1 use crate::consts::{constant, Constant};
2 use crate::utils::paths;
3 use crate::utils::sugg::Sugg;
6 expr_block, in_macro_or_desugar, is_allowed, is_expn_of, match_qpath, match_type, multispan_sugg, remove_blocks,
7 snippet, snippet_with_applicability, span_lint_and_sugg, span_lint_and_then, span_note_and_lint, walk_ptrs_ty,
9 use if_chain::if_chain;
10 use rustc::hir::def::CtorKind;
12 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
13 use rustc::ty::{self, Ty};
14 use rustc::{declare_lint_pass, declare_tool_lint};
15 use rustc_errors::Applicability;
16 use std::cmp::Ordering;
17 use std::collections::Bound;
19 use syntax::ast::LitKind;
20 use syntax::source_map::Span;
22 declare_clippy_lint! {
23 /// **What it does:** Checks for matches with a single arm where an `if let`
24 /// will usually suffice.
26 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
28 /// **Known problems:** None.
32 /// # fn bar(stool: &str) {}
33 /// # let x = Some("abc");
35 /// Some(ref foo) => bar(foo),
41 "a match statement with a single nontrivial arm (i.e., where the other arm is `_ => {}`) instead of `if let`"
44 declare_clippy_lint! {
45 /// **What it does:** Checks for matches with a two arms where an `if let else` will
48 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
50 /// **Known problems:** Personal style preferences may differ.
58 /// Some(ref foo) => bar(foo),
59 /// _ => bar(other_ref),
63 /// Using `if let` with `else`:
66 /// if let Some(ref foo) = x {
72 pub SINGLE_MATCH_ELSE,
74 "a match statement with a two arms where the second arm's pattern is a placeholder instead of a specific match pattern"
77 declare_clippy_lint! {
78 /// **What it does:** Checks for matches where all arms match a reference,
79 /// suggesting to remove the reference and deref the matched expression
80 /// instead. It also checks for `if let &foo = bar` blocks.
82 /// **Why is this bad?** It just makes the code less readable. That reference
83 /// destructuring adds nothing to the code.
85 /// **Known problems:** None.
90 /// &A(ref y) => foo(y),
97 "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
100 declare_clippy_lint! {
101 /// **What it does:** Checks for matches where match expression is a `bool`. It
102 /// suggests to replace the expression with an `if...else` block.
104 /// **Why is this bad?** It makes the code less readable.
106 /// **Known problems:** None.
112 /// let condition: bool = true;
113 /// match condition {
118 /// Use if/else instead:
122 /// let condition: bool = true;
131 "a match on a boolean expression instead of an `if..else` block"
134 declare_clippy_lint! {
135 /// **What it does:** Checks for overlapping match arms.
137 /// **Why is this bad?** It is likely to be an error and if not, makes the code
140 /// **Known problems:** None.
146 /// 1...10 => println!("1 ... 10"),
147 /// 5...15 => println!("5 ... 15"),
151 pub MATCH_OVERLAPPING_ARM,
153 "a match with overlapping arms"
156 declare_clippy_lint! {
157 /// **What it does:** Checks for arm which matches all errors with `Err(_)`
158 /// and take drastic actions like `panic!`.
160 /// **Why is this bad?** It is generally a bad practice, just like
161 /// catching all exceptions in java with `catch(Exception)`
163 /// **Known problems:** None.
167 /// let x: Result<i32, &str> = Ok(3);
169 /// Ok(_) => println!("ok"),
170 /// Err(_) => panic!("err"),
173 pub MATCH_WILD_ERR_ARM,
175 "a match with `Err(_)` arm and take drastic actions"
178 declare_clippy_lint! {
179 /// **What it does:** Checks for match which is used to add a reference to an
182 /// **Why is this bad?** Using `as_ref()` or `as_mut()` instead is shorter.
184 /// **Known problems:** None.
188 /// let x: Option<()> = None;
189 /// let r: Option<&()> = match x {
191 /// Some(ref v) => Some(v),
196 "a match on an Option value instead of using `as_ref()` or `as_mut`"
199 declare_clippy_lint! {
200 /// **What it does:** Checks for wildcard enum matches using `_`.
202 /// **Why is this bad?** New enum variants added by library updates can be missed.
204 /// **Known problems:** Suggested replacements may be incorrect if guards exhaustively cover some
205 /// variants, and also may not use correct path to enum if it's not present in the current scope.
214 pub WILDCARD_ENUM_MATCH_ARM,
216 "a wildcard enum match arm using `_`"
219 declare_lint_pass!(Matches => [
224 MATCH_OVERLAPPING_ARM,
227 WILDCARD_ENUM_MATCH_ARM
230 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Matches {
231 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
232 if in_external_macro(cx.sess(), expr.span) {
235 if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.node {
236 check_single_match(cx, ex, arms, expr);
237 check_match_bool(cx, ex, arms, expr);
238 check_overlapping_arms(cx, ex, arms);
239 check_wild_err_arm(cx, ex, arms);
240 check_wild_enum_match(cx, ex, arms);
241 check_match_as_ref(cx, ex, arms, expr);
243 if let ExprKind::Match(ref ex, ref arms, _) = expr.node {
244 check_match_ref_pats(cx, ex, arms, expr);
250 fn check_single_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
251 if arms.len() == 2 &&
252 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
253 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
254 let els = remove_blocks(&arms[1].body);
255 let els = if is_unit_expr(els) {
257 } else if let ExprKind::Block(_, _) = els.node {
258 // matches with blocks that contain statements are prettier as `if let + else`
261 // allow match arms with just expressions
264 let ty = cx.tables.expr_ty(ex);
265 if ty.sty != ty::Bool || is_allowed(cx, MATCH_BOOL, ex.hir_id) {
266 check_single_match_single_pattern(cx, ex, arms, expr, els);
267 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
272 fn check_single_match_single_pattern(
273 cx: &LateContext<'_, '_>,
279 if is_wild(&arms[1].pats[0]) {
280 report_single_match_single_pattern(cx, ex, arms, expr, els);
284 fn report_single_match_single_pattern(
285 cx: &LateContext<'_, '_>,
291 let lint = if els.is_some() { SINGLE_MATCH_ELSE } else { SINGLE_MATCH };
292 let els_str = els.map_or(String::new(), |els| {
293 format!(" else {}", expr_block(cx, els, None, ".."))
299 "you seem to be trying to use match for destructuring a single pattern. Consider using `if \
303 "if let {} = {} {}{}",
304 snippet(cx, arms[0].pats[0].span, ".."),
305 snippet(cx, ex.span, ".."),
306 expr_block(cx, &arms[0].body, None, ".."),
309 Applicability::HasPlaceholders,
313 fn check_single_match_opt_like(
314 cx: &LateContext<'_, '_>,
321 // list of candidate `Enum`s we know will never get any more members
323 (&*paths::COW, "Borrowed"),
324 (&*paths::COW, "Cow::Borrowed"),
325 (&*paths::COW, "Cow::Owned"),
326 (&*paths::COW, "Owned"),
327 (&*paths::OPTION, "None"),
328 (&*paths::RESULT, "Err"),
329 (&*paths::RESULT, "Ok"),
332 let path = match arms[1].pats[0].node {
333 PatKind::TupleStruct(ref path, ref inner, _) => {
334 // Contains any non wildcard patterns (e.g., `Err(err)`)?
335 if !inner.iter().all(is_wild) {
338 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
340 PatKind::Binding(BindingAnnotation::Unannotated, .., ident, None) => ident.to_string(),
341 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
345 for &(ty_path, pat_path) in candidates {
346 if path == *pat_path && match_type(cx, ty, ty_path) {
347 report_single_match_single_pattern(cx, ex, arms, expr, els);
352 fn check_match_bool(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
353 // Type of expression is `bool`.
354 if cx.tables.expr_ty(ex).sty == ty::Bool {
359 "you seem to be trying to match on a boolean expression",
361 if arms.len() == 2 && arms[0].pats.len() == 1 {
363 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
364 if let ExprKind::Lit(ref lit) = arm_bool.node {
366 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
367 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
377 if let Some((true_expr, false_expr)) = exprs {
378 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
379 (false, false) => Some(format!(
381 snippet(cx, ex.span, "b"),
382 expr_block(cx, true_expr, None, ".."),
383 expr_block(cx, false_expr, None, "..")
385 (false, true) => Some(format!(
387 snippet(cx, ex.span, "b"),
388 expr_block(cx, true_expr, None, "..")
391 let test = Sugg::hir(cx, ex, "..");
392 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
394 (true, true) => None,
397 if let Some(sugg) = sugg {
400 "consider using an if/else expression",
402 Applicability::HasPlaceholders,
412 fn check_overlapping_arms<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ex: &'tcx Expr, arms: &'tcx [Arm]) {
413 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
414 let ranges = all_ranges(cx, arms);
415 let type_ranges = type_ranges(&ranges);
416 if !type_ranges.is_empty() {
417 if let Some((start, end)) = overlapping(&type_ranges) {
420 MATCH_OVERLAPPING_ARM,
422 "some ranges overlap",
424 "overlaps with this",
431 fn is_wild(pat: &impl std::ops::Deref<Target = Pat>) -> bool {
433 PatKind::Wild => true,
438 fn check_wild_err_arm(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
439 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
440 if match_type(cx, ex_ty, &*paths::RESULT) {
442 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
443 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
445 if path_str == "Err";
446 if inner.iter().any(is_wild);
447 if let ExprKind::Block(ref block, _) = arm.body.node;
448 if is_panic_block(block);
450 // `Err(_)` arm with `panic!` found
451 span_note_and_lint(cx,
454 "Err(_) will match all errors, maybe not a good idea",
456 "to remove this warning, match each error separately \
457 or use unreachable macro");
465 fn check_wild_enum_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
466 let ty = cx.tables.expr_ty(ex);
468 // If there isn't a nice closed set of possible values that can be conveniently enumerated,
469 // don't complain about not enumerating the mall.
473 // First pass - check for violation, but don't do much book-keeping because this is hopefully
474 // the uncommon case, and the book-keeping is slightly expensive.
475 let mut wildcard_span = None;
476 let mut wildcard_ident = None;
478 for pat in &arm.pats {
479 if let PatKind::Wild = pat.node {
480 wildcard_span = Some(pat.span);
481 } else if let PatKind::Binding(_, _, ident, None) = pat.node {
482 wildcard_span = Some(pat.span);
483 wildcard_ident = Some(ident);
488 if let Some(wildcard_span) = wildcard_span {
489 // Accumulate the variants which should be put in place of the wildcard because they're not
492 let mut missing_variants = vec![];
493 if let ty::Adt(def, _) = ty.sty {
494 for variant in &def.variants {
495 missing_variants.push(variant);
500 if arm.guard.is_some() {
501 // Guards mean that this case probably isn't exhaustively covered. Technically
502 // this is incorrect, as we should really check whether each variant is exhaustively
503 // covered by the set of guards that cover it, but that's really hard to do.
506 for pat in &arm.pats {
507 if let PatKind::Path(ref path) = pat.deref().node {
508 if let QPath::Resolved(_, p) = path {
509 missing_variants.retain(|e| e.ctor_def_id != Some(p.res.def_id()));
511 } else if let PatKind::TupleStruct(ref path, ..) = pat.deref().node {
512 if let QPath::Resolved(_, p) = path {
513 missing_variants.retain(|e| e.ctor_def_id != Some(p.res.def_id()));
519 let suggestion: Vec<String> = missing_variants
522 let suffix = match v.ctor_kind {
523 CtorKind::Fn => "(..)",
524 CtorKind::Const | CtorKind::Fictive => "",
526 let ident_str = if let Some(ident) = wildcard_ident {
527 format!("{} @ ", ident.name)
531 // This path assumes that the enum type is imported into scope.
532 format!("{}{}{}", ident_str, cx.tcx.def_path_str(v.def_id), suffix)
536 if suggestion.is_empty() {
542 WILDCARD_ENUM_MATCH_ARM,
544 "wildcard match will miss any future added variants.",
546 suggestion.join(" | "),
547 Applicability::MachineApplicable,
552 // If the block contains only a `panic!` macro (as expression or statement)
553 fn is_panic_block(block: &Block) -> bool {
554 match (&block.expr, block.stmts.len(), block.stmts.first()) {
555 (&Some(ref exp), 0, _) => {
556 is_expn_of(exp.span, *sym::panic).is_some() && is_expn_of(exp.span, *sym::unreachable).is_none()
558 (&None, 1, Some(stmt)) => {
559 is_expn_of(stmt.span, *sym::panic).is_some() && is_expn_of(stmt.span, *sym::unreachable).is_none()
565 fn check_match_ref_pats(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
566 if has_only_ref_pats(arms) {
567 let mut suggs = Vec::new();
568 let (title, msg) = if let ExprKind::AddrOf(Mutability::MutImmutable, ref inner) = ex.node {
569 let span = ex.span.source_callsite();
570 suggs.push((span, Sugg::hir_with_macro_callsite(cx, inner, "..").to_string()));
572 "you don't need to add `&` to both the expression and the patterns",
576 let span = ex.span.source_callsite();
577 suggs.push((span, Sugg::hir_with_macro_callsite(cx, ex, "..").deref().to_string()));
579 "you don't need to add `&` to all patterns",
580 "instead of prefixing all patterns with `&`, you can dereference the expression",
584 suggs.extend(arms.iter().flat_map(|a| &a.pats).filter_map(|p| {
585 if let PatKind::Ref(ref refp, _) = p.node {
586 Some((p.span, snippet(cx, refp.span, "..").to_string()))
592 span_lint_and_then(cx, MATCH_REF_PATS, expr.span, title, |db| {
593 if !in_macro_or_desugar(expr.span) {
594 multispan_sugg(db, msg.to_owned(), suggs);
600 fn check_match_as_ref(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
602 && arms[0].pats.len() == 1
603 && arms[0].guard.is_none()
604 && arms[1].pats.len() == 1
605 && 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 {
620 let mut applicability = Applicability::MachineApplicable;
625 &format!("use {}() instead", suggestion),
629 snippet_with_applicability(cx, ex.span, "_", &mut applicability),
638 /// Gets all arms that are unbounded `PatRange`s.
639 fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &'tcx [Arm]) -> Vec<SpannedRange<Constant>> {
643 ref pats, guard: None, ..
651 if let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node {
652 let lhs = constant(cx, cx.tables, lhs)?.0;
653 let rhs = constant(cx, cx.tables, rhs)?.0;
654 let rhs = match *range_end {
655 RangeEnd::Included => Bound::Included(rhs),
656 RangeEnd::Excluded => Bound::Excluded(rhs),
658 return Some(SpannedRange {
664 if let PatKind::Lit(ref value) = pat.node {
665 let value = constant(cx, cx.tables, value)?.0;
666 return Some(SpannedRange {
668 node: (value.clone(), Bound::Included(value)),
678 #[derive(Debug, Eq, PartialEq)]
679 pub struct SpannedRange<T> {
681 pub node: (T, Bound<T>),
684 type TypedRanges = Vec<SpannedRange<u128>>;
686 /// Gets all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway
687 /// and other types than
688 /// `Uint` and `Int` probably don't make sense.
689 fn type_ranges(ranges: &[SpannedRange<Constant>]) -> TypedRanges {
692 .filter_map(|range| match range.node {
693 (Constant::Int(start), Bound::Included(Constant::Int(end))) => Some(SpannedRange {
695 node: (start, Bound::Included(end)),
697 (Constant::Int(start), Bound::Excluded(Constant::Int(end))) => Some(SpannedRange {
699 node: (start, Bound::Excluded(end)),
701 (Constant::Int(start), Bound::Unbounded) => Some(SpannedRange {
703 node: (start, Bound::Unbounded),
710 fn is_unit_expr(expr: &Expr) -> bool {
712 ExprKind::Tup(ref v) if v.is_empty() => true,
713 ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
718 // Checks if arm has the form `None => None`
719 fn is_none_arm(arm: &Arm) -> bool {
720 match arm.pats[0].node {
721 PatKind::Path(ref path) if match_qpath(path, &*paths::OPTION_NONE) => true,
726 // Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
727 fn is_ref_some_arm(arm: &Arm) -> Option<BindingAnnotation> {
729 if let PatKind::TupleStruct(ref path, ref pats, _) = arm.pats[0].node;
730 if pats.len() == 1 && match_qpath(path, &*paths::OPTION_SOME);
731 if let PatKind::Binding(rb, .., ident, _) = pats[0].node;
732 if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
733 if let ExprKind::Call(ref e, ref args) = remove_blocks(&arm.body).node;
734 if let ExprKind::Path(ref some_path) = e.node;
735 if match_qpath(some_path, &*paths::OPTION_SOME) && args.len() == 1;
736 if let ExprKind::Path(ref qpath) = args[0].node;
737 if let &QPath::Resolved(_, ref path2) = qpath;
738 if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
746 fn has_only_ref_pats(arms: &[Arm]) -> bool {
749 .flat_map(|a| &a.pats)
752 PatKind::Ref(..) => Some(true), // &-patterns
753 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
754 _ => None, // any other pattern is not fine
757 .collect::<Option<Vec<bool>>>();
758 // look for Some(v) where there's at least one true element
759 mapped.map_or(false, |v| v.iter().any(|el| *el))
762 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
766 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
767 enum Kind<'a, T: 'a> {
768 Start(T, &'a SpannedRange<T>),
769 End(Bound<T>, &'a SpannedRange<T>),
772 impl<'a, T: Copy> Kind<'a, T> {
773 fn range(&self) -> &'a SpannedRange<T> {
775 Kind::Start(_, r) | Kind::End(_, r) => r,
779 fn value(self) -> Bound<T> {
781 Kind::Start(t, _) => Bound::Included(t),
782 Kind::End(t, _) => t,
787 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
788 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
789 Some(self.cmp(other))
793 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
794 fn cmp(&self, other: &Self) -> Ordering {
795 match (self.value(), other.value()) {
796 (Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
797 // Range patterns cannot be unbounded (yet)
798 (Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(),
799 (Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) {
800 Ordering::Equal => Ordering::Greater,
803 (Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) {
804 Ordering::Equal => Ordering::Less,
811 let mut values = Vec::with_capacity(2 * ranges.len());
814 values.push(Kind::Start(r.node.0, r));
815 values.push(Kind::End(r.node.1, r));
820 for (a, b) in values.iter().zip(values.iter().skip(1)) {
822 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
823 if ra.node != rb.node {
824 return Some((ra, rb));
827 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
828 _ => return Some((a.range(), b.range())),