1 use clippy_utils::consts::{constant, constant_full_int, miri_to_const, FullInt};
2 use clippy_utils::diagnostics::{
3 multispan_sugg, span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then,
5 use clippy_utils::higher;
6 use clippy_utils::source::{expr_block, indent_of, snippet, snippet_block, snippet_opt, snippet_with_applicability};
7 use clippy_utils::sugg::Sugg;
8 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item, match_type, peel_mid_ty_refs};
9 use clippy_utils::visitors::is_local_used;
11 get_parent_expr, in_macro, is_expn_of, is_lang_ctor, is_lint_allowed, is_refutable, is_unit_expr, is_wild,
12 meets_msrv, msrvs, path_to_local, path_to_local_id, peel_hir_pat_refs, peel_n_hir_expr_refs, recurse_or_patterns,
13 remove_blocks, strip_pat_refs,
15 use clippy_utils::{paths, search_same, SpanlessEq, SpanlessHash};
17 use core::iter::{once, ExactSizeIterator};
18 use if_chain::if_chain;
19 use rustc_ast::ast::{Attribute, LitKind};
20 use rustc_errors::Applicability;
21 use rustc_hir::def::{CtorKind, DefKind, Res};
22 use rustc_hir::LangItem::{OptionNone, OptionSome};
24 self as hir, Arm, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, Guard, HirId, Local, MatchSource,
25 Mutability, Node, Pat, PatKind, PathSegment, QPath, RangeEnd, TyKind,
27 use rustc_hir::{HirIdMap, HirIdSet};
28 use rustc_lint::{LateContext, LateLintPass, LintContext};
29 use rustc_middle::lint::in_external_macro;
30 use rustc_middle::ty::{self, Ty, TyS, VariantDef};
31 use rustc_semver::RustcVersion;
32 use rustc_session::{declare_tool_lint, impl_lint_pass};
33 use rustc_span::source_map::{Span, Spanned};
35 use std::cmp::Ordering;
36 use std::collections::hash_map::Entry;
40 declare_clippy_lint! {
42 /// Checks for matches with a single arm where an `if let`
43 /// will usually suffice.
45 /// ### Why is this bad?
46 /// Just readability – `if let` nests less than a `match`.
50 /// # fn bar(stool: &str) {}
51 /// # let x = Some("abc");
54 /// Some(ref foo) => bar(foo),
59 /// if let Some(ref foo) = x {
65 "a `match` statement with a single nontrivial arm (i.e., where the other arm is `_ => {}`) instead of `if let`"
68 declare_clippy_lint! {
70 /// Checks for matches with two arms where an `if let else` will
73 /// ### Why is this bad?
74 /// Just readability – `if let` nests less than a `match`.
76 /// ### Known problems
77 /// Personal style preferences may differ.
83 /// # fn bar(foo: &usize) {}
84 /// # let other_ref: usize = 1;
85 /// # let x: Option<&usize> = Some(&1);
87 /// Some(ref foo) => bar(foo),
88 /// _ => bar(&other_ref),
92 /// Using `if let` with `else`:
95 /// # fn bar(foo: &usize) {}
96 /// # let other_ref: usize = 1;
97 /// # let x: Option<&usize> = Some(&1);
98 /// if let Some(ref foo) = x {
104 pub SINGLE_MATCH_ELSE,
106 "a `match` statement with two arms where the second arm's pattern is a placeholder instead of a specific match pattern"
109 declare_clippy_lint! {
111 /// Checks for matches where all arms match a reference,
112 /// suggesting to remove the reference and deref the matched expression
113 /// instead. It also checks for `if let &foo = bar` blocks.
115 /// ### Why is this bad?
116 /// It just makes the code less readable. That reference
117 /// destructuring adds nothing to the code.
123 /// &A(ref y) => foo(y),
130 /// A(ref y) => foo(y),
137 "a `match` or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
140 declare_clippy_lint! {
142 /// Checks for matches where match expression is a `bool`. It
143 /// suggests to replace the expression with an `if...else` block.
145 /// ### Why is this bad?
146 /// It makes the code less readable.
152 /// let condition: bool = true;
153 /// match condition {
158 /// Use if/else instead:
162 /// let condition: bool = true;
171 "a `match` on a boolean expression instead of an `if..else` block"
174 declare_clippy_lint! {
176 /// Checks for overlapping match arms.
178 /// ### Why is this bad?
179 /// It is likely to be an error and if not, makes the code
186 /// 1..=10 => println!("1 ... 10"),
187 /// 5..=15 => println!("5 ... 15"),
191 pub MATCH_OVERLAPPING_ARM,
193 "a `match` with overlapping arms"
196 declare_clippy_lint! {
198 /// Checks for arm which matches all errors with `Err(_)`
199 /// and take drastic actions like `panic!`.
201 /// ### Why is this bad?
202 /// It is generally a bad practice, similar to
203 /// catching all exceptions in java with `catch(Exception)`
207 /// let x: Result<i32, &str> = Ok(3);
209 /// Ok(_) => println!("ok"),
210 /// Err(_) => panic!("err"),
213 pub MATCH_WILD_ERR_ARM,
215 "a `match` with `Err(_)` arm and take drastic actions"
218 declare_clippy_lint! {
220 /// Checks for match which is used to add a reference to an
223 /// ### Why is this bad?
224 /// Using `as_ref()` or `as_mut()` instead is shorter.
228 /// let x: Option<()> = None;
231 /// let r: Option<&()> = match x {
233 /// Some(ref v) => Some(v),
237 /// let r: Option<&()> = x.as_ref();
241 "a `match` on an Option value instead of using `as_ref()` or `as_mut`"
244 declare_clippy_lint! {
246 /// Checks for wildcard enum matches using `_`.
248 /// ### Why is this bad?
249 /// New enum variants added by library updates can be missed.
251 /// ### Known problems
252 /// Suggested replacements may be incorrect if guards exhaustively cover some
253 /// variants, and also may not use correct path to enum if it's not present in the current scope.
257 /// # enum Foo { A(usize), B(usize) }
258 /// # let x = Foo::B(1);
271 pub WILDCARD_ENUM_MATCH_ARM,
273 "a wildcard enum match arm using `_`"
276 declare_clippy_lint! {
278 /// Checks for wildcard enum matches for a single variant.
280 /// ### Why is this bad?
281 /// New enum variants added by library updates can be missed.
283 /// ### Known problems
284 /// Suggested replacements may not use correct path to enum
285 /// if it's not present in the current scope.
289 /// # enum Foo { A, B, C }
290 /// # let x = Foo::B;
305 pub MATCH_WILDCARD_FOR_SINGLE_VARIANTS,
307 "a wildcard enum match for a single variant"
310 declare_clippy_lint! {
312 /// Checks for wildcard pattern used with others patterns in same match arm.
314 /// ### Why is this bad?
315 /// Wildcard pattern already covers any other pattern as it will match anyway.
316 /// It makes the code less readable, especially to spot wildcard pattern use in match arm.
332 pub WILDCARD_IN_OR_PATTERNS,
334 "a wildcard pattern used with others patterns in same match arm"
337 declare_clippy_lint! {
339 /// Checks for matches being used to destructure a single-variant enum
340 /// or tuple struct where a `let` will suffice.
342 /// ### Why is this bad?
343 /// Just readability – `let` doesn't nest, whereas a `match` does.
351 /// let wrapper = Wrapper::Data(42);
353 /// let data = match wrapper {
354 /// Wrapper::Data(i) => i,
358 /// The correct use would be:
364 /// let wrapper = Wrapper::Data(42);
365 /// let Wrapper::Data(data) = wrapper;
367 pub INFALLIBLE_DESTRUCTURING_MATCH,
369 "a `match` statement with a single infallible arm instead of a `let`"
372 declare_clippy_lint! {
374 /// Checks for useless match that binds to only one value.
376 /// ### Why is this bad?
377 /// Readability and needless complexity.
379 /// ### Known problems
380 /// Suggested replacements may be incorrect when `match`
381 /// is actually binding temporary value, bringing a 'dropped while borrowed' error.
396 /// let (c, d) = (a, b);
398 pub MATCH_SINGLE_BINDING,
400 "a match with a single binding instead of using `let` statement"
403 declare_clippy_lint! {
405 /// Checks for unnecessary '..' pattern binding on struct when all fields are explicitly matched.
407 /// ### Why is this bad?
408 /// Correctness and readability. It's like having a wildcard pattern after
409 /// matching all enum variants explicitly.
413 /// # struct A { a: i32 }
414 /// let a = A { a: 5 };
418 /// A { a: 5, .. } => {},
424 /// A { a: 5 } => {},
428 pub REST_PAT_IN_FULLY_BOUND_STRUCTS,
430 "a match on a struct that binds all fields but still uses the wildcard pattern"
433 declare_clippy_lint! {
435 /// Lint for redundant pattern matching over `Result`, `Option`,
436 /// `std::task::Poll` or `std::net::IpAddr`
438 /// ### Why is this bad?
439 /// It's more concise and clear to just use the proper
442 /// ### Known problems
443 /// This will change the drop order for the matched type. Both `if let` and
444 /// `while let` will drop the value at the end of the block, both `if` and `while` will drop the
445 /// value before entering the block. For most types this change will not matter, but for a few
446 /// types this will not be an acceptable change (e.g. locks). See the
447 /// [reference](https://doc.rust-lang.org/reference/destructors.html#drop-scopes) for more about
452 /// # use std::task::Poll;
453 /// # use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
454 /// if let Ok(_) = Ok::<i32, i32>(42) {}
455 /// if let Err(_) = Err::<i32, i32>(42) {}
456 /// if let None = None::<()> {}
457 /// if let Some(_) = Some(42) {}
458 /// if let Poll::Pending = Poll::Pending::<()> {}
459 /// if let Poll::Ready(_) = Poll::Ready(42) {}
460 /// if let IpAddr::V4(_) = IpAddr::V4(Ipv4Addr::LOCALHOST) {}
461 /// if let IpAddr::V6(_) = IpAddr::V6(Ipv6Addr::LOCALHOST) {}
462 /// match Ok::<i32, i32>(42) {
468 /// The more idiomatic use would be:
471 /// # use std::task::Poll;
472 /// # use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
473 /// if Ok::<i32, i32>(42).is_ok() {}
474 /// if Err::<i32, i32>(42).is_err() {}
475 /// if None::<()>.is_none() {}
476 /// if Some(42).is_some() {}
477 /// if Poll::Pending::<()>.is_pending() {}
478 /// if Poll::Ready(42).is_ready() {}
479 /// if IpAddr::V4(Ipv4Addr::LOCALHOST).is_ipv4() {}
480 /// if IpAddr::V6(Ipv6Addr::LOCALHOST).is_ipv6() {}
481 /// Ok::<i32, i32>(42).is_ok();
483 pub REDUNDANT_PATTERN_MATCHING,
485 "use the proper utility function avoiding an `if let`"
488 declare_clippy_lint! {
490 /// Checks for `match` or `if let` expressions producing a
491 /// `bool` that could be written using `matches!`
493 /// ### Why is this bad?
494 /// Readability and needless complexity.
496 /// ### Known problems
497 /// This lint falsely triggers, if there are arms with
498 /// `cfg` attributes that remove an arm evaluating to `false`.
505 /// let a = match x {
510 /// let a = if let Some(0) = x {
517 /// let a = matches!(x, Some(0));
519 pub MATCH_LIKE_MATCHES_MACRO,
521 "a match that could be written with the matches! macro"
524 declare_clippy_lint! {
526 /// Checks for `match` with identical arm bodies.
528 /// ### Why is this bad?
529 /// This is probably a copy & paste error. If arm bodies
530 /// are the same on purpose, you can factor them
531 /// [using `|`](https://doc.rust-lang.org/book/patterns.html#multiple-patterns).
533 /// ### Known problems
534 /// False positive possible with order dependent `match`
536 /// [#860](https://github.com/rust-lang/rust-clippy/issues/860)).
543 /// Baz => bar(), // <= oops
547 /// This should probably be
552 /// Baz => baz(), // <= fixed
556 /// or if the original code was not a typo:
559 /// Bar | Baz => bar(), // <= shows the intent better
565 "`match` with identical arm bodies"
570 msrv: Option<RustcVersion>,
571 infallible_destructuring_match_linted: bool,
576 pub fn new(msrv: Option<RustcVersion>) -> Self {
584 impl_lint_pass!(Matches => [
589 MATCH_OVERLAPPING_ARM,
592 WILDCARD_ENUM_MATCH_ARM,
593 MATCH_WILDCARD_FOR_SINGLE_VARIANTS,
594 WILDCARD_IN_OR_PATTERNS,
595 MATCH_SINGLE_BINDING,
596 INFALLIBLE_DESTRUCTURING_MATCH,
597 REST_PAT_IN_FULLY_BOUND_STRUCTS,
598 REDUNDANT_PATTERN_MATCHING,
599 MATCH_LIKE_MATCHES_MACRO,
603 impl<'tcx> LateLintPass<'tcx> for Matches {
604 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
605 if in_external_macro(cx.sess(), expr.span) || in_macro(expr.span) {
609 redundant_pattern_match::check(cx, expr);
611 if meets_msrv(self.msrv.as_ref(), &msrvs::MATCHES_MACRO) {
612 if !check_match_like_matches(cx, expr) {
613 lint_match_arms(cx, expr);
616 lint_match_arms(cx, expr);
619 if let ExprKind::Match(ex, arms, MatchSource::Normal) = expr.kind {
620 check_single_match(cx, ex, arms, expr);
621 check_match_bool(cx, ex, arms, expr);
622 check_overlapping_arms(cx, ex, arms);
623 check_wild_err_arm(cx, ex, arms);
624 check_wild_enum_match(cx, ex, arms);
625 check_match_as_ref(cx, ex, arms, expr);
626 check_wild_in_or_pats(cx, arms);
628 if self.infallible_destructuring_match_linted {
629 self.infallible_destructuring_match_linted = false;
631 check_match_single_binding(cx, ex, arms, expr);
634 if let ExprKind::Match(ex, arms, _) = expr.kind {
635 check_match_ref_pats(cx, ex, arms.iter().map(|el| el.pat), expr);
637 if let Some(higher::IfLet { let_pat, let_expr, .. }) = higher::IfLet::hir(cx, expr) {
638 check_match_ref_pats(cx, let_expr, once(let_pat), expr);
642 fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'_>) {
644 if !in_external_macro(cx.sess(), local.span);
645 if !in_macro(local.span);
646 if let Some(expr) = local.init;
647 if let ExprKind::Match(target, arms, MatchSource::Normal) = expr.kind;
648 if arms.len() == 1 && arms[0].guard.is_none();
649 if let PatKind::TupleStruct(
650 QPath::Resolved(None, variant_name), args, _) = arms[0].pat.kind;
652 if let PatKind::Binding(_, arg, ..) = strip_pat_refs(&args[0]).kind;
653 let body = remove_blocks(arms[0].body);
654 if path_to_local_id(body, arg);
657 let mut applicability = Applicability::MachineApplicable;
658 self.infallible_destructuring_match_linted = true;
661 INFALLIBLE_DESTRUCTURING_MATCH,
663 "you seem to be trying to use `match` to destructure a single infallible pattern. \
664 Consider using `let`",
668 snippet_with_applicability(cx, variant_name.span, "..", &mut applicability),
669 snippet_with_applicability(cx, local.pat.span, "..", &mut applicability),
670 snippet_with_applicability(cx, target.span, "..", &mut applicability),
678 fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
680 if !in_external_macro(cx.sess(), pat.span);
681 if !in_macro(pat.span);
682 if let PatKind::Struct(QPath::Resolved(_, path), fields, true) = pat.kind;
683 if let Some(def_id) = path.res.opt_def_id();
684 let ty = cx.tcx.type_of(def_id);
685 if let ty::Adt(def, _) = ty.kind();
686 if def.is_struct() || def.is_union();
687 if fields.len() == def.non_enum_variant().fields.len();
692 REST_PAT_IN_FULLY_BOUND_STRUCTS,
694 "unnecessary use of `..` pattern in struct binding. All fields were already bound",
696 "consider removing `..` from this binding",
702 extract_msrv_attr!(LateContext);
706 fn check_single_match(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
707 if arms.len() == 2 && arms[0].guard.is_none() && arms[1].guard.is_none() {
708 if in_macro(expr.span) {
709 // Don't lint match expressions present in
710 // macro_rules! block
713 if let PatKind::Or(..) = arms[0].pat.kind {
714 // don't lint for or patterns for now, this makes
715 // the lint noisy in unnecessary situations
718 let els = arms[1].body;
719 let els = if is_unit_expr(remove_blocks(els)) {
721 } else if let ExprKind::Block(Block { stmts, expr: block_expr, .. }, _) = els.kind {
722 if stmts.len() == 1 && block_expr.is_none() || stmts.is_empty() && block_expr.is_some() {
723 // single statement/expr "else" block, don't lint
726 // block with 2+ statements or 1 expr and 1+ statement
729 // not a block, don't lint
733 let ty = cx.typeck_results().expr_ty(ex);
734 if *ty.kind() != ty::Bool || is_lint_allowed(cx, MATCH_BOOL, ex.hir_id) {
735 check_single_match_single_pattern(cx, ex, arms, expr, els);
736 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
741 fn check_single_match_single_pattern(
742 cx: &LateContext<'_>,
746 els: Option<&Expr<'_>>,
748 if is_wild(arms[1].pat) {
749 report_single_match_single_pattern(cx, ex, arms, expr, els);
753 fn report_single_match_single_pattern(
754 cx: &LateContext<'_>,
758 els: Option<&Expr<'_>>,
760 let lint = if els.is_some() { SINGLE_MATCH_ELSE } else { SINGLE_MATCH };
761 let els_str = els.map_or(String::new(), |els| {
762 format!(" else {}", expr_block(cx, els, None, "..", Some(expr.span)))
765 let (pat, pat_ref_count) = peel_hir_pat_refs(arms[0].pat);
766 let (msg, sugg) = if_chain! {
767 if let PatKind::Path(_) | PatKind::Lit(_) = pat.kind;
768 let (ty, ty_ref_count) = peel_mid_ty_refs(cx.typeck_results().expr_ty(ex));
769 if let Some(spe_trait_id) = cx.tcx.lang_items().structural_peq_trait();
770 if let Some(pe_trait_id) = cx.tcx.lang_items().eq_trait();
771 if ty.is_integral() || ty.is_char() || ty.is_str()
772 || (implements_trait(cx, ty, spe_trait_id, &[])
773 && implements_trait(cx, ty, pe_trait_id, &[ty.into()]));
775 // scrutinee derives PartialEq and the pattern is a constant.
776 let pat_ref_count = match pat.kind {
777 // string literals are already a reference.
778 PatKind::Lit(Expr { kind: ExprKind::Lit(lit), .. }) if lit.node.is_str() => pat_ref_count + 1,
781 // References are only implicitly added to the pattern, so no overflow here.
782 // e.g. will work: match &Some(_) { Some(_) => () }
783 // will not: match Some(_) { &Some(_) => () }
784 let ref_count_diff = ty_ref_count - pat_ref_count;
786 // Try to remove address of expressions first.
787 let (ex, removed) = peel_n_hir_expr_refs(ex, ref_count_diff);
788 let ref_count_diff = ref_count_diff - removed;
790 let msg = "you seem to be trying to use `match` for an equality check. Consider using `if`";
792 "if {} == {}{} {}{}",
793 snippet(cx, ex.span, ".."),
794 // PartialEq for different reference counts may not exist.
795 "&".repeat(ref_count_diff),
796 snippet(cx, arms[0].pat.span, ".."),
797 expr_block(cx, arms[0].body, None, "..", Some(expr.span)),
802 let msg = "you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`";
804 "if let {} = {} {}{}",
805 snippet(cx, arms[0].pat.span, ".."),
806 snippet(cx, ex.span, ".."),
807 expr_block(cx, arms[0].body, None, "..", Some(expr.span)),
821 Applicability::HasPlaceholders,
825 fn check_single_match_opt_like(
826 cx: &LateContext<'_>,
831 els: Option<&Expr<'_>>,
833 // list of candidate `Enum`s we know will never get any more members
835 (&paths::COW, "Borrowed"),
836 (&paths::COW, "Cow::Borrowed"),
837 (&paths::COW, "Cow::Owned"),
838 (&paths::COW, "Owned"),
839 (&paths::OPTION, "None"),
840 (&paths::RESULT, "Err"),
841 (&paths::RESULT, "Ok"),
844 let path = match arms[1].pat.kind {
845 PatKind::TupleStruct(ref path, inner, _) => {
846 // Contains any non wildcard patterns (e.g., `Err(err)`)?
847 if !inner.iter().all(is_wild) {
850 rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_qpath(path, false))
852 PatKind::Binding(BindingAnnotation::Unannotated, .., ident, None) => ident.to_string(),
853 PatKind::Path(ref path) => {
854 rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_qpath(path, false))
859 for &(ty_path, pat_path) in candidates {
860 if path == *pat_path && match_type(cx, ty, ty_path) {
861 report_single_match_single_pattern(cx, ex, arms, expr, els);
866 fn check_match_bool(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
867 // Type of expression is `bool`.
868 if *cx.typeck_results().expr_ty(ex).kind() == ty::Bool {
873 "you seem to be trying to match on a boolean expression",
877 let exprs = if let PatKind::Lit(arm_bool) = arms[0].pat.kind {
878 if let ExprKind::Lit(ref lit) = arm_bool.kind {
880 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
881 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
891 if let Some((true_expr, false_expr)) = exprs {
892 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
893 (false, false) => Some(format!(
895 snippet(cx, ex.span, "b"),
896 expr_block(cx, true_expr, None, "..", Some(expr.span)),
897 expr_block(cx, false_expr, None, "..", Some(expr.span))
899 (false, true) => Some(format!(
901 snippet(cx, ex.span, "b"),
902 expr_block(cx, true_expr, None, "..", Some(expr.span))
905 let test = Sugg::hir(cx, ex, "..");
909 expr_block(cx, false_expr, None, "..", Some(expr.span))
912 (true, true) => None,
915 if let Some(sugg) = sugg {
916 diag.span_suggestion(
918 "consider using an `if`/`else` expression",
920 Applicability::HasPlaceholders,
930 fn check_overlapping_arms<'tcx>(cx: &LateContext<'tcx>, ex: &'tcx Expr<'_>, arms: &'tcx [Arm<'_>]) {
931 if arms.len() >= 2 && cx.typeck_results().expr_ty(ex).is_integral() {
932 let ranges = all_ranges(cx, arms, cx.typeck_results().expr_ty(ex));
933 if !ranges.is_empty() {
934 if let Some((start, end)) = overlapping(&ranges) {
937 MATCH_OVERLAPPING_ARM,
939 "some ranges overlap",
941 "overlaps with this",
948 fn check_wild_err_arm<'tcx>(cx: &LateContext<'tcx>, ex: &Expr<'tcx>, arms: &[Arm<'tcx>]) {
949 let ex_ty = cx.typeck_results().expr_ty(ex).peel_refs();
950 if is_type_diagnostic_item(cx, ex_ty, sym::Result) {
952 if let PatKind::TupleStruct(ref path, inner, _) = arm.pat.kind {
953 let path_str = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_qpath(path, false));
954 if path_str == "Err" {
955 let mut matching_wild = inner.iter().any(is_wild);
956 let mut ident_bind_name = String::from("_");
958 // Looking for unused bindings (i.e.: `_e`)
959 for pat in inner.iter() {
960 if let PatKind::Binding(_, id, ident, None) = pat.kind {
961 if ident.as_str().starts_with('_') && !is_local_used(cx, arm.body, id) {
962 ident_bind_name = (&ident.name.as_str()).to_string();
963 matching_wild = true;
970 if is_panic_call(arm.body);
972 // `Err(_)` or `Err(_e)` arm with `panic!` found
973 span_lint_and_note(cx,
976 &format!("`Err({})` matches all errors", &ident_bind_name),
978 "match each error separately or use the error output, or use `.except(msg)` if the error case is unreachable",
988 enum CommonPrefixSearcher<'a> {
990 Path(&'a [PathSegment<'a>]),
993 impl CommonPrefixSearcher<'a> {
994 fn with_path(&mut self, path: &'a [PathSegment<'a>]) {
996 [path @ .., _] => self.with_prefix(path),
1001 fn with_prefix(&mut self, path: &'a [PathSegment<'a>]) {
1003 Self::None => *self = Self::Path(path),
1004 Self::Path(self_path)
1007 .map(|p| p.ident.name)
1008 .eq(self_path.iter().map(|p| p.ident.name)) => {},
1009 Self::Path(_) => *self = Self::Mixed,
1015 fn is_hidden(cx: &LateContext<'_>, variant_def: &VariantDef) -> bool {
1016 let attrs = cx.tcx.get_attrs(variant_def.def_id);
1017 clippy_utils::attrs::is_doc_hidden(attrs) || clippy_utils::attrs::is_unstable(attrs)
1020 #[allow(clippy::too_many_lines)]
1021 fn check_wild_enum_match(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>]) {
1022 let ty = cx.typeck_results().expr_ty(ex).peel_refs();
1023 let adt_def = match ty.kind() {
1025 if adt_def.is_enum()
1026 && !(is_type_diagnostic_item(cx, ty, sym::Option) || is_type_diagnostic_item(cx, ty, sym::Result)) =>
1033 // First pass - check for violation, but don't do much book-keeping because this is hopefully
1034 // the uncommon case, and the book-keeping is slightly expensive.
1035 let mut wildcard_span = None;
1036 let mut wildcard_ident = None;
1037 let mut has_non_wild = false;
1039 match peel_hir_pat_refs(arm.pat).0.kind {
1040 PatKind::Wild => wildcard_span = Some(arm.pat.span),
1041 PatKind::Binding(_, _, ident, None) => {
1042 wildcard_span = Some(arm.pat.span);
1043 wildcard_ident = Some(ident);
1045 _ => has_non_wild = true,
1048 let wildcard_span = match wildcard_span {
1049 Some(x) if has_non_wild => x,
1053 // Accumulate the variants which should be put in place of the wildcard because they're not
1055 let has_hidden = adt_def.variants.iter().any(|x| is_hidden(cx, x));
1056 let mut missing_variants: Vec<_> = adt_def.variants.iter().filter(|x| !is_hidden(cx, x)).collect();
1058 let mut path_prefix = CommonPrefixSearcher::None;
1060 // Guards mean that this case probably isn't exhaustively covered. Technically
1061 // this is incorrect, as we should really check whether each variant is exhaustively
1062 // covered by the set of guards that cover it, but that's really hard to do.
1063 recurse_or_patterns(arm.pat, |pat| {
1064 let path = match &peel_hir_pat_refs(pat).0.kind {
1065 PatKind::Path(path) => {
1066 #[allow(clippy::match_same_arms)]
1067 let id = match cx.qpath_res(path, pat.hir_id) {
1068 Res::Def(DefKind::Const | DefKind::ConstParam | DefKind::AnonConst, _) => return,
1069 Res::Def(_, id) => id,
1072 if arm.guard.is_none() {
1073 missing_variants.retain(|e| e.ctor_def_id != Some(id));
1077 PatKind::TupleStruct(path, patterns, ..) => {
1078 if let Some(id) = cx.qpath_res(path, pat.hir_id).opt_def_id() {
1079 if arm.guard.is_none() && patterns.iter().all(|p| !is_refutable(cx, p)) {
1080 missing_variants.retain(|e| e.ctor_def_id != Some(id));
1085 PatKind::Struct(path, patterns, ..) => {
1086 if let Some(id) = cx.qpath_res(path, pat.hir_id).opt_def_id() {
1087 if arm.guard.is_none() && patterns.iter().all(|p| !is_refutable(cx, p.pat)) {
1088 missing_variants.retain(|e| e.def_id != id);
1096 QPath::Resolved(_, path) => path_prefix.with_path(path.segments),
1097 QPath::TypeRelative(
1099 kind: TyKind::Path(QPath::Resolved(_, path)),
1103 ) => path_prefix.with_prefix(path.segments),
1109 let format_suggestion = |variant: &VariantDef| {
1112 if let Some(ident) = wildcard_ident {
1113 format!("{} @ ", ident.name)
1117 if let CommonPrefixSearcher::Path(path_prefix) = path_prefix {
1118 let mut s = String::new();
1119 for seg in path_prefix {
1120 s.push_str(&seg.ident.as_str());
1125 let mut s = cx.tcx.def_path_str(adt_def.did);
1130 match variant.ctor_kind {
1131 CtorKind::Fn if variant.fields.len() == 1 => "(_)",
1132 CtorKind::Fn => "(..)",
1133 CtorKind::Const => "",
1134 CtorKind::Fictive => "{ .. }",
1139 match missing_variants.as_slice() {
1141 [x] if !adt_def.is_variant_list_non_exhaustive() && !has_hidden => span_lint_and_sugg(
1143 MATCH_WILDCARD_FOR_SINGLE_VARIANTS,
1145 "wildcard matches only a single variant and will also match any future added variants",
1147 format_suggestion(x),
1148 Applicability::MaybeIncorrect,
1151 let mut suggestions: Vec<_> = variants.iter().copied().map(format_suggestion).collect();
1152 let message = if adt_def.is_variant_list_non_exhaustive() || has_hidden {
1153 suggestions.push("_".into());
1154 "wildcard matches known variants and will also match future added variants"
1156 "wildcard match will also match any future added variants"
1161 WILDCARD_ENUM_MATCH_ARM,
1165 suggestions.join(" | "),
1166 Applicability::MaybeIncorrect,
1172 // If the block contains only a `panic!` macro (as expression or statement)
1173 fn is_panic_call(expr: &Expr<'_>) -> bool {
1174 // Unwrap any wrapping blocks
1175 let span = if let ExprKind::Block(block, _) = expr.kind {
1176 match (&block.expr, block.stmts.len(), block.stmts.first()) {
1177 (&Some(exp), 0, _) => exp.span,
1178 (&None, 1, Some(stmt)) => stmt.span,
1185 is_expn_of(span, "panic").is_some() && is_expn_of(span, "unreachable").is_none()
1188 fn check_match_ref_pats<'a, 'b, I>(cx: &LateContext<'_>, ex: &Expr<'_>, pats: I, expr: &Expr<'_>)
1191 I: Clone + Iterator<Item = &'a Pat<'b>>,
1193 if !has_multiple_ref_pats(pats.clone()) {
1197 let (first_sugg, msg, title);
1198 let span = ex.span.source_callsite();
1199 if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, inner) = ex.kind {
1200 first_sugg = once((span, Sugg::hir_with_macro_callsite(cx, inner, "..").to_string()));
1202 title = "you don't need to add `&` to both the expression and the patterns";
1204 first_sugg = once((span, Sugg::hir_with_macro_callsite(cx, ex, "..").deref().to_string()));
1205 msg = "instead of prefixing all patterns with `&`, you can dereference the expression";
1206 title = "you don't need to add `&` to all patterns";
1209 let remaining_suggs = pats.filter_map(|pat| {
1210 if let PatKind::Ref(refp, _) = pat.kind {
1211 Some((pat.span, snippet(cx, refp.span, "..").to_string()))
1217 span_lint_and_then(cx, MATCH_REF_PATS, expr.span, title, |diag| {
1218 if !expr.span.from_expansion() {
1219 multispan_sugg(diag, msg, first_sugg.chain(remaining_suggs));
1224 fn check_match_as_ref(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
1225 if arms.len() == 2 && arms[0].guard.is_none() && arms[1].guard.is_none() {
1226 let arm_ref: Option<BindingAnnotation> = if is_none_arm(cx, &arms[0]) {
1227 is_ref_some_arm(cx, &arms[1])
1228 } else if is_none_arm(cx, &arms[1]) {
1229 is_ref_some_arm(cx, &arms[0])
1233 if let Some(rb) = arm_ref {
1234 let suggestion = if rb == BindingAnnotation::Ref {
1240 let output_ty = cx.typeck_results().expr_ty(expr);
1241 let input_ty = cx.typeck_results().expr_ty(ex);
1243 let cast = if_chain! {
1244 if let ty::Adt(_, substs) = input_ty.kind();
1245 let input_ty = substs.type_at(0);
1246 if let ty::Adt(_, substs) = output_ty.kind();
1247 let output_ty = substs.type_at(0);
1248 if let ty::Ref(_, output_ty, _) = *output_ty.kind();
1249 if input_ty != output_ty;
1257 let mut applicability = Applicability::MachineApplicable;
1262 &format!("use `{}()` instead", suggestion),
1266 snippet_with_applicability(cx, ex.span, "_", &mut applicability),
1276 fn check_wild_in_or_pats(cx: &LateContext<'_>, arms: &[Arm<'_>]) {
1278 if let PatKind::Or(fields) = arm.pat.kind {
1279 // look for multiple fields in this arm that contains at least one Wild pattern
1280 if fields.len() > 1 && fields.iter().any(is_wild) {
1283 WILDCARD_IN_OR_PATTERNS,
1285 "wildcard pattern covers any other pattern as it will match anyway",
1287 "consider handling `_` separately",
1294 /// Lint a `match` or `if let .. { .. } else { .. }` expr that could be replaced by `matches!`
1295 fn check_match_like_matches<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
1296 if let Some(higher::IfLet {
1300 if_else: Some(if_else),
1301 }) = higher::IfLet::hir(cx, expr)
1303 return find_matches_sugg(
1306 array::IntoIter::new([(&[][..], Some(let_pat), if_then, None), (&[][..], None, if_else, None)]),
1312 if let ExprKind::Match(scrut, arms, MatchSource::Normal) = expr.kind {
1313 return find_matches_sugg(
1316 arms.iter().map(|arm| {
1318 cx.tcx.hir().attrs(arm.hir_id),
1332 /// Lint a `match` or `if let` for replacement by `matches!`
1333 fn find_matches_sugg<'a, 'b, I>(
1334 cx: &LateContext<'_>,
1343 + DoubleEndedIterator
1348 Option<&'a Pat<'b>>,
1350 Option<&'a Guard<'b>>,
1356 if cx.typeck_results().expr_ty(expr).is_bool();
1357 if let Some((_, last_pat_opt, last_expr, _)) = iter.next_back();
1358 let iter_without_last = iter.clone();
1359 if let Some((first_attrs, _, first_expr, first_guard)) = iter.next();
1360 if let Some(b0) = find_bool_lit(&first_expr.kind, is_if_let);
1361 if let Some(b1) = find_bool_lit(&last_expr.kind, is_if_let);
1363 if first_guard.is_none() || iter.len() == 0;
1364 if first_attrs.is_empty();
1367 find_bool_lit(&arm.2.kind, is_if_let).map_or(false, |b| b == b0) && arm.3.is_none() && arm.0.is_empty()
1370 if let Some(last_pat) = last_pat_opt {
1371 if !is_wild(last_pat) {
1376 // The suggestion may be incorrect, because some arms can have `cfg` attributes
1377 // evaluated into `false` and so such arms will be stripped before.
1378 let mut applicability = Applicability::MaybeIncorrect;
1380 use itertools::Itertools as _;
1383 let pat_span = arm.1?.span;
1384 Some(snippet_with_applicability(cx, pat_span, "..", &mut applicability))
1388 let pat_and_guard = if let Some(Guard::If(g)) = first_guard {
1389 format!("{} if {}", pat, snippet_with_applicability(cx, g.span, "..", &mut applicability))
1394 // strip potential borrows (#6503), but only if the type is a reference
1395 let mut ex_new = ex;
1396 if let ExprKind::AddrOf(BorrowKind::Ref, .., ex_inner) = ex.kind {
1397 if let ty::Ref(..) = cx.typeck_results().expr_ty(ex_inner).kind() {
1403 MATCH_LIKE_MATCHES_MACRO,
1405 &format!("{} expression looks like `matches!` macro", if is_if_let { "if let .. else" } else { "match" }),
1408 "{}matches!({}, {})",
1409 if b0 { "" } else { "!" },
1410 snippet_with_applicability(cx, ex_new.span, "..", &mut applicability),
1422 /// Extract a `bool` or `{ bool }`
1423 fn find_bool_lit(ex: &ExprKind<'_>, is_if_let: bool) -> Option<bool> {
1425 ExprKind::Lit(Spanned {
1426 node: LitKind::Bool(b), ..
1436 if let ExprKind::Lit(Spanned {
1437 node: LitKind::Bool(b), ..
1449 #[allow(clippy::too_many_lines)]
1450 fn check_match_single_binding<'a>(cx: &LateContext<'a>, ex: &Expr<'a>, arms: &[Arm<'_>], expr: &Expr<'_>) {
1451 if in_macro(expr.span) || arms.len() != 1 || is_refutable(cx, arms[0].pat) {
1456 // This is a hack to deal with arms that are excluded by macros like `#[cfg]`. It is only used here
1457 // to prevent false positives as there is currently no better way to detect if code was excluded by
1458 // a macro. See PR #6435
1460 if let Some(match_snippet) = snippet_opt(cx, expr.span);
1461 if let Some(arm_snippet) = snippet_opt(cx, arms[0].span);
1462 if let Some(ex_snippet) = snippet_opt(cx, ex.span);
1463 let rest_snippet = match_snippet.replace(&arm_snippet, "").replace(&ex_snippet, "");
1464 if rest_snippet.contains("=>");
1466 // The code it self contains another thick arrow "=>"
1467 // -> Either another arm or a comment
1472 let matched_vars = ex.span;
1473 let bind_names = arms[0].pat.span;
1474 let match_body = remove_blocks(arms[0].body);
1475 let mut snippet_body = if match_body.span.from_expansion() {
1476 Sugg::hir_with_macro_callsite(cx, match_body, "..").to_string()
1478 snippet_block(cx, match_body.span, "..", Some(expr.span)).to_string()
1481 // Do we need to add ';' to suggestion ?
1482 match match_body.kind {
1483 ExprKind::Block(block, _) => {
1484 // macro + expr_ty(body) == ()
1485 if block.span.from_expansion() && cx.typeck_results().expr_ty(match_body).is_unit() {
1486 snippet_body.push(';');
1490 // expr_ty(body) == ()
1491 if cx.typeck_results().expr_ty(match_body).is_unit() {
1492 snippet_body.push(';');
1497 let mut applicability = Applicability::MaybeIncorrect;
1498 match arms[0].pat.kind {
1499 PatKind::Binding(..) | PatKind::Tuple(_, _) | PatKind::Struct(..) => {
1500 // If this match is in a local (`let`) stmt
1501 let (target_span, sugg) = if let Some(parent_let_node) = opt_parent_let(cx, ex) {
1503 parent_let_node.span,
1505 "let {} = {};\n{}let {} = {};",
1506 snippet_with_applicability(cx, bind_names, "..", &mut applicability),
1507 snippet_with_applicability(cx, matched_vars, "..", &mut applicability),
1508 " ".repeat(indent_of(cx, expr.span).unwrap_or(0)),
1509 snippet_with_applicability(cx, parent_let_node.pat.span, "..", &mut applicability),
1514 // If we are in closure, we need curly braces around suggestion
1515 let mut indent = " ".repeat(indent_of(cx, ex.span).unwrap_or(0));
1516 let (mut cbrace_start, mut cbrace_end) = ("".to_string(), "".to_string());
1517 if let Some(parent_expr) = get_parent_expr(cx, expr) {
1518 if let ExprKind::Closure(..) = parent_expr.kind {
1519 cbrace_end = format!("\n{}}}", indent);
1520 // Fix body indent due to the closure
1521 indent = " ".repeat(indent_of(cx, bind_names).unwrap_or(0));
1522 cbrace_start = format!("{{\n{}", indent);
1525 // If the parent is already an arm, and the body is another match statement,
1526 // we need curly braces around suggestion
1527 let parent_node_id = cx.tcx.hir().get_parent_node(expr.hir_id);
1528 if let Node::Arm(arm) = &cx.tcx.hir().get(parent_node_id) {
1529 if let ExprKind::Match(..) = arm.body.kind {
1530 cbrace_end = format!("\n{}}}", indent);
1531 // Fix body indent due to the match
1532 indent = " ".repeat(indent_of(cx, bind_names).unwrap_or(0));
1533 cbrace_start = format!("{{\n{}", indent);
1539 "{}let {} = {};\n{}{}{}",
1541 snippet_with_applicability(cx, bind_names, "..", &mut applicability),
1542 snippet_with_applicability(cx, matched_vars, "..", &mut applicability),
1551 MATCH_SINGLE_BINDING,
1553 "this match could be written as a `let` statement",
1554 "consider using `let` statement",
1560 if ex.can_have_side_effects() {
1561 let indent = " ".repeat(indent_of(cx, expr.span).unwrap_or(0));
1564 snippet_with_applicability(cx, ex.span, "..", &mut applicability),
1570 MATCH_SINGLE_BINDING,
1572 "this match could be replaced by its scrutinee and body",
1573 "consider using the scrutinee and body instead",
1580 MATCH_SINGLE_BINDING,
1582 "this match could be replaced by its body itself",
1583 "consider using the match body instead",
1585 Applicability::MachineApplicable,
1593 /// Returns true if the `ex` match expression is in a local (`let`) statement
1594 fn opt_parent_let<'a>(cx: &LateContext<'a>, ex: &Expr<'a>) -> Option<&'a Local<'a>> {
1595 let map = &cx.tcx.hir();
1597 if let Some(Node::Expr(parent_arm_expr)) = map.find(map.get_parent_node(ex.hir_id));
1598 if let Some(Node::Local(parent_let_expr)) = map.find(map.get_parent_node(parent_arm_expr.hir_id));
1600 return Some(parent_let_expr);
1606 /// Gets all arms that are unbounded `PatRange`s.
1607 fn all_ranges<'tcx>(cx: &LateContext<'tcx>, arms: &'tcx [Arm<'_>], ty: Ty<'tcx>) -> Vec<SpannedRange<FullInt>> {
1610 if let Arm { pat, guard: None, .. } = *arm {
1611 if let PatKind::Range(ref lhs, ref rhs, range_end) = pat.kind {
1612 let lhs = match lhs {
1613 Some(lhs) => constant(cx, cx.typeck_results(), lhs)?.0,
1614 None => miri_to_const(ty.numeric_min_val(cx.tcx)?)?,
1616 let rhs = match rhs {
1617 Some(rhs) => constant(cx, cx.typeck_results(), rhs)?.0,
1618 None => miri_to_const(ty.numeric_max_val(cx.tcx)?)?,
1621 let lhs_val = lhs.int_value(cx, ty)?;
1622 let rhs_val = rhs.int_value(cx, ty)?;
1624 let rhs_bound = match range_end {
1625 RangeEnd::Included => Bound::Included(rhs_val),
1626 RangeEnd::Excluded => Bound::Excluded(rhs_val),
1628 return Some(SpannedRange {
1630 node: (lhs_val, rhs_bound),
1634 if let PatKind::Lit(value) = pat.kind {
1635 let value = constant_full_int(cx, cx.typeck_results(), value)?;
1636 return Some(SpannedRange {
1638 node: (value, Bound::Included(value)),
1647 #[derive(Debug, Eq, PartialEq)]
1648 pub struct SpannedRange<T> {
1650 pub node: (T, Bound<T>),
1653 // Checks if arm has the form `None => None`
1654 fn is_none_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
1655 matches!(arm.pat.kind, PatKind::Path(ref qpath) if is_lang_ctor(cx, qpath, OptionNone))
1658 // Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
1659 fn is_ref_some_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> Option<BindingAnnotation> {
1661 if let PatKind::TupleStruct(ref qpath, [first_pat, ..], _) = arm.pat.kind;
1662 if is_lang_ctor(cx, qpath, OptionSome);
1663 if let PatKind::Binding(rb, .., ident, _) = first_pat.kind;
1664 if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
1665 if let ExprKind::Call(e, args) = remove_blocks(arm.body).kind;
1666 if let ExprKind::Path(ref some_path) = e.kind;
1667 if is_lang_ctor(cx, some_path, OptionSome) && args.len() == 1;
1668 if let ExprKind::Path(QPath::Resolved(_, path2)) = args[0].kind;
1669 if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
1677 fn has_multiple_ref_pats<'a, 'b, I>(pats: I) -> bool
1680 I: Iterator<Item = &'a Pat<'b>>,
1682 let mut ref_count = 0;
1683 for opt in pats.map(|pat| match pat.kind {
1684 PatKind::Ref(..) => Some(true), // &-patterns
1685 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
1686 _ => None, // any other pattern is not fine
1688 if let Some(inner) = opt {
1699 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
1703 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
1705 Start(T, &'a SpannedRange<T>),
1706 End(Bound<T>, &'a SpannedRange<T>),
1709 impl<'a, T: Copy> Kind<'a, T> {
1710 fn range(&self) -> &'a SpannedRange<T> {
1712 Kind::Start(_, r) | Kind::End(_, r) => r,
1716 fn value(self) -> Bound<T> {
1718 Kind::Start(t, _) => Bound::Included(t),
1719 Kind::End(t, _) => t,
1724 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
1725 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
1726 Some(self.cmp(other))
1730 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
1731 fn cmp(&self, other: &Self) -> Ordering {
1732 match (self.value(), other.value()) {
1733 (Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
1734 // Range patterns cannot be unbounded (yet)
1735 (Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(),
1736 (Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) {
1737 Ordering::Equal => Ordering::Greater,
1740 (Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) {
1741 Ordering::Equal => Ordering::Less,
1748 let mut values = Vec::with_capacity(2 * ranges.len());
1751 values.push(Kind::Start(r.node.0, r));
1752 values.push(Kind::End(r.node.1, r));
1757 for (a, b) in iter::zip(&values, values.iter().skip(1)) {
1759 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
1760 if ra.node != rb.node {
1761 return Some((ra, rb));
1764 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
1766 // skip if the range `a` is completely included into the range `b`
1767 if let Ordering::Equal | Ordering::Less = a.cmp(b) {
1768 let kind_a = Kind::End(a.range().node.1, a.range());
1769 let kind_b = Kind::End(b.range().node.1, b.range());
1770 if let Ordering::Equal | Ordering::Greater = kind_a.cmp(&kind_b) {
1774 return Some((a.range(), b.range()));
1782 mod redundant_pattern_match {
1783 use super::REDUNDANT_PATTERN_MATCHING;
1784 use clippy_utils::diagnostics::span_lint_and_then;
1785 use clippy_utils::higher;
1786 use clippy_utils::source::{snippet, snippet_with_applicability};
1787 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item, is_type_lang_item, match_type};
1788 use clippy_utils::{is_lang_ctor, is_qpath_def_path, is_trait_method, paths};
1789 use if_chain::if_chain;
1790 use rustc_ast::ast::LitKind;
1791 use rustc_data_structures::fx::FxHashSet;
1792 use rustc_errors::Applicability;
1793 use rustc_hir::LangItem::{OptionNone, OptionSome, PollPending, PollReady, ResultErr, ResultOk};
1795 intravisit::{walk_expr, ErasedMap, NestedVisitorMap, Visitor},
1796 Arm, Block, Expr, ExprKind, LangItem, MatchSource, Node, Pat, PatKind, QPath,
1798 use rustc_lint::LateContext;
1799 use rustc_middle::ty::{self, subst::GenericArgKind, Ty};
1800 use rustc_span::sym;
1802 pub fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1803 if let Some(higher::IfLet {
1808 }) = higher::IfLet::hir(cx, expr)
1810 find_sugg_for_if_let(cx, expr, let_pat, let_expr, "if", if_else.is_some());
1812 if let ExprKind::Match(op, arms, MatchSource::Normal) = &expr.kind {
1813 find_sugg_for_match(cx, expr, op, arms);
1815 if let Some(higher::WhileLet { let_pat, let_expr, .. }) = higher::WhileLet::hir(expr) {
1816 find_sugg_for_if_let(cx, expr, let_pat, let_expr, "while", false);
1820 /// Checks if the drop order for a type matters. Some std types implement drop solely to
1821 /// deallocate memory. For these types, and composites containing them, changing the drop order
1822 /// won't result in any observable side effects.
1823 fn type_needs_ordered_drop(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
1824 type_needs_ordered_drop_inner(cx, ty, &mut FxHashSet::default())
1827 fn type_needs_ordered_drop_inner(cx: &LateContext<'tcx>, ty: Ty<'tcx>, seen: &mut FxHashSet<Ty<'tcx>>) -> bool {
1828 if !seen.insert(ty) {
1831 if !ty.needs_drop(cx.tcx, cx.param_env) {
1837 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1839 // This type doesn't implement drop, so no side effects here.
1840 // Check if any component type has any.
1842 ty::Tuple(_) => ty.tuple_fields().any(|ty| type_needs_ordered_drop_inner(cx, ty, seen)),
1843 ty::Array(ty, _) => type_needs_ordered_drop_inner(cx, ty, seen),
1844 ty::Adt(adt, subs) => adt
1846 .map(|f| f.ty(cx.tcx, subs))
1847 .any(|ty| type_needs_ordered_drop_inner(cx, ty, seen)),
1851 // Check for std types which implement drop, but only for memory allocation.
1852 else if is_type_diagnostic_item(cx, ty, sym::Vec)
1853 || is_type_lang_item(cx, ty, LangItem::OwnedBox)
1854 || is_type_diagnostic_item(cx, ty, sym::Rc)
1855 || is_type_diagnostic_item(cx, ty, sym::Arc)
1856 || is_type_diagnostic_item(cx, ty, sym::cstring_type)
1857 || is_type_diagnostic_item(cx, ty, sym::BTreeMap)
1858 || is_type_diagnostic_item(cx, ty, sym::LinkedList)
1859 || match_type(cx, ty, &paths::WEAK_RC)
1860 || match_type(cx, ty, &paths::WEAK_ARC)
1862 // Check all of the generic arguments.
1863 if let ty::Adt(_, subs) = ty.kind() {
1864 subs.types().any(|ty| type_needs_ordered_drop_inner(cx, ty, seen))
1873 // Extract the generic arguments out of a type
1874 fn try_get_generic_ty(ty: Ty<'_>, index: usize) -> Option<Ty<'_>> {
1876 if let ty::Adt(_, subs) = ty.kind();
1877 if let Some(sub) = subs.get(index);
1878 if let GenericArgKind::Type(sub_ty) = sub.unpack();
1887 // Checks if there are any temporaries created in the given expression for which drop order
1889 fn temporaries_need_ordered_drop(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
1890 struct V<'a, 'tcx> {
1891 cx: &'a LateContext<'tcx>,
1894 impl<'a, 'tcx> Visitor<'tcx> for V<'a, 'tcx> {
1895 type Map = ErasedMap<'tcx>;
1896 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1897 NestedVisitorMap::None
1900 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
1902 // Taking the reference of a value leaves a temporary
1903 // e.g. In `&String::new()` the string is a temporary value.
1904 // Remaining fields are temporary values
1905 // e.g. In `(String::new(), 0).1` the string is a temporary value.
1906 ExprKind::AddrOf(_, _, expr) | ExprKind::Field(expr, _) => {
1907 if !matches!(expr.kind, ExprKind::Path(_)) {
1908 if type_needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(expr)) {
1911 self.visit_expr(expr);
1915 // the base type is alway taken by reference.
1916 // e.g. In `(vec![0])[0]` the vector is a temporary value.
1917 ExprKind::Index(base, index) => {
1918 if !matches!(base.kind, ExprKind::Path(_)) {
1919 if type_needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(base)) {
1922 self.visit_expr(base);
1925 self.visit_expr(index);
1927 // Method calls can take self by reference.
1928 // e.g. In `String::new().len()` the string is a temporary value.
1929 ExprKind::MethodCall(_, _, [self_arg, args @ ..], _) => {
1930 if !matches!(self_arg.kind, ExprKind::Path(_)) {
1931 let self_by_ref = self
1934 .type_dependent_def_id(expr.hir_id)
1935 .map_or(false, |id| self.cx.tcx.fn_sig(id).skip_binder().inputs()[0].is_ref());
1937 && type_needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(self_arg))
1941 self.visit_expr(self_arg);
1944 args.iter().for_each(|arg| self.visit_expr(arg));
1946 // Either explicitly drops values, or changes control flow.
1947 ExprKind::DropTemps(_)
1949 | ExprKind::Break(..)
1950 | ExprKind::Yield(..)
1951 | ExprKind::Block(Block { expr: None, .. }, _)
1952 | ExprKind::Loop(..) => (),
1954 // Only consider the final expression.
1955 ExprKind::Block(Block { expr: Some(expr), .. }, _) => self.visit_expr(expr),
1957 _ => walk_expr(self, expr),
1962 let mut v = V { cx, res: false };
1967 fn find_sugg_for_if_let<'tcx>(
1968 cx: &LateContext<'tcx>,
1969 expr: &'tcx Expr<'_>,
1971 let_expr: &'tcx Expr<'_>,
1972 keyword: &'static str,
1975 // also look inside refs
1976 let mut kind = &let_pat.kind;
1977 // if we have &None for example, peel it so we can detect "if let None = x"
1978 if let PatKind::Ref(inner, _mutability) = kind {
1981 let op_ty = cx.typeck_results().expr_ty(let_expr);
1982 // Determine which function should be used, and the type contained by the corresponding
1984 let (good_method, inner_ty) = match kind {
1985 PatKind::TupleStruct(ref path, [sub_pat], _) => {
1986 if let PatKind::Wild = sub_pat.kind {
1987 if is_lang_ctor(cx, path, ResultOk) {
1988 ("is_ok()", try_get_generic_ty(op_ty, 0).unwrap_or(op_ty))
1989 } else if is_lang_ctor(cx, path, ResultErr) {
1990 ("is_err()", try_get_generic_ty(op_ty, 1).unwrap_or(op_ty))
1991 } else if is_lang_ctor(cx, path, OptionSome) {
1992 ("is_some()", op_ty)
1993 } else if is_lang_ctor(cx, path, PollReady) {
1994 ("is_ready()", op_ty)
1995 } else if is_qpath_def_path(cx, path, sub_pat.hir_id, &paths::IPADDR_V4) {
1996 ("is_ipv4()", op_ty)
1997 } else if is_qpath_def_path(cx, path, sub_pat.hir_id, &paths::IPADDR_V6) {
1998 ("is_ipv6()", op_ty)
2006 PatKind::Path(ref path) => {
2007 let method = if is_lang_ctor(cx, path, OptionNone) {
2009 } else if is_lang_ctor(cx, path, PollPending) {
2014 // `None` and `Pending` don't have an inner type.
2015 (method, cx.tcx.types.unit)
2020 // If this is the last expression in a block or there is an else clause then the whole
2021 // type needs to be considered, not just the inner type of the branch being matched on.
2022 // Note the last expression in a block is dropped after all local bindings.
2023 let check_ty = if has_else
2024 || (keyword == "if" && matches!(cx.tcx.hir().parent_iter(expr.hir_id).next(), Some((_, Node::Block(..)))))
2031 // All temporaries created in the scrutinee expression are dropped at the same time as the
2032 // scrutinee would be, so they have to be considered as well.
2033 // e.g. in `if let Some(x) = foo.lock().unwrap().baz.as_ref() { .. }` the lock will be held
2034 // for the duration if body.
2035 let needs_drop = type_needs_ordered_drop(cx, check_ty) || temporaries_need_ordered_drop(cx, let_expr);
2037 // check that `while_let_on_iterator` lint does not trigger
2039 if keyword == "while";
2040 if let ExprKind::MethodCall(method_path, _, _, _) = let_expr.kind;
2041 if method_path.ident.name == sym::next;
2042 if is_trait_method(cx, let_expr, sym::Iterator);
2048 let result_expr = match &let_expr.kind {
2049 ExprKind::AddrOf(_, _, borrowed) => borrowed,
2054 REDUNDANT_PATTERN_MATCHING,
2056 &format!("redundant pattern matching, consider using `{}`", good_method),
2058 // if/while let ... = ... { ... }
2059 // ^^^^^^^^^^^^^^^^^^^^^^^^^^^
2060 let expr_span = expr.span;
2062 // if/while let ... = ... { ... }
2064 let op_span = result_expr.span.source_callsite();
2066 // if/while let ... = ... { ... }
2067 // ^^^^^^^^^^^^^^^^^^^
2068 let span = expr_span.until(op_span.shrink_to_hi());
2070 let mut app = if needs_drop {
2071 Applicability::MaybeIncorrect
2073 Applicability::MachineApplicable
2075 let sugg = snippet_with_applicability(cx, op_span, "_", &mut app);
2077 diag.span_suggestion(span, "try this", format!("{} {}.{}", keyword, sugg, good_method), app);
2080 diag.note("this will change drop order of the result, as well as all temporaries");
2081 diag.note("add `#[allow(clippy::redundant_pattern_matching)]` if this is important");
2087 fn find_sugg_for_match<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, op: &Expr<'_>, arms: &[Arm<'_>]) {
2088 if arms.len() == 2 {
2089 let node_pair = (&arms[0].pat.kind, &arms[1].pat.kind);
2091 let found_good_method = match node_pair {
2093 PatKind::TupleStruct(ref path_left, patterns_left, _),
2094 PatKind::TupleStruct(ref path_right, patterns_right, _),
2095 ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
2096 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].kind, &patterns_right[0].kind) {
2097 find_good_method_for_match(
2108 find_good_method_for_match(
2123 (PatKind::TupleStruct(ref path_left, patterns, _), PatKind::Path(ref path_right))
2124 | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, patterns, _))
2125 if patterns.len() == 1 =>
2127 if let PatKind::Wild = patterns[0].kind {
2128 find_good_method_for_match(
2133 &paths::OPTION_SOME,
2134 &paths::OPTION_NONE,
2139 find_good_method_for_match(
2145 &paths::POLL_PENDING,
2157 if let Some(good_method) = found_good_method {
2158 let span = expr.span.to(op.span);
2159 let result_expr = match &op.kind {
2160 ExprKind::AddrOf(_, _, borrowed) => borrowed,
2165 REDUNDANT_PATTERN_MATCHING,
2167 &format!("redundant pattern matching, consider using `{}`", good_method),
2169 diag.span_suggestion(
2172 format!("{}.{}", snippet(cx, result_expr.span, "_"), good_method),
2173 Applicability::MaybeIncorrect, // snippet
2181 #[allow(clippy::too_many_arguments)]
2182 fn find_good_method_for_match<'a>(
2183 cx: &LateContext<'_>,
2185 path_left: &QPath<'_>,
2186 path_right: &QPath<'_>,
2187 expected_left: &[&str],
2188 expected_right: &[&str],
2189 should_be_left: &'a str,
2190 should_be_right: &'a str,
2191 ) -> Option<&'a str> {
2192 let body_node_pair = if is_qpath_def_path(cx, path_left, arms[0].pat.hir_id, expected_left)
2193 && is_qpath_def_path(cx, path_right, arms[1].pat.hir_id, expected_right)
2195 (&(*arms[0].body).kind, &(*arms[1].body).kind)
2196 } else if is_qpath_def_path(cx, path_right, arms[1].pat.hir_id, expected_left)
2197 && is_qpath_def_path(cx, path_left, arms[0].pat.hir_id, expected_right)
2199 (&(*arms[1].body).kind, &(*arms[0].body).kind)
2204 match body_node_pair {
2205 (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
2206 (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
2207 (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
2216 fn test_overlapping() {
2217 use rustc_span::source_map::DUMMY_SP;
2219 let sp = |s, e| SpannedRange {
2224 assert_eq!(None, overlapping::<u8>(&[]));
2225 assert_eq!(None, overlapping(&[sp(1, Bound::Included(4))]));
2228 overlapping(&[sp(1, Bound::Included(4)), sp(5, Bound::Included(6))])
2233 sp(1, Bound::Included(4)),
2234 sp(5, Bound::Included(6)),
2235 sp(10, Bound::Included(11))
2239 Some((&sp(1, Bound::Included(4)), &sp(3, Bound::Included(6)))),
2240 overlapping(&[sp(1, Bound::Included(4)), sp(3, Bound::Included(6))])
2243 Some((&sp(5, Bound::Included(6)), &sp(6, Bound::Included(11)))),
2245 sp(1, Bound::Included(4)),
2246 sp(5, Bound::Included(6)),
2247 sp(6, Bound::Included(11))
2252 /// Implementation of `MATCH_SAME_ARMS`.
2253 fn lint_match_arms<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>) {
2254 if let ExprKind::Match(_, arms, MatchSource::Normal) = expr.kind {
2255 let hash = |&(_, arm): &(usize, &Arm<'_>)| -> u64 {
2256 let mut h = SpanlessHash::new(cx);
2257 h.hash_expr(arm.body);
2261 let eq = |&(lindex, lhs): &(usize, &Arm<'_>), &(rindex, rhs): &(usize, &Arm<'_>)| -> bool {
2262 let min_index = usize::min(lindex, rindex);
2263 let max_index = usize::max(lindex, rindex);
2265 let mut local_map: HirIdMap<HirId> = HirIdMap::default();
2266 let eq_fallback = |a: &Expr<'_>, b: &Expr<'_>| {
2268 if let Some(a_id) = path_to_local(a);
2269 if let Some(b_id) = path_to_local(b);
2270 let entry = match local_map.entry(a_id) {
2271 Entry::Vacant(entry) => entry,
2272 // check if using the same bindings as before
2273 Entry::Occupied(entry) => return *entry.get() == b_id,
2275 // the names technically don't have to match; this makes the lint more conservative
2276 if cx.tcx.hir().name(a_id) == cx.tcx.hir().name(b_id);
2277 if TyS::same_type(cx.typeck_results().expr_ty(a), cx.typeck_results().expr_ty(b));
2278 if pat_contains_local(lhs.pat, a_id);
2279 if pat_contains_local(rhs.pat, b_id);
2288 // Arms with a guard are ignored, those can’t always be merged together
2289 // This is also the case for arms in-between each there is an arm with a guard
2290 (min_index..=max_index).all(|index| arms[index].guard.is_none())
2291 && SpanlessEq::new(cx)
2292 .expr_fallback(eq_fallback)
2293 .eq_expr(lhs.body, rhs.body)
2294 // these checks could be removed to allow unused bindings
2295 && bindings_eq(lhs.pat, local_map.keys().copied().collect())
2296 && bindings_eq(rhs.pat, local_map.values().copied().collect())
2299 let indexed_arms: Vec<(usize, &Arm<'_>)> = arms.iter().enumerate().collect();
2300 for (&(_, i), &(_, j)) in search_same(&indexed_arms, hash, eq) {
2305 "this `match` has identical arm bodies",
2307 diag.span_note(i.body.span, "same as this");
2309 // Note: this does not use `span_suggestion` on purpose:
2310 // there is no clean way
2311 // to remove the other arm. Building a span and suggest to replace it to ""
2312 // makes an even more confusing error message. Also in order not to make up a
2313 // span for the whole pattern, the suggestion is only shown when there is only
2314 // one pattern. The user should know about `|` if they are already using it…
2316 let lhs = snippet(cx, i.pat.span, "<pat1>");
2317 let rhs = snippet(cx, j.pat.span, "<pat2>");
2319 if let PatKind::Wild = j.pat.kind {
2320 // if the last arm is _, then i could be integrated into _
2321 // note that i.pat cannot be _, because that would mean that we're
2322 // hiding all the subsequent arms, and rust won't compile
2326 "`{}` has the same arm body as the `_` wildcard, consider removing it",
2331 diag.span_help(i.pat.span, &format!("consider refactoring into `{} | {}`", lhs, rhs,))
2332 .help("...or consider changing the match arm bodies");
2340 fn pat_contains_local(pat: &Pat<'_>, id: HirId) -> bool {
2341 let mut result = false;
2342 pat.walk_short(|p| {
2343 result |= matches!(p.kind, PatKind::Binding(_, binding_id, ..) if binding_id == id);
2349 /// Returns true if all the bindings in the `Pat` are in `ids` and vice versa
2350 fn bindings_eq(pat: &Pat<'_>, mut ids: HirIdSet) -> bool {
2351 let mut result = true;
2352 pat.each_binding_or_first(&mut |_, id, _, _| result &= ids.remove(&id));
2353 result && ids.is_empty()