1 #![allow(rustc::default_hash_types)]
4 use std::cmp::Ordering;
5 use std::collections::BTreeMap;
7 use if_chain::if_chain;
8 use rustc_ast::{FloatTy, IntTy, LitFloatType, LitIntType, LitKind, UintTy};
9 use rustc_errors::{Applicability, DiagnosticBuilder};
11 use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, FnKind, NestedVisitorMap, Visitor};
13 BinOpKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, FnSig, GenericArg, GenericParamKind, HirId, ImplItem,
14 ImplItemKind, Item, ItemKind, Lifetime, Local, MatchSource, MutTy, Mutability, QPath, Stmt, StmtKind, TraitFn,
15 TraitItem, TraitItemKind, TyKind, UnOp,
17 use rustc_lint::{LateContext, LateLintPass, LintContext};
18 use rustc_middle::hir::map::Map;
19 use rustc_middle::lint::in_external_macro;
20 use rustc_middle::ty::{self, InferTy, Ty, TyCtxt, TyS, TypeckResults};
21 use rustc_session::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
22 use rustc_span::hygiene::{ExpnKind, MacroKind};
23 use rustc_span::source_map::Span;
24 use rustc_span::symbol::sym;
25 use rustc_target::abi::LayoutOf;
26 use rustc_target::spec::abi::Abi;
27 use rustc_typeck::hir_ty_to_ty;
29 use crate::consts::{constant, Constant};
30 use crate::utils::paths;
32 clip, comparisons, differing_macro_contexts, higher, in_constant, indent_of, int_bits, is_type_diagnostic_item,
33 last_path_segment, match_def_path, match_path, method_chain_args, multispan_sugg, numeric_literal::NumericLiteral,
34 qpath_res, sext, snippet, snippet_block_with_applicability, snippet_opt, snippet_with_applicability,
35 snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then, unsext,
38 declare_clippy_lint! {
39 /// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
41 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
42 /// the heap. So if you `Box` it, you just add another level of indirection
43 /// without any benefit whatsoever.
45 /// **Known problems:** None.
50 /// values: Box<Vec<Foo>>,
63 "usage of `Box<Vec<T>>`, vector elements are already on the heap"
66 declare_clippy_lint! {
67 /// **What it does:** Checks for use of `Vec<Box<T>>` where T: Sized anywhere in the code.
69 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
70 /// the heap. So if you `Box` its contents, you just add another level of indirection.
72 /// **Known problems:** Vec<Box<T: Sized>> makes sense if T is a large type (see #3530,
78 /// values: Vec<Box<i32>>,
91 "usage of `Vec<Box<T>>` where T: Sized, vector elements are already on the heap"
94 declare_clippy_lint! {
95 /// **What it does:** Checks for use of `Option<Option<_>>` in function signatures and type
98 /// **Why is this bad?** `Option<_>` represents an optional value. `Option<Option<_>>`
99 /// represents an optional optional value which is logically the same thing as an optional
100 /// value but has an unneeded extra level of wrapping.
102 /// If you have a case where `Some(Some(_))`, `Some(None)` and `None` are distinct cases,
103 /// consider a custom `enum` instead, with clear names for each case.
105 /// **Known problems:** None.
109 /// fn get_data() -> Option<Option<u32>> {
117 /// pub enum Contents {
118 /// Data(Vec<u8>), // Was Some(Some(Vec<u8>))
119 /// NotYetFetched, // Was Some(None)
120 /// None, // Was None
123 /// fn get_data() -> Contents {
129 "usage of `Option<Option<T>>`"
132 declare_clippy_lint! {
133 /// **What it does:** Checks for usage of any `LinkedList`, suggesting to use a
134 /// `Vec` or a `VecDeque` (formerly called `RingBuf`).
136 /// **Why is this bad?** Gankro says:
138 /// > The TL;DR of `LinkedList` is that it's built on a massive amount of
139 /// pointers and indirection.
140 /// > It wastes memory, it has terrible cache locality, and is all-around slow.
142 /// > "only" amortized for push/pop, should be faster in the general case for
143 /// almost every possible
144 /// > workload, and isn't even amortized at all if you can predict the capacity
147 /// > `LinkedList`s are only really good if you're doing a lot of merging or
148 /// splitting of lists.
149 /// > This is because they can just mangle some pointers instead of actually
150 /// copying the data. Even
151 /// > if you're doing a lot of insertion in the middle of the list, `RingBuf`
152 /// can still be better
153 /// > because of how expensive it is to seek to the middle of a `LinkedList`.
155 /// **Known problems:** False positives – the instances where using a
156 /// `LinkedList` makes sense are few and far between, but they can still happen.
160 /// # use std::collections::LinkedList;
161 /// let x: LinkedList<usize> = LinkedList::new();
165 "usage of LinkedList, usually a vector is faster, or a more specialized data structure like a `VecDeque`"
168 declare_clippy_lint! {
169 /// **What it does:** Checks for use of `&Box<T>` anywhere in the code.
171 /// **Why is this bad?** Any `&Box<T>` can also be a `&T`, which is more
174 /// **Known problems:** None.
178 /// fn foo(bar: &Box<T>) { ... }
184 /// fn foo(bar: &T) { ... }
188 "a borrow of a boxed type"
191 declare_clippy_lint! {
192 /// **What it does:** Checks for use of redundant allocations anywhere in the code.
194 /// **Why is this bad?** Expressions such as `Rc<&T>`, `Rc<Rc<T>>`, `Rc<Box<T>>`, `Box<&T>`
195 /// add an unnecessary level of indirection.
197 /// **Known problems:** None.
201 /// # use std::rc::Rc;
202 /// fn foo(bar: Rc<&usize>) {}
208 /// fn foo(bar: &usize) {}
210 pub REDUNDANT_ALLOCATION,
212 "redundant allocation"
216 vec_box_size_threshold: u64,
219 impl_lint_pass!(Types => [BOX_VEC, VEC_BOX, OPTION_OPTION, LINKEDLIST, BORROWED_BOX, REDUNDANT_ALLOCATION]);
221 impl<'tcx> LateLintPass<'tcx> for Types {
222 fn check_fn(&mut self, cx: &LateContext<'_>, _: FnKind<'_>, decl: &FnDecl<'_>, _: &Body<'_>, _: Span, id: HirId) {
223 // Skip trait implementations; see issue #605.
224 if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(id)) {
225 if let ItemKind::Impl { of_trait: Some(_), .. } = item.kind {
230 self.check_fn_decl(cx, decl);
233 fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
234 self.check_ty(cx, &field.ty, false);
237 fn check_trait_item(&mut self, cx: &LateContext<'_>, item: &TraitItem<'_>) {
239 TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_ty(cx, ty, false),
240 TraitItemKind::Fn(ref sig, _) => self.check_fn_decl(cx, &sig.decl),
245 fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
246 if let Some(ref ty) = local.ty {
247 self.check_ty(cx, ty, true);
252 /// Checks if `qpath` has last segment with type parameter matching `path`
253 fn match_type_parameter(cx: &LateContext<'_>, qpath: &QPath<'_>, path: &[&str]) -> Option<Span> {
254 let last = last_path_segment(qpath);
256 if let Some(ref params) = last.args;
257 if !params.parenthesized;
258 if let Some(ty) = params.args.iter().find_map(|arg| match arg {
259 GenericArg::Type(ty) => Some(ty),
262 if let TyKind::Path(ref qpath) = ty.kind;
263 if let Some(did) = qpath_res(cx, qpath, ty.hir_id).opt_def_id();
264 if match_def_path(cx, did, path);
266 return Some(ty.span);
272 fn match_borrows_parameter(_cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<Span> {
273 let last = last_path_segment(qpath);
275 if let Some(ref params) = last.args;
276 if !params.parenthesized;
277 if let Some(ty) = params.args.iter().find_map(|arg| match arg {
278 GenericArg::Type(ty) => Some(ty),
281 if let TyKind::Rptr(..) = ty.kind;
283 return Some(ty.span);
290 pub fn new(vec_box_size_threshold: u64) -> Self {
291 Self { vec_box_size_threshold }
294 fn check_fn_decl(&mut self, cx: &LateContext<'_>, decl: &FnDecl<'_>) {
295 for input in decl.inputs {
296 self.check_ty(cx, input, false);
299 if let FnRetTy::Return(ref ty) = decl.output {
300 self.check_ty(cx, ty, false);
304 /// Recursively check for `TypePass` lints in the given type. Stop at the first
307 /// The parameter `is_local` distinguishes the context of the type; types from
308 /// local bindings should only be checked for the `BORROWED_BOX` lint.
309 #[allow(clippy::too_many_lines)]
310 fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, is_local: bool) {
311 if hir_ty.span.from_expansion() {
315 TyKind::Path(ref qpath) if !is_local => {
316 let hir_id = hir_ty.hir_id;
317 let res = qpath_res(cx, qpath, hir_id);
318 if let Some(def_id) = res.opt_def_id() {
319 if Some(def_id) == cx.tcx.lang_items().owned_box() {
320 if let Some(span) = match_borrows_parameter(cx, qpath) {
323 REDUNDANT_ALLOCATION,
325 "usage of `Box<&T>`",
327 snippet(cx, span, "..").to_string(),
328 Applicability::MachineApplicable,
330 return; // don't recurse into the type
332 if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
337 "you seem to be trying to use `Box<Vec<T>>`. Consider using just `Vec<T>`",
339 "`Vec<T>` is already on the heap, `Box<Vec<T>>` makes an extra allocation.",
341 return; // don't recurse into the type
343 } else if cx.tcx.is_diagnostic_item(sym::Rc, def_id) {
344 if let Some(span) = match_type_parameter(cx, qpath, &paths::RC) {
347 REDUNDANT_ALLOCATION,
349 "usage of `Rc<Rc<T>>`",
351 snippet(cx, span, "..").to_string(),
352 Applicability::MachineApplicable,
354 return; // don't recurse into the type
356 if let Some(span) = match_type_parameter(cx, qpath, &paths::BOX) {
359 REDUNDANT_ALLOCATION,
361 "usage of `Rc<Box<T>>`",
363 snippet(cx, span, "..").to_string(),
364 Applicability::MachineApplicable,
366 return; // don't recurse into the type
368 if let Some(span) = match_borrows_parameter(cx, qpath) {
371 REDUNDANT_ALLOCATION,
375 snippet(cx, span, "..").to_string(),
376 Applicability::MachineApplicable,
378 return; // don't recurse into the type
380 } else if cx.tcx.is_diagnostic_item(sym!(vec_type), def_id) {
382 // Get the _ part of Vec<_>
383 if let Some(ref last) = last_path_segment(qpath).args;
384 if let Some(ty) = last.args.iter().find_map(|arg| match arg {
385 GenericArg::Type(ty) => Some(ty),
388 // ty is now _ at this point
389 if let TyKind::Path(ref ty_qpath) = ty.kind;
390 let res = qpath_res(cx, ty_qpath, ty.hir_id);
391 if let Some(def_id) = res.opt_def_id();
392 if Some(def_id) == cx.tcx.lang_items().owned_box();
393 // At this point, we know ty is Box<T>, now get T
394 if let Some(ref last) = last_path_segment(ty_qpath).args;
395 if let Some(boxed_ty) = last.args.iter().find_map(|arg| match arg {
396 GenericArg::Type(ty) => Some(ty),
399 let ty_ty = hir_ty_to_ty(cx.tcx, boxed_ty);
400 if ty_ty.is_sized(cx.tcx.at(ty.span), cx.param_env);
401 if let Ok(ty_ty_size) = cx.layout_of(ty_ty).map(|l| l.size.bytes());
402 if ty_ty_size <= self.vec_box_size_threshold;
408 "`Vec<T>` is already on the heap, the boxing is unnecessary.",
410 format!("Vec<{}>", ty_ty),
411 Applicability::MachineApplicable,
413 return; // don't recurse into the type
416 } else if cx.tcx.is_diagnostic_item(sym!(option_type), def_id) {
417 if match_type_parameter(cx, qpath, &paths::OPTION).is_some() {
422 "consider using `Option<T>` instead of `Option<Option<T>>` or a custom \
423 enum if you need to distinguish all 3 cases",
425 return; // don't recurse into the type
427 } else if match_def_path(cx, def_id, &paths::LINKED_LIST) {
432 "I see you're using a LinkedList! Perhaps you meant some other data structure?",
434 "a `VecDeque` might work",
436 return; // don't recurse into the type
440 QPath::Resolved(Some(ref ty), ref p) => {
441 self.check_ty(cx, ty, is_local);
442 for ty in p.segments.iter().flat_map(|seg| {
445 .map_or_else(|| [].iter(), |params| params.args.iter())
446 .filter_map(|arg| match arg {
447 GenericArg::Type(ty) => Some(ty),
451 self.check_ty(cx, ty, is_local);
454 QPath::Resolved(None, ref p) => {
455 for ty in p.segments.iter().flat_map(|seg| {
458 .map_or_else(|| [].iter(), |params| params.args.iter())
459 .filter_map(|arg| match arg {
460 GenericArg::Type(ty) => Some(ty),
464 self.check_ty(cx, ty, is_local);
467 QPath::TypeRelative(ref ty, ref seg) => {
468 self.check_ty(cx, ty, is_local);
469 if let Some(ref params) = seg.args {
470 for ty in params.args.iter().filter_map(|arg| match arg {
471 GenericArg::Type(ty) => Some(ty),
474 self.check_ty(cx, ty, is_local);
478 QPath::LangItem(..) => {},
481 TyKind::Rptr(ref lt, ref mut_ty) => self.check_ty_rptr(cx, hir_ty, is_local, lt, mut_ty),
483 TyKind::Slice(ref ty) | TyKind::Array(ref ty, _) | TyKind::Ptr(MutTy { ref ty, .. }) => {
484 self.check_ty(cx, ty, is_local)
486 TyKind::Tup(tys) => {
488 self.check_ty(cx, ty, is_local);
497 cx: &LateContext<'_>,
498 hir_ty: &hir::Ty<'_>,
503 match mut_ty.ty.kind {
504 TyKind::Path(ref qpath) => {
505 let hir_id = mut_ty.ty.hir_id;
506 let def = qpath_res(cx, qpath, hir_id);
508 if let Some(def_id) = def.opt_def_id();
509 if Some(def_id) == cx.tcx.lang_items().owned_box();
510 if let QPath::Resolved(None, ref path) = *qpath;
511 if let [ref bx] = *path.segments;
512 if let Some(ref params) = bx.args;
513 if !params.parenthesized;
514 if let Some(inner) = params.args.iter().find_map(|arg| match arg {
515 GenericArg::Type(ty) => Some(ty),
519 if is_any_trait(inner) {
520 // Ignore `Box<Any>` types; see issue #1884 for details.
524 let ltopt = if lt.is_elided() {
527 format!("{} ", lt.name.ident().as_str())
530 if mut_ty.mutbl == Mutability::Mut {
531 // Ignore `&mut Box<T>` types; see issue #2907 for
535 let mut applicability = Applicability::MachineApplicable;
540 "you seem to be trying to use `&Box<T>`. Consider using just `&T`",
545 &snippet_with_applicability(cx, inner.span, "..", &mut applicability)
547 Applicability::Unspecified,
549 return; // don't recurse into the type
552 self.check_ty(cx, &mut_ty.ty, is_local);
554 _ => self.check_ty(cx, &mut_ty.ty, is_local),
559 // Returns true if given type is `Any` trait.
560 fn is_any_trait(t: &hir::Ty<'_>) -> bool {
562 if let TyKind::TraitObject(ref traits, _) = t.kind;
563 if !traits.is_empty();
564 // Only Send/Sync can be used as additional traits, so it is enough to
565 // check only the first trait.
566 if match_path(&traits[0].trait_ref.path, &paths::ANY_TRAIT);
575 declare_clippy_lint! {
576 /// **What it does:** Checks for binding a unit value.
578 /// **Why is this bad?** A unit value cannot usefully be used anywhere. So
579 /// binding one is kind of pointless.
581 /// **Known problems:** None.
591 "creating a `let` binding to a value of unit type, which usually can't be used afterwards"
594 declare_lint_pass!(LetUnitValue => [LET_UNIT_VALUE]);
596 impl<'tcx> LateLintPass<'tcx> for LetUnitValue {
597 fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
598 if let StmtKind::Local(ref local) = stmt.kind {
599 if is_unit(cx.typeck_results().pat_ty(&local.pat)) {
600 if in_external_macro(cx.sess(), stmt.span) || local.pat.span.from_expansion() {
603 if higher::is_from_for_desugar(local) {
610 "this let-binding has unit value",
612 if let Some(expr) = &local.init {
613 let snip = snippet_with_macro_callsite(cx, expr.span, "()");
614 diag.span_suggestion(
616 "omit the `let` binding",
617 format!("{};", snip),
618 Applicability::MachineApplicable, // snippet
628 declare_clippy_lint! {
629 /// **What it does:** Checks for comparisons to unit. This includes all binary
630 /// comparisons (like `==` and `<`) and asserts.
632 /// **Why is this bad?** Unit is always equal to itself, and thus is just a
633 /// clumsily written constant. Mostly this happens when someone accidentally
634 /// adds semicolons at the end of the operands.
636 /// **Known problems:** None.
667 /// assert_eq!({ foo(); }, { bar(); });
669 /// will always succeed
672 "comparing unit values"
675 declare_lint_pass!(UnitCmp => [UNIT_CMP]);
677 impl<'tcx> LateLintPass<'tcx> for UnitCmp {
678 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
679 if expr.span.from_expansion() {
680 if let Some(callee) = expr.span.source_callee() {
681 if let ExpnKind::Macro(MacroKind::Bang, symbol) = callee.kind {
682 if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
684 if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
685 let result = match &*symbol.as_str() {
686 "assert_eq" | "debug_assert_eq" => "succeed",
687 "assert_ne" | "debug_assert_ne" => "fail",
695 "`{}` of unit values detected. This will always {}",
706 if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
708 if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
709 let result = match op {
710 BinOpKind::Eq | BinOpKind::Le | BinOpKind::Ge => "true",
718 "{}-comparison of unit values detected. This will always be {}",
728 declare_clippy_lint! {
729 /// **What it does:** Checks for passing a unit value as an argument to a function without using a
730 /// unit literal (`()`).
732 /// **Why is this bad?** This is likely the result of an accidental semicolon.
734 /// **Known problems:** None.
745 "passing unit to a function"
748 declare_lint_pass!(UnitArg => [UNIT_ARG]);
750 impl<'tcx> LateLintPass<'tcx> for UnitArg {
751 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
752 if expr.span.from_expansion() {
756 // apparently stuff in the desugaring of `?` can trigger this
757 // so check for that here
758 // only the calls to `Try::from_error` is marked as desugared,
759 // so we need to check both the current Expr and its parent.
760 if is_questionmark_desugar_marked_call(expr) {
764 let map = &cx.tcx.hir();
765 let opt_parent_node = map.find(map.get_parent_node(expr.hir_id));
766 if let Some(hir::Node::Expr(parent_expr)) = opt_parent_node;
767 if is_questionmark_desugar_marked_call(parent_expr);
774 ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args, _) => {
775 let args_to_recover = args
778 if is_unit(cx.typeck_results().expr_ty(arg)) && !is_unit_literal(arg) {
779 !matches!(&arg.kind, ExprKind::Match(.., MatchSource::TryDesugar))
784 .collect::<Vec<_>>();
785 if !args_to_recover.is_empty() {
786 lint_unit_args(cx, expr, &args_to_recover);
794 fn lint_unit_args(cx: &LateContext<'_>, expr: &Expr<'_>, args_to_recover: &[&Expr<'_>]) {
795 let mut applicability = Applicability::MachineApplicable;
796 let (singular, plural) = if args_to_recover.len() > 1 {
805 &format!("passing {}unit value{} to a function", singular, plural),
812 if let ExprKind::Block(block, _) = arg.kind;
813 if block.expr.is_none();
814 if let Some(last_stmt) = block.stmts.iter().last();
815 if let StmtKind::Semi(last_expr) = last_stmt.kind;
816 if let Some(snip) = snippet_opt(cx, last_expr.span);
828 .for_each(|(span, sugg)| {
831 "remove the semicolon from the last statement in the block",
833 Applicability::MaybeIncorrect,
837 let sugg = args_to_recover
839 .filter(|arg| !is_empty_block(arg))
842 let indent = if i == 0 {
845 indent_of(cx, expr.span).unwrap_or(0)
850 snippet_block_with_applicability(cx, arg.span, "..", Some(expr.span), &mut applicability)
853 .collect::<Vec<String>>();
855 if !sugg.is_empty() {
856 let plural = if sugg.len() > 1 { "s" } else { "" };
858 expr.span.with_hi(expr.span.lo()),
859 &format!("{}move the expression{} in front of the call...", or, plural),
860 format!("{}\n", sugg.join("\n")),
865 db.multipart_suggestion(
866 &format!("{}use {}unit literal{} instead", and, singular, plural),
869 .map(|arg| (arg.span, "()".to_string()))
870 .collect::<Vec<_>>(),
877 fn is_empty_block(expr: &Expr<'_>) -> bool {
882 stmts: &[], expr: None, ..
889 fn is_questionmark_desugar_marked_call(expr: &Expr<'_>) -> bool {
890 use rustc_span::hygiene::DesugaringKind;
891 if let ExprKind::Call(ref callee, _) = expr.kind {
892 callee.span.is_desugaring(DesugaringKind::QuestionMark)
898 fn is_unit(ty: Ty<'_>) -> bool {
899 matches!(ty.kind, ty::Tuple(slice) if slice.is_empty())
902 fn is_unit_literal(expr: &Expr<'_>) -> bool {
903 matches!(expr.kind, ExprKind::Tup(ref slice) if slice.is_empty())
906 declare_clippy_lint! {
907 /// **What it does:** Checks for casts from any numerical to a float type where
908 /// the receiving type cannot store all values from the original type without
909 /// rounding errors. This possible rounding is to be expected, so this lint is
910 /// `Allow` by default.
912 /// Basically, this warns on casting any integer with 32 or more bits to `f32`
913 /// or any 64-bit integer to `f64`.
915 /// **Why is this bad?** It's not bad at all. But in some applications it can be
916 /// helpful to know where precision loss can take place. This lint can help find
917 /// those places in the code.
919 /// **Known problems:** None.
923 /// let x = u64::MAX;
926 pub CAST_PRECISION_LOSS,
928 "casts that cause loss of precision, e.g., `x as f32` where `x: u64`"
931 declare_clippy_lint! {
932 /// **What it does:** Checks for casts from a signed to an unsigned numerical
933 /// type. In this case, negative values wrap around to large positive values,
934 /// which can be quite surprising in practice. However, as the cast works as
935 /// defined, this lint is `Allow` by default.
937 /// **Why is this bad?** Possibly surprising results. You can activate this lint
938 /// as a one-time check to see where numerical wrapping can arise.
940 /// **Known problems:** None.
945 /// y as u128; // will return 18446744073709551615
949 "casts from signed types to unsigned types, e.g., `x as u32` where `x: i32`"
952 declare_clippy_lint! {
953 /// **What it does:** Checks for casts between numerical types that may
954 /// truncate large values. This is expected behavior, so the cast is `Allow` by
957 /// **Why is this bad?** In some problem domains, it is good practice to avoid
958 /// truncation. This lint can be activated to help assess where additional
959 /// checks could be beneficial.
961 /// **Known problems:** None.
965 /// fn as_u8(x: u64) -> u8 {
969 pub CAST_POSSIBLE_TRUNCATION,
971 "casts that may cause truncation of the value, e.g., `x as u8` where `x: u32`, or `x as i32` where `x: f32`"
974 declare_clippy_lint! {
975 /// **What it does:** Checks for casts from an unsigned type to a signed type of
976 /// the same size. Performing such a cast is a 'no-op' for the compiler,
977 /// i.e., nothing is changed at the bit level, and the binary representation of
978 /// the value is reinterpreted. This can cause wrapping if the value is too big
979 /// for the target signed type. However, the cast works as defined, so this lint
980 /// is `Allow` by default.
982 /// **Why is this bad?** While such a cast is not bad in itself, the results can
983 /// be surprising when this is not the intended behavior, as demonstrated by the
986 /// **Known problems:** None.
990 /// u32::MAX as i32; // will yield a value of `-1`
992 pub CAST_POSSIBLE_WRAP,
994 "casts that may cause wrapping around the value, e.g., `x as i32` where `x: u32` and `x > i32::MAX`"
997 declare_clippy_lint! {
998 /// **What it does:** Checks for casts between numerical types that may
999 /// be replaced by safe conversion functions.
1001 /// **Why is this bad?** Rust's `as` keyword will perform many kinds of
1002 /// conversions, including silently lossy conversions. Conversion functions such
1003 /// as `i32::from` will only perform lossless conversions. Using the conversion
1004 /// functions prevents conversions from turning into silent lossy conversions if
1005 /// the types of the input expressions ever change, and make it easier for
1006 /// people reading the code to know that the conversion is lossless.
1008 /// **Known problems:** None.
1012 /// fn as_u64(x: u8) -> u64 {
1017 /// Using `::from` would look like this:
1020 /// fn as_u64(x: u8) -> u64 {
1026 "casts using `as` that are known to be lossless, e.g., `x as u64` where `x: u8`"
1029 declare_clippy_lint! {
1030 /// **What it does:** Checks for casts to the same type.
1032 /// **Why is this bad?** It's just unnecessary.
1034 /// **Known problems:** None.
1038 /// let _ = 2i32 as i32;
1040 pub UNNECESSARY_CAST,
1042 "cast to the same type, e.g., `x as i32` where `x: i32`"
1045 declare_clippy_lint! {
1046 /// **What it does:** Checks for casts from a less-strictly-aligned pointer to a
1047 /// more-strictly-aligned pointer
1049 /// **Why is this bad?** Dereferencing the resulting pointer may be undefined
1052 /// **Known problems:** Using `std::ptr::read_unaligned` and `std::ptr::write_unaligned` or similar
1053 /// on the resulting pointer is fine. Is over-zealous: Casts with manual alignment checks or casts like
1054 /// u64-> u8 -> u16 can be fine. Miri is able to do a more in-depth analysis.
1058 /// let _ = (&1u8 as *const u8) as *const u16;
1059 /// let _ = (&mut 1u8 as *mut u8) as *mut u16;
1061 pub CAST_PTR_ALIGNMENT,
1063 "cast from a pointer to a more-strictly-aligned pointer"
1066 declare_clippy_lint! {
1067 /// **What it does:** Checks for casts of function pointers to something other than usize
1069 /// **Why is this bad?**
1070 /// Casting a function pointer to anything other than usize/isize is not portable across
1071 /// architectures, because you end up losing bits if the target type is too small or end up with a
1072 /// bunch of extra bits that waste space and add more instructions to the final binary than
1073 /// strictly necessary for the problem
1075 /// Casting to isize also doesn't make sense since there are no signed addresses.
1081 /// fn fun() -> i32 { 1 }
1082 /// let a = fun as i64;
1085 /// fn fun2() -> i32 { 1 }
1086 /// let a = fun2 as usize;
1088 pub FN_TO_NUMERIC_CAST,
1090 "casting a function pointer to a numeric type other than usize"
1093 declare_clippy_lint! {
1094 /// **What it does:** Checks for casts of a function pointer to a numeric type not wide enough to
1097 /// **Why is this bad?**
1098 /// Such a cast discards some bits of the function's address. If this is intended, it would be more
1099 /// clearly expressed by casting to usize first, then casting the usize to the intended type (with
1100 /// a comment) to perform the truncation.
1106 /// fn fn1() -> i16 {
1109 /// let _ = fn1 as i32;
1111 /// // Better: Cast to usize first, then comment with the reason for the truncation
1112 /// fn fn2() -> i16 {
1115 /// let fn_ptr = fn2 as usize;
1116 /// let fn_ptr_truncated = fn_ptr as i32;
1118 pub FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1120 "casting a function pointer to a numeric type not wide enough to store the address"
1123 /// Returns the size in bits of an integral type.
1124 /// Will return 0 if the type is not an int or uint variant
1125 fn int_ty_to_nbits(typ: Ty<'_>, tcx: TyCtxt<'_>) -> u64 {
1127 ty::Int(i) => match i {
1128 IntTy::Isize => tcx.data_layout.pointer_size.bits(),
1135 ty::Uint(i) => match i {
1136 UintTy::Usize => tcx.data_layout.pointer_size.bits(),
1141 UintTy::U128 => 128,
1147 fn is_isize_or_usize(typ: Ty<'_>) -> bool {
1148 matches!(typ.kind, ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
1151 fn span_precision_loss_lint(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to_f64: bool) {
1152 let mantissa_nbits = if cast_to_f64 { 52 } else { 23 };
1153 let arch_dependent = is_isize_or_usize(cast_from) && cast_to_f64;
1154 let arch_dependent_str = "on targets with 64-bit wide pointers ";
1155 let from_nbits_str = if arch_dependent {
1157 } else if is_isize_or_usize(cast_from) {
1158 "32 or 64".to_owned()
1160 int_ty_to_nbits(cast_from, cx.tcx).to_string()
1164 CAST_PRECISION_LOSS,
1167 "casting `{0}` to `{1}` causes a loss of precision {2}(`{0}` is {3} bits wide, \
1168 but `{1}`'s mantissa is only {4} bits wide)",
1170 if cast_to_f64 { "f64" } else { "f32" },
1171 if arch_dependent { arch_dependent_str } else { "" },
1178 fn should_strip_parens(op: &Expr<'_>, snip: &str) -> bool {
1179 if let ExprKind::Binary(_, _, _) = op.kind {
1180 if snip.starts_with('(') && snip.ends_with(')') {
1187 fn span_lossless_lint(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1188 // Do not suggest using From in consts/statics until it is valid to do so (see #2267).
1189 if in_constant(cx, expr.hir_id) {
1192 // The suggestion is to use a function call, so if the original expression
1193 // has parens on the outside, they are no longer needed.
1194 let mut applicability = Applicability::MachineApplicable;
1195 let opt = snippet_opt(cx, op.span);
1196 let sugg = opt.as_ref().map_or_else(
1198 applicability = Applicability::HasPlaceholders;
1202 if should_strip_parens(op, snip) {
1203 &snip[1..snip.len() - 1]
1215 "casting `{}` to `{}` may become silently lossy if you later change the type",
1219 format!("{}::from({})", cast_to, sugg),
1230 fn check_loss_of_sign(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1231 if !cast_from.is_signed() || cast_to.is_signed() {
1235 // don't lint for positive constants
1236 let const_val = constant(cx, &cx.typeck_results(), op);
1238 if let Some((const_val, _)) = const_val;
1239 if let Constant::Int(n) = const_val;
1240 if let ty::Int(ity) = cast_from.kind;
1241 if sext(cx.tcx, n, ity) >= 0;
1247 // don't lint for the result of methods that always return non-negative values
1248 if let ExprKind::MethodCall(ref path, _, _, _) = op.kind {
1249 let mut method_name = path.ident.name.as_str();
1250 let allowed_methods = ["abs", "checked_abs", "rem_euclid", "checked_rem_euclid"];
1253 if method_name == "unwrap";
1254 if let Some(arglist) = method_chain_args(op, &["unwrap"]);
1255 if let ExprKind::MethodCall(ref inner_path, _, _, _) = &arglist[0][0].kind;
1257 method_name = inner_path.ident.name.as_str();
1261 if allowed_methods.iter().any(|&name| method_name == name) {
1271 "casting `{}` to `{}` may lose the sign of the value",
1277 fn check_truncation_and_wrapping(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1278 let arch_64_suffix = " on targets with 64-bit wide pointers";
1279 let arch_32_suffix = " on targets with 32-bit wide pointers";
1280 let cast_unsigned_to_signed = !cast_from.is_signed() && cast_to.is_signed();
1281 let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1282 let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1283 let (span_truncation, suffix_truncation, span_wrap, suffix_wrap) =
1284 match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
1285 (true, true) | (false, false) => (
1286 to_nbits < from_nbits,
1288 to_nbits == from_nbits && cast_unsigned_to_signed,
1298 to_nbits <= 32 && cast_unsigned_to_signed,
1304 cast_unsigned_to_signed,
1305 if from_nbits == 64 {
1312 if span_truncation {
1315 CAST_POSSIBLE_TRUNCATION,
1318 "casting `{}` to `{}` may truncate the value{}",
1321 match suffix_truncation {
1322 ArchSuffix::_32 => arch_32_suffix,
1323 ArchSuffix::_64 => arch_64_suffix,
1324 ArchSuffix::None => "",
1335 "casting `{}` to `{}` may wrap around the value{}",
1339 ArchSuffix::_32 => arch_32_suffix,
1340 ArchSuffix::_64 => arch_64_suffix,
1341 ArchSuffix::None => "",
1348 fn check_lossless(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1349 let cast_signed_to_unsigned = cast_from.is_signed() && !cast_to.is_signed();
1350 let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1351 let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1352 if !is_isize_or_usize(cast_from) && !is_isize_or_usize(cast_to) && from_nbits < to_nbits && !cast_signed_to_unsigned
1354 span_lossless_lint(cx, expr, op, cast_from, cast_to);
1358 declare_lint_pass!(Casts => [
1359 CAST_PRECISION_LOSS,
1361 CAST_POSSIBLE_TRUNCATION,
1367 FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1370 // Check if the given type is either `core::ffi::c_void` or
1371 // one of the platform specific `libc::<platform>::c_void` of libc.
1372 fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
1373 if let ty::Adt(adt, _) = ty.kind {
1374 let names = cx.get_def_path(adt.did);
1376 if names.is_empty() {
1379 if names[0] == sym!(libc) || names[0] == sym::core && *names.last().unwrap() == sym!(c_void) {
1386 /// Returns the mantissa bits wide of a fp type.
1387 /// Will return 0 if the type is not a fp
1388 fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
1390 ty::Float(FloatTy::F32) => 23,
1391 ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
1396 impl<'tcx> LateLintPass<'tcx> for Casts {
1397 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1398 if expr.span.from_expansion() {
1401 if let ExprKind::Cast(ref ex, _) = expr.kind {
1402 let (cast_from, cast_to) = (cx.typeck_results().expr_ty(ex), cx.typeck_results().expr_ty(expr));
1403 lint_fn_to_numeric_cast(cx, expr, ex, cast_from, cast_to);
1404 if let ExprKind::Lit(ref lit) = ex.kind {
1406 if let LitKind::Int(n, _) = lit.node;
1407 if let Some(src) = snippet_opt(cx, lit.span);
1408 if cast_to.is_floating_point();
1409 if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node);
1410 let from_nbits = 128 - n.leading_zeros();
1411 let to_nbits = fp_ty_mantissa_nbits(cast_to);
1412 if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
1418 &format!("casting integer literal to `{}` is unnecessary", cast_to),
1420 format!("{}_{}", n, cast_to),
1421 Applicability::MachineApplicable,
1427 LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
1429 if cast_from.kind == cast_to.kind && !in_external_macro(cx.sess(), expr.span) {
1435 "casting to the same type is unnecessary (`{}` -> `{}`)",
1443 if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx.sess(), expr.span) {
1444 lint_numeric_casts(cx, expr, ex, cast_from, cast_to);
1447 lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
1452 fn lint_numeric_casts<'tcx>(
1453 cx: &LateContext<'tcx>,
1455 cast_expr: &Expr<'_>,
1456 cast_from: Ty<'tcx>,
1459 match (cast_from.is_integral(), cast_to.is_integral()) {
1461 let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1462 let to_nbits = if let ty::Float(FloatTy::F32) = cast_to.kind {
1467 if is_isize_or_usize(cast_from) || from_nbits >= to_nbits {
1468 span_precision_loss_lint(cx, expr, cast_from, to_nbits == 64);
1470 if from_nbits < to_nbits {
1471 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1477 CAST_POSSIBLE_TRUNCATION,
1479 &format!("casting `{}` to `{}` may truncate the value", cast_from, cast_to),
1481 if !cast_to.is_signed() {
1487 "casting `{}` to `{}` may lose the sign of the value",
1494 check_loss_of_sign(cx, expr, cast_expr, cast_from, cast_to);
1495 check_truncation_and_wrapping(cx, expr, cast_from, cast_to);
1496 check_lossless(cx, expr, cast_expr, cast_from, cast_to);
1499 if let (&ty::Float(FloatTy::F64), &ty::Float(FloatTy::F32)) = (&cast_from.kind, &cast_to.kind) {
1502 CAST_POSSIBLE_TRUNCATION,
1504 "casting `f64` to `f32` may truncate the value",
1507 if let (&ty::Float(FloatTy::F32), &ty::Float(FloatTy::F64)) = (&cast_from.kind, &cast_to.kind) {
1508 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1514 fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
1516 if let ty::RawPtr(from_ptr_ty) = &cast_from.kind;
1517 if let ty::RawPtr(to_ptr_ty) = &cast_to.kind;
1518 if let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty);
1519 if let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty);
1520 if from_layout.align.abi < to_layout.align.abi;
1521 // with c_void, we inherently need to trust the user
1522 if !is_c_void(cx, from_ptr_ty.ty);
1523 // when casting from a ZST, we don't know enough to properly lint
1524 if !from_layout.is_zst();
1531 "casting from `{}` to a more-strictly-aligned pointer (`{}`) ({} < {} bytes)",
1534 from_layout.align.abi.bytes(),
1535 to_layout.align.abi.bytes(),
1542 fn lint_fn_to_numeric_cast(
1543 cx: &LateContext<'_>,
1545 cast_expr: &Expr<'_>,
1549 // We only want to check casts to `ty::Uint` or `ty::Int`
1550 match cast_to.kind {
1551 ty::Uint(_) | ty::Int(..) => { /* continue on */ },
1554 match cast_from.kind {
1555 ty::FnDef(..) | ty::FnPtr(_) => {
1556 let mut applicability = Applicability::MaybeIncorrect;
1557 let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
1559 let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1560 if to_nbits < cx.tcx.data_layout.pointer_size.bits() {
1563 FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1566 "casting function pointer `{}` to `{}`, which truncates the value",
1567 from_snippet, cast_to
1570 format!("{} as usize", from_snippet),
1573 } else if cast_to.kind != ty::Uint(UintTy::Usize) {
1578 &format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
1580 format!("{} as usize", from_snippet),
1589 declare_clippy_lint! {
1590 /// **What it does:** Checks for types used in structs, parameters and `let`
1591 /// declarations above a certain complexity threshold.
1593 /// **Why is this bad?** Too complex types make the code less readable. Consider
1594 /// using a `type` definition to simplify them.
1596 /// **Known problems:** None.
1600 /// # use std::rc::Rc;
1602 /// inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>>,
1605 pub TYPE_COMPLEXITY,
1607 "usage of very complex types that might be better factored into `type` definitions"
1610 pub struct TypeComplexity {
1614 impl TypeComplexity {
1616 pub fn new(threshold: u64) -> Self {
1621 impl_lint_pass!(TypeComplexity => [TYPE_COMPLEXITY]);
1623 impl<'tcx> LateLintPass<'tcx> for TypeComplexity {
1626 cx: &LateContext<'tcx>,
1628 decl: &'tcx FnDecl<'_>,
1633 self.check_fndecl(cx, decl);
1636 fn check_struct_field(&mut self, cx: &LateContext<'tcx>, field: &'tcx hir::StructField<'_>) {
1637 // enum variants are also struct fields now
1638 self.check_type(cx, &field.ty);
1641 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
1643 ItemKind::Static(ref ty, _, _) | ItemKind::Const(ref ty, _) => self.check_type(cx, ty),
1644 // functions, enums, structs, impls and traits are covered
1649 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
1651 TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_type(cx, ty),
1652 TraitItemKind::Fn(FnSig { ref decl, .. }, TraitFn::Required(_)) => self.check_fndecl(cx, decl),
1653 // methods with default impl are covered by check_fn
1658 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
1660 ImplItemKind::Const(ref ty, _) | ImplItemKind::TyAlias(ref ty) => self.check_type(cx, ty),
1661 // methods are covered by check_fn
1666 fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'_>) {
1667 if let Some(ref ty) = local.ty {
1668 self.check_type(cx, ty);
1673 impl<'tcx> TypeComplexity {
1674 fn check_fndecl(&self, cx: &LateContext<'tcx>, decl: &'tcx FnDecl<'_>) {
1675 for arg in decl.inputs {
1676 self.check_type(cx, arg);
1678 if let FnRetTy::Return(ref ty) = decl.output {
1679 self.check_type(cx, ty);
1683 fn check_type(&self, cx: &LateContext<'_>, ty: &hir::Ty<'_>) {
1684 if ty.span.from_expansion() {
1688 let mut visitor = TypeComplexityVisitor { score: 0, nest: 1 };
1689 visitor.visit_ty(ty);
1693 if score > self.threshold {
1698 "very complex type used. Consider factoring parts into `type` definitions",
1704 /// Walks a type and assigns a complexity score to it.
1705 struct TypeComplexityVisitor {
1706 /// total complexity score of the type
1708 /// current nesting level
1712 impl<'tcx> Visitor<'tcx> for TypeComplexityVisitor {
1713 type Map = Map<'tcx>;
1715 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
1716 let (add_score, sub_nest) = match ty.kind {
1717 // _, &x and *x have only small overhead; don't mess with nesting level
1718 TyKind::Infer | TyKind::Ptr(..) | TyKind::Rptr(..) => (1, 0),
1720 // the "normal" components of a type: named types, arrays/tuples
1721 TyKind::Path(..) | TyKind::Slice(..) | TyKind::Tup(..) | TyKind::Array(..) => (10 * self.nest, 1),
1723 // function types bring a lot of overhead
1724 TyKind::BareFn(ref bare) if bare.abi == Abi::Rust => (50 * self.nest, 1),
1726 TyKind::TraitObject(ref param_bounds, _) => {
1727 let has_lifetime_parameters = param_bounds.iter().any(|bound| {
1729 .bound_generic_params
1731 .any(|gen| matches!(gen.kind, GenericParamKind::Lifetime { .. }))
1733 if has_lifetime_parameters {
1734 // complex trait bounds like A<'a, 'b>
1737 // simple trait bounds like A + B
1744 self.score += add_score;
1745 self.nest += sub_nest;
1747 self.nest -= sub_nest;
1749 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1750 NestedVisitorMap::None
1754 declare_clippy_lint! {
1755 /// **What it does:** Checks for expressions where a character literal is cast
1756 /// to `u8` and suggests using a byte literal instead.
1758 /// **Why is this bad?** In general, casting values to smaller types is
1759 /// error-prone and should be avoided where possible. In the particular case of
1760 /// converting a character literal to u8, it is easy to avoid by just using a
1761 /// byte literal instead. As an added bonus, `b'a'` is even slightly shorter
1762 /// than `'a' as u8`.
1764 /// **Known problems:** None.
1771 /// A better version, using the byte literal:
1778 "casting a character literal to `u8` truncates"
1781 declare_lint_pass!(CharLitAsU8 => [CHAR_LIT_AS_U8]);
1783 impl<'tcx> LateLintPass<'tcx> for CharLitAsU8 {
1784 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1786 if !expr.span.from_expansion();
1787 if let ExprKind::Cast(e, _) = &expr.kind;
1788 if let ExprKind::Lit(l) = &e.kind;
1789 if let LitKind::Char(c) = l.node;
1790 if ty::Uint(UintTy::U8) == cx.typeck_results().expr_ty(expr).kind;
1792 let mut applicability = Applicability::MachineApplicable;
1793 let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
1799 "casting a character literal to `u8` truncates",
1801 diag.note("`char` is four bytes wide, but `u8` is a single byte");
1804 diag.span_suggestion(
1806 "use a byte literal instead",
1807 format!("b{}", snippet),
1817 declare_clippy_lint! {
1818 /// **What it does:** Checks for comparisons where one side of the relation is
1819 /// either the minimum or maximum value for its type and warns if it involves a
1820 /// case that is always true or always false. Only integer and boolean types are
1823 /// **Why is this bad?** An expression like `min <= x` may misleadingly imply
1824 /// that it is possible for `x` to be less than the minimum. Expressions like
1825 /// `max < x` are probably mistakes.
1827 /// **Known problems:** For `usize` the size of the current compile target will
1828 /// be assumed (e.g., 64 bits on 64 bit systems). This means code that uses such
1829 /// a comparison to detect target pointer width will trigger this lint. One can
1830 /// use `mem::sizeof` and compare its value or conditional compilation
1832 /// like `#[cfg(target_pointer_width = "64")] ..` instead.
1837 /// let vec: Vec<isize> = Vec::new();
1838 /// if vec.len() <= 0 {}
1839 /// if 100 > i32::MAX {}
1841 pub ABSURD_EXTREME_COMPARISONS,
1843 "a comparison with a maximum or minimum value that is always true or false"
1846 declare_lint_pass!(AbsurdExtremeComparisons => [ABSURD_EXTREME_COMPARISONS]);
1853 struct ExtremeExpr<'a> {
1858 enum AbsurdComparisonResult {
1861 InequalityImpossible,
1864 fn is_cast_between_fixed_and_target<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
1865 if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
1866 let precast_ty = cx.typeck_results().expr_ty(cast_exp);
1867 let cast_ty = cx.typeck_results().expr_ty(expr);
1869 return is_isize_or_usize(precast_ty) != is_isize_or_usize(cast_ty);
1875 fn detect_absurd_comparison<'tcx>(
1876 cx: &LateContext<'tcx>,
1878 lhs: &'tcx Expr<'_>,
1879 rhs: &'tcx Expr<'_>,
1880 ) -> Option<(ExtremeExpr<'tcx>, AbsurdComparisonResult)> {
1881 use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
1882 use crate::types::ExtremeType::{Maximum, Minimum};
1883 use crate::utils::comparisons::{normalize_comparison, Rel};
1885 // absurd comparison only makes sense on primitive types
1886 // primitive types don't implement comparison operators with each other
1887 if cx.typeck_results().expr_ty(lhs) != cx.typeck_results().expr_ty(rhs) {
1891 // comparisons between fix sized types and target sized types are considered unanalyzable
1892 if is_cast_between_fixed_and_target(cx, lhs) || is_cast_between_fixed_and_target(cx, rhs) {
1896 let (rel, normalized_lhs, normalized_rhs) = normalize_comparison(op, lhs, rhs)?;
1898 let lx = detect_extreme_expr(cx, normalized_lhs);
1899 let rx = detect_extreme_expr(cx, normalized_rhs);
1904 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, AlwaysFalse), // max < x
1905 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, AlwaysFalse), // x < min
1911 (Some(l @ ExtremeExpr { which: Minimum, .. }), _) => (l, AlwaysTrue), // min <= x
1912 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, InequalityImpossible), // max <= x
1913 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, InequalityImpossible), // x <= min
1914 (_, Some(r @ ExtremeExpr { which: Maximum, .. })) => (r, AlwaysTrue), // x <= max
1918 Rel::Ne | Rel::Eq => return None,
1922 fn detect_extreme_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<ExtremeExpr<'tcx>> {
1923 use crate::types::ExtremeType::{Maximum, Minimum};
1925 let ty = cx.typeck_results().expr_ty(expr);
1927 let cv = constant(cx, cx.typeck_results(), expr)?.0;
1929 let which = match (&ty.kind, cv) {
1930 (&ty::Bool, Constant::Bool(false)) | (&ty::Uint(_), Constant::Int(0)) => Minimum,
1931 (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MIN >> (128 - int_bits(cx.tcx, ity)), ity) => {
1935 (&ty::Bool, Constant::Bool(true)) => Maximum,
1936 (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MAX >> (128 - int_bits(cx.tcx, ity)), ity) => {
1939 (&ty::Uint(uty), Constant::Int(i)) if clip(cx.tcx, u128::MAX, uty) == i => Maximum,
1943 Some(ExtremeExpr { which, expr })
1946 impl<'tcx> LateLintPass<'tcx> for AbsurdExtremeComparisons {
1947 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1948 use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
1949 use crate::types::ExtremeType::{Maximum, Minimum};
1951 if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
1952 if let Some((culprit, result)) = detect_absurd_comparison(cx, cmp.node, lhs, rhs) {
1953 if !expr.span.from_expansion() {
1954 let msg = "this comparison involving the minimum or maximum element for this \
1955 type contains a case that is always true or always false";
1957 let conclusion = match result {
1958 AlwaysFalse => "this comparison is always false".to_owned(),
1959 AlwaysTrue => "this comparison is always true".to_owned(),
1960 InequalityImpossible => format!(
1961 "the case where the two sides are not equal never occurs, consider using `{} == {}` \
1963 snippet(cx, lhs.span, "lhs"),
1964 snippet(cx, rhs.span, "rhs")
1969 "because `{}` is the {} value for this type, {}",
1970 snippet(cx, culprit.expr.span, "x"),
1971 match culprit.which {
1972 Minimum => "minimum",
1973 Maximum => "maximum",
1978 span_lint_and_help(cx, ABSURD_EXTREME_COMPARISONS, expr.span, msg, None, &help);
1985 declare_clippy_lint! {
1986 /// **What it does:** Checks for comparisons where the relation is always either
1987 /// true or false, but where one side has been upcast so that the comparison is
1988 /// necessary. Only integer types are checked.
1990 /// **Why is this bad?** An expression like `let x : u8 = ...; (x as u32) > 300`
1991 /// will mistakenly imply that it is possible for `x` to be outside the range of
1994 /// **Known problems:**
1995 /// https://github.com/rust-lang/rust-clippy/issues/886
2000 /// (x as u32) > 300;
2002 pub INVALID_UPCAST_COMPARISONS,
2004 "a comparison involving an upcast which is always true or false"
2007 declare_lint_pass!(InvalidUpcastComparisons => [INVALID_UPCAST_COMPARISONS]);
2009 #[derive(Copy, Clone, Debug, Eq)]
2016 #[allow(clippy::cast_sign_loss)]
2018 fn cmp_s_u(s: i128, u: u128) -> Ordering {
2021 } else if u > (i128::MAX as u128) {
2029 impl PartialEq for FullInt {
2031 fn eq(&self, other: &Self) -> bool {
2032 self.partial_cmp(other).expect("`partial_cmp` only returns `Some(_)`") == Ordering::Equal
2036 impl PartialOrd for FullInt {
2038 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2039 Some(match (self, other) {
2040 (&Self::S(s), &Self::S(o)) => s.cmp(&o),
2041 (&Self::U(s), &Self::U(o)) => s.cmp(&o),
2042 (&Self::S(s), &Self::U(o)) => Self::cmp_s_u(s, o),
2043 (&Self::U(s), &Self::S(o)) => Self::cmp_s_u(o, s).reverse(),
2047 impl Ord for FullInt {
2049 fn cmp(&self, other: &Self) -> Ordering {
2050 self.partial_cmp(other)
2051 .expect("`partial_cmp` for FullInt can never return `None`")
2055 fn numeric_cast_precast_bounds<'a>(cx: &LateContext<'_>, expr: &'a Expr<'_>) -> Option<(FullInt, FullInt)> {
2056 if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
2057 let pre_cast_ty = cx.typeck_results().expr_ty(cast_exp);
2058 let cast_ty = cx.typeck_results().expr_ty(expr);
2059 // if it's a cast from i32 to u32 wrapping will invalidate all these checks
2060 if cx.layout_of(pre_cast_ty).ok().map(|l| l.size) == cx.layout_of(cast_ty).ok().map(|l| l.size) {
2063 match pre_cast_ty.kind {
2064 ty::Int(int_ty) => Some(match int_ty {
2065 IntTy::I8 => (FullInt::S(i128::from(i8::MIN)), FullInt::S(i128::from(i8::MAX))),
2066 IntTy::I16 => (FullInt::S(i128::from(i16::MIN)), FullInt::S(i128::from(i16::MAX))),
2067 IntTy::I32 => (FullInt::S(i128::from(i32::MIN)), FullInt::S(i128::from(i32::MAX))),
2068 IntTy::I64 => (FullInt::S(i128::from(i64::MIN)), FullInt::S(i128::from(i64::MAX))),
2069 IntTy::I128 => (FullInt::S(i128::MIN), FullInt::S(i128::MAX)),
2070 IntTy::Isize => (FullInt::S(isize::MIN as i128), FullInt::S(isize::MAX as i128)),
2072 ty::Uint(uint_ty) => Some(match uint_ty {
2073 UintTy::U8 => (FullInt::U(u128::from(u8::MIN)), FullInt::U(u128::from(u8::MAX))),
2074 UintTy::U16 => (FullInt::U(u128::from(u16::MIN)), FullInt::U(u128::from(u16::MAX))),
2075 UintTy::U32 => (FullInt::U(u128::from(u32::MIN)), FullInt::U(u128::from(u32::MAX))),
2076 UintTy::U64 => (FullInt::U(u128::from(u64::MIN)), FullInt::U(u128::from(u64::MAX))),
2077 UintTy::U128 => (FullInt::U(u128::MIN), FullInt::U(u128::MAX)),
2078 UintTy::Usize => (FullInt::U(usize::MIN as u128), FullInt::U(usize::MAX as u128)),
2087 fn node_as_const_fullint<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<FullInt> {
2088 let val = constant(cx, cx.typeck_results(), expr)?.0;
2089 if let Constant::Int(const_int) = val {
2090 match cx.typeck_results().expr_ty(expr).kind {
2091 ty::Int(ity) => Some(FullInt::S(sext(cx.tcx, const_int, ity))),
2092 ty::Uint(_) => Some(FullInt::U(const_int)),
2100 fn err_upcast_comparison(cx: &LateContext<'_>, span: Span, expr: &Expr<'_>, always: bool) {
2101 if let ExprKind::Cast(ref cast_val, _) = expr.kind {
2104 INVALID_UPCAST_COMPARISONS,
2107 "because of the numeric bounds on `{}` prior to casting, this expression is always {}",
2108 snippet(cx, cast_val.span, "the expression"),
2109 if always { "true" } else { "false" },
2115 fn upcast_comparison_bounds_err<'tcx>(
2116 cx: &LateContext<'tcx>,
2118 rel: comparisons::Rel,
2119 lhs_bounds: Option<(FullInt, FullInt)>,
2120 lhs: &'tcx Expr<'_>,
2121 rhs: &'tcx Expr<'_>,
2124 use crate::utils::comparisons::Rel;
2126 if let Some((lb, ub)) = lhs_bounds {
2127 if let Some(norm_rhs_val) = node_as_const_fullint(cx, rhs) {
2128 if rel == Rel::Eq || rel == Rel::Ne {
2129 if norm_rhs_val < lb || norm_rhs_val > ub {
2130 err_upcast_comparison(cx, span, lhs, rel == Rel::Ne);
2132 } else if match rel {
2147 Rel::Eq | Rel::Ne => unreachable!(),
2149 err_upcast_comparison(cx, span, lhs, true)
2150 } else if match rel {
2165 Rel::Eq | Rel::Ne => unreachable!(),
2167 err_upcast_comparison(cx, span, lhs, false)
2173 impl<'tcx> LateLintPass<'tcx> for InvalidUpcastComparisons {
2174 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2175 if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
2176 let normalized = comparisons::normalize_comparison(cmp.node, lhs, rhs);
2177 let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
2183 let lhs_bounds = numeric_cast_precast_bounds(cx, normalized_lhs);
2184 let rhs_bounds = numeric_cast_precast_bounds(cx, normalized_rhs);
2186 upcast_comparison_bounds_err(cx, expr.span, rel, lhs_bounds, normalized_lhs, normalized_rhs, false);
2187 upcast_comparison_bounds_err(cx, expr.span, rel, rhs_bounds, normalized_rhs, normalized_lhs, true);
2192 declare_clippy_lint! {
2193 /// **What it does:** Checks for public `impl` or `fn` missing generalization
2194 /// over different hashers and implicitly defaulting to the default hashing
2195 /// algorithm (`SipHash`).
2197 /// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
2200 /// **Known problems:** Suggestions for replacing constructors can contain
2201 /// false-positives. Also applying suggestions can require modification of other
2202 /// pieces of code, possibly including external crates.
2206 /// # use std::collections::HashMap;
2207 /// # use std::hash::{Hash, BuildHasher};
2208 /// # trait Serialize {};
2209 /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
2211 /// pub fn foo(map: &mut HashMap<i32, i32>) { }
2213 /// could be rewritten as
2215 /// # use std::collections::HashMap;
2216 /// # use std::hash::{Hash, BuildHasher};
2217 /// # trait Serialize {};
2218 /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
2220 /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
2222 pub IMPLICIT_HASHER,
2224 "missing generalization over different hashers"
2227 declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
2229 impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
2230 #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
2231 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
2232 use rustc_span::BytePos;
2234 fn suggestion<'tcx>(
2235 cx: &LateContext<'tcx>,
2236 diag: &mut DiagnosticBuilder<'_>,
2237 generics_span: Span,
2238 generics_suggestion_span: Span,
2239 target: &ImplicitHasherType<'_>,
2240 vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
2242 let generics_snip = snippet(cx, generics_span, "");
2244 let generics_snip = if generics_snip.is_empty() {
2247 &generics_snip[1..generics_snip.len() - 1]
2252 "consider adding a type parameter",
2255 generics_suggestion_span,
2257 "<{}{}S: ::std::hash::BuildHasher{}>",
2259 if generics_snip.is_empty() { "" } else { ", " },
2260 if vis.suggestions.is_empty() {
2263 // request users to add `Default` bound so that generic constructors can be used
2270 format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
2275 if !vis.suggestions.is_empty() {
2276 multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
2280 if !cx.access_levels.is_exported(item.hir_id) {
2291 let mut vis = ImplicitHasherTypeVisitor::new(cx);
2294 for target in &vis.found {
2295 if differing_macro_contexts(item.span, target.span()) {
2299 let generics_suggestion_span = generics.span.substitute_dummy({
2300 let pos = snippet_opt(cx, item.span.until(target.span()))
2301 .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
2302 if let Some(pos) = pos {
2303 Span::new(pos, pos, item.span.data().ctxt)
2309 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2310 for item in items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
2311 ctr_vis.visit_impl_item(item);
2319 "impl for `{}` should be generalized over different hashers",
2323 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
2328 ItemKind::Fn(ref sig, ref generics, body_id) => {
2329 let body = cx.tcx.hir().body(body_id);
2331 for ty in sig.decl.inputs {
2332 let mut vis = ImplicitHasherTypeVisitor::new(cx);
2335 for target in &vis.found {
2336 if in_external_macro(cx.sess(), generics.span) {
2339 let generics_suggestion_span = generics.span.substitute_dummy({
2340 let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
2342 let i = snip.find("fn")?;
2343 Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
2345 .expect("failed to create span for type parameters");
2346 Span::new(pos, pos, item.span.data().ctxt)
2349 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2350 ctr_vis.visit_body(body);
2357 "parameter of type `{}` should be generalized over different hashers",
2361 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
2372 enum ImplicitHasherType<'tcx> {
2373 HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
2374 HashSet(Span, Ty<'tcx>, Cow<'static, str>),
2377 impl<'tcx> ImplicitHasherType<'tcx> {
2378 /// Checks that `ty` is a target type without a `BuildHasher`.
2379 fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
2380 if let TyKind::Path(QPath::Resolved(None, ref path)) = hir_ty.kind {
2381 let params: Vec<_> = path
2389 .filter_map(|arg| match arg {
2390 GenericArg::Type(ty) => Some(ty),
2394 let params_len = params.len();
2396 let ty = hir_ty_to_ty(cx.tcx, hir_ty);
2398 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) && params_len == 2 {
2399 Some(ImplicitHasherType::HashMap(
2402 snippet(cx, params[0].span, "K"),
2403 snippet(cx, params[1].span, "V"),
2405 } else if is_type_diagnostic_item(cx, ty, sym!(hashset_type)) && params_len == 1 {
2406 Some(ImplicitHasherType::HashSet(
2409 snippet(cx, params[0].span, "T"),
2419 fn type_name(&self) -> &'static str {
2421 ImplicitHasherType::HashMap(..) => "HashMap",
2422 ImplicitHasherType::HashSet(..) => "HashSet",
2426 fn type_arguments(&self) -> String {
2428 ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
2429 ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
2433 fn ty(&self) -> Ty<'tcx> {
2435 ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
2439 fn span(&self) -> Span {
2441 ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
2446 struct ImplicitHasherTypeVisitor<'a, 'tcx> {
2447 cx: &'a LateContext<'tcx>,
2448 found: Vec<ImplicitHasherType<'tcx>>,
2451 impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
2452 fn new(cx: &'a LateContext<'tcx>) -> Self {
2453 Self { cx, found: vec![] }
2457 impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
2458 type Map = Map<'tcx>;
2460 fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
2461 if let Some(target) = ImplicitHasherType::new(self.cx, t) {
2462 self.found.push(target);
2468 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2469 NestedVisitorMap::None
2473 /// Looks for default-hasher-dependent constructors like `HashMap::new`.
2474 struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2475 cx: &'a LateContext<'tcx>,
2476 maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
2477 target: &'b ImplicitHasherType<'tcx>,
2478 suggestions: BTreeMap<Span, String>,
2481 impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2482 fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
2485 maybe_typeck_results: cx.maybe_typeck_results(),
2487 suggestions: BTreeMap::new(),
2492 impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2493 type Map = Map<'tcx>;
2495 fn visit_body(&mut self, body: &'tcx Body<'_>) {
2496 let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
2497 walk_body(self, body);
2498 self.maybe_typeck_results = old_maybe_typeck_results;
2501 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
2503 if let ExprKind::Call(ref fun, ref args) = e.kind;
2504 if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
2505 if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
2507 if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
2511 if match_path(ty_path, &paths::HASHMAP) {
2512 if method.ident.name == sym!(new) {
2514 .insert(e.span, "HashMap::default()".to_string());
2515 } else if method.ident.name == sym!(with_capacity) {
2516 self.suggestions.insert(
2519 "HashMap::with_capacity_and_hasher({}, Default::default())",
2520 snippet(self.cx, args[0].span, "capacity"),
2524 } else if match_path(ty_path, &paths::HASHSET) {
2525 if method.ident.name == sym!(new) {
2527 .insert(e.span, "HashSet::default()".to_string());
2528 } else if method.ident.name == sym!(with_capacity) {
2529 self.suggestions.insert(
2532 "HashSet::with_capacity_and_hasher({}, Default::default())",
2533 snippet(self.cx, args[0].span, "capacity"),
2544 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2545 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2549 declare_clippy_lint! {
2550 /// **What it does:** Checks for casts of `&T` to `&mut T` anywhere in the code.
2552 /// **Why is this bad?** It’s basically guaranteed to be undefined behaviour.
2553 /// `UnsafeCell` is the only way to obtain aliasable data that is considered
2556 /// **Known problems:** None.
2562 /// *(r as *const _ as *mut _) += 1;
2567 /// Instead consider using interior mutability types.
2570 /// use std::cell::UnsafeCell;
2572 /// fn x(r: &UnsafeCell<i32>) {
2578 pub CAST_REF_TO_MUT,
2580 "a cast of reference to a mutable pointer"
2583 declare_lint_pass!(RefToMut => [CAST_REF_TO_MUT]);
2585 impl<'tcx> LateLintPass<'tcx> for RefToMut {
2586 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2588 if let ExprKind::Unary(UnOp::UnDeref, e) = &expr.kind;
2589 if let ExprKind::Cast(e, t) = &e.kind;
2590 if let TyKind::Ptr(MutTy { mutbl: Mutability::Mut, .. }) = t.kind;
2591 if let ExprKind::Cast(e, t) = &e.kind;
2592 if let TyKind::Ptr(MutTy { mutbl: Mutability::Not, .. }) = t.kind;
2593 if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind;
2599 "casting `&T` to `&mut T` may cause undefined behavior, consider instead using an `UnsafeCell`",