1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution.
4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
7 // option. This file may not be copied, modified, or distributed
8 // except according to those terms.
11 use crate::rustc::hir::*;
12 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass, in_external_macro, LintContext};
13 use crate::rustc::{declare_tool_lint, lint_array};
14 use if_chain::if_chain;
15 use crate::rustc::ty::{self, Ty};
16 use std::cmp::Ordering;
17 use std::collections::Bound;
18 use crate::syntax::ast::LitKind;
19 use crate::syntax::source_map::Span;
20 use crate::utils::paths;
21 use crate::utils::{expr_block, in_macro, is_allowed, is_expn_of, match_qpath, match_type,
22 multispan_sugg, remove_blocks, snippet, span_lint_and_sugg, span_lint_and_then,
23 span_note_and_lint, walk_ptrs_ty};
24 use crate::utils::sugg::Sugg;
25 use crate::consts::{constant, Constant};
26 use crate::rustc_errors::Applicability;
28 /// **What it does:** Checks for matches with a single arm where an `if let`
29 /// will usually suffice.
31 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
33 /// **Known problems:** None.
38 /// Some(ref foo) => bar(foo),
42 declare_clippy_lint! {
45 "a match statement with a single nontrivial arm (i.e. where the other arm \
46 is `_ => {}`) instead of `if let`"
49 /// **What it does:** Checks for matches with a two arms where an `if let` will
52 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
54 /// **Known problems:** Personal style preferences may differ.
59 /// Some(ref foo) => bar(foo),
60 /// _ => bar(other_ref),
63 declare_clippy_lint! {
64 pub SINGLE_MATCH_ELSE,
66 "a match statement with a two arms where the second arm's pattern is a wildcard \
70 /// **What it does:** Checks for matches where all arms match a reference,
71 /// suggesting to remove the reference and deref the matched expression
72 /// instead. It also checks for `if let &foo = bar` blocks.
74 /// **Why is this bad?** It just makes the code less readable. That reference
75 /// destructuring adds nothing to the code.
77 /// **Known problems:** None.
82 /// &A(ref y) => foo(y),
87 declare_clippy_lint! {
90 "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
93 /// **What it does:** Checks for matches where match expression is a `bool`. It
94 /// suggests to replace the expression with an `if...else` block.
96 /// **Why is this bad?** It makes the code less readable.
98 /// **Known problems:** None.
102 /// let condition: bool = true;
103 /// match condition {
108 /// Use if/else instead:
110 /// let condition: bool = true;
117 declare_clippy_lint! {
120 "a match on a boolean expression instead of an `if..else` block"
123 /// **What it does:** Checks for overlapping match arms.
125 /// **Why is this bad?** It is likely to be an error and if not, makes the code
128 /// **Known problems:** None.
134 /// 1 ... 10 => println!("1 ... 10"),
135 /// 5 ... 15 => println!("5 ... 15"),
139 declare_clippy_lint! {
140 pub MATCH_OVERLAPPING_ARM,
142 "a match with overlapping arms"
145 /// **What it does:** Checks for arm which matches all errors with `Err(_)`
146 /// and take drastic actions like `panic!`.
148 /// **Why is this bad?** It is generally a bad practice, just like
149 /// catching all exceptions in java with `catch(Exception)`
151 /// **Known problems:** None.
155 /// let x : Result(i32, &str) = Ok(3);
157 /// Ok(_) => println!("ok"),
158 /// Err(_) => panic!("err"),
161 declare_clippy_lint! {
162 pub MATCH_WILD_ERR_ARM,
164 "a match with `Err(_)` arm and take drastic actions"
167 /// **What it does:** Checks for match which is used to add a reference to an
170 /// **Why is this bad?** Using `as_ref()` or `as_mut()` instead is shorter.
172 /// **Known problems:** None.
176 /// let x: Option<()> = None;
177 /// let r: Option<&()> = match x {
179 /// Some(ref v) => Some(v),
182 declare_clippy_lint! {
185 "a match on an Option value instead of using `as_ref()` or `as_mut`"
188 #[allow(missing_copy_implementations)]
189 pub struct MatchPass;
191 impl LintPass for MatchPass {
192 fn get_lints(&self) -> LintArray {
198 MATCH_OVERLAPPING_ARM,
205 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
206 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
207 if in_external_macro(cx.sess(), expr.span) {
210 if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.node {
211 check_single_match(cx, ex, arms, expr);
212 check_match_bool(cx, ex, arms, expr);
213 check_overlapping_arms(cx, ex, arms);
214 check_wild_err_arm(cx, ex, arms);
215 check_match_as_ref(cx, ex, arms, expr);
217 if let ExprKind::Match(ref ex, ref arms, _) = expr.node {
218 check_match_ref_pats(cx, ex, arms, expr);
224 fn check_single_match(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
225 if arms.len() == 2 &&
226 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
227 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
228 let els = remove_blocks(&arms[1].body);
229 let els = if is_unit_expr(els) {
231 } else if let ExprKind::Block(_, _) = els.node {
232 // matches with blocks that contain statements are prettier as `if let + else`
235 // allow match arms with just expressions
238 let ty = cx.tables.expr_ty(ex);
239 if ty.sty != ty::Bool || is_allowed(cx, MATCH_BOOL, ex.id) {
240 check_single_match_single_pattern(cx, ex, arms, expr, els);
241 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
246 fn check_single_match_single_pattern(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
247 if is_wild(&arms[1].pats[0]) {
248 report_single_match_single_pattern(cx, ex, arms, expr, els);
252 fn report_single_match_single_pattern(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
253 let lint = if els.is_some() {
258 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
263 "you seem to be trying to use match for destructuring a single pattern. Consider using `if \
267 "if let {} = {} {}{}",
268 snippet(cx, arms[0].pats[0].span, ".."),
269 snippet(cx, ex.span, ".."),
270 expr_block(cx, &arms[0].body, None, ".."),
273 Applicability::Unspecified,
277 fn check_single_match_opt_like(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr, ty: Ty<'_>, els: Option<&Expr>) {
278 // list of candidate Enums we know will never get any more members
280 (&paths::COW, "Borrowed"),
281 (&paths::COW, "Cow::Borrowed"),
282 (&paths::COW, "Cow::Owned"),
283 (&paths::COW, "Owned"),
284 (&paths::OPTION, "None"),
285 (&paths::RESULT, "Err"),
286 (&paths::RESULT, "Ok"),
289 let path = match arms[1].pats[0].node {
290 PatKind::TupleStruct(ref path, ref inner, _) => {
291 // contains any non wildcard patterns? e.g. Err(err)
292 if !inner.iter().all(is_wild) {
295 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
297 PatKind::Binding(BindingAnnotation::Unannotated, _, ident, None) => ident.to_string(),
298 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
302 for &(ty_path, pat_path) in candidates {
303 if path == *pat_path && match_type(cx, ty, ty_path) {
304 report_single_match_single_pattern(cx, ex, arms, expr, els);
309 fn check_match_bool(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
310 // type of expression == bool
311 if cx.tables.expr_ty(ex).sty == ty::Bool {
316 "you seem to be trying to match on a boolean expression",
318 if arms.len() == 2 && arms[0].pats.len() == 1 {
320 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
321 if let ExprKind::Lit(ref lit) = arm_bool.node {
323 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
324 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
334 if let Some((true_expr, false_expr)) = exprs {
335 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
336 (false, false) => Some(format!(
338 snippet(cx, ex.span, "b"),
339 expr_block(cx, true_expr, None, ".."),
340 expr_block(cx, false_expr, None, "..")
342 (false, true) => Some(format!(
344 snippet(cx, ex.span, "b"),
345 expr_block(cx, true_expr, None, "..")
348 let test = Sugg::hir(cx, ex, "..");
349 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
351 (true, true) => None,
354 if let Some(sugg) = sugg {
355 db.span_suggestion_with_applicability(
357 "consider using an if/else expression",
359 Applicability::HasPlaceholders,
369 fn check_overlapping_arms<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ex: &'tcx Expr, arms: &'tcx [Arm]) {
370 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
371 let ranges = all_ranges(cx, arms);
372 let type_ranges = type_ranges(&ranges);
373 if !type_ranges.is_empty() {
374 if let Some((start, end)) = overlapping(&type_ranges) {
377 MATCH_OVERLAPPING_ARM,
379 "some ranges overlap",
381 "overlaps with this",
388 fn is_wild(pat: &impl std::ops::Deref<Target = Pat>) -> bool {
390 PatKind::Wild => true,
395 fn check_wild_err_arm(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm]) {
396 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
397 if match_type(cx, ex_ty, &paths::RESULT) {
399 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
400 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
402 if path_str == "Err";
403 if inner.iter().any(is_wild);
404 if let ExprKind::Block(ref block, _) = arm.body.node;
405 if is_panic_block(block);
407 // `Err(_)` arm with `panic!` found
408 span_note_and_lint(cx,
411 "Err(_) will match all errors, maybe not a good idea",
413 "to remove this warning, match each error separately \
414 or use unreachable macro");
422 // If the block contains only a `panic!` macro (as expression or statement)
423 fn is_panic_block(block: &Block) -> bool {
424 match (&block.expr, block.stmts.len(), block.stmts.first()) {
425 (&Some(ref exp), 0, _) => {
426 is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
428 (&None, 1, Some(stmt)) => {
429 is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
435 fn check_match_ref_pats(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
436 if has_only_ref_pats(arms) {
437 let mut suggs = Vec::new();
438 let (title, msg) = if let ExprKind::AddrOf(Mutability::MutImmutable, ref inner) = ex.node {
439 suggs.push((ex.span, Sugg::hir(cx, inner, "..").to_string()));
441 "you don't need to add `&` to both the expression and the patterns",
445 suggs.push((ex.span, Sugg::hir(cx, ex, "..").deref().to_string()));
447 "you don't need to add `&` to all patterns",
448 "instead of prefixing all patterns with `&`, you can dereference the expression",
452 suggs.extend(arms.iter().flat_map(|a| &a.pats).filter_map(|p| {
453 if let PatKind::Ref(ref refp, _) = p.node {
454 Some((p.span, snippet(cx, refp.span, "..").to_string()))
460 span_lint_and_then(cx, MATCH_REF_PATS, expr.span, title, |db| {
461 if !in_macro(expr.span) {
462 multispan_sugg(db, msg.to_owned(), suggs);
468 fn check_match_as_ref(cx: &LateContext<'_, '_>, ex: &Expr, arms: &[Arm], expr: &Expr) {
469 if arms.len() == 2 &&
470 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
471 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
472 let arm_ref: Option<BindingAnnotation> = if is_none_arm(&arms[0]) {
473 is_ref_some_arm(&arms[1])
474 } else if is_none_arm(&arms[1]) {
475 is_ref_some_arm(&arms[0])
479 if let Some(rb) = arm_ref {
480 let suggestion = if rb == BindingAnnotation::Ref { "as_ref" } else { "as_mut" };
485 &format!("use {}() instead", suggestion),
487 format!("{}.{}()", snippet(cx, ex.span, "_"), suggestion),
488 Applicability::Unspecified,
494 /// Get all arms that are unbounded `PatRange`s.
495 fn all_ranges<'a, 'tcx>(
496 cx: &LateContext<'a, 'tcx>,
498 ) -> Vec<SpannedRange<Constant>> {
511 if let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node {
512 let lhs = constant(cx, cx.tables, lhs)?.0;
513 let rhs = constant(cx, cx.tables, rhs)?.0;
514 let rhs = match *range_end {
515 RangeEnd::Included => Bound::Included(rhs),
516 RangeEnd::Excluded => Bound::Excluded(rhs),
518 return Some(SpannedRange { span: pat.span, node: (lhs, rhs) });
521 if let PatKind::Lit(ref value) = pat.node {
522 let value = constant(cx, cx.tables, value)?.0;
523 return Some(SpannedRange { span: pat.span, node: (value.clone(), Bound::Included(value)) });
532 #[derive(Debug, Eq, PartialEq)]
533 pub struct SpannedRange<T> {
535 pub node: (T, Bound<T>),
538 type TypedRanges = Vec<SpannedRange<u128>>;
540 /// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway
541 /// and other types than
542 /// `Uint` and `Int` probably don't make sense.
543 fn type_ranges(ranges: &[SpannedRange<Constant>]) -> TypedRanges {
546 .filter_map(|range| match range.node {
548 Constant::Int(start),
549 Bound::Included(Constant::Int(end)),
550 ) => Some(SpannedRange {
552 node: (start, Bound::Included(end)),
555 Constant::Int(start),
556 Bound::Excluded(Constant::Int(end)),
557 ) => Some(SpannedRange {
559 node: (start, Bound::Excluded(end)),
562 Constant::Int(start),
564 ) => Some(SpannedRange {
566 node: (start, Bound::Unbounded),
573 fn is_unit_expr(expr: &Expr) -> bool {
575 ExprKind::Tup(ref v) if v.is_empty() => true,
576 ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
581 // Checks if arm has the form `None => None`
582 fn is_none_arm(arm: &Arm) -> bool {
583 match arm.pats[0].node {
584 PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => true,
589 // Checks if arm has the form `Some(ref v) => Some(v)` (checks for `ref` and `ref mut`)
590 fn is_ref_some_arm(arm: &Arm) -> Option<BindingAnnotation> {
592 if let PatKind::TupleStruct(ref path, ref pats, _) = arm.pats[0].node;
593 if pats.len() == 1 && match_qpath(path, &paths::OPTION_SOME);
594 if let PatKind::Binding(rb, _, ident, _) = pats[0].node;
595 if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
596 if let ExprKind::Call(ref e, ref args) = remove_blocks(&arm.body).node;
597 if let ExprKind::Path(ref some_path) = e.node;
598 if match_qpath(some_path, &paths::OPTION_SOME) && args.len() == 1;
599 if let ExprKind::Path(ref qpath) = args[0].node;
600 if let &QPath::Resolved(_, ref path2) = qpath;
601 if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
609 fn has_only_ref_pats(arms: &[Arm]) -> bool {
610 let mapped = arms.iter()
611 .flat_map(|a| &a.pats)
614 PatKind::Ref(..) => Some(true), // &-patterns
615 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
616 _ => None, // any other pattern is not fine
619 .collect::<Option<Vec<bool>>>();
620 // look for Some(v) where there's at least one true element
621 mapped.map_or(false, |v| v.iter().any(|el| *el))
624 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
628 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
629 enum Kind<'a, T: 'a> {
630 Start(T, &'a SpannedRange<T>),
631 End(Bound<T>, &'a SpannedRange<T>),
634 impl<'a, T: Copy> Kind<'a, T> {
635 fn range(&self) -> &'a SpannedRange<T> {
637 Kind::Start(_, r) | Kind::End(_, r) => r,
641 fn value(self) -> Bound<T> {
643 Kind::Start(t, _) => Bound::Included(t),
644 Kind::End(t, _) => t,
649 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
650 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
651 Some(self.cmp(other))
655 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
656 fn cmp(&self, other: &Self) -> Ordering {
657 match (self.value(), other.value()) {
658 (Bound::Included(a), Bound::Included(b)) | (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
659 // Range patterns cannot be unbounded (yet)
660 (Bound::Unbounded, _) | (_, Bound::Unbounded) => unimplemented!(),
661 (Bound::Included(a), Bound::Excluded(b)) => match a.cmp(&b) {
662 Ordering::Equal => Ordering::Greater,
665 (Bound::Excluded(a), Bound::Included(b)) => match a.cmp(&b) {
666 Ordering::Equal => Ordering::Less,
673 let mut values = Vec::with_capacity(2 * ranges.len());
676 values.push(Kind::Start(r.node.0, r));
677 values.push(Kind::End(r.node.1, r));
682 for (a, b) in values.iter().zip(values.iter().skip(1)) {
684 (&Kind::Start(_, ra), &Kind::End(_, rb)) => if ra.node != rb.node {
685 return Some((ra, rb));
687 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
688 _ => return Some((a.range(), b.range())),