3 use rustc::middle::const_val::ConstVal;
5 use rustc_const_eval::EvalHint::ExprTypeChecked;
6 use rustc_const_eval::ConstContext;
7 use rustc_const_math::ConstInt;
8 use std::cmp::Ordering;
9 use std::collections::Bound;
10 use syntax::ast::LitKind;
11 use syntax::codemap::Span;
13 use utils::{match_type, snippet, span_note_and_lint, span_lint_and_then, in_external_macro, expr_block, walk_ptrs_ty,
15 use utils::sugg::Sugg;
17 /// **What it does:** Checks for matches with a single arm where an `if let`
18 /// will usually suffice.
20 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
22 /// **Known problems:** None.
27 /// Some(ref foo) => bar(foo),
34 "a match statement with a single nontrivial arm (i.e, where the other arm \
35 is `_ => {}`) instead of `if let`"
38 /// **What it does:** Checks for matches with a two arms where an `if let` will
41 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
43 /// **Known problems:** Personal style preferences may differ.
48 /// Some(ref foo) => bar(foo),
49 /// _ => bar(other_ref),
53 pub SINGLE_MATCH_ELSE,
55 "a match statement with a two arms where the second arm's pattern is a wildcard \
59 /// **What it does:** Checks for matches where all arms match a reference,
60 /// suggesting to remove the reference and deref the matched expression
61 /// instead. It also checks for `if let &foo = bar` blocks.
63 /// **Why is this bad?** It just makes the code less readable. That reference
64 /// destructuring adds nothing to the code.
66 /// **Known problems:** None.
71 /// &A(ref y) => foo(y),
79 "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
82 /// **What it does:** Checks for matches where match expression is a `bool`. It
83 /// suggests to replace the expression with an `if...else` block.
85 /// **Why is this bad?** It makes the code less readable.
87 /// **Known problems:** None.
91 /// let condition: bool = true;
100 "a match on a boolean expression instead of an `if..else` block"
103 /// **What it does:** Checks for overlapping match arms.
105 /// **Why is this bad?** It is likely to be an error and if not, makes the code
108 /// **Known problems:** None.
114 /// 1 ... 10 => println!("1 ... 10"),
115 /// 5 ... 15 => println!("5 ... 15"),
120 pub MATCH_OVERLAPPING_ARM,
122 "a match with overlapping arms"
125 /// **What it does:** Checks for arm which matches all errors with `Err(_)`
126 /// and take drastic actions like `panic!`.
128 /// **Why is this bad?** It is generally a bad practice, just like
129 /// catching all exceptions in java with `catch(Exception)`
131 /// **Known problems:** None.
135 /// let x : Result(i32, &str) = Ok(3);
137 /// Ok(_) => println!("ok"),
138 /// Err(_) => panic!("err"),
142 pub MATCH_WILD_ERR_ARM,
144 "a match with `Err(_)` arm and take drastic actions"
147 #[allow(missing_copy_implementations)]
148 pub struct MatchPass;
150 impl LintPass for MatchPass {
151 fn get_lints(&self) -> LintArray {
152 lint_array!(SINGLE_MATCH,
156 MATCH_OVERLAPPING_ARM,
161 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
162 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
163 if in_external_macro(cx, expr.span) {
166 if let ExprMatch(ref ex, ref arms, MatchSource::Normal) = expr.node {
167 check_single_match(cx, ex, arms, expr);
168 check_match_bool(cx, ex, arms, expr);
169 check_overlapping_arms(cx, ex, arms);
170 check_wild_err_arm(cx, ex, arms);
172 if let ExprMatch(ref ex, ref arms, source) = expr.node {
173 check_match_ref_pats(cx, ex, arms, source, expr);
178 #[cfg_attr(rustfmt, rustfmt_skip)]
179 fn check_single_match(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
180 if arms.len() == 2 &&
181 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
182 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
183 let els = if is_unit_expr(&arms[1].body) {
185 } else if let ExprBlock(_) = arms[1].body.node {
186 // matches with blocks that contain statements are prettier as `if let + else`
189 // allow match arms with just expressions
192 let ty = cx.tables.expr_ty(ex);
193 if ty.sty != ty::TyBool || cx.current_level(MATCH_BOOL) == Allow {
194 check_single_match_single_pattern(cx, ex, arms, expr, els);
195 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
200 fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
201 if arms[1].pats[0].node == PatKind::Wild {
202 let lint = if els.is_some() {
207 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
208 span_lint_and_then(cx,
211 "you seem to be trying to use match for destructuring a single pattern. \
212 Consider using `if let`",
214 db.span_suggestion(expr.span,
216 format!("if let {} = {} {}{}",
217 snippet(cx, arms[0].pats[0].span, ".."),
218 snippet(cx, ex.span, ".."),
219 expr_block(cx, &arms[0].body, None, ".."),
225 fn check_single_match_opt_like(
233 // list of candidate Enums we know will never get any more members
234 let candidates = &[(&paths::COW, "Borrowed"),
235 (&paths::COW, "Cow::Borrowed"),
236 (&paths::COW, "Cow::Owned"),
237 (&paths::COW, "Owned"),
238 (&paths::OPTION, "None"),
239 (&paths::RESULT, "Err"),
240 (&paths::RESULT, "Ok")];
242 let path = match arms[1].pats[0].node {
243 PatKind::TupleStruct(ref path, ref inner, _) => {
244 // contains any non wildcard patterns? e.g. Err(err)
245 if inner.iter().any(|pat| pat.node != PatKind::Wild) {
248 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
250 PatKind::Binding(BindByValue(MutImmutable), _, ident, None) => ident.node.to_string(),
251 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
255 for &(ty_path, pat_path) in candidates {
256 if &path == pat_path && match_type(cx, ty, ty_path) {
257 let lint = if els.is_some() {
262 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
263 span_lint_and_then(cx,
266 "you seem to be trying to use match for destructuring a single pattern. Consider \
269 db.span_suggestion(expr.span,
271 format!("if let {} = {} {}{}",
272 snippet(cx, arms[0].pats[0].span, ".."),
273 snippet(cx, ex.span, ".."),
274 expr_block(cx, &arms[0].body, None, ".."),
281 fn check_match_bool(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
282 // type of expression == bool
283 if cx.tables.expr_ty(ex).sty == ty::TyBool {
284 span_lint_and_then(cx,
287 "you seem to be trying to match on a boolean expression",
289 if arms.len() == 2 && arms[0].pats.len() == 1 {
291 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
292 if let ExprLit(ref lit) = arm_bool.node {
294 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
295 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
305 if let Some((true_expr, false_expr)) = exprs {
306 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
308 Some(format!("if {} {} else {}",
309 snippet(cx, ex.span, "b"),
310 expr_block(cx, true_expr, None, ".."),
311 expr_block(cx, false_expr, None, "..")))
314 Some(format!("if {} {}", snippet(cx, ex.span, "b"), expr_block(cx, true_expr, None, "..")))
317 let test = Sugg::hir(cx, ex, "..");
318 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
320 (true, true) => None,
323 if let Some(sugg) = sugg {
324 db.span_suggestion(expr.span, "consider using an if/else expression", sugg);
333 fn check_overlapping_arms(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
334 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
335 let ranges = all_ranges(cx, arms);
336 let type_ranges = type_ranges(&ranges);
337 if !type_ranges.is_empty() {
338 if let Some((start, end)) = overlapping(&type_ranges) {
339 span_note_and_lint(cx,
340 MATCH_OVERLAPPING_ARM,
342 "some ranges overlap",
344 "overlaps with this");
350 fn check_wild_err_arm(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
351 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
352 if match_type(cx, ex_ty, &paths::RESULT) {
354 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
355 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
358 inner.iter().any(|pat| pat.node == PatKind::Wild),
359 let ExprBlock(ref block) = arm.body.node,
360 is_panic_block(cx, block)
362 // `Err(_)` arm with `panic!` found
363 span_note_and_lint(cx,
366 "Err(_) will match all errors, maybe not a good idea",
368 "to remove this warning, match each error seperately \
369 or use unreachable macro");
376 // If the block contains only a `panic!` macro (as expression or statement)
377 fn is_panic_block(cx: &LateContext, block: &Block) -> bool {
378 match (&block.expr, block.stmts.len(), block.stmts.first()) {
379 (&Some(ref exp), 0, _) => {
380 is_expn_of(cx, exp.span, "panic").is_some() && is_expn_of(cx, exp.span, "unreachable").is_none()
382 (&None, 1, Some(stmt)) => {
383 is_expn_of(cx, stmt.span, "panic").is_some() && is_expn_of(cx, stmt.span, "unreachable").is_none()
389 fn check_match_ref_pats(cx: &LateContext, ex: &Expr, arms: &[Arm], source: MatchSource, expr: &Expr) {
390 if has_only_ref_pats(arms) {
391 if let ExprAddrOf(Mutability::MutImmutable, ref inner) = ex.node {
392 span_lint_and_then(cx,
395 "you don't need to add `&` to both the expression and the patterns",
397 let inner = Sugg::hir(cx, inner, "..");
398 let template = match_template(expr.span, source, inner);
399 db.span_suggestion(expr.span, "try", template);
402 span_lint_and_then(cx,
405 "you don't need to add `&` to all patterns",
407 let ex = Sugg::hir(cx, ex, "..");
408 let template = match_template(expr.span, source, ex.deref());
409 db.span_suggestion(expr.span,
410 "instead of prefixing all patterns with `&`, you can dereference the expression",
417 /// Get all arms that are unbounded `PatRange`s.
418 fn all_ranges(cx: &LateContext, arms: &[Arm]) -> Vec<SpannedRange<ConstVal>> {
419 let constcx = ConstContext::with_tables(cx.tcx, cx.tables);
422 if let Arm { ref pats, guard: None, .. } = *arm {
429 let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node,
430 let Ok(lhs) = constcx.eval(lhs, ExprTypeChecked),
431 let Ok(rhs) = constcx.eval(rhs, ExprTypeChecked)
433 let rhs = match *range_end {
434 RangeEnd::Included => Bound::Included(rhs),
435 RangeEnd::Excluded => Bound::Excluded(rhs),
437 return Some(SpannedRange { span: pat.span, node: (lhs, rhs) });
441 let PatKind::Lit(ref value) = pat.node,
442 let Ok(value) = constcx.eval(value, ExprTypeChecked)
444 return Some(SpannedRange { span: pat.span, node: (value.clone(), Bound::Included(value)) });
453 #[derive(Debug, Eq, PartialEq)]
454 pub struct SpannedRange<T> {
456 pub node: (T, Bound<T>),
459 type TypedRanges = Vec<SpannedRange<ConstInt>>;
461 /// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway and other types than
462 /// `Uint` and `Int` probably don't make sense.
463 fn type_ranges(ranges: &[SpannedRange<ConstVal>]) -> TypedRanges {
465 .filter_map(|range| match range.node {
466 (ConstVal::Integral(start), Bound::Included(ConstVal::Integral(end))) => {
469 node: (start, Bound::Included(end)),
472 (ConstVal::Integral(start), Bound::Excluded(ConstVal::Integral(end))) => {
475 node: (start, Bound::Excluded(end)),
478 (ConstVal::Integral(start), Bound::Unbounded) => {
481 node: (start, Bound::Unbounded),
489 fn is_unit_expr(expr: &Expr) -> bool {
491 ExprTup(ref v) if v.is_empty() => true,
492 ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
497 fn has_only_ref_pats(arms: &[Arm]) -> bool {
498 let mapped = arms.iter()
499 .flat_map(|a| &a.pats)
502 PatKind::Ref(..) => Some(true), // &-patterns
503 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
504 _ => None, // any other pattern is not fine
507 .collect::<Option<Vec<bool>>>();
508 // look for Some(v) where there's at least one true element
509 mapped.map_or(false, |v| v.iter().any(|el| *el))
512 fn match_template(span: Span, source: MatchSource, expr: Sugg) -> String {
514 MatchSource::Normal => format!("match {} {{ .. }}", expr),
515 MatchSource::IfLetDesugar { .. } => format!("if let .. = {} {{ .. }}", expr),
516 MatchSource::WhileLetDesugar => format!("while let .. = {} {{ .. }}", expr),
517 MatchSource::ForLoopDesugar => span_bug!(span, "for loop desugared to match with &-patterns!"),
518 MatchSource::TryDesugar => span_bug!(span, "`?` operator desugared to match with &-patterns!"),
522 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
525 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
526 enum Kind<'a, T: 'a> {
527 Start(T, &'a SpannedRange<T>),
528 End(Bound<T>, &'a SpannedRange<T>),
531 impl<'a, T: Copy> Kind<'a, T> {
532 fn range(&self) -> &'a SpannedRange<T> {
535 Kind::End(_, r) => r,
539 fn value(self) -> Bound<T> {
541 Kind::Start(t, _) => Bound::Included(t),
542 Kind::End(t, _) => t,
547 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
548 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
549 Some(self.cmp(other))
553 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
554 fn cmp(&self, other: &Self) -> Ordering {
555 match (self.value(), other.value()) {
556 (Bound::Included(a), Bound::Included(b)) |
557 (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
558 // Range patterns cannot be unbounded (yet)
559 (Bound::Unbounded, _) |
560 (_, Bound::Unbounded) => unimplemented!(),
561 (Bound::Included(a), Bound::Excluded(b)) => {
563 Ordering::Equal => Ordering::Greater,
567 (Bound::Excluded(a), Bound::Included(b)) => {
569 Ordering::Equal => Ordering::Less,
577 let mut values = Vec::with_capacity(2 * ranges.len());
580 values.push(Kind::Start(r.node.0, r));
581 values.push(Kind::End(r.node.1, r));
586 for (a, b) in values.iter().zip(values.iter().skip(1)) {
588 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
589 if ra.node != rb.node {
590 return Some((ra, rb));
593 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
594 _ => return Some((a.range(), b.range())),