3 use rustc::middle::const_val::ConstVal;
5 use rustc_const_eval::ConstContext;
6 use rustc_const_math::ConstInt;
7 use std::cmp::Ordering;
8 use std::collections::Bound;
9 use syntax::ast::LitKind;
10 use syntax::codemap::Span;
12 use utils::{match_type, snippet, span_note_and_lint, span_lint_and_then, in_external_macro, expr_block, walk_ptrs_ty,
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 which matches all errors with `Err(_)`
125 /// and take drastic actions like `panic!`.
127 /// **Why is this bad?** It is generally a bad practice, just like
128 /// catching all exceptions in java with `catch(Exception)`
130 /// **Known problems:** None.
134 /// let x : Result(i32, &str) = Ok(3);
136 /// Ok(_) => println!("ok"),
137 /// Err(_) => panic!("err"),
141 pub MATCH_WILD_ERR_ARM,
143 "a match with `Err(_)` arm and take drastic actions"
146 #[allow(missing_copy_implementations)]
147 pub struct MatchPass;
149 impl LintPass for MatchPass {
150 fn get_lints(&self) -> LintArray {
151 lint_array!(SINGLE_MATCH,
155 MATCH_OVERLAPPING_ARM,
160 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
161 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
162 if in_external_macro(cx, expr.span) {
165 if let ExprMatch(ref ex, ref arms, MatchSource::Normal) = expr.node {
166 check_single_match(cx, ex, arms, expr);
167 check_match_bool(cx, ex, arms, expr);
168 check_overlapping_arms(cx, ex, arms);
169 check_wild_err_arm(cx, ex, arms);
171 if let ExprMatch(ref ex, ref arms, source) = expr.node {
172 check_match_ref_pats(cx, ex, arms, source, expr);
177 #[cfg_attr(rustfmt, rustfmt_skip)]
178 fn check_single_match(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
179 if arms.len() == 2 &&
180 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
181 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
182 let els = if is_unit_expr(&arms[1].body) {
184 } else if let ExprBlock(_) = arms[1].body.node {
185 // matches with blocks that contain statements are prettier as `if let + else`
188 // allow match arms with just expressions
191 let ty = cx.tables.expr_ty(ex);
192 if ty.sty != ty::TyBool || cx.current_level(MATCH_BOOL) == Allow {
193 check_single_match_single_pattern(cx, ex, arms, expr, els);
194 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
199 fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
200 if arms[1].pats[0].node == PatKind::Wild {
201 let lint = if els.is_some() {
206 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
207 span_lint_and_then(cx,
210 "you seem to be trying to use match for destructuring a single pattern. \
211 Consider using `if let`",
213 db.span_suggestion(expr.span,
215 format!("if let {} = {} {}{}",
216 snippet(cx, arms[0].pats[0].span, ".."),
217 snippet(cx, ex.span, ".."),
218 expr_block(cx, &arms[0].body, None, ".."),
224 fn check_single_match_opt_like(
232 // list of candidate Enums we know will never get any more members
233 let candidates = &[(&paths::COW, "Borrowed"),
234 (&paths::COW, "Cow::Borrowed"),
235 (&paths::COW, "Cow::Owned"),
236 (&paths::COW, "Owned"),
237 (&paths::OPTION, "None"),
238 (&paths::RESULT, "Err"),
239 (&paths::RESULT, "Ok")];
241 let path = match arms[1].pats[0].node {
242 PatKind::TupleStruct(ref path, ref inner, _) => {
243 // contains any non wildcard patterns? e.g. Err(err)
244 if inner.iter().any(|pat| pat.node != PatKind::Wild) {
247 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
249 PatKind::Binding(BindByValue(MutImmutable), _, ident, None) => ident.node.to_string(),
250 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
254 for &(ty_path, pat_path) in candidates {
255 if &path == pat_path && match_type(cx, ty, ty_path) {
256 let lint = if els.is_some() {
261 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
262 span_lint_and_then(cx,
265 "you seem to be trying to use match for destructuring a single pattern. Consider \
268 db.span_suggestion(expr.span,
270 format!("if let {} = {} {}{}",
271 snippet(cx, arms[0].pats[0].span, ".."),
272 snippet(cx, ex.span, ".."),
273 expr_block(cx, &arms[0].body, None, ".."),
280 fn check_match_bool(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
281 // type of expression == bool
282 if cx.tables.expr_ty(ex).sty == ty::TyBool {
283 span_lint_and_then(cx,
286 "you seem to be trying to match on a boolean expression",
288 if arms.len() == 2 && arms[0].pats.len() == 1 {
290 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
291 if let ExprLit(ref lit) = arm_bool.node {
293 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
294 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
304 if let Some((true_expr, false_expr)) = exprs {
305 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
307 Some(format!("if {} {} else {}",
308 snippet(cx, ex.span, "b"),
309 expr_block(cx, true_expr, None, ".."),
310 expr_block(cx, false_expr, None, "..")))
313 Some(format!("if {} {}", snippet(cx, ex.span, "b"), expr_block(cx, true_expr, None, "..")))
316 let test = Sugg::hir(cx, ex, "..");
317 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
319 (true, true) => None,
322 if let Some(sugg) = sugg {
323 db.span_suggestion(expr.span, "consider using an if/else expression", sugg);
332 fn check_overlapping_arms(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
333 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
334 let ranges = all_ranges(cx, arms);
335 let type_ranges = type_ranges(&ranges);
336 if !type_ranges.is_empty() {
337 if let Some((start, end)) = overlapping(&type_ranges) {
338 span_note_and_lint(cx,
339 MATCH_OVERLAPPING_ARM,
341 "some ranges overlap",
343 "overlaps with this");
349 fn check_wild_err_arm(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
350 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
351 if match_type(cx, ex_ty, &paths::RESULT) {
353 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
354 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
357 inner.iter().any(|pat| pat.node == PatKind::Wild),
358 let ExprBlock(ref block) = arm.body.node,
359 is_panic_block(cx, block)
361 // `Err(_)` arm with `panic!` found
362 span_note_and_lint(cx,
365 "Err(_) will match all errors, maybe not a good idea",
367 "to remove this warning, match each error seperately \
368 or use unreachable macro");
375 // If the block contains only a `panic!` macro (as expression or statement)
376 fn is_panic_block(cx: &LateContext, block: &Block) -> bool {
377 match (&block.expr, block.stmts.len(), block.stmts.first()) {
378 (&Some(ref exp), 0, _) => {
379 is_expn_of(cx, exp.span, "panic").is_some() && is_expn_of(cx, exp.span, "unreachable").is_none()
381 (&None, 1, Some(stmt)) => {
382 is_expn_of(cx, stmt.span, "panic").is_some() && is_expn_of(cx, stmt.span, "unreachable").is_none()
388 fn check_match_ref_pats(cx: &LateContext, ex: &Expr, arms: &[Arm], source: MatchSource, expr: &Expr) {
389 if has_only_ref_pats(arms) {
390 if let ExprAddrOf(Mutability::MutImmutable, ref inner) = ex.node {
391 span_lint_and_then(cx,
394 "you don't need to add `&` to both the expression and the patterns",
396 let inner = Sugg::hir(cx, inner, "..");
397 let template = match_template(expr.span, source, &inner);
398 db.span_suggestion(expr.span, "try", template);
401 span_lint_and_then(cx,
404 "you don't need to add `&` to all patterns",
406 let ex = Sugg::hir(cx, ex, "..");
407 let template = match_template(expr.span, source, &ex.deref());
408 db.span_suggestion(expr.span,
409 "instead of prefixing all patterns with `&`, you can dereference the expression",
416 /// Get all arms that are unbounded `PatRange`s.
417 fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &[Arm]) -> Vec<SpannedRange<ConstVal<'tcx>>> {
418 let constcx = ConstContext::with_tables(cx.tcx, cx.tables);
421 if let Arm { ref pats, guard: None, .. } = *arm {
428 let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node,
429 let Ok(lhs) = constcx.eval(lhs),
430 let Ok(rhs) = constcx.eval(rhs)
432 let rhs = match *range_end {
433 RangeEnd::Included => Bound::Included(rhs),
434 RangeEnd::Excluded => Bound::Excluded(rhs),
436 return Some(SpannedRange { span: pat.span, node: (lhs, rhs) });
440 let PatKind::Lit(ref value) = pat.node,
441 let Ok(value) = constcx.eval(value)
443 return Some(SpannedRange { span: pat.span, node: (value.clone(), Bound::Included(value)) });
452 #[derive(Debug, Eq, PartialEq)]
453 pub struct SpannedRange<T> {
455 pub node: (T, Bound<T>),
458 type TypedRanges = Vec<SpannedRange<ConstInt>>;
460 /// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway and other types than
461 /// `Uint` and `Int` probably don't make sense.
462 fn type_ranges(ranges: &[SpannedRange<ConstVal>]) -> TypedRanges {
464 .filter_map(|range| match range.node {
465 (ConstVal::Integral(start), Bound::Included(ConstVal::Integral(end))) => {
468 node: (start, Bound::Included(end)),
471 (ConstVal::Integral(start), Bound::Excluded(ConstVal::Integral(end))) => {
474 node: (start, Bound::Excluded(end)),
477 (ConstVal::Integral(start), Bound::Unbounded) => {
480 node: (start, Bound::Unbounded),
488 fn is_unit_expr(expr: &Expr) -> bool {
490 ExprTup(ref v) if v.is_empty() => true,
491 ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
496 fn has_only_ref_pats(arms: &[Arm]) -> bool {
497 let mapped = arms.iter()
498 .flat_map(|a| &a.pats)
501 PatKind::Ref(..) => Some(true), // &-patterns
502 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
503 _ => None, // any other pattern is not fine
506 .collect::<Option<Vec<bool>>>();
507 // look for Some(v) where there's at least one true element
508 mapped.map_or(false, |v| v.iter().any(|el| *el))
511 fn match_template(span: Span, source: MatchSource, expr: &Sugg) -> String {
513 MatchSource::Normal => format!("match {} {{ .. }}", expr),
514 MatchSource::IfLetDesugar { .. } => format!("if let .. = {} {{ .. }}", expr),
515 MatchSource::WhileLetDesugar => format!("while let .. = {} {{ .. }}", expr),
516 MatchSource::ForLoopDesugar => span_bug!(span, "for loop desugared to match with &-patterns!"),
517 MatchSource::TryDesugar => span_bug!(span, "`?` operator desugared to match with &-patterns!"),
521 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
524 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
525 enum Kind<'a, T: 'a> {
526 Start(T, &'a SpannedRange<T>),
527 End(Bound<T>, &'a SpannedRange<T>),
530 impl<'a, T: Copy> Kind<'a, T> {
531 fn range(&self) -> &'a SpannedRange<T> {
534 Kind::End(_, r) => r,
538 fn value(self) -> Bound<T> {
540 Kind::Start(t, _) => Bound::Included(t),
541 Kind::End(t, _) => t,
546 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
547 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
548 Some(self.cmp(other))
552 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
553 fn cmp(&self, other: &Self) -> Ordering {
554 match (self.value(), other.value()) {
555 (Bound::Included(a), Bound::Included(b)) |
556 (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
557 // Range patterns cannot be unbounded (yet)
558 (Bound::Unbounded, _) |
559 (_, Bound::Unbounded) => unimplemented!(),
560 (Bound::Included(a), Bound::Excluded(b)) => {
562 Ordering::Equal => Ordering::Greater,
566 (Bound::Excluded(a), Bound::Included(b)) => {
568 Ordering::Equal => Ordering::Less,
576 let mut values = Vec::with_capacity(2 * ranges.len());
579 values.push(Kind::Start(r.node.0, r));
580 values.push(Kind::End(r.node.1, r));
585 for (a, b) in values.iter().zip(values.iter().skip(1)) {
587 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
588 if ra.node != rb.node {
589 return Some((ra, rb));
592 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
593 _ => return Some((a.range(), b.range())),