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::def::Res;
12 use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, FnKind, NestedVisitorMap, Visitor};
14 BinOpKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, FnSig, GenericArg, GenericBounds, GenericParamKind, HirId,
15 ImplItem, ImplItemKind, Item, ItemKind, Lifetime, Lit, Local, MatchSource, MutTy, Mutability, Node, QPath, Stmt,
16 StmtKind, SyntheticTyParamKind, TraitFn, TraitItem, TraitItemKind, TyKind, UnOp,
18 use rustc_lint::{LateContext, LateLintPass, LintContext};
19 use rustc_middle::hir::map::Map;
20 use rustc_middle::lint::in_external_macro;
21 use rustc_middle::ty::TypeFoldable;
22 use rustc_middle::ty::{self, InferTy, Ty, TyCtxt, TyS, TypeckResults};
23 use rustc_session::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
24 use rustc_span::hygiene::{ExpnKind, MacroKind};
25 use rustc_span::source_map::Span;
26 use rustc_span::symbol::sym;
27 use rustc_target::abi::LayoutOf;
28 use rustc_target::spec::abi::Abi;
29 use rustc_typeck::hir_ty_to_ty;
31 use crate::consts::{constant, Constant};
32 use crate::utils::paths;
34 clip, comparisons, differing_macro_contexts, higher, in_constant, indent_of, int_bits, is_type_diagnostic_item,
35 last_path_segment, match_def_path, match_path, method_chain_args, multispan_sugg, numeric_literal::NumericLiteral,
36 qpath_res, reindent_multiline, sext, snippet, snippet_opt, snippet_with_applicability, snippet_with_macro_callsite,
37 span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then, unsext,
40 declare_clippy_lint! {
41 /// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
42 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
44 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
45 /// the heap. So if you `Box` it, you just add another level of indirection
46 /// without any benefit whatsoever.
48 /// **Known problems:** None.
53 /// values: Box<Vec<Foo>>,
66 "usage of `Box<Vec<T>>`, vector elements are already on the heap"
69 declare_clippy_lint! {
70 /// **What it does:** Checks for use of `Vec<Box<T>>` where T: Sized anywhere in the code.
71 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
73 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
74 /// the heap. So if you `Box` its contents, you just add another level of indirection.
76 /// **Known problems:** Vec<Box<T: Sized>> makes sense if T is a large type (see #3530,
82 /// values: Vec<Box<i32>>,
95 "usage of `Vec<Box<T>>` where T: Sized, vector elements are already on the heap"
98 declare_clippy_lint! {
99 /// **What it does:** Checks for use of `Option<Option<_>>` in function signatures and type
102 /// **Why is this bad?** `Option<_>` represents an optional value. `Option<Option<_>>`
103 /// represents an optional optional value which is logically the same thing as an optional
104 /// value but has an unneeded extra level of wrapping.
106 /// If you have a case where `Some(Some(_))`, `Some(None)` and `None` are distinct cases,
107 /// consider a custom `enum` instead, with clear names for each case.
109 /// **Known problems:** None.
113 /// fn get_data() -> Option<Option<u32>> {
121 /// pub enum Contents {
122 /// Data(Vec<u8>), // Was Some(Some(Vec<u8>))
123 /// NotYetFetched, // Was Some(None)
124 /// None, // Was None
127 /// fn get_data() -> Contents {
133 "usage of `Option<Option<T>>`"
136 declare_clippy_lint! {
137 /// **What it does:** Checks for usage of any `LinkedList`, suggesting to use a
138 /// `Vec` or a `VecDeque` (formerly called `RingBuf`).
140 /// **Why is this bad?** Gankro says:
142 /// > The TL;DR of `LinkedList` is that it's built on a massive amount of
143 /// pointers and indirection.
144 /// > It wastes memory, it has terrible cache locality, and is all-around slow.
146 /// > "only" amortized for push/pop, should be faster in the general case for
147 /// almost every possible
148 /// > workload, and isn't even amortized at all if you can predict the capacity
151 /// > `LinkedList`s are only really good if you're doing a lot of merging or
152 /// splitting of lists.
153 /// > This is because they can just mangle some pointers instead of actually
154 /// copying the data. Even
155 /// > if you're doing a lot of insertion in the middle of the list, `RingBuf`
156 /// can still be better
157 /// > because of how expensive it is to seek to the middle of a `LinkedList`.
159 /// **Known problems:** False positives – the instances where using a
160 /// `LinkedList` makes sense are few and far between, but they can still happen.
164 /// # use std::collections::LinkedList;
165 /// let x: LinkedList<usize> = LinkedList::new();
169 "usage of LinkedList, usually a vector is faster, or a more specialized data structure like a `VecDeque`"
172 declare_clippy_lint! {
173 /// **What it does:** Checks for use of `&Box<T>` anywhere in the code.
174 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
176 /// **Why is this bad?** Any `&Box<T>` can also be a `&T`, which is more
179 /// **Known problems:** None.
183 /// fn foo(bar: &Box<T>) { ... }
189 /// fn foo(bar: &T) { ... }
193 "a borrow of a boxed type"
196 declare_clippy_lint! {
197 /// **What it does:** Checks for use of redundant allocations anywhere in the code.
199 /// **Why is this bad?** Expressions such as `Rc<&T>`, `Rc<Rc<T>>`, `Rc<Box<T>>`, `Box<&T>`
200 /// add an unnecessary level of indirection.
202 /// **Known problems:** None.
206 /// # use std::rc::Rc;
207 /// fn foo(bar: Rc<&usize>) {}
213 /// fn foo(bar: &usize) {}
215 pub REDUNDANT_ALLOCATION,
217 "redundant allocation"
220 declare_clippy_lint! {
221 /// **What it does:** Checks for `Rc<T>` and `Arc<T>` when `T` is a mutable buffer type such as `String` or `Vec`.
223 /// **Why is this bad?** Expressions such as `Rc<String>` usually have no advantage over `Rc<str>`, since
224 /// it is larger and involves an extra level of indirection, and doesn't implement `Borrow<str>`.
226 /// While mutating a buffer type would still be possible with `Rc::get_mut()`, it only
227 /// works if there are no additional references yet, which usually defeats the purpose of
228 /// enclosing it in a shared ownership type. Instead, additionally wrapping the inner
229 /// type with an interior mutable container (such as `RefCell` or `Mutex`) would normally
232 /// **Known problems:** This pattern can be desirable to avoid the overhead of a `RefCell` or `Mutex` for
233 /// cases where mutation only happens before there are any additional references.
237 /// # use std::rc::Rc;
238 /// fn foo(interned: Rc<String>) { ... }
244 /// fn foo(interned: Rc<str>) { ... }
248 "shared ownership of a buffer type"
252 vec_box_size_threshold: u64,
255 impl_lint_pass!(Types => [BOX_VEC, VEC_BOX, OPTION_OPTION, LINKEDLIST, BORROWED_BOX, REDUNDANT_ALLOCATION, RC_BUFFER]);
257 impl<'tcx> LateLintPass<'tcx> for Types {
258 fn check_fn(&mut self, cx: &LateContext<'_>, _: FnKind<'_>, decl: &FnDecl<'_>, _: &Body<'_>, _: Span, id: HirId) {
259 // Skip trait implementations; see issue #605.
260 if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(id)) {
261 if let ItemKind::Impl { of_trait: Some(_), .. } = item.kind {
266 self.check_fn_decl(cx, decl);
269 fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
270 self.check_ty(cx, &field.ty, false);
273 fn check_trait_item(&mut self, cx: &LateContext<'_>, item: &TraitItem<'_>) {
275 TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_ty(cx, ty, false),
276 TraitItemKind::Fn(ref sig, _) => self.check_fn_decl(cx, &sig.decl),
281 fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
282 if let Some(ref ty) = local.ty {
283 self.check_ty(cx, ty, true);
288 /// Checks if `qpath` has last segment with type parameter matching `path`
289 fn match_type_parameter(cx: &LateContext<'_>, qpath: &QPath<'_>, path: &[&str]) -> Option<Span> {
290 let last = last_path_segment(qpath);
292 if let Some(ref params) = last.args;
293 if !params.parenthesized;
294 if let Some(ty) = params.args.iter().find_map(|arg| match arg {
295 GenericArg::Type(ty) => Some(ty),
298 if let TyKind::Path(ref qpath) = ty.kind;
299 if let Some(did) = qpath_res(cx, qpath, ty.hir_id).opt_def_id();
300 if match_def_path(cx, did, path);
302 return Some(ty.span);
308 fn match_buffer_type(cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<&'static str> {
309 if match_type_parameter(cx, qpath, &paths::STRING).is_some() {
312 if match_type_parameter(cx, qpath, &paths::OS_STRING).is_some() {
313 return Some("std::ffi::OsStr");
315 if match_type_parameter(cx, qpath, &paths::PATH_BUF).is_some() {
316 return Some("std::path::Path");
321 fn match_borrows_parameter(_cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<Span> {
322 let last = last_path_segment(qpath);
324 if let Some(ref params) = last.args;
325 if !params.parenthesized;
326 if let Some(ty) = params.args.iter().find_map(|arg| match arg {
327 GenericArg::Type(ty) => Some(ty),
330 if let TyKind::Rptr(..) = ty.kind;
332 return Some(ty.span);
339 pub fn new(vec_box_size_threshold: u64) -> Self {
340 Self { vec_box_size_threshold }
343 fn check_fn_decl(&mut self, cx: &LateContext<'_>, decl: &FnDecl<'_>) {
344 for input in decl.inputs {
345 self.check_ty(cx, input, false);
348 if let FnRetTy::Return(ref ty) = decl.output {
349 self.check_ty(cx, ty, false);
353 /// Recursively check for `TypePass` lints in the given type. Stop at the first
356 /// The parameter `is_local` distinguishes the context of the type; types from
357 /// local bindings should only be checked for the `BORROWED_BOX` lint.
358 #[allow(clippy::too_many_lines)]
359 fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, is_local: bool) {
360 if hir_ty.span.from_expansion() {
364 TyKind::Path(ref qpath) if !is_local => {
365 let hir_id = hir_ty.hir_id;
366 let res = qpath_res(cx, qpath, hir_id);
367 if let Some(def_id) = res.opt_def_id() {
368 if Some(def_id) == cx.tcx.lang_items().owned_box() {
369 if let Some(span) = match_borrows_parameter(cx, qpath) {
370 let mut applicability = Applicability::MachineApplicable;
373 REDUNDANT_ALLOCATION,
375 "usage of `Box<&T>`",
377 snippet_with_applicability(cx, span, "..", &mut applicability).to_string(),
380 return; // don't recurse into the type
382 if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
387 "you seem to be trying to use `Box<Vec<T>>`. Consider using just `Vec<T>`",
389 "`Vec<T>` is already on the heap, `Box<Vec<T>>` makes an extra allocation.",
391 return; // don't recurse into the type
393 } else if cx.tcx.is_diagnostic_item(sym::Rc, def_id) {
394 if let Some(span) = match_type_parameter(cx, qpath, &paths::RC) {
395 let mut applicability = Applicability::MachineApplicable;
398 REDUNDANT_ALLOCATION,
400 "usage of `Rc<Rc<T>>`",
402 snippet_with_applicability(cx, span, "..", &mut applicability).to_string(),
405 return; // don't recurse into the type
407 if match_type_parameter(cx, qpath, &paths::BOX).is_some() {
408 let box_ty = match &last_path_segment(qpath).args.unwrap().args[0] {
409 GenericArg::Type(ty) => match &ty.kind {
410 TyKind::Path(qpath) => qpath,
415 let inner_span = match &last_path_segment(&box_ty).args.unwrap().args[0] {
416 GenericArg::Type(ty) => ty.span,
419 let mut applicability = Applicability::MachineApplicable;
422 REDUNDANT_ALLOCATION,
424 "usage of `Rc<Box<T>>`",
428 snippet_with_applicability(cx, inner_span, "..", &mut applicability)
432 return; // don't recurse into the type
434 if let Some(alternate) = match_buffer_type(cx, qpath) {
439 "usage of `Rc<T>` when T is a buffer type",
441 format!("Rc<{}>", alternate),
442 Applicability::MachineApplicable,
444 return; // don't recurse into the type
446 if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
447 let vec_ty = match &last_path_segment(qpath).args.unwrap().args[0] {
448 GenericArg::Type(ty) => match &ty.kind {
449 TyKind::Path(qpath) => qpath,
454 let inner_span = match &last_path_segment(&vec_ty).args.unwrap().args[0] {
455 GenericArg::Type(ty) => ty.span,
458 let mut applicability = Applicability::MachineApplicable;
463 "usage of `Rc<T>` when T is a buffer type",
467 snippet_with_applicability(cx, inner_span, "..", &mut applicability)
469 Applicability::MachineApplicable,
471 return; // don't recurse into the type
473 if let Some(span) = match_borrows_parameter(cx, qpath) {
474 let mut applicability = Applicability::MachineApplicable;
477 REDUNDANT_ALLOCATION,
481 snippet_with_applicability(cx, span, "..", &mut applicability).to_string(),
484 return; // don't recurse into the type
486 } else if cx.tcx.is_diagnostic_item(sym::Arc, def_id) {
487 if let Some(alternate) = match_buffer_type(cx, qpath) {
492 "usage of `Arc<T>` when T is a buffer type",
494 format!("Arc<{}>", alternate),
495 Applicability::MachineApplicable,
497 return; // don't recurse into the type
499 if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
500 let vec_ty = match &last_path_segment(qpath).args.unwrap().args[0] {
501 GenericArg::Type(ty) => match &ty.kind {
502 TyKind::Path(qpath) => qpath,
507 let inner_span = match &last_path_segment(&vec_ty).args.unwrap().args[0] {
508 GenericArg::Type(ty) => ty.span,
511 let mut applicability = Applicability::MachineApplicable;
516 "usage of `Arc<T>` when T is a buffer type",
520 snippet_with_applicability(cx, inner_span, "..", &mut applicability)
522 Applicability::MachineApplicable,
524 return; // don't recurse into the type
526 } else if cx.tcx.is_diagnostic_item(sym::vec_type, def_id) {
528 // Get the _ part of Vec<_>
529 if let Some(ref last) = last_path_segment(qpath).args;
530 if let Some(ty) = last.args.iter().find_map(|arg| match arg {
531 GenericArg::Type(ty) => Some(ty),
534 // ty is now _ at this point
535 if let TyKind::Path(ref ty_qpath) = ty.kind;
536 let res = qpath_res(cx, ty_qpath, ty.hir_id);
537 if let Some(def_id) = res.opt_def_id();
538 if Some(def_id) == cx.tcx.lang_items().owned_box();
539 // At this point, we know ty is Box<T>, now get T
540 if let Some(ref last) = last_path_segment(ty_qpath).args;
541 if let Some(boxed_ty) = last.args.iter().find_map(|arg| match arg {
542 GenericArg::Type(ty) => Some(ty),
545 let ty_ty = hir_ty_to_ty(cx.tcx, boxed_ty);
546 if !ty_ty.has_escaping_bound_vars();
547 if ty_ty.is_sized(cx.tcx.at(ty.span), cx.param_env);
548 if let Ok(ty_ty_size) = cx.layout_of(ty_ty).map(|l| l.size.bytes());
549 if ty_ty_size <= self.vec_box_size_threshold;
555 "`Vec<T>` is already on the heap, the boxing is unnecessary.",
557 format!("Vec<{}>", snippet(cx, boxed_ty.span, "..")),
558 Applicability::MachineApplicable,
560 return; // don't recurse into the type
563 } else if cx.tcx.is_diagnostic_item(sym::option_type, def_id) {
564 if match_type_parameter(cx, qpath, &paths::OPTION).is_some() {
569 "consider using `Option<T>` instead of `Option<Option<T>>` or a custom \
570 enum if you need to distinguish all 3 cases",
572 return; // don't recurse into the type
574 } else if match_def_path(cx, def_id, &paths::LINKED_LIST) {
579 "I see you're using a LinkedList! Perhaps you meant some other data structure?",
581 "a `VecDeque` might work",
583 return; // don't recurse into the type
587 QPath::Resolved(Some(ref ty), ref p) => {
588 self.check_ty(cx, ty, is_local);
589 for ty in p.segments.iter().flat_map(|seg| {
592 .map_or_else(|| [].iter(), |params| params.args.iter())
593 .filter_map(|arg| match arg {
594 GenericArg::Type(ty) => Some(ty),
598 self.check_ty(cx, ty, is_local);
601 QPath::Resolved(None, ref p) => {
602 for ty in p.segments.iter().flat_map(|seg| {
605 .map_or_else(|| [].iter(), |params| params.args.iter())
606 .filter_map(|arg| match arg {
607 GenericArg::Type(ty) => Some(ty),
611 self.check_ty(cx, ty, is_local);
614 QPath::TypeRelative(ref ty, ref seg) => {
615 self.check_ty(cx, ty, is_local);
616 if let Some(ref params) = seg.args {
617 for ty in params.args.iter().filter_map(|arg| match arg {
618 GenericArg::Type(ty) => Some(ty),
621 self.check_ty(cx, ty, is_local);
625 QPath::LangItem(..) => {},
628 TyKind::Rptr(ref lt, ref mut_ty) => self.check_ty_rptr(cx, hir_ty, is_local, lt, mut_ty),
630 TyKind::Slice(ref ty) | TyKind::Array(ref ty, _) | TyKind::Ptr(MutTy { ref ty, .. }) => {
631 self.check_ty(cx, ty, is_local)
633 TyKind::Tup(tys) => {
635 self.check_ty(cx, ty, is_local);
644 cx: &LateContext<'_>,
645 hir_ty: &hir::Ty<'_>,
650 match mut_ty.ty.kind {
651 TyKind::Path(ref qpath) => {
652 let hir_id = mut_ty.ty.hir_id;
653 let def = qpath_res(cx, qpath, hir_id);
655 if let Some(def_id) = def.opt_def_id();
656 if Some(def_id) == cx.tcx.lang_items().owned_box();
657 if let QPath::Resolved(None, ref path) = *qpath;
658 if let [ref bx] = *path.segments;
659 if let Some(ref params) = bx.args;
660 if !params.parenthesized;
661 if let Some(inner) = params.args.iter().find_map(|arg| match arg {
662 GenericArg::Type(ty) => Some(ty),
666 if is_any_trait(inner) {
667 // Ignore `Box<Any>` types; see issue #1884 for details.
671 let ltopt = if lt.is_elided() {
674 format!("{} ", lt.name.ident().as_str())
677 if mut_ty.mutbl == Mutability::Mut {
678 // Ignore `&mut Box<T>` types; see issue #2907 for
683 // When trait objects or opaque types have lifetime or auto-trait bounds,
684 // we need to add parentheses to avoid a syntax error due to its ambiguity.
685 // Originally reported as the issue #3128.
686 let inner_snippet = snippet(cx, inner.span, "..");
687 let suggestion = match &inner.kind {
688 TyKind::TraitObject(bounds, lt_bound) if bounds.len() > 1 || !lt_bound.is_elided() => {
689 format!("&{}({})", ltopt, &inner_snippet)
692 if get_bounds_if_impl_trait(cx, qpath, inner.hir_id)
693 .map_or(false, |bounds| bounds.len() > 1) =>
695 format!("&{}({})", ltopt, &inner_snippet)
697 _ => format!("&{}{}", ltopt, &inner_snippet),
703 "you seem to be trying to use `&Box<T>`. Consider using just `&T`",
706 // To make this `MachineApplicable`, at least one needs to check if it isn't a trait item
707 // because the trait impls of it will break otherwise;
708 // and there may be other cases that result in invalid code.
709 // For example, type coercion doesn't work nicely.
710 Applicability::Unspecified,
712 return; // don't recurse into the type
715 self.check_ty(cx, &mut_ty.ty, is_local);
717 _ => self.check_ty(cx, &mut_ty.ty, is_local),
722 // Returns true if given type is `Any` trait.
723 fn is_any_trait(t: &hir::Ty<'_>) -> bool {
725 if let TyKind::TraitObject(ref traits, _) = t.kind;
726 if !traits.is_empty();
727 // Only Send/Sync can be used as additional traits, so it is enough to
728 // check only the first trait.
729 if match_path(&traits[0].trait_ref.path, &paths::ANY_TRAIT);
738 fn get_bounds_if_impl_trait<'tcx>(cx: &LateContext<'tcx>, qpath: &QPath<'_>, id: HirId) -> Option<GenericBounds<'tcx>> {
740 if let Some(did) = qpath_res(cx, qpath, id).opt_def_id();
741 if let Some(Node::GenericParam(generic_param)) = cx.tcx.hir().get_if_local(did);
742 if let GenericParamKind::Type { synthetic, .. } = generic_param.kind;
743 if synthetic == Some(SyntheticTyParamKind::ImplTrait);
745 Some(generic_param.bounds)
752 declare_clippy_lint! {
753 /// **What it does:** Checks for binding a unit value.
755 /// **Why is this bad?** A unit value cannot usefully be used anywhere. So
756 /// binding one is kind of pointless.
758 /// **Known problems:** None.
768 "creating a `let` binding to a value of unit type, which usually can't be used afterwards"
771 declare_lint_pass!(LetUnitValue => [LET_UNIT_VALUE]);
773 impl<'tcx> LateLintPass<'tcx> for LetUnitValue {
774 fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
775 if let StmtKind::Local(ref local) = stmt.kind {
776 if is_unit(cx.typeck_results().pat_ty(&local.pat)) {
777 if in_external_macro(cx.sess(), stmt.span) || local.pat.span.from_expansion() {
780 if higher::is_from_for_desugar(local) {
787 "this let-binding has unit value",
789 if let Some(expr) = &local.init {
790 let snip = snippet_with_macro_callsite(cx, expr.span, "()");
791 diag.span_suggestion(
793 "omit the `let` binding",
794 format!("{};", snip),
795 Applicability::MachineApplicable, // snippet
805 declare_clippy_lint! {
806 /// **What it does:** Checks for comparisons to unit. This includes all binary
807 /// comparisons (like `==` and `<`) and asserts.
809 /// **Why is this bad?** Unit is always equal to itself, and thus is just a
810 /// clumsily written constant. Mostly this happens when someone accidentally
811 /// adds semicolons at the end of the operands.
813 /// **Known problems:** None.
844 /// assert_eq!({ foo(); }, { bar(); });
846 /// will always succeed
849 "comparing unit values"
852 declare_lint_pass!(UnitCmp => [UNIT_CMP]);
854 impl<'tcx> LateLintPass<'tcx> for UnitCmp {
855 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
856 if expr.span.from_expansion() {
857 if let Some(callee) = expr.span.source_callee() {
858 if let ExpnKind::Macro(MacroKind::Bang, symbol) = callee.kind {
859 if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
861 if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
862 let result = match &*symbol.as_str() {
863 "assert_eq" | "debug_assert_eq" => "succeed",
864 "assert_ne" | "debug_assert_ne" => "fail",
872 "`{}` of unit values detected. This will always {}",
883 if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
885 if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
886 let result = match op {
887 BinOpKind::Eq | BinOpKind::Le | BinOpKind::Ge => "true",
895 "{}-comparison of unit values detected. This will always be {}",
905 declare_clippy_lint! {
906 /// **What it does:** Checks for passing a unit value as an argument to a function without using a
907 /// unit literal (`()`).
909 /// **Why is this bad?** This is likely the result of an accidental semicolon.
911 /// **Known problems:** None.
922 "passing unit to a function"
925 declare_lint_pass!(UnitArg => [UNIT_ARG]);
927 impl<'tcx> LateLintPass<'tcx> for UnitArg {
928 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
929 if expr.span.from_expansion() {
933 // apparently stuff in the desugaring of `?` can trigger this
934 // so check for that here
935 // only the calls to `Try::from_error` is marked as desugared,
936 // so we need to check both the current Expr and its parent.
937 if is_questionmark_desugar_marked_call(expr) {
941 let map = &cx.tcx.hir();
942 let opt_parent_node = map.find(map.get_parent_node(expr.hir_id));
943 if let Some(hir::Node::Expr(parent_expr)) = opt_parent_node;
944 if is_questionmark_desugar_marked_call(parent_expr);
951 ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args, _) => {
952 let args_to_recover = args
955 if is_unit(cx.typeck_results().expr_ty(arg)) && !is_unit_literal(arg) {
956 !matches!(&arg.kind, ExprKind::Match(.., MatchSource::TryDesugar))
961 .collect::<Vec<_>>();
962 if !args_to_recover.is_empty() {
963 lint_unit_args(cx, expr, &args_to_recover);
971 fn fmt_stmts_and_call(
972 cx: &LateContext<'_>,
973 call_expr: &Expr<'_>,
975 args_snippets: &[impl AsRef<str>],
976 non_empty_block_args_snippets: &[impl AsRef<str>],
978 let call_expr_indent = indent_of(cx, call_expr.span).unwrap_or(0);
979 let call_snippet_with_replacements = args_snippets
981 .fold(call_snippet.to_owned(), |acc, arg| acc.replacen(arg.as_ref(), "()", 1));
983 let mut stmts_and_call = non_empty_block_args_snippets
985 .map(|it| it.as_ref().to_owned())
986 .collect::<Vec<_>>();
987 stmts_and_call.push(call_snippet_with_replacements);
988 stmts_and_call = stmts_and_call
990 .map(|v| reindent_multiline(v.into(), true, Some(call_expr_indent)).into_owned())
993 let mut stmts_and_call_snippet = stmts_and_call.join(&format!("{}{}", ";\n", " ".repeat(call_expr_indent)));
994 // expr is not in a block statement or result expression position, wrap in a block
995 let parent_node = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(call_expr.hir_id));
996 if !matches!(parent_node, Some(Node::Block(_))) && !matches!(parent_node, Some(Node::Stmt(_))) {
997 let block_indent = call_expr_indent + 4;
998 stmts_and_call_snippet =
999 reindent_multiline(stmts_and_call_snippet.into(), true, Some(block_indent)).into_owned();
1000 stmts_and_call_snippet = format!(
1002 " ".repeat(block_indent),
1003 &stmts_and_call_snippet,
1004 " ".repeat(call_expr_indent)
1007 stmts_and_call_snippet
1010 fn lint_unit_args(cx: &LateContext<'_>, expr: &Expr<'_>, args_to_recover: &[&Expr<'_>]) {
1011 let mut applicability = Applicability::MachineApplicable;
1012 let (singular, plural) = if args_to_recover.len() > 1 {
1021 &format!("passing {}unit value{} to a function", singular, plural),
1028 if let ExprKind::Block(block, _) = arg.kind;
1029 if block.expr.is_none();
1030 if let Some(last_stmt) = block.stmts.iter().last();
1031 if let StmtKind::Semi(last_expr) = last_stmt.kind;
1032 if let Some(snip) = snippet_opt(cx, last_expr.span);
1044 .for_each(|(span, sugg)| {
1047 "remove the semicolon from the last statement in the block",
1049 Applicability::MaybeIncorrect,
1052 applicability = Applicability::MaybeIncorrect;
1055 let arg_snippets: Vec<String> = args_to_recover
1057 .filter_map(|arg| snippet_opt(cx, arg.span))
1059 let arg_snippets_without_empty_blocks: Vec<String> = args_to_recover
1061 .filter(|arg| !is_empty_block(arg))
1062 .filter_map(|arg| snippet_opt(cx, arg.span))
1065 if let Some(call_snippet) = snippet_opt(cx, expr.span) {
1066 let sugg = fmt_stmts_and_call(
1071 &arg_snippets_without_empty_blocks,
1074 if arg_snippets_without_empty_blocks.is_empty() {
1075 db.multipart_suggestion(
1076 &format!("use {}unit literal{} instead", singular, plural),
1079 .map(|arg| (arg.span, "()".to_string()))
1080 .collect::<Vec<_>>(),
1084 let plural = arg_snippets_without_empty_blocks.len() > 1;
1085 let empty_or_s = if plural { "s" } else { "" };
1086 let it_or_them = if plural { "them" } else { "it" };
1090 "{}move the expression{} in front of the call and replace {} with the unit literal `()`",
1091 or, empty_or_s, it_or_them
1102 fn is_empty_block(expr: &Expr<'_>) -> bool {
1116 fn is_questionmark_desugar_marked_call(expr: &Expr<'_>) -> bool {
1117 use rustc_span::hygiene::DesugaringKind;
1118 if let ExprKind::Call(ref callee, _) = expr.kind {
1119 callee.span.is_desugaring(DesugaringKind::QuestionMark)
1125 fn is_unit(ty: Ty<'_>) -> bool {
1126 matches!(ty.kind(), ty::Tuple(slice) if slice.is_empty())
1129 fn is_unit_literal(expr: &Expr<'_>) -> bool {
1130 matches!(expr.kind, ExprKind::Tup(ref slice) if slice.is_empty())
1133 declare_clippy_lint! {
1134 /// **What it does:** Checks for casts from any numerical to a float type where
1135 /// the receiving type cannot store all values from the original type without
1136 /// rounding errors. This possible rounding is to be expected, so this lint is
1137 /// `Allow` by default.
1139 /// Basically, this warns on casting any integer with 32 or more bits to `f32`
1140 /// or any 64-bit integer to `f64`.
1142 /// **Why is this bad?** It's not bad at all. But in some applications it can be
1143 /// helpful to know where precision loss can take place. This lint can help find
1144 /// those places in the code.
1146 /// **Known problems:** None.
1150 /// let x = u64::MAX;
1153 pub CAST_PRECISION_LOSS,
1155 "casts that cause loss of precision, e.g., `x as f32` where `x: u64`"
1158 declare_clippy_lint! {
1159 /// **What it does:** Checks for casts from a signed to an unsigned numerical
1160 /// type. In this case, negative values wrap around to large positive values,
1161 /// which can be quite surprising in practice. However, as the cast works as
1162 /// defined, this lint is `Allow` by default.
1164 /// **Why is this bad?** Possibly surprising results. You can activate this lint
1165 /// as a one-time check to see where numerical wrapping can arise.
1167 /// **Known problems:** None.
1172 /// y as u128; // will return 18446744073709551615
1176 "casts from signed types to unsigned types, e.g., `x as u32` where `x: i32`"
1179 declare_clippy_lint! {
1180 /// **What it does:** Checks for casts between numerical types that may
1181 /// truncate large values. This is expected behavior, so the cast is `Allow` by
1184 /// **Why is this bad?** In some problem domains, it is good practice to avoid
1185 /// truncation. This lint can be activated to help assess where additional
1186 /// checks could be beneficial.
1188 /// **Known problems:** None.
1192 /// fn as_u8(x: u64) -> u8 {
1196 pub CAST_POSSIBLE_TRUNCATION,
1198 "casts that may cause truncation of the value, e.g., `x as u8` where `x: u32`, or `x as i32` where `x: f32`"
1201 declare_clippy_lint! {
1202 /// **What it does:** Checks for casts from an unsigned type to a signed type of
1203 /// the same size. Performing such a cast is a 'no-op' for the compiler,
1204 /// i.e., nothing is changed at the bit level, and the binary representation of
1205 /// the value is reinterpreted. This can cause wrapping if the value is too big
1206 /// for the target signed type. However, the cast works as defined, so this lint
1207 /// is `Allow` by default.
1209 /// **Why is this bad?** While such a cast is not bad in itself, the results can
1210 /// be surprising when this is not the intended behavior, as demonstrated by the
1213 /// **Known problems:** None.
1217 /// u32::MAX as i32; // will yield a value of `-1`
1219 pub CAST_POSSIBLE_WRAP,
1221 "casts that may cause wrapping around the value, e.g., `x as i32` where `x: u32` and `x > i32::MAX`"
1224 declare_clippy_lint! {
1225 /// **What it does:** Checks for casts between numerical types that may
1226 /// be replaced by safe conversion functions.
1228 /// **Why is this bad?** Rust's `as` keyword will perform many kinds of
1229 /// conversions, including silently lossy conversions. Conversion functions such
1230 /// as `i32::from` will only perform lossless conversions. Using the conversion
1231 /// functions prevents conversions from turning into silent lossy conversions if
1232 /// the types of the input expressions ever change, and make it easier for
1233 /// people reading the code to know that the conversion is lossless.
1235 /// **Known problems:** None.
1239 /// fn as_u64(x: u8) -> u64 {
1244 /// Using `::from` would look like this:
1247 /// fn as_u64(x: u8) -> u64 {
1253 "casts using `as` that are known to be lossless, e.g., `x as u64` where `x: u8`"
1256 declare_clippy_lint! {
1257 /// **What it does:** Checks for casts to the same type, casts of int literals to integer types
1258 /// and casts of float literals to float types.
1260 /// **Why is this bad?** It's just unnecessary.
1262 /// **Known problems:** None.
1266 /// let _ = 2i32 as i32;
1267 /// let _ = 0.5 as f32;
1274 /// let _ = 0.5_f32;
1276 pub UNNECESSARY_CAST,
1278 "cast to the same type, e.g., `x as i32` where `x: i32`"
1281 declare_clippy_lint! {
1282 /// **What it does:** Checks for casts from a less-strictly-aligned pointer to a
1283 /// more-strictly-aligned pointer
1285 /// **Why is this bad?** Dereferencing the resulting pointer may be undefined
1288 /// **Known problems:** Using `std::ptr::read_unaligned` and `std::ptr::write_unaligned` or similar
1289 /// on the resulting pointer is fine. Is over-zealous: Casts with manual alignment checks or casts like
1290 /// u64-> u8 -> u16 can be fine. Miri is able to do a more in-depth analysis.
1294 /// let _ = (&1u8 as *const u8) as *const u16;
1295 /// let _ = (&mut 1u8 as *mut u8) as *mut u16;
1297 pub CAST_PTR_ALIGNMENT,
1299 "cast from a pointer to a more-strictly-aligned pointer"
1302 declare_clippy_lint! {
1303 /// **What it does:** Checks for casts of function pointers to something other than usize
1305 /// **Why is this bad?**
1306 /// Casting a function pointer to anything other than usize/isize is not portable across
1307 /// architectures, because you end up losing bits if the target type is too small or end up with a
1308 /// bunch of extra bits that waste space and add more instructions to the final binary than
1309 /// strictly necessary for the problem
1311 /// Casting to isize also doesn't make sense since there are no signed addresses.
1317 /// fn fun() -> i32 { 1 }
1318 /// let a = fun as i64;
1321 /// fn fun2() -> i32 { 1 }
1322 /// let a = fun2 as usize;
1324 pub FN_TO_NUMERIC_CAST,
1326 "casting a function pointer to a numeric type other than usize"
1329 declare_clippy_lint! {
1330 /// **What it does:** Checks for casts of a function pointer to a numeric type not wide enough to
1333 /// **Why is this bad?**
1334 /// Such a cast discards some bits of the function's address. If this is intended, it would be more
1335 /// clearly expressed by casting to usize first, then casting the usize to the intended type (with
1336 /// a comment) to perform the truncation.
1342 /// fn fn1() -> i16 {
1345 /// let _ = fn1 as i32;
1347 /// // Better: Cast to usize first, then comment with the reason for the truncation
1348 /// fn fn2() -> i16 {
1351 /// let fn_ptr = fn2 as usize;
1352 /// let fn_ptr_truncated = fn_ptr as i32;
1354 pub FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1356 "casting a function pointer to a numeric type not wide enough to store the address"
1359 /// Returns the size in bits of an integral type.
1360 /// Will return 0 if the type is not an int or uint variant
1361 fn int_ty_to_nbits(typ: Ty<'_>, tcx: TyCtxt<'_>) -> u64 {
1363 ty::Int(i) => match i {
1364 IntTy::Isize => tcx.data_layout.pointer_size.bits(),
1371 ty::Uint(i) => match i {
1372 UintTy::Usize => tcx.data_layout.pointer_size.bits(),
1377 UintTy::U128 => 128,
1383 fn is_isize_or_usize(typ: Ty<'_>) -> bool {
1384 matches!(typ.kind(), ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
1387 fn span_precision_loss_lint(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to_f64: bool) {
1388 let mantissa_nbits = if cast_to_f64 { 52 } else { 23 };
1389 let arch_dependent = is_isize_or_usize(cast_from) && cast_to_f64;
1390 let arch_dependent_str = "on targets with 64-bit wide pointers ";
1391 let from_nbits_str = if arch_dependent {
1393 } else if is_isize_or_usize(cast_from) {
1394 "32 or 64".to_owned()
1396 int_ty_to_nbits(cast_from, cx.tcx).to_string()
1400 CAST_PRECISION_LOSS,
1403 "casting `{0}` to `{1}` causes a loss of precision {2}(`{0}` is {3} bits wide, \
1404 but `{1}`'s mantissa is only {4} bits wide)",
1406 if cast_to_f64 { "f64" } else { "f32" },
1407 if arch_dependent { arch_dependent_str } else { "" },
1414 fn should_strip_parens(op: &Expr<'_>, snip: &str) -> bool {
1415 if let ExprKind::Binary(_, _, _) = op.kind {
1416 if snip.starts_with('(') && snip.ends_with(')') {
1423 fn span_lossless_lint(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1424 // Do not suggest using From in consts/statics until it is valid to do so (see #2267).
1425 if in_constant(cx, expr.hir_id) {
1428 // The suggestion is to use a function call, so if the original expression
1429 // has parens on the outside, they are no longer needed.
1430 let mut applicability = Applicability::MachineApplicable;
1431 let opt = snippet_opt(cx, op.span);
1432 let sugg = opt.as_ref().map_or_else(
1434 applicability = Applicability::HasPlaceholders;
1438 if should_strip_parens(op, snip) {
1439 &snip[1..snip.len() - 1]
1451 "casting `{}` to `{}` may become silently lossy if you later change the type",
1455 format!("{}::from({})", cast_to, sugg),
1466 fn check_loss_of_sign(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1467 if !cast_from.is_signed() || cast_to.is_signed() {
1471 // don't lint for positive constants
1472 let const_val = constant(cx, &cx.typeck_results(), op);
1474 if let Some((Constant::Int(n), _)) = const_val;
1475 if let ty::Int(ity) = *cast_from.kind();
1476 if sext(cx.tcx, n, ity) >= 0;
1482 // don't lint for the result of methods that always return non-negative values
1483 if let ExprKind::MethodCall(ref path, _, _, _) = op.kind {
1484 let mut method_name = path.ident.name.as_str();
1485 let allowed_methods = ["abs", "checked_abs", "rem_euclid", "checked_rem_euclid"];
1488 if method_name == "unwrap";
1489 if let Some(arglist) = method_chain_args(op, &["unwrap"]);
1490 if let ExprKind::MethodCall(ref inner_path, _, _, _) = &arglist[0][0].kind;
1492 method_name = inner_path.ident.name.as_str();
1496 if allowed_methods.iter().any(|&name| method_name == name) {
1506 "casting `{}` to `{}` may lose the sign of the value",
1512 fn check_truncation_and_wrapping(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1513 let arch_64_suffix = " on targets with 64-bit wide pointers";
1514 let arch_32_suffix = " on targets with 32-bit wide pointers";
1515 let cast_unsigned_to_signed = !cast_from.is_signed() && cast_to.is_signed();
1516 let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1517 let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1518 let (span_truncation, suffix_truncation, span_wrap, suffix_wrap) =
1519 match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
1520 (true, true) | (false, false) => (
1521 to_nbits < from_nbits,
1523 to_nbits == from_nbits && cast_unsigned_to_signed,
1533 to_nbits <= 32 && cast_unsigned_to_signed,
1539 cast_unsigned_to_signed,
1540 if from_nbits == 64 {
1547 if span_truncation {
1550 CAST_POSSIBLE_TRUNCATION,
1553 "casting `{}` to `{}` may truncate the value{}",
1556 match suffix_truncation {
1557 ArchSuffix::_32 => arch_32_suffix,
1558 ArchSuffix::_64 => arch_64_suffix,
1559 ArchSuffix::None => "",
1570 "casting `{}` to `{}` may wrap around the value{}",
1574 ArchSuffix::_32 => arch_32_suffix,
1575 ArchSuffix::_64 => arch_64_suffix,
1576 ArchSuffix::None => "",
1583 fn check_lossless(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1584 let cast_signed_to_unsigned = cast_from.is_signed() && !cast_to.is_signed();
1585 let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1586 let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1587 if !is_isize_or_usize(cast_from) && !is_isize_or_usize(cast_to) && from_nbits < to_nbits && !cast_signed_to_unsigned
1589 span_lossless_lint(cx, expr, op, cast_from, cast_to);
1593 declare_lint_pass!(Casts => [
1594 CAST_PRECISION_LOSS,
1596 CAST_POSSIBLE_TRUNCATION,
1602 FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1605 // Check if the given type is either `core::ffi::c_void` or
1606 // one of the platform specific `libc::<platform>::c_void` of libc.
1607 fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
1608 if let ty::Adt(adt, _) = ty.kind() {
1609 let names = cx.get_def_path(adt.did);
1611 if names.is_empty() {
1614 if names[0] == sym::libc || names[0] == sym::core && *names.last().unwrap() == sym!(c_void) {
1621 /// Returns the mantissa bits wide of a fp type.
1622 /// Will return 0 if the type is not a fp
1623 fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
1625 ty::Float(FloatTy::F32) => 23,
1626 ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
1631 impl<'tcx> LateLintPass<'tcx> for Casts {
1632 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1633 if expr.span.from_expansion() {
1636 if let ExprKind::Cast(ref ex, cast_to) = expr.kind {
1637 if let TyKind::Path(QPath::Resolved(_, path)) = cast_to.kind {
1638 if let Res::Def(_, def_id) = path.res {
1639 if cx.tcx.has_attr(def_id, sym::cfg) || cx.tcx.has_attr(def_id, sym::cfg_attr) {
1644 let (cast_from, cast_to) = (cx.typeck_results().expr_ty(ex), cx.typeck_results().expr_ty(expr));
1645 lint_fn_to_numeric_cast(cx, expr, ex, cast_from, cast_to);
1646 if let Some(lit) = get_numeric_literal(ex) {
1647 let literal_str = snippet_opt(cx, ex.span).unwrap_or_default();
1650 if let LitKind::Int(n, _) = lit.node;
1651 if let Some(src) = snippet_opt(cx, lit.span);
1652 if cast_to.is_floating_point();
1653 if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node);
1654 let from_nbits = 128 - n.leading_zeros();
1655 let to_nbits = fp_ty_mantissa_nbits(cast_to);
1656 if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
1658 let literal_str = if is_unary_neg(ex) { format!("-{}", num_lit.integer) } else { num_lit.integer.into() };
1659 show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1665 LitKind::Int(_, LitIntType::Unsuffixed) if cast_to.is_integral() => {
1666 show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1668 LitKind::Float(_, LitFloatType::Unsuffixed) if cast_to.is_floating_point() => {
1669 show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1671 LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
1673 if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
1679 "casting to the same type is unnecessary (`{}` -> `{}`)",
1687 if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx.sess(), expr.span) {
1688 lint_numeric_casts(cx, expr, ex, cast_from, cast_to);
1691 lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
1696 fn is_unary_neg(expr: &Expr<'_>) -> bool {
1697 matches!(expr.kind, ExprKind::Unary(UnOp::UnNeg, _))
1700 fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
1702 ExprKind::Lit(ref lit) => Some(lit),
1703 ExprKind::Unary(UnOp::UnNeg, e) => {
1704 if let ExprKind::Lit(ref lit) = e.kind {
1714 fn show_unnecessary_cast(cx: &LateContext<'_>, expr: &Expr<'_>, literal_str: &str, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1715 let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
1720 &format!("casting {} literal to `{}` is unnecessary", literal_kind_name, cast_to),
1722 format!("{}_{}", literal_str.trim_end_matches('.'), cast_to),
1723 Applicability::MachineApplicable,
1727 fn lint_numeric_casts<'tcx>(
1728 cx: &LateContext<'tcx>,
1730 cast_expr: &Expr<'_>,
1731 cast_from: Ty<'tcx>,
1734 match (cast_from.is_integral(), cast_to.is_integral()) {
1736 let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1737 let to_nbits = if let ty::Float(FloatTy::F32) = cast_to.kind() {
1742 if is_isize_or_usize(cast_from) || from_nbits >= to_nbits {
1743 span_precision_loss_lint(cx, expr, cast_from, to_nbits == 64);
1745 if from_nbits < to_nbits {
1746 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1752 CAST_POSSIBLE_TRUNCATION,
1754 &format!("casting `{}` to `{}` may truncate the value", cast_from, cast_to),
1756 if !cast_to.is_signed() {
1762 "casting `{}` to `{}` may lose the sign of the value",
1769 check_loss_of_sign(cx, expr, cast_expr, cast_from, cast_to);
1770 check_truncation_and_wrapping(cx, expr, cast_from, cast_to);
1771 check_lossless(cx, expr, cast_expr, cast_from, cast_to);
1774 if let (&ty::Float(FloatTy::F64), &ty::Float(FloatTy::F32)) = (&cast_from.kind(), &cast_to.kind()) {
1777 CAST_POSSIBLE_TRUNCATION,
1779 "casting `f64` to `f32` may truncate the value",
1782 if let (&ty::Float(FloatTy::F32), &ty::Float(FloatTy::F64)) = (&cast_from.kind(), &cast_to.kind()) {
1783 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1789 fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
1791 if let ty::RawPtr(from_ptr_ty) = &cast_from.kind();
1792 if let ty::RawPtr(to_ptr_ty) = &cast_to.kind();
1793 if let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty);
1794 if let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty);
1795 if from_layout.align.abi < to_layout.align.abi;
1796 // with c_void, we inherently need to trust the user
1797 if !is_c_void(cx, from_ptr_ty.ty);
1798 // when casting from a ZST, we don't know enough to properly lint
1799 if !from_layout.is_zst();
1806 "casting from `{}` to a more-strictly-aligned pointer (`{}`) ({} < {} bytes)",
1809 from_layout.align.abi.bytes(),
1810 to_layout.align.abi.bytes(),
1817 fn lint_fn_to_numeric_cast(
1818 cx: &LateContext<'_>,
1820 cast_expr: &Expr<'_>,
1824 // We only want to check casts to `ty::Uint` or `ty::Int`
1825 match cast_to.kind() {
1826 ty::Uint(_) | ty::Int(..) => { /* continue on */ },
1829 match cast_from.kind() {
1830 ty::FnDef(..) | ty::FnPtr(_) => {
1831 let mut applicability = Applicability::MaybeIncorrect;
1832 let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
1834 let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1835 if to_nbits < cx.tcx.data_layout.pointer_size.bits() {
1838 FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1841 "casting function pointer `{}` to `{}`, which truncates the value",
1842 from_snippet, cast_to
1845 format!("{} as usize", from_snippet),
1848 } else if *cast_to.kind() != ty::Uint(UintTy::Usize) {
1853 &format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
1855 format!("{} as usize", from_snippet),
1864 declare_clippy_lint! {
1865 /// **What it does:** Checks for types used in structs, parameters and `let`
1866 /// declarations above a certain complexity threshold.
1868 /// **Why is this bad?** Too complex types make the code less readable. Consider
1869 /// using a `type` definition to simplify them.
1871 /// **Known problems:** None.
1875 /// # use std::rc::Rc;
1877 /// inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>>,
1880 pub TYPE_COMPLEXITY,
1882 "usage of very complex types that might be better factored into `type` definitions"
1885 pub struct TypeComplexity {
1889 impl TypeComplexity {
1891 pub fn new(threshold: u64) -> Self {
1896 impl_lint_pass!(TypeComplexity => [TYPE_COMPLEXITY]);
1898 impl<'tcx> LateLintPass<'tcx> for TypeComplexity {
1901 cx: &LateContext<'tcx>,
1903 decl: &'tcx FnDecl<'_>,
1908 self.check_fndecl(cx, decl);
1911 fn check_struct_field(&mut self, cx: &LateContext<'tcx>, field: &'tcx hir::StructField<'_>) {
1912 // enum variants are also struct fields now
1913 self.check_type(cx, &field.ty);
1916 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
1918 ItemKind::Static(ref ty, _, _) | ItemKind::Const(ref ty, _) => self.check_type(cx, ty),
1919 // functions, enums, structs, impls and traits are covered
1924 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
1926 TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_type(cx, ty),
1927 TraitItemKind::Fn(FnSig { ref decl, .. }, TraitFn::Required(_)) => self.check_fndecl(cx, decl),
1928 // methods with default impl are covered by check_fn
1933 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
1935 ImplItemKind::Const(ref ty, _) | ImplItemKind::TyAlias(ref ty) => self.check_type(cx, ty),
1936 // methods are covered by check_fn
1941 fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'_>) {
1942 if let Some(ref ty) = local.ty {
1943 self.check_type(cx, ty);
1948 impl<'tcx> TypeComplexity {
1949 fn check_fndecl(&self, cx: &LateContext<'tcx>, decl: &'tcx FnDecl<'_>) {
1950 for arg in decl.inputs {
1951 self.check_type(cx, arg);
1953 if let FnRetTy::Return(ref ty) = decl.output {
1954 self.check_type(cx, ty);
1958 fn check_type(&self, cx: &LateContext<'_>, ty: &hir::Ty<'_>) {
1959 if ty.span.from_expansion() {
1963 let mut visitor = TypeComplexityVisitor { score: 0, nest: 1 };
1964 visitor.visit_ty(ty);
1968 if score > self.threshold {
1973 "very complex type used. Consider factoring parts into `type` definitions",
1979 /// Walks a type and assigns a complexity score to it.
1980 struct TypeComplexityVisitor {
1981 /// total complexity score of the type
1983 /// current nesting level
1987 impl<'tcx> Visitor<'tcx> for TypeComplexityVisitor {
1988 type Map = Map<'tcx>;
1990 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
1991 let (add_score, sub_nest) = match ty.kind {
1992 // _, &x and *x have only small overhead; don't mess with nesting level
1993 TyKind::Infer | TyKind::Ptr(..) | TyKind::Rptr(..) => (1, 0),
1995 // the "normal" components of a type: named types, arrays/tuples
1996 TyKind::Path(..) | TyKind::Slice(..) | TyKind::Tup(..) | TyKind::Array(..) => (10 * self.nest, 1),
1998 // function types bring a lot of overhead
1999 TyKind::BareFn(ref bare) if bare.abi == Abi::Rust => (50 * self.nest, 1),
2001 TyKind::TraitObject(ref param_bounds, _) => {
2002 let has_lifetime_parameters = param_bounds.iter().any(|bound| {
2004 .bound_generic_params
2006 .any(|gen| matches!(gen.kind, GenericParamKind::Lifetime { .. }))
2008 if has_lifetime_parameters {
2009 // complex trait bounds like A<'a, 'b>
2012 // simple trait bounds like A + B
2019 self.score += add_score;
2020 self.nest += sub_nest;
2022 self.nest -= sub_nest;
2024 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2025 NestedVisitorMap::None
2029 declare_clippy_lint! {
2030 /// **What it does:** Checks for expressions where a character literal is cast
2031 /// to `u8` and suggests using a byte literal instead.
2033 /// **Why is this bad?** In general, casting values to smaller types is
2034 /// error-prone and should be avoided where possible. In the particular case of
2035 /// converting a character literal to u8, it is easy to avoid by just using a
2036 /// byte literal instead. As an added bonus, `b'a'` is even slightly shorter
2037 /// than `'a' as u8`.
2039 /// **Known problems:** None.
2046 /// A better version, using the byte literal:
2053 "casting a character literal to `u8` truncates"
2056 declare_lint_pass!(CharLitAsU8 => [CHAR_LIT_AS_U8]);
2058 impl<'tcx> LateLintPass<'tcx> for CharLitAsU8 {
2059 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2061 if !expr.span.from_expansion();
2062 if let ExprKind::Cast(e, _) = &expr.kind;
2063 if let ExprKind::Lit(l) = &e.kind;
2064 if let LitKind::Char(c) = l.node;
2065 if ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(expr).kind();
2067 let mut applicability = Applicability::MachineApplicable;
2068 let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
2074 "casting a character literal to `u8` truncates",
2076 diag.note("`char` is four bytes wide, but `u8` is a single byte");
2079 diag.span_suggestion(
2081 "use a byte literal instead",
2082 format!("b{}", snippet),
2092 declare_clippy_lint! {
2093 /// **What it does:** Checks for comparisons where one side of the relation is
2094 /// either the minimum or maximum value for its type and warns if it involves a
2095 /// case that is always true or always false. Only integer and boolean types are
2098 /// **Why is this bad?** An expression like `min <= x` may misleadingly imply
2099 /// that it is possible for `x` to be less than the minimum. Expressions like
2100 /// `max < x` are probably mistakes.
2102 /// **Known problems:** For `usize` the size of the current compile target will
2103 /// be assumed (e.g., 64 bits on 64 bit systems). This means code that uses such
2104 /// a comparison to detect target pointer width will trigger this lint. One can
2105 /// use `mem::sizeof` and compare its value or conditional compilation
2107 /// like `#[cfg(target_pointer_width = "64")] ..` instead.
2112 /// let vec: Vec<isize> = Vec::new();
2113 /// if vec.len() <= 0 {}
2114 /// if 100 > i32::MAX {}
2116 pub ABSURD_EXTREME_COMPARISONS,
2118 "a comparison with a maximum or minimum value that is always true or false"
2121 declare_lint_pass!(AbsurdExtremeComparisons => [ABSURD_EXTREME_COMPARISONS]);
2128 struct ExtremeExpr<'a> {
2133 enum AbsurdComparisonResult {
2136 InequalityImpossible,
2139 fn is_cast_between_fixed_and_target<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
2140 if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
2141 let precast_ty = cx.typeck_results().expr_ty(cast_exp);
2142 let cast_ty = cx.typeck_results().expr_ty(expr);
2144 return is_isize_or_usize(precast_ty) != is_isize_or_usize(cast_ty);
2150 fn detect_absurd_comparison<'tcx>(
2151 cx: &LateContext<'tcx>,
2153 lhs: &'tcx Expr<'_>,
2154 rhs: &'tcx Expr<'_>,
2155 ) -> Option<(ExtremeExpr<'tcx>, AbsurdComparisonResult)> {
2156 use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
2157 use crate::types::ExtremeType::{Maximum, Minimum};
2158 use crate::utils::comparisons::{normalize_comparison, Rel};
2160 // absurd comparison only makes sense on primitive types
2161 // primitive types don't implement comparison operators with each other
2162 if cx.typeck_results().expr_ty(lhs) != cx.typeck_results().expr_ty(rhs) {
2166 // comparisons between fix sized types and target sized types are considered unanalyzable
2167 if is_cast_between_fixed_and_target(cx, lhs) || is_cast_between_fixed_and_target(cx, rhs) {
2171 let (rel, normalized_lhs, normalized_rhs) = normalize_comparison(op, lhs, rhs)?;
2173 let lx = detect_extreme_expr(cx, normalized_lhs);
2174 let rx = detect_extreme_expr(cx, normalized_rhs);
2179 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, AlwaysFalse), // max < x
2180 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, AlwaysFalse), // x < min
2186 (Some(l @ ExtremeExpr { which: Minimum, .. }), _) => (l, AlwaysTrue), // min <= x
2187 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, InequalityImpossible), // max <= x
2188 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, InequalityImpossible), // x <= min
2189 (_, Some(r @ ExtremeExpr { which: Maximum, .. })) => (r, AlwaysTrue), // x <= max
2193 Rel::Ne | Rel::Eq => return None,
2197 fn detect_extreme_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<ExtremeExpr<'tcx>> {
2198 use crate::types::ExtremeType::{Maximum, Minimum};
2200 let ty = cx.typeck_results().expr_ty(expr);
2202 let cv = constant(cx, cx.typeck_results(), expr)?.0;
2204 let which = match (ty.kind(), cv) {
2205 (&ty::Bool, Constant::Bool(false)) | (&ty::Uint(_), Constant::Int(0)) => Minimum,
2206 (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MIN >> (128 - int_bits(cx.tcx, ity)), ity) => {
2210 (&ty::Bool, Constant::Bool(true)) => Maximum,
2211 (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MAX >> (128 - int_bits(cx.tcx, ity)), ity) => {
2214 (&ty::Uint(uty), Constant::Int(i)) if clip(cx.tcx, u128::MAX, uty) == i => Maximum,
2218 Some(ExtremeExpr { which, expr })
2221 impl<'tcx> LateLintPass<'tcx> for AbsurdExtremeComparisons {
2222 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2223 use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
2224 use crate::types::ExtremeType::{Maximum, Minimum};
2226 if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
2227 if let Some((culprit, result)) = detect_absurd_comparison(cx, cmp.node, lhs, rhs) {
2228 if !expr.span.from_expansion() {
2229 let msg = "this comparison involving the minimum or maximum element for this \
2230 type contains a case that is always true or always false";
2232 let conclusion = match result {
2233 AlwaysFalse => "this comparison is always false".to_owned(),
2234 AlwaysTrue => "this comparison is always true".to_owned(),
2235 InequalityImpossible => format!(
2236 "the case where the two sides are not equal never occurs, consider using `{} == {}` \
2238 snippet(cx, lhs.span, "lhs"),
2239 snippet(cx, rhs.span, "rhs")
2244 "because `{}` is the {} value for this type, {}",
2245 snippet(cx, culprit.expr.span, "x"),
2246 match culprit.which {
2247 Minimum => "minimum",
2248 Maximum => "maximum",
2253 span_lint_and_help(cx, ABSURD_EXTREME_COMPARISONS, expr.span, msg, None, &help);
2260 declare_clippy_lint! {
2261 /// **What it does:** Checks for comparisons where the relation is always either
2262 /// true or false, but where one side has been upcast so that the comparison is
2263 /// necessary. Only integer types are checked.
2265 /// **Why is this bad?** An expression like `let x : u8 = ...; (x as u32) > 300`
2266 /// will mistakenly imply that it is possible for `x` to be outside the range of
2269 /// **Known problems:**
2270 /// https://github.com/rust-lang/rust-clippy/issues/886
2275 /// (x as u32) > 300;
2277 pub INVALID_UPCAST_COMPARISONS,
2279 "a comparison involving an upcast which is always true or false"
2282 declare_lint_pass!(InvalidUpcastComparisons => [INVALID_UPCAST_COMPARISONS]);
2284 #[derive(Copy, Clone, Debug, Eq)]
2291 #[allow(clippy::cast_sign_loss)]
2293 fn cmp_s_u(s: i128, u: u128) -> Ordering {
2296 } else if u > (i128::MAX as u128) {
2304 impl PartialEq for FullInt {
2306 fn eq(&self, other: &Self) -> bool {
2307 self.partial_cmp(other).expect("`partial_cmp` only returns `Some(_)`") == Ordering::Equal
2311 impl PartialOrd for FullInt {
2313 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2314 Some(match (self, other) {
2315 (&Self::S(s), &Self::S(o)) => s.cmp(&o),
2316 (&Self::U(s), &Self::U(o)) => s.cmp(&o),
2317 (&Self::S(s), &Self::U(o)) => Self::cmp_s_u(s, o),
2318 (&Self::U(s), &Self::S(o)) => Self::cmp_s_u(o, s).reverse(),
2323 impl Ord for FullInt {
2325 fn cmp(&self, other: &Self) -> Ordering {
2326 self.partial_cmp(other)
2327 .expect("`partial_cmp` for FullInt can never return `None`")
2331 fn numeric_cast_precast_bounds<'a>(cx: &LateContext<'_>, expr: &'a Expr<'_>) -> Option<(FullInt, FullInt)> {
2332 if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
2333 let pre_cast_ty = cx.typeck_results().expr_ty(cast_exp);
2334 let cast_ty = cx.typeck_results().expr_ty(expr);
2335 // if it's a cast from i32 to u32 wrapping will invalidate all these checks
2336 if cx.layout_of(pre_cast_ty).ok().map(|l| l.size) == cx.layout_of(cast_ty).ok().map(|l| l.size) {
2339 match pre_cast_ty.kind() {
2340 ty::Int(int_ty) => Some(match int_ty {
2341 IntTy::I8 => (FullInt::S(i128::from(i8::MIN)), FullInt::S(i128::from(i8::MAX))),
2342 IntTy::I16 => (FullInt::S(i128::from(i16::MIN)), FullInt::S(i128::from(i16::MAX))),
2343 IntTy::I32 => (FullInt::S(i128::from(i32::MIN)), FullInt::S(i128::from(i32::MAX))),
2344 IntTy::I64 => (FullInt::S(i128::from(i64::MIN)), FullInt::S(i128::from(i64::MAX))),
2345 IntTy::I128 => (FullInt::S(i128::MIN), FullInt::S(i128::MAX)),
2346 IntTy::Isize => (FullInt::S(isize::MIN as i128), FullInt::S(isize::MAX as i128)),
2348 ty::Uint(uint_ty) => Some(match uint_ty {
2349 UintTy::U8 => (FullInt::U(u128::from(u8::MIN)), FullInt::U(u128::from(u8::MAX))),
2350 UintTy::U16 => (FullInt::U(u128::from(u16::MIN)), FullInt::U(u128::from(u16::MAX))),
2351 UintTy::U32 => (FullInt::U(u128::from(u32::MIN)), FullInt::U(u128::from(u32::MAX))),
2352 UintTy::U64 => (FullInt::U(u128::from(u64::MIN)), FullInt::U(u128::from(u64::MAX))),
2353 UintTy::U128 => (FullInt::U(u128::MIN), FullInt::U(u128::MAX)),
2354 UintTy::Usize => (FullInt::U(usize::MIN as u128), FullInt::U(usize::MAX as u128)),
2363 fn node_as_const_fullint<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<FullInt> {
2364 let val = constant(cx, cx.typeck_results(), expr)?.0;
2365 if let Constant::Int(const_int) = val {
2366 match *cx.typeck_results().expr_ty(expr).kind() {
2367 ty::Int(ity) => Some(FullInt::S(sext(cx.tcx, const_int, ity))),
2368 ty::Uint(_) => Some(FullInt::U(const_int)),
2376 fn err_upcast_comparison(cx: &LateContext<'_>, span: Span, expr: &Expr<'_>, always: bool) {
2377 if let ExprKind::Cast(ref cast_val, _) = expr.kind {
2380 INVALID_UPCAST_COMPARISONS,
2383 "because of the numeric bounds on `{}` prior to casting, this expression is always {}",
2384 snippet(cx, cast_val.span, "the expression"),
2385 if always { "true" } else { "false" },
2391 fn upcast_comparison_bounds_err<'tcx>(
2392 cx: &LateContext<'tcx>,
2394 rel: comparisons::Rel,
2395 lhs_bounds: Option<(FullInt, FullInt)>,
2396 lhs: &'tcx Expr<'_>,
2397 rhs: &'tcx Expr<'_>,
2400 use crate::utils::comparisons::Rel;
2402 if let Some((lb, ub)) = lhs_bounds {
2403 if let Some(norm_rhs_val) = node_as_const_fullint(cx, rhs) {
2404 if rel == Rel::Eq || rel == Rel::Ne {
2405 if norm_rhs_val < lb || norm_rhs_val > ub {
2406 err_upcast_comparison(cx, span, lhs, rel == Rel::Ne);
2408 } else if match rel {
2423 Rel::Eq | Rel::Ne => unreachable!(),
2425 err_upcast_comparison(cx, span, lhs, true)
2426 } else if match rel {
2441 Rel::Eq | Rel::Ne => unreachable!(),
2443 err_upcast_comparison(cx, span, lhs, false)
2449 impl<'tcx> LateLintPass<'tcx> for InvalidUpcastComparisons {
2450 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2451 if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
2452 let normalized = comparisons::normalize_comparison(cmp.node, lhs, rhs);
2453 let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
2459 let lhs_bounds = numeric_cast_precast_bounds(cx, normalized_lhs);
2460 let rhs_bounds = numeric_cast_precast_bounds(cx, normalized_rhs);
2462 upcast_comparison_bounds_err(cx, expr.span, rel, lhs_bounds, normalized_lhs, normalized_rhs, false);
2463 upcast_comparison_bounds_err(cx, expr.span, rel, rhs_bounds, normalized_rhs, normalized_lhs, true);
2468 declare_clippy_lint! {
2469 /// **What it does:** Checks for public `impl` or `fn` missing generalization
2470 /// over different hashers and implicitly defaulting to the default hashing
2471 /// algorithm (`SipHash`).
2473 /// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
2476 /// **Known problems:** Suggestions for replacing constructors can contain
2477 /// false-positives. Also applying suggestions can require modification of other
2478 /// pieces of code, possibly including external crates.
2482 /// # use std::collections::HashMap;
2483 /// # use std::hash::{Hash, BuildHasher};
2484 /// # trait Serialize {};
2485 /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
2487 /// pub fn foo(map: &mut HashMap<i32, i32>) { }
2489 /// could be rewritten as
2491 /// # use std::collections::HashMap;
2492 /// # use std::hash::{Hash, BuildHasher};
2493 /// # trait Serialize {};
2494 /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
2496 /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
2498 pub IMPLICIT_HASHER,
2500 "missing generalization over different hashers"
2503 declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
2505 impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
2506 #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
2507 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
2508 use rustc_span::BytePos;
2510 fn suggestion<'tcx>(
2511 cx: &LateContext<'tcx>,
2512 diag: &mut DiagnosticBuilder<'_>,
2513 generics_span: Span,
2514 generics_suggestion_span: Span,
2515 target: &ImplicitHasherType<'_>,
2516 vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
2518 let generics_snip = snippet(cx, generics_span, "");
2520 let generics_snip = if generics_snip.is_empty() {
2523 &generics_snip[1..generics_snip.len() - 1]
2528 "consider adding a type parameter",
2531 generics_suggestion_span,
2533 "<{}{}S: ::std::hash::BuildHasher{}>",
2535 if generics_snip.is_empty() { "" } else { ", " },
2536 if vis.suggestions.is_empty() {
2539 // request users to add `Default` bound so that generic constructors can be used
2546 format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
2551 if !vis.suggestions.is_empty() {
2552 multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
2556 if !cx.access_levels.is_exported(item.hir_id) {
2567 let mut vis = ImplicitHasherTypeVisitor::new(cx);
2570 for target in &vis.found {
2571 if differing_macro_contexts(item.span, target.span()) {
2575 let generics_suggestion_span = generics.span.substitute_dummy({
2576 let pos = snippet_opt(cx, item.span.until(target.span()))
2577 .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
2578 if let Some(pos) = pos {
2579 Span::new(pos, pos, item.span.data().ctxt)
2585 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2586 for item in items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
2587 ctr_vis.visit_impl_item(item);
2595 "impl for `{}` should be generalized over different hashers",
2599 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
2604 ItemKind::Fn(ref sig, ref generics, body_id) => {
2605 let body = cx.tcx.hir().body(body_id);
2607 for ty in sig.decl.inputs {
2608 let mut vis = ImplicitHasherTypeVisitor::new(cx);
2611 for target in &vis.found {
2612 if in_external_macro(cx.sess(), generics.span) {
2615 let generics_suggestion_span = generics.span.substitute_dummy({
2616 let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
2618 let i = snip.find("fn")?;
2619 Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
2621 .expect("failed to create span for type parameters");
2622 Span::new(pos, pos, item.span.data().ctxt)
2625 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2626 ctr_vis.visit_body(body);
2633 "parameter of type `{}` should be generalized over different hashers",
2637 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
2648 enum ImplicitHasherType<'tcx> {
2649 HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
2650 HashSet(Span, Ty<'tcx>, Cow<'static, str>),
2653 impl<'tcx> ImplicitHasherType<'tcx> {
2654 /// Checks that `ty` is a target type without a `BuildHasher`.
2655 fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
2656 if let TyKind::Path(QPath::Resolved(None, ref path)) = hir_ty.kind {
2657 let params: Vec<_> = path
2665 .filter_map(|arg| match arg {
2666 GenericArg::Type(ty) => Some(ty),
2670 let params_len = params.len();
2672 let ty = hir_ty_to_ty(cx.tcx, hir_ty);
2674 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) && params_len == 2 {
2675 Some(ImplicitHasherType::HashMap(
2678 snippet(cx, params[0].span, "K"),
2679 snippet(cx, params[1].span, "V"),
2681 } else if is_type_diagnostic_item(cx, ty, sym!(hashset_type)) && params_len == 1 {
2682 Some(ImplicitHasherType::HashSet(
2685 snippet(cx, params[0].span, "T"),
2695 fn type_name(&self) -> &'static str {
2697 ImplicitHasherType::HashMap(..) => "HashMap",
2698 ImplicitHasherType::HashSet(..) => "HashSet",
2702 fn type_arguments(&self) -> String {
2704 ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
2705 ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
2709 fn ty(&self) -> Ty<'tcx> {
2711 ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
2715 fn span(&self) -> Span {
2717 ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
2722 struct ImplicitHasherTypeVisitor<'a, 'tcx> {
2723 cx: &'a LateContext<'tcx>,
2724 found: Vec<ImplicitHasherType<'tcx>>,
2727 impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
2728 fn new(cx: &'a LateContext<'tcx>) -> Self {
2729 Self { cx, found: vec![] }
2733 impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
2734 type Map = Map<'tcx>;
2736 fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
2737 if let Some(target) = ImplicitHasherType::new(self.cx, t) {
2738 self.found.push(target);
2744 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2745 NestedVisitorMap::None
2749 /// Looks for default-hasher-dependent constructors like `HashMap::new`.
2750 struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2751 cx: &'a LateContext<'tcx>,
2752 maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
2753 target: &'b ImplicitHasherType<'tcx>,
2754 suggestions: BTreeMap<Span, String>,
2757 impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2758 fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
2761 maybe_typeck_results: cx.maybe_typeck_results(),
2763 suggestions: BTreeMap::new(),
2768 impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2769 type Map = Map<'tcx>;
2771 fn visit_body(&mut self, body: &'tcx Body<'_>) {
2772 let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
2773 walk_body(self, body);
2774 self.maybe_typeck_results = old_maybe_typeck_results;
2777 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
2779 if let ExprKind::Call(ref fun, ref args) = e.kind;
2780 if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
2781 if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
2783 if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
2787 if match_path(ty_path, &paths::HASHMAP) {
2788 if method.ident.name == sym::new {
2790 .insert(e.span, "HashMap::default()".to_string());
2791 } else if method.ident.name == sym!(with_capacity) {
2792 self.suggestions.insert(
2795 "HashMap::with_capacity_and_hasher({}, Default::default())",
2796 snippet(self.cx, args[0].span, "capacity"),
2800 } else if match_path(ty_path, &paths::HASHSET) {
2801 if method.ident.name == sym::new {
2803 .insert(e.span, "HashSet::default()".to_string());
2804 } else if method.ident.name == sym!(with_capacity) {
2805 self.suggestions.insert(
2808 "HashSet::with_capacity_and_hasher({}, Default::default())",
2809 snippet(self.cx, args[0].span, "capacity"),
2820 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2821 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2825 declare_clippy_lint! {
2826 /// **What it does:** Checks for casts of `&T` to `&mut T` anywhere in the code.
2828 /// **Why is this bad?** It’s basically guaranteed to be undefined behaviour.
2829 /// `UnsafeCell` is the only way to obtain aliasable data that is considered
2832 /// **Known problems:** None.
2838 /// *(r as *const _ as *mut _) += 1;
2843 /// Instead consider using interior mutability types.
2846 /// use std::cell::UnsafeCell;
2848 /// fn x(r: &UnsafeCell<i32>) {
2854 pub CAST_REF_TO_MUT,
2856 "a cast of reference to a mutable pointer"
2859 declare_lint_pass!(RefToMut => [CAST_REF_TO_MUT]);
2861 impl<'tcx> LateLintPass<'tcx> for RefToMut {
2862 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2864 if let ExprKind::Unary(UnOp::UnDeref, e) = &expr.kind;
2865 if let ExprKind::Cast(e, t) = &e.kind;
2866 if let TyKind::Ptr(MutTy { mutbl: Mutability::Mut, .. }) = t.kind;
2867 if let ExprKind::Cast(e, t) = &e.kind;
2868 if let TyKind::Ptr(MutTy { mutbl: Mutability::Not, .. }) = t.kind;
2869 if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind();
2875 "casting `&T` to `&mut T` may cause undefined behavior, consider instead using an `UnsafeCell`",