit, from_sym))
	} else {
	None
	}
	};

	// `from_type::from(to_type::maxmin_value())`
	let limit_from: Option<(&Expr, &str)> = call_from_cast.or_else(\|\| {
	if_chain! {
	// `from_type::from, to_type::maxmin_value()`
	if let ExprKind::Call(ref from_func, ref args) = &expr.node;
	// `to_type::maxmin_value()`
	if args.len() == 1;
	if let limit = &args[0];
	// `from_type::from`
	if let ExprKind::Path(ref path) = &from_func.node;
	if let Some(from_sym) = get_implementing_type(path, INTS, FROM);

	then {
	Some((limit, from_sym))
	} else {
	None
	}
	}
	});

	if let Some((limit, from_type)) = limit_from {
	if_chain! {
	if let ExprKind::Call(ref fun_name, _) = &limit.node;
	// `to_type, maxmin_value`
	if let ExprKind::Path(ref path) = &fun_name.node;
	// `to_type`
	if let Some(to_type) = get_implementing_type(path, types, func);

	then {
	Some((from_type, to_type))
	} else {
	None
	}
	}
	} else {
	None
	}
	}

	/// Gets the type which implements the called function
	fn get_implementing_type<'a>(path: &QPath, candidates: &'a [&str], function: &str) -> Option<&'a str> {
	if_chain! {
	if let QPath::TypeRelative(ref ty, ref path) = &path;
	if path.ident.name.as_str() == function;
	if let TyKind::Path(QPath::Resolved(None, ref tp)) = &ty.node;
	if let [int] = &*tp.segments;
	let name = &int.ident.name.as_str();

	then {
	candidates.iter().find(\|c\| name == *c).cloned()
	} else {
	None
	}
	}
	}

	/// Gets the type as a string, if it is a supported integer
	fn int_ty_to_sym(path: &QPath) -> Option<&str> {
	if_chain! {
	if let QPath::Resolved(_, ref path) = *path;
	if let [ty] = &*path.segments;
	let name = &ty.ident.name.as_str();

	then {
	INTS.iter().find(\|c\| name == *c).cloned()
	} else {
	None
	}
	}
	}

	/// (Option<T>, Option<U>) -> Option<(T, U)>
	fn transpose<T, U>(lhs: Option<T>, rhs: Option<U>) -> Option<(T, U)> {
	match (lhs, rhs) {
	(Some(l), Some(r)) => Some((l, r)),
	_ => None,
	}
	}

	/// Will return the expressions as if they were expr1 <= expr2
	fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr, right: &'a Expr) -> Option<(&'a Expr, &'a Expr)> {
	match op.node {
	BinOpKind::Le => Some((left, right)),
	BinOpKind::Ge => Some((right, left)),
	_ => None,
	}
	}

	// Constants
	const FROM: &str = "from";
	const MAX_VALUE: &str = "max_value";
	const MIN_VALUE: &str = "min_value";

	const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
	const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
	const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];