1 use crate::consts::{constant, Constant};
2 use crate::reexport::*;
3 use crate::utils::paths;
4 use crate::utils::usage::{is_unused, mutated_variables};
6 get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
7 is_integer_const, is_no_std_crate, is_refutable, last_path_segment, match_trait_method, match_type, match_var,
8 multispan_sugg, snippet, snippet_opt, snippet_with_applicability, span_help_and_lint, span_lint,
9 span_lint_and_sugg, span_lint_and_then, SpanlessEq,
11 use crate::utils::{is_type_diagnostic_item, qpath_res, same_tys, sext, sugg};
12 use if_chain::if_chain;
13 use itertools::Itertools;
14 use rustc::hir::map::Map;
15 use rustc::lint::in_external_macro;
16 use rustc::middle::region;
17 use rustc::ty::{self, Ty};
18 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
19 use rustc_errors::Applicability;
20 use rustc_hir::def::{DefKind, Res};
21 use rustc_hir::def_id;
22 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
24 use rustc_lint::{LateContext, LateLintPass, LintContext};
25 use rustc_session::{declare_lint_pass, declare_tool_lint};
26 use rustc_span::source_map::Span;
27 use rustc_span::{BytePos, Symbol};
28 use rustc_typeck::expr_use_visitor::*;
29 use std::iter::{once, Iterator};
33 declare_clippy_lint! {
34 /// **What it does:** Checks for for-loops that manually copy items between
35 /// slices that could be optimized by having a memcpy.
37 /// **Why is this bad?** It is not as fast as a memcpy.
39 /// **Known problems:** None.
43 /// # let src = vec![1];
44 /// # let mut dst = vec![0; 65];
45 /// for i in 0..src.len() {
46 /// dst[i + 64] = src[i];
49 /// Could be written as:
51 /// # let src = vec![1];
52 /// # let mut dst = vec![0; 65];
53 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
57 "manually copying items between slices"
60 declare_clippy_lint! {
61 /// **What it does:** Checks for looping over the range of `0..len` of some
62 /// collection just to get the values by index.
64 /// **Why is this bad?** Just iterating the collection itself makes the intent
65 /// more clear and is probably faster.
67 /// **Known problems:** None.
71 /// let vec = vec!['a', 'b', 'c'];
72 /// for i in 0..vec.len() {
73 /// println!("{}", vec[i]);
76 /// Could be written as:
78 /// let vec = vec!['a', 'b', 'c'];
80 /// println!("{}", i);
83 pub NEEDLESS_RANGE_LOOP,
85 "for-looping over a range of indices where an iterator over items would do"
88 declare_clippy_lint! {
89 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
90 /// suggests the latter.
92 /// **Why is this bad?** Readability.
94 /// **Known problems:** False negatives. We currently only warn on some known
99 /// // with `y` a `Vec` or slice:
100 /// # let y = vec![1];
101 /// for x in y.iter() {
105 /// can be rewritten to
107 /// # let y = vec![1];
112 pub EXPLICIT_ITER_LOOP,
114 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
117 declare_clippy_lint! {
118 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
119 /// suggests the latter.
121 /// **Why is this bad?** Readability.
123 /// **Known problems:** None
127 /// # let y = vec![1];
128 /// // with `y` a `Vec` or slice:
129 /// for x in y.into_iter() {
133 /// can be rewritten to
135 /// # let y = vec![1];
140 pub EXPLICIT_INTO_ITER_LOOP,
142 "for-looping over `_.into_iter()` when `_` would do"
145 declare_clippy_lint! {
146 /// **What it does:** Checks for loops on `x.next()`.
148 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
149 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
150 /// implements `IntoIterator`, so that possibly one value will be iterated,
151 /// leading to some hard to find bugs. No one will want to write such code
152 /// [except to win an Underhanded Rust
153 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
155 /// **Known problems:** None.
159 /// for x in y.next() {
165 "for-looping over `_.next()` which is probably not intended"
168 declare_clippy_lint! {
169 /// **What it does:** Checks for `for` loops over `Option` values.
171 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
174 /// **Known problems:** None.
178 /// for x in option {
185 /// if let Some(x) = option {
189 pub FOR_LOOP_OVER_OPTION,
191 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
194 declare_clippy_lint! {
195 /// **What it does:** Checks for `for` loops over `Result` values.
197 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
200 /// **Known problems:** None.
204 /// for x in result {
211 /// if let Ok(x) = result {
215 pub FOR_LOOP_OVER_RESULT,
217 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
220 declare_clippy_lint! {
221 /// **What it does:** Detects `loop + match` combinations that are easier
222 /// written as a `while let` loop.
224 /// **Why is this bad?** The `while let` loop is usually shorter and more
227 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
231 /// # let y = Some(1);
233 /// let x = match y {
237 /// // .. do something with x
239 /// // is easier written as
240 /// while let Some(x) = y {
241 /// // .. do something with x
246 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
249 declare_clippy_lint! {
250 /// **What it does:** Checks for functions collecting an iterator when collect
253 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
254 /// when this allocation may not be needed.
256 /// **Known problems:**
261 /// # let iterator = vec![1].into_iter();
262 /// let len = iterator.clone().collect::<Vec<_>>().len();
264 /// let len = iterator.count();
266 pub NEEDLESS_COLLECT,
268 "collecting an iterator when collect is not needed"
271 declare_clippy_lint! {
272 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
273 /// are constant and `x` is greater or equal to `y`, unless the range is
274 /// reversed or has a negative `.step_by(_)`.
276 /// **Why is it bad?** Such loops will either be skipped or loop until
277 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
280 /// **Known problems:** The lint cannot catch loops over dynamically defined
281 /// ranges. Doing this would require simulating all possible inputs and code
282 /// paths through the program, which would be complex and error-prone.
286 /// for x in 5..10 - 5 {
288 /// } // oops, stray `-`
290 pub REVERSE_RANGE_LOOP,
292 "iteration over an empty range, such as `10..0` or `5..5`"
295 declare_clippy_lint! {
296 /// **What it does:** Checks `for` loops over slices with an explicit counter
297 /// and suggests the use of `.enumerate()`.
299 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
300 /// declutters the code and may be faster in some instances.
302 /// **Known problems:** None.
306 /// # let v = vec![1];
307 /// # fn bar(bar: usize, baz: usize) {}
314 /// Could be written as
316 /// # let v = vec![1];
317 /// # fn bar(bar: usize, baz: usize) {}
318 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
320 pub EXPLICIT_COUNTER_LOOP,
322 "for-looping with an explicit counter when `_.enumerate()` would do"
325 declare_clippy_lint! {
326 /// **What it does:** Checks for empty `loop` expressions.
328 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
329 /// anything. Think of the environment and either block on something or at least
330 /// make the thread sleep for some microseconds.
332 /// **Known problems:** None.
340 "empty `loop {}`, which should block or sleep"
343 declare_clippy_lint! {
344 /// **What it does:** Checks for `while let` expressions on iterators.
346 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
347 /// the intent better.
349 /// **Known problems:** None.
353 /// while let Some(val) = iter() {
357 pub WHILE_LET_ON_ITERATOR,
359 "using a while-let loop instead of a for loop on an iterator"
362 declare_clippy_lint! {
363 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
364 /// ignoring either the keys or values.
366 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
367 /// can be used to express that don't need the values or keys.
369 /// **Known problems:** None.
373 /// for (k, _) in &map {
378 /// could be replaced by
381 /// for k in map.keys() {
387 "looping on a map using `iter` when `keys` or `values` would do"
390 declare_clippy_lint! {
391 /// **What it does:** Checks for loops that will always `break`, `return` or
392 /// `continue` an outer loop.
394 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
397 /// **Known problems:** None
408 "any loop that will always `break` or `return`"
411 declare_clippy_lint! {
412 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
414 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
416 /// **Known problems:** None
420 /// let mut foo = 42;
421 /// for i in 0..foo {
423 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
428 "for loop over a range where one of the bounds is a mutable variable"
431 declare_clippy_lint! {
432 /// **What it does:** Checks whether variables used within while loop condition
433 /// can be (and are) mutated in the body.
435 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
436 /// will lead to an infinite loop.
438 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
439 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
440 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
446 /// println!("let me loop forever!");
449 pub WHILE_IMMUTABLE_CONDITION,
451 "variables used within while expression are not mutated in the body"
454 declare_lint_pass!(Loops => [
458 EXPLICIT_INTO_ITER_LOOP,
460 FOR_LOOP_OVER_RESULT,
461 FOR_LOOP_OVER_OPTION,
465 EXPLICIT_COUNTER_LOOP,
467 WHILE_LET_ON_ITERATOR,
471 WHILE_IMMUTABLE_CONDITION,
474 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
475 #[allow(clippy::too_many_lines)]
476 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
477 if let Some((pat, arg, body)) = higher::for_loop(expr) {
478 // we don't want to check expanded macros
479 // this check is not at the top of the function
480 // since higher::for_loop expressions are marked as expansions
481 if body.span.from_expansion() {
484 check_for_loop(cx, pat, arg, body, expr);
487 // we don't want to check expanded macros
488 if expr.span.from_expansion() {
492 // check for never_loop
493 if let ExprKind::Loop(ref block, _, _) = expr.kind {
494 match never_loop_block(block, expr.hir_id) {
495 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
496 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
500 // check for `loop { if let {} else break }` that could be `while let`
501 // (also matches an explicit "match" instead of "if let")
502 // (even if the "match" or "if let" is used for declaration)
503 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
504 // also check for empty `loop {}` statements
505 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) {
510 "empty `loop {}` detected. You may want to either use `panic!()` or add \
511 `std::thread::sleep(..);` to the loop body.",
515 // extract the expression from the first statement (if any) in a block
516 let inner_stmt_expr = extract_expr_from_first_stmt(block);
517 // or extract the first expression (if any) from the block
518 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
519 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
520 // ensure "if let" compatible match structure
522 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
524 && arms[0].guard.is_none()
525 && arms[1].guard.is_none()
526 && is_simple_break_expr(&arms[1].body)
528 if in_external_macro(cx.sess(), expr.span) {
532 // NOTE: we used to build a body here instead of using
533 // ellipsis, this was removed because:
534 // 1) it was ugly with big bodies;
535 // 2) it was not indented properly;
536 // 3) it wasn’t very smart (see #675).
537 let mut applicability = Applicability::HasPlaceholders;
542 "this loop could be written as a `while let` loop",
545 "while let {} = {} {{ .. }}",
546 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
547 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
558 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
559 let pat = &arms[0].pat.kind;
561 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
562 &ExprKind::MethodCall(ref method_path, _, ref method_args),
563 ) = (pat, &match_expr.kind)
565 let iter_expr = &method_args[0];
566 let lhs_constructor = last_path_segment(qpath);
567 if method_path.ident.name == sym!(next)
568 && match_trait_method(cx, match_expr, &paths::ITERATOR)
569 && lhs_constructor.ident.name == sym!(Some)
570 && (pat_args.is_empty()
571 || !is_refutable(cx, &pat_args[0])
572 && !is_used_inside(cx, iter_expr, &arms[0].body)
573 && !is_iterator_used_after_while_let(cx, iter_expr)
574 && !is_nested(cx, expr, &method_args[0]))
576 let iterator = snippet(cx, method_args[0].span, "_");
577 let loop_var = if pat_args.is_empty() {
580 snippet(cx, pat_args[0].span, "_").into_owned()
584 WHILE_LET_ON_ITERATOR,
586 "this loop could be written as a `for` loop",
588 format!("for {} in {} {{ .. }}", loop_var, iterator),
589 Applicability::HasPlaceholders,
595 if let Some((cond, body)) = higher::while_loop(&expr) {
596 check_infinite_loop(cx, cond, body);
599 check_needless_collect(expr, cx);
603 enum NeverLoopResult {
604 // A break/return always get triggered but not necessarily for the main loop.
606 // A continue may occur for the main loop.
612 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
614 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
615 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
619 // Combine two results for parts that are called in order.
621 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
623 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
624 NeverLoopResult::Otherwise => second,
628 // Combine two results where both parts are called but not necessarily in order.
630 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
631 match (left, right) {
632 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
633 NeverLoopResult::MayContinueMainLoop
635 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
636 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
640 // Combine two results where only one of the part may have been executed.
642 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
644 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
645 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
646 NeverLoopResult::MayContinueMainLoop
648 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
652 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
653 let stmts = block.stmts.iter().map(stmt_to_expr);
654 let expr = once(block.expr.as_ref().map(|p| &**p));
655 let mut iter = stmts.chain(expr).filter_map(|e| e);
656 never_loop_expr_seq(&mut iter, main_loop_id)
659 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
661 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
662 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
667 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
670 | ExprKind::Unary(_, ref e)
671 | ExprKind::Cast(ref e, _)
672 | ExprKind::Type(ref e, _)
673 | ExprKind::Field(ref e, _)
674 | ExprKind::AddrOf(_, _, ref e)
675 | ExprKind::Struct(_, _, Some(ref e))
676 | ExprKind::Repeat(ref e, _)
677 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
678 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
679 never_loop_expr_all(&mut es.iter(), main_loop_id)
681 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
682 ExprKind::Binary(_, ref e1, ref e2)
683 | ExprKind::Assign(ref e1, ref e2, _)
684 | ExprKind::AssignOp(_, ref e1, ref e2)
685 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
686 ExprKind::Loop(ref b, _, _) => {
687 // Break can come from the inner loop so remove them.
688 absorb_break(&never_loop_block(b, main_loop_id))
690 ExprKind::Match(ref e, ref arms, _) => {
691 let e = never_loop_expr(e, main_loop_id);
695 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
699 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
700 ExprKind::Continue(d) => {
703 .expect("target ID can only be missing in the presence of compilation errors");
704 if id == main_loop_id {
705 NeverLoopResult::MayContinueMainLoop
707 NeverLoopResult::AlwaysBreak
710 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
711 if let Some(ref e) = *e {
712 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
714 NeverLoopResult::AlwaysBreak
717 ExprKind::Struct(_, _, None)
718 | ExprKind::Yield(_, _)
719 | ExprKind::Closure(_, _, _, _, _)
720 | ExprKind::InlineAsm(_)
723 | ExprKind::Err => NeverLoopResult::Otherwise,
727 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
728 es.map(|e| never_loop_expr(e, main_loop_id))
729 .fold(NeverLoopResult::Otherwise, combine_seq)
732 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
733 es.map(|e| never_loop_expr(e, main_loop_id))
734 .fold(NeverLoopResult::Otherwise, combine_both)
737 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
738 e.map(|e| never_loop_expr(e, main_loop_id))
739 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
742 fn check_for_loop<'a, 'tcx>(
743 cx: &LateContext<'a, 'tcx>,
746 body: &'tcx Expr<'_>,
747 expr: &'tcx Expr<'_>,
749 check_for_loop_range(cx, pat, arg, body, expr);
750 check_for_loop_reverse_range(cx, arg, expr);
751 check_for_loop_arg(cx, pat, arg, expr);
752 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
753 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
754 check_for_mut_range_bound(cx, arg, body);
755 detect_manual_memcpy(cx, pat, arg, body, expr);
758 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
760 if let ExprKind::Path(ref qpath) = expr.kind;
761 if let QPath::Resolved(None, ref path) = *qpath;
762 if path.segments.len() == 1;
763 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
780 fn negative(s: String) -> Self {
781 Self { value: s, negate: true }
784 fn positive(s: String) -> Self {
792 struct FixedOffsetVar {
797 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
798 let is_slice = match ty.kind {
799 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
800 ty::Slice(..) | ty::Array(..) => true,
804 is_slice || is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) || match_type(cx, ty, &paths::VEC_DEQUE)
807 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId) -> Option<FixedOffsetVar> {
808 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr<'_>, var: HirId) -> Option<String> {
810 ExprKind::Lit(ref l) => match l.node {
811 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
814 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
819 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind {
820 let ty = cx.tables.expr_ty(seqexpr);
821 if !is_slice_like(cx, ty) {
825 let offset = match idx.kind {
826 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
828 let offset_opt = if same_var(cx, lhs, var) {
829 extract_offset(cx, rhs, var)
830 } else if same_var(cx, rhs, var) {
831 extract_offset(cx, lhs, var)
836 offset_opt.map(Offset::positive)
838 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
841 ExprKind::Path(..) => {
842 if same_var(cx, idx, var) {
843 Some(Offset::positive("0".into()))
851 offset.map(|o| FixedOffsetVar {
852 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
860 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
861 cx: &LateContext<'a, 'tcx>,
864 ) -> Option<FixedOffsetVar> {
866 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
867 if method.ident.name == sym!(clone);
869 if let Some(arg) = args.get(0);
871 return get_fixed_offset_var(cx, arg, var);
875 get_fixed_offset_var(cx, expr, var)
878 fn get_indexed_assignments<'a, 'tcx>(
879 cx: &LateContext<'a, 'tcx>,
882 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
883 fn get_assignment<'a, 'tcx>(
884 cx: &LateContext<'a, 'tcx>,
887 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
888 if let ExprKind::Assign(ref lhs, ref rhs, _) = e.kind {
890 get_fixed_offset_var(cx, lhs, var),
891 fetch_cloned_fixed_offset_var(cx, rhs, var),
893 (Some(offset_left), Some(offset_right)) => {
894 // Source and destination must be different
895 if offset_left.var_name == offset_right.var_name {
898 Some((offset_left, offset_right))
908 if let ExprKind::Block(ref b, _) = body.kind {
910 ref stmts, ref expr, ..
915 .map(|stmt| match stmt.kind {
916 StmtKind::Local(..) | StmtKind::Item(..) => None,
917 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
919 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
921 .collect::<Option<Vec<_>>>()
922 .unwrap_or_else(|| vec![])
924 get_assignment(cx, body, var).into_iter().collect()
928 /// Checks for for loops that sequentially copy items from one slice-like
929 /// object to another.
930 fn detect_manual_memcpy<'a, 'tcx>(
931 cx: &LateContext<'a, 'tcx>,
934 body: &'tcx Expr<'_>,
935 expr: &'tcx Expr<'_>,
937 if let Some(higher::Range {
941 }) = higher::range(cx, arg)
943 // the var must be a single name
944 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
945 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
946 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
947 ("0", _, "0", _) => "".into(),
948 ("0", _, x, false) | (x, false, "0", false) => x.into(),
949 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
950 (x, false, y, false) => format!("({} + {})", x, y),
951 (x, false, y, true) => {
955 format!("({} - {})", x, y)
958 (x, true, y, false) => {
962 format!("({} - {})", y, x)
965 (x, true, y, true) => format!("-({} + {})", x, y),
969 let print_limit = |end: &Option<&Expr<'_>>, offset: Offset, var_name: &str| {
970 if let Some(end) = *end {
972 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.kind;
973 if method.ident.name == sym!(len);
974 if len_args.len() == 1;
975 if let Some(arg) = len_args.get(0);
976 if snippet(cx, arg.span, "??") == var_name;
978 return if offset.negate {
979 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
986 let end_str = match limits {
987 ast::RangeLimits::Closed => {
988 let end = sugg::Sugg::hir(cx, end, "<count>");
989 format!("{}", end + sugg::ONE)
991 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
994 print_sum(&Offset::positive(end_str), &offset)
1000 // The only statements in the for loops can be indexed assignments from
1001 // indexed retrievals.
1002 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1004 let big_sugg = manual_copies
1006 .map(|(dst_var, src_var)| {
1007 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1008 let dst_offset = print_sum(&start_str, &dst_var.offset);
1009 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1010 let src_offset = print_sum(&start_str, &src_var.offset);
1011 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1012 let dst = if dst_offset == "" && dst_limit == "" {
1015 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1019 "{}.clone_from_slice(&{}[{}..{}])",
1020 dst, src_var.var_name, src_offset, src_limit
1025 if !big_sugg.is_empty() {
1030 "it looks like you're manually copying between slices",
1031 "try replacing the loop by",
1033 Applicability::Unspecified,
1040 /// Checks for looping over a range and then indexing a sequence with it.
1041 /// The iteratee must be a range literal.
1042 #[allow(clippy::too_many_lines)]
1043 fn check_for_loop_range<'a, 'tcx>(
1044 cx: &LateContext<'a, 'tcx>,
1046 arg: &'tcx Expr<'_>,
1047 body: &'tcx Expr<'_>,
1048 expr: &'tcx Expr<'_>,
1050 if let Some(higher::Range {
1054 }) = higher::range(cx, arg)
1056 // the var must be a single name
1057 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1058 let mut visitor = VarVisitor {
1061 indexed_mut: FxHashSet::default(),
1062 indexed_indirectly: FxHashMap::default(),
1063 indexed_directly: FxHashMap::default(),
1064 referenced: FxHashSet::default(),
1066 prefer_mutable: false,
1068 walk_expr(&mut visitor, body);
1070 // linting condition: we only indexed one variable, and indexed it directly
1071 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1072 let (indexed, (indexed_extent, indexed_ty)) = visitor
1076 .expect("already checked that we have exactly 1 element");
1078 // ensure that the indexed variable was declared before the loop, see #601
1079 if let Some(indexed_extent) = indexed_extent {
1080 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1081 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1082 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1083 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1084 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1089 // don't lint if the container that is indexed does not have .iter() method
1090 let has_iter = has_iter_method(cx, indexed_ty);
1091 if has_iter.is_none() {
1095 // don't lint if the container that is indexed into is also used without
1097 if visitor.referenced.contains(&indexed) {
1101 let starts_at_zero = is_integer_const(cx, start, 0);
1103 let skip = if starts_at_zero {
1106 format!(".skip({})", snippet(cx, start.span, ".."))
1109 let mut end_is_start_plus_val = false;
1111 let take = if let Some(end) = *end {
1112 let mut take_expr = end;
1114 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1115 if let BinOpKind::Add = op.node {
1116 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1117 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1119 if start_equal_left {
1121 } else if start_equal_right {
1125 end_is_start_plus_val = start_equal_left | start_equal_right;
1129 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1133 ast::RangeLimits::Closed => {
1134 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1135 format!(".take({})", take_expr + sugg::ONE)
1137 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1144 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1145 ("mut ", "iter_mut")
1150 let take_is_empty = take.is_empty();
1151 let mut method_1 = take;
1152 let mut method_2 = skip;
1154 if end_is_start_plus_val {
1155 mem::swap(&mut method_1, &mut method_2);
1158 if visitor.nonindex {
1161 NEEDLESS_RANGE_LOOP,
1163 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1167 "consider using an iterator".to_string(),
1169 (pat.span, format!("({}, <item>)", ident.name)),
1172 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1179 let repl = if starts_at_zero && take_is_empty {
1180 format!("&{}{}", ref_mut, indexed)
1182 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1187 NEEDLESS_RANGE_LOOP,
1190 "the loop variable `{}` is only used to index `{}`.",
1196 "consider using an iterator".to_string(),
1197 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1207 fn is_len_call(expr: &Expr<'_>, var: Name) -> bool {
1209 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.kind;
1210 if len_args.len() == 1;
1211 if method.ident.name == sym!(len);
1212 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1213 if path.segments.len() == 1;
1214 if path.segments[0].ident.name == var;
1223 fn is_end_eq_array_len<'tcx>(
1224 cx: &LateContext<'_, 'tcx>,
1226 limits: ast::RangeLimits,
1227 indexed_ty: Ty<'tcx>,
1230 if let ExprKind::Lit(ref lit) = end.kind;
1231 if let ast::LitKind::Int(end_int, _) = lit.node;
1232 if let ty::Array(_, arr_len_const) = indexed_ty.kind;
1233 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1235 return match limits {
1236 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1237 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1245 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
1246 // if this for loop is iterating over a two-sided range...
1247 if let Some(higher::Range {
1251 }) = higher::range(cx, arg)
1253 // ...and both sides are compile-time constant integers...
1254 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1255 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1256 // ...and the start index is greater than the end index,
1257 // this loop will never run. This is often confusing for developers
1258 // who think that this will iterate from the larger value to the
1260 let ty = cx.tables.expr_ty(start);
1261 let (sup, eq) = match (start_idx, end_idx) {
1262 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1264 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1265 ty::Uint(_) => start_idx > end_idx,
1268 start_idx == end_idx,
1270 _ => (false, false),
1274 let start_snippet = snippet(cx, start.span, "_");
1275 let end_snippet = snippet(cx, end.span, "_");
1276 let dots = if limits == ast::RangeLimits::Closed {
1286 "this range is empty so this for loop will never run",
1290 "consider using the following if you are attempting to iterate over this \
1293 "({end}{dots}{start}).rev()",
1296 start = start_snippet
1298 Applicability::MaybeIncorrect,
1302 } else if eq && limits != ast::RangeLimits::Closed {
1303 // if they are equal, it's also problematic - this loop
1309 "this range is empty so this for loop will never run",
1317 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1318 let mut applicability = Applicability::MachineApplicable;
1319 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1320 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1325 "it is more concise to loop over references to containers instead of using explicit \
1327 "to write this more concisely, try",
1328 format!("&{}{}", muta, object),
1333 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1334 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1335 if let ExprKind::MethodCall(ref method, _, ref args) = arg.kind {
1336 // just the receiver, no arguments
1337 if args.len() == 1 {
1338 let method_name = &*method.ident.as_str();
1339 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1340 if method_name == "iter" || method_name == "iter_mut" {
1341 if is_ref_iterable_type(cx, &args[0]) {
1342 lint_iter_method(cx, args, arg, method_name);
1344 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1345 let receiver_ty = cx.tables.expr_ty(&args[0]);
1346 let receiver_ty_adjusted = cx.tables.expr_ty_adjusted(&args[0]);
1347 if same_tys(cx, receiver_ty, receiver_ty_adjusted) {
1348 let mut applicability = Applicability::MachineApplicable;
1349 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1352 EXPLICIT_INTO_ITER_LOOP,
1354 "it is more concise to loop over containers instead of using explicit \
1356 "to write this more concisely, try",
1361 let ref_receiver_ty = cx.tcx.mk_ref(
1362 cx.tcx.lifetimes.re_erased,
1365 mutbl: Mutability::Not,
1368 if same_tys(cx, receiver_ty_adjusted, ref_receiver_ty) {
1369 lint_iter_method(cx, args, arg, method_name)
1372 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1377 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1378 probably not what you want",
1380 next_loop_linted = true;
1384 if !next_loop_linted {
1385 check_arg_type(cx, pat, arg);
1389 /// Checks for `for` loops over `Option`s and `Result`s.
1390 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1391 let ty = cx.tables.expr_ty(arg);
1392 if match_type(cx, ty, &paths::OPTION) {
1395 FOR_LOOP_OVER_OPTION,
1398 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1399 `if let` statement.",
1400 snippet(cx, arg.span, "_")
1403 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1404 snippet(cx, pat.span, "_"),
1405 snippet(cx, arg.span, "_")
1408 } else if match_type(cx, ty, &paths::RESULT) {
1411 FOR_LOOP_OVER_RESULT,
1414 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1415 `if let` statement.",
1416 snippet(cx, arg.span, "_")
1419 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1420 snippet(cx, pat.span, "_"),
1421 snippet(cx, arg.span, "_")
1427 fn check_for_loop_explicit_counter<'a, 'tcx>(
1428 cx: &LateContext<'a, 'tcx>,
1430 arg: &'tcx Expr<'_>,
1431 body: &'tcx Expr<'_>,
1432 expr: &'tcx Expr<'_>,
1434 // Look for variables that are incremented once per loop iteration.
1435 let mut visitor = IncrementVisitor {
1437 states: FxHashMap::default(),
1441 walk_expr(&mut visitor, body);
1443 // For each candidate, check the parent block to see if
1444 // it's initialized to zero at the start of the loop.
1445 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1446 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1447 let mut visitor2 = InitializeVisitor {
1451 state: VarState::IncrOnce,
1456 walk_block(&mut visitor2, block);
1458 if visitor2.state == VarState::Warn {
1459 if let Some(name) = visitor2.name {
1460 let mut applicability = Applicability::MachineApplicable;
1462 // for some reason this is the only way to get the `Span`
1463 // of the entire `for` loop
1464 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1472 EXPLICIT_COUNTER_LOOP,
1473 for_span.with_hi(arg.span.hi()),
1474 &format!("the variable `{}` is used as a loop counter.", name),
1477 "for ({}, {}) in {}.enumerate()",
1479 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1480 make_iterator_snippet(cx, arg, &mut applicability),
1490 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1491 /// actual `Iterator` that the loop uses.
1492 fn make_iterator_snippet(cx: &LateContext<'_, '_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1493 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR)
1494 .map_or(false, |id| implements_trait(cx, cx.tables.expr_ty(arg), id, &[]));
1498 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1501 // (&x).into_iter() ==> x.iter()
1502 // (&mut x).into_iter() ==> x.iter_mut()
1504 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1505 if has_iter_method(cx, cx.tables.expr_ty(&arg_inner)).is_some() =>
1507 let meth_name = match mutability {
1508 Mutability::Mut => "iter_mut",
1509 Mutability::Not => "iter",
1513 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1519 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1525 /// Checks for the `FOR_KV_MAP` lint.
1526 fn check_for_loop_over_map_kv<'a, 'tcx>(
1527 cx: &LateContext<'a, 'tcx>,
1529 arg: &'tcx Expr<'_>,
1530 body: &'tcx Expr<'_>,
1531 expr: &'tcx Expr<'_>,
1533 let pat_span = pat.span;
1535 if let PatKind::Tuple(ref pat, _) = pat.kind {
1537 let arg_span = arg.span;
1538 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).kind {
1539 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1540 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1541 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1546 let mutbl = match mutbl {
1547 Mutability::Not => "",
1548 Mutability::Mut => "_mut",
1550 let arg = match arg.kind {
1551 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1555 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1560 &format!("you seem to want to iterate on a map's {}s", kind),
1562 let map = sugg::Sugg::hir(cx, arg, "map");
1565 "use the corresponding method".into(),
1567 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1568 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1578 struct MutatePairDelegate {
1579 hir_id_low: Option<HirId>,
1580 hir_id_high: Option<HirId>,
1581 span_low: Option<Span>,
1582 span_high: Option<Span>,
1585 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1586 fn consume(&mut self, _: &Place<'tcx>, _: ConsumeMode) {}
1588 fn borrow(&mut self, cmt: &Place<'tcx>, bk: ty::BorrowKind) {
1589 if let ty::BorrowKind::MutBorrow = bk {
1590 if let PlaceBase::Local(id) = cmt.base {
1591 if Some(id) == self.hir_id_low {
1592 self.span_low = Some(cmt.span)
1594 if Some(id) == self.hir_id_high {
1595 self.span_high = Some(cmt.span)
1601 fn mutate(&mut self, cmt: &Place<'tcx>) {
1602 if let PlaceBase::Local(id) = cmt.base {
1603 if Some(id) == self.hir_id_low {
1604 self.span_low = Some(cmt.span)
1606 if Some(id) == self.hir_id_high {
1607 self.span_high = Some(cmt.span)
1613 impl<'tcx> MutatePairDelegate {
1614 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1615 (self.span_low, self.span_high)
1619 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr<'_>, body: &Expr<'_>) {
1620 if let Some(higher::Range {
1624 }) = higher::range(cx, arg)
1626 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1627 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1628 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1629 mut_warn_with_span(cx, span_low);
1630 mut_warn_with_span(cx, span_high);
1635 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1636 if let Some(sp) = span {
1641 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1646 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr<'_>) -> Option<HirId> {
1648 if let ExprKind::Path(ref qpath) = bound.kind;
1649 if let QPath::Resolved(None, _) = *qpath;
1651 let res = qpath_res(cx, qpath, bound.hir_id);
1652 if let Res::Local(node_id) = res {
1653 let node_str = cx.tcx.hir().get(node_id);
1655 if let Node::Binding(pat) = node_str;
1656 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1657 if let BindingAnnotation::Mutable = bind_ann;
1659 return Some(node_id);
1668 fn check_for_mutation(
1669 cx: &LateContext<'_, '_>,
1671 bound_ids: &[Option<HirId>],
1672 ) -> (Option<Span>, Option<Span>) {
1673 let mut delegate = MutatePairDelegate {
1674 hir_id_low: bound_ids[0],
1675 hir_id_high: bound_ids[1],
1679 let def_id = def_id::DefId::local(body.hir_id.owner);
1680 cx.tcx.infer_ctxt().enter(|infcx| {
1681 ExprUseVisitor::new(&mut delegate, &infcx, def_id, cx.param_env, cx.tables).walk_expr(body);
1683 delegate.mutation_span()
1686 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1687 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
1689 PatKind::Wild => true,
1690 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
1695 struct LocalUsedVisitor<'a, 'tcx> {
1696 cx: &'a LateContext<'a, 'tcx>,
1701 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1702 type Map = Map<'tcx>;
1704 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1705 if same_var(self.cx, expr, self.local) {
1708 walk_expr(self, expr);
1712 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
1713 NestedVisitorMap::None
1717 struct VarVisitor<'a, 'tcx> {
1718 /// context reference
1719 cx: &'a LateContext<'a, 'tcx>,
1720 /// var name to look for as index
1722 /// indexed variables that are used mutably
1723 indexed_mut: FxHashSet<Name>,
1724 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1725 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1726 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1727 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1728 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1729 /// Any names that are used outside an index operation.
1730 /// Used to detect things like `&mut vec` used together with `vec[i]`
1731 referenced: FxHashSet<Name>,
1732 /// has the loop variable been used in expressions other than the index of
1735 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1736 /// takes `&mut self`
1737 prefer_mutable: bool,
1740 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1741 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
1743 // the indexed container is referenced by a name
1744 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
1745 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1746 if seqvar.segments.len() == 1;
1748 let index_used_directly = same_var(self.cx, idx, self.var);
1749 let indexed_indirectly = {
1750 let mut used_visitor = LocalUsedVisitor {
1755 walk_expr(&mut used_visitor, idx);
1759 if indexed_indirectly || index_used_directly {
1760 if self.prefer_mutable {
1761 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1763 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
1765 Res::Local(hir_id) => {
1766 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1767 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1768 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1769 if indexed_indirectly {
1770 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1772 if index_used_directly {
1773 self.indexed_directly.insert(
1774 seqvar.segments[0].ident.name,
1775 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1778 return false; // no need to walk further *on the variable*
1780 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1781 if indexed_indirectly {
1782 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1784 if index_used_directly {
1785 self.indexed_directly.insert(
1786 seqvar.segments[0].ident.name,
1787 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1790 return false; // no need to walk further *on the variable*
1801 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1802 type Map = Map<'tcx>;
1804 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1807 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.kind;
1808 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1809 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1810 if !self.check(&args[1], &args[0], expr);
1816 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
1817 if !self.check(idx, seqexpr, expr);
1822 // directly using a variable
1823 if let ExprKind::Path(ref qpath) = expr.kind;
1824 if let QPath::Resolved(None, ref path) = *qpath;
1825 if path.segments.len() == 1;
1827 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
1828 if local_id == self.var {
1829 self.nonindex = true;
1831 // not the correct variable, but still a variable
1832 self.referenced.insert(path.segments[0].ident.name);
1838 let old = self.prefer_mutable;
1840 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
1841 self.prefer_mutable = true;
1842 self.visit_expr(lhs);
1843 self.prefer_mutable = false;
1844 self.visit_expr(rhs);
1846 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
1847 if mutbl == Mutability::Mut {
1848 self.prefer_mutable = true;
1850 self.visit_expr(expr);
1852 ExprKind::Call(ref f, args) => {
1855 let ty = self.cx.tables.expr_ty_adjusted(expr);
1856 self.prefer_mutable = false;
1857 if let ty::Ref(_, _, mutbl) = ty.kind {
1858 if mutbl == Mutability::Mut {
1859 self.prefer_mutable = true;
1862 self.visit_expr(expr);
1865 ExprKind::MethodCall(_, _, args) => {
1866 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1867 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1868 self.prefer_mutable = false;
1869 if let ty::Ref(_, _, mutbl) = ty.kind {
1870 if mutbl == Mutability::Mut {
1871 self.prefer_mutable = true;
1874 self.visit_expr(expr);
1877 ExprKind::Closure(_, _, body_id, ..) => {
1878 let body = self.cx.tcx.hir().body(body_id);
1879 self.visit_expr(&body.value);
1881 _ => walk_expr(self, expr),
1883 self.prefer_mutable = old;
1885 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
1886 NestedVisitorMap::None
1890 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
1891 let def_id = match var_def_id(cx, expr) {
1893 None => return false,
1895 if let Some(used_mutably) = mutated_variables(container, cx) {
1896 if used_mutably.contains(&def_id) {
1903 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
1904 let def_id = match var_def_id(cx, iter_expr) {
1906 None => return false,
1908 let mut visitor = VarUsedAfterLoopVisitor {
1911 iter_expr_id: iter_expr.hir_id,
1912 past_while_let: false,
1913 var_used_after_while_let: false,
1915 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1916 walk_block(&mut visitor, enclosing_block);
1918 visitor.var_used_after_while_let
1921 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1922 cx: &'a LateContext<'a, 'tcx>,
1924 iter_expr_id: HirId,
1925 past_while_let: bool,
1926 var_used_after_while_let: bool,
1929 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1930 type Map = Map<'tcx>;
1932 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1933 if self.past_while_let {
1934 if Some(self.def_id) == var_def_id(self.cx, expr) {
1935 self.var_used_after_while_let = true;
1937 } else if self.iter_expr_id == expr.hir_id {
1938 self.past_while_let = true;
1940 walk_expr(self, expr);
1942 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
1943 NestedVisitorMap::None
1947 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1948 /// for `&T` and `&mut T`, such as `Vec`.
1950 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr<'_>) -> bool {
1951 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1952 // will allow further borrows afterwards
1953 let ty = cx.tables.expr_ty(e);
1954 is_iterable_array(ty, cx) ||
1955 is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) ||
1956 match_type(cx, ty, &paths::LINKED_LIST) ||
1957 match_type(cx, ty, &paths::HASHMAP) ||
1958 match_type(cx, ty, &paths::HASHSET) ||
1959 match_type(cx, ty, &paths::VEC_DEQUE) ||
1960 match_type(cx, ty, &paths::BINARY_HEAP) ||
1961 match_type(cx, ty, &paths::BTREEMAP) ||
1962 match_type(cx, ty, &paths::BTREESET)
1965 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1966 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1968 ty::Array(_, n) => {
1969 if let Some(val) = n.try_eval_usize(cx.tcx, cx.param_env) {
1970 (0..=32).contains(&val)
1979 /// If a block begins with a statement (possibly a `let` binding) and has an
1980 /// expression, return it.
1981 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
1982 if block.stmts.is_empty() {
1985 if let StmtKind::Local(ref local) = block.stmts[0].kind {
1986 if let Some(expr) = local.init {
1996 /// If a block begins with an expression (with or without semicolon), return it.
1997 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
1999 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2000 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2001 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2002 StmtKind::Local(..) | StmtKind::Item(..) => None,
2008 /// Returns `true` if expr contains a single break expr without destination label
2010 /// passed expression. The expression may be within a block.
2011 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2013 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2014 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2019 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2020 // incremented exactly once in the loop body, and initialized to zero
2021 // at the start of the loop.
2022 #[derive(Debug, PartialEq)]
2024 Initial, // Not examined yet
2025 IncrOnce, // Incremented exactly once, may be a loop counter
2026 Declared, // Declared but not (yet) initialized to zero
2031 /// Scan a for loop for variables that are incremented exactly once.
2032 struct IncrementVisitor<'a, 'tcx> {
2033 cx: &'a LateContext<'a, 'tcx>, // context reference
2034 states: FxHashMap<HirId, VarState>, // incremented variables
2035 depth: u32, // depth of conditional expressions
2039 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2040 type Map = Map<'tcx>;
2042 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2047 // If node is a variable
2048 if let Some(def_id) = var_def_id(self.cx, expr) {
2049 if let Some(parent) = get_parent_expr(self.cx, expr) {
2050 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2053 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2054 if lhs.hir_id == expr.hir_id {
2055 if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) {
2056 *state = match *state {
2057 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2058 _ => VarState::DontWarn,
2061 // Assigned some other value
2062 *state = VarState::DontWarn;
2066 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2067 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2068 *state = VarState::DontWarn
2073 } else if is_loop(expr) || is_conditional(expr) {
2075 walk_expr(self, expr);
2078 } else if let ExprKind::Continue(_) = expr.kind {
2082 walk_expr(self, expr);
2084 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2085 NestedVisitorMap::None
2089 /// Checks whether a variable is initialized to zero at the start of a loop.
2090 struct InitializeVisitor<'a, 'tcx> {
2091 cx: &'a LateContext<'a, 'tcx>, // context reference
2092 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2096 depth: u32, // depth of conditional expressions
2100 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2101 type Map = Map<'tcx>;
2103 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2104 // Look for declarations of the variable
2105 if let StmtKind::Local(ref local) = stmt.kind {
2106 if local.pat.hir_id == self.var_id {
2107 if let PatKind::Binding(.., ident, _) = local.pat.kind {
2108 self.name = Some(ident.name);
2110 self.state = if let Some(ref init) = local.init {
2111 if is_integer_const(&self.cx, init, 0) {
2122 walk_stmt(self, stmt);
2125 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2126 if self.state == VarState::DontWarn {
2129 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2130 self.past_loop = true;
2133 // No need to visit expressions before the variable is
2135 if self.state == VarState::IncrOnce {
2139 // If node is the desired variable, see how it's used
2140 if var_def_id(self.cx, expr) == Some(self.var_id) {
2141 if let Some(parent) = get_parent_expr(self.cx, expr) {
2143 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2144 self.state = VarState::DontWarn;
2146 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2147 self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 {
2153 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2154 self.state = VarState::DontWarn
2161 self.state = VarState::DontWarn;
2164 } else if !self.past_loop && is_loop(expr) {
2165 self.state = VarState::DontWarn;
2167 } else if is_conditional(expr) {
2169 walk_expr(self, expr);
2173 walk_expr(self, expr);
2176 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2177 NestedVisitorMap::OnlyBodies(&self.cx.tcx.hir())
2181 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> Option<HirId> {
2182 if let ExprKind::Path(ref qpath) = expr.kind {
2183 let path_res = qpath_res(cx, qpath, expr.hir_id);
2184 if let Res::Local(node_id) = path_res {
2185 return Some(node_id);
2191 fn is_loop(expr: &Expr<'_>) -> bool {
2193 ExprKind::Loop(..) => true,
2198 fn is_conditional(expr: &Expr<'_>) -> bool {
2200 ExprKind::Match(..) => true,
2205 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2207 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2208 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2209 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2211 return is_loop_nested(cx, loop_expr, iter_expr)
2217 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2218 let mut id = loop_expr.hir_id;
2219 let iter_name = if let Some(name) = path_name(iter_expr) {
2225 let parent = cx.tcx.hir().get_parent_node(id);
2229 match cx.tcx.hir().find(parent) {
2230 Some(Node::Expr(expr)) => {
2231 if let ExprKind::Loop(..) = expr.kind {
2235 Some(Node::Block(block)) => {
2236 let mut block_visitor = LoopNestVisitor {
2238 iterator: iter_name,
2241 walk_block(&mut block_visitor, block);
2242 if block_visitor.nesting == RuledOut {
2246 Some(Node::Stmt(_)) => (),
2255 #[derive(PartialEq, Eq)]
2257 Unknown, // no nesting detected yet
2258 RuledOut, // the iterator is initialized or assigned within scope
2259 LookFurther, // no nesting detected, no further walk required
2262 use self::Nesting::{LookFurther, RuledOut, Unknown};
2264 struct LoopNestVisitor {
2270 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2271 type Map = Map<'tcx>;
2273 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2274 if stmt.hir_id == self.hir_id {
2275 self.nesting = LookFurther;
2276 } else if self.nesting == Unknown {
2277 walk_stmt(self, stmt);
2281 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2282 if self.nesting != Unknown {
2285 if expr.hir_id == self.hir_id {
2286 self.nesting = LookFurther;
2290 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2291 if match_var(path, self.iterator) {
2292 self.nesting = RuledOut;
2295 _ => walk_expr(self, expr),
2299 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2300 if self.nesting != Unknown {
2303 if let PatKind::Binding(.., span_name, _) = pat.kind {
2304 if self.iterator == span_name.name {
2305 self.nesting = RuledOut;
2312 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2313 NestedVisitorMap::None
2317 fn path_name(e: &Expr<'_>) -> Option<Name> {
2318 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2319 let segments = &path.segments;
2320 if segments.len() == 1 {
2321 return Some(segments[0].ident.name);
2327 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2328 if constant(cx, cx.tables, cond).is_some() {
2329 // A pure constant condition (e.g., `while false`) is not linted.
2333 let mut var_visitor = VarCollectorVisitor {
2335 ids: FxHashSet::default(),
2336 def_ids: FxHashMap::default(),
2339 var_visitor.visit_expr(cond);
2340 if var_visitor.skip {
2343 let used_in_condition = &var_visitor.ids;
2344 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2345 used_in_condition.is_disjoint(&used_mutably)
2349 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2351 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2352 has_break_or_return: false,
2354 has_break_or_return_visitor.visit_expr(expr);
2355 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2357 if no_cond_variable_mutated && !mutable_static_in_cond {
2360 WHILE_IMMUTABLE_CONDITION,
2362 "variables in the condition are not mutated in the loop body",
2364 db.note("this may lead to an infinite or to a never running loop");
2366 if has_break_or_return {
2367 db.note("this loop contains `return`s or `break`s");
2368 db.help("rewrite it as `if cond { loop { } }`");
2375 struct HasBreakOrReturnVisitor {
2376 has_break_or_return: bool,
2379 impl<'a, 'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2380 type Map = Map<'tcx>;
2382 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2383 if self.has_break_or_return {
2388 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2389 self.has_break_or_return = true;
2395 walk_expr(self, expr);
2398 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2399 NestedVisitorMap::None
2403 /// Collects the set of variables in an expression
2404 /// Stops analysis if a function call is found
2405 /// Note: In some cases such as `self`, there are no mutable annotation,
2406 /// All variables definition IDs are collected
2407 struct VarCollectorVisitor<'a, 'tcx> {
2408 cx: &'a LateContext<'a, 'tcx>,
2409 ids: FxHashSet<HirId>,
2410 def_ids: FxHashMap<def_id::DefId, bool>,
2414 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2415 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2417 if let ExprKind::Path(ref qpath) = ex.kind;
2418 if let QPath::Resolved(None, _) = *qpath;
2419 let res = qpath_res(self.cx, qpath, ex.hir_id);
2422 Res::Local(node_id) => {
2423 self.ids.insert(node_id);
2425 Res::Def(DefKind::Static, def_id) => {
2426 let mutable = self.cx.tcx.is_mutable_static(def_id);
2427 self.def_ids.insert(def_id, mutable);
2436 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2437 type Map = Map<'tcx>;
2439 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2441 ExprKind::Path(_) => self.insert_def_id(ex),
2442 // If there is any function/method call… we just stop analysis
2443 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2445 _ => walk_expr(self, ex),
2449 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2450 NestedVisitorMap::None
2454 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2456 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'a, 'tcx>) {
2458 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
2459 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].kind;
2460 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2461 if let Some(ref generic_args) = chain_method.args;
2462 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2464 let ty = cx.tables.node_type(ty.hir_id);
2465 if is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) ||
2466 match_type(cx, ty, &paths::VEC_DEQUE) ||
2467 match_type(cx, ty, &paths::BTREEMAP) ||
2468 match_type(cx, ty, &paths::HASHMAP) {
2469 if method.ident.name == sym!(len) {
2470 let span = shorten_needless_collect_span(expr);
2471 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2475 ".count()".to_string(),
2476 Applicability::MachineApplicable,
2480 if method.ident.name == sym!(is_empty) {
2481 let span = shorten_needless_collect_span(expr);
2482 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2486 ".next().is_none()".to_string(),
2487 Applicability::MachineApplicable,
2491 if method.ident.name == sym!(contains) {
2492 let contains_arg = snippet(cx, args[1].span, "??");
2493 let span = shorten_needless_collect_span(expr);
2494 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2495 let (arg, pred) = if contains_arg.starts_with('&') {
2496 ("x", &contains_arg[1..])
2498 ("&x", &*contains_arg)
2504 ".any(|{}| x == {})",
2507 Applicability::MachineApplicable,
2516 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
2518 if let ExprKind::MethodCall(_, _, ref args) = expr.kind;
2519 if let ExprKind::MethodCall(_, ref span, _) = args[0].kind;
2521 return expr.span.with_lo(span.lo() - BytePos(1));