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 // Scans for the usage of the for loop pattern
1056 struct ForPatternVisitor<'a, 'tcx> {
1057 found_pattern: bool,
1058 // Pattern that we are searching for
1059 for_pattern: &'a Pat<'tcx>,
1060 cx: &'a LateContext<'tcx>,
1063 impl<'a, 'tcx> Visitor<'tcx> for ForPatternVisitor<'a, 'tcx> {
1064 type Map = Map<'tcx>;
1066 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1067 // Recursively explore an expression until a ExprKind::Path is found
1069 ExprKind::Array(expr_list) | ExprKind::MethodCall(_, _, expr_list, _) | ExprKind::Tup(expr_list) => {
1070 for expr in *expr_list {
1071 self.visit_expr(expr)
1074 ExprKind::Binary(_, lhs_expr, rhs_expr) => {
1075 self.visit_expr(lhs_expr);
1076 self.visit_expr(rhs_expr);
1079 | ExprKind::Unary(_, expr)
1080 | ExprKind::Cast(expr, _)
1081 | ExprKind::Type(expr, _)
1082 | ExprKind::AddrOf(_, _, expr)
1083 | ExprKind::Field(expr, _)
1084 | ExprKind::Struct(_, _, Some(expr)) => self.visit_expr(expr),
1086 // Exploration cannot continue ... calculate the hir_id of the current
1087 // expr assuming it is a Path
1088 if let Some(hir_id) = var_def_id(self.cx, &expr) {
1090 if hir_id == self.for_pattern.hir_id {
1091 self.found_pattern = true;
1093 // If the for loop pattern is a tuple, determine whether the current
1094 // expr is inside that tuple pattern
1095 if let PatKind::Tuple(pat_list, _) = &self.for_pattern.kind {
1096 let hir_id_list: Vec<HirId> = pat_list.iter().map(|p| p.hir_id).collect();
1097 if hir_id_list.contains(&hir_id) {
1098 self.found_pattern = true;
1106 // This is triggered by walk_expr() for the case of vec.push(pat)
1107 fn visit_qpath(&mut self, qpath: &'tcx QPath<'_>, _: HirId, _: Span) {
1109 if let QPath::Resolved(_, path) = qpath;
1110 if let Res::Local(hir_id) = &path.res;
1112 if *hir_id == self.for_pattern.hir_id{
1113 self.found_pattern = true;
1116 if let PatKind::Tuple(pat_list, _) = &self.for_pattern.kind {
1117 let hir_id_list: Vec<HirId> = pat_list.iter().map(|p| p.hir_id).collect();
1118 if hir_id_list.contains(&hir_id) {
1119 self.found_pattern = true;
1126 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1127 NestedVisitorMap::None
1131 // Scans the body of the for loop and determines whether lint should be given
1132 struct SameItemPushVisitor<'a, 'tcx> {
1134 // this field holds the last vec push operation visited, which should be the only push seen
1135 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1136 cx: &'a LateContext<'tcx>,
1139 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1140 type Map = Map<'tcx>;
1142 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1144 // Non-determinism may occur ... don't give a lint
1145 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1146 ExprKind::Block(block, _) => self.visit_block(block),
1151 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1152 for stmt in b.stmts.iter() {
1153 self.visit_stmt(stmt);
1157 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1158 let vec_push_option = get_vec_push(self.cx, s);
1159 if vec_push_option.is_none() {
1160 // Current statement is not a push so visit inside
1162 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1166 // Current statement is a push ...check whether another
1167 // push had been previously done
1168 if self.vec_push.is_none() {
1169 self.vec_push = vec_push_option;
1171 // There are multiple pushes ... don't lint
1172 self.should_lint = false;
1177 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1178 NestedVisitorMap::None
1182 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1183 // the Vec being pushed into and the item being pushed
1184 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1186 // Extract method being called
1187 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1188 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1189 // Figure out the parameters for the method call
1190 if let Some(self_expr) = args.get(0);
1191 if let Some(pushed_item) = args.get(1);
1192 // Check that the method being called is push() on a Vec
1193 if match_type(cx, cx.typeck_results().expr_ty(self_expr), &paths::VEC);
1194 if path.ident.name.as_str() == "push";
1196 return Some((self_expr, pushed_item))
1202 /// Detects for loop pushing the same item into a Vec
1203 fn detect_same_item_push<'tcx>(
1204 cx: &LateContext<'tcx>,
1207 body: &'tcx Expr<'_>,
1210 // Determine whether it is safe to lint the body
1211 let mut same_item_push_visitor = SameItemPushVisitor {
1216 walk_expr(&mut same_item_push_visitor, body);
1217 if same_item_push_visitor.should_lint {
1218 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1219 // Make sure that the push does not involve possibly mutating values
1220 if mutated_variables(pushed_item, cx).map_or(false, |mutvars| mutvars.is_empty()) {
1221 // Walk through the expression being pushed and make sure that it
1222 // does not contain the for loop pattern
1223 let mut for_pat_visitor = ForPatternVisitor {
1224 found_pattern: false,
1228 walk_expr(&mut for_pat_visitor, pushed_item);
1230 if !for_pat_visitor.found_pattern {
1231 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1232 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1238 "it looks like the same item is being pushed into this Vec",
1241 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1242 item_str, vec_str, item_str
1251 /// Checks for looping over a range and then indexing a sequence with it.
1252 /// The iteratee must be a range literal.
1253 #[allow(clippy::too_many_lines)]
1254 fn check_for_loop_range<'tcx>(
1255 cx: &LateContext<'tcx>,
1257 arg: &'tcx Expr<'_>,
1258 body: &'tcx Expr<'_>,
1259 expr: &'tcx Expr<'_>,
1261 if let Some(higher::Range {
1265 }) = higher::range(cx, arg)
1267 // the var must be a single name
1268 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1269 let mut visitor = VarVisitor {
1272 indexed_mut: FxHashSet::default(),
1273 indexed_indirectly: FxHashMap::default(),
1274 indexed_directly: FxHashMap::default(),
1275 referenced: FxHashSet::default(),
1277 prefer_mutable: false,
1279 walk_expr(&mut visitor, body);
1281 // linting condition: we only indexed one variable, and indexed it directly
1282 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1283 let (indexed, (indexed_extent, indexed_ty)) = visitor
1287 .expect("already checked that we have exactly 1 element");
1289 // ensure that the indexed variable was declared before the loop, see #601
1290 if let Some(indexed_extent) = indexed_extent {
1291 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1292 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1293 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1294 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1295 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1300 // don't lint if the container that is indexed does not have .iter() method
1301 let has_iter = has_iter_method(cx, indexed_ty);
1302 if has_iter.is_none() {
1306 // don't lint if the container that is indexed into is also used without
1308 if visitor.referenced.contains(&indexed) {
1312 let starts_at_zero = is_integer_const(cx, start, 0);
1314 let skip = if starts_at_zero {
1317 format!(".skip({})", snippet(cx, start.span, ".."))
1320 let mut end_is_start_plus_val = false;
1322 let take = if let Some(end) = *end {
1323 let mut take_expr = end;
1325 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1326 if let BinOpKind::Add = op.node {
1327 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1328 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1330 if start_equal_left {
1332 } else if start_equal_right {
1336 end_is_start_plus_val = start_equal_left | start_equal_right;
1340 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1344 ast::RangeLimits::Closed => {
1345 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1346 format!(".take({})", take_expr + sugg::ONE)
1348 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1355 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1356 ("mut ", "iter_mut")
1361 let take_is_empty = take.is_empty();
1362 let mut method_1 = take;
1363 let mut method_2 = skip;
1365 if end_is_start_plus_val {
1366 mem::swap(&mut method_1, &mut method_2);
1369 if visitor.nonindex {
1372 NEEDLESS_RANGE_LOOP,
1374 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1378 "consider using an iterator",
1380 (pat.span, format!("({}, <item>)", ident.name)),
1383 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1390 let repl = if starts_at_zero && take_is_empty {
1391 format!("&{}{}", ref_mut, indexed)
1393 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1398 NEEDLESS_RANGE_LOOP,
1401 "the loop variable `{}` is only used to index `{}`.",
1407 "consider using an iterator",
1408 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1418 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1420 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1421 if len_args.len() == 1;
1422 if method.ident.name == sym!(len);
1423 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1424 if path.segments.len() == 1;
1425 if path.segments[0].ident.name == var;
1434 fn is_end_eq_array_len<'tcx>(
1435 cx: &LateContext<'tcx>,
1437 limits: ast::RangeLimits,
1438 indexed_ty: Ty<'tcx>,
1441 if let ExprKind::Lit(ref lit) = end.kind;
1442 if let ast::LitKind::Int(end_int, _) = lit.node;
1443 if let ty::Array(_, arr_len_const) = indexed_ty.kind;
1444 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1446 return match limits {
1447 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1448 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1456 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1457 let mut applicability = Applicability::MachineApplicable;
1458 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1459 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1464 "it is more concise to loop over references to containers instead of using explicit \
1466 "to write this more concisely, try",
1467 format!("&{}{}", muta, object),
1472 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1473 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1474 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1475 // just the receiver, no arguments
1476 if args.len() == 1 {
1477 let method_name = &*method.ident.as_str();
1478 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1479 if method_name == "iter" || method_name == "iter_mut" {
1480 if is_ref_iterable_type(cx, &args[0]) {
1481 lint_iter_method(cx, args, arg, method_name);
1483 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1484 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1485 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1486 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1487 let mut applicability = Applicability::MachineApplicable;
1488 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1491 EXPLICIT_INTO_ITER_LOOP,
1493 "it is more concise to loop over containers instead of using explicit \
1495 "to write this more concisely, try",
1500 let ref_receiver_ty = cx.tcx.mk_ref(
1501 cx.tcx.lifetimes.re_erased,
1504 mutbl: Mutability::Not,
1507 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1508 lint_iter_method(cx, args, arg, method_name)
1511 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1516 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1517 probably not what you want",
1519 next_loop_linted = true;
1523 if !next_loop_linted {
1524 check_arg_type(cx, pat, arg);
1528 /// Checks for `for` loops over `Option`s and `Result`s.
1529 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1530 let ty = cx.typeck_results().expr_ty(arg);
1531 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1534 FOR_LOOPS_OVER_FALLIBLES,
1537 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1538 `if let` statement.",
1539 snippet(cx, arg.span, "_")
1543 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1544 snippet(cx, pat.span, "_"),
1545 snippet(cx, arg.span, "_")
1548 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1551 FOR_LOOPS_OVER_FALLIBLES,
1554 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1555 `if let` statement.",
1556 snippet(cx, arg.span, "_")
1560 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1561 snippet(cx, pat.span, "_"),
1562 snippet(cx, arg.span, "_")
1568 fn check_for_loop_explicit_counter<'tcx>(
1569 cx: &LateContext<'tcx>,
1571 arg: &'tcx Expr<'_>,
1572 body: &'tcx Expr<'_>,
1573 expr: &'tcx Expr<'_>,
1575 // Look for variables that are incremented once per loop iteration.
1576 let mut visitor = IncrementVisitor {
1578 states: FxHashMap::default(),
1582 walk_expr(&mut visitor, body);
1584 // For each candidate, check the parent block to see if
1585 // it's initialized to zero at the start of the loop.
1586 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1587 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1588 let mut visitor2 = InitializeVisitor {
1592 state: VarState::IncrOnce,
1597 walk_block(&mut visitor2, block);
1599 if visitor2.state == VarState::Warn {
1600 if let Some(name) = visitor2.name {
1601 let mut applicability = Applicability::MachineApplicable;
1603 // for some reason this is the only way to get the `Span`
1604 // of the entire `for` loop
1605 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1613 EXPLICIT_COUNTER_LOOP,
1614 for_span.with_hi(arg.span.hi()),
1615 &format!("the variable `{}` is used as a loop counter.", name),
1618 "for ({}, {}) in {}.enumerate()",
1620 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1621 make_iterator_snippet(cx, arg, &mut applicability),
1631 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1632 /// actual `Iterator` that the loop uses.
1633 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1634 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1635 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1640 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1643 // (&x).into_iter() ==> x.iter()
1644 // (&mut x).into_iter() ==> x.iter_mut()
1646 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1647 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1649 let meth_name = match mutability {
1650 Mutability::Mut => "iter_mut",
1651 Mutability::Not => "iter",
1655 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1661 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1667 /// Checks for the `FOR_KV_MAP` lint.
1668 fn check_for_loop_over_map_kv<'tcx>(
1669 cx: &LateContext<'tcx>,
1671 arg: &'tcx Expr<'_>,
1672 body: &'tcx Expr<'_>,
1673 expr: &'tcx Expr<'_>,
1675 let pat_span = pat.span;
1677 if let PatKind::Tuple(ref pat, _) = pat.kind {
1679 let arg_span = arg.span;
1680 let (new_pat_span, kind, ty, mutbl) = match cx.typeck_results().expr_ty(arg).kind {
1681 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1682 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1683 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1688 let mutbl = match mutbl {
1689 Mutability::Not => "",
1690 Mutability::Mut => "_mut",
1692 let arg = match arg.kind {
1693 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1697 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1702 &format!("you seem to want to iterate on a map's {}s", kind),
1704 let map = sugg::Sugg::hir(cx, arg, "map");
1707 "use the corresponding method",
1709 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1710 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1720 struct MutatePairDelegate<'a, 'tcx> {
1721 cx: &'a LateContext<'tcx>,
1722 hir_id_low: Option<HirId>,
1723 hir_id_high: Option<HirId>,
1724 span_low: Option<Span>,
1725 span_high: Option<Span>,
1728 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1729 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1731 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1732 if let ty::BorrowKind::MutBorrow = bk {
1733 if let PlaceBase::Local(id) = cmt.place.base {
1734 if Some(id) == self.hir_id_low {
1735 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1737 if Some(id) == self.hir_id_high {
1738 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1744 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>) {
1745 if let PlaceBase::Local(id) = cmt.place.base {
1746 if Some(id) == self.hir_id_low {
1747 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1749 if Some(id) == self.hir_id_high {
1750 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1756 impl MutatePairDelegate<'_, '_> {
1757 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1758 (self.span_low, self.span_high)
1762 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1763 if let Some(higher::Range {
1767 }) = higher::range(cx, arg)
1769 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1770 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1771 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1772 mut_warn_with_span(cx, span_low);
1773 mut_warn_with_span(cx, span_high);
1778 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
1779 if let Some(sp) = span {
1784 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1789 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
1791 if let ExprKind::Path(ref qpath) = bound.kind;
1792 if let QPath::Resolved(None, _) = *qpath;
1794 let res = qpath_res(cx, qpath, bound.hir_id);
1795 if let Res::Local(hir_id) = res {
1796 let node_str = cx.tcx.hir().get(hir_id);
1798 if let Node::Binding(pat) = node_str;
1799 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1800 if let BindingAnnotation::Mutable = bind_ann;
1802 return Some(hir_id);
1811 fn check_for_mutation<'tcx>(
1812 cx: &LateContext<'tcx>,
1814 bound_ids: &[Option<HirId>],
1815 ) -> (Option<Span>, Option<Span>) {
1816 let mut delegate = MutatePairDelegate {
1818 hir_id_low: bound_ids[0],
1819 hir_id_high: bound_ids[1],
1823 let def_id = body.hir_id.owner.to_def_id();
1824 cx.tcx.infer_ctxt().enter(|infcx| {
1825 ExprUseVisitor::new(
1828 def_id.expect_local(),
1830 cx.typeck_results(),
1834 delegate.mutation_span()
1837 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1838 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
1840 PatKind::Wild => true,
1841 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
1846 struct LocalUsedVisitor<'a, 'tcx> {
1847 cx: &'a LateContext<'tcx>,
1852 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1853 type Map = Map<'tcx>;
1855 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1856 if same_var(self.cx, expr, self.local) {
1859 walk_expr(self, expr);
1863 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1864 NestedVisitorMap::None
1868 struct VarVisitor<'a, 'tcx> {
1869 /// context reference
1870 cx: &'a LateContext<'tcx>,
1871 /// var name to look for as index
1873 /// indexed variables that are used mutably
1874 indexed_mut: FxHashSet<Symbol>,
1875 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1876 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
1877 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1878 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1879 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
1880 /// Any names that are used outside an index operation.
1881 /// Used to detect things like `&mut vec` used together with `vec[i]`
1882 referenced: FxHashSet<Symbol>,
1883 /// has the loop variable been used in expressions other than the index of
1886 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1887 /// takes `&mut self`
1888 prefer_mutable: bool,
1891 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1892 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
1894 // the indexed container is referenced by a name
1895 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
1896 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1897 if seqvar.segments.len() == 1;
1899 let index_used_directly = same_var(self.cx, idx, self.var);
1900 let indexed_indirectly = {
1901 let mut used_visitor = LocalUsedVisitor {
1906 walk_expr(&mut used_visitor, idx);
1910 if indexed_indirectly || index_used_directly {
1911 if self.prefer_mutable {
1912 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1914 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
1916 Res::Local(hir_id) => {
1917 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1918 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1919 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1920 if indexed_indirectly {
1921 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1923 if index_used_directly {
1924 self.indexed_directly.insert(
1925 seqvar.segments[0].ident.name,
1926 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
1929 return false; // no need to walk further *on the variable*
1931 Res::Def(DefKind::Static | DefKind::Const, ..) => {
1932 if indexed_indirectly {
1933 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1935 if index_used_directly {
1936 self.indexed_directly.insert(
1937 seqvar.segments[0].ident.name,
1938 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
1941 return false; // no need to walk further *on the variable*
1952 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1953 type Map = Map<'tcx>;
1955 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1958 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
1959 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1960 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1961 if !self.check(&args[1], &args[0], expr);
1967 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
1968 if !self.check(idx, seqexpr, expr);
1973 // directly using a variable
1974 if let ExprKind::Path(ref qpath) = expr.kind;
1975 if let QPath::Resolved(None, ref path) = *qpath;
1976 if path.segments.len() == 1;
1978 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
1979 if local_id == self.var {
1980 self.nonindex = true;
1982 // not the correct variable, but still a variable
1983 self.referenced.insert(path.segments[0].ident.name);
1989 let old = self.prefer_mutable;
1991 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
1992 self.prefer_mutable = true;
1993 self.visit_expr(lhs);
1994 self.prefer_mutable = false;
1995 self.visit_expr(rhs);
1997 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
1998 if mutbl == Mutability::Mut {
1999 self.prefer_mutable = true;
2001 self.visit_expr(expr);
2003 ExprKind::Call(ref f, args) => {
2006 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2007 self.prefer_mutable = false;
2008 if let ty::Ref(_, _, mutbl) = ty.kind {
2009 if mutbl == Mutability::Mut {
2010 self.prefer_mutable = true;
2013 self.visit_expr(expr);
2016 ExprKind::MethodCall(_, _, args, _) => {
2017 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2018 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2019 self.prefer_mutable = false;
2020 if let ty::Ref(_, _, mutbl) = ty.kind {
2021 if mutbl == Mutability::Mut {
2022 self.prefer_mutable = true;
2025 self.visit_expr(expr);
2028 ExprKind::Closure(_, _, body_id, ..) => {
2029 let body = self.cx.tcx.hir().body(body_id);
2030 self.visit_expr(&body.value);
2032 _ => walk_expr(self, expr),
2034 self.prefer_mutable = old;
2036 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2037 NestedVisitorMap::None
2041 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2042 let def_id = match var_def_id(cx, expr) {
2044 None => return false,
2046 if let Some(used_mutably) = mutated_variables(container, cx) {
2047 if used_mutably.contains(&def_id) {
2054 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2055 let def_id = match var_def_id(cx, iter_expr) {
2057 None => return false,
2059 let mut visitor = VarUsedAfterLoopVisitor {
2062 iter_expr_id: iter_expr.hir_id,
2063 past_while_let: false,
2064 var_used_after_while_let: false,
2066 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2067 walk_block(&mut visitor, enclosing_block);
2069 visitor.var_used_after_while_let
2072 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2073 cx: &'a LateContext<'tcx>,
2075 iter_expr_id: HirId,
2076 past_while_let: bool,
2077 var_used_after_while_let: bool,
2080 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2081 type Map = Map<'tcx>;
2083 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2084 if self.past_while_let {
2085 if Some(self.def_id) == var_def_id(self.cx, expr) {
2086 self.var_used_after_while_let = true;
2088 } else if self.iter_expr_id == expr.hir_id {
2089 self.past_while_let = true;
2091 walk_expr(self, expr);
2093 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2094 NestedVisitorMap::None
2098 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2099 /// for `&T` and `&mut T`, such as `Vec`.
2101 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2102 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2103 // will allow further borrows afterwards
2104 let ty = cx.typeck_results().expr_ty(e);
2105 is_iterable_array(ty, cx) ||
2106 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2107 match_type(cx, ty, &paths::LINKED_LIST) ||
2108 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2109 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2110 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2111 match_type(cx, ty, &paths::BINARY_HEAP) ||
2112 match_type(cx, ty, &paths::BTREEMAP) ||
2113 match_type(cx, ty, &paths::BTREESET)
2116 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2117 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2119 ty::Array(_, n) => n
2120 .try_eval_usize(cx.tcx, cx.param_env)
2121 .map_or(false, |val| (0..=32).contains(&val)),
2126 /// If a block begins with a statement (possibly a `let` binding) and has an
2127 /// expression, return it.
2128 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2129 if block.stmts.is_empty() {
2132 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2133 local.init //.map(|expr| expr)
2139 /// If a block begins with an expression (with or without semicolon), return it.
2140 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2142 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2143 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2144 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2145 StmtKind::Local(..) | StmtKind::Item(..) => None,
2151 /// Returns `true` if expr contains a single break expr without destination label
2153 /// passed expression. The expression may be within a block.
2154 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2156 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2157 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2162 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2163 // incremented exactly once in the loop body, and initialized to zero
2164 // at the start of the loop.
2165 #[derive(Debug, PartialEq)]
2167 Initial, // Not examined yet
2168 IncrOnce, // Incremented exactly once, may be a loop counter
2169 Declared, // Declared but not (yet) initialized to zero
2174 /// Scan a for loop for variables that are incremented exactly once.
2175 struct IncrementVisitor<'a, 'tcx> {
2176 cx: &'a LateContext<'tcx>, // context reference
2177 states: FxHashMap<HirId, VarState>, // incremented variables
2178 depth: u32, // depth of conditional expressions
2182 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2183 type Map = Map<'tcx>;
2185 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2190 // If node is a variable
2191 if let Some(def_id) = var_def_id(self.cx, expr) {
2192 if let Some(parent) = get_parent_expr(self.cx, expr) {
2193 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2196 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2197 if lhs.hir_id == expr.hir_id {
2198 if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) {
2199 *state = match *state {
2200 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2201 _ => VarState::DontWarn,
2204 // Assigned some other value
2205 *state = VarState::DontWarn;
2209 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2210 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2211 *state = VarState::DontWarn
2216 } else if is_loop(expr) || is_conditional(expr) {
2218 walk_expr(self, expr);
2221 } else if let ExprKind::Continue(_) = expr.kind {
2225 walk_expr(self, expr);
2227 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2228 NestedVisitorMap::None
2232 /// Checks whether a variable is initialized to zero at the start of a loop.
2233 struct InitializeVisitor<'a, 'tcx> {
2234 cx: &'a LateContext<'tcx>, // context reference
2235 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2238 name: Option<Symbol>,
2239 depth: u32, // depth of conditional expressions
2243 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2244 type Map = Map<'tcx>;
2246 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2247 // Look for declarations of the variable
2248 if let StmtKind::Local(ref local) = stmt.kind {
2249 if local.pat.hir_id == self.var_id {
2250 if let PatKind::Binding(.., ident, _) = local.pat.kind {
2251 self.name = Some(ident.name);
2253 self.state = local.init.as_ref().map_or(VarState::Declared, |init| {
2254 if is_integer_const(&self.cx, init, 0) {
2263 walk_stmt(self, stmt);
2266 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2267 if self.state == VarState::DontWarn {
2270 if expr.hir_id == self.end_expr.hir_id {
2271 self.past_loop = true;
2274 // No need to visit expressions before the variable is
2276 if self.state == VarState::IncrOnce {
2280 // If node is the desired variable, see how it's used
2281 if var_def_id(self.cx, expr) == Some(self.var_id) {
2282 if let Some(parent) = get_parent_expr(self.cx, expr) {
2284 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2285 self.state = VarState::DontWarn;
2287 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2288 self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 {
2294 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2295 self.state = VarState::DontWarn
2302 self.state = VarState::DontWarn;
2305 } else if !self.past_loop && is_loop(expr) {
2306 self.state = VarState::DontWarn;
2308 } else if is_conditional(expr) {
2310 walk_expr(self, expr);
2314 walk_expr(self, expr);
2317 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2318 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2322 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2323 if let ExprKind::Path(ref qpath) = expr.kind {
2324 let path_res = qpath_res(cx, qpath, expr.hir_id);
2325 if let Res::Local(hir_id) = path_res {
2326 return Some(hir_id);
2332 fn is_loop(expr: &Expr<'_>) -> bool {
2333 matches!(expr.kind, ExprKind::Loop(..))
2336 fn is_conditional(expr: &Expr<'_>) -> bool {
2337 matches!(expr.kind, ExprKind::Match(..))
2340 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2342 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2343 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2344 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2346 return is_loop_nested(cx, loop_expr, iter_expr)
2352 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2353 let mut id = loop_expr.hir_id;
2354 let iter_name = if let Some(name) = path_name(iter_expr) {
2360 let parent = cx.tcx.hir().get_parent_node(id);
2364 match cx.tcx.hir().find(parent) {
2365 Some(Node::Expr(expr)) => {
2366 if let ExprKind::Loop(..) = expr.kind {
2370 Some(Node::Block(block)) => {
2371 let mut block_visitor = LoopNestVisitor {
2373 iterator: iter_name,
2376 walk_block(&mut block_visitor, block);
2377 if block_visitor.nesting == RuledOut {
2381 Some(Node::Stmt(_)) => (),
2390 #[derive(PartialEq, Eq)]
2392 Unknown, // no nesting detected yet
2393 RuledOut, // the iterator is initialized or assigned within scope
2394 LookFurther, // no nesting detected, no further walk required
2397 use self::Nesting::{LookFurther, RuledOut, Unknown};
2399 struct LoopNestVisitor {
2405 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2406 type Map = Map<'tcx>;
2408 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2409 if stmt.hir_id == self.hir_id {
2410 self.nesting = LookFurther;
2411 } else if self.nesting == Unknown {
2412 walk_stmt(self, stmt);
2416 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2417 if self.nesting != Unknown {
2420 if expr.hir_id == self.hir_id {
2421 self.nesting = LookFurther;
2425 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2426 if match_var(path, self.iterator) {
2427 self.nesting = RuledOut;
2430 _ => walk_expr(self, expr),
2434 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2435 if self.nesting != Unknown {
2438 if let PatKind::Binding(.., span_name, _) = pat.kind {
2439 if self.iterator == span_name.name {
2440 self.nesting = RuledOut;
2447 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2448 NestedVisitorMap::None
2452 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2453 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2454 let segments = &path.segments;
2455 if segments.len() == 1 {
2456 return Some(segments[0].ident.name);
2462 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2463 if constant(cx, cx.typeck_results(), cond).is_some() {
2464 // A pure constant condition (e.g., `while false`) is not linted.
2468 let mut var_visitor = VarCollectorVisitor {
2470 ids: FxHashSet::default(),
2471 def_ids: FxHashMap::default(),
2474 var_visitor.visit_expr(cond);
2475 if var_visitor.skip {
2478 let used_in_condition = &var_visitor.ids;
2479 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2480 used_in_condition.is_disjoint(&used_mutably)
2484 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2486 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2487 has_break_or_return: false,
2489 has_break_or_return_visitor.visit_expr(expr);
2490 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2492 if no_cond_variable_mutated && !mutable_static_in_cond {
2495 WHILE_IMMUTABLE_CONDITION,
2497 "variables in the condition are not mutated in the loop body",
2499 diag.note("this may lead to an infinite or to a never running loop");
2501 if has_break_or_return {
2502 diag.note("this loop contains `return`s or `break`s");
2503 diag.help("rewrite it as `if cond { loop { } }`");
2510 struct HasBreakOrReturnVisitor {
2511 has_break_or_return: bool,
2514 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2515 type Map = Map<'tcx>;
2517 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2518 if self.has_break_or_return {
2523 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2524 self.has_break_or_return = true;
2530 walk_expr(self, expr);
2533 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2534 NestedVisitorMap::None
2538 /// Collects the set of variables in an expression
2539 /// Stops analysis if a function call is found
2540 /// Note: In some cases such as `self`, there are no mutable annotation,
2541 /// All variables definition IDs are collected
2542 struct VarCollectorVisitor<'a, 'tcx> {
2543 cx: &'a LateContext<'tcx>,
2544 ids: FxHashSet<HirId>,
2545 def_ids: FxHashMap<def_id::DefId, bool>,
2549 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2550 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2552 if let ExprKind::Path(ref qpath) = ex.kind;
2553 if let QPath::Resolved(None, _) = *qpath;
2554 let res = qpath_res(self.cx, qpath, ex.hir_id);
2557 Res::Local(hir_id) => {
2558 self.ids.insert(hir_id);
2560 Res::Def(DefKind::Static, def_id) => {
2561 let mutable = self.cx.tcx.is_mutable_static(def_id);
2562 self.def_ids.insert(def_id, mutable);
2571 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2572 type Map = Map<'tcx>;
2574 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2576 ExprKind::Path(_) => self.insert_def_id(ex),
2577 // If there is any function/method call… we just stop analysis
2578 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2580 _ => walk_expr(self, ex),
2584 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2585 NestedVisitorMap::None
2589 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2591 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2592 check_needless_collect_direct_usage(expr, cx);
2593 check_needless_collect_indirect_usage(expr, cx);
2595 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2597 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2598 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2599 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2600 if let Some(ref generic_args) = chain_method.args;
2601 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2603 let ty = cx.typeck_results().node_type(ty.hir_id);
2604 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2605 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2606 match_type(cx, ty, &paths::BTREEMAP) ||
2607 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2608 if method.ident.name == sym!(len) {
2609 let span = shorten_span(expr, sym!(collect));
2614 NEEDLESS_COLLECT_MSG,
2616 "count()".to_string(),
2617 Applicability::MachineApplicable,
2620 if method.ident.name == sym!(is_empty) {
2621 let span = shorten_span(expr, sym!(iter));
2626 NEEDLESS_COLLECT_MSG,
2628 "get(0).is_none()".to_string(),
2629 Applicability::MachineApplicable,
2632 if method.ident.name == sym!(contains) {
2633 let contains_arg = snippet(cx, args[1].span, "??");
2634 let span = shorten_span(expr, sym!(collect));
2639 NEEDLESS_COLLECT_MSG,
2641 let (arg, pred) = if contains_arg.starts_with('&') {
2642 ("x", &contains_arg[1..])
2644 ("&x", &*contains_arg)
2646 diag.span_suggestion(
2650 "any(|{}| x == {})",
2653 Applicability::MachineApplicable,
2663 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2664 if let ExprKind::Block(ref block, _) = expr.kind {
2665 for ref stmt in block.stmts {
2667 if let StmtKind::Local(
2668 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2669 init: Some(ref init_expr), .. }
2671 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2672 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2673 if let Some(ref generic_args) = method_name.args;
2674 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2675 if let ty = cx.typeck_results().node_type(ty.hir_id);
2676 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2677 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2678 match_type(cx, ty, &paths::LINKED_LIST);
2679 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2680 if iter_calls.len() == 1;
2682 // Suggest replacing iter_call with iter_replacement, and removing stmt
2683 let iter_call = &iter_calls[0];
2687 stmt.span.until(iter_call.span),
2688 NEEDLESS_COLLECT_MSG,
2690 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2691 diag.multipart_suggestion(
2692 iter_call.get_suggestion_text(),
2694 (stmt.span, String::new()),
2695 (iter_call.span, iter_replacement)
2697 Applicability::MachineApplicable,// MaybeIncorrect,
2707 struct IterFunction {
2708 func: IterFunctionKind,
2712 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2714 IterFunctionKind::IntoIter => String::new(),
2715 IterFunctionKind::Len => String::from(".count()"),
2716 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2717 IterFunctionKind::Contains(span) => format!(".any(|x| x == {})", snippet(cx, *span, "..")),
2720 fn get_suggestion_text(&self) -> &'static str {
2722 IterFunctionKind::IntoIter => {
2723 "Use the original Iterator instead of collecting it and then producing a new one"
2725 IterFunctionKind::Len => {
2726 "Take the original Iterator's count instead of collecting it and finding the length"
2728 IterFunctionKind::IsEmpty => {
2729 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
2731 IterFunctionKind::Contains(_) => {
2732 "Check if the original Iterator contains an element instead of collecting then checking"
2737 enum IterFunctionKind {
2744 struct IterFunctionVisitor {
2745 uses: Vec<IterFunction>,
2749 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
2750 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
2751 // Check function calls on our collection
2753 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
2754 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
2755 if let &[name] = &path.segments;
2756 if name.ident == self.target;
2758 let len = sym!(len);
2759 let is_empty = sym!(is_empty);
2760 let contains = sym!(contains);
2761 match method_name.ident.name {
2762 sym::into_iter => self.uses.push(
2763 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
2765 name if name == len => self.uses.push(
2766 IterFunction { func: IterFunctionKind::Len, span: expr.span }
2768 name if name == is_empty => self.uses.push(
2769 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
2771 name if name == contains => self.uses.push(
2772 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
2774 _ => self.seen_other = true,
2779 // Check if the collection is used for anything else
2781 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
2782 if let &[name] = &path.segments;
2783 if name.ident == self.target;
2785 self.seen_other = true;
2787 walk_expr(self, expr);
2792 type Map = Map<'tcx>;
2793 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2794 NestedVisitorMap::None
2798 /// Detect the occurences of calls to `iter` or `into_iter` for the
2799 /// given identifier
2800 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
2801 let mut visitor = IterFunctionVisitor {
2806 visitor.visit_block(block);
2807 if visitor.seen_other {
2814 fn shorten_span(expr: &Expr<'_>, target_fn_name: Symbol) -> Span {
2815 let mut current_expr = expr;
2816 while let ExprKind::MethodCall(ref path, ref span, ref args, _) = current_expr.kind {
2817 if path.ident.name == target_fn_name {
2818 return expr.span.with_lo(span.lo());
2820 current_expr = &args[0];