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, is_expn_of};
14 use utils::sugg::Sugg;
16 /// **What it does:** Checks for matches with a single arm where an `if let`
17 /// will usually suffice.
19 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
21 /// **Known problems:** None.
26 /// Some(ref foo) => bar(foo),
33 "a match statement with a single nontrivial arm (i.e, where the other arm \
34 is `_ => {}`) instead of `if let`"
37 /// **What it does:** Checks for matches with a two arms where an `if let` will
40 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
42 /// **Known problems:** Personal style preferences may differ.
47 /// Some(ref foo) => bar(foo),
48 /// _ => bar(other_ref),
52 pub SINGLE_MATCH_ELSE,
54 "a match statement with a two arms where the second arm's pattern is a wildcard \
58 /// **What it does:** Checks for matches where all arms match a reference,
59 /// suggesting to remove the reference and deref the matched expression
60 /// instead. It also checks for `if let &foo = bar` blocks.
62 /// **Why is this bad?** It just makes the code less readable. That reference
63 /// destructuring adds nothing to the code.
65 /// **Known problems:** None.
70 /// &A(ref y) => foo(y),
78 "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
81 /// **What it does:** Checks for matches where match expression is a `bool`. It
82 /// suggests to replace the expression with an `if...else` block.
84 /// **Why is this bad?** It makes the code less readable.
86 /// **Known problems:** None.
90 /// let condition: bool = true;
99 "a match on a boolean expression instead of an `if..else` block"
102 /// **What it does:** Checks for overlapping match arms.
104 /// **Why is this bad?** It is likely to be an error and if not, makes the code
107 /// **Known problems:** None.
113 /// 1 ... 10 => println!("1 ... 10"),
114 /// 5 ... 15 => println!("5 ... 15"),
119 pub MATCH_OVERLAPPING_ARM,
121 "a match with overlapping arms"
124 /// **What it does:** Checks for arm matches all errors with `Err(_)`.
126 /// **Why is this bad?** It is a bad practice to catch all errors the same way
128 /// **Known problems:** None.
132 /// let x : Result(i32, &str) = Ok(3);
134 /// Ok(_) => println!("ok"),
135 /// Err(_) => println!("err"),
139 pub MATCH_WILD_ERR_ARM,
141 "a match with `Err(_)` arm"
144 #[allow(missing_copy_implementations)]
145 pub struct MatchPass;
147 impl LintPass for MatchPass {
148 fn get_lints(&self) -> LintArray {
149 lint_array!(SINGLE_MATCH,
153 MATCH_OVERLAPPING_ARM,
158 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
159 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
160 if in_external_macro(cx, expr.span) {
163 if let ExprMatch(ref ex, ref arms, MatchSource::Normal) = expr.node {
164 check_single_match(cx, ex, arms, expr);
165 check_match_bool(cx, ex, arms, expr);
166 check_overlapping_arms(cx, ex, arms);
167 check_wild_err_arm(cx, ex, arms);
169 if let ExprMatch(ref ex, ref arms, source) = expr.node {
170 check_match_ref_pats(cx, ex, arms, source, expr);
175 #[cfg_attr(rustfmt, rustfmt_skip)]
176 fn check_single_match(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
177 if arms.len() == 2 &&
178 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
179 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
180 let els = if is_unit_expr(&arms[1].body) {
182 } else if let ExprBlock(_) = arms[1].body.node {
183 // matches with blocks that contain statements are prettier as `if let + else`
186 // allow match arms with just expressions
189 let ty = cx.tables.expr_ty(ex);
190 if ty.sty != ty::TyBool || cx.current_level(MATCH_BOOL) == Allow {
191 check_single_match_single_pattern(cx, ex, arms, expr, els);
192 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
197 fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
198 if arms[1].pats[0].node == PatKind::Wild {
199 let lint = if els.is_some() {
204 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
205 span_lint_and_then(cx,
208 "you seem to be trying to use match for destructuring a single pattern. \
209 Consider using `if let`",
211 db.span_suggestion(expr.span,
213 format!("if let {} = {} {}{}",
214 snippet(cx, arms[0].pats[0].span, ".."),
215 snippet(cx, ex.span, ".."),
216 expr_block(cx, &arms[0].body, None, ".."),
222 fn check_single_match_opt_like(
230 // list of candidate Enums we know will never get any more members
231 let candidates = &[(&paths::COW, "Borrowed"),
232 (&paths::COW, "Cow::Borrowed"),
233 (&paths::COW, "Cow::Owned"),
234 (&paths::COW, "Owned"),
235 (&paths::OPTION, "None"),
236 (&paths::RESULT, "Err"),
237 (&paths::RESULT, "Ok")];
239 let path = match arms[1].pats[0].node {
240 PatKind::TupleStruct(ref path, ref inner, _) => {
241 // contains any non wildcard patterns? e.g. Err(err)
242 if inner.iter().any(|pat| pat.node != PatKind::Wild) {
245 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
247 PatKind::Binding(BindByValue(MutImmutable), _, ident, None) => ident.node.to_string(),
248 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
252 for &(ty_path, pat_path) in candidates {
253 if &path == pat_path && match_type(cx, ty, ty_path) {
254 let lint = if els.is_some() {
259 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
260 span_lint_and_then(cx,
263 "you seem to be trying to use match for destructuring a single pattern. Consider \
266 db.span_suggestion(expr.span,
268 format!("if let {} = {} {}{}",
269 snippet(cx, arms[0].pats[0].span, ".."),
270 snippet(cx, ex.span, ".."),
271 expr_block(cx, &arms[0].body, None, ".."),
278 fn check_match_bool(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
279 // type of expression == bool
280 if cx.tables.expr_ty(ex).sty == ty::TyBool {
281 span_lint_and_then(cx,
284 "you seem to be trying to match on a boolean expression",
286 if arms.len() == 2 && arms[0].pats.len() == 1 {
288 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
289 if let ExprLit(ref lit) = arm_bool.node {
291 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
292 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
302 if let Some((true_expr, false_expr)) = exprs {
303 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
305 Some(format!("if {} {} else {}",
306 snippet(cx, ex.span, "b"),
307 expr_block(cx, true_expr, None, ".."),
308 expr_block(cx, false_expr, None, "..")))
311 Some(format!("if {} {}", snippet(cx, ex.span, "b"), expr_block(cx, true_expr, None, "..")))
314 let test = Sugg::hir(cx, ex, "..");
315 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
317 (true, true) => None,
320 if let Some(sugg) = sugg {
321 db.span_suggestion(expr.span, "consider using an if/else expression", sugg);
330 fn check_overlapping_arms(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
331 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
332 let ranges = all_ranges(cx, arms);
333 let type_ranges = type_ranges(&ranges);
334 if !type_ranges.is_empty() {
335 if let Some((start, end)) = overlapping(&type_ranges) {
336 span_note_and_lint(cx,
337 MATCH_OVERLAPPING_ARM,
339 "some ranges overlap",
341 "overlaps with this");
347 fn check_wild_err_arm(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
348 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
349 if match_type(cx, ex_ty, &paths::RESULT) {
351 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
352 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
353 if inner.iter().any(|pat| pat.node == PatKind::Wild) &&
355 // `Err(_)` arm found
356 let mut need_lint = true;
357 if let ExprBlock(ref block) = arm.body.node {
358 if is_unreachable_block(cx, block) {
364 span_note_and_lint(cx,
367 "Err(_) will match all errors, maybe not a good idea",
369 "to remove this warning, match each error seperately or use unreachable macro");
377 // If the block contains only a `unreachable!` macro (as expression or statement)
378 fn is_unreachable_block(cx: &LateContext, block: &Block) -> bool {
379 match (&block.expr, block.stmts.len(), block.stmts.first()) {
380 (&Some(ref exp), 0, _) => is_expn_of(cx, exp.span, "unreachable").is_some(),
381 (&None, 1, Some(ref stmt)) => is_expn_of(cx, stmt.span, "unreachable").is_some(),
386 fn check_match_ref_pats(cx: &LateContext, ex: &Expr, arms: &[Arm], source: MatchSource, expr: &Expr) {
387 if has_only_ref_pats(arms) {
388 if let ExprAddrOf(Mutability::MutImmutable, ref inner) = ex.node {
389 span_lint_and_then(cx,
392 "you don't need to add `&` to both the expression and the patterns",
394 let inner = Sugg::hir(cx, inner, "..");
395 let template = match_template(expr.span, source, inner);
396 db.span_suggestion(expr.span, "try", template);
399 span_lint_and_then(cx,
402 "you don't need to add `&` to all patterns",
404 let ex = Sugg::hir(cx, ex, "..");
405 let template = match_template(expr.span, source, ex.deref());
406 db.span_suggestion(expr.span,
407 "instead of prefixing all patterns with `&`, you can dereference the expression",
414 /// Get all arms that are unbounded `PatRange`s.
415 fn all_ranges(cx: &LateContext, arms: &[Arm]) -> Vec<SpannedRange<ConstVal>> {
416 let constcx = ConstContext::with_tables(cx.tcx, cx.tables);
419 if let Arm { ref pats, guard: None, .. } = *arm {
426 let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node,
427 let Ok(lhs) = constcx.eval(lhs, ExprTypeChecked),
428 let Ok(rhs) = constcx.eval(rhs, ExprTypeChecked)
430 let rhs = match *range_end {
431 RangeEnd::Included => Bound::Included(rhs),
432 RangeEnd::Excluded => Bound::Excluded(rhs),
434 return Some(SpannedRange { span: pat.span, node: (lhs, rhs) });
438 let PatKind::Lit(ref value) = pat.node,
439 let Ok(value) = constcx.eval(value, ExprTypeChecked)
441 return Some(SpannedRange { span: pat.span, node: (value.clone(), Bound::Included(value)) });
450 #[derive(Debug, Eq, PartialEq)]
451 pub struct SpannedRange<T> {
453 pub node: (T, Bound<T>),
456 type TypedRanges = Vec<SpannedRange<ConstInt>>;
458 /// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway and other types than
459 /// `Uint` and `Int` probably don't make sense.
460 fn type_ranges(ranges: &[SpannedRange<ConstVal>]) -> TypedRanges {
462 .filter_map(|range| match range.node {
463 (ConstVal::Integral(start), Bound::Included(ConstVal::Integral(end))) => {
466 node: (start, Bound::Included(end)),
469 (ConstVal::Integral(start), Bound::Excluded(ConstVal::Integral(end))) => {
472 node: (start, Bound::Excluded(end)),
475 (ConstVal::Integral(start), Bound::Unbounded) => {
478 node: (start, Bound::Unbounded),
486 fn is_unit_expr(expr: &Expr) -> bool {
488 ExprTup(ref v) if v.is_empty() => true,
489 ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
494 fn has_only_ref_pats(arms: &[Arm]) -> bool {
495 let mapped = arms.iter()
496 .flat_map(|a| &a.pats)
499 PatKind::Ref(..) => Some(true), // &-patterns
500 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
501 _ => None, // any other pattern is not fine
504 .collect::<Option<Vec<bool>>>();
505 // look for Some(v) where there's at least one true element
506 mapped.map_or(false, |v| v.iter().any(|el| *el))
509 fn match_template(span: Span, source: MatchSource, expr: Sugg) -> String {
511 MatchSource::Normal => format!("match {} {{ .. }}", expr),
512 MatchSource::IfLetDesugar { .. } => format!("if let .. = {} {{ .. }}", expr),
513 MatchSource::WhileLetDesugar => format!("while let .. = {} {{ .. }}", expr),
514 MatchSource::ForLoopDesugar => span_bug!(span, "for loop desugared to match with &-patterns!"),
515 MatchSource::TryDesugar => span_bug!(span, "`?` operator desugared to match with &-patterns!"),
519 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
522 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
523 enum Kind<'a, T: 'a> {
524 Start(T, &'a SpannedRange<T>),
525 End(Bound<T>, &'a SpannedRange<T>),
528 impl<'a, T: Copy> Kind<'a, T> {
529 fn range(&self) -> &'a SpannedRange<T> {
532 Kind::End(_, r) => r,
536 fn value(self) -> Bound<T> {
538 Kind::Start(t, _) => Bound::Included(t),
539 Kind::End(t, _) => t,
544 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
545 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
546 Some(self.cmp(other))
550 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
551 fn cmp(&self, other: &Self) -> Ordering {
552 match (self.value(), other.value()) {
553 (Bound::Included(a), Bound::Included(b)) |
554 (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
555 // Range patterns cannot be unbounded (yet)
556 (Bound::Unbounded, _) |
557 (_, Bound::Unbounded) => unimplemented!(),
558 (Bound::Included(a), Bound::Excluded(b)) => {
560 Ordering::Equal => Ordering::Greater,
564 (Bound::Excluded(a), Bound::Included(b)) => {
566 Ordering::Equal => Ordering::Less,
574 let mut values = Vec::with_capacity(2 * ranges.len());
577 values.push(Kind::Start(r.node.0, r));
578 values.push(Kind::End(r.node.1, r));
583 for (a, b) in values.iter().zip(values.iter().skip(1)) {
585 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
586 if ra.node != rb.node {
587 return Some((ra, rb));
590 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
591 _ => return Some((a.range(), b.range())),