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};
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 {
153 lint_array!(SINGLE_MATCH,
157 MATCH_OVERLAPPING_ARM,
162 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchPass {
163 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
164 if in_external_macro(cx, expr.span) {
167 if let ExprMatch(ref ex, ref arms, MatchSource::Normal) = expr.node {
168 check_single_match(cx, ex, arms, expr);
169 check_match_bool(cx, ex, arms, expr);
170 check_overlapping_arms(cx, ex, arms);
171 check_wild_err_arm(cx, ex, arms);
173 if let ExprMatch(ref ex, ref arms, source) = expr.node {
174 check_match_ref_pats(cx, ex, arms, source, expr);
179 #[cfg_attr(rustfmt, rustfmt_skip)]
180 fn check_single_match(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
181 if arms.len() == 2 &&
182 arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
183 arms[1].pats.len() == 1 && arms[1].guard.is_none() {
184 let els = remove_blocks(&arms[1].body);
185 let els = if is_unit_expr(els) {
187 } else if let ExprBlock(_) = els.node {
188 // matches with blocks that contain statements are prettier as `if let + else`
191 // allow match arms with just expressions
194 let ty = cx.tables.expr_ty(ex);
195 if ty.sty != ty::TyBool || cx.current_level(MATCH_BOOL) == Allow {
196 check_single_match_single_pattern(cx, ex, arms, expr, els);
197 check_single_match_opt_like(cx, ex, arms, expr, ty, els);
202 fn check_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
203 if arms[1].pats[0].node == PatKind::Wild {
204 report_single_match_single_pattern(cx, ex, arms, expr, els);
208 fn report_single_match_single_pattern(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, els: Option<&Expr>) {
209 let lint = if els.is_some() {
214 let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
215 span_lint_and_sugg(cx,
218 "you seem to be trying to use match for destructuring a single pattern. Consider using `if \
221 format!("if let {} = {} {}{}",
222 snippet(cx, arms[0].pats[0].span, ".."),
223 snippet(cx, ex.span, ".."),
224 expr_block(cx, &arms[0].body, None, ".."),
228 fn check_single_match_opt_like(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr, ty: Ty, els: Option<&Expr>) {
229 // list of candidate Enums we know will never get any more members
230 let candidates = &[(&paths::COW, "Borrowed"),
231 (&paths::COW, "Cow::Borrowed"),
232 (&paths::COW, "Cow::Owned"),
233 (&paths::COW, "Owned"),
234 (&paths::OPTION, "None"),
235 (&paths::RESULT, "Err"),
236 (&paths::RESULT, "Ok")];
238 let path = match arms[1].pats[0].node {
239 PatKind::TupleStruct(ref path, ref inner, _) => {
240 // contains any non wildcard patterns? e.g. Err(err)
241 if inner.iter().any(|pat| pat.node != PatKind::Wild) {
244 print::to_string(print::NO_ANN, |s| s.print_qpath(path, false))
246 PatKind::Binding(BindingAnnotation::Unannotated, _, ident, None) => ident.node.to_string(),
247 PatKind::Path(ref path) => print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
251 for &(ty_path, pat_path) in candidates {
252 if path == *pat_path && match_type(cx, ty, ty_path) {
253 report_single_match_single_pattern(cx, ex, arms, expr, els);
258 fn check_match_bool(cx: &LateContext, ex: &Expr, arms: &[Arm], expr: &Expr) {
259 // type of expression == bool
260 if cx.tables.expr_ty(ex).sty == ty::TyBool {
261 span_lint_and_then(cx,
264 "you seem to be trying to match on a boolean expression",
266 if arms.len() == 2 && arms[0].pats.len() == 1 {
268 let exprs = if let PatKind::Lit(ref arm_bool) = arms[0].pats[0].node {
269 if let ExprLit(ref lit) = arm_bool.node {
271 LitKind::Bool(true) => Some((&*arms[0].body, &*arms[1].body)),
272 LitKind::Bool(false) => Some((&*arms[1].body, &*arms[0].body)),
282 if let Some((true_expr, false_expr)) = exprs {
283 let sugg = match (is_unit_expr(true_expr), is_unit_expr(false_expr)) {
285 Some(format!("if {} {} else {}",
286 snippet(cx, ex.span, "b"),
287 expr_block(cx, true_expr, None, ".."),
288 expr_block(cx, false_expr, None, "..")))
291 Some(format!("if {} {}", snippet(cx, ex.span, "b"), expr_block(cx, true_expr, None, "..")))
294 let test = Sugg::hir(cx, ex, "..");
295 Some(format!("if {} {}", !test, expr_block(cx, false_expr, None, "..")))
297 (true, true) => None,
300 if let Some(sugg) = sugg {
301 db.span_suggestion(expr.span, "consider using an if/else expression", sugg);
310 fn check_overlapping_arms(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
311 if arms.len() >= 2 && cx.tables.expr_ty(ex).is_integral() {
312 let ranges = all_ranges(cx, arms, ex.id);
313 let type_ranges = type_ranges(&ranges);
314 if !type_ranges.is_empty() {
315 if let Some((start, end)) = overlapping(&type_ranges) {
316 span_note_and_lint(cx,
317 MATCH_OVERLAPPING_ARM,
319 "some ranges overlap",
321 "overlaps with this");
327 fn check_wild_err_arm(cx: &LateContext, ex: &Expr, arms: &[Arm]) {
328 let ex_ty = walk_ptrs_ty(cx.tables.expr_ty(ex));
329 if match_type(cx, ex_ty, &paths::RESULT) {
331 if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pats[0].node {
332 let path_str = print::to_string(print::NO_ANN, |s| s.print_qpath(path, false));
335 inner.iter().any(|pat| pat.node == PatKind::Wild),
336 let ExprBlock(ref block) = arm.body.node,
337 is_panic_block(block)
339 // `Err(_)` arm with `panic!` found
340 span_note_and_lint(cx,
343 "Err(_) will match all errors, maybe not a good idea",
345 "to remove this warning, match each error seperately \
346 or use unreachable macro");
353 // If the block contains only a `panic!` macro (as expression or statement)
354 fn is_panic_block(block: &Block) -> bool {
355 match (&block.expr, block.stmts.len(), block.stmts.first()) {
356 (&Some(ref exp), 0, _) => {
357 is_expn_of(exp.span, "panic").is_some() && is_expn_of(exp.span, "unreachable").is_none()
359 (&None, 1, Some(stmt)) => {
360 is_expn_of(stmt.span, "panic").is_some() && is_expn_of(stmt.span, "unreachable").is_none()
366 fn check_match_ref_pats(cx: &LateContext, ex: &Expr, arms: &[Arm], source: MatchSource, expr: &Expr) {
367 if has_only_ref_pats(arms) {
368 if let ExprAddrOf(Mutability::MutImmutable, ref inner) = ex.node {
369 span_lint_and_then(cx,
372 "you don't need to add `&` to both the expression and the patterns",
374 let inner = Sugg::hir(cx, inner, "..");
375 let template = match_template(expr.span, source, &inner);
376 db.span_suggestion(expr.span, "try", template);
379 span_lint_and_then(cx,
382 "you don't need to add `&` to all patterns",
384 let ex = Sugg::hir(cx, ex, "..");
385 let template = match_template(expr.span, source, &ex.deref());
386 db.span_suggestion(expr.span,
387 "instead of prefixing all patterns with `&`, you can dereference the expression",
394 /// Get all arms that are unbounded `PatRange`s.
395 fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &[Arm], id: NodeId) -> Vec<SpannedRange<ConstVal<'tcx>>> {
396 let parent_item = cx.tcx.hir.get_parent(id);
397 let parent_def_id = cx.tcx.hir.local_def_id(parent_item);
398 let substs = Substs::identity_for_item(cx.tcx, parent_def_id);
399 let constcx = ConstContext::new(cx.tcx, cx.param_env.and(substs), cx.tables);
402 if let Arm { ref pats, guard: None, .. } = *arm {
409 let PatKind::Range(ref lhs, ref rhs, ref range_end) = pat.node,
410 let Ok(lhs) = constcx.eval(lhs),
411 let Ok(rhs) = constcx.eval(rhs)
413 let rhs = match *range_end {
414 RangeEnd::Included => Bound::Included(rhs),
415 RangeEnd::Excluded => Bound::Excluded(rhs),
417 return Some(SpannedRange { span: pat.span, node: (lhs, rhs) });
421 let PatKind::Lit(ref value) = pat.node,
422 let Ok(value) = constcx.eval(value)
424 return Some(SpannedRange { span: pat.span, node: (value.clone(), Bound::Included(value)) });
433 #[derive(Debug, Eq, PartialEq)]
434 pub struct SpannedRange<T> {
436 pub node: (T, Bound<T>),
439 type TypedRanges = Vec<SpannedRange<ConstInt>>;
441 /// Get all `Int` ranges or all `Uint` ranges. Mixed types are an error anyway and other types than
442 /// `Uint` and `Int` probably don't make sense.
443 fn type_ranges(ranges: &[SpannedRange<ConstVal>]) -> TypedRanges {
445 .filter_map(|range| match range.node {
446 (ConstVal::Integral(start), Bound::Included(ConstVal::Integral(end))) => {
449 node: (start, Bound::Included(end)),
452 (ConstVal::Integral(start), Bound::Excluded(ConstVal::Integral(end))) => {
455 node: (start, Bound::Excluded(end)),
458 (ConstVal::Integral(start), Bound::Unbounded) => {
461 node: (start, Bound::Unbounded),
469 fn is_unit_expr(expr: &Expr) -> bool {
471 ExprTup(ref v) if v.is_empty() => true,
472 ExprBlock(ref b) if b.stmts.is_empty() && b.expr.is_none() => true,
477 fn has_only_ref_pats(arms: &[Arm]) -> bool {
478 let mapped = arms.iter()
479 .flat_map(|a| &a.pats)
482 PatKind::Ref(..) => Some(true), // &-patterns
483 PatKind::Wild => Some(false), // an "anything" wildcard is also fine
484 _ => None, // any other pattern is not fine
487 .collect::<Option<Vec<bool>>>();
488 // look for Some(v) where there's at least one true element
489 mapped.map_or(false, |v| v.iter().any(|el| *el))
492 fn match_template(span: Span, source: MatchSource, expr: &Sugg) -> String {
494 MatchSource::Normal => format!("match {} {{ .. }}", expr),
495 MatchSource::IfLetDesugar { .. } => format!("if let .. = {} {{ .. }}", expr),
496 MatchSource::WhileLetDesugar => format!("while let .. = {} {{ .. }}", expr),
497 MatchSource::ForLoopDesugar => span_bug!(span, "for loop desugared to match with &-patterns!"),
498 MatchSource::TryDesugar => span_bug!(span, "`?` operator desugared to match with &-patterns!"),
502 pub fn overlapping<T>(ranges: &[SpannedRange<T>]) -> Option<(&SpannedRange<T>, &SpannedRange<T>)>
505 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
506 enum Kind<'a, T: 'a> {
507 Start(T, &'a SpannedRange<T>),
508 End(Bound<T>, &'a SpannedRange<T>),
511 impl<'a, T: Copy> Kind<'a, T> {
512 fn range(&self) -> &'a SpannedRange<T> {
515 Kind::End(_, r) => r,
519 fn value(self) -> Bound<T> {
521 Kind::Start(t, _) => Bound::Included(t),
522 Kind::End(t, _) => t,
527 impl<'a, T: Copy + Ord> PartialOrd for Kind<'a, T> {
528 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
529 Some(self.cmp(other))
533 impl<'a, T: Copy + Ord> Ord for Kind<'a, T> {
534 fn cmp(&self, other: &Self) -> Ordering {
535 match (self.value(), other.value()) {
536 (Bound::Included(a), Bound::Included(b)) |
537 (Bound::Excluded(a), Bound::Excluded(b)) => a.cmp(&b),
538 // Range patterns cannot be unbounded (yet)
539 (Bound::Unbounded, _) |
540 (_, Bound::Unbounded) => unimplemented!(),
541 (Bound::Included(a), Bound::Excluded(b)) => {
543 Ordering::Equal => Ordering::Greater,
547 (Bound::Excluded(a), Bound::Included(b)) => {
549 Ordering::Equal => Ordering::Less,
557 let mut values = Vec::with_capacity(2 * ranges.len());
560 values.push(Kind::Start(r.node.0, r));
561 values.push(Kind::End(r.node.1, r));
566 for (a, b) in values.iter().zip(values.iter().skip(1)) {
568 (&Kind::Start(_, ra), &Kind::End(_, rb)) => {
569 if ra.node != rb.node {
570 return Some((ra, rb));
573 (&Kind::End(a, _), &Kind::Start(b, _)) if a != Bound::Included(b) => (),
574 _ => return Some((a.range(), b.range())),