1 use crate::consts::constant;
2 use crate::utils::paths;
3 use crate::utils::sugg::Sugg;
4 use crate::utils::usage::{is_unused, mutated_variables};
6 get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher,
7 implements_trait, is_integer_const, is_no_std_crate, is_refutable, is_type_diagnostic_item,
8 last_path_segment, match_trait_method, match_type, match_var, multispan_sugg, qpath_res,
9 snippet, snippet_opt, snippet_with_applicability, snippet_with_macro_callsite, span_lint,
10 span_lint_and_help, span_lint_and_sugg, span_lint_and_then, sugg, SpanlessEq,
12 use if_chain::if_chain;
14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
15 use rustc_errors::Applicability;
16 use rustc_hir::def::{DefKind, Res};
17 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
19 def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, InlineAsmOperand,
20 Local, LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
22 use rustc_infer::infer::TyCtxtInferExt;
23 use rustc_lint::{LateContext, LateLintPass, LintContext};
24 use rustc_middle::hir::map::Map;
25 use rustc_middle::lint::in_external_macro;
26 use rustc_middle::middle::region;
27 use rustc_middle::ty::{self, Ty, TyS};
28 use rustc_session::{declare_lint_pass, declare_tool_lint};
29 use rustc_span::source_map::Span;
30 use rustc_span::symbol::{sym, Ident, Symbol};
31 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
32 use std::iter::{once, Iterator};
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// # let src = vec![1];
46 /// # let mut dst = vec![0; 65];
47 /// for i in 0..src.len() {
48 /// dst[i + 64] = src[i];
51 /// Could be written as:
53 /// # let src = vec![1];
54 /// # let mut dst = vec![0; 65];
55 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
59 "manually copying items between slices"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for looping over the range of `0..len` of some
64 /// collection just to get the values by index.
66 /// **Why is this bad?** Just iterating the collection itself makes the intent
67 /// more clear and is probably faster.
69 /// **Known problems:** None.
73 /// let vec = vec!['a', 'b', 'c'];
74 /// for i in 0..vec.len() {
75 /// println!("{}", vec[i]);
78 /// Could be written as:
80 /// let vec = vec!['a', 'b', 'c'];
82 /// println!("{}", i);
85 pub NEEDLESS_RANGE_LOOP,
87 "for-looping over a range of indices where an iterator over items would do"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
92 /// suggests the latter.
94 /// **Why is this bad?** Readability.
96 /// **Known problems:** False negatives. We currently only warn on some known
101 /// // with `y` a `Vec` or slice:
102 /// # let y = vec![1];
103 /// for x in y.iter() {
107 /// can be rewritten to
109 /// # let y = vec![1];
114 pub EXPLICIT_ITER_LOOP,
116 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
121 /// suggests the latter.
123 /// **Why is this bad?** Readability.
125 /// **Known problems:** None
129 /// # let y = vec![1];
130 /// // with `y` a `Vec` or slice:
131 /// for x in y.into_iter() {
135 /// can be rewritten to
137 /// # let y = vec![1];
142 pub EXPLICIT_INTO_ITER_LOOP,
144 "for-looping over `_.into_iter()` when `_` would do"
147 declare_clippy_lint! {
148 /// **What it does:** Checks for loops on `x.next()`.
150 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
151 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
152 /// implements `IntoIterator`, so that possibly one value will be iterated,
153 /// leading to some hard to find bugs. No one will want to write such code
154 /// [except to win an Underhanded Rust
155 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
157 /// **Known problems:** None.
161 /// for x in y.next() {
167 "for-looping over `_.next()` which is probably not intended"
170 declare_clippy_lint! {
171 /// **What it does:** Checks for `for` loops over `Option` or `Result` values.
173 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
176 /// **Known problems:** None.
180 /// # let opt = Some(1);
188 /// if let Some(x) = opt {
196 /// # let res: Result<i32, std::io::Error> = Ok(1);
204 /// if let Ok(x) = res {
208 pub FOR_LOOPS_OVER_FALLIBLES,
210 "for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
213 declare_clippy_lint! {
214 /// **What it does:** Detects `loop + match` combinations that are easier
215 /// written as a `while let` loop.
217 /// **Why is this bad?** The `while let` loop is usually shorter and more
220 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
224 /// # let y = Some(1);
226 /// let x = match y {
230 /// // .. do something with x
232 /// // is easier written as
233 /// while let Some(x) = y {
234 /// // .. do something with x
239 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
242 declare_clippy_lint! {
243 /// **What it does:** Checks for functions collecting an iterator when collect
246 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
247 /// when this allocation may not be needed.
249 /// **Known problems:**
254 /// # let iterator = vec![1].into_iter();
255 /// let len = iterator.clone().collect::<Vec<_>>().len();
257 /// let len = iterator.count();
259 pub NEEDLESS_COLLECT,
261 "collecting an iterator when collect is not needed"
264 declare_clippy_lint! {
265 /// **What it does:** Checks `for` loops over slices with an explicit counter
266 /// and suggests the use of `.enumerate()`.
268 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
269 /// declutters the code and may be faster in some instances.
271 /// **Known problems:** None.
275 /// # let v = vec![1];
276 /// # fn bar(bar: usize, baz: usize) {}
283 /// Could be written as
285 /// # let v = vec![1];
286 /// # fn bar(bar: usize, baz: usize) {}
287 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
289 pub EXPLICIT_COUNTER_LOOP,
291 "for-looping with an explicit counter when `_.enumerate()` would do"
294 declare_clippy_lint! {
295 /// **What it does:** Checks for empty `loop` expressions.
297 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
298 /// anything. Think of the environment and either block on something or at least
299 /// make the thread sleep for some microseconds.
301 /// **Known problems:** None.
309 "empty `loop {}`, which should block or sleep"
312 declare_clippy_lint! {
313 /// **What it does:** Checks for `while let` expressions on iterators.
315 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
316 /// the intent better.
318 /// **Known problems:** None.
322 /// while let Some(val) = iter() {
326 pub WHILE_LET_ON_ITERATOR,
328 "using a while-let loop instead of a for loop on an iterator"
331 declare_clippy_lint! {
332 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
333 /// ignoring either the keys or values.
335 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
336 /// can be used to express that don't need the values or keys.
338 /// **Known problems:** None.
342 /// for (k, _) in &map {
347 /// could be replaced by
350 /// for k in map.keys() {
356 "looping on a map using `iter` when `keys` or `values` would do"
359 declare_clippy_lint! {
360 /// **What it does:** Checks for loops that will always `break`, `return` or
361 /// `continue` an outer loop.
363 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
366 /// **Known problems:** None
377 "any loop that will always `break` or `return`"
380 declare_clippy_lint! {
381 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
383 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
385 /// **Known problems:** None
389 /// let mut foo = 42;
390 /// for i in 0..foo {
392 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
397 "for loop over a range where one of the bounds is a mutable variable"
400 declare_clippy_lint! {
401 /// **What it does:** Checks whether variables used within while loop condition
402 /// can be (and are) mutated in the body.
404 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
405 /// will lead to an infinite loop.
407 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
408 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
409 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
415 /// println!("let me loop forever!");
418 pub WHILE_IMMUTABLE_CONDITION,
420 "variables used within while expression are not mutated in the body"
423 declare_clippy_lint! {
424 /// **What it does:** Checks whether a for loop is being used to push a constant
425 /// value into a Vec.
427 /// **Why is this bad?** This kind of operation can be expressed more succinctly with
428 /// `vec![item;SIZE]` or `vec.resize(NEW_SIZE, item)` and using these alternatives may also
429 /// have better performance.
430 /// **Known problems:** None
436 /// let mut vec: Vec<u8> = Vec::new();
444 /// could be written as
448 /// let mut vec: Vec<u8> = vec![item1; 20];
449 /// vec.resize(20 + 30, item2);
453 "the same item is pushed inside of a for loop"
456 declare_lint_pass!(Loops => [
460 EXPLICIT_INTO_ITER_LOOP,
462 FOR_LOOPS_OVER_FALLIBLES,
465 EXPLICIT_COUNTER_LOOP,
467 WHILE_LET_ON_ITERATOR,
471 WHILE_IMMUTABLE_CONDITION,
475 impl<'tcx> LateLintPass<'tcx> for Loops {
476 #[allow(clippy::too_many_lines)]
477 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
478 if let Some((pat, arg, body)) = higher::for_loop(expr) {
479 // we don't want to check expanded macros
480 // this check is not at the top of the function
481 // since higher::for_loop expressions are marked as expansions
482 if body.span.from_expansion() {
485 check_for_loop(cx, pat, arg, body, expr);
488 // we don't want to check expanded macros
489 if expr.span.from_expansion() {
493 // check for never_loop
494 if let ExprKind::Loop(ref block, _, _) = expr.kind {
495 match never_loop_block(block, expr.hir_id) {
496 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
497 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
501 // check for `loop { if let {} else break }` that could be `while let`
502 // (also matches an explicit "match" instead of "if let")
503 // (even if the "match" or "if let" is used for declaration)
504 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
505 // also check for empty `loop {}` statements
506 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) {
511 "empty `loop {}` detected. You may want to either use `panic!()` or add \
512 `std::thread::sleep(..);` to the loop body.",
516 // extract the expression from the first statement (if any) in a block
517 let inner_stmt_expr = extract_expr_from_first_stmt(block);
518 // or extract the first expression (if any) from the block
519 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
520 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
521 // ensure "if let" compatible match structure
523 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
525 && arms[0].guard.is_none()
526 && arms[1].guard.is_none()
527 && is_simple_break_expr(&arms[1].body)
529 if in_external_macro(cx.sess(), expr.span) {
533 // NOTE: we used to build a body here instead of using
534 // ellipsis, this was removed because:
535 // 1) it was ugly with big bodies;
536 // 2) it was not indented properly;
537 // 3) it wasn’t very smart (see #675).
538 let mut applicability = Applicability::HasPlaceholders;
543 "this loop could be written as a `while let` loop",
546 "while let {} = {} {{ .. }}",
547 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
548 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
559 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
560 let pat = &arms[0].pat.kind;
562 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
563 &ExprKind::MethodCall(ref method_path, _, ref method_args, _),
564 ) = (pat, &match_expr.kind)
566 let iter_expr = &method_args[0];
568 // Don't lint when the iterator is recreated on every iteration
570 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
571 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
572 if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
578 let lhs_constructor = last_path_segment(qpath);
579 if method_path.ident.name == sym!(next)
580 && match_trait_method(cx, match_expr, &paths::ITERATOR)
581 && lhs_constructor.ident.name == sym!(Some)
582 && (pat_args.is_empty()
583 || !is_refutable(cx, &pat_args[0])
584 && !is_used_inside(cx, iter_expr, &arms[0].body)
585 && !is_iterator_used_after_while_let(cx, iter_expr)
586 && !is_nested(cx, expr, &method_args[0]))
588 let mut applicability = Applicability::MachineApplicable;
589 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
590 let loop_var = if pat_args.is_empty() {
593 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
597 WHILE_LET_ON_ITERATOR,
598 expr.span.with_hi(match_expr.span.hi()),
599 "this loop could be written as a `for` loop",
601 format!("for {} in {}", loop_var, iterator),
608 if let Some((cond, body)) = higher::while_loop(&expr) {
609 check_infinite_loop(cx, cond, body);
612 check_needless_collect(expr, cx);
616 enum NeverLoopResult {
617 // A break/return always get triggered but not necessarily for the main loop.
619 // A continue may occur for the main loop.
625 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
627 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
628 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
632 // Combine two results for parts that are called in order.
634 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
636 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
637 NeverLoopResult::Otherwise => second,
641 // Combine two results where both parts are called but not necessarily in order.
643 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
644 match (left, right) {
645 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
646 NeverLoopResult::MayContinueMainLoop
648 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
649 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
653 // Combine two results where only one of the part may have been executed.
655 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
657 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
658 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
659 NeverLoopResult::MayContinueMainLoop
661 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
665 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
666 let stmts = block.stmts.iter().map(stmt_to_expr);
667 let expr = once(block.expr.as_deref());
668 let mut iter = stmts.chain(expr).filter_map(|e| e);
669 never_loop_expr_seq(&mut iter, main_loop_id)
672 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
674 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
675 StmtKind::Local(ref local) => local.init.as_deref(),
680 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
683 | ExprKind::Unary(_, ref e)
684 | ExprKind::Cast(ref e, _)
685 | ExprKind::Type(ref e, _)
686 | ExprKind::Field(ref e, _)
687 | ExprKind::AddrOf(_, _, ref e)
688 | ExprKind::Struct(_, _, Some(ref e))
689 | ExprKind::Repeat(ref e, _)
690 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
691 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
692 never_loop_expr_all(&mut es.iter(), main_loop_id)
694 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
695 ExprKind::Binary(_, ref e1, ref e2)
696 | ExprKind::Assign(ref e1, ref e2, _)
697 | ExprKind::AssignOp(_, ref e1, ref e2)
698 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
699 ExprKind::Loop(ref b, _, _) => {
700 // Break can come from the inner loop so remove them.
701 absorb_break(&never_loop_block(b, main_loop_id))
703 ExprKind::Match(ref e, ref arms, _) => {
704 let e = never_loop_expr(e, main_loop_id);
708 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
712 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
713 ExprKind::Continue(d) => {
716 .expect("target ID can only be missing in the presence of compilation errors");
717 if id == main_loop_id {
718 NeverLoopResult::MayContinueMainLoop
720 NeverLoopResult::AlwaysBreak
723 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
724 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
726 ExprKind::InlineAsm(ref asm) => asm
730 InlineAsmOperand::In { expr, .. }
731 | InlineAsmOperand::InOut { expr, .. }
732 | InlineAsmOperand::Const { expr }
733 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
734 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
735 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
736 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
739 .fold(NeverLoopResult::Otherwise, combine_both),
740 ExprKind::Struct(_, _, None)
741 | ExprKind::Yield(_, _)
742 | ExprKind::Closure(_, _, _, _, _)
743 | ExprKind::LlvmInlineAsm(_)
746 | ExprKind::Err => NeverLoopResult::Otherwise,
750 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
751 es.map(|e| never_loop_expr(e, main_loop_id))
752 .fold(NeverLoopResult::Otherwise, combine_seq)
755 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
756 es.map(|e| never_loop_expr(e, main_loop_id))
757 .fold(NeverLoopResult::Otherwise, combine_both)
760 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
761 e.map(|e| never_loop_expr(e, main_loop_id))
762 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
765 fn check_for_loop<'tcx>(
766 cx: &LateContext<'tcx>,
769 body: &'tcx Expr<'_>,
770 expr: &'tcx Expr<'_>,
772 check_for_loop_range(cx, pat, arg, body, expr);
773 check_for_loop_arg(cx, pat, arg, expr);
774 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
775 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
776 check_for_mut_range_bound(cx, arg, body);
777 detect_manual_memcpy(cx, pat, arg, body, expr);
778 detect_same_item_push(cx, pat, arg, body, expr);
781 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
783 if let ExprKind::Path(qpath) = &expr.kind;
784 if let QPath::Resolved(None, path) = qpath;
785 if path.segments.len() == 1;
786 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
796 #[derive(Clone, Copy)]
808 fn negative(value: String) -> Self {
811 sign: OffsetSign::Negative,
815 fn positive(value: String) -> Self {
818 sign: OffsetSign::Positive,
823 struct FixedOffsetVar<'hir> {
824 var: &'hir Expr<'hir>,
828 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
829 let is_slice = match ty.kind {
830 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
831 ty::Slice(..) | ty::Array(..) => true,
835 is_slice || is_type_diagnostic_item(cx, ty, sym!(vec_type)) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
838 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
840 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
841 if method.ident.name == sym!(clone);
843 if let Some(arg) = args.get(0);
844 then { arg } else { expr }
848 fn get_offset<'tcx>(cx: &LateContext<'tcx>, idx: &Expr<'_>, var: HirId) -> Option<Offset> {
849 fn extract_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, var: HirId) -> Option<String> {
851 ExprKind::Lit(l) => match l.node {
852 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
855 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
861 ExprKind::Binary(op, lhs, rhs) => match op.node {
863 let offset_opt = if same_var(cx, lhs, var) {
864 extract_offset(cx, rhs, var)
865 } else if same_var(cx, rhs, var) {
866 extract_offset(cx, lhs, var)
871 offset_opt.map(Offset::positive)
873 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
876 ExprKind::Path(..) if same_var(cx, idx, var) => Some(Offset::positive("0".into())),
881 fn get_assignments<'tcx>(body: &'tcx Expr<'tcx>) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> {
882 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
883 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
890 // This is one of few ways to return different iterators
891 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
892 let mut iter_a = None;
893 let mut iter_b = None;
895 if let ExprKind::Block(b, _) = body.kind {
896 let Block { stmts, expr, .. } = *b;
900 .filter_map(|stmt| match stmt.kind {
901 StmtKind::Local(..) | StmtKind::Item(..) => None,
902 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
904 .chain(expr.into_iter())
908 iter_b = Some(get_assignment(body))
911 iter_a.into_iter().flatten().chain(iter_b.into_iter())
914 fn build_manual_memcpy_suggestion<'tcx>(
915 cx: &LateContext<'tcx>,
918 limits: ast::RangeLimits,
919 dst_var: FixedOffsetVar<'_>,
920 src_var: FixedOffsetVar<'_>,
922 fn print_sum(arg1: &str, arg2: &Offset) -> String {
923 match (arg1, &arg2.value[..], arg2.sign) {
924 ("0", "0", _) => "0".into(),
925 ("0", x, OffsetSign::Positive) | (x, "0", _) => x.into(),
926 ("0", x, OffsetSign::Negative) => format!("-{}", x),
927 (x, y, OffsetSign::Positive) => format!("({} + {})", x, y),
928 (x, y, OffsetSign::Negative) => {
932 format!("({} - {})", x, y)
938 fn print_offset(start_str: &str, inline_offset: &Offset) -> String {
939 let offset = print_sum(start_str, inline_offset);
940 if offset.as_str() == "0" {
947 let print_limit = |end: &Expr<'_>, offset: Offset, var: &Expr<'_>| {
949 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
950 if method.ident.name == sym!(len);
951 if len_args.len() == 1;
952 if let Some(arg) = len_args.get(0);
953 if var_def_id(cx, arg) == var_def_id(cx, var);
956 OffsetSign::Negative => format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value),
957 OffsetSign::Positive => "".into(),
960 let end_str = match limits {
961 ast::RangeLimits::Closed => {
962 let end = sugg::Sugg::hir(cx, end, "<count>");
963 format!("{}", end + sugg::ONE)
965 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
968 print_sum(&end_str, &offset)
973 let start_str = snippet(cx, start.span, "").to_string();
974 let dst_offset = print_offset(&start_str, &dst_var.offset);
975 let dst_limit = print_limit(end, dst_var.offset, dst_var.var);
976 let src_offset = print_offset(&start_str, &src_var.offset);
977 let src_limit = print_limit(end, src_var.offset, src_var.var);
979 let dst_var_name = snippet_opt(cx, dst_var.var.span).unwrap_or_else(|| "???".into());
980 let src_var_name = snippet_opt(cx, src_var.var.span).unwrap_or_else(|| "???".into());
982 let dst = if dst_offset == "" && dst_limit == "" {
985 format!("{}[{}..{}]", dst_var_name, dst_offset, dst_limit)
989 "{}.clone_from_slice(&{}[{}..{}])",
990 dst, src_var_name, src_offset, src_limit
993 /// Checks for for loops that sequentially copy items from one slice-like
994 /// object to another.
995 fn detect_manual_memcpy<'tcx>(
996 cx: &LateContext<'tcx>,
999 body: &'tcx Expr<'_>,
1000 expr: &'tcx Expr<'_>,
1002 if let Some(higher::Range {
1006 }) = higher::range(cx, arg)
1008 // the var must be a single name
1009 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1010 // The only statements in the for loops can be indexed assignments from
1011 // indexed retrievals.
1012 let big_sugg = get_assignments(body)
1014 o.and_then(|(lhs, rhs)| {
1015 let rhs = fetch_cloned_expr(rhs);
1017 if let ExprKind::Index(seqexpr_left, idx_left) = lhs.kind;
1018 if let ExprKind::Index(seqexpr_right, idx_right) = rhs.kind;
1019 if is_slice_like(cx, cx.typeck_results().expr_ty(seqexpr_left))
1020 && is_slice_like(cx, cx.typeck_results().expr_ty(seqexpr_right));
1021 if let Some(offset_left) = get_offset(cx, &idx_left, canonical_id);
1022 if let Some(offset_right) = get_offset(cx, &idx_right, canonical_id);
1024 // Source and destination must be different
1025 if var_def_id(cx, seqexpr_left) != var_def_id(cx, seqexpr_right);
1027 Some((FixedOffsetVar { var: seqexpr_left, offset: offset_left },
1028 FixedOffsetVar { var: seqexpr_right, offset: offset_right }))
1035 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, dst, src)))
1036 .collect::<Option<Vec<_>>>()
1037 .filter(|v| !v.is_empty())
1038 .map(|v| v.join("\n "));
1040 if let Some(big_sugg) = big_sugg {
1045 "it looks like you're manually copying between slices",
1046 "try replacing the loop by",
1048 Applicability::Unspecified,
1055 // Delegate that traverses expression and detects mutable variables being used
1056 struct UsesMutableDelegate {
1057 found_mutable: bool,
1060 impl<'tcx> Delegate<'tcx> for UsesMutableDelegate {
1061 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1063 fn borrow(&mut self, _: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1064 // Mutable variable is found
1065 if let ty::BorrowKind::MutBorrow = bk {
1066 self.found_mutable = true;
1070 fn mutate(&mut self, _: &PlaceWithHirId<'tcx>) {}
1073 // Uses UsesMutableDelegate to find mutable variables in an expression expr
1074 fn has_mutable_variables<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
1075 let mut delegate = UsesMutableDelegate { found_mutable: false };
1076 let def_id = expr.hir_id.owner.to_def_id();
1077 cx.tcx.infer_ctxt().enter(|infcx| {
1078 ExprUseVisitor::new(
1081 def_id.expect_local(),
1083 cx.typeck_results(),
1088 delegate.found_mutable
1091 // Scans for the usage of the for loop pattern
1092 struct ForPatternVisitor<'a, 'tcx> {
1093 found_pattern: bool,
1094 // Pattern that we are searching for
1095 for_pattern: &'a Pat<'tcx>,
1096 cx: &'a LateContext<'tcx>,
1099 impl<'a, 'tcx> Visitor<'tcx> for ForPatternVisitor<'a, 'tcx> {
1100 type Map = Map<'tcx>;
1102 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1103 // Recursively explore an expression until a ExprKind::Path is found
1105 ExprKind::Array(expr_list) | ExprKind::MethodCall(_, _, expr_list, _) | ExprKind::Tup(expr_list) => {
1106 for expr in *expr_list {
1107 self.visit_expr(expr)
1110 ExprKind::Binary(_, lhs_expr, rhs_expr) => {
1111 self.visit_expr(lhs_expr);
1112 self.visit_expr(rhs_expr);
1115 | ExprKind::Unary(_, expr)
1116 | ExprKind::Cast(expr, _)
1117 | ExprKind::Type(expr, _)
1118 | ExprKind::AddrOf(_, _, expr)
1119 | ExprKind::Field(expr, _)
1120 | ExprKind::Struct(_, _, Some(expr)) => self.visit_expr(expr),
1122 // Exploration cannot continue ... calculate the hir_id of the current
1123 // expr assuming it is a Path
1124 if let Some(hir_id) = var_def_id(self.cx, &expr) {
1126 if hir_id == self.for_pattern.hir_id {
1127 self.found_pattern = true;
1129 // If the for loop pattern is a tuple, determine whether the current
1130 // expr is inside that tuple pattern
1131 if let PatKind::Tuple(pat_list, _) = &self.for_pattern.kind {
1132 let hir_id_list: Vec<HirId> = pat_list.iter().map(|p| p.hir_id).collect();
1133 if hir_id_list.contains(&hir_id) {
1134 self.found_pattern = true;
1142 // This is triggered by walk_expr() for the case of vec.push(pat)
1143 fn visit_qpath(&mut self, qpath: &'tcx QPath<'_>, _: HirId, _: Span) {
1145 if let QPath::Resolved(_, path) = qpath;
1146 if let Res::Local(hir_id) = &path.res;
1148 if *hir_id == self.for_pattern.hir_id{
1149 self.found_pattern = true;
1152 if let PatKind::Tuple(pat_list, _) = &self.for_pattern.kind {
1153 let hir_id_list: Vec<HirId> = pat_list.iter().map(|p| p.hir_id).collect();
1154 if hir_id_list.contains(&hir_id) {
1155 self.found_pattern = true;
1162 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1163 NestedVisitorMap::None
1167 // Scans the body of the for loop and determines whether lint should be given
1168 struct SameItemPushVisitor<'a, 'tcx> {
1170 // this field holds the last vec push operation visited, which should be the only push seen
1171 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1172 cx: &'a LateContext<'tcx>,
1175 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1176 type Map = Map<'tcx>;
1178 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1180 // Non-determinism may occur ... don't give a lint
1181 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1182 ExprKind::Block(block, _) => self.visit_block(block),
1187 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1188 for stmt in b.stmts.iter() {
1189 self.visit_stmt(stmt);
1193 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1194 let vec_push_option = get_vec_push(self.cx, s);
1195 if vec_push_option.is_none() {
1196 // Current statement is not a push so visit inside
1198 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1202 // Current statement is a push ...check whether another
1203 // push had been previously done
1204 if self.vec_push.is_none() {
1205 self.vec_push = vec_push_option;
1207 // There are multiple pushes ... don't lint
1208 self.should_lint = false;
1213 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1214 NestedVisitorMap::None
1218 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1219 // the Vec being pushed into and the item being pushed
1220 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1222 // Extract method being called
1223 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1224 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1225 // Figure out the parameters for the method call
1226 if let Some(self_expr) = args.get(0);
1227 if let Some(pushed_item) = args.get(1);
1228 // Check that the method being called is push() on a Vec
1229 if match_type(cx, cx.typeck_results().expr_ty(self_expr), &paths::VEC);
1230 if path.ident.name.as_str() == "push";
1232 return Some((self_expr, pushed_item))
1238 /// Detects for loop pushing the same item into a Vec
1239 fn detect_same_item_push<'tcx>(
1240 cx: &LateContext<'tcx>,
1243 body: &'tcx Expr<'_>,
1246 // Determine whether it is safe to lint the body
1247 let mut same_item_push_visitor = SameItemPushVisitor {
1252 walk_expr(&mut same_item_push_visitor, body);
1253 if same_item_push_visitor.should_lint {
1254 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1255 // Make sure that the push does not involve possibly mutating values
1256 if !has_mutable_variables(cx, pushed_item) {
1257 // Walk through the expression being pushed and make sure that it
1258 // does not contain the for loop pattern
1259 let mut for_pat_visitor = ForPatternVisitor {
1260 found_pattern: false,
1264 walk_expr(&mut for_pat_visitor, pushed_item);
1266 if !for_pat_visitor.found_pattern {
1267 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1268 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1274 "it looks like the same item is being pushed into this Vec",
1277 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1278 item_str, vec_str, item_str
1287 /// Checks for looping over a range and then indexing a sequence with it.
1288 /// The iteratee must be a range literal.
1289 #[allow(clippy::too_many_lines)]
1290 fn check_for_loop_range<'tcx>(
1291 cx: &LateContext<'tcx>,
1293 arg: &'tcx Expr<'_>,
1294 body: &'tcx Expr<'_>,
1295 expr: &'tcx Expr<'_>,
1297 if let Some(higher::Range {
1301 }) = higher::range(cx, arg)
1303 // the var must be a single name
1304 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1305 let mut visitor = VarVisitor {
1308 indexed_mut: FxHashSet::default(),
1309 indexed_indirectly: FxHashMap::default(),
1310 indexed_directly: FxHashMap::default(),
1311 referenced: FxHashSet::default(),
1313 prefer_mutable: false,
1315 walk_expr(&mut visitor, body);
1317 // linting condition: we only indexed one variable, and indexed it directly
1318 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1319 let (indexed, (indexed_extent, indexed_ty)) = visitor
1323 .expect("already checked that we have exactly 1 element");
1325 // ensure that the indexed variable was declared before the loop, see #601
1326 if let Some(indexed_extent) = indexed_extent {
1327 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1328 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1329 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1330 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1331 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1336 // don't lint if the container that is indexed does not have .iter() method
1337 let has_iter = has_iter_method(cx, indexed_ty);
1338 if has_iter.is_none() {
1342 // don't lint if the container that is indexed into is also used without
1344 if visitor.referenced.contains(&indexed) {
1348 let starts_at_zero = is_integer_const(cx, start, 0);
1350 let skip = if starts_at_zero {
1353 format!(".skip({})", snippet(cx, start.span, ".."))
1356 let mut end_is_start_plus_val = false;
1358 let take = if let Some(end) = *end {
1359 let mut take_expr = end;
1361 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1362 if let BinOpKind::Add = op.node {
1363 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1364 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1366 if start_equal_left {
1368 } else if start_equal_right {
1372 end_is_start_plus_val = start_equal_left | start_equal_right;
1376 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1380 ast::RangeLimits::Closed => {
1381 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1382 format!(".take({})", take_expr + sugg::ONE)
1384 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1391 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1392 ("mut ", "iter_mut")
1397 let take_is_empty = take.is_empty();
1398 let mut method_1 = take;
1399 let mut method_2 = skip;
1401 if end_is_start_plus_val {
1402 mem::swap(&mut method_1, &mut method_2);
1405 if visitor.nonindex {
1408 NEEDLESS_RANGE_LOOP,
1410 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1414 "consider using an iterator",
1416 (pat.span, format!("({}, <item>)", ident.name)),
1419 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1426 let repl = if starts_at_zero && take_is_empty {
1427 format!("&{}{}", ref_mut, indexed)
1429 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1434 NEEDLESS_RANGE_LOOP,
1437 "the loop variable `{}` is only used to index `{}`.",
1443 "consider using an iterator",
1444 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1454 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1456 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1457 if len_args.len() == 1;
1458 if method.ident.name == sym!(len);
1459 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1460 if path.segments.len() == 1;
1461 if path.segments[0].ident.name == var;
1470 fn is_end_eq_array_len<'tcx>(
1471 cx: &LateContext<'tcx>,
1473 limits: ast::RangeLimits,
1474 indexed_ty: Ty<'tcx>,
1477 if let ExprKind::Lit(ref lit) = end.kind;
1478 if let ast::LitKind::Int(end_int, _) = lit.node;
1479 if let ty::Array(_, arr_len_const) = indexed_ty.kind;
1480 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1482 return match limits {
1483 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1484 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1492 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1493 let mut applicability = Applicability::MachineApplicable;
1494 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1495 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1500 "it is more concise to loop over references to containers instead of using explicit \
1502 "to write this more concisely, try",
1503 format!("&{}{}", muta, object),
1508 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1509 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1510 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1511 // just the receiver, no arguments
1512 if args.len() == 1 {
1513 let method_name = &*method.ident.as_str();
1514 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1515 if method_name == "iter" || method_name == "iter_mut" {
1516 if is_ref_iterable_type(cx, &args[0]) {
1517 lint_iter_method(cx, args, arg, method_name);
1519 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1520 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1521 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1522 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1523 let mut applicability = Applicability::MachineApplicable;
1524 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1527 EXPLICIT_INTO_ITER_LOOP,
1529 "it is more concise to loop over containers instead of using explicit \
1531 "to write this more concisely, try",
1536 let ref_receiver_ty = cx.tcx.mk_ref(
1537 cx.tcx.lifetimes.re_erased,
1540 mutbl: Mutability::Not,
1543 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1544 lint_iter_method(cx, args, arg, method_name)
1547 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1552 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1553 probably not what you want",
1555 next_loop_linted = true;
1559 if !next_loop_linted {
1560 check_arg_type(cx, pat, arg);
1564 /// Checks for `for` loops over `Option`s and `Result`s.
1565 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1566 let ty = cx.typeck_results().expr_ty(arg);
1567 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1570 FOR_LOOPS_OVER_FALLIBLES,
1573 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1574 `if let` statement.",
1575 snippet(cx, arg.span, "_")
1579 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1580 snippet(cx, pat.span, "_"),
1581 snippet(cx, arg.span, "_")
1584 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1587 FOR_LOOPS_OVER_FALLIBLES,
1590 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1591 `if let` statement.",
1592 snippet(cx, arg.span, "_")
1596 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1597 snippet(cx, pat.span, "_"),
1598 snippet(cx, arg.span, "_")
1604 fn check_for_loop_explicit_counter<'tcx>(
1605 cx: &LateContext<'tcx>,
1607 arg: &'tcx Expr<'_>,
1608 body: &'tcx Expr<'_>,
1609 expr: &'tcx Expr<'_>,
1611 // Look for variables that are incremented once per loop iteration.
1612 let mut visitor = IncrementVisitor {
1614 states: FxHashMap::default(),
1618 walk_expr(&mut visitor, body);
1620 // For each candidate, check the parent block to see if
1621 // it's initialized to zero at the start of the loop.
1622 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1623 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1624 let mut visitor2 = InitializeVisitor {
1628 state: VarState::IncrOnce,
1633 walk_block(&mut visitor2, block);
1635 if visitor2.state == VarState::Warn {
1636 if let Some(name) = visitor2.name {
1637 let mut applicability = Applicability::MachineApplicable;
1639 // for some reason this is the only way to get the `Span`
1640 // of the entire `for` loop
1641 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1649 EXPLICIT_COUNTER_LOOP,
1650 for_span.with_hi(arg.span.hi()),
1651 &format!("the variable `{}` is used as a loop counter.", name),
1654 "for ({}, {}) in {}.enumerate()",
1656 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1657 make_iterator_snippet(cx, arg, &mut applicability),
1667 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1668 /// actual `Iterator` that the loop uses.
1669 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1670 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1671 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1676 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1679 // (&x).into_iter() ==> x.iter()
1680 // (&mut x).into_iter() ==> x.iter_mut()
1682 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1683 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1685 let meth_name = match mutability {
1686 Mutability::Mut => "iter_mut",
1687 Mutability::Not => "iter",
1691 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1697 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1703 /// Checks for the `FOR_KV_MAP` lint.
1704 fn check_for_loop_over_map_kv<'tcx>(
1705 cx: &LateContext<'tcx>,
1707 arg: &'tcx Expr<'_>,
1708 body: &'tcx Expr<'_>,
1709 expr: &'tcx Expr<'_>,
1711 let pat_span = pat.span;
1713 if let PatKind::Tuple(ref pat, _) = pat.kind {
1715 let arg_span = arg.span;
1716 let (new_pat_span, kind, ty, mutbl) = match cx.typeck_results().expr_ty(arg).kind {
1717 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1718 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1719 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1724 let mutbl = match mutbl {
1725 Mutability::Not => "",
1726 Mutability::Mut => "_mut",
1728 let arg = match arg.kind {
1729 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1733 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1738 &format!("you seem to want to iterate on a map's {}s", kind),
1740 let map = sugg::Sugg::hir(cx, arg, "map");
1743 "use the corresponding method",
1745 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1746 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1756 struct MutatePairDelegate<'a, 'tcx> {
1757 cx: &'a LateContext<'tcx>,
1758 hir_id_low: Option<HirId>,
1759 hir_id_high: Option<HirId>,
1760 span_low: Option<Span>,
1761 span_high: Option<Span>,
1764 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1765 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1767 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1768 if let ty::BorrowKind::MutBorrow = bk {
1769 if let PlaceBase::Local(id) = cmt.place.base {
1770 if Some(id) == self.hir_id_low {
1771 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1773 if Some(id) == self.hir_id_high {
1774 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1780 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>) {
1781 if let PlaceBase::Local(id) = cmt.place.base {
1782 if Some(id) == self.hir_id_low {
1783 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1785 if Some(id) == self.hir_id_high {
1786 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1792 impl MutatePairDelegate<'_, '_> {
1793 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1794 (self.span_low, self.span_high)
1798 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1799 if let Some(higher::Range {
1803 }) = higher::range(cx, arg)
1805 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1806 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1807 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1808 mut_warn_with_span(cx, span_low);
1809 mut_warn_with_span(cx, span_high);
1814 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
1815 if let Some(sp) = span {
1820 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1825 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
1827 if let ExprKind::Path(ref qpath) = bound.kind;
1828 if let QPath::Resolved(None, _) = *qpath;
1830 let res = qpath_res(cx, qpath, bound.hir_id);
1831 if let Res::Local(hir_id) = res {
1832 let node_str = cx.tcx.hir().get(hir_id);
1834 if let Node::Binding(pat) = node_str;
1835 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1836 if let BindingAnnotation::Mutable = bind_ann;
1838 return Some(hir_id);
1847 fn check_for_mutation<'tcx>(
1848 cx: &LateContext<'tcx>,
1850 bound_ids: &[Option<HirId>],
1851 ) -> (Option<Span>, Option<Span>) {
1852 let mut delegate = MutatePairDelegate {
1854 hir_id_low: bound_ids[0],
1855 hir_id_high: bound_ids[1],
1859 let def_id = body.hir_id.owner.to_def_id();
1860 cx.tcx.infer_ctxt().enter(|infcx| {
1861 ExprUseVisitor::new(
1864 def_id.expect_local(),
1866 cx.typeck_results(),
1870 delegate.mutation_span()
1873 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1874 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
1876 PatKind::Wild => true,
1877 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
1882 struct LocalUsedVisitor<'a, 'tcx> {
1883 cx: &'a LateContext<'tcx>,
1888 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1889 type Map = Map<'tcx>;
1891 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1892 if same_var(self.cx, expr, self.local) {
1895 walk_expr(self, expr);
1899 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1900 NestedVisitorMap::None
1904 struct VarVisitor<'a, 'tcx> {
1905 /// context reference
1906 cx: &'a LateContext<'tcx>,
1907 /// var name to look for as index
1909 /// indexed variables that are used mutably
1910 indexed_mut: FxHashSet<Symbol>,
1911 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1912 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
1913 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1914 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1915 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
1916 /// Any names that are used outside an index operation.
1917 /// Used to detect things like `&mut vec` used together with `vec[i]`
1918 referenced: FxHashSet<Symbol>,
1919 /// has the loop variable been used in expressions other than the index of
1922 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1923 /// takes `&mut self`
1924 prefer_mutable: bool,
1927 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1928 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
1930 // the indexed container is referenced by a name
1931 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
1932 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1933 if seqvar.segments.len() == 1;
1935 let index_used_directly = same_var(self.cx, idx, self.var);
1936 let indexed_indirectly = {
1937 let mut used_visitor = LocalUsedVisitor {
1942 walk_expr(&mut used_visitor, idx);
1946 if indexed_indirectly || index_used_directly {
1947 if self.prefer_mutable {
1948 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1950 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
1952 Res::Local(hir_id) => {
1953 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1954 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1955 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1956 if indexed_indirectly {
1957 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1959 if index_used_directly {
1960 self.indexed_directly.insert(
1961 seqvar.segments[0].ident.name,
1962 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
1965 return false; // no need to walk further *on the variable*
1967 Res::Def(DefKind::Static | DefKind::Const, ..) => {
1968 if indexed_indirectly {
1969 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1971 if index_used_directly {
1972 self.indexed_directly.insert(
1973 seqvar.segments[0].ident.name,
1974 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
1977 return false; // no need to walk further *on the variable*
1988 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1989 type Map = Map<'tcx>;
1991 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1994 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
1995 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1996 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1997 if !self.check(&args[1], &args[0], expr);
2003 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2004 if !self.check(idx, seqexpr, expr);
2009 // directly using a variable
2010 if let ExprKind::Path(ref qpath) = expr.kind;
2011 if let QPath::Resolved(None, ref path) = *qpath;
2012 if path.segments.len() == 1;
2014 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2015 if local_id == self.var {
2016 self.nonindex = true;
2018 // not the correct variable, but still a variable
2019 self.referenced.insert(path.segments[0].ident.name);
2025 let old = self.prefer_mutable;
2027 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2028 self.prefer_mutable = true;
2029 self.visit_expr(lhs);
2030 self.prefer_mutable = false;
2031 self.visit_expr(rhs);
2033 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2034 if mutbl == Mutability::Mut {
2035 self.prefer_mutable = true;
2037 self.visit_expr(expr);
2039 ExprKind::Call(ref f, args) => {
2042 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2043 self.prefer_mutable = false;
2044 if let ty::Ref(_, _, mutbl) = ty.kind {
2045 if mutbl == Mutability::Mut {
2046 self.prefer_mutable = true;
2049 self.visit_expr(expr);
2052 ExprKind::MethodCall(_, _, args, _) => {
2053 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2054 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2055 self.prefer_mutable = false;
2056 if let ty::Ref(_, _, mutbl) = ty.kind {
2057 if mutbl == Mutability::Mut {
2058 self.prefer_mutable = true;
2061 self.visit_expr(expr);
2064 ExprKind::Closure(_, _, body_id, ..) => {
2065 let body = self.cx.tcx.hir().body(body_id);
2066 self.visit_expr(&body.value);
2068 _ => walk_expr(self, expr),
2070 self.prefer_mutable = old;
2072 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2073 NestedVisitorMap::None
2077 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2078 let def_id = match var_def_id(cx, expr) {
2080 None => return false,
2082 if let Some(used_mutably) = mutated_variables(container, cx) {
2083 if used_mutably.contains(&def_id) {
2090 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2091 let def_id = match var_def_id(cx, iter_expr) {
2093 None => return false,
2095 let mut visitor = VarUsedAfterLoopVisitor {
2098 iter_expr_id: iter_expr.hir_id,
2099 past_while_let: false,
2100 var_used_after_while_let: false,
2102 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2103 walk_block(&mut visitor, enclosing_block);
2105 visitor.var_used_after_while_let
2108 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2109 cx: &'a LateContext<'tcx>,
2111 iter_expr_id: HirId,
2112 past_while_let: bool,
2113 var_used_after_while_let: bool,
2116 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2117 type Map = Map<'tcx>;
2119 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2120 if self.past_while_let {
2121 if Some(self.def_id) == var_def_id(self.cx, expr) {
2122 self.var_used_after_while_let = true;
2124 } else if self.iter_expr_id == expr.hir_id {
2125 self.past_while_let = true;
2127 walk_expr(self, expr);
2129 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2130 NestedVisitorMap::None
2134 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2135 /// for `&T` and `&mut T`, such as `Vec`.
2137 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2138 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2139 // will allow further borrows afterwards
2140 let ty = cx.typeck_results().expr_ty(e);
2141 is_iterable_array(ty, cx) ||
2142 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2143 match_type(cx, ty, &paths::LINKED_LIST) ||
2144 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2145 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2146 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2147 match_type(cx, ty, &paths::BINARY_HEAP) ||
2148 match_type(cx, ty, &paths::BTREEMAP) ||
2149 match_type(cx, ty, &paths::BTREESET)
2152 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2153 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2155 ty::Array(_, n) => n
2156 .try_eval_usize(cx.tcx, cx.param_env)
2157 .map_or(false, |val| (0..=32).contains(&val)),
2162 /// If a block begins with a statement (possibly a `let` binding) and has an
2163 /// expression, return it.
2164 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2165 if block.stmts.is_empty() {
2168 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2169 local.init //.map(|expr| expr)
2175 /// If a block begins with an expression (with or without semicolon), return it.
2176 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2178 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2179 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2180 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2181 StmtKind::Local(..) | StmtKind::Item(..) => None,
2187 /// Returns `true` if expr contains a single break expr without destination label
2189 /// passed expression. The expression may be within a block.
2190 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2192 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2193 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2198 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2199 // incremented exactly once in the loop body, and initialized to zero
2200 // at the start of the loop.
2201 #[derive(Debug, PartialEq)]
2203 Initial, // Not examined yet
2204 IncrOnce, // Incremented exactly once, may be a loop counter
2205 Declared, // Declared but not (yet) initialized to zero
2210 /// Scan a for loop for variables that are incremented exactly once.
2211 struct IncrementVisitor<'a, 'tcx> {
2212 cx: &'a LateContext<'tcx>, // context reference
2213 states: FxHashMap<HirId, VarState>, // incremented variables
2214 depth: u32, // depth of conditional expressions
2218 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2219 type Map = Map<'tcx>;
2221 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2226 // If node is a variable
2227 if let Some(def_id) = var_def_id(self.cx, expr) {
2228 if let Some(parent) = get_parent_expr(self.cx, expr) {
2229 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2232 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2233 if lhs.hir_id == expr.hir_id {
2234 if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) {
2235 *state = match *state {
2236 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2237 _ => VarState::DontWarn,
2240 // Assigned some other value
2241 *state = VarState::DontWarn;
2245 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2246 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2247 *state = VarState::DontWarn
2252 } else if is_loop(expr) || is_conditional(expr) {
2254 walk_expr(self, expr);
2257 } else if let ExprKind::Continue(_) = expr.kind {
2261 walk_expr(self, expr);
2263 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2264 NestedVisitorMap::None
2268 /// Checks whether a variable is initialized to zero at the start of a loop.
2269 struct InitializeVisitor<'a, 'tcx> {
2270 cx: &'a LateContext<'tcx>, // context reference
2271 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2274 name: Option<Symbol>,
2275 depth: u32, // depth of conditional expressions
2279 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2280 type Map = Map<'tcx>;
2282 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2283 // Look for declarations of the variable
2284 if let StmtKind::Local(ref local) = stmt.kind {
2285 if local.pat.hir_id == self.var_id {
2286 if let PatKind::Binding(.., ident, _) = local.pat.kind {
2287 self.name = Some(ident.name);
2289 self.state = local.init.as_ref().map_or(VarState::Declared, |init| {
2290 if is_integer_const(&self.cx, init, 0) {
2299 walk_stmt(self, stmt);
2302 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2303 if self.state == VarState::DontWarn {
2306 if expr.hir_id == self.end_expr.hir_id {
2307 self.past_loop = true;
2310 // No need to visit expressions before the variable is
2312 if self.state == VarState::IncrOnce {
2316 // If node is the desired variable, see how it's used
2317 if var_def_id(self.cx, expr) == Some(self.var_id) {
2318 if let Some(parent) = get_parent_expr(self.cx, expr) {
2320 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2321 self.state = VarState::DontWarn;
2323 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2324 self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 {
2330 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2331 self.state = VarState::DontWarn
2338 self.state = VarState::DontWarn;
2341 } else if !self.past_loop && is_loop(expr) {
2342 self.state = VarState::DontWarn;
2344 } else if is_conditional(expr) {
2346 walk_expr(self, expr);
2350 walk_expr(self, expr);
2353 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2354 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2358 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2359 if let ExprKind::Path(ref qpath) = expr.kind {
2360 let path_res = qpath_res(cx, qpath, expr.hir_id);
2361 if let Res::Local(hir_id) = path_res {
2362 return Some(hir_id);
2368 fn is_loop(expr: &Expr<'_>) -> bool {
2369 matches!(expr.kind, ExprKind::Loop(..))
2372 fn is_conditional(expr: &Expr<'_>) -> bool {
2373 matches!(expr.kind, ExprKind::Match(..))
2376 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2378 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2379 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2380 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2382 return is_loop_nested(cx, loop_expr, iter_expr)
2388 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2389 let mut id = loop_expr.hir_id;
2390 let iter_name = if let Some(name) = path_name(iter_expr) {
2396 let parent = cx.tcx.hir().get_parent_node(id);
2400 match cx.tcx.hir().find(parent) {
2401 Some(Node::Expr(expr)) => {
2402 if let ExprKind::Loop(..) = expr.kind {
2406 Some(Node::Block(block)) => {
2407 let mut block_visitor = LoopNestVisitor {
2409 iterator: iter_name,
2412 walk_block(&mut block_visitor, block);
2413 if block_visitor.nesting == RuledOut {
2417 Some(Node::Stmt(_)) => (),
2426 #[derive(PartialEq, Eq)]
2428 Unknown, // no nesting detected yet
2429 RuledOut, // the iterator is initialized or assigned within scope
2430 LookFurther, // no nesting detected, no further walk required
2433 use self::Nesting::{LookFurther, RuledOut, Unknown};
2435 struct LoopNestVisitor {
2441 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2442 type Map = Map<'tcx>;
2444 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2445 if stmt.hir_id == self.hir_id {
2446 self.nesting = LookFurther;
2447 } else if self.nesting == Unknown {
2448 walk_stmt(self, stmt);
2452 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2453 if self.nesting != Unknown {
2456 if expr.hir_id == self.hir_id {
2457 self.nesting = LookFurther;
2461 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2462 if match_var(path, self.iterator) {
2463 self.nesting = RuledOut;
2466 _ => walk_expr(self, expr),
2470 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2471 if self.nesting != Unknown {
2474 if let PatKind::Binding(.., span_name, _) = pat.kind {
2475 if self.iterator == span_name.name {
2476 self.nesting = RuledOut;
2483 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2484 NestedVisitorMap::None
2488 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2489 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2490 let segments = &path.segments;
2491 if segments.len() == 1 {
2492 return Some(segments[0].ident.name);
2498 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2499 if constant(cx, cx.typeck_results(), cond).is_some() {
2500 // A pure constant condition (e.g., `while false`) is not linted.
2504 let mut var_visitor = VarCollectorVisitor {
2506 ids: FxHashSet::default(),
2507 def_ids: FxHashMap::default(),
2510 var_visitor.visit_expr(cond);
2511 if var_visitor.skip {
2514 let used_in_condition = &var_visitor.ids;
2515 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2516 used_in_condition.is_disjoint(&used_mutably)
2520 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2522 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2523 has_break_or_return: false,
2525 has_break_or_return_visitor.visit_expr(expr);
2526 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2528 if no_cond_variable_mutated && !mutable_static_in_cond {
2531 WHILE_IMMUTABLE_CONDITION,
2533 "variables in the condition are not mutated in the loop body",
2535 diag.note("this may lead to an infinite or to a never running loop");
2537 if has_break_or_return {
2538 diag.note("this loop contains `return`s or `break`s");
2539 diag.help("rewrite it as `if cond { loop { } }`");
2546 struct HasBreakOrReturnVisitor {
2547 has_break_or_return: bool,
2550 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2551 type Map = Map<'tcx>;
2553 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2554 if self.has_break_or_return {
2559 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2560 self.has_break_or_return = true;
2566 walk_expr(self, expr);
2569 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2570 NestedVisitorMap::None
2574 /// Collects the set of variables in an expression
2575 /// Stops analysis if a function call is found
2576 /// Note: In some cases such as `self`, there are no mutable annotation,
2577 /// All variables definition IDs are collected
2578 struct VarCollectorVisitor<'a, 'tcx> {
2579 cx: &'a LateContext<'tcx>,
2580 ids: FxHashSet<HirId>,
2581 def_ids: FxHashMap<def_id::DefId, bool>,
2585 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2586 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2588 if let ExprKind::Path(ref qpath) = ex.kind;
2589 if let QPath::Resolved(None, _) = *qpath;
2590 let res = qpath_res(self.cx, qpath, ex.hir_id);
2593 Res::Local(hir_id) => {
2594 self.ids.insert(hir_id);
2596 Res::Def(DefKind::Static, def_id) => {
2597 let mutable = self.cx.tcx.is_mutable_static(def_id);
2598 self.def_ids.insert(def_id, mutable);
2607 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2608 type Map = Map<'tcx>;
2610 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2612 ExprKind::Path(_) => self.insert_def_id(ex),
2613 // If there is any function/method call… we just stop analysis
2614 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2616 _ => walk_expr(self, ex),
2620 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2621 NestedVisitorMap::None
2625 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2627 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2628 check_needless_collect_direct_usage(expr, cx);
2629 check_needless_collect_indirect_usage(expr, cx);
2631 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2633 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2634 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2635 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2636 if let Some(ref generic_args) = chain_method.args;
2637 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2639 let ty = cx.typeck_results().node_type(ty.hir_id);
2640 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2641 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2642 match_type(cx, ty, &paths::BTREEMAP) ||
2643 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2644 if method.ident.name == sym!(len) {
2645 let span = shorten_span(expr, sym!(collect));
2650 NEEDLESS_COLLECT_MSG,
2652 "count()".to_string(),
2653 Applicability::MachineApplicable,
2656 if method.ident.name == sym!(is_empty) {
2657 let span = shorten_span(expr, sym!(iter));
2662 NEEDLESS_COLLECT_MSG,
2664 "get(0).is_none()".to_string(),
2665 Applicability::MachineApplicable,
2668 if method.ident.name == sym!(contains) {
2669 let contains_arg = snippet(cx, args[1].span, "??");
2670 let span = shorten_span(expr, sym!(collect));
2675 NEEDLESS_COLLECT_MSG,
2677 let (arg, pred) = if contains_arg.starts_with('&') {
2678 ("x", &contains_arg[1..])
2680 ("&x", &*contains_arg)
2682 diag.span_suggestion(
2686 "any(|{}| x == {})",
2689 Applicability::MachineApplicable,
2699 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2700 if let ExprKind::Block(ref block, _) = expr.kind {
2701 for ref stmt in block.stmts {
2703 if let StmtKind::Local(
2704 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2705 init: Some(ref init_expr), .. }
2707 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2708 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2709 if let Some(ref generic_args) = method_name.args;
2710 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2711 if let ty = cx.typeck_results().node_type(ty.hir_id);
2712 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2713 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2714 match_type(cx, ty, &paths::LINKED_LIST);
2715 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2716 if iter_calls.len() == 1;
2718 // Suggest replacing iter_call with iter_replacement, and removing stmt
2719 let iter_call = &iter_calls[0];
2723 stmt.span.until(iter_call.span),
2724 NEEDLESS_COLLECT_MSG,
2726 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2727 diag.multipart_suggestion(
2728 iter_call.get_suggestion_text(),
2730 (stmt.span, String::new()),
2731 (iter_call.span, iter_replacement)
2733 Applicability::MachineApplicable,// MaybeIncorrect,
2743 struct IterFunction {
2744 func: IterFunctionKind,
2748 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2750 IterFunctionKind::IntoIter => String::new(),
2751 IterFunctionKind::Len => String::from(".count()"),
2752 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2753 IterFunctionKind::Contains(span) => format!(".any(|x| x == {})", snippet(cx, *span, "..")),
2756 fn get_suggestion_text(&self) -> &'static str {
2758 IterFunctionKind::IntoIter => {
2759 "Use the original Iterator instead of collecting it and then producing a new one"
2761 IterFunctionKind::Len => {
2762 "Take the original Iterator's count instead of collecting it and finding the length"
2764 IterFunctionKind::IsEmpty => {
2765 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
2767 IterFunctionKind::Contains(_) => {
2768 "Check if the original Iterator contains an element instead of collecting then checking"
2773 enum IterFunctionKind {
2780 struct IterFunctionVisitor {
2781 uses: Vec<IterFunction>,
2785 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
2786 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
2787 // Check function calls on our collection
2789 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
2790 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
2791 if let &[name] = &path.segments;
2792 if name.ident == self.target;
2794 let len = sym!(len);
2795 let is_empty = sym!(is_empty);
2796 let contains = sym!(contains);
2797 match method_name.ident.name {
2798 sym::into_iter => self.uses.push(
2799 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
2801 name if name == len => self.uses.push(
2802 IterFunction { func: IterFunctionKind::Len, span: expr.span }
2804 name if name == is_empty => self.uses.push(
2805 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
2807 name if name == contains => self.uses.push(
2808 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
2810 _ => self.seen_other = true,
2815 // Check if the collection is used for anything else
2817 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
2818 if let &[name] = &path.segments;
2819 if name.ident == self.target;
2821 self.seen_other = true;
2823 walk_expr(self, expr);
2828 type Map = Map<'tcx>;
2829 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2830 NestedVisitorMap::None
2834 /// Detect the occurences of calls to `iter` or `into_iter` for the
2835 /// given identifier
2836 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
2837 let mut visitor = IterFunctionVisitor {
2842 visitor.visit_block(block);
2843 if visitor.seen_other {
2850 fn shorten_span(expr: &Expr<'_>, target_fn_name: Symbol) -> Span {
2851 let mut current_expr = expr;
2852 while let ExprKind::MethodCall(ref path, ref span, ref args, _) = current_expr.kind {
2853 if path.ident.name == target_fn_name {
2854 return expr.span.with_lo(span.lo());
2856 current_expr = &args[0];