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::hir::def::CtorKind;
11 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
12 use rustc::ty::{self, Ty};
13 use rustc::{declare_lint_pass, declare_tool_lint};
14 use rustc_errors::Applicability;
15 use std::cmp::Ordering;
16 use std::collections::Bound;
17 use syntax::ast::LitKind;
18 use syntax::source_map::Span;
20 declare_clippy_lint! {
21 /// **What it does:** Checks for matches with a single arm where an `if let`
22 /// will usually suffice.
24 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
26 /// **Known problems:** None.
30 /// # fn bar(stool: &str) {}
31 /// # let x = Some("abc");
33 /// Some(ref foo) => bar(foo),
39 "a match statement with a single nontrivial arm (i.e., where the other arm is `_ => {}`) instead of `if let`"
42 declare_clippy_lint! {
43 /// **What it does:** Checks for matches with two arms where an `if let else` will
46 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
48 /// **Known problems:** Personal style preferences may differ.
55 /// # fn bar(foo: &usize) {}
56 /// # let other_ref: usize = 1;
57 /// # let x: Option<&usize> = Some(&1);
59 /// Some(ref foo) => bar(foo),
60 /// _ => bar(&other_ref),
64 /// Using `if let` with `else`:
67 /// # fn bar(foo: &usize) {}
68 /// # let other_ref: usize = 1;
69 /// # let x: Option<&usize> = Some(&1);
70 /// if let Some(ref foo) = x {
76 pub SINGLE_MATCH_ELSE,
78 "a match statement with two arms where the second arm's pattern is a placeholder instead of a specific match pattern"
81 declare_clippy_lint! {
82 /// **What it does:** Checks for matches where all arms match a reference,
83 /// suggesting to remove the reference and deref the matched expression
84 /// instead. It also checks for `if let &foo = bar` blocks.
86 /// **Why is this bad?** It just makes the code less readable. That reference
87 /// destructuring adds nothing to the code.
89 /// **Known problems:** None.
94 /// &A(ref y) => foo(y),
101 "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
104 declare_clippy_lint! {
105 /// **What it does:** Checks for matches where match expression is a `bool`. It
106 /// suggests to replace the expression with an `if...else` block.
108 /// **Why is this bad?** It makes the code less readable.
110 /// **Known problems:** None.
116 /// let condition: bool = true;
117 /// match condition {
122 /// Use if/else instead:
126 /// let condition: bool = true;
135 "a match on a boolean expression instead of an `if..else` block"
138 declare_clippy_lint! {
139 /// **What it does:** Checks for overlapping match arms.
141 /// **Why is this bad?** It is likely to be an error and if not, makes the code
144 /// **Known problems:** None.
150 /// 1...10 => println!("1 ... 10"),
151 /// 5...15 => println!("5 ... 15"),
155 pub MATCH_OVERLAPPING_ARM,
157 "a match with overlapping arms"
160 declare_clippy_lint! {
161 /// **What it does:** Checks for arm which matches all errors with `Err(_)`
162 /// and take drastic actions like `panic!`.
164 /// **Why is this bad?** It is generally a bad practice, just like
165 /// catching all exceptions in java with `catch(Exception)`
167 /// **Known problems:** None.
171 /// let x: Result<i32, &str> = Ok(3);
173 /// Ok(_) => println!("ok"),
174 /// Err(_) => panic!("err"),
177 pub MATCH_WILD_ERR_ARM,
179 "a match with `Err(_)` arm and take drastic actions"
182 declare_clippy_lint! {
183 /// **What it does:** Checks for match which is used to add a reference to an
186 /// **Why is this bad?** Using `as_ref()` or `as_mut()` instead is shorter.
188 /// **Known problems:** None.
192 /// let x: Option<()> = None;
193 /// let r: Option<&()> = match x {
195 /// Some(ref v) => Some(v),
200 "a match on an Option value instead of using `as_ref()` or `as_mut`"
203 declare_clippy_lint! {
204 /// **What it does:** Checks for wildcard enum matches using `_`.
206 /// **Why is this bad?** New enum variants added by library updates can be missed.
208 /// **Known problems:** Suggested replacements may be incorrect if guards exhaustively cover some
209 /// variants, and also may not use correct path to enum if it's not present in the current scope.
213 /// # enum Foo { A(usize), B(usize) }
214 /// # let x = Foo::B(1);
220 pub WILDCARD_ENUM_MATCH_ARM,
222 "a wildcard enum match arm using `_`"
225 declare_lint_pass!(Matches => [
230 MATCH_OVERLAPPING_ARM,
233 WILDCARD_ENUM_MATCH_ARM
236 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Matches {
237 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
238 if in_external_macro(cx.sess(), expr.span) {
241 if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.kind {
242 check_single_match(cx, ex, arms, expr);
243 check_match_bool(cx, ex, arms, expr);
244 check_overlapping_arms(cx, ex, arms);
245 check_wild_err_arm(cx, ex, arms);
246 check_wild_enum_match(cx, ex, arms);
247 check_match_as_ref(cx, ex, arms, expr);
249 if let ExprKind::Match(ref ex, ref arms, _) = expr.kind {
250 check_match_ref_pats(cx, ex, arms, expr);
256 fn check_single_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
257 if arms.len() == 2 && arms[0].guard.is_none() && arms[1].guard.is_none() {
258 if let PatKind::Or(..) = arms[0].pat.kind {
259 // don't lint for or patterns for now, this makes
260 // the lint noisy in unnecessary situations
263 let els = remove_blocks(&arms[1].body);
264 let els = if is_unit_expr(els) {
266 } else if let ExprKind::Block(_, _) = els.kind {
267 // matches with blocks that contain statements are prettier as `if let + else`
270 // allow match arms with just expressions
273 let ty = cx.tables.expr_ty(ex);
274 if ty.kind != ty::Bool || is_allowed(cx, MATCH_BOOL, ex.hir_id) {
275 check_single_match_single_pattern(cx, ex, arms, expr, els);
276 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
281 fn check_single_match_single_pattern(
282 cx: &LateContext<'_, '_>,
288 if is_wild(&arms[1].pat) {
289 report_single_match_single_pattern(cx, ex, arms, expr, els);
293 fn report_single_match_single_pattern(
294 cx: &LateContext<'_, '_>,
300 let lint = if els.is_some() { SINGLE_MATCH_ELSE } else { SINGLE_MATCH };
301 let els_str = els.map_or(String::new(), |els| {
302 format!(" else {}", expr_block(cx, els, None, ".."))
308 "you seem to be trying to use match for destructuring a single pattern. Consider using `if \
312 "if let {} = {} {}{}",
313 snippet(cx, arms[0].pat.span, ".."),
314 snippet(cx, ex.span, ".."),
315 expr_block(cx, &arms[0].body, None, ".."),
318 Applicability::HasPlaceholders,
322 fn check_single_match_opt_like(
323 cx: &LateContext<'_, '_>,
330 // list of candidate `Enum`s we know will never get any more members
332 (&paths::COW, "Borrowed"),
333 (&paths::COW, "Cow::Borrowed"),
334 (&paths::COW, "Cow::Owned"),
335 (&paths::COW, "Owned"),
336 (&paths::OPTION, "None"),
337 (&paths::RESULT, "Err"),
338 (&paths::RESULT, "Ok"),
341 let path = match arms[1].pat.kind {
342 PatKind::TupleStruct(ref path, ref inner, _) => {
343 // Contains any non wildcard patterns (e.g., `Err(err)`)?
344 if !inner.iter().all(is_wild) {
347 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
349 PatKind::Binding(BindingAnnotation::Unannotated, .., ident, None) => ident.to_string(),
350 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
354 for &(ty_path, pat_path) in candidates {
355 if path == *pat_path && match_type(cx, ty, ty_path) {
356 report_single_match_single_pattern(cx, ex, arms, expr, els);
361 fn check_match_bool(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
362 // Type of expression is `bool`.
363 if cx.tables.expr_ty(ex).kind == ty::Bool {
368 "you seem to be trying to match on a boolean expression",
372 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pat.kind {
373 if let ExprKind::Lit(ref lit) = arm_bool.kind {
375 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
376 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
386 if let Some((true_expr, false_expr)) = exprs {
387 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
388 (false, false) => Some(format!(
390 snippet(cx, ex.span, "b"),
391 expr_block(cx, true_expr, None, ".."),
392 expr_block(cx, false_expr, None, "..")
394 (false, true) => Some(format!(
396 snippet(cx, ex.span, "b"),
397 expr_block(cx, true_expr, None, "..")
400 let test = Sugg::hir(cx, ex, "..");
401 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
403 (true, true) => None,
406 if let Some(sugg) = sugg {
409 "consider using an if/else expression",
411 Applicability::HasPlaceholders,
421 fn check_overlapping_arms<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ex: &'tcx Expr, arms: &'tcx [Arm]) {
422 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
423 let ranges = all_ranges(cx, arms);
424 let type_ranges = type_ranges(&ranges);
425 if !type_ranges.is_empty() {
426 if let Some((start, end)) = overlapping(&type_ranges) {
429 MATCH_OVERLAPPING_ARM,
431 "some ranges overlap",
433 "overlaps with this",
440 fn is_wild(pat: &impl std::ops::Deref<Target = Pat>) -> bool {
442 PatKind::Wild => true,
447 fn check_wild_err_arm(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
448 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
449 if match_type(cx, ex_ty, &paths::RESULT) {
451 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pat.kind {
452 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
454 if path_str == "Err";
455 if inner.iter().any(is_wild);
456 if let ExprKind::Block(ref block, _) = arm.body.kind;
457 if is_panic_block(block);
459 // `Err(_)` arm with `panic!` found
460 span_note_and_lint(cx,
463 "Err(_) will match all errors, maybe not a good idea",
465 "to remove this warning, match each error separately \
466 or use unreachable macro");
474 fn check_wild_enum_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
475 let ty = cx.tables.expr_ty(ex);
477 // If there isn't a nice closed set of possible values that can be conveniently enumerated,
478 // don't complain about not enumerating the mall.
482 // First pass - check for violation, but don't do much book-keeping because this is hopefully
483 // the uncommon case, and the book-keeping is slightly expensive.
484 let mut wildcard_span = None;
485 let mut wildcard_ident = None;
487 if let PatKind::Wild = arm.pat.kind {
488 wildcard_span = Some(arm.pat.span);
489 } else if let PatKind::Binding(_, _, ident, None) = arm.pat.kind {
490 wildcard_span = Some(arm.pat.span);
491 wildcard_ident = Some(ident);
495 if let Some(wildcard_span) = wildcard_span {
496 // Accumulate the variants which should be put in place of the wildcard because they're not
499 let mut missing_variants = vec![];
500 if let ty::Adt(def, _) = ty.kind {
501 for variant in &def.variants {
502 missing_variants.push(variant);
507 if arm.guard.is_some() {
508 // Guards mean that this case probably isn't exhaustively covered. Technically
509 // this is incorrect, as we should really check whether each variant is exhaustively
510 // covered by the set of guards that cover it, but that's really hard to do.
513 if let PatKind::Path(ref path) = arm.pat.kind {
514 if let QPath::Resolved(_, p) = path {
515 missing_variants.retain(|e| e.ctor_def_id != Some(p.res.def_id()));
517 } else if let PatKind::TupleStruct(ref path, ..) = arm.pat.kind {
518 if let QPath::Resolved(_, p) = path {
519 missing_variants.retain(|e| e.ctor_def_id != Some(p.res.def_id()));
524 let suggestion: Vec<String> = missing_variants
527 let suffix = match v.ctor_kind {
528 CtorKind::Fn => "(..)",
529 CtorKind::Const | CtorKind::Fictive => "",
531 let ident_str = if let Some(ident) = wildcard_ident {
532 format!("{} @ ", ident.name)
536 // This path assumes that the enum type is imported into scope.
537 format!("{}{}{}", ident_str, cx.tcx.def_path_str(v.def_id), suffix)
541 if suggestion.is_empty() {
547 WILDCARD_ENUM_MATCH_ARM,
549 "wildcard match will miss any future added variants.",
551 suggestion.join(" | "),
552 Applicability::MachineApplicable,
557 // If the block contains only a `panic!` macro (as expression or statement)
558 fn is_panic_block(block: &Block) -> bool {
559 match (&block.expr, block.stmts.len(), block.stmts.first()) {
560 (&Some(ref exp), 0, _) => {
561 is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
563 (&None, 1, Some(stmt)) => {
564 is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
570 fn check_match_ref_pats(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
571 if has_only_ref_pats(arms) {
572 let mut suggs = Vec::new();
573 let (title, msg) = if let ExprKind::AddrOf(Mutability::Immutable, ref inner) = ex.kind {
574 let span = ex.span.source_callsite();
575 suggs.push((span, Sugg::hir_with_macro_callsite(cx, inner, "..").to_string()));
577 "you don't need to add `&` to both the expression and the patterns",
581 let span = ex.span.source_callsite();
582 suggs.push((span, Sugg::hir_with_macro_callsite(cx, ex, "..").deref().to_string()));
584 "you don't need to add `&` to all patterns",
585 "instead of prefixing all patterns with `&`, you can dereference the expression",
589 suggs.extend(arms.iter().filter_map(|a| {
590 if let PatKind::Ref(ref refp, _) = a.pat.kind {
591 Some((a.pat.span, snippet(cx, refp.span, "..").to_string()))
597 span_lint_and_then(cx, MATCH_REF_PATS, expr.span, title, |db| {
598 if !expr.span.from_expansion() {
599 multispan_sugg(db, msg.to_owned(), suggs);
605 fn check_match_as_ref(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
606 if arms.len() == 2 && arms[0].guard.is_none() && arms[1].guard.is_none() {
607 let arm_ref: Option<BindingAnnotation> = if is_none_arm(&arms[0]) {
608 is_ref_some_arm(&arms[1])
609 } else if is_none_arm(&arms[1]) {
610 is_ref_some_arm(&arms[0])
614 if let Some(rb) = arm_ref {
615 let suggestion = if rb == BindingAnnotation::Ref {
621 let output_ty = cx.tables.expr_ty(expr);
622 let input_ty = cx.tables.expr_ty(ex);
624 let cast = if_chain! {
625 if let ty::Adt(_, substs) = input_ty.kind;
626 let input_ty = substs.type_at(0);
627 if let ty::Adt(_, substs) = output_ty.kind;
628 let output_ty = substs.type_at(0);
629 if let ty::Ref(_, output_ty, _) = output_ty.kind;
630 if input_ty != output_ty;
638 let mut applicability = Applicability::MachineApplicable;
643 &format!("use {}() instead", suggestion),
647 snippet_with_applicability(cx, ex.span, "_", &mut applicability),
657 /// Gets all arms that are unbounded `PatRange`s.
658 fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &'tcx [Arm]) -> Vec<SpannedRange<Constant>> {
662 ref pat, guard: None, ..
665 if let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.kind {
666 let lhs = constant(cx, cx.tables, lhs)?.0;
667 let rhs = constant(cx, cx.tables, rhs)?.0;
668 let rhs = match *range_end {
669 RangeEnd::Included => Bound::Included(rhs),
670 RangeEnd::Excluded => Bound::Excluded(rhs),
672 return Some(SpannedRange {
678 if let PatKind::Lit(ref value) = pat.kind {
679 let value = constant(cx, cx.tables, value)?.0;
680 return Some(SpannedRange {
682 node: (value.clone(), Bound::Included(value)),
691 #[derive(Debug, Eq, PartialEq)]
692 pub struct SpannedRange<T> {
694 pub node: (T, Bound<T>),
697 type TypedRanges = Vec<SpannedRange<u128>>;
699 /// Gets all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway
700 /// and other types than
701 /// `Uint` and `Int` probably don't make sense.
702 fn type_ranges(ranges: &[SpannedRange<Constant>]) -> TypedRanges {
705 .filter_map(|range| match range.node {
706 (Constant::Int(start), Bound::Included(Constant::Int(end))) => Some(SpannedRange {
708 node: (start, Bound::Included(end)),
710 (Constant::Int(start), Bound::Excluded(Constant::Int(end))) => Some(SpannedRange {
712 node: (start, Bound::Excluded(end)),
714 (Constant::Int(start), Bound::Unbounded) => Some(SpannedRange {
716 node: (start, Bound::Unbounded),
723 fn is_unit_expr(expr: &Expr) -> bool {
725 ExprKind::Tup(ref v) if v.is_empty() => true,
726 ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
731 // Checks if arm has the form `None => None`
732 fn is_none_arm(arm: &Arm) -> bool {
734 PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => true,
739 // Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
740 fn is_ref_some_arm(arm: &Arm) -> Option<BindingAnnotation> {
742 if let PatKind::TupleStruct(ref path, ref pats, _) = arm.pat.kind;
743 if pats.len() == 1 && match_qpath(path, &paths::OPTION_SOME);
744 if let PatKind::Binding(rb, .., ident, _) = pats[0].kind;
745 if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
746 if let ExprKind::Call(ref e, ref args) = remove_blocks(&arm.body).kind;
747 if let ExprKind::Path(ref some_path) = e.kind;
748 if match_qpath(some_path, &paths::OPTION_SOME) && args.len() == 1;
749 if let ExprKind::Path(ref qpath) = args[0].kind;
750 if let &QPath::Resolved(_, ref path2) = qpath;
751 if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
759 fn has_only_ref_pats(arms: &[Arm]) -> bool {
764 PatKind::Ref(..) => Some(true), // &-patterns
765 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
766 _ => None, // any other pattern is not fine
769 .collect::<Option<Vec<bool>>>();
770 // look for Some(v) where there's at least one true element
771 mapped.map_or(false, |v| v.iter().any(|el| *el))
774 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
778 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
780 Start(T, &'a SpannedRange<T>),
781 End(Bound<T>, &'a SpannedRange<T>),
784 impl<'a, T: Copy> Kind<'a, T> {
785 fn range(&self) -> &'a SpannedRange<T> {
787 Kind::Start(_, r) | Kind::End(_, r) => r,
791 fn value(self) -> Bound<T> {
793 Kind::Start(t, _) => Bound::Included(t),
794 Kind::End(t, _) => t,
799 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
800 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
801 Some(self.cmp(other))
805 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
806 fn cmp(&self, other: &Self) -> Ordering {
807 match (self.value(), other.value()) {
808 (Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
809 // Range patterns cannot be unbounded (yet)
810 (Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(),
811 (Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) {
812 Ordering::Equal => Ordering::Greater,
815 (Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) {
816 Ordering::Equal => Ordering::Less,
823 let mut values = Vec::with_capacity(2 * ranges.len());
826 values.push(Kind::Start(r.node.0, r));
827 values.push(Kind::End(r.node.1, r));
832 for (a, b) in values.iter().zip(values.iter().skip(1)) {
834 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
835 if ra.node != rb.node {
836 return Some((ra, rb));
839 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
840 _ => return Some((a.range(), b.range())),