1 use crate::consts::{constant, Constant};
2 use crate::utils::paths;
3 use crate::utils::sugg::Sugg;
5 expr_block, in_macro, 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, TyKind};
13 use rustc::{declare_tool_lint, lint_array};
14 use rustc_errors::Applicability;
15 use std::cmp::Ordering;
16 use std::collections::Bound;
18 use syntax::ast::LitKind;
19 use syntax::source_map::Span;
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 a 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.
57 /// Some(ref foo) => bar(foo),
58 /// _ => bar(other_ref),
62 /// Using `if let` with `else`:
65 /// if let Some(ref foo) = x {
71 pub SINGLE_MATCH_ELSE,
73 "a match statement with a two arms where the second arm's pattern is a placeholder instead of a specific match pattern"
76 declare_clippy_lint! {
77 /// **What it does:** Checks for matches where all arms match a reference,
78 /// suggesting to remove the reference and deref the matched expression
79 /// instead. It also checks for `if let &foo = bar` blocks.
81 /// **Why is this bad?** It just makes the code less readable. That reference
82 /// destructuring adds nothing to the code.
84 /// **Known problems:** None.
89 /// &A(ref y) => foo(y),
96 "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
99 declare_clippy_lint! {
100 /// **What it does:** Checks for matches where match expression is a `bool`. It
101 /// suggests to replace the expression with an `if...else` block.
103 /// **Why is this bad?** It makes the code less readable.
105 /// **Known problems:** None.
111 /// let condition: bool = true;
112 /// match condition {
117 /// Use if/else instead:
121 /// let condition: bool = true;
130 "a match on a boolean expression instead of an `if..else` block"
133 declare_clippy_lint! {
134 /// **What it does:** Checks for overlapping match arms.
136 /// **Why is this bad?** It is likely to be an error and if not, makes the code
139 /// **Known problems:** None.
145 /// 1...10 => println!("1 ... 10"),
146 /// 5...15 => println!("5 ... 15"),
150 pub MATCH_OVERLAPPING_ARM,
152 "a match with overlapping arms"
155 declare_clippy_lint! {
156 /// **What it does:** Checks for arm which matches all errors with `Err(_)`
157 /// and take drastic actions like `panic!`.
159 /// **Why is this bad?** It is generally a bad practice, just like
160 /// catching all exceptions in java with `catch(Exception)`
162 /// **Known problems:** None.
166 /// let x: Result<i32, &str> = Ok(3);
168 /// Ok(_) => println!("ok"),
169 /// Err(_) => panic!("err"),
172 pub MATCH_WILD_ERR_ARM,
174 "a match with `Err(_)` arm and take drastic actions"
177 declare_clippy_lint! {
178 /// **What it does:** Checks for match which is used to add a reference to an
181 /// **Why is this bad?** Using `as_ref()` or `as_mut()` instead is shorter.
183 /// **Known problems:** None.
187 /// let x: Option<()> = None;
188 /// let r: Option<&()> = match x {
190 /// Some(ref v) => Some(v),
195 "a match on an Option value instead of using `as_ref()` or `as_mut`"
198 declare_clippy_lint! {
199 /// **What it does:** Checks for wildcard enum matches using `_`.
201 /// **Why is this bad?** New enum variants added by library updates can be missed.
203 /// **Known problems:** Suggested replacements may be incorrect if guards exhaustively cover some
204 /// variants, and also may not use correct path to enum if it's not present in the current scope.
213 pub WILDCARD_ENUM_MATCH_ARM,
215 "a wildcard enum match arm using `_`"
218 #[allow(missing_copy_implementations)]
219 pub struct MatchPass;
221 impl LintPass for MatchPass {
222 fn get_lints(&self) -> LintArray {
228 MATCH_OVERLAPPING_ARM,
231 WILDCARD_ENUM_MATCH_ARM
235 fn name(&self) -> &'static str {
240 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
241 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
242 if in_external_macro(cx.sess(), expr.span) {
245 if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.node {
246 check_single_match(cx, ex, arms, expr);
247 check_match_bool(cx, ex, arms, expr);
248 check_overlapping_arms(cx, ex, arms);
249 check_wild_err_arm(cx, ex, arms);
250 check_wild_enum_match(cx, ex, arms);
251 check_match_as_ref(cx, ex, arms, expr);
253 if let ExprKind::Match(ref ex, ref arms, _) = expr.node {
254 check_match_ref_pats(cx, ex, arms, expr);
260 fn check_single_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
261 if arms.len() == 2 &&
262 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
263 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
264 let els = remove_blocks(&arms[1].body);
265 let els = if is_unit_expr(els) {
267 } else if let ExprKind::Block(_, _) = els.node {
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.sty != 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<'_, '_>,
289 if is_wild(&arms[1].pats[0]) {
290 report_single_match_single_pattern(cx, ex, arms, expr, els);
294 fn report_single_match_single_pattern(
295 cx: &LateContext<'_, '_>,
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].pats[0].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<'_, '_>,
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].pats[0].node {
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).sty == ty::Bool {
369 "you seem to be trying to match on a boolean expression",
371 if arms.len() == 2 && arms[0].pats.len() == 1 {
373 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
374 if let ExprKind::Lit(ref lit) = arm_bool.node {
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(pat: &impl std::ops::Deref<Target = Pat>) -> 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.pats[0].node {
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.node;
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 for pat in &arm.pats {
489 if let PatKind::Wild = pat.node {
490 wildcard_span = Some(pat.span);
491 } else if let PatKind::Binding(_, _, ident, None) = pat.node {
492 wildcard_span = Some(pat.span);
493 wildcard_ident = Some(ident);
498 if let Some(wildcard_span) = wildcard_span {
499 // Accumulate the variants which should be put in place of the wildcard because they're not
502 let mut missing_variants = vec![];
503 if let TyKind::Adt(def, _) = ty.sty {
504 for variant in &def.variants {
505 missing_variants.push(variant);
510 if arm.guard.is_some() {
511 // Guards mean that this case probably isn't exhaustively covered. Technically
512 // this is incorrect, as we should really check whether each variant is exhaustively
513 // covered by the set of guards that cover it, but that's really hard to do.
516 for pat in &arm.pats {
517 if let PatKind::Path(ref path) = pat.deref().node {
518 if let QPath::Resolved(_, p) = path {
519 missing_variants.retain(|e| e.ctor_def_id != Some(p.def.def_id()));
521 } else if let PatKind::TupleStruct(ref path, ..) = pat.deref().node {
522 if let QPath::Resolved(_, p) = path {
523 missing_variants.retain(|e| e.ctor_def_id != Some(p.def.def_id()));
529 let suggestion: Vec<String> = missing_variants
532 let suffix = match v.ctor_kind {
533 CtorKind::Fn => "(..)",
534 CtorKind::Const | CtorKind::Fictive => "",
536 let ident_str = if let Some(ident) = wildcard_ident {
537 format!("{} @ ", ident.name)
541 // This path assumes that the enum type is imported into scope.
542 format!("{}{}{}", ident_str, cx.tcx.def_path_str(v.def_id), suffix)
546 if suggestion.is_empty() {
552 WILDCARD_ENUM_MATCH_ARM,
554 "wildcard match will miss any future added variants.",
556 suggestion.join(" | "),
557 Applicability::MachineApplicable,
562 // If the block contains only a `panic!` macro (as expression or statement)
563 fn is_panic_block(block: &Block) -> bool {
564 match (&block.expr, block.stmts.len(), block.stmts.first()) {
565 (&Some(ref exp), 0, _) => {
566 is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
568 (&None, 1, Some(stmt)) => {
569 is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
575 fn check_match_ref_pats(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
576 if has_only_ref_pats(arms) {
577 let mut suggs = Vec::new();
578 let (title, msg) = if let ExprKind::AddrOf(Mutability::MutImmutable, ref inner) = ex.node {
579 let span = ex.span.source_callsite();
580 suggs.push((span, Sugg::hir_with_macro_callsite(cx, inner, "..").to_string()));
582 "you don't need to add `&` to both the expression and the patterns",
586 let span = ex.span.source_callsite();
587 suggs.push((span, Sugg::hir_with_macro_callsite(cx, ex, "..").deref().to_string()));
589 "you don't need to add `&` to all patterns",
590 "instead of prefixing all patterns with `&`, you can dereference the expression",
594 suggs.extend(arms.iter().flat_map(|a| &a.pats).filter_map(|p| {
595 if let PatKind::Ref(ref refp, _) = p.node {
596 Some((p.span, snippet(cx, refp.span, "..").to_string()))
602 span_lint_and_then(cx, MATCH_REF_PATS, expr.span, title, |db| {
603 if !in_macro(expr.span) {
604 multispan_sugg(db, msg.to_owned(), suggs);
610 fn check_match_as_ref(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
612 && arms[0].pats.len() == 1
613 && arms[0].guard.is_none()
614 && arms[1].pats.len() == 1
615 && 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 {
630 let mut applicability = Applicability::MachineApplicable;
635 &format!("use {}() instead", suggestion),
639 snippet_with_applicability(cx, ex.span, "_", &mut applicability),
648 /// Gets all arms that are unbounded `PatRange`s.
649 fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &'tcx [Arm]) -> Vec<SpannedRange<Constant>> {
653 ref pats, guard: None, ..
661 if let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node {
662 let lhs = constant(cx, cx.tables, lhs)?.0;
663 let rhs = constant(cx, cx.tables, rhs)?.0;
664 let rhs = match *range_end {
665 RangeEnd::Included => Bound::Included(rhs),
666 RangeEnd::Excluded => Bound::Excluded(rhs),
668 return Some(SpannedRange {
674 if let PatKind::Lit(ref value) = pat.node {
675 let value = constant(cx, cx.tables, value)?.0;
676 return Some(SpannedRange {
678 node: (value.clone(), Bound::Included(value)),
688 #[derive(Debug, Eq, PartialEq)]
689 pub struct SpannedRange<T> {
691 pub node: (T, Bound<T>),
694 type TypedRanges = Vec<SpannedRange<u128>>;
696 /// Gets all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway
697 /// and other types than
698 /// `Uint` and `Int` probably don't make sense.
699 fn type_ranges(ranges: &[SpannedRange<Constant>]) -> TypedRanges {
702 .filter_map(|range| match range.node {
703 (Constant::Int(start), Bound::Included(Constant::Int(end))) => Some(SpannedRange {
705 node: (start, Bound::Included(end)),
707 (Constant::Int(start), Bound::Excluded(Constant::Int(end))) => Some(SpannedRange {
709 node: (start, Bound::Excluded(end)),
711 (Constant::Int(start), Bound::Unbounded) => Some(SpannedRange {
713 node: (start, Bound::Unbounded),
720 fn is_unit_expr(expr: &Expr) -> bool {
722 ExprKind::Tup(ref v) if v.is_empty() => true,
723 ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
728 // Checks if arm has the form `None => None`
729 fn is_none_arm(arm: &Arm) -> bool {
730 match arm.pats[0].node {
731 PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => true,
736 // Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
737 fn is_ref_some_arm(arm: &Arm) -> Option<BindingAnnotation> {
739 if let PatKind::TupleStruct(ref path, ref pats, _) = arm.pats[0].node;
740 if pats.len() == 1 && match_qpath(path, &paths::OPTION_SOME);
741 if let PatKind::Binding(rb, .., ident, _) = pats[0].node;
742 if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
743 if let ExprKind::Call(ref e, ref args) = remove_blocks(&arm.body).node;
744 if let ExprKind::Path(ref some_path) = e.node;
745 if match_qpath(some_path, &paths::OPTION_SOME) && args.len() == 1;
746 if let ExprKind::Path(ref qpath) = args[0].node;
747 if let &QPath::Resolved(_, ref path2) = qpath;
748 if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
756 fn has_only_ref_pats(arms: &[Arm]) -> bool {
759 .flat_map(|a| &a.pats)
762 PatKind::Ref(..) => Some(true), // &-patterns
763 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
764 _ => None, // any other pattern is not fine
767 .collect::<Option<Vec<bool>>>();
768 // look for Some(v) where there's at least one true element
769 mapped.map_or(false, |v| v.iter().any(|el| *el))
772 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
776 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
777 enum Kind<'a, T: 'a> {
778 Start(T, &'a SpannedRange<T>),
779 End(Bound<T>, &'a SpannedRange<T>),
782 impl<'a, T: Copy> Kind<'a, T> {
783 fn range(&self) -> &'a SpannedRange<T> {
785 Kind::Start(_, r) | Kind::End(_, r) => r,
789 fn value(self) -> Bound<T> {
791 Kind::Start(t, _) => Bound::Included(t),
792 Kind::End(t, _) => t,
797 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
798 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
799 Some(self.cmp(other))
803 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
804 fn cmp(&self, other: &Self) -> Ordering {
805 match (self.value(), other.value()) {
806 (Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
807 // Range patterns cannot be unbounded (yet)
808 (Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(),
809 (Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) {
810 Ordering::Equal => Ordering::Greater,
813 (Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) {
814 Ordering::Equal => Ordering::Less,
821 let mut values = Vec::with_capacity(2 * ranges.len());
824 values.push(Kind::Start(r.node.0, r));
825 values.push(Kind::End(r.node.1, r));
830 for (a, b) in values.iter().zip(values.iter().skip(1)) {
832 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
833 if ra.node != rb.node {
834 return Some((ra, rb));
837 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
838 _ => return Some((a.range(), b.range())),