1 #![allow(rustc::default_hash_types)]
8 mod redundant_allocation;
13 use std::cmp::Ordering;
14 use std::collections::BTreeMap;
16 use if_chain::if_chain;
17 use rustc_errors::{Applicability, DiagnosticBuilder};
19 use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, FnKind, NestedVisitorMap, Visitor};
21 BinOpKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, FnSig, GenericArg, GenericParamKind, HirId, ImplItem,
22 ImplItemKind, Item, ItemKind, Local, MatchSource, MutTy, Node, QPath, Stmt, StmtKind, TraitFn, TraitItem,
23 TraitItemKind, TyKind,
25 use rustc_lint::{LateContext, LateLintPass, LintContext};
26 use rustc_middle::hir::map::Map;
27 use rustc_middle::lint::in_external_macro;
28 use rustc_middle::ty::{self, IntTy, Ty, TyS, TypeckResults, UintTy};
29 use rustc_session::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
30 use rustc_span::hygiene::{ExpnKind, MacroKind};
31 use rustc_span::source_map::Span;
32 use rustc_span::symbol::sym;
33 use rustc_target::abi::LayoutOf;
34 use rustc_target::spec::abi::Abi;
35 use rustc_typeck::hir_ty_to_ty;
37 use crate::consts::{constant, Constant};
38 use crate::utils::paths;
40 clip, comparisons, differing_macro_contexts, higher, indent_of, int_bits, is_isize_or_usize,
41 is_type_diagnostic_item, match_path, multispan_sugg, reindent_multiline, sext, snippet, snippet_opt,
42 snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_then, unsext,
45 declare_clippy_lint! {
46 /// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
47 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
49 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
50 /// the heap. So if you `Box` it, you just add another level of indirection
51 /// without any benefit whatsoever.
53 /// **Known problems:** None.
58 /// values: Box<Vec<Foo>>,
71 "usage of `Box<Vec<T>>`, vector elements are already on the heap"
74 declare_clippy_lint! {
75 /// **What it does:** Checks for use of `Vec<Box<T>>` where T: Sized anywhere in the code.
76 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
78 /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
79 /// the heap. So if you `Box` its contents, you just add another level of indirection.
81 /// **Known problems:** Vec<Box<T: Sized>> makes sense if T is a large type (see [#3530](https://github.com/rust-lang/rust-clippy/issues/3530),
87 /// values: Vec<Box<i32>>,
100 "usage of `Vec<Box<T>>` where T: Sized, vector elements are already on the heap"
103 declare_clippy_lint! {
104 /// **What it does:** Checks for use of `Option<Option<_>>` in function signatures and type
107 /// **Why is this bad?** `Option<_>` represents an optional value. `Option<Option<_>>`
108 /// represents an optional optional value which is logically the same thing as an optional
109 /// value but has an unneeded extra level of wrapping.
111 /// If you have a case where `Some(Some(_))`, `Some(None)` and `None` are distinct cases,
112 /// consider a custom `enum` instead, with clear names for each case.
114 /// **Known problems:** None.
118 /// fn get_data() -> Option<Option<u32>> {
126 /// pub enum Contents {
127 /// Data(Vec<u8>), // Was Some(Some(Vec<u8>))
128 /// NotYetFetched, // Was Some(None)
129 /// None, // Was None
132 /// fn get_data() -> Contents {
138 "usage of `Option<Option<T>>`"
141 declare_clippy_lint! {
142 /// **What it does:** Checks for usage of any `LinkedList`, suggesting to use a
143 /// `Vec` or a `VecDeque` (formerly called `RingBuf`).
145 /// **Why is this bad?** Gankro says:
147 /// > The TL;DR of `LinkedList` is that it's built on a massive amount of
148 /// pointers and indirection.
149 /// > It wastes memory, it has terrible cache locality, and is all-around slow.
151 /// > "only" amortized for push/pop, should be faster in the general case for
152 /// almost every possible
153 /// > workload, and isn't even amortized at all if you can predict the capacity
156 /// > `LinkedList`s are only really good if you're doing a lot of merging or
157 /// splitting of lists.
158 /// > This is because they can just mangle some pointers instead of actually
159 /// copying the data. Even
160 /// > if you're doing a lot of insertion in the middle of the list, `RingBuf`
161 /// can still be better
162 /// > because of how expensive it is to seek to the middle of a `LinkedList`.
164 /// **Known problems:** False positives – the instances where using a
165 /// `LinkedList` makes sense are few and far between, but they can still happen.
169 /// # use std::collections::LinkedList;
170 /// let x: LinkedList<usize> = LinkedList::new();
174 "usage of LinkedList, usually a vector is faster, or a more specialized data structure like a `VecDeque`"
177 declare_clippy_lint! {
178 /// **What it does:** Checks for use of `&Box<T>` anywhere in the code.
179 /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
181 /// **Why is this bad?** Any `&Box<T>` can also be a `&T`, which is more
184 /// **Known problems:** None.
188 /// fn foo(bar: &Box<T>) { ... }
194 /// fn foo(bar: &T) { ... }
198 "a borrow of a boxed type"
201 declare_clippy_lint! {
202 /// **What it does:** Checks for use of redundant allocations anywhere in the code.
204 /// **Why is this bad?** Expressions such as `Rc<&T>`, `Rc<Rc<T>>`, `Rc<Box<T>>`, `Box<&T>`
205 /// add an unnecessary level of indirection.
207 /// **Known problems:** None.
211 /// # use std::rc::Rc;
212 /// fn foo(bar: Rc<&usize>) {}
218 /// fn foo(bar: &usize) {}
220 pub REDUNDANT_ALLOCATION,
222 "redundant allocation"
225 declare_clippy_lint! {
226 /// **What it does:** Checks for `Rc<T>` and `Arc<T>` when `T` is a mutable buffer type such as `String` or `Vec`.
228 /// **Why is this bad?** Expressions such as `Rc<String>` usually have no advantage over `Rc<str>`, since
229 /// it is larger and involves an extra level of indirection, and doesn't implement `Borrow<str>`.
231 /// While mutating a buffer type would still be possible with `Rc::get_mut()`, it only
232 /// works if there are no additional references yet, which usually defeats the purpose of
233 /// enclosing it in a shared ownership type. Instead, additionally wrapping the inner
234 /// type with an interior mutable container (such as `RefCell` or `Mutex`) would normally
237 /// **Known problems:** This pattern can be desirable to avoid the overhead of a `RefCell` or `Mutex` for
238 /// cases where mutation only happens before there are any additional references.
242 /// # use std::rc::Rc;
243 /// fn foo(interned: Rc<String>) { ... }
249 /// fn foo(interned: Rc<str>) { ... }
253 "shared ownership of a buffer type"
257 vec_box_size_threshold: u64,
260 impl_lint_pass!(Types => [BOX_VEC, VEC_BOX, OPTION_OPTION, LINKEDLIST, BORROWED_BOX, REDUNDANT_ALLOCATION, RC_BUFFER]);
262 impl<'tcx> LateLintPass<'tcx> for Types {
263 fn check_fn(&mut self, cx: &LateContext<'_>, _: FnKind<'_>, decl: &FnDecl<'_>, _: &Body<'_>, _: Span, id: HirId) {
264 // Skip trait implementations; see issue #605.
265 if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(id)) {
266 if let ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = item.kind {
271 self.check_fn_decl(cx, decl);
274 fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
275 self.check_ty(cx, &field.ty, false);
278 fn check_trait_item(&mut self, cx: &LateContext<'_>, item: &TraitItem<'_>) {
280 TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_ty(cx, ty, false),
281 TraitItemKind::Fn(ref sig, _) => self.check_fn_decl(cx, &sig.decl),
286 fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
287 if let Some(ref ty) = local.ty {
288 self.check_ty(cx, ty, true);
294 pub fn new(vec_box_size_threshold: u64) -> Self {
295 Self { vec_box_size_threshold }
298 fn check_fn_decl(&mut self, cx: &LateContext<'_>, decl: &FnDecl<'_>) {
299 for input in decl.inputs {
300 self.check_ty(cx, input, false);
303 if let FnRetTy::Return(ref ty) = decl.output {
304 self.check_ty(cx, ty, false);
308 /// Recursively check for `TypePass` lints in the given type. Stop at the first
311 /// The parameter `is_local` distinguishes the context of the type.
312 fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, is_local: bool) {
313 if hir_ty.span.from_expansion() {
317 TyKind::Path(ref qpath) if !is_local => {
318 let hir_id = hir_ty.hir_id;
319 let res = cx.qpath_res(qpath, hir_id);
320 if let Some(def_id) = res.opt_def_id() {
321 let mut triggered = false;
322 triggered |= box_vec::check(cx, hir_ty, qpath, def_id);
323 triggered |= redundant_allocation::check(cx, hir_ty, qpath, def_id);
324 triggered |= rc_buffer::check(cx, hir_ty, qpath, def_id);
325 triggered |= vec_box::check(cx, hir_ty, qpath, def_id, self.vec_box_size_threshold);
326 triggered |= option_option::check(cx, hir_ty, qpath, def_id);
327 triggered |= linked_list::check(cx, hir_ty, def_id);
334 QPath::Resolved(Some(ref ty), ref p) => {
335 self.check_ty(cx, ty, is_local);
336 for ty in p.segments.iter().flat_map(|seg| {
339 .map_or_else(|| [].iter(), |params| params.args.iter())
340 .filter_map(|arg| match arg {
341 GenericArg::Type(ty) => Some(ty),
345 self.check_ty(cx, ty, is_local);
348 QPath::Resolved(None, ref p) => {
349 for ty in p.segments.iter().flat_map(|seg| {
352 .map_or_else(|| [].iter(), |params| params.args.iter())
353 .filter_map(|arg| match arg {
354 GenericArg::Type(ty) => Some(ty),
358 self.check_ty(cx, ty, is_local);
361 QPath::TypeRelative(ref ty, ref seg) => {
362 self.check_ty(cx, ty, is_local);
363 if let Some(ref params) = seg.args {
364 for ty in params.args.iter().filter_map(|arg| match arg {
365 GenericArg::Type(ty) => Some(ty),
368 self.check_ty(cx, ty, is_local);
372 QPath::LangItem(..) => {},
375 TyKind::Rptr(ref lt, ref mut_ty) => {
376 if !borrowed_box::check(cx, hir_ty, lt, mut_ty) {
377 self.check_ty(cx, &mut_ty.ty, is_local);
380 TyKind::Slice(ref ty) | TyKind::Array(ref ty, _) | TyKind::Ptr(MutTy { ref ty, .. }) => {
381 self.check_ty(cx, ty, is_local)
383 TyKind::Tup(tys) => {
385 self.check_ty(cx, ty, is_local);
393 declare_clippy_lint! {
394 /// **What it does:** Checks for binding a unit value.
396 /// **Why is this bad?** A unit value cannot usefully be used anywhere. So
397 /// binding one is kind of pointless.
399 /// **Known problems:** None.
409 "creating a `let` binding to a value of unit type, which usually can't be used afterwards"
412 declare_lint_pass!(LetUnitValue => [LET_UNIT_VALUE]);
414 impl<'tcx> LateLintPass<'tcx> for LetUnitValue {
415 fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
416 if let StmtKind::Local(ref local) = stmt.kind {
417 if is_unit(cx.typeck_results().pat_ty(&local.pat)) {
418 if in_external_macro(cx.sess(), stmt.span) || local.pat.span.from_expansion() {
421 if higher::is_from_for_desugar(local) {
428 "this let-binding has unit value",
430 if let Some(expr) = &local.init {
431 let snip = snippet_with_macro_callsite(cx, expr.span, "()");
432 diag.span_suggestion(
434 "omit the `let` binding",
435 format!("{};", snip),
436 Applicability::MachineApplicable, // snippet
446 declare_clippy_lint! {
447 /// **What it does:** Checks for comparisons to unit. This includes all binary
448 /// comparisons (like `==` and `<`) and asserts.
450 /// **Why is this bad?** Unit is always equal to itself, and thus is just a
451 /// clumsily written constant. Mostly this happens when someone accidentally
452 /// adds semicolons at the end of the operands.
454 /// **Known problems:** None.
485 /// assert_eq!({ foo(); }, { bar(); });
487 /// will always succeed
490 "comparing unit values"
493 declare_lint_pass!(UnitCmp => [UNIT_CMP]);
495 impl<'tcx> LateLintPass<'tcx> for UnitCmp {
496 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
497 if expr.span.from_expansion() {
498 if let Some(callee) = expr.span.source_callee() {
499 if let ExpnKind::Macro(MacroKind::Bang, symbol) = callee.kind {
500 if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
502 if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
503 let result = match &*symbol.as_str() {
504 "assert_eq" | "debug_assert_eq" => "succeed",
505 "assert_ne" | "debug_assert_ne" => "fail",
513 "`{}` of unit values detected. This will always {}",
524 if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
526 if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
527 let result = match op {
528 BinOpKind::Eq | BinOpKind::Le | BinOpKind::Ge => "true",
536 "{}-comparison of unit values detected. This will always be {}",
546 declare_clippy_lint! {
547 /// **What it does:** Checks for passing a unit value as an argument to a function without using a
548 /// unit literal (`()`).
550 /// **Why is this bad?** This is likely the result of an accidental semicolon.
552 /// **Known problems:** None.
563 "passing unit to a function"
566 declare_lint_pass!(UnitArg => [UNIT_ARG]);
568 impl<'tcx> LateLintPass<'tcx> for UnitArg {
569 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
570 if expr.span.from_expansion() {
574 // apparently stuff in the desugaring of `?` can trigger this
575 // so check for that here
576 // only the calls to `Try::from_error` is marked as desugared,
577 // so we need to check both the current Expr and its parent.
578 if is_questionmark_desugar_marked_call(expr) {
582 let map = &cx.tcx.hir();
583 let opt_parent_node = map.find(map.get_parent_node(expr.hir_id));
584 if let Some(hir::Node::Expr(parent_expr)) = opt_parent_node;
585 if is_questionmark_desugar_marked_call(parent_expr);
592 ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args, _) => {
593 let args_to_recover = args
596 if is_unit(cx.typeck_results().expr_ty(arg)) && !is_unit_literal(arg) {
599 ExprKind::Match(.., MatchSource::TryDesugar) | ExprKind::Path(..)
605 .collect::<Vec<_>>();
606 if !args_to_recover.is_empty() {
607 lint_unit_args(cx, expr, &args_to_recover);
615 fn fmt_stmts_and_call(
616 cx: &LateContext<'_>,
617 call_expr: &Expr<'_>,
619 args_snippets: &[impl AsRef<str>],
620 non_empty_block_args_snippets: &[impl AsRef<str>],
622 let call_expr_indent = indent_of(cx, call_expr.span).unwrap_or(0);
623 let call_snippet_with_replacements = args_snippets
625 .fold(call_snippet.to_owned(), |acc, arg| acc.replacen(arg.as_ref(), "()", 1));
627 let mut stmts_and_call = non_empty_block_args_snippets
629 .map(|it| it.as_ref().to_owned())
630 .collect::<Vec<_>>();
631 stmts_and_call.push(call_snippet_with_replacements);
632 stmts_and_call = stmts_and_call
634 .map(|v| reindent_multiline(v.into(), true, Some(call_expr_indent)).into_owned())
637 let mut stmts_and_call_snippet = stmts_and_call.join(&format!("{}{}", ";\n", " ".repeat(call_expr_indent)));
638 // expr is not in a block statement or result expression position, wrap in a block
639 let parent_node = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(call_expr.hir_id));
640 if !matches!(parent_node, Some(Node::Block(_))) && !matches!(parent_node, Some(Node::Stmt(_))) {
641 let block_indent = call_expr_indent + 4;
642 stmts_and_call_snippet =
643 reindent_multiline(stmts_and_call_snippet.into(), true, Some(block_indent)).into_owned();
644 stmts_and_call_snippet = format!(
646 " ".repeat(block_indent),
647 &stmts_and_call_snippet,
648 " ".repeat(call_expr_indent)
651 stmts_and_call_snippet
654 fn lint_unit_args(cx: &LateContext<'_>, expr: &Expr<'_>, args_to_recover: &[&Expr<'_>]) {
655 let mut applicability = Applicability::MachineApplicable;
656 let (singular, plural) = if args_to_recover.len() > 1 {
665 &format!("passing {}unit value{} to a function", singular, plural),
672 if let ExprKind::Block(block, _) = arg.kind;
673 if block.expr.is_none();
674 if let Some(last_stmt) = block.stmts.iter().last();
675 if let StmtKind::Semi(last_expr) = last_stmt.kind;
676 if let Some(snip) = snippet_opt(cx, last_expr.span);
688 .for_each(|(span, sugg)| {
691 "remove the semicolon from the last statement in the block",
693 Applicability::MaybeIncorrect,
696 applicability = Applicability::MaybeIncorrect;
699 let arg_snippets: Vec<String> = args_to_recover
701 .filter_map(|arg| snippet_opt(cx, arg.span))
703 let arg_snippets_without_empty_blocks: Vec<String> = args_to_recover
705 .filter(|arg| !is_empty_block(arg))
706 .filter_map(|arg| snippet_opt(cx, arg.span))
709 if let Some(call_snippet) = snippet_opt(cx, expr.span) {
710 let sugg = fmt_stmts_and_call(
715 &arg_snippets_without_empty_blocks,
718 if arg_snippets_without_empty_blocks.is_empty() {
719 db.multipart_suggestion(
720 &format!("use {}unit literal{} instead", singular, plural),
723 .map(|arg| (arg.span, "()".to_string()))
724 .collect::<Vec<_>>(),
728 let plural = arg_snippets_without_empty_blocks.len() > 1;
729 let empty_or_s = if plural { "s" } else { "" };
730 let it_or_them = if plural { "them" } else { "it" };
734 "{}move the expression{} in front of the call and replace {} with the unit literal `()`",
735 or, empty_or_s, it_or_them
746 fn is_empty_block(expr: &Expr<'_>) -> bool {
760 fn is_questionmark_desugar_marked_call(expr: &Expr<'_>) -> bool {
761 use rustc_span::hygiene::DesugaringKind;
762 if let ExprKind::Call(ref callee, _) = expr.kind {
763 callee.span.is_desugaring(DesugaringKind::QuestionMark)
769 fn is_unit(ty: Ty<'_>) -> bool {
770 matches!(ty.kind(), ty::Tuple(slice) if slice.is_empty())
773 fn is_unit_literal(expr: &Expr<'_>) -> bool {
774 matches!(expr.kind, ExprKind::Tup(ref slice) if slice.is_empty())
777 declare_clippy_lint! {
778 /// **What it does:** Checks for types used in structs, parameters and `let`
779 /// declarations above a certain complexity threshold.
781 /// **Why is this bad?** Too complex types make the code less readable. Consider
782 /// using a `type` definition to simplify them.
784 /// **Known problems:** None.
788 /// # use std::rc::Rc;
790 /// inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>>,
795 "usage of very complex types that might be better factored into `type` definitions"
798 pub struct TypeComplexity {
802 impl TypeComplexity {
804 pub fn new(threshold: u64) -> Self {
809 impl_lint_pass!(TypeComplexity => [TYPE_COMPLEXITY]);
811 impl<'tcx> LateLintPass<'tcx> for TypeComplexity {
814 cx: &LateContext<'tcx>,
816 decl: &'tcx FnDecl<'_>,
821 self.check_fndecl(cx, decl);
824 fn check_struct_field(&mut self, cx: &LateContext<'tcx>, field: &'tcx hir::StructField<'_>) {
825 // enum variants are also struct fields now
826 self.check_type(cx, &field.ty);
829 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
831 ItemKind::Static(ref ty, _, _) | ItemKind::Const(ref ty, _) => self.check_type(cx, ty),
832 // functions, enums, structs, impls and traits are covered
837 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
839 TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_type(cx, ty),
840 TraitItemKind::Fn(FnSig { ref decl, .. }, TraitFn::Required(_)) => self.check_fndecl(cx, decl),
841 // methods with default impl are covered by check_fn
846 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
848 ImplItemKind::Const(ref ty, _) | ImplItemKind::TyAlias(ref ty) => self.check_type(cx, ty),
849 // methods are covered by check_fn
854 fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'_>) {
855 if let Some(ref ty) = local.ty {
856 self.check_type(cx, ty);
861 impl<'tcx> TypeComplexity {
862 fn check_fndecl(&self, cx: &LateContext<'tcx>, decl: &'tcx FnDecl<'_>) {
863 for arg in decl.inputs {
864 self.check_type(cx, arg);
866 if let FnRetTy::Return(ref ty) = decl.output {
867 self.check_type(cx, ty);
871 fn check_type(&self, cx: &LateContext<'_>, ty: &hir::Ty<'_>) {
872 if ty.span.from_expansion() {
876 let mut visitor = TypeComplexityVisitor { score: 0, nest: 1 };
877 visitor.visit_ty(ty);
881 if score > self.threshold {
886 "very complex type used. Consider factoring parts into `type` definitions",
892 /// Walks a type and assigns a complexity score to it.
893 struct TypeComplexityVisitor {
894 /// total complexity score of the type
896 /// current nesting level
900 impl<'tcx> Visitor<'tcx> for TypeComplexityVisitor {
901 type Map = Map<'tcx>;
903 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
904 let (add_score, sub_nest) = match ty.kind {
905 // _, &x and *x have only small overhead; don't mess with nesting level
906 TyKind::Infer | TyKind::Ptr(..) | TyKind::Rptr(..) => (1, 0),
908 // the "normal" components of a type: named types, arrays/tuples
909 TyKind::Path(..) | TyKind::Slice(..) | TyKind::Tup(..) | TyKind::Array(..) => (10 * self.nest, 1),
911 // function types bring a lot of overhead
912 TyKind::BareFn(ref bare) if bare.abi == Abi::Rust => (50 * self.nest, 1),
914 TyKind::TraitObject(ref param_bounds, _) => {
915 let has_lifetime_parameters = param_bounds.iter().any(|bound| {
917 .bound_generic_params
919 .any(|gen| matches!(gen.kind, GenericParamKind::Lifetime { .. }))
921 if has_lifetime_parameters {
922 // complex trait bounds like A<'a, 'b>
925 // simple trait bounds like A + B
932 self.score += add_score;
933 self.nest += sub_nest;
935 self.nest -= sub_nest;
937 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
938 NestedVisitorMap::None
942 declare_clippy_lint! {
943 /// **What it does:** Checks for comparisons where one side of the relation is
944 /// either the minimum or maximum value for its type and warns if it involves a
945 /// case that is always true or always false. Only integer and boolean types are
948 /// **Why is this bad?** An expression like `min <= x` may misleadingly imply
949 /// that it is possible for `x` to be less than the minimum. Expressions like
950 /// `max < x` are probably mistakes.
952 /// **Known problems:** For `usize` the size of the current compile target will
953 /// be assumed (e.g., 64 bits on 64 bit systems). This means code that uses such
954 /// a comparison to detect target pointer width will trigger this lint. One can
955 /// use `mem::sizeof` and compare its value or conditional compilation
957 /// like `#[cfg(target_pointer_width = "64")] ..` instead.
962 /// let vec: Vec<isize> = Vec::new();
963 /// if vec.len() <= 0 {}
964 /// if 100 > i32::MAX {}
966 pub ABSURD_EXTREME_COMPARISONS,
968 "a comparison with a maximum or minimum value that is always true or false"
971 declare_lint_pass!(AbsurdExtremeComparisons => [ABSURD_EXTREME_COMPARISONS]);
978 struct ExtremeExpr<'a> {
983 enum AbsurdComparisonResult {
986 InequalityImpossible,
989 fn is_cast_between_fixed_and_target<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
990 if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
991 let precast_ty = cx.typeck_results().expr_ty(cast_exp);
992 let cast_ty = cx.typeck_results().expr_ty(expr);
994 return is_isize_or_usize(precast_ty) != is_isize_or_usize(cast_ty);
1000 fn detect_absurd_comparison<'tcx>(
1001 cx: &LateContext<'tcx>,
1003 lhs: &'tcx Expr<'_>,
1004 rhs: &'tcx Expr<'_>,
1005 ) -> Option<(ExtremeExpr<'tcx>, AbsurdComparisonResult)> {
1006 use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
1007 use crate::types::ExtremeType::{Maximum, Minimum};
1008 use crate::utils::comparisons::{normalize_comparison, Rel};
1010 // absurd comparison only makes sense on primitive types
1011 // primitive types don't implement comparison operators with each other
1012 if cx.typeck_results().expr_ty(lhs) != cx.typeck_results().expr_ty(rhs) {
1016 // comparisons between fix sized types and target sized types are considered unanalyzable
1017 if is_cast_between_fixed_and_target(cx, lhs) || is_cast_between_fixed_and_target(cx, rhs) {
1021 let (rel, normalized_lhs, normalized_rhs) = normalize_comparison(op, lhs, rhs)?;
1023 let lx = detect_extreme_expr(cx, normalized_lhs);
1024 let rx = detect_extreme_expr(cx, normalized_rhs);
1029 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, AlwaysFalse), // max < x
1030 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, AlwaysFalse), // x < min
1036 (Some(l @ ExtremeExpr { which: Minimum, .. }), _) => (l, AlwaysTrue), // min <= x
1037 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, InequalityImpossible), // max <= x
1038 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, InequalityImpossible), // x <= min
1039 (_, Some(r @ ExtremeExpr { which: Maximum, .. })) => (r, AlwaysTrue), // x <= max
1043 Rel::Ne | Rel::Eq => return None,
1047 fn detect_extreme_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<ExtremeExpr<'tcx>> {
1048 use crate::types::ExtremeType::{Maximum, Minimum};
1050 let ty = cx.typeck_results().expr_ty(expr);
1052 let cv = constant(cx, cx.typeck_results(), expr)?.0;
1054 let which = match (ty.kind(), cv) {
1055 (&ty::Bool, Constant::Bool(false)) | (&ty::Uint(_), Constant::Int(0)) => Minimum,
1056 (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MIN >> (128 - int_bits(cx.tcx, ity)), ity) => {
1060 (&ty::Bool, Constant::Bool(true)) => Maximum,
1061 (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MAX >> (128 - int_bits(cx.tcx, ity)), ity) => {
1064 (&ty::Uint(uty), Constant::Int(i)) if clip(cx.tcx, u128::MAX, uty) == i => Maximum,
1068 Some(ExtremeExpr { which, expr })
1071 impl<'tcx> LateLintPass<'tcx> for AbsurdExtremeComparisons {
1072 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1073 use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
1074 use crate::types::ExtremeType::{Maximum, Minimum};
1076 if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
1077 if let Some((culprit, result)) = detect_absurd_comparison(cx, cmp.node, lhs, rhs) {
1078 if !expr.span.from_expansion() {
1079 let msg = "this comparison involving the minimum or maximum element for this \
1080 type contains a case that is always true or always false";
1082 let conclusion = match result {
1083 AlwaysFalse => "this comparison is always false".to_owned(),
1084 AlwaysTrue => "this comparison is always true".to_owned(),
1085 InequalityImpossible => format!(
1086 "the case where the two sides are not equal never occurs, consider using `{} == {}` \
1088 snippet(cx, lhs.span, "lhs"),
1089 snippet(cx, rhs.span, "rhs")
1094 "because `{}` is the {} value for this type, {}",
1095 snippet(cx, culprit.expr.span, "x"),
1096 match culprit.which {
1097 Minimum => "minimum",
1098 Maximum => "maximum",
1103 span_lint_and_help(cx, ABSURD_EXTREME_COMPARISONS, expr.span, msg, None, &help);
1110 declare_clippy_lint! {
1111 /// **What it does:** Checks for comparisons where the relation is always either
1112 /// true or false, but where one side has been upcast so that the comparison is
1113 /// necessary. Only integer types are checked.
1115 /// **Why is this bad?** An expression like `let x : u8 = ...; (x as u32) > 300`
1116 /// will mistakenly imply that it is possible for `x` to be outside the range of
1119 /// **Known problems:**
1120 /// https://github.com/rust-lang/rust-clippy/issues/886
1125 /// (x as u32) > 300;
1127 pub INVALID_UPCAST_COMPARISONS,
1129 "a comparison involving an upcast which is always true or false"
1132 declare_lint_pass!(InvalidUpcastComparisons => [INVALID_UPCAST_COMPARISONS]);
1134 #[derive(Copy, Clone, Debug, Eq)]
1141 #[allow(clippy::cast_sign_loss)]
1143 fn cmp_s_u(s: i128, u: u128) -> Ordering {
1146 } else if u > (i128::MAX as u128) {
1154 impl PartialEq for FullInt {
1156 fn eq(&self, other: &Self) -> bool {
1157 self.partial_cmp(other).expect("`partial_cmp` only returns `Some(_)`") == Ordering::Equal
1161 impl PartialOrd for FullInt {
1163 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
1164 Some(match (self, other) {
1165 (&Self::S(s), &Self::S(o)) => s.cmp(&o),
1166 (&Self::U(s), &Self::U(o)) => s.cmp(&o),
1167 (&Self::S(s), &Self::U(o)) => Self::cmp_s_u(s, o),
1168 (&Self::U(s), &Self::S(o)) => Self::cmp_s_u(o, s).reverse(),
1173 impl Ord for FullInt {
1175 fn cmp(&self, other: &Self) -> Ordering {
1176 self.partial_cmp(other)
1177 .expect("`partial_cmp` for FullInt can never return `None`")
1181 fn numeric_cast_precast_bounds<'a>(cx: &LateContext<'_>, expr: &'a Expr<'_>) -> Option<(FullInt, FullInt)> {
1182 if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
1183 let pre_cast_ty = cx.typeck_results().expr_ty(cast_exp);
1184 let cast_ty = cx.typeck_results().expr_ty(expr);
1185 // if it's a cast from i32 to u32 wrapping will invalidate all these checks
1186 if cx.layout_of(pre_cast_ty).ok().map(|l| l.size) == cx.layout_of(cast_ty).ok().map(|l| l.size) {
1189 match pre_cast_ty.kind() {
1190 ty::Int(int_ty) => Some(match int_ty {
1191 IntTy::I8 => (FullInt::S(i128::from(i8::MIN)), FullInt::S(i128::from(i8::MAX))),
1192 IntTy::I16 => (FullInt::S(i128::from(i16::MIN)), FullInt::S(i128::from(i16::MAX))),
1193 IntTy::I32 => (FullInt::S(i128::from(i32::MIN)), FullInt::S(i128::from(i32::MAX))),
1194 IntTy::I64 => (FullInt::S(i128::from(i64::MIN)), FullInt::S(i128::from(i64::MAX))),
1195 IntTy::I128 => (FullInt::S(i128::MIN), FullInt::S(i128::MAX)),
1196 IntTy::Isize => (FullInt::S(isize::MIN as i128), FullInt::S(isize::MAX as i128)),
1198 ty::Uint(uint_ty) => Some(match uint_ty {
1199 UintTy::U8 => (FullInt::U(u128::from(u8::MIN)), FullInt::U(u128::from(u8::MAX))),
1200 UintTy::U16 => (FullInt::U(u128::from(u16::MIN)), FullInt::U(u128::from(u16::MAX))),
1201 UintTy::U32 => (FullInt::U(u128::from(u32::MIN)), FullInt::U(u128::from(u32::MAX))),
1202 UintTy::U64 => (FullInt::U(u128::from(u64::MIN)), FullInt::U(u128::from(u64::MAX))),
1203 UintTy::U128 => (FullInt::U(u128::MIN), FullInt::U(u128::MAX)),
1204 UintTy::Usize => (FullInt::U(usize::MIN as u128), FullInt::U(usize::MAX as u128)),
1213 fn node_as_const_fullint<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<FullInt> {
1214 let val = constant(cx, cx.typeck_results(), expr)?.0;
1215 if let Constant::Int(const_int) = val {
1216 match *cx.typeck_results().expr_ty(expr).kind() {
1217 ty::Int(ity) => Some(FullInt::S(sext(cx.tcx, const_int, ity))),
1218 ty::Uint(_) => Some(FullInt::U(const_int)),
1226 fn err_upcast_comparison(cx: &LateContext<'_>, span: Span, expr: &Expr<'_>, always: bool) {
1227 if let ExprKind::Cast(ref cast_val, _) = expr.kind {
1230 INVALID_UPCAST_COMPARISONS,
1233 "because of the numeric bounds on `{}` prior to casting, this expression is always {}",
1234 snippet(cx, cast_val.span, "the expression"),
1235 if always { "true" } else { "false" },
1241 fn upcast_comparison_bounds_err<'tcx>(
1242 cx: &LateContext<'tcx>,
1244 rel: comparisons::Rel,
1245 lhs_bounds: Option<(FullInt, FullInt)>,
1246 lhs: &'tcx Expr<'_>,
1247 rhs: &'tcx Expr<'_>,
1250 use crate::utils::comparisons::Rel;
1252 if let Some((lb, ub)) = lhs_bounds {
1253 if let Some(norm_rhs_val) = node_as_const_fullint(cx, rhs) {
1254 if rel == Rel::Eq || rel == Rel::Ne {
1255 if norm_rhs_val < lb || norm_rhs_val > ub {
1256 err_upcast_comparison(cx, span, lhs, rel == Rel::Ne);
1258 } else if match rel {
1273 Rel::Eq | Rel::Ne => unreachable!(),
1275 err_upcast_comparison(cx, span, lhs, true)
1276 } else if match rel {
1291 Rel::Eq | Rel::Ne => unreachable!(),
1293 err_upcast_comparison(cx, span, lhs, false)
1299 impl<'tcx> LateLintPass<'tcx> for InvalidUpcastComparisons {
1300 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1301 if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
1302 let normalized = comparisons::normalize_comparison(cmp.node, lhs, rhs);
1303 let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
1309 let lhs_bounds = numeric_cast_precast_bounds(cx, normalized_lhs);
1310 let rhs_bounds = numeric_cast_precast_bounds(cx, normalized_rhs);
1312 upcast_comparison_bounds_err(cx, expr.span, rel, lhs_bounds, normalized_lhs, normalized_rhs, false);
1313 upcast_comparison_bounds_err(cx, expr.span, rel, rhs_bounds, normalized_rhs, normalized_lhs, true);
1318 declare_clippy_lint! {
1319 /// **What it does:** Checks for public `impl` or `fn` missing generalization
1320 /// over different hashers and implicitly defaulting to the default hashing
1321 /// algorithm (`SipHash`).
1323 /// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
1326 /// **Known problems:** Suggestions for replacing constructors can contain
1327 /// false-positives. Also applying suggestions can require modification of other
1328 /// pieces of code, possibly including external crates.
1332 /// # use std::collections::HashMap;
1333 /// # use std::hash::{Hash, BuildHasher};
1334 /// # trait Serialize {};
1335 /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
1337 /// pub fn foo(map: &mut HashMap<i32, i32>) { }
1339 /// could be rewritten as
1341 /// # use std::collections::HashMap;
1342 /// # use std::hash::{Hash, BuildHasher};
1343 /// # trait Serialize {};
1344 /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
1346 /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
1348 pub IMPLICIT_HASHER,
1350 "missing generalization over different hashers"
1353 declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
1355 impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
1356 #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
1357 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
1358 use rustc_span::BytePos;
1360 fn suggestion<'tcx>(
1361 cx: &LateContext<'tcx>,
1362 diag: &mut DiagnosticBuilder<'_>,
1363 generics_span: Span,
1364 generics_suggestion_span: Span,
1365 target: &ImplicitHasherType<'_>,
1366 vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
1368 let generics_snip = snippet(cx, generics_span, "");
1370 let generics_snip = if generics_snip.is_empty() {
1373 &generics_snip[1..generics_snip.len() - 1]
1378 "consider adding a type parameter",
1381 generics_suggestion_span,
1383 "<{}{}S: ::std::hash::BuildHasher{}>",
1385 if generics_snip.is_empty() { "" } else { ", " },
1386 if vis.suggestions.is_empty() {
1389 // request users to add `Default` bound so that generic constructors can be used
1396 format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
1401 if !vis.suggestions.is_empty() {
1402 multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
1406 if !cx.access_levels.is_exported(item.hir_id()) {
1411 ItemKind::Impl(ref impl_) => {
1412 let mut vis = ImplicitHasherTypeVisitor::new(cx);
1413 vis.visit_ty(impl_.self_ty);
1415 for target in &vis.found {
1416 if differing_macro_contexts(item.span, target.span()) {
1420 let generics_suggestion_span = impl_.generics.span.substitute_dummy({
1421 let pos = snippet_opt(cx, item.span.until(target.span()))
1422 .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
1423 if let Some(pos) = pos {
1424 Span::new(pos, pos, item.span.data().ctxt)
1430 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
1431 for item in impl_.items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
1432 ctr_vis.visit_impl_item(item);
1440 "impl for `{}` should be generalized over different hashers",
1444 suggestion(cx, diag, impl_.generics.span, generics_suggestion_span, target, ctr_vis);
1449 ItemKind::Fn(ref sig, ref generics, body_id) => {
1450 let body = cx.tcx.hir().body(body_id);
1452 for ty in sig.decl.inputs {
1453 let mut vis = ImplicitHasherTypeVisitor::new(cx);
1456 for target in &vis.found {
1457 if in_external_macro(cx.sess(), generics.span) {
1460 let generics_suggestion_span = generics.span.substitute_dummy({
1461 let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
1463 let i = snip.find("fn")?;
1464 Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
1466 .expect("failed to create span for type parameters");
1467 Span::new(pos, pos, item.span.data().ctxt)
1470 let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
1471 ctr_vis.visit_body(body);
1478 "parameter of type `{}` should be generalized over different hashers",
1482 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
1493 enum ImplicitHasherType<'tcx> {
1494 HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
1495 HashSet(Span, Ty<'tcx>, Cow<'static, str>),
1498 impl<'tcx> ImplicitHasherType<'tcx> {
1499 /// Checks that `ty` is a target type without a `BuildHasher`.
1500 fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
1501 if let TyKind::Path(QPath::Resolved(None, ref path)) = hir_ty.kind {
1502 let params: Vec<_> = path
1510 .filter_map(|arg| match arg {
1511 GenericArg::Type(ty) => Some(ty),
1515 let params_len = params.len();
1517 let ty = hir_ty_to_ty(cx.tcx, hir_ty);
1519 if is_type_diagnostic_item(cx, ty, sym::hashmap_type) && params_len == 2 {
1520 Some(ImplicitHasherType::HashMap(
1523 snippet(cx, params[0].span, "K"),
1524 snippet(cx, params[1].span, "V"),
1526 } else if is_type_diagnostic_item(cx, ty, sym::hashset_type) && params_len == 1 {
1527 Some(ImplicitHasherType::HashSet(
1530 snippet(cx, params[0].span, "T"),
1540 fn type_name(&self) -> &'static str {
1542 ImplicitHasherType::HashMap(..) => "HashMap",
1543 ImplicitHasherType::HashSet(..) => "HashSet",
1547 fn type_arguments(&self) -> String {
1549 ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
1550 ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
1554 fn ty(&self) -> Ty<'tcx> {
1556 ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
1560 fn span(&self) -> Span {
1562 ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
1567 struct ImplicitHasherTypeVisitor<'a, 'tcx> {
1568 cx: &'a LateContext<'tcx>,
1569 found: Vec<ImplicitHasherType<'tcx>>,
1572 impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
1573 fn new(cx: &'a LateContext<'tcx>) -> Self {
1574 Self { cx, found: vec![] }
1578 impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
1579 type Map = Map<'tcx>;
1581 fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
1582 if let Some(target) = ImplicitHasherType::new(self.cx, t) {
1583 self.found.push(target);
1589 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1590 NestedVisitorMap::None
1594 /// Looks for default-hasher-dependent constructors like `HashMap::new`.
1595 struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
1596 cx: &'a LateContext<'tcx>,
1597 maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
1598 target: &'b ImplicitHasherType<'tcx>,
1599 suggestions: BTreeMap<Span, String>,
1602 impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
1603 fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
1606 maybe_typeck_results: cx.maybe_typeck_results(),
1608 suggestions: BTreeMap::new(),
1613 impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
1614 type Map = Map<'tcx>;
1616 fn visit_body(&mut self, body: &'tcx Body<'_>) {
1617 let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
1618 walk_body(self, body);
1619 self.maybe_typeck_results = old_maybe_typeck_results;
1622 fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
1624 if let ExprKind::Call(ref fun, ref args) = e.kind;
1625 if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
1626 if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
1628 if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
1632 if match_path(ty_path, &paths::HASHMAP) {
1633 if method.ident.name == sym::new {
1635 .insert(e.span, "HashMap::default()".to_string());
1636 } else if method.ident.name == sym!(with_capacity) {
1637 self.suggestions.insert(
1640 "HashMap::with_capacity_and_hasher({}, Default::default())",
1641 snippet(self.cx, args[0].span, "capacity"),
1645 } else if match_path(ty_path, &paths::HASHSET) {
1646 if method.ident.name == sym::new {
1648 .insert(e.span, "HashSet::default()".to_string());
1649 } else if method.ident.name == sym!(with_capacity) {
1650 self.suggestions.insert(
1653 "HashSet::with_capacity_and_hasher({}, Default::default())",
1654 snippet(self.cx, args[0].span, "capacity"),
1665 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1666 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())