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};
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 #[allow(missing_copy_implementations)]
125 pub struct MatchPass;
127 impl LintPass for MatchPass {
128 fn get_lints(&self) -> LintArray {
129 lint_array!(SINGLE_MATCH,
133 MATCH_OVERLAPPING_ARM)
137 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
138 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
139 if in_external_macro(cx, expr.span) {
142 if let ExprMatch(ref ex, ref arms, MatchSource::Normal) = expr.node {
143 check_single_match(cx, ex, arms, expr);
144 check_match_bool(cx, ex, arms, expr);
145 check_overlapping_arms(cx, ex, arms);
147 if let ExprMatch(ref ex, ref arms, source) = expr.node {
148 check_match_ref_pats(cx, ex, arms, source, expr);
153 #[cfg_attr(rustfmt, rustfmt_skip)]
154 fn check_single_match(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
155 if arms.len() == 2 &&
156 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
157 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
158 let els = if is_unit_expr(&arms[1].body) {
160 } else if let ExprBlock(_) = arms[1].body.node {
161 // matches with blocks that contain statements are prettier as `if let + else`
164 // allow match arms with just expressions
167 let ty = cx.tables.expr_ty(ex);
168 if ty.sty != ty::TyBool || cx.current_level(MATCH_BOOL) == Allow {
169 check_single_match_single_pattern(cx, ex, arms, expr, els);
170 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
175 fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
176 if arms[1].pats[0].node == PatKind::Wild {
177 let lint = if els.is_some() {
182 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
183 span_lint_and_then(cx,
186 "you seem to be trying to use match for destructuring a single pattern. \
187 Consider using `if let`",
189 db.span_suggestion(expr.span,
191 format!("if let {} = {} {}{}",
192 snippet(cx, arms[0].pats[0].span, ".."),
193 snippet(cx, ex.span, ".."),
194 expr_block(cx, &arms[0].body, None, ".."),
200 fn check_single_match_opt_like(
208 // list of candidate Enums we know will never get any more members
209 let candidates = &[(&paths::COW, "Borrowed"),
210 (&paths::COW, "Cow::Borrowed"),
211 (&paths::COW, "Cow::Owned"),
212 (&paths::COW, "Owned"),
213 (&paths::OPTION, "None"),
214 (&paths::RESULT, "Err"),
215 (&paths::RESULT, "Ok")];
217 let path = match arms[1].pats[0].node {
218 PatKind::TupleStruct(ref path, ref inner, _) => {
219 // contains any non wildcard patterns? e.g. Err(err)
220 if inner.iter().any(|pat| pat.node != PatKind::Wild) {
223 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
225 PatKind::Binding(BindByValue(MutImmutable), _, ident, None) => ident.node.to_string(),
226 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
230 for &(ty_path, pat_path) in candidates {
231 if &path == pat_path && match_type(cx, ty, ty_path) {
232 let lint = if els.is_some() {
237 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
238 span_lint_and_then(cx,
241 "you seem to be trying to use match for destructuring a single pattern. Consider \
244 db.span_suggestion(expr.span,
246 format!("if let {} = {} {}{}",
247 snippet(cx, arms[0].pats[0].span, ".."),
248 snippet(cx, ex.span, ".."),
249 expr_block(cx, &arms[0].body, None, ".."),
256 fn check_match_bool(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
257 // type of expression == bool
258 if cx.tables.expr_ty(ex).sty == ty::TyBool {
259 span_lint_and_then(cx,
262 "you seem to be trying to match on a boolean expression",
264 if arms.len() == 2 && arms[0].pats.len() == 1 {
266 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
267 if let ExprLit(ref lit) = arm_bool.node {
269 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
270 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
280 if let Some((true_expr, false_expr)) = exprs {
281 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
283 Some(format!("if {} {} else {}",
284 snippet(cx, ex.span, "b"),
285 expr_block(cx, true_expr, None, ".."),
286 expr_block(cx, false_expr, None, "..")))
289 Some(format!("if {} {}", snippet(cx, ex.span, "b"), expr_block(cx, true_expr, None, "..")))
292 let test = Sugg::hir(cx, ex, "..");
293 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
295 (true, true) => None,
298 if let Some(sugg) = sugg {
299 db.span_suggestion(expr.span, "consider using an if/else expression", sugg);
308 fn check_overlapping_arms(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
309 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
310 let ranges = all_ranges(cx, arms);
311 let type_ranges = type_ranges(&ranges);
312 if !type_ranges.is_empty() {
313 if let Some((start, end)) = overlapping(&type_ranges) {
314 span_note_and_lint(cx,
315 MATCH_OVERLAPPING_ARM,
317 "some ranges overlap",
319 "overlaps with this");
325 fn check_match_ref_pats(cx: &LateContext, ex: &Expr, arms: &[Arm], source: MatchSource, expr: &Expr) {
326 if has_only_ref_pats(arms) {
327 if let ExprAddrOf(Mutability::MutImmutable, ref inner) = ex.node {
328 span_lint_and_then(cx,
331 "you don't need to add `&` to both the expression and the patterns",
333 let inner = Sugg::hir(cx, inner, "..");
334 let template = match_template(expr.span, source, inner);
335 db.span_suggestion(expr.span, "try", template);
338 span_lint_and_then(cx,
341 "you don't need to add `&` to all patterns",
343 let ex = Sugg::hir(cx, ex, "..");
344 let template = match_template(expr.span, source, ex.deref());
345 db.span_suggestion(expr.span,
346 "instead of prefixing all patterns with `&`, you can dereference the expression",
353 /// Get all arms that are unbounded `PatRange`s.
354 fn all_ranges(cx: &LateContext, arms: &[Arm]) -> Vec<SpannedRange<ConstVal>> {
355 let constcx = ConstContext::with_tables(cx.tcx, cx.tables);
358 if let Arm { ref pats, guard: None, .. } = *arm {
365 let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node,
366 let Ok(lhs) = constcx.eval(lhs, ExprTypeChecked),
367 let Ok(rhs) = constcx.eval(rhs, ExprTypeChecked)
369 let rhs = match *range_end {
370 RangeEnd::Included => Bound::Included(rhs),
371 RangeEnd::Excluded => Bound::Excluded(rhs),
373 return Some(SpannedRange { span: pat.span, node: (lhs, rhs) });
377 let PatKind::Lit(ref value) = pat.node,
378 let Ok(value) = constcx.eval(value, ExprTypeChecked)
380 return Some(SpannedRange { span: pat.span, node: (value.clone(), Bound::Included(value)) });
389 #[derive(Debug, Eq, PartialEq)]
390 pub struct SpannedRange<T> {
392 pub node: (T, Bound<T>),
395 type TypedRanges = Vec<SpannedRange<ConstInt>>;
397 /// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway and other types than
398 /// `Uint` and `Int` probably don't make sense.
399 fn type_ranges(ranges: &[SpannedRange<ConstVal>]) -> TypedRanges {
401 .filter_map(|range| match range.node {
402 (ConstVal::Integral(start), Bound::Included(ConstVal::Integral(end))) => {
405 node: (start, Bound::Included(end)),
408 (ConstVal::Integral(start), Bound::Excluded(ConstVal::Integral(end))) => {
411 node: (start, Bound::Excluded(end)),
414 (ConstVal::Integral(start), Bound::Unbounded) => {
417 node: (start, Bound::Unbounded),
425 fn is_unit_expr(expr: &Expr) -> bool {
427 ExprTup(ref v) if v.is_empty() => true,
428 ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
433 fn has_only_ref_pats(arms: &[Arm]) -> bool {
434 let mapped = arms.iter()
435 .flat_map(|a| &a.pats)
438 PatKind::Ref(..) => Some(true), // &-patterns
439 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
440 _ => None, // any other pattern is not fine
443 .collect::<Option<Vec<bool>>>();
444 // look for Some(v) where there's at least one true element
445 mapped.map_or(false, |v| v.iter().any(|el| *el))
448 fn match_template(span: Span, source: MatchSource, expr: Sugg) -> String {
450 MatchSource::Normal => format!("match {} {{ .. }}", expr),
451 MatchSource::IfLetDesugar { .. } => format!("if let .. = {} {{ .. }}", expr),
452 MatchSource::WhileLetDesugar => format!("while let .. = {} {{ .. }}", expr),
453 MatchSource::ForLoopDesugar => span_bug!(span, "for loop desugared to match with &-patterns!"),
454 MatchSource::TryDesugar => span_bug!(span, "`?` operator desugared to match with &-patterns!"),
458 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
461 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
462 enum Kind<'a, T: 'a> {
463 Start(T, &'a SpannedRange<T>),
464 End(Bound<T>, &'a SpannedRange<T>),
467 impl<'a, T: Copy> Kind<'a, T> {
468 fn range(&self) -> &'a SpannedRange<T> {
471 Kind::End(_, r) => r,
475 fn value(self) -> Bound<T> {
477 Kind::Start(t, _) => Bound::Included(t),
478 Kind::End(t, _) => t,
483 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
484 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
485 Some(self.cmp(other))
489 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
490 fn cmp(&self, other: &Self) -> Ordering {
491 match (self.value(), other.value()) {
492 (Bound::Included(a), Bound::Included(b)) |
493 (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
494 (Bound::Unbounded, _) |
495 (_, Bound::Unbounded) => unimplemented!(),
496 (Bound::Included(a), Bound::Excluded(b)) => {
498 Ordering::Equal => Ordering::Greater,
502 (Bound::Excluded(a), Bound::Included(b)) => {
504 Ordering::Equal => Ordering::Less,
512 let mut values = Vec::with_capacity(2 * ranges.len());
515 values.push(Kind::Start(r.node.0, r));
516 values.push(Kind::End(r.node.1, r));
521 for (a, b) in values.iter().zip(values.iter().skip(1)) {
523 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
524 if ra.node != rb.node {
525 return Some((ra, rb));
528 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
529 _ => return Some((a.range(), b.range())),