1 use crate::consts::{constant, Constant};
2 use crate::reexport::Name;
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_lint, span_lint_and_help,
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;
15 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
16 use rustc_errors::Applicability;
17 use rustc_hir::def::{DefKind, Res};
18 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
20 def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, LoopSource,
21 MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
23 use rustc_infer::infer::TyCtxtInferExt;
24 use rustc_lint::{LateContext, LateLintPass, LintContext};
25 use rustc_middle::hir::map::Map;
26 use rustc_middle::lint::in_external_macro;
27 use rustc_middle::middle::region;
28 use rustc_middle::ty::{self, Ty};
29 use rustc_session::{declare_lint_pass, declare_tool_lint};
30 use rustc_span::source_map::Span;
31 use rustc_span::BytePos;
32 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase};
33 use std::iter::{once, Iterator};
36 declare_clippy_lint! {
37 /// **What it does:** Checks for for-loops that manually copy items between
38 /// slices that could be optimized by having a memcpy.
40 /// **Why is this bad?** It is not as fast as a memcpy.
42 /// **Known problems:** None.
46 /// # let src = vec![1];
47 /// # let mut dst = vec![0; 65];
48 /// for i in 0..src.len() {
49 /// dst[i + 64] = src[i];
52 /// Could be written as:
54 /// # let src = vec![1];
55 /// # let mut dst = vec![0; 65];
56 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
60 "manually copying items between slices"
63 declare_clippy_lint! {
64 /// **What it does:** Checks for looping over the range of `0..len` of some
65 /// collection just to get the values by index.
67 /// **Why is this bad?** Just iterating the collection itself makes the intent
68 /// more clear and is probably faster.
70 /// **Known problems:** None.
74 /// let vec = vec!['a', 'b', 'c'];
75 /// for i in 0..vec.len() {
76 /// println!("{}", vec[i]);
79 /// Could be written as:
81 /// let vec = vec!['a', 'b', 'c'];
83 /// println!("{}", i);
86 pub NEEDLESS_RANGE_LOOP,
88 "for-looping over a range of indices where an iterator over items would do"
91 declare_clippy_lint! {
92 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
93 /// suggests the latter.
95 /// **Why is this bad?** Readability.
97 /// **Known problems:** False negatives. We currently only warn on some known
102 /// // with `y` a `Vec` or slice:
103 /// # let y = vec![1];
104 /// for x in y.iter() {
108 /// can be rewritten to
110 /// # let y = vec![1];
115 pub EXPLICIT_ITER_LOOP,
117 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
120 declare_clippy_lint! {
121 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
122 /// suggests the latter.
124 /// **Why is this bad?** Readability.
126 /// **Known problems:** None
130 /// # let y = vec![1];
131 /// // with `y` a `Vec` or slice:
132 /// for x in y.into_iter() {
136 /// can be rewritten to
138 /// # let y = vec![1];
143 pub EXPLICIT_INTO_ITER_LOOP,
145 "for-looping over `_.into_iter()` when `_` would do"
148 declare_clippy_lint! {
149 /// **What it does:** Checks for loops on `x.next()`.
151 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
152 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
153 /// implements `IntoIterator`, so that possibly one value will be iterated,
154 /// leading to some hard to find bugs. No one will want to write such code
155 /// [except to win an Underhanded Rust
156 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
158 /// **Known problems:** None.
162 /// for x in y.next() {
168 "for-looping over `_.next()` which is probably not intended"
171 declare_clippy_lint! {
172 /// **What it does:** Checks for `for` loops over `Option` values.
174 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
177 /// **Known problems:** None.
181 /// for x in option {
188 /// if let Some(x) = option {
192 pub FOR_LOOP_OVER_OPTION,
194 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
197 declare_clippy_lint! {
198 /// **What it does:** Checks for `for` loops over `Result` values.
200 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
203 /// **Known problems:** None.
207 /// for x in result {
214 /// if let Ok(x) = result {
218 pub FOR_LOOP_OVER_RESULT,
220 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
223 declare_clippy_lint! {
224 /// **What it does:** Detects `loop + match` combinations that are easier
225 /// written as a `while let` loop.
227 /// **Why is this bad?** The `while let` loop is usually shorter and more
230 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
234 /// # let y = Some(1);
236 /// let x = match y {
240 /// // .. do something with x
242 /// // is easier written as
243 /// while let Some(x) = y {
244 /// // .. do something with x
249 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
252 declare_clippy_lint! {
253 /// **What it does:** Checks for functions collecting an iterator when collect
256 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
257 /// when this allocation may not be needed.
259 /// **Known problems:**
264 /// # let iterator = vec![1].into_iter();
265 /// let len = iterator.clone().collect::<Vec<_>>().len();
267 /// let len = iterator.count();
269 pub NEEDLESS_COLLECT,
271 "collecting an iterator when collect is not needed"
274 declare_clippy_lint! {
275 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
276 /// are constant and `x` is greater or equal to `y`, unless the range is
277 /// reversed or has a negative `.step_by(_)`.
279 /// **Why is it bad?** Such loops will either be skipped or loop until
280 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
283 /// **Known problems:** The lint cannot catch loops over dynamically defined
284 /// ranges. Doing this would require simulating all possible inputs and code
285 /// paths through the program, which would be complex and error-prone.
289 /// for x in 5..10 - 5 {
291 /// } // oops, stray `-`
293 pub REVERSE_RANGE_LOOP,
295 "iteration over an empty range, such as `10..0` or `5..5`"
298 declare_clippy_lint! {
299 /// **What it does:** Checks `for` loops over slices with an explicit counter
300 /// and suggests the use of `.enumerate()`.
302 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
303 /// declutters the code and may be faster in some instances.
305 /// **Known problems:** None.
309 /// # let v = vec![1];
310 /// # fn bar(bar: usize, baz: usize) {}
317 /// Could be written as
319 /// # let v = vec![1];
320 /// # fn bar(bar: usize, baz: usize) {}
321 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
323 pub EXPLICIT_COUNTER_LOOP,
325 "for-looping with an explicit counter when `_.enumerate()` would do"
328 declare_clippy_lint! {
329 /// **What it does:** Checks for empty `loop` expressions.
331 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
332 /// anything. Think of the environment and either block on something or at least
333 /// make the thread sleep for some microseconds.
335 /// **Known problems:** None.
343 "empty `loop {}`, which should block or sleep"
346 declare_clippy_lint! {
347 /// **What it does:** Checks for `while let` expressions on iterators.
349 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
350 /// the intent better.
352 /// **Known problems:** None.
356 /// while let Some(val) = iter() {
360 pub WHILE_LET_ON_ITERATOR,
362 "using a while-let loop instead of a for loop on an iterator"
365 declare_clippy_lint! {
366 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
367 /// ignoring either the keys or values.
369 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
370 /// can be used to express that don't need the values or keys.
372 /// **Known problems:** None.
376 /// for (k, _) in &map {
381 /// could be replaced by
384 /// for k in map.keys() {
390 "looping on a map using `iter` when `keys` or `values` would do"
393 declare_clippy_lint! {
394 /// **What it does:** Checks for loops that will always `break`, `return` or
395 /// `continue` an outer loop.
397 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
400 /// **Known problems:** None
411 "any loop that will always `break` or `return`"
414 declare_clippy_lint! {
415 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
417 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
419 /// **Known problems:** None
423 /// let mut foo = 42;
424 /// for i in 0..foo {
426 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
431 "for loop over a range where one of the bounds is a mutable variable"
434 declare_clippy_lint! {
435 /// **What it does:** Checks whether variables used within while loop condition
436 /// can be (and are) mutated in the body.
438 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
439 /// will lead to an infinite loop.
441 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
442 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
443 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
449 /// println!("let me loop forever!");
452 pub WHILE_IMMUTABLE_CONDITION,
454 "variables used within while expression are not mutated in the body"
457 declare_lint_pass!(Loops => [
461 EXPLICIT_INTO_ITER_LOOP,
463 FOR_LOOP_OVER_RESULT,
464 FOR_LOOP_OVER_OPTION,
468 EXPLICIT_COUNTER_LOOP,
470 WHILE_LET_ON_ITERATOR,
474 WHILE_IMMUTABLE_CONDITION,
477 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
478 #[allow(clippy::too_many_lines)]
479 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
480 if let Some((pat, arg, body)) = higher::for_loop(expr) {
481 // we don't want to check expanded macros
482 // this check is not at the top of the function
483 // since higher::for_loop expressions are marked as expansions
484 if body.span.from_expansion() {
487 check_for_loop(cx, pat, arg, body, expr);
490 // we don't want to check expanded macros
491 if expr.span.from_expansion() {
495 // check for never_loop
496 if let ExprKind::Loop(ref block, _, _) = expr.kind {
497 match never_loop_block(block, expr.hir_id) {
498 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
499 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
503 // check for `loop { if let {} else break }` that could be `while let`
504 // (also matches an explicit "match" instead of "if let")
505 // (even if the "match" or "if let" is used for declaration)
506 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
507 // also check for empty `loop {}` statements
508 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) {
513 "empty `loop {}` detected. You may want to either use `panic!()` or add \
514 `std::thread::sleep(..);` to the loop body.",
518 // extract the expression from the first statement (if any) in a block
519 let inner_stmt_expr = extract_expr_from_first_stmt(block);
520 // or extract the first expression (if any) from the block
521 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
522 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
523 // ensure "if let" compatible match structure
525 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
527 && arms[0].guard.is_none()
528 && arms[1].guard.is_none()
529 && is_simple_break_expr(&arms[1].body)
531 if in_external_macro(cx.sess(), expr.span) {
535 // NOTE: we used to build a body here instead of using
536 // ellipsis, this was removed because:
537 // 1) it was ugly with big bodies;
538 // 2) it was not indented properly;
539 // 3) it wasn’t very smart (see #675).
540 let mut applicability = Applicability::HasPlaceholders;
545 "this loop could be written as a `while let` loop",
548 "while let {} = {} {{ .. }}",
549 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
550 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
561 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
562 let pat = &arms[0].pat.kind;
564 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
565 &ExprKind::MethodCall(ref method_path, _, ref method_args),
566 ) = (pat, &match_expr.kind)
568 let iter_expr = &method_args[0];
570 // Don't lint when the iterator is recreated on every iteration
572 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
573 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
574 if implements_trait(cx, cx.tables.expr_ty(iter_expr), iter_def_id, &[]);
580 let lhs_constructor = last_path_segment(qpath);
581 if method_path.ident.name == sym!(next)
582 && match_trait_method(cx, match_expr, &paths::ITERATOR)
583 && lhs_constructor.ident.name == sym!(Some)
584 && (pat_args.is_empty()
585 || !is_refutable(cx, &pat_args[0])
586 && !is_used_inside(cx, iter_expr, &arms[0].body)
587 && !is_iterator_used_after_while_let(cx, iter_expr)
588 && !is_nested(cx, expr, &method_args[0]))
590 let mut applicability = Applicability::MachineApplicable;
591 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
592 let loop_var = if pat_args.is_empty() {
595 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
599 WHILE_LET_ON_ITERATOR,
600 expr.span.with_hi(match_expr.span.hi()),
601 "this loop could be written as a `for` loop",
603 format!("for {} in {}", loop_var, iterator),
610 if let Some((cond, body)) = higher::while_loop(&expr) {
611 check_infinite_loop(cx, cond, body);
614 check_needless_collect(expr, cx);
618 enum NeverLoopResult {
619 // A break/return always get triggered but not necessarily for the main loop.
621 // A continue may occur for the main loop.
627 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
629 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
630 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
634 // Combine two results for parts that are called in order.
636 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
638 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
639 NeverLoopResult::Otherwise => second,
643 // Combine two results where both parts are called but not necessarily in order.
645 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
646 match (left, right) {
647 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
648 NeverLoopResult::MayContinueMainLoop
650 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
651 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
655 // Combine two results where only one of the part may have been executed.
657 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
659 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
660 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
661 NeverLoopResult::MayContinueMainLoop
663 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
667 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
668 let stmts = block.stmts.iter().map(stmt_to_expr);
669 let expr = once(block.expr.as_deref());
670 let mut iter = stmts.chain(expr).filter_map(|e| e);
671 never_loop_expr_seq(&mut iter, main_loop_id)
674 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
676 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
677 StmtKind::Local(ref local) => local.init.as_deref(),
682 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
685 | ExprKind::Unary(_, ref e)
686 | ExprKind::Cast(ref e, _)
687 | ExprKind::Type(ref e, _)
688 | ExprKind::Field(ref e, _)
689 | ExprKind::AddrOf(_, _, ref e)
690 | ExprKind::Struct(_, _, Some(ref e))
691 | ExprKind::Repeat(ref e, _)
692 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
693 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
694 never_loop_expr_all(&mut es.iter(), main_loop_id)
696 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
697 ExprKind::Binary(_, ref e1, ref e2)
698 | ExprKind::Assign(ref e1, ref e2, _)
699 | ExprKind::AssignOp(_, ref e1, ref e2)
700 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
701 ExprKind::Loop(ref b, _, _) => {
702 // Break can come from the inner loop so remove them.
703 absorb_break(&never_loop_block(b, main_loop_id))
705 ExprKind::Match(ref e, ref arms, _) => {
706 let e = never_loop_expr(e, main_loop_id);
710 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
714 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
715 ExprKind::Continue(d) => {
718 .expect("target ID can only be missing in the presence of compilation errors");
719 if id == main_loop_id {
720 NeverLoopResult::MayContinueMainLoop
722 NeverLoopResult::AlwaysBreak
725 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
726 if let Some(ref e) = *e {
727 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
729 NeverLoopResult::AlwaysBreak
732 ExprKind::Struct(_, _, None)
733 | ExprKind::Yield(_, _)
734 | ExprKind::Closure(_, _, _, _, _)
735 | ExprKind::LlvmInlineAsm(_)
738 | ExprKind::Err => NeverLoopResult::Otherwise,
742 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
743 es.map(|e| never_loop_expr(e, main_loop_id))
744 .fold(NeverLoopResult::Otherwise, combine_seq)
747 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
748 es.map(|e| never_loop_expr(e, main_loop_id))
749 .fold(NeverLoopResult::Otherwise, combine_both)
752 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
753 e.map(|e| never_loop_expr(e, main_loop_id))
754 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
757 fn check_for_loop<'a, 'tcx>(
758 cx: &LateContext<'a, 'tcx>,
761 body: &'tcx Expr<'_>,
762 expr: &'tcx Expr<'_>,
764 check_for_loop_range(cx, pat, arg, body, expr);
765 check_for_loop_reverse_range(cx, arg, expr);
766 check_for_loop_arg(cx, pat, arg, expr);
767 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
768 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
769 check_for_mut_range_bound(cx, arg, body);
770 detect_manual_memcpy(cx, pat, arg, body, expr);
773 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
775 if let ExprKind::Path(ref qpath) = expr.kind;
776 if let QPath::Resolved(None, ref path) = *qpath;
777 if path.segments.len() == 1;
778 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
795 fn negative(s: String) -> Self {
796 Self { value: s, negate: true }
799 fn positive(s: String) -> Self {
807 struct FixedOffsetVar {
812 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
813 let is_slice = match ty.kind {
814 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
815 ty::Slice(..) | ty::Array(..) => true,
819 is_slice || is_type_diagnostic_item(cx, ty, sym!(vec_type)) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
822 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId) -> Option<FixedOffsetVar> {
823 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr<'_>, var: HirId) -> Option<String> {
825 ExprKind::Lit(ref l) => match l.node {
826 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
829 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
834 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind {
835 let ty = cx.tables.expr_ty(seqexpr);
836 if !is_slice_like(cx, ty) {
840 let offset = match idx.kind {
841 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
843 let offset_opt = if same_var(cx, lhs, var) {
844 extract_offset(cx, rhs, var)
845 } else if same_var(cx, rhs, var) {
846 extract_offset(cx, lhs, var)
851 offset_opt.map(Offset::positive)
853 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
856 ExprKind::Path(..) => {
857 if same_var(cx, idx, var) {
858 Some(Offset::positive("0".into()))
866 offset.map(|o| FixedOffsetVar {
867 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
875 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
876 cx: &LateContext<'a, 'tcx>,
879 ) -> Option<FixedOffsetVar> {
881 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
882 if method.ident.name == sym!(clone);
884 if let Some(arg) = args.get(0);
886 return get_fixed_offset_var(cx, arg, var);
890 get_fixed_offset_var(cx, expr, var)
893 fn get_indexed_assignments<'a, 'tcx>(
894 cx: &LateContext<'a, 'tcx>,
897 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
898 fn get_assignment<'a, 'tcx>(
899 cx: &LateContext<'a, 'tcx>,
902 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
903 if let ExprKind::Assign(ref lhs, ref rhs, _) = e.kind {
905 get_fixed_offset_var(cx, lhs, var),
906 fetch_cloned_fixed_offset_var(cx, rhs, var),
908 (Some(offset_left), Some(offset_right)) => {
909 // Source and destination must be different
910 if offset_left.var_name == offset_right.var_name {
913 Some((offset_left, offset_right))
923 if let ExprKind::Block(ref b, _) = body.kind {
925 ref stmts, ref expr, ..
930 .map(|stmt| match stmt.kind {
931 StmtKind::Local(..) | StmtKind::Item(..) => None,
932 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
934 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
936 .collect::<Option<Vec<_>>>()
939 get_assignment(cx, body, var).into_iter().collect()
943 /// Checks for for loops that sequentially copy items from one slice-like
944 /// object to another.
945 fn detect_manual_memcpy<'a, 'tcx>(
946 cx: &LateContext<'a, 'tcx>,
949 body: &'tcx Expr<'_>,
950 expr: &'tcx Expr<'_>,
952 if let Some(higher::Range {
956 }) = higher::range(cx, arg)
958 // the var must be a single name
959 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
960 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
961 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
962 ("0", _, "0", _) => "".into(),
963 ("0", _, x, false) | (x, false, "0", false) => x.into(),
964 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
965 (x, false, y, false) => format!("({} + {})", x, y),
966 (x, false, y, true) => {
970 format!("({} - {})", x, y)
973 (x, true, y, false) => {
977 format!("({} - {})", y, x)
980 (x, true, y, true) => format!("-({} + {})", x, y),
984 let print_limit = |end: &Option<&Expr<'_>>, offset: Offset, var_name: &str| {
985 if let Some(end) = *end {
987 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.kind;
988 if method.ident.name == sym!(len);
989 if len_args.len() == 1;
990 if let Some(arg) = len_args.get(0);
991 if snippet(cx, arg.span, "??") == var_name;
993 return if offset.negate {
994 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
1001 let end_str = match limits {
1002 ast::RangeLimits::Closed => {
1003 let end = sugg::Sugg::hir(cx, end, "<count>");
1004 format!("{}", end + sugg::ONE)
1006 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1009 print_sum(&Offset::positive(end_str), &offset)
1015 // The only statements in the for loops can be indexed assignments from
1016 // indexed retrievals.
1017 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1019 let big_sugg = manual_copies
1021 .map(|(dst_var, src_var)| {
1022 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1023 let dst_offset = print_sum(&start_str, &dst_var.offset);
1024 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1025 let src_offset = print_sum(&start_str, &src_var.offset);
1026 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1027 let dst = if dst_offset == "" && dst_limit == "" {
1030 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1034 "{}.clone_from_slice(&{}[{}..{}])",
1035 dst, src_var.var_name, src_offset, src_limit
1040 if !big_sugg.is_empty() {
1045 "it looks like you're manually copying between slices",
1046 "try replacing the loop by",
1048 Applicability::Unspecified,
1055 /// Checks for looping over a range and then indexing a sequence with it.
1056 /// The iteratee must be a range literal.
1057 #[allow(clippy::too_many_lines)]
1058 fn check_for_loop_range<'a, 'tcx>(
1059 cx: &LateContext<'a, 'tcx>,
1061 arg: &'tcx Expr<'_>,
1062 body: &'tcx Expr<'_>,
1063 expr: &'tcx Expr<'_>,
1065 if let Some(higher::Range {
1069 }) = higher::range(cx, arg)
1071 // the var must be a single name
1072 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1073 let mut visitor = VarVisitor {
1076 indexed_mut: FxHashSet::default(),
1077 indexed_indirectly: FxHashMap::default(),
1078 indexed_directly: FxHashMap::default(),
1079 referenced: FxHashSet::default(),
1081 prefer_mutable: false,
1083 walk_expr(&mut visitor, body);
1085 // linting condition: we only indexed one variable, and indexed it directly
1086 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1087 let (indexed, (indexed_extent, indexed_ty)) = visitor
1091 .expect("already checked that we have exactly 1 element");
1093 // ensure that the indexed variable was declared before the loop, see #601
1094 if let Some(indexed_extent) = indexed_extent {
1095 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1096 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1097 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1098 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1099 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1104 // don't lint if the container that is indexed does not have .iter() method
1105 let has_iter = has_iter_method(cx, indexed_ty);
1106 if has_iter.is_none() {
1110 // don't lint if the container that is indexed into is also used without
1112 if visitor.referenced.contains(&indexed) {
1116 let starts_at_zero = is_integer_const(cx, start, 0);
1118 let skip = if starts_at_zero {
1121 format!(".skip({})", snippet(cx, start.span, ".."))
1124 let mut end_is_start_plus_val = false;
1126 let take = if let Some(end) = *end {
1127 let mut take_expr = end;
1129 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1130 if let BinOpKind::Add = op.node {
1131 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1132 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1134 if start_equal_left {
1136 } else if start_equal_right {
1140 end_is_start_plus_val = start_equal_left | start_equal_right;
1144 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1148 ast::RangeLimits::Closed => {
1149 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1150 format!(".take({})", take_expr + sugg::ONE)
1152 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1159 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1160 ("mut ", "iter_mut")
1165 let take_is_empty = take.is_empty();
1166 let mut method_1 = take;
1167 let mut method_2 = skip;
1169 if end_is_start_plus_val {
1170 mem::swap(&mut method_1, &mut method_2);
1173 if visitor.nonindex {
1176 NEEDLESS_RANGE_LOOP,
1178 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1182 "consider using an iterator".to_string(),
1184 (pat.span, format!("({}, <item>)", ident.name)),
1187 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1194 let repl = if starts_at_zero && take_is_empty {
1195 format!("&{}{}", ref_mut, indexed)
1197 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1202 NEEDLESS_RANGE_LOOP,
1205 "the loop variable `{}` is only used to index `{}`.",
1211 "consider using an iterator".to_string(),
1212 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1222 fn is_len_call(expr: &Expr<'_>, var: Name) -> bool {
1224 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.kind;
1225 if len_args.len() == 1;
1226 if method.ident.name == sym!(len);
1227 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1228 if path.segments.len() == 1;
1229 if path.segments[0].ident.name == var;
1238 fn is_end_eq_array_len<'tcx>(
1239 cx: &LateContext<'_, 'tcx>,
1241 limits: ast::RangeLimits,
1242 indexed_ty: Ty<'tcx>,
1245 if let ExprKind::Lit(ref lit) = end.kind;
1246 if let ast::LitKind::Int(end_int, _) = lit.node;
1247 if let ty::Array(_, arr_len_const) = indexed_ty.kind;
1248 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1250 return match limits {
1251 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1252 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1260 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
1261 // if this for loop is iterating over a two-sided range...
1262 if let Some(higher::Range {
1266 }) = higher::range(cx, arg)
1268 // ...and both sides are compile-time constant integers...
1269 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1270 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1271 // ...and the start index is greater than the end index,
1272 // this loop will never run. This is often confusing for developers
1273 // who think that this will iterate from the larger value to the
1275 let ty = cx.tables.expr_ty(start);
1276 let (sup, eq) = match (start_idx, end_idx) {
1277 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1279 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1280 ty::Uint(_) => start_idx > end_idx,
1283 start_idx == end_idx,
1285 _ => (false, false),
1289 let start_snippet = snippet(cx, start.span, "_");
1290 let end_snippet = snippet(cx, end.span, "_");
1291 let dots = if limits == ast::RangeLimits::Closed {
1301 "this range is empty so this for loop will never run",
1303 diag.span_suggestion(
1305 "consider using the following if you are attempting to iterate over this \
1308 "({end}{dots}{start}).rev()",
1311 start = start_snippet
1313 Applicability::MaybeIncorrect,
1317 } else if eq && limits != ast::RangeLimits::Closed {
1318 // if they are equal, it's also problematic - this loop
1324 "this range is empty so this for loop will never run",
1332 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1333 let mut applicability = Applicability::MachineApplicable;
1334 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1335 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1340 "it is more concise to loop over references to containers instead of using explicit \
1342 "to write this more concisely, try",
1343 format!("&{}{}", muta, object),
1348 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1349 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1350 if let ExprKind::MethodCall(ref method, _, ref args) = arg.kind {
1351 // just the receiver, no arguments
1352 if args.len() == 1 {
1353 let method_name = &*method.ident.as_str();
1354 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1355 if method_name == "iter" || method_name == "iter_mut" {
1356 if is_ref_iterable_type(cx, &args[0]) {
1357 lint_iter_method(cx, args, arg, method_name);
1359 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1360 let receiver_ty = cx.tables.expr_ty(&args[0]);
1361 let receiver_ty_adjusted = cx.tables.expr_ty_adjusted(&args[0]);
1362 if same_tys(cx, receiver_ty, receiver_ty_adjusted) {
1363 let mut applicability = Applicability::MachineApplicable;
1364 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1367 EXPLICIT_INTO_ITER_LOOP,
1369 "it is more concise to loop over containers instead of using explicit \
1371 "to write this more concisely, try",
1376 let ref_receiver_ty = cx.tcx.mk_ref(
1377 cx.tcx.lifetimes.re_erased,
1380 mutbl: Mutability::Not,
1383 if same_tys(cx, receiver_ty_adjusted, ref_receiver_ty) {
1384 lint_iter_method(cx, args, arg, method_name)
1387 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1392 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1393 probably not what you want",
1395 next_loop_linted = true;
1399 if !next_loop_linted {
1400 check_arg_type(cx, pat, arg);
1404 /// Checks for `for` loops over `Option`s and `Result`s.
1405 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1406 let ty = cx.tables.expr_ty(arg);
1407 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1410 FOR_LOOP_OVER_OPTION,
1413 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1414 `if let` statement.",
1415 snippet(cx, arg.span, "_")
1419 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1420 snippet(cx, pat.span, "_"),
1421 snippet(cx, arg.span, "_")
1424 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1427 FOR_LOOP_OVER_RESULT,
1430 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1431 `if let` statement.",
1432 snippet(cx, arg.span, "_")
1436 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1437 snippet(cx, pat.span, "_"),
1438 snippet(cx, arg.span, "_")
1444 fn check_for_loop_explicit_counter<'a, 'tcx>(
1445 cx: &LateContext<'a, 'tcx>,
1447 arg: &'tcx Expr<'_>,
1448 body: &'tcx Expr<'_>,
1449 expr: &'tcx Expr<'_>,
1451 // Look for variables that are incremented once per loop iteration.
1452 let mut visitor = IncrementVisitor {
1454 states: FxHashMap::default(),
1458 walk_expr(&mut visitor, body);
1460 // For each candidate, check the parent block to see if
1461 // it's initialized to zero at the start of the loop.
1462 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1463 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1464 let mut visitor2 = InitializeVisitor {
1468 state: VarState::IncrOnce,
1473 walk_block(&mut visitor2, block);
1475 if visitor2.state == VarState::Warn {
1476 if let Some(name) = visitor2.name {
1477 let mut applicability = Applicability::MachineApplicable;
1479 // for some reason this is the only way to get the `Span`
1480 // of the entire `for` loop
1481 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1489 EXPLICIT_COUNTER_LOOP,
1490 for_span.with_hi(arg.span.hi()),
1491 &format!("the variable `{}` is used as a loop counter.", name),
1494 "for ({}, {}) in {}.enumerate()",
1496 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1497 make_iterator_snippet(cx, arg, &mut applicability),
1507 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1508 /// actual `Iterator` that the loop uses.
1509 fn make_iterator_snippet(cx: &LateContext<'_, '_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1510 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR)
1511 .map_or(false, |id| implements_trait(cx, cx.tables.expr_ty(arg), id, &[]));
1515 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1518 // (&x).into_iter() ==> x.iter()
1519 // (&mut x).into_iter() ==> x.iter_mut()
1521 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1522 if has_iter_method(cx, cx.tables.expr_ty(&arg_inner)).is_some() =>
1524 let meth_name = match mutability {
1525 Mutability::Mut => "iter_mut",
1526 Mutability::Not => "iter",
1530 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1536 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1542 /// Checks for the `FOR_KV_MAP` lint.
1543 fn check_for_loop_over_map_kv<'a, 'tcx>(
1544 cx: &LateContext<'a, 'tcx>,
1546 arg: &'tcx Expr<'_>,
1547 body: &'tcx Expr<'_>,
1548 expr: &'tcx Expr<'_>,
1550 let pat_span = pat.span;
1552 if let PatKind::Tuple(ref pat, _) = pat.kind {
1554 let arg_span = arg.span;
1555 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).kind {
1556 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1557 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1558 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1563 let mutbl = match mutbl {
1564 Mutability::Not => "",
1565 Mutability::Mut => "_mut",
1567 let arg = match arg.kind {
1568 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1572 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1577 &format!("you seem to want to iterate on a map's {}s", kind),
1579 let map = sugg::Sugg::hir(cx, arg, "map");
1582 "use the corresponding method".into(),
1584 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1585 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1595 struct MutatePairDelegate {
1596 hir_id_low: Option<HirId>,
1597 hir_id_high: Option<HirId>,
1598 span_low: Option<Span>,
1599 span_high: Option<Span>,
1602 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1603 fn consume(&mut self, _: &Place<'tcx>, _: ConsumeMode) {}
1605 fn borrow(&mut self, cmt: &Place<'tcx>, bk: ty::BorrowKind) {
1606 if let ty::BorrowKind::MutBorrow = bk {
1607 if let PlaceBase::Local(id) = cmt.base {
1608 if Some(id) == self.hir_id_low {
1609 self.span_low = Some(cmt.span)
1611 if Some(id) == self.hir_id_high {
1612 self.span_high = Some(cmt.span)
1618 fn mutate(&mut self, cmt: &Place<'tcx>) {
1619 if let PlaceBase::Local(id) = cmt.base {
1620 if Some(id) == self.hir_id_low {
1621 self.span_low = Some(cmt.span)
1623 if Some(id) == self.hir_id_high {
1624 self.span_high = Some(cmt.span)
1630 impl<'tcx> MutatePairDelegate {
1631 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1632 (self.span_low, self.span_high)
1636 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr<'_>, body: &Expr<'_>) {
1637 if let Some(higher::Range {
1641 }) = higher::range(cx, arg)
1643 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1644 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1645 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1646 mut_warn_with_span(cx, span_low);
1647 mut_warn_with_span(cx, span_high);
1652 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1653 if let Some(sp) = span {
1658 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1663 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr<'_>) -> Option<HirId> {
1665 if let ExprKind::Path(ref qpath) = bound.kind;
1666 if let QPath::Resolved(None, _) = *qpath;
1668 let res = qpath_res(cx, qpath, bound.hir_id);
1669 if let Res::Local(hir_id) = res {
1670 let node_str = cx.tcx.hir().get(hir_id);
1672 if let Node::Binding(pat) = node_str;
1673 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1674 if let BindingAnnotation::Mutable = bind_ann;
1676 return Some(hir_id);
1685 fn check_for_mutation(
1686 cx: &LateContext<'_, '_>,
1688 bound_ids: &[Option<HirId>],
1689 ) -> (Option<Span>, Option<Span>) {
1690 let mut delegate = MutatePairDelegate {
1691 hir_id_low: bound_ids[0],
1692 hir_id_high: bound_ids[1],
1696 let def_id = body.hir_id.owner.to_def_id();
1697 cx.tcx.infer_ctxt().enter(|infcx| {
1698 ExprUseVisitor::new(&mut delegate, &infcx, def_id.expect_local(), cx.param_env, cx.tables).walk_expr(body);
1700 delegate.mutation_span()
1703 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1704 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
1706 PatKind::Wild => true,
1707 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
1712 struct LocalUsedVisitor<'a, 'tcx> {
1713 cx: &'a LateContext<'a, 'tcx>,
1718 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1719 type Map = Map<'tcx>;
1721 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1722 if same_var(self.cx, expr, self.local) {
1725 walk_expr(self, expr);
1729 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1730 NestedVisitorMap::None
1734 struct VarVisitor<'a, 'tcx> {
1735 /// context reference
1736 cx: &'a LateContext<'a, 'tcx>,
1737 /// var name to look for as index
1739 /// indexed variables that are used mutably
1740 indexed_mut: FxHashSet<Name>,
1741 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1742 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1743 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1744 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1745 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1746 /// Any names that are used outside an index operation.
1747 /// Used to detect things like `&mut vec` used together with `vec[i]`
1748 referenced: FxHashSet<Name>,
1749 /// has the loop variable been used in expressions other than the index of
1752 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1753 /// takes `&mut self`
1754 prefer_mutable: bool,
1757 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1758 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
1760 // the indexed container is referenced by a name
1761 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
1762 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1763 if seqvar.segments.len() == 1;
1765 let index_used_directly = same_var(self.cx, idx, self.var);
1766 let indexed_indirectly = {
1767 let mut used_visitor = LocalUsedVisitor {
1772 walk_expr(&mut used_visitor, idx);
1776 if indexed_indirectly || index_used_directly {
1777 if self.prefer_mutable {
1778 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1780 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
1782 Res::Local(hir_id) => {
1783 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1784 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1785 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1786 if indexed_indirectly {
1787 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1789 if index_used_directly {
1790 self.indexed_directly.insert(
1791 seqvar.segments[0].ident.name,
1792 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1795 return false; // no need to walk further *on the variable*
1797 Res::Def(DefKind::Static | DefKind::Const, ..) => {
1798 if indexed_indirectly {
1799 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1801 if index_used_directly {
1802 self.indexed_directly.insert(
1803 seqvar.segments[0].ident.name,
1804 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1807 return false; // no need to walk further *on the variable*
1818 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1819 type Map = Map<'tcx>;
1821 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1824 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.kind;
1825 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1826 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1827 if !self.check(&args[1], &args[0], expr);
1833 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
1834 if !self.check(idx, seqexpr, expr);
1839 // directly using a variable
1840 if let ExprKind::Path(ref qpath) = expr.kind;
1841 if let QPath::Resolved(None, ref path) = *qpath;
1842 if path.segments.len() == 1;
1844 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
1845 if local_id == self.var {
1846 self.nonindex = true;
1848 // not the correct variable, but still a variable
1849 self.referenced.insert(path.segments[0].ident.name);
1855 let old = self.prefer_mutable;
1857 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
1858 self.prefer_mutable = true;
1859 self.visit_expr(lhs);
1860 self.prefer_mutable = false;
1861 self.visit_expr(rhs);
1863 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
1864 if mutbl == Mutability::Mut {
1865 self.prefer_mutable = true;
1867 self.visit_expr(expr);
1869 ExprKind::Call(ref f, args) => {
1872 let ty = self.cx.tables.expr_ty_adjusted(expr);
1873 self.prefer_mutable = false;
1874 if let ty::Ref(_, _, mutbl) = ty.kind {
1875 if mutbl == Mutability::Mut {
1876 self.prefer_mutable = true;
1879 self.visit_expr(expr);
1882 ExprKind::MethodCall(_, _, args) => {
1883 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1884 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1885 self.prefer_mutable = false;
1886 if let ty::Ref(_, _, mutbl) = ty.kind {
1887 if mutbl == Mutability::Mut {
1888 self.prefer_mutable = true;
1891 self.visit_expr(expr);
1894 ExprKind::Closure(_, _, body_id, ..) => {
1895 let body = self.cx.tcx.hir().body(body_id);
1896 self.visit_expr(&body.value);
1898 _ => walk_expr(self, expr),
1900 self.prefer_mutable = old;
1902 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1903 NestedVisitorMap::None
1907 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
1908 let def_id = match var_def_id(cx, expr) {
1910 None => return false,
1912 if let Some(used_mutably) = mutated_variables(container, cx) {
1913 if used_mutably.contains(&def_id) {
1920 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
1921 let def_id = match var_def_id(cx, iter_expr) {
1923 None => return false,
1925 let mut visitor = VarUsedAfterLoopVisitor {
1928 iter_expr_id: iter_expr.hir_id,
1929 past_while_let: false,
1930 var_used_after_while_let: false,
1932 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1933 walk_block(&mut visitor, enclosing_block);
1935 visitor.var_used_after_while_let
1938 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1939 cx: &'a LateContext<'a, 'tcx>,
1941 iter_expr_id: HirId,
1942 past_while_let: bool,
1943 var_used_after_while_let: bool,
1946 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1947 type Map = Map<'tcx>;
1949 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1950 if self.past_while_let {
1951 if Some(self.def_id) == var_def_id(self.cx, expr) {
1952 self.var_used_after_while_let = true;
1954 } else if self.iter_expr_id == expr.hir_id {
1955 self.past_while_let = true;
1957 walk_expr(self, expr);
1959 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1960 NestedVisitorMap::None
1964 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1965 /// for `&T` and `&mut T`, such as `Vec`.
1967 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr<'_>) -> bool {
1968 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1969 // will allow further borrows afterwards
1970 let ty = cx.tables.expr_ty(e);
1971 is_iterable_array(ty, cx) ||
1972 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
1973 match_type(cx, ty, &paths::LINKED_LIST) ||
1974 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
1975 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
1976 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
1977 match_type(cx, ty, &paths::BINARY_HEAP) ||
1978 match_type(cx, ty, &paths::BTREEMAP) ||
1979 match_type(cx, ty, &paths::BTREESET)
1982 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1983 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1985 ty::Array(_, n) => {
1986 if let Some(val) = n.try_eval_usize(cx.tcx, cx.param_env) {
1987 (0..=32).contains(&val)
1996 /// If a block begins with a statement (possibly a `let` binding) and has an
1997 /// expression, return it.
1998 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
1999 if block.stmts.is_empty() {
2002 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2003 if let Some(expr) = local.init {
2013 /// If a block begins with an expression (with or without semicolon), return it.
2014 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2016 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2017 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2018 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2019 StmtKind::Local(..) | StmtKind::Item(..) => None,
2025 /// Returns `true` if expr contains a single break expr without destination label
2027 /// passed expression. The expression may be within a block.
2028 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2030 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2031 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2036 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2037 // incremented exactly once in the loop body, and initialized to zero
2038 // at the start of the loop.
2039 #[derive(Debug, PartialEq)]
2041 Initial, // Not examined yet
2042 IncrOnce, // Incremented exactly once, may be a loop counter
2043 Declared, // Declared but not (yet) initialized to zero
2048 /// Scan a for loop for variables that are incremented exactly once.
2049 struct IncrementVisitor<'a, 'tcx> {
2050 cx: &'a LateContext<'a, 'tcx>, // context reference
2051 states: FxHashMap<HirId, VarState>, // incremented variables
2052 depth: u32, // depth of conditional expressions
2056 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2057 type Map = Map<'tcx>;
2059 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2064 // If node is a variable
2065 if let Some(def_id) = var_def_id(self.cx, expr) {
2066 if let Some(parent) = get_parent_expr(self.cx, expr) {
2067 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2070 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2071 if lhs.hir_id == expr.hir_id {
2072 if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) {
2073 *state = match *state {
2074 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2075 _ => VarState::DontWarn,
2078 // Assigned some other value
2079 *state = VarState::DontWarn;
2083 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2084 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2085 *state = VarState::DontWarn
2090 } else if is_loop(expr) || is_conditional(expr) {
2092 walk_expr(self, expr);
2095 } else if let ExprKind::Continue(_) = expr.kind {
2099 walk_expr(self, expr);
2101 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2102 NestedVisitorMap::None
2106 /// Checks whether a variable is initialized to zero at the start of a loop.
2107 struct InitializeVisitor<'a, 'tcx> {
2108 cx: &'a LateContext<'a, 'tcx>, // context reference
2109 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2113 depth: u32, // depth of conditional expressions
2117 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2118 type Map = Map<'tcx>;
2120 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2121 // Look for declarations of the variable
2122 if let StmtKind::Local(ref local) = stmt.kind {
2123 if local.pat.hir_id == self.var_id {
2124 if let PatKind::Binding(.., ident, _) = local.pat.kind {
2125 self.name = Some(ident.name);
2127 self.state = if let Some(ref init) = local.init {
2128 if is_integer_const(&self.cx, init, 0) {
2139 walk_stmt(self, stmt);
2142 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2143 if self.state == VarState::DontWarn {
2146 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2147 self.past_loop = true;
2150 // No need to visit expressions before the variable is
2152 if self.state == VarState::IncrOnce {
2156 // If node is the desired variable, see how it's used
2157 if var_def_id(self.cx, expr) == Some(self.var_id) {
2158 if let Some(parent) = get_parent_expr(self.cx, expr) {
2160 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2161 self.state = VarState::DontWarn;
2163 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2164 self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 {
2170 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2171 self.state = VarState::DontWarn
2178 self.state = VarState::DontWarn;
2181 } else if !self.past_loop && is_loop(expr) {
2182 self.state = VarState::DontWarn;
2184 } else if is_conditional(expr) {
2186 walk_expr(self, expr);
2190 walk_expr(self, expr);
2193 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2194 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2198 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> Option<HirId> {
2199 if let ExprKind::Path(ref qpath) = expr.kind {
2200 let path_res = qpath_res(cx, qpath, expr.hir_id);
2201 if let Res::Local(hir_id) = path_res {
2202 return Some(hir_id);
2208 fn is_loop(expr: &Expr<'_>) -> bool {
2210 ExprKind::Loop(..) => true,
2215 fn is_conditional(expr: &Expr<'_>) -> bool {
2217 ExprKind::Match(..) => true,
2222 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2224 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2225 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2226 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2228 return is_loop_nested(cx, loop_expr, iter_expr)
2234 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2235 let mut id = loop_expr.hir_id;
2236 let iter_name = if let Some(name) = path_name(iter_expr) {
2242 let parent = cx.tcx.hir().get_parent_node(id);
2246 match cx.tcx.hir().find(parent) {
2247 Some(Node::Expr(expr)) => {
2248 if let ExprKind::Loop(..) = expr.kind {
2252 Some(Node::Block(block)) => {
2253 let mut block_visitor = LoopNestVisitor {
2255 iterator: iter_name,
2258 walk_block(&mut block_visitor, block);
2259 if block_visitor.nesting == RuledOut {
2263 Some(Node::Stmt(_)) => (),
2272 #[derive(PartialEq, Eq)]
2274 Unknown, // no nesting detected yet
2275 RuledOut, // the iterator is initialized or assigned within scope
2276 LookFurther, // no nesting detected, no further walk required
2279 use self::Nesting::{LookFurther, RuledOut, Unknown};
2281 struct LoopNestVisitor {
2287 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2288 type Map = Map<'tcx>;
2290 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2291 if stmt.hir_id == self.hir_id {
2292 self.nesting = LookFurther;
2293 } else if self.nesting == Unknown {
2294 walk_stmt(self, stmt);
2298 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2299 if self.nesting != Unknown {
2302 if expr.hir_id == self.hir_id {
2303 self.nesting = LookFurther;
2307 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2308 if match_var(path, self.iterator) {
2309 self.nesting = RuledOut;
2312 _ => walk_expr(self, expr),
2316 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2317 if self.nesting != Unknown {
2320 if let PatKind::Binding(.., span_name, _) = pat.kind {
2321 if self.iterator == span_name.name {
2322 self.nesting = RuledOut;
2329 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2330 NestedVisitorMap::None
2334 fn path_name(e: &Expr<'_>) -> Option<Name> {
2335 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2336 let segments = &path.segments;
2337 if segments.len() == 1 {
2338 return Some(segments[0].ident.name);
2344 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2345 if constant(cx, cx.tables, cond).is_some() {
2346 // A pure constant condition (e.g., `while false`) is not linted.
2350 let mut var_visitor = VarCollectorVisitor {
2352 ids: FxHashSet::default(),
2353 def_ids: FxHashMap::default(),
2356 var_visitor.visit_expr(cond);
2357 if var_visitor.skip {
2360 let used_in_condition = &var_visitor.ids;
2361 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2362 used_in_condition.is_disjoint(&used_mutably)
2366 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2368 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2369 has_break_or_return: false,
2371 has_break_or_return_visitor.visit_expr(expr);
2372 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2374 if no_cond_variable_mutated && !mutable_static_in_cond {
2377 WHILE_IMMUTABLE_CONDITION,
2379 "variables in the condition are not mutated in the loop body",
2381 diag.note("this may lead to an infinite or to a never running loop");
2383 if has_break_or_return {
2384 diag.note("this loop contains `return`s or `break`s");
2385 diag.help("rewrite it as `if cond { loop { } }`");
2392 struct HasBreakOrReturnVisitor {
2393 has_break_or_return: bool,
2396 impl<'a, 'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2397 type Map = Map<'tcx>;
2399 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2400 if self.has_break_or_return {
2405 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2406 self.has_break_or_return = true;
2412 walk_expr(self, expr);
2415 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2416 NestedVisitorMap::None
2420 /// Collects the set of variables in an expression
2421 /// Stops analysis if a function call is found
2422 /// Note: In some cases such as `self`, there are no mutable annotation,
2423 /// All variables definition IDs are collected
2424 struct VarCollectorVisitor<'a, 'tcx> {
2425 cx: &'a LateContext<'a, 'tcx>,
2426 ids: FxHashSet<HirId>,
2427 def_ids: FxHashMap<def_id::DefId, bool>,
2431 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2432 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2434 if let ExprKind::Path(ref qpath) = ex.kind;
2435 if let QPath::Resolved(None, _) = *qpath;
2436 let res = qpath_res(self.cx, qpath, ex.hir_id);
2439 Res::Local(hir_id) => {
2440 self.ids.insert(hir_id);
2442 Res::Def(DefKind::Static, def_id) => {
2443 let mutable = self.cx.tcx.is_mutable_static(def_id);
2444 self.def_ids.insert(def_id, mutable);
2453 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2454 type Map = Map<'tcx>;
2456 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2458 ExprKind::Path(_) => self.insert_def_id(ex),
2459 // If there is any function/method call… we just stop analysis
2460 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2462 _ => walk_expr(self, ex),
2466 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2467 NestedVisitorMap::None
2471 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2473 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'a, 'tcx>) {
2475 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
2476 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].kind;
2477 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2478 if let Some(ref generic_args) = chain_method.args;
2479 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2481 let ty = cx.tables.node_type(ty.hir_id);
2482 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2483 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2484 match_type(cx, ty, &paths::BTREEMAP) ||
2485 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2486 if method.ident.name == sym!(len) {
2487 let span = shorten_needless_collect_span(expr);
2492 NEEDLESS_COLLECT_MSG,
2494 ".count()".to_string(),
2495 Applicability::MachineApplicable,
2498 if method.ident.name == sym!(is_empty) {
2499 let span = shorten_needless_collect_span(expr);
2504 NEEDLESS_COLLECT_MSG,
2506 ".next().is_none()".to_string(),
2507 Applicability::MachineApplicable,
2510 if method.ident.name == sym!(contains) {
2511 let contains_arg = snippet(cx, args[1].span, "??");
2512 let span = shorten_needless_collect_span(expr);
2517 NEEDLESS_COLLECT_MSG,
2519 let (arg, pred) = if contains_arg.starts_with('&') {
2520 ("x", &contains_arg[1..])
2522 ("&x", &*contains_arg)
2524 diag.span_suggestion(
2528 ".any(|{}| x == {})",
2531 Applicability::MachineApplicable,
2541 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
2543 if let ExprKind::MethodCall(_, _, ref args) = expr.kind;
2544 if let ExprKind::MethodCall(_, ref span, _) = args[0].kind;
2546 return expr.span.with_lo(span.lo() - BytePos(1));