3 use rustc::middle::const_val::ConstVal;
4 use rustc::ty::{self, Ty};
5 use rustc::ty::subst::Substs;
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::ast::NodeId;
12 use syntax::codemap::Span;
14 use utils::{match_type, snippet, span_note_and_lint, span_lint_and_then, span_lint_and_sugg, in_external_macro,
15 expr_block, walk_ptrs_ty, is_expn_of, remove_blocks, is_allowed};
16 use utils::sugg::Sugg;
18 /// **What it does:** Checks for matches with a single arm where an `if let`
19 /// will usually suffice.
21 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
23 /// **Known problems:** None.
28 /// Some(ref foo) => bar(foo),
35 "a match statement with a single nontrivial arm (i.e. where the other arm \
36 is `_ => {}`) instead of `if let`"
39 /// **What it does:** Checks for matches with a two arms where an `if let` will
42 /// **Why is this bad?** Just readability – `if let` nests less than a `match`.
44 /// **Known problems:** Personal style preferences may differ.
49 /// Some(ref foo) => bar(foo),
50 /// _ => bar(other_ref),
54 pub SINGLE_MATCH_ELSE,
56 "a match statement with a two arms where the second arm's pattern is a wildcard \
60 /// **What it does:** Checks for matches where all arms match a reference,
61 /// suggesting to remove the reference and deref the matched expression
62 /// instead. It also checks for `if let &foo = bar` blocks.
64 /// **Why is this bad?** It just makes the code less readable. That reference
65 /// destructuring adds nothing to the code.
67 /// **Known problems:** None.
72 /// &A(ref y) => foo(y),
80 "a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression"
83 /// **What it does:** Checks for matches where match expression is a `bool`. It
84 /// suggests to replace the expression with an `if...else` block.
86 /// **Why is this bad?** It makes the code less readable.
88 /// **Known problems:** None.
92 /// let condition: bool = true;
101 "a match on a boolean expression instead of an `if..else` block"
104 /// **What it does:** Checks for overlapping match arms.
106 /// **Why is this bad?** It is likely to be an error and if not, makes the code
109 /// **Known problems:** None.
115 /// 1 ... 10 => println!("1 ... 10"),
116 /// 5 ... 15 => println!("5 ... 15"),
121 pub MATCH_OVERLAPPING_ARM,
123 "a match with overlapping arms"
126 /// **What it does:** Checks for arm which matches all errors with `Err(_)`
127 /// and take drastic actions like `panic!`.
129 /// **Why is this bad?** It is generally a bad practice, just like
130 /// catching all exceptions in java with `catch(Exception)`
132 /// **Known problems:** None.
136 /// let x : Result(i32, &str) = Ok(3);
138 /// Ok(_) => println!("ok"),
139 /// Err(_) => panic!("err"),
143 pub MATCH_WILD_ERR_ARM,
145 "a match with `Err(_)` arm and take drastic actions"
148 #[allow(missing_copy_implementations)]
149 pub struct MatchPass;
151 impl LintPass for MatchPass {
152 fn get_lints(&self) -> LintArray {
158 MATCH_OVERLAPPING_ARM,
164 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
165 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
166 if in_external_macro(cx, expr.span) {
169 if let ExprMatch(ref ex, ref arms, MatchSource::Normal) = expr.node {
170 check_single_match(cx, ex, arms, expr);
171 check_match_bool(cx, ex, arms, expr);
172 check_overlapping_arms(cx, ex, arms);
173 check_wild_err_arm(cx, ex, arms);
175 if let ExprMatch(ref ex, ref arms, source) = expr.node {
176 check_match_ref_pats(cx, ex, arms, source, expr);
181 #[cfg_attr(rustfmt, rustfmt_skip)]
182 fn check_single_match(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
183 if arms.len() == 2 &&
184 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
185 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
186 let els = remove_blocks(&arms[1].body);
187 let els = if is_unit_expr(els) {
189 } else if let ExprBlock(_) = els.node {
190 // matches with blocks that contain statements are prettier as `if let + else`
193 // allow match arms with just expressions
196 let ty = cx.tables.expr_ty(ex);
197 if ty.sty != ty::TyBool || is_allowed(cx, MATCH_BOOL, ex.id) {
198 check_single_match_single_pattern(cx, ex, arms, expr, els);
199 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
204 fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
205 if arms[1].pats[0].node == PatKind::Wild {
206 report_single_match_single_pattern(cx, ex, arms, expr, els);
210 fn report_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
211 let lint = if els.is_some() {
216 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
221 "you seem to be trying to use match for destructuring a single pattern. Consider using `if \
225 "if let {} = {} {}{}",
226 snippet(cx, arms[0].pats[0].span, ".."),
227 snippet(cx, ex.span, ".."),
228 expr_block(cx, &arms[0].body, None, ".."),
234 fn check_single_match_opt_like(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, ty: Ty, els: Option<&Expr>) {
235 // list of candidate Enums we know will never get any more members
237 (&paths::COW, "Borrowed"),
238 (&paths::COW, "Cow::Borrowed"),
239 (&paths::COW, "Cow::Owned"),
240 (&paths::COW, "Owned"),
241 (&paths::OPTION, "None"),
242 (&paths::RESULT, "Err"),
243 (&paths::RESULT, "Ok"),
246 let path = match arms[1].pats[0].node {
247 PatKind::TupleStruct(ref path, ref inner, _) => {
248 // contains any non wildcard patterns? e.g. Err(err)
249 if inner.iter().any(|pat| pat.node != PatKind::Wild) {
252 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
254 PatKind::Binding(BindingAnnotation::Unannotated, _, ident, None) => ident.node.to_string(),
255 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
259 for &(ty_path, pat_path) in candidates {
260 if path == *pat_path && match_type(cx, ty, ty_path) {
261 report_single_match_single_pattern(cx, ex, arms, expr, els);
266 fn check_match_bool(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
267 // type of expression == bool
268 if cx.tables.expr_ty(ex).sty == ty::TyBool {
273 "you seem to be trying to match on a boolean expression",
275 if arms.len() == 2 && arms[0].pats.len() == 1 {
277 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
278 if let ExprLit(ref lit) = arm_bool.node {
280 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
281 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
291 if let Some((true_expr, false_expr)) = exprs {
292 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
296 snippet(cx, ex.span, "b"),
297 expr_block(cx, true_expr, None, ".."),
298 expr_block(cx, false_expr, None, "..")
304 snippet(cx, ex.span, "b"),
305 expr_block(cx, true_expr, None, "..")
309 let test = Sugg::hir(cx, ex, "..");
310 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
312 (true, true) => None,
315 if let Some(sugg) = sugg {
316 db.span_suggestion(expr.span, "consider using an if/else expression", sugg);
326 fn check_overlapping_arms(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
327 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
328 let ranges = all_ranges(cx, arms, ex.id);
329 let type_ranges = type_ranges(&ranges);
330 if !type_ranges.is_empty() {
331 if let Some((start, end)) = overlapping(&type_ranges) {
334 MATCH_OVERLAPPING_ARM,
336 "some ranges overlap",
338 "overlaps with this",
345 fn check_wild_err_arm(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
346 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
347 if match_type(cx, ex_ty, &paths::RESULT) {
349 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
350 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
353 inner.iter().any(|pat| pat.node == PatKind::Wild),
354 let ExprBlock(ref block) = arm.body.node,
355 is_panic_block(block)
357 // `Err(_)` arm with `panic!` found
358 span_note_and_lint(cx,
361 "Err(_) will match all errors, maybe not a good idea",
363 "to remove this warning, match each error seperately \
364 or use unreachable macro");
371 // If the block contains only a `panic!` macro (as expression or statement)
372 fn is_panic_block(block: &Block) -> bool {
373 match (&block.expr, block.stmts.len(), block.stmts.first()) {
374 (&Some(ref exp), 0, _) => {
375 is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
377 (&None, 1, Some(stmt)) => {
378 is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
384 fn check_match_ref_pats(cx: &LateContext, ex: &Expr, arms: &[Arm], source: MatchSource, expr: &Expr) {
385 if has_only_ref_pats(arms) {
386 if let ExprAddrOf(Mutability::MutImmutable, ref inner) = ex.node {
387 span_lint_and_then(cx,
390 "you don't need to add `&` to both the expression and the patterns",
392 let inner = Sugg::hir(cx, inner, "..");
393 let template = match_template(expr.span, source, &inner);
394 db.span_suggestion(expr.span, "try", template);
401 "you don't need to add `&` to all patterns",
403 let ex = Sugg::hir(cx, ex, "..");
404 let template = match_template(expr.span, source, &ex.deref());
407 "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], id: NodeId) -> Vec<SpannedRange<ConstVal<'tcx>>> {
418 let parent_item = cx.tcx.hir.get_parent(id);
419 let parent_def_id = cx.tcx.hir.local_def_id(parent_item);
420 let substs = Substs::identity_for_item(cx.tcx, parent_def_id);
421 let constcx = ConstContext::new(cx.tcx, cx.param_env.and(substs), cx.tables);
435 let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node,
436 let Ok(lhs) = constcx.eval(lhs),
437 let Ok(rhs) = constcx.eval(rhs)
439 let rhs = match *range_end {
440 RangeEnd::Included => Bound::Included(rhs),
441 RangeEnd::Excluded => Bound::Excluded(rhs),
443 return Some(SpannedRange { span: pat.span, node: (lhs, rhs) });
447 let PatKind::Lit(ref value) = pat.node,
448 let Ok(value) = constcx.eval(value)
450 return Some(SpannedRange { span: pat.span, node: (value.clone(), Bound::Included(value)) });
459 #[derive(Debug, Eq, PartialEq)]
460 pub struct SpannedRange<T> {
462 pub node: (T, Bound<T>),
465 type TypedRanges = Vec<SpannedRange<ConstInt>>;
467 /// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway
468 /// and other types than
469 /// `Uint` and `Int` probably don't make sense.
470 fn type_ranges(ranges: &[SpannedRange<ConstVal>]) -> TypedRanges {
473 .filter_map(|range| match range.node {
474 (ConstVal::Integral(start), Bound::Included(ConstVal::Integral(end))) => {
477 node: (start, Bound::Included(end)),
480 (ConstVal::Integral(start), Bound::Excluded(ConstVal::Integral(end))) => {
483 node: (start, Bound::Excluded(end)),
486 (ConstVal::Integral(start), Bound::Unbounded) => {
489 node: (start, Bound::Unbounded),
497 fn is_unit_expr(expr: &Expr) -> bool {
499 ExprTup(ref v) if v.is_empty() => true,
500 ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
505 fn has_only_ref_pats(arms: &[Arm]) -> bool {
506 let mapped = arms.iter()
507 .flat_map(|a| &a.pats)
510 PatKind::Ref(..) => Some(true), // &-patterns
511 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
512 _ => None, // any other pattern is not fine
515 .collect::<Option<Vec<bool>>>();
516 // look for Some(v) where there's at least one true element
517 mapped.map_or(false, |v| v.iter().any(|el| *el))
520 fn match_template(span: Span, source: MatchSource, expr: &Sugg) -> String {
522 MatchSource::Normal => format!("match {} {{ .. }}", expr),
523 MatchSource::IfLetDesugar { .. } => format!("if let .. = {} {{ .. }}", expr),
524 MatchSource::WhileLetDesugar => format!("while let .. = {} {{ .. }}", expr),
525 MatchSource::ForLoopDesugar => span_bug!(span, "for loop desugared to match with &-patterns!"),
526 MatchSource::TryDesugar => span_bug!(span, "`?` operator desugared to match with &-patterns!"),
530 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
534 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
535 enum Kind<'a, T: 'a> {
536 Start(T, &'a SpannedRange<T>),
537 End(Bound<T>, &'a SpannedRange<T>),
540 impl<'a, T: Copy> Kind<'a, T> {
541 fn range(&self) -> &'a SpannedRange<T> {
544 Kind::End(_, r) => r,
548 fn value(self) -> Bound<T> {
550 Kind::Start(t, _) => Bound::Included(t),
551 Kind::End(t, _) => t,
556 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
557 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
558 Some(self.cmp(other))
562 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
563 fn cmp(&self, other: &Self) -> Ordering {
564 match (self.value(), other.value()) {
565 (Bound::Included(a), Bound::Included(b)) |
566 (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
567 // Range patterns cannot be unbounded (yet)
568 (Bound::Unbounded, _) |
569 (_, Bound::Unbounded) => unimplemented!(),
570 (Bound::Included(a), Bound::Excluded(b)) => {
572 Ordering::Equal => Ordering::Greater,
576 (Bound::Excluded(a), Bound::Included(b)) => {
578 Ordering::Equal => Ordering::Less,
586 let mut values = Vec::with_capacity(2 * ranges.len());
589 values.push(Kind::Start(r.node.0, r));
590 values.push(Kind::End(r.node.1, r));
595 for (a, b) in values.iter().zip(values.iter().skip(1)) {
597 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
598 if ra.node != rb.node {
599 return Some((ra, rb));
602 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
603 _ => return Some((a.range(), b.range())),