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};
13 use rustc::{declare_lint_pass, declare_tool_lint};
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 declare_lint_pass!(Matches => [
223 MATCH_OVERLAPPING_ARM,
226 WILDCARD_ENUM_MATCH_ARM
229 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Matches {
230 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
231 if in_external_macro(cx.sess(), expr.span) {
234 if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.node {
235 check_single_match(cx, ex, arms, expr);
236 check_match_bool(cx, ex, arms, expr);
237 check_overlapping_arms(cx, ex, arms);
238 check_wild_err_arm(cx, ex, arms);
239 check_wild_enum_match(cx, ex, arms);
240 check_match_as_ref(cx, ex, arms, expr);
242 if let ExprKind::Match(ref ex, ref arms, _) = expr.node {
243 check_match_ref_pats(cx, ex, arms, expr);
249 fn check_single_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
250 if arms.len() == 2 &&
251 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
252 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
253 let els = remove_blocks(&arms[1].body);
254 let els = if is_unit_expr(els) {
256 } else if let ExprKind::Block(_, _) = els.node {
257 // matches with blocks that contain statements are prettier as `if let + else`
260 // allow match arms with just expressions
263 let ty = cx.tables.expr_ty(ex);
264 if ty.sty != ty::Bool || is_allowed(cx, MATCH_BOOL, ex.hir_id) {
265 check_single_match_single_pattern(cx, ex, arms, expr, els);
266 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
271 fn check_single_match_single_pattern(
272 cx: &LateContext<'_, '_>,
278 if is_wild(&arms[1].pats[0]) {
279 report_single_match_single_pattern(cx, ex, arms, expr, els);
283 fn report_single_match_single_pattern(
284 cx: &LateContext<'_, '_>,
290 let lint = if els.is_some() { SINGLE_MATCH_ELSE } else { SINGLE_MATCH };
291 let els_str = els.map_or(String::new(), |els| {
292 format!(" else {}", expr_block(cx, els, None, ".."))
298 "you seem to be trying to use match for destructuring a single pattern. Consider using `if \
302 "if let {} = {} {}{}",
303 snippet(cx, arms[0].pats[0].span, ".."),
304 snippet(cx, ex.span, ".."),
305 expr_block(cx, &arms[0].body, None, ".."),
308 Applicability::HasPlaceholders,
312 fn check_single_match_opt_like(
313 cx: &LateContext<'_, '_>,
320 // list of candidate `Enum`s we know will never get any more members
322 (&paths::COW, "Borrowed"),
323 (&paths::COW, "Cow::Borrowed"),
324 (&paths::COW, "Cow::Owned"),
325 (&paths::COW, "Owned"),
326 (&paths::OPTION, "None"),
327 (&paths::RESULT, "Err"),
328 (&paths::RESULT, "Ok"),
331 let path = match arms[1].pats[0].node {
332 PatKind::TupleStruct(ref path, ref inner, _) => {
333 // Contains any non wildcard patterns (e.g., `Err(err)`)?
334 if !inner.iter().all(is_wild) {
337 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
339 PatKind::Binding(BindingAnnotation::Unannotated, .., ident, None) => ident.to_string(),
340 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
344 for &(ty_path, pat_path) in candidates {
345 if path == *pat_path && match_type(cx, ty, ty_path) {
346 report_single_match_single_pattern(cx, ex, arms, expr, els);
351 fn check_match_bool(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
352 // Type of expression is `bool`.
353 if cx.tables.expr_ty(ex).sty == ty::Bool {
358 "you seem to be trying to match on a boolean expression",
360 if arms.len() == 2 && arms[0].pats.len() == 1 {
362 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
363 if let ExprKind::Lit(ref lit) = arm_bool.node {
365 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
366 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
376 if let Some((true_expr, false_expr)) = exprs {
377 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
378 (false, false) => Some(format!(
380 snippet(cx, ex.span, "b"),
381 expr_block(cx, true_expr, None, ".."),
382 expr_block(cx, false_expr, None, "..")
384 (false, true) => Some(format!(
386 snippet(cx, ex.span, "b"),
387 expr_block(cx, true_expr, None, "..")
390 let test = Sugg::hir(cx, ex, "..");
391 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
393 (true, true) => None,
396 if let Some(sugg) = sugg {
399 "consider using an if/else expression",
401 Applicability::HasPlaceholders,
411 fn check_overlapping_arms<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ex: &'tcx Expr, arms: &'tcx [Arm]) {
412 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
413 let ranges = all_ranges(cx, arms);
414 let type_ranges = type_ranges(&ranges);
415 if !type_ranges.is_empty() {
416 if let Some((start, end)) = overlapping(&type_ranges) {
419 MATCH_OVERLAPPING_ARM,
421 "some ranges overlap",
423 "overlaps with this",
430 fn is_wild(pat: &impl std::ops::Deref<Target = Pat>) -> bool {
432 PatKind::Wild => true,
437 fn check_wild_err_arm(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
438 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
439 if match_type(cx, ex_ty, &paths::RESULT) {
441 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
442 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
444 if path_str == "Err";
445 if inner.iter().any(is_wild);
446 if let ExprKind::Block(ref block, _) = arm.body.node;
447 if is_panic_block(block);
449 // `Err(_)` arm with `panic!` found
450 span_note_and_lint(cx,
453 "Err(_) will match all errors, maybe not a good idea",
455 "to remove this warning, match each error separately \
456 or use unreachable macro");
464 fn check_wild_enum_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
465 let ty = cx.tables.expr_ty(ex);
467 // If there isn't a nice closed set of possible values that can be conveniently enumerated,
468 // don't complain about not enumerating the mall.
472 // First pass - check for violation, but don't do much book-keeping because this is hopefully
473 // the uncommon case, and the book-keeping is slightly expensive.
474 let mut wildcard_span = None;
475 let mut wildcard_ident = None;
477 for pat in &arm.pats {
478 if let PatKind::Wild = pat.node {
479 wildcard_span = Some(pat.span);
480 } else if let PatKind::Binding(_, _, ident, None) = pat.node {
481 wildcard_span = Some(pat.span);
482 wildcard_ident = Some(ident);
487 if let Some(wildcard_span) = wildcard_span {
488 // Accumulate the variants which should be put in place of the wildcard because they're not
491 let mut missing_variants = vec![];
492 if let ty::Adt(def, _) = ty.sty {
493 for variant in &def.variants {
494 missing_variants.push(variant);
499 if arm.guard.is_some() {
500 // Guards mean that this case probably isn't exhaustively covered. Technically
501 // this is incorrect, as we should really check whether each variant is exhaustively
502 // covered by the set of guards that cover it, but that's really hard to do.
505 for pat in &arm.pats {
506 if let PatKind::Path(ref path) = pat.deref().node {
507 if let QPath::Resolved(_, p) = path {
508 missing_variants.retain(|e| e.ctor_def_id != Some(p.def.def_id()));
510 } else if let PatKind::TupleStruct(ref path, ..) = pat.deref().node {
511 if let QPath::Resolved(_, p) = path {
512 missing_variants.retain(|e| e.ctor_def_id != Some(p.def.def_id()));
518 let suggestion: Vec<String> = missing_variants
521 let suffix = match v.ctor_kind {
522 CtorKind::Fn => "(..)",
523 CtorKind::Const | CtorKind::Fictive => "",
525 let ident_str = if let Some(ident) = wildcard_ident {
526 format!("{} @ ", ident.name)
530 // This path assumes that the enum type is imported into scope.
531 format!("{}{}{}", ident_str, cx.tcx.def_path_str(v.def_id), suffix)
535 if suggestion.is_empty() {
541 WILDCARD_ENUM_MATCH_ARM,
543 "wildcard match will miss any future added variants.",
545 suggestion.join(" | "),
546 Applicability::MachineApplicable,
551 // If the block contains only a `panic!` macro (as expression or statement)
552 fn is_panic_block(block: &Block) -> bool {
553 match (&block.expr, block.stmts.len(), block.stmts.first()) {
554 (&Some(ref exp), 0, _) => {
555 is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
557 (&None, 1, Some(stmt)) => {
558 is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
564 fn check_match_ref_pats(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
565 if has_only_ref_pats(arms) {
566 let mut suggs = Vec::new();
567 let (title, msg) = if let ExprKind::AddrOf(Mutability::MutImmutable, ref inner) = ex.node {
568 let span = ex.span.source_callsite();
569 suggs.push((span, Sugg::hir_with_macro_callsite(cx, inner, "..").to_string()));
571 "you don't need to add `&` to both the expression and the patterns",
575 let span = ex.span.source_callsite();
576 suggs.push((span, Sugg::hir_with_macro_callsite(cx, ex, "..").deref().to_string()));
578 "you don't need to add `&` to all patterns",
579 "instead of prefixing all patterns with `&`, you can dereference the expression",
583 suggs.extend(arms.iter().flat_map(|a| &a.pats).filter_map(|p| {
584 if let PatKind::Ref(ref refp, _) = p.node {
585 Some((p.span, snippet(cx, refp.span, "..").to_string()))
591 span_lint_and_then(cx, MATCH_REF_PATS, expr.span, title, |db| {
592 if !in_macro(expr.span) {
593 multispan_sugg(db, msg.to_owned(), suggs);
599 fn check_match_as_ref(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
601 && arms[0].pats.len() == 1
602 && arms[0].guard.is_none()
603 && arms[1].pats.len() == 1
604 && arms[1].guard.is_none()
606 let arm_ref: Option<BindingAnnotation> = if is_none_arm(&arms[0]) {
607 is_ref_some_arm(&arms[1])
608 } else if is_none_arm(&arms[1]) {
609 is_ref_some_arm(&arms[0])
613 if let Some(rb) = arm_ref {
614 let suggestion = if rb == BindingAnnotation::Ref {
619 let mut applicability = Applicability::MachineApplicable;
624 &format!("use {}() instead", suggestion),
628 snippet_with_applicability(cx, ex.span, "_", &mut applicability),
637 /// Gets all arms that are unbounded `PatRange`s.
638 fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &'tcx [Arm]) -> Vec<SpannedRange<Constant>> {
642 ref pats, guard: None, ..
650 if let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node {
651 let lhs = constant(cx, cx.tables, lhs)?.0;
652 let rhs = constant(cx, cx.tables, rhs)?.0;
653 let rhs = match *range_end {
654 RangeEnd::Included => Bound::Included(rhs),
655 RangeEnd::Excluded => Bound::Excluded(rhs),
657 return Some(SpannedRange {
663 if let PatKind::Lit(ref value) = pat.node {
664 let value = constant(cx, cx.tables, value)?.0;
665 return Some(SpannedRange {
667 node: (value.clone(), Bound::Included(value)),
677 #[derive(Debug, Eq, PartialEq)]
678 pub struct SpannedRange<T> {
680 pub node: (T, Bound<T>),
683 type TypedRanges = Vec<SpannedRange<u128>>;
685 /// Gets all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway
686 /// and other types than
687 /// `Uint` and `Int` probably don't make sense.
688 fn type_ranges(ranges: &[SpannedRange<Constant>]) -> TypedRanges {
691 .filter_map(|range| match range.node {
692 (Constant::Int(start), Bound::Included(Constant::Int(end))) => Some(SpannedRange {
694 node: (start, Bound::Included(end)),
696 (Constant::Int(start), Bound::Excluded(Constant::Int(end))) => Some(SpannedRange {
698 node: (start, Bound::Excluded(end)),
700 (Constant::Int(start), Bound::Unbounded) => Some(SpannedRange {
702 node: (start, Bound::Unbounded),
709 fn is_unit_expr(expr: &Expr) -> bool {
711 ExprKind::Tup(ref v) if v.is_empty() => true,
712 ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
717 // Checks if arm has the form `None => None`
718 fn is_none_arm(arm: &Arm) -> bool {
719 match arm.pats[0].node {
720 PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => true,
725 // Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
726 fn is_ref_some_arm(arm: &Arm) -> Option<BindingAnnotation> {
728 if let PatKind::TupleStruct(ref path, ref pats, _) = arm.pats[0].node;
729 if pats.len() == 1 && match_qpath(path, &paths::OPTION_SOME);
730 if let PatKind::Binding(rb, .., ident, _) = pats[0].node;
731 if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
732 if let ExprKind::Call(ref e, ref args) = remove_blocks(&arm.body).node;
733 if let ExprKind::Path(ref some_path) = e.node;
734 if match_qpath(some_path, &paths::OPTION_SOME) && args.len() == 1;
735 if let ExprKind::Path(ref qpath) = args[0].node;
736 if let &QPath::Resolved(_, ref path2) = qpath;
737 if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
745 fn has_only_ref_pats(arms: &[Arm]) -> bool {
748 .flat_map(|a| &a.pats)
751 PatKind::Ref(..) => Some(true), // &-patterns
752 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
753 _ => None, // any other pattern is not fine
756 .collect::<Option<Vec<bool>>>();
757 // look for Some(v) where there's at least one true element
758 mapped.map_or(false, |v| v.iter().any(|el| *el))
761 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
765 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
766 enum Kind<'a, T: 'a> {
767 Start(T, &'a SpannedRange<T>),
768 End(Bound<T>, &'a SpannedRange<T>),
771 impl<'a, T: Copy> Kind<'a, T> {
772 fn range(&self) -> &'a SpannedRange<T> {
774 Kind::Start(_, r) | Kind::End(_, r) => r,
778 fn value(self) -> Bound<T> {
780 Kind::Start(t, _) => Bound::Included(t),
781 Kind::End(t, _) => t,
786 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
787 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
788 Some(self.cmp(other))
792 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
793 fn cmp(&self, other: &Self) -> Ordering {
794 match (self.value(), other.value()) {
795 (Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
796 // Range patterns cannot be unbounded (yet)
797 (Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(),
798 (Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) {
799 Ordering::Equal => Ordering::Greater,
802 (Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) {
803 Ordering::Equal => Ordering::Less,
810 let mut values = Vec::with_capacity(2 * ranges.len());
813 values.push(Kind::Start(r.node.0, r));
814 values.push(Kind::End(r.node.1, r));
819 for (a, b) in values.iter().zip(values.iter().skip(1)) {
821 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
822 if ra.node != rb.node {
823 return Some((ra, rb));
826 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
827 _ => return Some((a.range(), b.range())),