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;
10 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
11 use rustc::ty::{self, Ty};
12 use rustc::{declare_tool_lint, lint_array};
13 use rustc_errors::Applicability;
14 use std::cmp::Ordering;
15 use std::collections::Bound;
16 use syntax::ast::LitKind;
17 use syntax::source_map::Span;
19 /// **What it does:** Checks for matches with a single arm where an `if let`
20 /// will usually suffice.
22 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
24 /// **Known problems:** None.
29 /// Some(ref foo) => bar(foo),
33 declare_clippy_lint! {
36 "a match statement with a single nontrivial arm (i.e. where the other arm is `_ => {}`) instead of `if let`"
39 /// **What it does:** Checks for matches with a two arms where an `if let else` will
42 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
44 /// **Known problems:** Personal style preferences may differ.
52 /// Some(ref foo) => bar(foo),
53 /// _ => bar(other_ref),
57 /// Using `if let` with `else`:
60 /// if let Some(ref foo) = x {
66 declare_clippy_lint! {
67 pub SINGLE_MATCH_ELSE,
69 "a match statement with a two arms where the second arm's pattern is a placeholder instead of a specific match pattern"
72 /// **What it does:** Checks for matches where all arms match a reference,
73 /// suggesting to remove the reference and deref the matched expression
74 /// instead. It also checks for `if let &foo = bar` blocks.
76 /// **Why is this bad?** It just makes the code less readable. That reference
77 /// destructuring adds nothing to the code.
79 /// **Known problems:** None.
84 /// &A(ref y) => foo(y),
89 declare_clippy_lint! {
92 "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
95 /// **What it does:** Checks for matches where match expression is a `bool`. It
96 /// suggests to replace the expression with an `if...else` block.
98 /// **Why is this bad?** It makes the code less readable.
100 /// **Known problems:** None.
104 /// let condition: bool = true;
105 /// match condition {
110 /// Use if/else instead:
112 /// let condition: bool = true;
119 declare_clippy_lint! {
122 "a match on a boolean expression instead of an `if..else` block"
125 /// **What it does:** Checks for overlapping match arms.
127 /// **Why is this bad?** It is likely to be an error and if not, makes the code
130 /// **Known problems:** None.
136 /// 1...10 => println!("1 ... 10"),
137 /// 5...15 => println!("5 ... 15"),
141 declare_clippy_lint! {
142 pub MATCH_OVERLAPPING_ARM,
144 "a match with overlapping arms"
147 /// **What it does:** Checks for arm which matches all errors with `Err(_)`
148 /// and take drastic actions like `panic!`.
150 /// **Why is this bad?** It is generally a bad practice, just like
151 /// catching all exceptions in java with `catch(Exception)`
153 /// **Known problems:** None.
157 /// let x: Result(i32, &str) = Ok(3);
159 /// Ok(_) => println!("ok"),
160 /// Err(_) => panic!("err"),
163 declare_clippy_lint! {
164 pub MATCH_WILD_ERR_ARM,
166 "a match with `Err(_)` arm and take drastic actions"
169 /// **What it does:** Checks for match which is used to add a reference to an
172 /// **Why is this bad?** Using `as_ref()` or `as_mut()` instead is shorter.
174 /// **Known problems:** None.
178 /// let x: Option<()> = None;
179 /// let r: Option<&()> = match x {
181 /// Some(ref v) => Some(v),
184 declare_clippy_lint! {
187 "a match on an Option value instead of using `as_ref()` or `as_mut`"
190 /// **What it does:** Checks for wildcard matches using `_`.
192 /// **Why is this bad?** New variants added by library updates can be missed.
194 /// **Known problems:** None.
203 declare_clippy_lint! {
204 pub WILDCARD_MATCH_ARM,
206 "a wildcard match arm using `_`"
209 #[allow(missing_copy_implementations)]
210 pub struct MatchPass;
212 impl LintPass for MatchPass {
213 fn get_lints(&self) -> LintArray {
219 MATCH_OVERLAPPING_ARM,
226 fn name(&self) -> &'static str {
231 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
232 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
233 if in_external_macro(cx.sess(), expr.span) {
236 if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.node {
237 check_single_match(cx, ex, arms, expr);
238 check_match_bool(cx, ex, arms, expr);
239 check_overlapping_arms(cx, ex, arms);
240 check_wild_err_arm(cx, ex, arms);
241 check_wild_arm(cx, ex, arms);
242 check_match_as_ref(cx, ex, arms, expr);
244 if let ExprKind::Match(ref ex, ref arms, _) = expr.node {
245 check_match_ref_pats(cx, ex, arms, expr);
251 fn check_single_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
252 if arms.len() == 2 &&
253 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
254 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
255 let els = remove_blocks(&arms[1].body);
256 let els = if is_unit_expr(els) {
258 } else if let ExprKind::Block(_, _) = els.node {
259 // matches with blocks that contain statements are prettier as `if let + else`
262 // allow match arms with just expressions
265 let ty = cx.tables.expr_ty(ex);
266 if ty.sty != ty::Bool || is_allowed(cx, MATCH_BOOL, ex.id) {
267 check_single_match_single_pattern(cx, ex, arms, expr, els);
268 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
273 fn check_single_match_single_pattern(
274 cx: &LateContext<'_, '_>,
280 if is_wild(&arms[1].pats[0]) {
281 report_single_match_single_pattern(cx, ex, arms, expr, els);
285 fn report_single_match_single_pattern(
286 cx: &LateContext<'_, '_>,
292 let lint = if els.is_some() { SINGLE_MATCH_ELSE } else { SINGLE_MATCH };
293 let els_str = els.map_or(String::new(), |els| {
294 format!(" else {}", expr_block(cx, els, None, ".."))
300 "you seem to be trying to use match for destructuring a single pattern. Consider using `if \
304 "if let {} = {} {}{}",
305 snippet(cx, arms[0].pats[0].span, ".."),
306 snippet(cx, ex.span, ".."),
307 expr_block(cx, &arms[0].body, None, ".."),
310 Applicability::HasPlaceholders,
314 fn check_single_match_opt_like(
315 cx: &LateContext<'_, '_>,
322 // list of candidate Enums we know will never get any more members
324 (&paths::COW, "Borrowed"),
325 (&paths::COW, "Cow::Borrowed"),
326 (&paths::COW, "Cow::Owned"),
327 (&paths::COW, "Owned"),
328 (&paths::OPTION, "None"),
329 (&paths::RESULT, "Err"),
330 (&paths::RESULT, "Ok"),
333 let path = match arms[1].pats[0].node {
334 PatKind::TupleStruct(ref path, ref inner, _) => {
335 // contains any non wildcard patterns? e.g. Err(err)
336 if !inner.iter().all(is_wild) {
339 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
341 PatKind::Binding(BindingAnnotation::Unannotated, _, ident, None) => ident.to_string(),
342 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
346 for &(ty_path, pat_path) in candidates {
347 if path == *pat_path && match_type(cx, ty, ty_path) {
348 report_single_match_single_pattern(cx, ex, arms, expr, els);
353 fn check_match_bool(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
354 // type of expression == bool
355 if cx.tables.expr_ty(ex).sty == ty::Bool {
360 "you seem to be trying to match on a boolean expression",
362 if arms.len() == 2 && arms[0].pats.len() == 1 {
364 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
365 if let ExprKind::Lit(ref lit) = arm_bool.node {
367 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
368 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
378 if let Some((true_expr, false_expr)) = exprs {
379 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
380 (false, false) => Some(format!(
382 snippet(cx, ex.span, "b"),
383 expr_block(cx, true_expr, None, ".."),
384 expr_block(cx, false_expr, None, "..")
386 (false, true) => Some(format!(
388 snippet(cx, ex.span, "b"),
389 expr_block(cx, true_expr, None, "..")
392 let test = Sugg::hir(cx, ex, "..");
393 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
395 (true, true) => None,
398 if let Some(sugg) = sugg {
401 "consider using an if/else expression",
403 Applicability::HasPlaceholders,
413 fn check_overlapping_arms<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ex: &'tcx Expr, arms: &'tcx [Arm]) {
414 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
415 let ranges = all_ranges(cx, arms);
416 let type_ranges = type_ranges(&ranges);
417 if !type_ranges.is_empty() {
418 if let Some((start, end)) = overlapping(&type_ranges) {
421 MATCH_OVERLAPPING_ARM,
423 "some ranges overlap",
425 "overlaps with this",
432 fn is_wild(pat: &impl std::ops::Deref<Target = Pat>) -> bool {
434 PatKind::Wild => true,
439 fn check_wild_err_arm(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
440 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
441 if match_type(cx, ex_ty, &paths::RESULT) {
443 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
444 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
446 if path_str == "Err";
447 if inner.iter().any(is_wild);
448 if let ExprKind::Block(ref block, _) = arm.body.node;
449 if is_panic_block(block);
451 // `Err(_)` arm with `panic!` found
452 span_note_and_lint(cx,
455 "Err(_) will match all errors, maybe not a good idea",
457 "to remove this warning, match each error separately \
458 or use unreachable macro");
466 fn check_wild_arm(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
467 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
468 if match_type(cx, ex_ty, &paths::RESULT) {
470 if is_wild(&arm.pats[0]) {
471 span_note_and_lint(cx,
474 "wildcard match will miss any future added variants.",
476 "to resolve, match each variant explicitly");
482 // If the block contains only a `panic!` macro (as expression or statement)
483 fn is_panic_block(block: &Block) -> bool {
484 match (&block.expr, block.stmts.len(), block.stmts.first()) {
485 (&Some(ref exp), 0, _) => {
486 is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
488 (&None, 1, Some(stmt)) => {
489 is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
495 fn check_match_ref_pats(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
496 if has_only_ref_pats(arms) {
497 let mut suggs = Vec::new();
498 let (title, msg) = if let ExprKind::AddrOf(Mutability::MutImmutable, ref inner) = ex.node {
499 suggs.push((ex.span, Sugg::hir(cx, inner, "..").to_string()));
501 "you don't need to add `&` to both the expression and the patterns",
505 suggs.push((ex.span, Sugg::hir(cx, ex, "..").deref().to_string()));
507 "you don't need to add `&` to all patterns",
508 "instead of prefixing all patterns with `&`, you can dereference the expression",
512 suggs.extend(arms.iter().flat_map(|a| &a.pats).filter_map(|p| {
513 if let PatKind::Ref(ref refp, _) = p.node {
514 Some((p.span, snippet(cx, refp.span, "..").to_string()))
520 span_lint_and_then(cx, MATCH_REF_PATS, expr.span, title, |db| {
521 if !in_macro(expr.span) {
522 multispan_sugg(db, msg.to_owned(), suggs);
528 fn check_match_as_ref(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
530 && arms[0].pats.len() == 1
531 && arms[0].guard.is_none()
532 && arms[1].pats.len() == 1
533 && arms[1].guard.is_none()
535 let arm_ref: Option<BindingAnnotation> = if is_none_arm(&arms[0]) {
536 is_ref_some_arm(&arms[1])
537 } else if is_none_arm(&arms[1]) {
538 is_ref_some_arm(&arms[0])
542 if let Some(rb) = arm_ref {
543 let suggestion = if rb == BindingAnnotation::Ref {
548 let mut applicability = Applicability::MachineApplicable;
553 &format!("use {}() instead", suggestion),
557 snippet_with_applicability(cx, ex.span, "_", &mut applicability),
566 /// Get all arms that are unbounded `PatRange`s.
567 fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &'tcx [Arm]) -> Vec<SpannedRange<Constant>> {
571 ref pats, guard: None, ..
579 if let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node {
580 let lhs = constant(cx, cx.tables, lhs)?.0;
581 let rhs = constant(cx, cx.tables, rhs)?.0;
582 let rhs = match *range_end {
583 RangeEnd::Included => Bound::Included(rhs),
584 RangeEnd::Excluded => Bound::Excluded(rhs),
586 return Some(SpannedRange {
592 if let PatKind::Lit(ref value) = pat.node {
593 let value = constant(cx, cx.tables, value)?.0;
594 return Some(SpannedRange {
596 node: (value.clone(), Bound::Included(value)),
606 #[derive(Debug, Eq, PartialEq)]
607 pub struct SpannedRange<T> {
609 pub node: (T, Bound<T>),
612 type TypedRanges = Vec<SpannedRange<u128>>;
614 /// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway
615 /// and other types than
616 /// `Uint` and `Int` probably don't make sense.
617 fn type_ranges(ranges: &[SpannedRange<Constant>]) -> TypedRanges {
620 .filter_map(|range| match range.node {
621 (Constant::Int(start), Bound::Included(Constant::Int(end))) => Some(SpannedRange {
623 node: (start, Bound::Included(end)),
625 (Constant::Int(start), Bound::Excluded(Constant::Int(end))) => Some(SpannedRange {
627 node: (start, Bound::Excluded(end)),
629 (Constant::Int(start), Bound::Unbounded) => Some(SpannedRange {
631 node: (start, Bound::Unbounded),
638 fn is_unit_expr(expr: &Expr) -> bool {
640 ExprKind::Tup(ref v) if v.is_empty() => true,
641 ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
646 // Checks if arm has the form `None => None`
647 fn is_none_arm(arm: &Arm) -> bool {
648 match arm.pats[0].node {
649 PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => true,
654 // Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
655 fn is_ref_some_arm(arm: &Arm) -> Option<BindingAnnotation> {
657 if let PatKind::TupleStruct(ref path, ref pats, _) = arm.pats[0].node;
658 if pats.len() == 1 && match_qpath(path, &paths::OPTION_SOME);
659 if let PatKind::Binding(rb, _, ident, _) = pats[0].node;
660 if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
661 if let ExprKind::Call(ref e, ref args) = remove_blocks(&arm.body).node;
662 if let ExprKind::Path(ref some_path) = e.node;
663 if match_qpath(some_path, &paths::OPTION_SOME) && args.len() == 1;
664 if let ExprKind::Path(ref qpath) = args[0].node;
665 if let &QPath::Resolved(_, ref path2) = qpath;
666 if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
674 fn has_only_ref_pats(arms: &[Arm]) -> bool {
677 .flat_map(|a| &a.pats)
680 PatKind::Ref(..) => Some(true), // &-patterns
681 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
682 _ => None, // any other pattern is not fine
685 .collect::<Option<Vec<bool>>>();
686 // look for Some(v) where there's at least one true element
687 mapped.map_or(false, |v| v.iter().any(|el| *el))
690 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
694 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
695 enum Kind<'a, T: 'a> {
696 Start(T, &'a SpannedRange<T>),
697 End(Bound<T>, &'a SpannedRange<T>),
700 impl<'a, T: Copy> Kind<'a, T> {
701 fn range(&self) -> &'a SpannedRange<T> {
703 Kind::Start(_, r) | Kind::End(_, r) => r,
707 fn value(self) -> Bound<T> {
709 Kind::Start(t, _) => Bound::Included(t),
710 Kind::End(t, _) => t,
715 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
716 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
717 Some(self.cmp(other))
721 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
722 fn cmp(&self, other: &Self) -> Ordering {
723 match (self.value(), other.value()) {
724 (Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
725 // Range patterns cannot be unbounded (yet)
726 (Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(),
727 (Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) {
728 Ordering::Equal => Ordering::Greater,
731 (Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) {
732 Ordering::Equal => Ordering::Less,
739 let mut values = Vec::with_capacity(2 * ranges.len());
742 values.push(Kind::Start(r.node.0, r));
743 values.push(Kind::End(r.node.1, r));
748 for (a, b) in values.iter().zip(values.iter().skip(1)) {
750 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
751 if ra.node != rb.node {
752 return Some((ra, rb));
755 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
756 _ => return Some((a.range(), b.range())),