3 use rustc::hir::intravisit::{FnKind, Visitor, walk_ty};
6 use std::cmp::Ordering;
7 use syntax::ast::{IntTy, UintTy, FloatTy};
8 use syntax::codemap::Span;
9 use utils::{comparisons, higher, in_external_macro, in_macro, match_def_path, snippet,
10 span_help_and_lint, span_lint};
13 /// Handles all the linting of funky types
14 #[allow(missing_copy_implementations)]
17 /// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
19 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
20 /// the heap. So if you `Box` it, you just add another level of indirection
21 /// without any benefit whatsoever.
23 /// **Known problems:** None.
28 /// values: Box<Vec<Foo>>,
34 "usage of `Box<Vec<T>>`, vector elements are already on the heap"
37 /// **What it does:** Checks for usage of any `LinkedList`, suggesting to use a
38 /// `Vec` or a `VecDeque` (formerly called `RingBuf`).
40 /// **Why is this bad?** Gankro says:
42 /// > The TL;DR of `LinkedList` is that it's built on a massive amount of pointers and indirection.
43 /// > It wastes memory, it has terrible cache locality, and is all-around slow. `RingBuf`, while
44 /// > "only" amortized for push/pop, should be faster in the general case for almost every possible
45 /// > workload, and isn't even amortized at all if you can predict the capacity you need.
47 /// > `LinkedList`s are only really good if you're doing a lot of merging or splitting of lists.
48 /// > This is because they can just mangle some pointers instead of actually copying the data. Even
49 /// > if you're doing a lot of insertion in the middle of the list, `RingBuf` can still be better
50 /// > because of how expensive it is to seek to the middle of a `LinkedList`.
52 /// **Known problems:** False positives – the instances where using a
53 /// `LinkedList` makes sense are few and far between, but they can still happen.
57 /// let x = LinkedList::new();
62 "usage of LinkedList, usually a vector is faster, or a more specialized data \
63 structure like a VecDeque"
66 impl LintPass for TypePass {
67 fn get_lints(&self) -> LintArray {
68 lint_array!(BOX_VEC, LINKEDLIST)
72 impl LateLintPass for TypePass {
73 fn check_ty(&mut self, cx: &LateContext, ast_ty: &Ty) {
74 if in_macro(cx, ast_ty.span) {
77 if let Some(did) = cx.tcx.def_map.borrow().get(&ast_ty.id) {
78 if let def::Def::Struct(..) = did.full_def() {
79 if Some(did.full_def().def_id()) == cx.tcx.lang_items.owned_box() {
81 let TyPath(_, ref path) = ast_ty.node,
82 let Some(ref last) = path.segments.last(),
83 let PathParameters::AngleBracketedParameters(ref ag) = last.parameters,
84 let Some(ref vec) = ag.types.get(0),
85 let Some(did) = cx.tcx.def_map.borrow().get(&vec.id),
86 let def::Def::Struct(..) = did.full_def(),
87 match_def_path(cx, did.full_def().def_id(), &paths::VEC),
89 span_help_and_lint(cx,
92 "you seem to be trying to use `Box<Vec<T>>`. Consider using just `Vec<T>`",
93 "`Vec<T>` is already on the heap, `Box<Vec<T>>` makes an extra allocation.");
95 } else if match_def_path(cx, did.full_def().def_id(), &paths::LINKED_LIST) {
96 span_help_and_lint(cx,
99 "I see you're using a LinkedList! Perhaps you meant some other data structure?",
100 "a VecDeque might work");
107 #[allow(missing_copy_implementations)]
110 /// **What it does:** Checks for binding a unit value.
112 /// **Why is this bad?** A unit value cannot usefully be used anywhere. So
113 /// binding one is kind of pointless.
115 /// **Known problems:** None.
124 "creating a let binding to a value of unit type, which usually can't be used afterwards"
127 fn check_let_unit(cx: &LateContext, decl: &Decl) {
128 if let DeclLocal(ref local) = decl.node {
129 let bindtype = &cx.tcx.pat_ty(&local.pat).sty;
130 if *bindtype == ty::TyTuple(&[]) {
131 if in_external_macro(cx, decl.span) || in_macro(cx, local.pat.span) {
134 if higher::is_from_for_desugar(decl) {
140 &format!("this let-binding has unit value. Consider omitting `let {} =`",
141 snippet(cx, local.pat.span, "..")));
146 impl LintPass for LetPass {
147 fn get_lints(&self) -> LintArray {
148 lint_array!(LET_UNIT_VALUE)
152 impl LateLintPass for LetPass {
153 fn check_decl(&mut self, cx: &LateContext, decl: &Decl) {
154 check_let_unit(cx, decl)
158 /// **What it does:** Checks for comparisons to unit.
160 /// **Why is this bad?** Unit is always equal to itself, and thus is just a
161 /// clumsily written constant. Mostly this happens when someone accidentally
162 /// adds semicolons at the end of the operands.
164 /// **Known problems:** None.
168 /// if { foo(); } == { bar(); } { baz(); }
172 /// { foo(); bar(); baz(); }
177 "comparing unit values"
180 #[allow(missing_copy_implementations)]
183 impl LintPass for UnitCmp {
184 fn get_lints(&self) -> LintArray {
185 lint_array!(UNIT_CMP)
189 impl LateLintPass for UnitCmp {
190 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
191 if in_macro(cx, expr.span) {
194 if let ExprBinary(ref cmp, ref left, _) = expr.node {
196 let sty = &cx.tcx.expr_ty(left).sty;
197 if *sty == ty::TyTuple(&[]) && op.is_comparison() {
198 let result = match op {
199 BiEq | BiLe | BiGe => "true",
205 &format!("{}-comparison of unit values detected. This will always be {}",
215 /// **What it does:** Checks for casts from any numerical to a float type where
216 /// the receiving type cannot store all values from the original type without
217 /// rounding errors. This possible rounding is to be expected, so this lint is
218 /// `Allow` by default.
220 /// Basically, this warns on casting any integer with 32 or more bits to `f32`
221 /// or any 64-bit integer to `f64`.
223 /// **Why is this bad?** It's not bad at all. But in some applications it can be
224 /// helpful to know where precision loss can take place. This lint can help find
225 /// those places in the code.
227 /// **Known problems:** None.
231 /// let x = u64::MAX; x as f64
234 pub CAST_PRECISION_LOSS,
236 "casts that cause loss of precision, e.g `x as f32` where `x: u64`"
239 /// **What it does:** Checks for casts from a signed to an unsigned numerical
240 /// type. In this case, negative values wrap around to large positive values,
241 /// which can be quite surprising in practice. However, as the cast works as
242 /// defined, this lint is `Allow` by default.
244 /// **Why is this bad?** Possibly surprising results. You can activate this lint
245 /// as a one-time check to see where numerical wrapping can arise.
247 /// **Known problems:** None.
252 /// y as u64 // will return 18446744073709551615
257 "casts from signed types to unsigned types, e.g `x as u32` where `x: i32`"
260 /// **What it does:** Checks for on casts between numerical types that may
261 /// truncate large values. This is expected behavior, so the cast is `Allow` by
264 /// **Why is this bad?** In some problem domains, it is good practice to avoid
265 /// truncation. This lint can be activated to help assess where additional
266 /// checks could be beneficial.
268 /// **Known problems:** None.
272 /// fn as_u8(x: u64) -> u8 { x as u8 }
275 pub CAST_POSSIBLE_TRUNCATION,
277 "casts that may cause truncation of the value, e.g `x as u8` where `x: u32`, \
278 or `x as i32` where `x: f32`"
281 /// **What it does:** Checks for casts from an unsigned type to a signed type of
282 /// the same size. Performing such a cast is a 'no-op' for the compiler,
283 /// i.e. nothing is changed at the bit level, and the binary representation of
284 /// the value is reinterpreted. This can cause wrapping if the value is too big
285 /// for the target signed type. However, the cast works as defined, so this lint
286 /// is `Allow` by default.
288 /// **Why is this bad?** While such a cast is not bad in itself, the results can
289 /// be surprising when this is not the intended behavior, as demonstrated by the
292 /// **Known problems:** None.
296 /// u32::MAX as i32 // will yield a value of `-1`
299 pub CAST_POSSIBLE_WRAP,
301 "casts that may cause wrapping around the value, e.g `x as i32` where `x: u32` \
305 /// Returns the size in bits of an integral type.
306 /// Will return 0 if the type is not an int or uint variant
307 fn int_ty_to_nbits(typ: &ty::TyS) -> usize {
308 let n = match typ.sty {
309 ty::TyInt(i) => 4 << (i as usize),
310 ty::TyUint(u) => 4 << (u as usize),
313 // n == 4 is the usize/isize case
315 ::std::mem::size_of::<usize>() * 8
321 fn is_isize_or_usize(typ: &ty::TyS) -> bool {
323 ty::TyInt(IntTy::Is) |
324 ty::TyUint(UintTy::Us) => true,
329 fn span_precision_loss_lint(cx: &LateContext, expr: &Expr, cast_from: &ty::TyS, cast_to_f64: bool) {
330 let mantissa_nbits = if cast_to_f64 {
335 let arch_dependent = is_isize_or_usize(cast_from) && cast_to_f64;
336 let arch_dependent_str = "on targets with 64-bit wide pointers ";
337 let from_nbits_str = if arch_dependent {
339 } else if is_isize_or_usize(cast_from) {
340 "32 or 64".to_owned()
342 int_ty_to_nbits(cast_from).to_string()
347 &format!("casting {0} to {1} causes a loss of precision {2}({0} is {3} bits wide, but {1}'s mantissa \
348 is only {4} bits wide)",
370 fn check_truncation_and_wrapping(cx: &LateContext, expr: &Expr, cast_from: &ty::TyS, cast_to: &ty::TyS) {
371 let arch_64_suffix = " on targets with 64-bit wide pointers";
372 let arch_32_suffix = " on targets with 32-bit wide pointers";
373 let cast_unsigned_to_signed = !cast_from.is_signed() && cast_to.is_signed();
374 let (from_nbits, to_nbits) = (int_ty_to_nbits(cast_from), int_ty_to_nbits(cast_to));
375 let (span_truncation, suffix_truncation, span_wrap, suffix_wrap) = match (is_isize_or_usize(cast_from),
376 is_isize_or_usize(cast_to)) {
377 (true, true) | (false, false) => {
378 (to_nbits < from_nbits,
380 to_nbits == from_nbits && cast_unsigned_to_signed,
390 to_nbits <= 32 && cast_unsigned_to_signed,
396 cast_unsigned_to_signed,
397 if from_nbits == 64 {
406 CAST_POSSIBLE_TRUNCATION,
408 &format!("casting {} to {} may truncate the value{}",
411 match suffix_truncation {
412 ArchSuffix::_32 => arch_32_suffix,
413 ArchSuffix::_64 => arch_64_suffix,
414 ArchSuffix::None => "",
421 &format!("casting {} to {} may wrap around the value{}",
425 ArchSuffix::_32 => arch_32_suffix,
426 ArchSuffix::_64 => arch_64_suffix,
427 ArchSuffix::None => "",
432 impl LintPass for CastPass {
433 fn get_lints(&self) -> LintArray {
434 lint_array!(CAST_PRECISION_LOSS,
436 CAST_POSSIBLE_TRUNCATION,
441 impl LateLintPass for CastPass {
442 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
443 if let ExprCast(ref ex, _) = expr.node {
444 let (cast_from, cast_to) = (cx.tcx.expr_ty(ex), cx.tcx.expr_ty(expr));
445 if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx, expr.span) {
446 match (cast_from.is_integral(), cast_to.is_integral()) {
448 let from_nbits = int_ty_to_nbits(cast_from);
449 let to_nbits = if let ty::TyFloat(FloatTy::F32) = cast_to.sty {
454 if is_isize_or_usize(cast_from) || from_nbits >= to_nbits {
455 span_precision_loss_lint(cx, expr, cast_from, to_nbits == 64);
460 CAST_POSSIBLE_TRUNCATION,
462 &format!("casting {} to {} may truncate the value", cast_from, cast_to));
463 if !cast_to.is_signed() {
467 &format!("casting {} to {} may lose the sign of the value", cast_from, cast_to));
471 if cast_from.is_signed() && !cast_to.is_signed() {
475 &format!("casting {} to {} may lose the sign of the value", cast_from, cast_to));
477 check_truncation_and_wrapping(cx, expr, cast_from, cast_to);
480 if let (&ty::TyFloat(FloatTy::F64), &ty::TyFloat(FloatTy::F32)) = (&cast_from.sty,
483 CAST_POSSIBLE_TRUNCATION,
485 "casting f64 to f32 may truncate the value");
494 /// **What it does:** Checks for types used in structs, parameters and `let`
495 /// declarations above a certain complexity threshold.
497 /// **Why is this bad?** Too complex types make the code less readable. Consider
498 /// using a `type` definition to simplify them.
500 /// **Known problems:** None.
504 /// struct Foo { inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>> }
509 "usage of very complex types that might be better factored into `type` definitions"
512 #[allow(missing_copy_implementations)]
513 pub struct TypeComplexityPass {
517 impl TypeComplexityPass {
518 pub fn new(threshold: u64) -> Self {
519 TypeComplexityPass { threshold: threshold }
523 impl LintPass for TypeComplexityPass {
524 fn get_lints(&self) -> LintArray {
525 lint_array!(TYPE_COMPLEXITY)
529 impl LateLintPass for TypeComplexityPass {
530 fn check_fn(&mut self, cx: &LateContext, _: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
531 self.check_fndecl(cx, decl);
534 fn check_struct_field(&mut self, cx: &LateContext, field: &StructField) {
535 // enum variants are also struct fields now
536 self.check_type(cx, &field.ty);
539 fn check_item(&mut self, cx: &LateContext, item: &Item) {
541 ItemStatic(ref ty, _, _) |
542 ItemConst(ref ty, _) => self.check_type(cx, ty),
543 // functions, enums, structs, impls and traits are covered
548 fn check_trait_item(&mut self, cx: &LateContext, item: &TraitItem) {
550 ConstTraitItem(ref ty, _) |
551 TypeTraitItem(_, Some(ref ty)) => self.check_type(cx, ty),
552 MethodTraitItem(MethodSig { ref decl, .. }, None) => self.check_fndecl(cx, decl),
553 // methods with default impl are covered by check_fn
558 fn check_impl_item(&mut self, cx: &LateContext, item: &ImplItem) {
560 ImplItemKind::Const(ref ty, _) |
561 ImplItemKind::Type(ref ty) => self.check_type(cx, ty),
562 // methods are covered by check_fn
567 fn check_local(&mut self, cx: &LateContext, local: &Local) {
568 if let Some(ref ty) = local.ty {
569 self.check_type(cx, ty);
574 impl TypeComplexityPass {
575 fn check_fndecl(&self, cx: &LateContext, decl: &FnDecl) {
576 for arg in &decl.inputs {
577 self.check_type(cx, &arg.ty);
579 if let Return(ref ty) = decl.output {
580 self.check_type(cx, ty);
584 fn check_type(&self, cx: &LateContext, ty: &Ty) {
585 if in_macro(cx, ty.span) {
589 let mut visitor = TypeComplexityVisitor {
593 visitor.visit_ty(ty);
597 if score > self.threshold {
601 "very complex type used. Consider factoring parts into `type` definitions");
606 /// Walks a type and assigns a complexity score to it.
607 struct TypeComplexityVisitor {
608 /// total complexity score of the type
610 /// current nesting level
614 impl<'v> Visitor<'v> for TypeComplexityVisitor {
615 fn visit_ty(&mut self, ty: &'v Ty) {
616 let (add_score, sub_nest) = match ty.node {
617 // _, &x and *x have only small overhead; don't mess with nesting level
618 TyInfer | TyPtr(..) | TyRptr(..) => (1, 0),
620 // the "normal" components of a type: named types, arrays/tuples
624 TyFixedLengthVec(..) => (10 * self.nest, 1),
626 // "Sum" of trait bounds
627 TyObjectSum(..) => (20 * self.nest, 0),
629 // function types and "for<...>" bring a lot of overhead
631 TyPolyTraitRef(..) => (50 * self.nest, 1),
635 self.score += add_score;
636 self.nest += sub_nest;
638 self.nest -= sub_nest;
642 /// **What it does:** Checks for expressions where a character literal is cast
643 /// to `u8` and suggests using a byte literal instead.
645 /// **Why is this bad?** In general, casting values to smaller types is
646 /// error-prone and should be avoided where possible. In the particular case of
647 /// converting a character literal to u8, it is easy to avoid by just using a
648 /// byte literal instead. As an added bonus, `b'a'` is even slightly shorter
649 /// than `'a' as u8`.
651 /// **Known problems:** None.
660 "casting a character literal to u8"
663 pub struct CharLitAsU8;
665 impl LintPass for CharLitAsU8 {
666 fn get_lints(&self) -> LintArray {
667 lint_array!(CHAR_LIT_AS_U8)
671 impl LateLintPass for CharLitAsU8 {
672 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
673 use syntax::ast::{LitKind, UintTy};
675 if let ExprCast(ref e, _) = expr.node {
676 if let ExprLit(ref l) = e.node {
677 if let LitKind::Char(_) = l.node {
678 if ty::TyUint(UintTy::U8) == cx.tcx.expr_ty(expr).sty && !in_macro(cx, expr.span) {
679 let msg = "casting character literal to u8. `char`s \
680 are 4 bytes wide in rust, so casting to u8 \
682 let help = format!("Consider using a byte literal \
684 snippet(cx, e.span, "'x'"));
685 span_help_and_lint(cx, CHAR_LIT_AS_U8, expr.span, msg, &help);
693 /// **What it does:** Checks for comparisons where one side of the relation is
694 /// either the minimum or maximum value for its type and warns if it involves a
695 /// case that is always true or always false. Only integer and boolean types are
698 /// **Why is this bad?** An expression like `min <= x` may misleadingly imply
699 /// that is is possible for `x` to be less than the minimum. Expressions like
700 /// `max < x` are probably mistakes.
702 /// **Known problems:** None.
707 /// 100 > std::i32::MAX
710 pub ABSURD_EXTREME_COMPARISONS,
712 "a comparison with a maximum or minimum value that is always true or false"
715 pub struct AbsurdExtremeComparisons;
717 impl LintPass for AbsurdExtremeComparisons {
718 fn get_lints(&self) -> LintArray {
719 lint_array!(ABSURD_EXTREME_COMPARISONS)
728 struct ExtremeExpr<'a> {
733 enum AbsurdComparisonResult {
736 InequalityImpossible,
741 fn detect_absurd_comparison<'a>(cx: &LateContext, op: BinOp_, lhs: &'a Expr, rhs: &'a Expr)
742 -> Option<(ExtremeExpr<'a>, AbsurdComparisonResult)> {
743 use types::ExtremeType::*;
744 use types::AbsurdComparisonResult::*;
745 use utils::comparisons::*;
746 type Extr<'a> = ExtremeExpr<'a>;
748 let normalized = normalize_comparison(op, lhs, rhs);
749 let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
755 let lx = detect_extreme_expr(cx, normalized_lhs);
756 let rx = detect_extreme_expr(cx, normalized_rhs);
761 (Some(l @ Extr { which: Maximum, .. }), _) => (l, AlwaysFalse), // max < x
762 (_, Some(r @ Extr { which: Minimum, .. })) => (r, AlwaysFalse), // x < min
768 (Some(l @ Extr { which: Minimum, .. }), _) => (l, AlwaysTrue), // min <= x
769 (Some(l @ Extr { which: Maximum, .. }), _) => (l, InequalityImpossible), //max <= x
770 (_, Some(r @ Extr { which: Minimum, .. })) => (r, InequalityImpossible), // x <= min
771 (_, Some(r @ Extr { which: Maximum, .. })) => (r, AlwaysTrue), // x <= max
775 Rel::Ne | Rel::Eq => return None,
779 fn detect_extreme_expr<'a>(cx: &LateContext, expr: &'a Expr) -> Option<ExtremeExpr<'a>> {
780 use rustc::middle::const_val::ConstVal::*;
781 use rustc_const_math::*;
782 use rustc_const_eval::EvalHint::ExprTypeChecked;
783 use rustc_const_eval::*;
784 use types::ExtremeType::*;
786 let ty = &cx.tcx.expr_ty(expr).sty;
789 ty::TyBool | ty::TyInt(_) | ty::TyUint(_) => (),
793 let cv = match eval_const_expr_partial(cx.tcx, expr, ExprTypeChecked, None) {
795 Err(_) => return None,
798 let which = match (ty, cv) {
799 (&ty::TyBool, Bool(false)) |
800 (&ty::TyInt(IntTy::Is), Integral(Isize(Is32(::std::i32::MIN)))) |
801 (&ty::TyInt(IntTy::Is), Integral(Isize(Is64(::std::i64::MIN)))) |
802 (&ty::TyInt(IntTy::I8), Integral(I8(::std::i8::MIN))) |
803 (&ty::TyInt(IntTy::I16), Integral(I16(::std::i16::MIN))) |
804 (&ty::TyInt(IntTy::I32), Integral(I32(::std::i32::MIN))) |
805 (&ty::TyInt(IntTy::I64), Integral(I64(::std::i64::MIN))) |
806 (&ty::TyUint(UintTy::Us), Integral(Usize(Us32(::std::u32::MIN)))) |
807 (&ty::TyUint(UintTy::Us), Integral(Usize(Us64(::std::u64::MIN)))) |
808 (&ty::TyUint(UintTy::U8), Integral(U8(::std::u8::MIN))) |
809 (&ty::TyUint(UintTy::U16), Integral(U16(::std::u16::MIN))) |
810 (&ty::TyUint(UintTy::U32), Integral(U32(::std::u32::MIN))) |
811 (&ty::TyUint(UintTy::U64), Integral(U64(::std::u64::MIN))) => Minimum,
813 (&ty::TyBool, Bool(true)) |
814 (&ty::TyInt(IntTy::Is), Integral(Isize(Is32(::std::i32::MAX)))) |
815 (&ty::TyInt(IntTy::Is), Integral(Isize(Is64(::std::i64::MAX)))) |
816 (&ty::TyInt(IntTy::I8), Integral(I8(::std::i8::MAX))) |
817 (&ty::TyInt(IntTy::I16), Integral(I16(::std::i16::MAX))) |
818 (&ty::TyInt(IntTy::I32), Integral(I32(::std::i32::MAX))) |
819 (&ty::TyInt(IntTy::I64), Integral(I64(::std::i64::MAX))) |
820 (&ty::TyUint(UintTy::Us), Integral(Usize(Us32(::std::u32::MAX)))) |
821 (&ty::TyUint(UintTy::Us), Integral(Usize(Us64(::std::u64::MAX)))) |
822 (&ty::TyUint(UintTy::U8), Integral(U8(::std::u8::MAX))) |
823 (&ty::TyUint(UintTy::U16), Integral(U16(::std::u16::MAX))) |
824 (&ty::TyUint(UintTy::U32), Integral(U32(::std::u32::MAX))) |
825 (&ty::TyUint(UintTy::U64), Integral(U64(::std::u64::MAX))) => Maximum,
835 impl LateLintPass for AbsurdExtremeComparisons {
836 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
837 use types::ExtremeType::*;
838 use types::AbsurdComparisonResult::*;
840 if let ExprBinary(ref cmp, ref lhs, ref rhs) = expr.node {
841 if let Some((culprit, result)) = detect_absurd_comparison(cx, cmp.node, lhs, rhs) {
842 if !in_macro(cx, expr.span) {
843 let msg = "this comparison involving the minimum or maximum element for this \
844 type contains a case that is always true or always false";
846 let conclusion = match result {
847 AlwaysFalse => "this comparison is always false".to_owned(),
848 AlwaysTrue => "this comparison is always true".to_owned(),
849 InequalityImpossible => {
850 format!("the case where the two sides are not equal never occurs, consider using {} == {} \
852 snippet(cx, lhs.span, "lhs"),
853 snippet(cx, rhs.span, "rhs"))
857 let help = format!("because {} is the {} value for this type, {}",
858 snippet(cx, culprit.expr.span, "x"),
859 match culprit.which {
860 Minimum => "minimum",
861 Maximum => "maximum",
865 span_help_and_lint(cx, ABSURD_EXTREME_COMPARISONS, expr.span, msg, &help);
872 /// **What it does:** Checks for comparisons where the relation is always either
873 /// true or false, but where one side has been upcast so that the comparison is
874 /// necessary. Only integer types are checked.
876 /// **Why is this bad?** An expression like `let x : u8 = ...; (x as u32) > 300`
877 /// will mistakenly imply that it is possible for `x` to be outside the range of
880 /// **Known problems:** https://github.com/Manishearth/rust-clippy/issues/886
884 /// let x : u8 = ...; (x as u32) > 300
887 pub INVALID_UPCAST_COMPARISONS,
889 "a comparison involving an upcast which is always true or false"
892 pub struct InvalidUpcastComparisons;
894 impl LintPass for InvalidUpcastComparisons {
895 fn get_lints(&self) -> LintArray {
896 lint_array!(INVALID_UPCAST_COMPARISONS)
900 #[derive(Copy, Clone, Debug, Eq)]
907 #[allow(cast_sign_loss)]
908 fn cmp_s_u(s: i64, u: u64) -> Ordering {
911 } else if u > (i64::max_value() as u64) {
919 impl PartialEq for FullInt {
920 fn eq(&self, other: &Self) -> bool {
921 self.partial_cmp(other).expect("partial_cmp only returns Some(_)") == Ordering::Equal
925 impl PartialOrd for FullInt {
926 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
927 Some(match (self, other) {
928 (&FullInt::S(s), &FullInt::S(o)) => s.cmp(&o),
929 (&FullInt::U(s), &FullInt::U(o)) => s.cmp(&o),
930 (&FullInt::S(s), &FullInt::U(o)) => Self::cmp_s_u(s, o),
931 (&FullInt::U(s), &FullInt::S(o)) => Self::cmp_s_u(o, s).reverse(),
935 impl Ord for FullInt {
936 fn cmp(&self, other: &Self) -> Ordering {
937 self.partial_cmp(other).expect("partial_cmp for FullInt can never return None")
942 fn numeric_cast_precast_bounds<'a>(cx: &LateContext, expr: &'a Expr) -> Option<(FullInt, FullInt)> {
943 use rustc::ty::TypeVariants::{TyInt, TyUint};
944 use syntax::ast::{IntTy, UintTy};
947 if let ExprCast(ref cast_exp, _) = expr.node {
948 match cx.tcx.expr_ty(cast_exp).sty {
951 IntTy::I8 => (FullInt::S(i8::min_value() as i64), FullInt::S(i8::max_value() as i64)),
952 IntTy::I16 => (FullInt::S(i16::min_value() as i64), FullInt::S(i16::max_value() as i64)),
953 IntTy::I32 => (FullInt::S(i32::min_value() as i64), FullInt::S(i32::max_value() as i64)),
954 IntTy::I64 => (FullInt::S(i64::min_value() as i64), FullInt::S(i64::max_value() as i64)),
955 IntTy::Is => (FullInt::S(isize::min_value() as i64), FullInt::S(isize::max_value() as i64)),
960 UintTy::U8 => (FullInt::U(u8::min_value() as u64), FullInt::U(u8::max_value() as u64)),
961 UintTy::U16 => (FullInt::U(u16::min_value() as u64), FullInt::U(u16::max_value() as u64)),
962 UintTy::U32 => (FullInt::U(u32::min_value() as u64), FullInt::U(u32::max_value() as u64)),
963 UintTy::U64 => (FullInt::U(u64::min_value() as u64), FullInt::U(u64::max_value() as u64)),
964 UintTy::Us => (FullInt::U(usize::min_value() as u64), FullInt::U(usize::max_value() as u64)),
974 fn node_as_const_fullint(cx: &LateContext, expr: &Expr) -> Option<FullInt> {
975 use rustc::middle::const_val::ConstVal::*;
976 use rustc_const_eval::EvalHint::ExprTypeChecked;
977 use rustc_const_eval::eval_const_expr_partial;
978 use rustc_const_math::ConstInt;
980 match eval_const_expr_partial(cx.tcx, expr, ExprTypeChecked, None) {
982 if let Integral(const_int) = val {
983 Some(match const_int.erase_type() {
984 ConstInt::InferSigned(x) => FullInt::S(x as i64),
985 ConstInt::Infer(x) => FullInt::U(x as u64),
996 fn err_upcast_comparison(cx: &LateContext, span: &Span, expr: &Expr, always: bool) {
997 if let ExprCast(ref cast_val, _) = expr.node {
999 INVALID_UPCAST_COMPARISONS,
1002 "because of the numeric bounds on `{}` prior to casting, this expression is always {}",
1003 snippet(cx, cast_val.span, "the expression"),
1004 if always { "true" } else { "false" },
1009 fn upcast_comparison_bounds_err(cx: &LateContext, span: &Span, rel: comparisons::Rel,
1010 lhs_bounds: Option<(FullInt, FullInt)>, lhs: &Expr, rhs: &Expr, invert: bool) {
1011 use utils::comparisons::*;
1013 if let Some((lb, ub)) = lhs_bounds {
1014 if let Some(norm_rhs_val) = node_as_const_fullint(cx, rhs) {
1015 if rel == Rel::Eq || rel == Rel::Ne {
1016 if norm_rhs_val < lb || norm_rhs_val > ub {
1017 err_upcast_comparison(cx, span, lhs, rel == Rel::Ne);
1019 } else if match rel {
1034 Rel::Eq | Rel::Ne => unreachable!(),
1036 err_upcast_comparison(cx, span, lhs, true)
1037 } else if match rel {
1052 Rel::Eq | Rel::Ne => unreachable!(),
1054 err_upcast_comparison(cx, span, lhs, false)
1060 impl LateLintPass for InvalidUpcastComparisons {
1061 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
1062 if let ExprBinary(ref cmp, ref lhs, ref rhs) = expr.node {
1064 let normalized = comparisons::normalize_comparison(cmp.node, lhs, rhs);
1065 let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
1071 let lhs_bounds = numeric_cast_precast_bounds(cx, normalized_lhs);
1072 let rhs_bounds = numeric_cast_precast_bounds(cx, normalized_rhs);
1074 upcast_comparison_bounds_err(cx, &expr.span, rel, lhs_bounds, normalized_lhs, normalized_rhs, false);
1075 upcast_comparison_bounds_err(cx, &expr.span, rel, rhs_bounds, normalized_rhs, normalized_lhs, true);