1 use crate::consts::{constant, Constant};
2 use crate::utils::paths;
3 use crate::utils::sugg::Sugg;
5 expr_block, is_allowed, is_expn_of, match_qpath, match_type, multispan_sugg, remove_blocks, snippet,
6 snippet_with_applicability, span_lint_and_sugg, span_lint_and_then, span_note_and_lint, walk_ptrs_ty,
8 use if_chain::if_chain;
9 use rustc::declare_lint_pass;
10 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
11 use rustc::ty::{self, Ty};
12 use rustc_errors::Applicability;
13 use rustc_hir::def::CtorKind;
15 use rustc_session::declare_tool_lint;
16 use rustc_span::source_map::Span;
17 use std::cmp::Ordering;
18 use std::collections::Bound;
19 use syntax::ast::LitKind;
21 declare_clippy_lint! {
22 /// **What it does:** Checks for matches with a single arm where an `if let`
23 /// will usually suffice.
25 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
27 /// **Known problems:** None.
31 /// # fn bar(stool: &str) {}
32 /// # let x = Some("abc");
34 /// Some(ref foo) => bar(foo),
40 "a match statement with a single nontrivial arm (i.e., where the other arm is `_ => {}`) instead of `if let`"
43 declare_clippy_lint! {
44 /// **What it does:** Checks for matches with two arms where an `if let else` will
47 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
49 /// **Known problems:** Personal style preferences may differ.
56 /// # fn bar(foo: &usize) {}
57 /// # let other_ref: usize = 1;
58 /// # let x: Option<&usize> = Some(&1);
60 /// Some(ref foo) => bar(foo),
61 /// _ => bar(&other_ref),
65 /// Using `if let` with `else`:
68 /// # fn bar(foo: &usize) {}
69 /// # let other_ref: usize = 1;
70 /// # let x: Option<&usize> = Some(&1);
71 /// if let Some(ref foo) = x {
77 pub SINGLE_MATCH_ELSE,
79 "a match statement with two arms where the second arm's pattern is a placeholder instead of a specific match pattern"
82 declare_clippy_lint! {
83 /// **What it does:** Checks for matches where all arms match a reference,
84 /// suggesting to remove the reference and deref the matched expression
85 /// instead. It also checks for `if let &foo = bar` blocks.
87 /// **Why is this bad?** It just makes the code less readable. That reference
88 /// destructuring adds nothing to the code.
90 /// **Known problems:** None.
95 /// &A(ref y) => foo(y),
102 "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
105 declare_clippy_lint! {
106 /// **What it does:** Checks for matches where match expression is a `bool`. It
107 /// suggests to replace the expression with an `if...else` block.
109 /// **Why is this bad?** It makes the code less readable.
111 /// **Known problems:** None.
117 /// let condition: bool = true;
118 /// match condition {
123 /// Use if/else instead:
127 /// let condition: bool = true;
136 "a match on a boolean expression instead of an `if..else` block"
139 declare_clippy_lint! {
140 /// **What it does:** Checks for overlapping match arms.
142 /// **Why is this bad?** It is likely to be an error and if not, makes the code
145 /// **Known problems:** None.
151 /// 1...10 => println!("1 ... 10"),
152 /// 5...15 => println!("5 ... 15"),
156 pub MATCH_OVERLAPPING_ARM,
158 "a match with overlapping arms"
161 declare_clippy_lint! {
162 /// **What it does:** Checks for arm which matches all errors with `Err(_)`
163 /// and take drastic actions like `panic!`.
165 /// **Why is this bad?** It is generally a bad practice, just like
166 /// catching all exceptions in java with `catch(Exception)`
168 /// **Known problems:** None.
172 /// let x: Result<i32, &str> = Ok(3);
174 /// Ok(_) => println!("ok"),
175 /// Err(_) => panic!("err"),
178 pub MATCH_WILD_ERR_ARM,
180 "a match with `Err(_)` arm and take drastic actions"
183 declare_clippy_lint! {
184 /// **What it does:** Checks for match which is used to add a reference to an
187 /// **Why is this bad?** Using `as_ref()` or `as_mut()` instead is shorter.
189 /// **Known problems:** None.
193 /// let x: Option<()> = None;
194 /// let r: Option<&()> = match x {
196 /// Some(ref v) => Some(v),
201 "a match on an Option value instead of using `as_ref()` or `as_mut`"
204 declare_clippy_lint! {
205 /// **What it does:** Checks for wildcard enum matches using `_`.
207 /// **Why is this bad?** New enum variants added by library updates can be missed.
209 /// **Known problems:** Suggested replacements may be incorrect if guards exhaustively cover some
210 /// variants, and also may not use correct path to enum if it's not present in the current scope.
214 /// # enum Foo { A(usize), B(usize) }
215 /// # let x = Foo::B(1);
221 pub WILDCARD_ENUM_MATCH_ARM,
223 "a wildcard enum match arm using `_`"
226 declare_lint_pass!(Matches => [
231 MATCH_OVERLAPPING_ARM,
234 WILDCARD_ENUM_MATCH_ARM
237 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Matches {
238 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
239 if in_external_macro(cx.sess(), expr.span) {
242 if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.kind {
243 check_single_match(cx, ex, arms, expr);
244 check_match_bool(cx, ex, arms, expr);
245 check_overlapping_arms(cx, ex, arms);
246 check_wild_err_arm(cx, ex, arms);
247 check_wild_enum_match(cx, ex, arms);
248 check_match_as_ref(cx, ex, arms, expr);
250 if let ExprKind::Match(ref ex, ref arms, _) = expr.kind {
251 check_match_ref_pats(cx, ex, arms, expr);
257 fn check_single_match(cx: &LateContext<'_, '_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
258 if arms.len() == 2 && arms[0].guard.is_none() && arms[1].guard.is_none() {
259 if let PatKind::Or(..) = arms[0].pat.kind {
260 // don't lint for or patterns for now, this makes
261 // the lint noisy in unnecessary situations
264 let els = remove_blocks(&arms[1].body);
265 let els = if is_unit_expr(els) {
267 } else if let ExprKind::Block(_, _) = els.kind {
268 // matches with blocks that contain statements are prettier as `if let + else`
271 // allow match arms with just expressions
274 let ty = cx.tables.expr_ty(ex);
275 if ty.kind != ty::Bool || is_allowed(cx, MATCH_BOOL, ex.hir_id) {
276 check_single_match_single_pattern(cx, ex, arms, expr, els);
277 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
282 fn check_single_match_single_pattern(
283 cx: &LateContext<'_, '_>,
287 els: Option<&Expr<'_>>,
289 if is_wild(&arms[1].pat) {
290 report_single_match_single_pattern(cx, ex, arms, expr, els);
294 fn report_single_match_single_pattern(
295 cx: &LateContext<'_, '_>,
299 els: Option<&Expr<'_>>,
301 let lint = if els.is_some() { SINGLE_MATCH_ELSE } else { SINGLE_MATCH };
302 let els_str = els.map_or(String::new(), |els| {
303 format!(" else {}", expr_block(cx, els, None, ".."))
309 "you seem to be trying to use match for destructuring a single pattern. Consider using `if \
313 "if let {} = {} {}{}",
314 snippet(cx, arms[0].pat.span, ".."),
315 snippet(cx, ex.span, ".."),
316 expr_block(cx, &arms[0].body, None, ".."),
319 Applicability::HasPlaceholders,
323 fn check_single_match_opt_like(
324 cx: &LateContext<'_, '_>,
329 els: Option<&Expr<'_>>,
331 // list of candidate `Enum`s we know will never get any more members
333 (&paths::COW, "Borrowed"),
334 (&paths::COW, "Cow::Borrowed"),
335 (&paths::COW, "Cow::Owned"),
336 (&paths::COW, "Owned"),
337 (&paths::OPTION, "None"),
338 (&paths::RESULT, "Err"),
339 (&paths::RESULT, "Ok"),
342 let path = match arms[1].pat.kind {
343 PatKind::TupleStruct(ref path, ref inner, _) => {
344 // Contains any non wildcard patterns (e.g., `Err(err)`)?
345 if !inner.iter().all(is_wild) {
348 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
350 PatKind::Binding(BindingAnnotation::Unannotated, .., ident, None) => ident.to_string(),
351 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
355 for &(ty_path, pat_path) in candidates {
356 if path == *pat_path && match_type(cx, ty, ty_path) {
357 report_single_match_single_pattern(cx, ex, arms, expr, els);
362 fn check_match_bool(cx: &LateContext<'_, '_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
363 // Type of expression is `bool`.
364 if cx.tables.expr_ty(ex).kind == ty::Bool {
369 "you seem to be trying to match on a boolean expression",
373 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pat.kind {
374 if let ExprKind::Lit(ref lit) = arm_bool.kind {
376 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
377 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
387 if let Some((true_expr, false_expr)) = exprs {
388 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
389 (false, false) => Some(format!(
391 snippet(cx, ex.span, "b"),
392 expr_block(cx, true_expr, None, ".."),
393 expr_block(cx, false_expr, None, "..")
395 (false, true) => Some(format!(
397 snippet(cx, ex.span, "b"),
398 expr_block(cx, true_expr, None, "..")
401 let test = Sugg::hir(cx, ex, "..");
402 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
404 (true, true) => None,
407 if let Some(sugg) = sugg {
410 "consider using an if/else expression",
412 Applicability::HasPlaceholders,
422 fn check_overlapping_arms<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ex: &'tcx Expr<'_>, arms: &'tcx [Arm<'_>]) {
423 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
424 let ranges = all_ranges(cx, arms);
425 let type_ranges = type_ranges(&ranges);
426 if !type_ranges.is_empty() {
427 if let Some((start, end)) = overlapping(&type_ranges) {
430 MATCH_OVERLAPPING_ARM,
432 "some ranges overlap",
434 "overlaps with this",
441 fn is_wild<'tcx>(pat: &impl std::ops::Deref<Target = Pat<'tcx>>) -> bool {
443 PatKind::Wild => true,
448 fn check_wild_err_arm(cx: &LateContext<'_, '_>, ex: &Expr<'_>, arms: &[Arm<'_>]) {
449 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
450 if match_type(cx, ex_ty, &paths::RESULT) {
452 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pat.kind {
453 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
455 if path_str == "Err";
456 if inner.iter().any(is_wild);
457 if let ExprKind::Block(ref block, _) = arm.body.kind;
458 if is_panic_block(block);
460 // `Err(_)` arm with `panic!` found
461 span_note_and_lint(cx,
464 "Err(_) will match all errors, maybe not a good idea",
466 "to remove this warning, match each error separately \
467 or use unreachable macro");
475 fn check_wild_enum_match(cx: &LateContext<'_, '_>, ex: &Expr<'_>, arms: &[Arm<'_>]) {
476 let ty = cx.tables.expr_ty(ex);
478 // If there isn't a nice closed set of possible values that can be conveniently enumerated,
479 // don't complain about not enumerating the mall.
483 // First pass - check for violation, but don't do much book-keeping because this is hopefully
484 // the uncommon case, and the book-keeping is slightly expensive.
485 let mut wildcard_span = None;
486 let mut wildcard_ident = None;
488 if let PatKind::Wild = arm.pat.kind {
489 wildcard_span = Some(arm.pat.span);
490 } else if let PatKind::Binding(_, _, ident, None) = arm.pat.kind {
491 wildcard_span = Some(arm.pat.span);
492 wildcard_ident = Some(ident);
496 if let Some(wildcard_span) = wildcard_span {
497 // Accumulate the variants which should be put in place of the wildcard because they're not
500 let mut missing_variants = vec![];
501 if let ty::Adt(def, _) = ty.kind {
502 for variant in &def.variants {
503 missing_variants.push(variant);
508 if arm.guard.is_some() {
509 // Guards mean that this case probably isn't exhaustively covered. Technically
510 // this is incorrect, as we should really check whether each variant is exhaustively
511 // covered by the set of guards that cover it, but that's really hard to do.
514 if let PatKind::Path(ref path) = arm.pat.kind {
515 if let QPath::Resolved(_, p) = path {
516 missing_variants.retain(|e| e.ctor_def_id != Some(p.res.def_id()));
518 } else if let PatKind::TupleStruct(ref path, ..) = arm.pat.kind {
519 if let QPath::Resolved(_, p) = path {
520 missing_variants.retain(|e| e.ctor_def_id != Some(p.res.def_id()));
525 let mut suggestion: Vec<String> = missing_variants
528 let suffix = match v.ctor_kind {
529 CtorKind::Fn => "(..)",
530 CtorKind::Const | CtorKind::Fictive => "",
532 let ident_str = if let Some(ident) = wildcard_ident {
533 format!("{} @ ", ident.name)
537 // This path assumes that the enum type is imported into scope.
538 format!("{}{}{}", ident_str, cx.tcx.def_path_str(v.def_id), suffix)
542 if suggestion.is_empty() {
546 let mut message = "wildcard match will miss any future added variants";
548 if let ty::Adt(def, _) = ty.kind {
549 if def.is_variant_list_non_exhaustive() {
550 message = "match on non-exhaustive enum doesn't explicitly match all known variants";
551 suggestion.push(String::from("_"));
557 WILDCARD_ENUM_MATCH_ARM,
561 suggestion.join(" | "),
562 Applicability::MachineApplicable,
567 // If the block contains only a `panic!` macro (as expression or statement)
568 fn is_panic_block(block: &Block<'_>) -> bool {
569 match (&block.expr, block.stmts.len(), block.stmts.first()) {
570 (&Some(ref exp), 0, _) => {
571 is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
573 (&None, 1, Some(stmt)) => {
574 is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
580 fn check_match_ref_pats(cx: &LateContext<'_, '_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
581 if has_only_ref_pats(arms) {
582 let mut suggs = Vec::new();
583 let (title, msg) = if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, ref inner) = ex.kind {
584 let span = ex.span.source_callsite();
585 suggs.push((span, Sugg::hir_with_macro_callsite(cx, inner, "..").to_string()));
587 "you don't need to add `&` to both the expression and the patterns",
591 let span = ex.span.source_callsite();
592 suggs.push((span, Sugg::hir_with_macro_callsite(cx, ex, "..").deref().to_string()));
594 "you don't need to add `&` to all patterns",
595 "instead of prefixing all patterns with `&`, you can dereference the expression",
599 suggs.extend(arms.iter().filter_map(|a| {
600 if let PatKind::Ref(ref refp, _) = a.pat.kind {
601 Some((a.pat.span, snippet(cx, refp.span, "..").to_string()))
607 span_lint_and_then(cx, MATCH_REF_PATS, expr.span, title, |db| {
608 if !expr.span.from_expansion() {
609 multispan_sugg(db, msg.to_owned(), suggs);
615 fn check_match_as_ref(cx: &LateContext<'_, '_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
616 if arms.len() == 2 && arms[0].guard.is_none() && arms[1].guard.is_none() {
617 let arm_ref: Option<BindingAnnotation> = if is_none_arm(&arms[0]) {
618 is_ref_some_arm(&arms[1])
619 } else if is_none_arm(&arms[1]) {
620 is_ref_some_arm(&arms[0])
624 if let Some(rb) = arm_ref {
625 let suggestion = if rb == BindingAnnotation::Ref {
631 let output_ty = cx.tables.expr_ty(expr);
632 let input_ty = cx.tables.expr_ty(ex);
634 let cast = if_chain! {
635 if let ty::Adt(_, substs) = input_ty.kind;
636 let input_ty = substs.type_at(0);
637 if let ty::Adt(_, substs) = output_ty.kind;
638 let output_ty = substs.type_at(0);
639 if let ty::Ref(_, output_ty, _) = output_ty.kind;
640 if input_ty != output_ty;
648 let mut applicability = Applicability::MachineApplicable;
653 &format!("use {}() instead", suggestion),
657 snippet_with_applicability(cx, ex.span, "_", &mut applicability),
667 /// Gets all arms that are unbounded `PatRange`s.
668 fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &'tcx [Arm<'_>]) -> Vec<SpannedRange<Constant>> {
672 ref pat, guard: None, ..
675 if let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.kind {
676 let lhs = constant(cx, cx.tables, lhs)?.0;
677 let rhs = constant(cx, cx.tables, rhs)?.0;
678 let rhs = match *range_end {
679 RangeEnd::Included => Bound::Included(rhs),
680 RangeEnd::Excluded => Bound::Excluded(rhs),
682 return Some(SpannedRange {
688 if let PatKind::Lit(ref value) = pat.kind {
689 let value = constant(cx, cx.tables, value)?.0;
690 return Some(SpannedRange {
692 node: (value.clone(), Bound::Included(value)),
701 #[derive(Debug, Eq, PartialEq)]
702 pub struct SpannedRange<T> {
704 pub node: (T, Bound<T>),
707 type TypedRanges = Vec<SpannedRange<u128>>;
709 /// Gets all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway
710 /// and other types than
711 /// `Uint` and `Int` probably don't make sense.
712 fn type_ranges(ranges: &[SpannedRange<Constant>]) -> TypedRanges {
715 .filter_map(|range| match range.node {
716 (Constant::Int(start), Bound::Included(Constant::Int(end))) => Some(SpannedRange {
718 node: (start, Bound::Included(end)),
720 (Constant::Int(start), Bound::Excluded(Constant::Int(end))) => Some(SpannedRange {
722 node: (start, Bound::Excluded(end)),
724 (Constant::Int(start), Bound::Unbounded) => Some(SpannedRange {
726 node: (start, Bound::Unbounded),
733 fn is_unit_expr(expr: &Expr<'_>) -> bool {
735 ExprKind::Tup(ref v) if v.is_empty() => true,
736 ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
741 // Checks if arm has the form `None => None`
742 fn is_none_arm(arm: &Arm<'_>) -> bool {
744 PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => true,
749 // Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
750 fn is_ref_some_arm(arm: &Arm<'_>) -> Option<BindingAnnotation> {
752 if let PatKind::TupleStruct(ref path, ref pats, _) = arm.pat.kind;
753 if pats.len() == 1 && match_qpath(path, &paths::OPTION_SOME);
754 if let PatKind::Binding(rb, .., ident, _) = pats[0].kind;
755 if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
756 if let ExprKind::Call(ref e, ref args) = remove_blocks(&arm.body).kind;
757 if let ExprKind::Path(ref some_path) = e.kind;
758 if match_qpath(some_path, &paths::OPTION_SOME) && args.len() == 1;
759 if let ExprKind::Path(ref qpath) = args[0].kind;
760 if let &QPath::Resolved(_, ref path2) = qpath;
761 if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
769 fn has_only_ref_pats(arms: &[Arm<'_>]) -> bool {
774 PatKind::Ref(..) => Some(true), // &-patterns
775 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
776 _ => None, // any other pattern is not fine
779 .collect::<Option<Vec<bool>>>();
780 // look for Some(v) where there's at least one true element
781 mapped.map_or(false, |v| v.iter().any(|el| *el))
784 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
788 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
790 Start(T, &'a SpannedRange<T>),
791 End(Bound<T>, &'a SpannedRange<T>),
794 impl<'a, T: Copy> Kind<'a, T> {
795 fn range(&self) -> &'a SpannedRange<T> {
797 Kind::Start(_, r) | Kind::End(_, r) => r,
801 fn value(self) -> Bound<T> {
803 Kind::Start(t, _) => Bound::Included(t),
804 Kind::End(t, _) => t,
809 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
810 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
811 Some(self.cmp(other))
815 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
816 fn cmp(&self, other: &Self) -> Ordering {
817 match (self.value(), other.value()) {
818 (Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
819 // Range patterns cannot be unbounded (yet)
820 (Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(),
821 (Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) {
822 Ordering::Equal => Ordering::Greater,
825 (Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) {
826 Ordering::Equal => Ordering::Less,
833 let mut values = Vec::with_capacity(2 * ranges.len());
836 values.push(Kind::Start(r.node.0, r));
837 values.push(Kind::End(r.node.1, r));
842 for (a, b) in values.iter().zip(values.iter().skip(1)) {
844 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
845 if ra.node != rb.node {
846 return Some((ra, rb));
849 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
850 _ => return Some((a.range(), b.range())),