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};
5 use crate::utils::visitors::LocalUsedVisitor;
7 contains_name, get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
8 indent_of, is_in_panic_handler, is_integer_const, is_no_std_crate, is_refutable, is_type_diagnostic_item,
9 last_path_segment, match_trait_method, match_type, match_var, multispan_sugg, qpath_res, single_segment_path,
10 snippet, snippet_with_applicability, snippet_with_macro_callsite, span_lint, span_lint_and_help,
11 span_lint_and_sugg, span_lint_and_then, sugg, SpanlessEq,
13 use if_chain::if_chain;
15 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
16 use rustc_errors::Applicability;
17 use rustc_hir::def::{DefKind, Res};
18 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
20 def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, InlineAsmOperand,
21 Local, LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
23 use rustc_infer::infer::TyCtxtInferExt;
24 use rustc_lint::{LateContext, LateLintPass, LintContext};
25 use rustc_middle::hir::map::Map;
26 use rustc_middle::lint::in_external_macro;
27 use rustc_middle::middle::region;
28 use rustc_middle::ty::{self, Ty, TyS};
29 use rustc_session::{declare_lint_pass, declare_tool_lint};
30 use rustc_span::source_map::Span;
31 use rustc_span::symbol::{sym, Ident, Symbol};
32 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
33 use std::iter::{once, Iterator};
36 declare_clippy_lint! {
37 /// **What it does:** Checks for for-loops that manually copy items between
38 /// slices that could be optimized by having a memcpy.
40 /// **Why is this bad?** It is not as fast as a memcpy.
42 /// **Known problems:** None.
46 /// # let src = vec![1];
47 /// # let mut dst = vec![0; 65];
48 /// for i in 0..src.len() {
49 /// dst[i + 64] = src[i];
52 /// Could be written as:
54 /// # let src = vec![1];
55 /// # let mut dst = vec![0; 65];
56 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
60 "manually copying items between slices"
63 declare_clippy_lint! {
64 /// **What it does:** Checks for looping over the range of `0..len` of some
65 /// collection just to get the values by index.
67 /// **Why is this bad?** Just iterating the collection itself makes the intent
68 /// more clear and is probably faster.
70 /// **Known problems:** None.
74 /// let vec = vec!['a', 'b', 'c'];
75 /// for i in 0..vec.len() {
76 /// println!("{}", vec[i]);
79 /// Could be written as:
81 /// let vec = vec!['a', 'b', 'c'];
83 /// println!("{}", i);
86 pub NEEDLESS_RANGE_LOOP,
88 "for-looping over a range of indices where an iterator over items would do"
91 declare_clippy_lint! {
92 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
93 /// suggests the latter.
95 /// **Why is this bad?** Readability.
97 /// **Known problems:** False negatives. We currently only warn on some known
102 /// // with `y` a `Vec` or slice:
103 /// # let y = vec![1];
104 /// for x in y.iter() {
108 /// can be rewritten to
110 /// # let y = vec![1];
115 pub EXPLICIT_ITER_LOOP,
117 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
120 declare_clippy_lint! {
121 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
122 /// suggests the latter.
124 /// **Why is this bad?** Readability.
126 /// **Known problems:** None
130 /// # let y = vec![1];
131 /// // with `y` a `Vec` or slice:
132 /// for x in y.into_iter() {
136 /// can be rewritten to
138 /// # let y = vec![1];
143 pub EXPLICIT_INTO_ITER_LOOP,
145 "for-looping over `_.into_iter()` when `_` would do"
148 declare_clippy_lint! {
149 /// **What it does:** Checks for loops on `x.next()`.
151 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
152 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
153 /// implements `IntoIterator`, so that possibly one value will be iterated,
154 /// leading to some hard to find bugs. No one will want to write such code
155 /// [except to win an Underhanded Rust
156 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
158 /// **Known problems:** None.
162 /// for x in y.next() {
168 "for-looping over `_.next()` which is probably not intended"
171 declare_clippy_lint! {
172 /// **What it does:** Checks for `for` loops over `Option` or `Result` values.
174 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
177 /// **Known problems:** None.
181 /// # let opt = Some(1);
189 /// if let Some(x) = opt {
197 /// # let res: Result<i32, std::io::Error> = Ok(1);
205 /// if let Ok(x) = res {
209 pub FOR_LOOPS_OVER_FALLIBLES,
211 "for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
214 declare_clippy_lint! {
215 /// **What it does:** Detects `loop + match` combinations that are easier
216 /// written as a `while let` loop.
218 /// **Why is this bad?** The `while let` loop is usually shorter and more
221 /// **Known problems:** Sometimes the wrong binding is displayed ([#383](https://github.com/rust-lang/rust-clippy/issues/383)).
225 /// # let y = Some(1);
227 /// let x = match y {
231 /// // .. do something with x
233 /// // is easier written as
234 /// while let Some(x) = y {
235 /// // .. do something with x
240 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
243 declare_clippy_lint! {
244 /// **What it does:** Checks for functions collecting an iterator when collect
247 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
248 /// when this allocation may not be needed.
250 /// **Known problems:**
255 /// # let iterator = vec![1].into_iter();
256 /// let len = iterator.clone().collect::<Vec<_>>().len();
258 /// let len = iterator.count();
260 pub NEEDLESS_COLLECT,
262 "collecting an iterator when collect is not needed"
265 declare_clippy_lint! {
266 /// **What it does:** Checks `for` loops over slices with an explicit counter
267 /// and suggests the use of `.enumerate()`.
269 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
270 /// declutters the code and may be faster in some instances.
272 /// **Known problems:** None.
276 /// # let v = vec![1];
277 /// # fn bar(bar: usize, baz: usize) {}
284 /// Could be written as
286 /// # let v = vec![1];
287 /// # fn bar(bar: usize, baz: usize) {}
288 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
290 pub EXPLICIT_COUNTER_LOOP,
292 "for-looping with an explicit counter when `_.enumerate()` would do"
295 declare_clippy_lint! {
296 /// **What it does:** Checks for empty `loop` expressions.
298 /// **Why is this bad?** These busy loops burn CPU cycles without doing
299 /// anything. It is _almost always_ a better idea to `panic!` than to have
302 /// If panicking isn't possible, think of the environment and either:
303 /// - block on something
304 /// - sleep the thread for some microseconds
305 /// - yield or pause the thread
307 /// For `std` targets, this can be done with
308 /// [`std::thread::sleep`](https://doc.rust-lang.org/std/thread/fn.sleep.html)
309 /// or [`std::thread::yield_now`](https://doc.rust-lang.org/std/thread/fn.yield_now.html).
311 /// For `no_std` targets, doing this is more complicated, especially because
312 /// `#[panic_handler]`s can't panic. To stop/pause the thread, you will
313 /// probably need to invoke some target-specific intrinsic. Examples include:
314 /// - [`x86_64::instructions::hlt`](https://docs.rs/x86_64/0.12.2/x86_64/instructions/fn.hlt.html)
315 /// - [`cortex_m::asm::wfi`](https://docs.rs/cortex-m/0.6.3/cortex_m/asm/fn.wfi.html)
317 /// **Known problems:** None.
325 "empty `loop {}`, which should block or sleep"
328 declare_clippy_lint! {
329 /// **What it does:** Checks for `while let` expressions on iterators.
331 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
332 /// the intent better.
334 /// **Known problems:** None.
338 /// while let Some(val) = iter() {
342 pub WHILE_LET_ON_ITERATOR,
344 "using a while-let loop instead of a for loop on an iterator"
347 declare_clippy_lint! {
348 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
349 /// ignoring either the keys or values.
351 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
352 /// can be used to express that don't need the values or keys.
354 /// **Known problems:** None.
358 /// for (k, _) in &map {
363 /// could be replaced by
366 /// for k in map.keys() {
372 "looping on a map using `iter` when `keys` or `values` would do"
375 declare_clippy_lint! {
376 /// **What it does:** Checks for loops that will always `break`, `return` or
377 /// `continue` an outer loop.
379 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
382 /// **Known problems:** None
393 "any loop that will always `break` or `return`"
396 declare_clippy_lint! {
397 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
399 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
401 /// **Known problems:** None
405 /// let mut foo = 42;
406 /// for i in 0..foo {
408 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
413 "for loop over a range where one of the bounds is a mutable variable"
416 declare_clippy_lint! {
417 /// **What it does:** Checks whether variables used within while loop condition
418 /// can be (and are) mutated in the body.
420 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
421 /// will lead to an infinite loop.
423 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
424 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
425 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
431 /// println!("let me loop forever!");
434 pub WHILE_IMMUTABLE_CONDITION,
436 "variables used within while expression are not mutated in the body"
439 declare_clippy_lint! {
440 /// **What it does:** Checks whether a for loop is being used to push a constant
441 /// value into a Vec.
443 /// **Why is this bad?** This kind of operation can be expressed more succinctly with
444 /// `vec![item;SIZE]` or `vec.resize(NEW_SIZE, item)` and using these alternatives may also
445 /// have better performance.
446 /// **Known problems:** None
452 /// let mut vec: Vec<u8> = Vec::new();
460 /// could be written as
464 /// let mut vec: Vec<u8> = vec![item1; 20];
465 /// vec.resize(20 + 30, item2);
469 "the same item is pushed inside of a for loop"
472 declare_clippy_lint! {
473 /// **What it does:** Checks whether a for loop has a single element.
475 /// **Why is this bad?** There is no reason to have a loop of a
477 /// **Known problems:** None
482 /// for item in &[item1] {
483 /// println!("{}", item);
486 /// could be written as
489 /// let item = &item1;
490 /// println!("{}", item);
492 pub SINGLE_ELEMENT_LOOP,
494 "there is no reason to have a single element loop"
497 declare_lint_pass!(Loops => [
501 EXPLICIT_INTO_ITER_LOOP,
503 FOR_LOOPS_OVER_FALLIBLES,
506 EXPLICIT_COUNTER_LOOP,
508 WHILE_LET_ON_ITERATOR,
512 WHILE_IMMUTABLE_CONDITION,
517 impl<'tcx> LateLintPass<'tcx> for Loops {
518 #[allow(clippy::too_many_lines)]
519 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
520 if let Some((pat, arg, body)) = higher::for_loop(expr) {
521 // we don't want to check expanded macros
522 // this check is not at the top of the function
523 // since higher::for_loop expressions are marked as expansions
524 if body.span.from_expansion() {
527 check_for_loop(cx, pat, arg, body, expr);
530 // we don't want to check expanded macros
531 if expr.span.from_expansion() {
535 // check for never_loop
536 if let ExprKind::Loop(ref block, _, _) = expr.kind {
537 match never_loop_block(block, expr.hir_id) {
538 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
539 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
543 // check for `loop { if let {} else break }` that could be `while let`
544 // (also matches an explicit "match" instead of "if let")
545 // (even if the "match" or "if let" is used for declaration)
546 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
547 // also check for empty `loop {}` statements, skipping those in #[panic_handler]
548 if block.stmts.is_empty() && block.expr.is_none() && !is_in_panic_handler(cx, expr) {
549 let msg = "empty `loop {}` wastes CPU cycles";
550 let help = if is_no_std_crate(cx.tcx.hir().krate()) {
551 "you should either use `panic!()` or add a call pausing or sleeping the thread to the loop body"
553 "you should either use `panic!()` or add `std::thread::sleep(..);` to the loop body"
555 span_lint_and_help(cx, EMPTY_LOOP, expr.span, msg, None, help);
558 // extract the expression from the first statement (if any) in a block
559 let inner_stmt_expr = extract_expr_from_first_stmt(block);
560 // or extract the first expression (if any) from the block
561 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
562 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
563 // ensure "if let" compatible match structure
565 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
567 && arms[0].guard.is_none()
568 && arms[1].guard.is_none()
569 && is_simple_break_expr(&arms[1].body)
571 if in_external_macro(cx.sess(), expr.span) {
575 // NOTE: we used to build a body here instead of using
576 // ellipsis, this was removed because:
577 // 1) it was ugly with big bodies;
578 // 2) it was not indented properly;
579 // 3) it wasn’t very smart (see #675).
580 let mut applicability = Applicability::HasPlaceholders;
585 "this loop could be written as a `while let` loop",
588 "while let {} = {} {{ .. }}",
589 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
590 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
601 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
602 let pat = &arms[0].pat.kind;
604 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
605 &ExprKind::MethodCall(ref method_path, _, ref method_args, _),
606 ) = (pat, &match_expr.kind)
608 let iter_expr = &method_args[0];
610 // Don't lint when the iterator is recreated on every iteration
612 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
613 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
614 if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
620 let lhs_constructor = last_path_segment(qpath);
621 if method_path.ident.name == sym::next
622 && match_trait_method(cx, match_expr, &paths::ITERATOR)
623 && lhs_constructor.ident.name == sym::Some
624 && (pat_args.is_empty()
625 || !is_refutable(cx, &pat_args[0])
626 && !is_used_inside(cx, iter_expr, &arms[0].body)
627 && !is_iterator_used_after_while_let(cx, iter_expr)
628 && !is_nested(cx, expr, &method_args[0]))
630 let mut applicability = Applicability::MachineApplicable;
631 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
632 let loop_var = if pat_args.is_empty() {
635 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
639 WHILE_LET_ON_ITERATOR,
640 expr.span.with_hi(match_expr.span.hi()),
641 "this loop could be written as a `for` loop",
643 format!("for {} in {}", loop_var, iterator),
650 if let Some((cond, body)) = higher::while_loop(&expr) {
651 check_infinite_loop(cx, cond, body);
654 check_needless_collect(expr, cx);
658 enum NeverLoopResult {
659 // A break/return always get triggered but not necessarily for the main loop.
661 // A continue may occur for the main loop.
667 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
669 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
670 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
674 // Combine two results for parts that are called in order.
676 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
678 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
679 NeverLoopResult::Otherwise => second,
683 // Combine two results where both parts are called but not necessarily in order.
685 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
686 match (left, right) {
687 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
688 NeverLoopResult::MayContinueMainLoop
690 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
691 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
695 // Combine two results where only one of the part may have been executed.
697 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
699 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
700 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
701 NeverLoopResult::MayContinueMainLoop
703 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
707 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
708 let stmts = block.stmts.iter().map(stmt_to_expr);
709 let expr = once(block.expr.as_deref());
710 let mut iter = stmts.chain(expr).filter_map(|e| e);
711 never_loop_expr_seq(&mut iter, main_loop_id)
714 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
716 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
717 StmtKind::Local(ref local) => local.init.as_deref(),
722 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
725 | ExprKind::Unary(_, ref e)
726 | ExprKind::Cast(ref e, _)
727 | ExprKind::Type(ref e, _)
728 | ExprKind::Field(ref e, _)
729 | ExprKind::AddrOf(_, _, ref e)
730 | ExprKind::Struct(_, _, Some(ref e))
731 | ExprKind::Repeat(ref e, _)
732 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
733 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
734 never_loop_expr_all(&mut es.iter(), main_loop_id)
736 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
737 ExprKind::Binary(_, ref e1, ref e2)
738 | ExprKind::Assign(ref e1, ref e2, _)
739 | ExprKind::AssignOp(_, ref e1, ref e2)
740 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
741 ExprKind::Loop(ref b, _, _) => {
742 // Break can come from the inner loop so remove them.
743 absorb_break(&never_loop_block(b, main_loop_id))
745 ExprKind::Match(ref e, ref arms, _) => {
746 let e = never_loop_expr(e, main_loop_id);
750 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
754 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
755 ExprKind::Continue(d) => {
758 .expect("target ID can only be missing in the presence of compilation errors");
759 if id == main_loop_id {
760 NeverLoopResult::MayContinueMainLoop
762 NeverLoopResult::AlwaysBreak
765 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
766 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
768 ExprKind::InlineAsm(ref asm) => asm
771 .map(|(o, _)| match o {
772 InlineAsmOperand::In { expr, .. }
773 | InlineAsmOperand::InOut { expr, .. }
774 | InlineAsmOperand::Const { expr }
775 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
776 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
777 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
778 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
781 .fold(NeverLoopResult::Otherwise, combine_both),
782 ExprKind::Struct(_, _, None)
783 | ExprKind::Yield(_, _)
784 | ExprKind::Closure(_, _, _, _, _)
785 | ExprKind::LlvmInlineAsm(_)
787 | ExprKind::ConstBlock(_)
789 | ExprKind::Err => NeverLoopResult::Otherwise,
793 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
794 es.map(|e| never_loop_expr(e, main_loop_id))
795 .fold(NeverLoopResult::Otherwise, combine_seq)
798 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
799 es.map(|e| never_loop_expr(e, main_loop_id))
800 .fold(NeverLoopResult::Otherwise, combine_both)
803 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
804 e.map(|e| never_loop_expr(e, main_loop_id))
805 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
808 fn check_for_loop<'tcx>(
809 cx: &LateContext<'tcx>,
812 body: &'tcx Expr<'_>,
813 expr: &'tcx Expr<'_>,
815 let is_manual_memcpy_triggered = detect_manual_memcpy(cx, pat, arg, body, expr);
816 if !is_manual_memcpy_triggered {
817 check_for_loop_range(cx, pat, arg, body, expr);
818 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
820 check_for_loop_arg(cx, pat, arg, expr);
821 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
822 check_for_mut_range_bound(cx, arg, body);
823 check_for_single_element_loop(cx, pat, arg, body, expr);
824 detect_same_item_push(cx, pat, arg, body, expr);
827 // this function assumes the given expression is a `for` loop.
828 fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
829 // for some reason this is the only way to get the `Span`
830 // of the entire `for` loop
831 if let ExprKind::Match(_, arms, _) = &expr.kind {
838 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
840 if let ExprKind::Path(qpath) = &expr.kind;
841 if let QPath::Resolved(None, path) = qpath;
842 if path.segments.len() == 1;
843 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
853 /// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
854 /// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
855 /// it exists for the convenience of the overloaded operators while normal functions can do the
858 struct MinifyingSugg<'a>(Sugg<'a>);
860 impl<'a> MinifyingSugg<'a> {
861 fn as_str(&self) -> &str {
862 let Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) = &self.0;
866 fn into_sugg(self) -> Sugg<'a> {
871 impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
872 fn from(sugg: Sugg<'a>) -> Self {
877 impl std::ops::Add for &MinifyingSugg<'static> {
878 type Output = MinifyingSugg<'static>;
879 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
880 match (self.as_str(), rhs.as_str()) {
881 ("0", _) => rhs.clone(),
882 (_, "0") => self.clone(),
883 (_, _) => (&self.0 + &rhs.0).into(),
888 impl std::ops::Sub for &MinifyingSugg<'static> {
889 type Output = MinifyingSugg<'static>;
890 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
891 match (self.as_str(), rhs.as_str()) {
892 (_, "0") => self.clone(),
893 ("0", _) => (-rhs.0.clone()).into(),
894 (x, y) if x == y => sugg::ZERO.into(),
895 (_, _) => (&self.0 - &rhs.0).into(),
900 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
901 type Output = MinifyingSugg<'static>;
902 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
903 match (self.as_str(), rhs.as_str()) {
904 ("0", _) => rhs.clone(),
906 (_, _) => (self.0 + &rhs.0).into(),
911 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
912 type Output = MinifyingSugg<'static>;
913 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
914 match (self.as_str(), rhs.as_str()) {
916 ("0", _) => (-rhs.0.clone()).into(),
917 (x, y) if x == y => sugg::ZERO.into(),
918 (_, _) => (self.0 - &rhs.0).into(),
923 /// a wrapper around `MinifyingSugg`, which carries a operator like currying
924 /// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
926 value: MinifyingSugg<'static>,
930 #[derive(Clone, Copy)]
937 fn negative(value: Sugg<'static>) -> Self {
940 sign: OffsetSign::Negative,
944 fn positive(value: Sugg<'static>) -> Self {
947 sign: OffsetSign::Positive,
952 Self::positive(sugg::ZERO)
956 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
958 OffsetSign::Positive => lhs + &rhs.value,
959 OffsetSign::Negative => lhs - &rhs.value,
963 #[derive(Debug, Clone, Copy)]
964 enum StartKind<'hir> {
966 Counter { initializer: &'hir Expr<'hir> },
969 struct IndexExpr<'hir> {
970 base: &'hir Expr<'hir>,
971 idx: StartKind<'hir>,
977 kind: StartKind<'hir>,
980 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
981 let is_slice = match ty.kind() {
982 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
983 ty::Slice(..) | ty::Array(..) => true,
987 is_slice || is_type_diagnostic_item(cx, ty, sym::vec_type) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
990 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
992 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
993 if method.ident.name == sym::clone;
995 if let Some(arg) = args.get(0);
996 then { arg } else { expr }
1000 fn get_details_from_idx<'tcx>(
1001 cx: &LateContext<'tcx>,
1003 starts: &[Start<'tcx>],
1004 ) -> Option<(StartKind<'tcx>, Offset)> {
1005 fn get_start<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
1006 starts.iter().find_map(|start| {
1007 if same_var(cx, e, start.id) {
1015 fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
1017 ExprKind::Lit(l) => match l.node {
1018 ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
1021 ExprKind::Path(..) if get_start(cx, e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
1027 ExprKind::Binary(op, lhs, rhs) => match op.node {
1029 let offset_opt = get_start(cx, lhs, starts)
1030 .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
1031 .or_else(|| get_start(cx, rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
1033 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
1036 get_start(cx, lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
1040 ExprKind::Path(..) => get_start(cx, idx, starts).map(|s| (s, Offset::empty())),
1045 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1046 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1053 /// Get assignments from the given block.
1054 /// The returned iterator yields `None` if no assignment expressions are there,
1055 /// filtering out the increments of the given whitelisted loop counters;
1056 /// because its job is to make sure there's nothing other than assignments and the increments.
1057 fn get_assignments<'a: 'c, 'tcx: 'c, 'c>(
1058 cx: &'a LateContext<'tcx>,
1059 Block { stmts, expr, .. }: &'tcx Block<'tcx>,
1060 loop_counters: &'c [Start<'tcx>],
1061 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'c {
1062 // As the `filter` and `map` below do different things, I think putting together
1063 // just increases complexity. (cc #3188 and #4193)
1064 #[allow(clippy::filter_map)]
1067 .filter_map(move |stmt| match stmt.kind {
1068 StmtKind::Local(..) | StmtKind::Item(..) => None,
1069 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
1071 .chain((*expr).into_iter())
1073 if let ExprKind::AssignOp(_, place, _) = e.kind {
1076 // skip the first item which should be `StartKind::Range`
1077 // this makes it possible to use the slice with `StartKind::Range` in the same iterator loop.
1079 .any(|counter| same_var(cx, place, counter.id))
1084 .map(get_assignment)
1087 fn get_loop_counters<'a, 'tcx>(
1088 cx: &'a LateContext<'tcx>,
1089 body: &'tcx Block<'tcx>,
1090 expr: &'tcx Expr<'_>,
1091 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1092 // Look for variables that are incremented once per loop iteration.
1093 let mut increment_visitor = IncrementVisitor::new(cx);
1094 walk_block(&mut increment_visitor, body);
1096 // For each candidate, check the parent block to see if
1097 // it's initialized to zero at the start of the loop.
1098 get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
1101 .filter_map(move |var_id| {
1102 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1103 walk_block(&mut initialize_visitor, block);
1105 initialize_visitor.get_result().map(|(_, initializer)| Start {
1107 kind: StartKind::Counter { initializer },
1114 fn build_manual_memcpy_suggestion<'tcx>(
1115 cx: &LateContext<'tcx>,
1118 limits: ast::RangeLimits,
1119 dst: &IndexExpr<'_>,
1120 src: &IndexExpr<'_>,
1122 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1123 if offset.as_str() == "0" {
1130 let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
1132 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1133 if method.ident.name == sym!(len);
1134 if len_args.len() == 1;
1135 if let Some(arg) = len_args.get(0);
1136 if var_def_id(cx, arg) == var_def_id(cx, base);
1138 if sugg.as_str() == end_str {
1145 ast::RangeLimits::Closed => {
1146 sugg + &sugg::ONE.into()
1148 ast::RangeLimits::HalfOpen => sugg,
1154 let start_str = Sugg::hir(cx, start, "").into();
1155 let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
1157 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1158 StartKind::Range => (
1159 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
1164 apply_offset(&end_str, &idx_expr.idx_offset),
1168 StartKind::Counter { initializer } => {
1169 let counter_start = Sugg::hir(cx, initializer, "").into();
1171 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
1176 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1183 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1184 let (src_offset, src_limit) = print_offset_and_limit(&src);
1186 let dst_base_str = snippet(cx, dst.base.span, "???");
1187 let src_base_str = snippet(cx, src.base.span, "???");
1189 let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
1195 dst_offset.maybe_par(),
1196 dst_limit.maybe_par()
1202 "{}.clone_from_slice(&{}[{}..{}]);",
1205 src_offset.maybe_par(),
1206 src_limit.maybe_par()
1210 /// Checks for for loops that sequentially copy items from one slice-like
1211 /// object to another.
1212 fn detect_manual_memcpy<'tcx>(
1213 cx: &LateContext<'tcx>,
1215 arg: &'tcx Expr<'_>,
1216 body: &'tcx Expr<'_>,
1217 expr: &'tcx Expr<'_>,
1219 if let Some(higher::Range {
1223 }) = higher::range(arg)
1225 // the var must be a single name
1226 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1227 let mut starts = vec![Start {
1229 kind: StartKind::Range,
1232 // This is one of few ways to return different iterators
1233 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1234 let mut iter_a = None;
1235 let mut iter_b = None;
1237 if let ExprKind::Block(block, _) = body.kind {
1238 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1239 starts.extend(loop_counters);
1241 iter_a = Some(get_assignments(cx, block, &starts));
1243 iter_b = Some(get_assignment(body));
1246 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1248 let big_sugg = assignments
1249 // The only statements in the for loops can be indexed assignments from
1250 // indexed retrievals (except increments of loop counters).
1252 o.and_then(|(lhs, rhs)| {
1253 let rhs = fetch_cloned_expr(rhs);
1255 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1256 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1257 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1258 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1259 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1260 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1262 // Source and destination must be different
1263 if var_def_id(cx, base_left) != var_def_id(cx, base_right);
1265 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1266 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1273 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1274 .collect::<Option<Vec<_>>>()
1275 .filter(|v| !v.is_empty())
1276 .map(|v| v.join("\n "));
1278 if let Some(big_sugg) = big_sugg {
1282 get_span_of_entire_for_loop(expr),
1283 "it looks like you're manually copying between slices",
1284 "try replacing the loop by",
1286 Applicability::Unspecified,
1295 // Scans the body of the for loop and determines whether lint should be given
1296 struct SameItemPushVisitor<'a, 'tcx> {
1298 // this field holds the last vec push operation visited, which should be the only push seen
1299 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1300 cx: &'a LateContext<'tcx>,
1303 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1304 type Map = Map<'tcx>;
1306 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1308 // Non-determinism may occur ... don't give a lint
1309 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1310 ExprKind::Block(block, _) => self.visit_block(block),
1315 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1316 for stmt in b.stmts.iter() {
1317 self.visit_stmt(stmt);
1321 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1322 let vec_push_option = get_vec_push(self.cx, s);
1323 if vec_push_option.is_none() {
1324 // Current statement is not a push so visit inside
1326 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1330 // Current statement is a push ...check whether another
1331 // push had been previously done
1332 if self.vec_push.is_none() {
1333 self.vec_push = vec_push_option;
1335 // There are multiple pushes ... don't lint
1336 self.should_lint = false;
1341 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1342 NestedVisitorMap::None
1346 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1347 // the Vec being pushed into and the item being pushed
1348 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1350 // Extract method being called
1351 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1352 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1353 // Figure out the parameters for the method call
1354 if let Some(self_expr) = args.get(0);
1355 if let Some(pushed_item) = args.get(1);
1356 // Check that the method being called is push() on a Vec
1357 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::vec_type);
1358 if path.ident.name.as_str() == "push";
1360 return Some((self_expr, pushed_item))
1366 /// Detects for loop pushing the same item into a Vec
1367 fn detect_same_item_push<'tcx>(
1368 cx: &LateContext<'tcx>,
1371 body: &'tcx Expr<'_>,
1374 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1375 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1376 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1382 "it looks like the same item is being pushed into this Vec",
1385 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1386 item_str, vec_str, item_str
1391 if !matches!(pat.kind, PatKind::Wild) {
1395 // Determine whether it is safe to lint the body
1396 let mut same_item_push_visitor = SameItemPushVisitor {
1401 walk_expr(&mut same_item_push_visitor, body);
1402 if same_item_push_visitor.should_lint {
1403 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1404 let vec_ty = cx.typeck_results().expr_ty(vec);
1405 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1410 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1412 // Make sure that the push does not involve possibly mutating values
1413 match pushed_item.kind {
1414 ExprKind::Path(ref qpath) => {
1415 match qpath_res(cx, qpath, pushed_item.hir_id) {
1416 // immutable bindings that are initialized with literal or constant
1417 Res::Local(hir_id) => {
1419 let node = cx.tcx.hir().get(hir_id);
1420 if let Node::Binding(pat) = node;
1421 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1422 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1423 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1424 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1425 if let Some(init) = parent_let_expr.init;
1428 // immutable bindings that are initialized with literal
1429 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1430 // immutable bindings that are initialized with constant
1431 ExprKind::Path(ref path) => {
1432 if let Res::Def(DefKind::Const, ..) = qpath_res(cx, path, init.hir_id) {
1433 emit_lint(cx, vec, pushed_item);
1442 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1446 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1454 /// Checks for looping over a range and then indexing a sequence with it.
1455 /// The iteratee must be a range literal.
1456 #[allow(clippy::too_many_lines)]
1457 fn check_for_loop_range<'tcx>(
1458 cx: &LateContext<'tcx>,
1460 arg: &'tcx Expr<'_>,
1461 body: &'tcx Expr<'_>,
1462 expr: &'tcx Expr<'_>,
1464 if let Some(higher::Range {
1468 }) = higher::range(arg)
1470 // the var must be a single name
1471 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1472 let mut visitor = VarVisitor {
1475 indexed_mut: FxHashSet::default(),
1476 indexed_indirectly: FxHashMap::default(),
1477 indexed_directly: FxHashMap::default(),
1478 referenced: FxHashSet::default(),
1480 prefer_mutable: false,
1482 walk_expr(&mut visitor, body);
1484 // linting condition: we only indexed one variable, and indexed it directly
1485 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1486 let (indexed, (indexed_extent, indexed_ty)) = visitor
1490 .expect("already checked that we have exactly 1 element");
1492 // ensure that the indexed variable was declared before the loop, see #601
1493 if let Some(indexed_extent) = indexed_extent {
1494 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1495 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1496 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1497 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1498 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1503 // don't lint if the container that is indexed does not have .iter() method
1504 let has_iter = has_iter_method(cx, indexed_ty);
1505 if has_iter.is_none() {
1509 // don't lint if the container that is indexed into is also used without
1511 if visitor.referenced.contains(&indexed) {
1515 let starts_at_zero = is_integer_const(cx, start, 0);
1517 let skip = if starts_at_zero {
1519 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
1522 format!(".skip({})", snippet(cx, start.span, ".."))
1525 let mut end_is_start_plus_val = false;
1527 let take = if let Some(end) = *end {
1528 let mut take_expr = end;
1530 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1531 if let BinOpKind::Add = op.node {
1532 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1533 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1535 if start_equal_left {
1537 } else if start_equal_right {
1541 end_is_start_plus_val = start_equal_left | start_equal_right;
1545 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1547 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
1551 ast::RangeLimits::Closed => {
1552 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1553 format!(".take({})", take_expr + sugg::ONE)
1555 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1562 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1563 ("mut ", "iter_mut")
1568 let take_is_empty = take.is_empty();
1569 let mut method_1 = take;
1570 let mut method_2 = skip;
1572 if end_is_start_plus_val {
1573 mem::swap(&mut method_1, &mut method_2);
1576 if visitor.nonindex {
1579 NEEDLESS_RANGE_LOOP,
1581 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1585 "consider using an iterator",
1587 (pat.span, format!("({}, <item>)", ident.name)),
1590 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1597 let repl = if starts_at_zero && take_is_empty {
1598 format!("&{}{}", ref_mut, indexed)
1600 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1605 NEEDLESS_RANGE_LOOP,
1608 "the loop variable `{}` is only used to index `{}`.",
1614 "consider using an iterator",
1615 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1625 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1627 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1628 if len_args.len() == 1;
1629 if method.ident.name == sym!(len);
1630 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1631 if path.segments.len() == 1;
1632 if path.segments[0].ident.name == var;
1641 fn is_end_eq_array_len<'tcx>(
1642 cx: &LateContext<'tcx>,
1644 limits: ast::RangeLimits,
1645 indexed_ty: Ty<'tcx>,
1648 if let ExprKind::Lit(ref lit) = end.kind;
1649 if let ast::LitKind::Int(end_int, _) = lit.node;
1650 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1651 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1653 return match limits {
1654 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1655 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1663 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1664 let mut applicability = Applicability::MachineApplicable;
1665 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1666 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1671 "it is more concise to loop over references to containers instead of using explicit \
1673 "to write this more concisely, try",
1674 format!("&{}{}", muta, object),
1679 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1680 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1681 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1682 // just the receiver, no arguments
1683 if args.len() == 1 {
1684 let method_name = &*method.ident.as_str();
1685 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1686 if method_name == "iter" || method_name == "iter_mut" {
1687 if is_ref_iterable_type(cx, &args[0]) {
1688 lint_iter_method(cx, args, arg, method_name);
1690 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1691 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1692 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1693 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1694 let mut applicability = Applicability::MachineApplicable;
1695 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1698 EXPLICIT_INTO_ITER_LOOP,
1700 "it is more concise to loop over containers instead of using explicit \
1702 "to write this more concisely, try",
1707 let ref_receiver_ty = cx.tcx.mk_ref(
1708 cx.tcx.lifetimes.re_erased,
1711 mutbl: Mutability::Not,
1714 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1715 lint_iter_method(cx, args, arg, method_name)
1718 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1723 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1724 probably not what you want",
1726 next_loop_linted = true;
1730 if !next_loop_linted {
1731 check_arg_type(cx, pat, arg);
1735 /// Checks for `for` loops over `Option`s and `Result`s.
1736 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1737 let ty = cx.typeck_results().expr_ty(arg);
1738 if is_type_diagnostic_item(cx, ty, sym::option_type) {
1741 FOR_LOOPS_OVER_FALLIBLES,
1744 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1745 `if let` statement.",
1746 snippet(cx, arg.span, "_")
1750 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1751 snippet(cx, pat.span, "_"),
1752 snippet(cx, arg.span, "_")
1755 } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
1758 FOR_LOOPS_OVER_FALLIBLES,
1761 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1762 `if let` statement.",
1763 snippet(cx, arg.span, "_")
1767 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1768 snippet(cx, pat.span, "_"),
1769 snippet(cx, arg.span, "_")
1775 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1776 // incremented exactly once in the loop body, and initialized to zero
1777 // at the start of the loop.
1778 fn check_for_loop_explicit_counter<'tcx>(
1779 cx: &LateContext<'tcx>,
1781 arg: &'tcx Expr<'_>,
1782 body: &'tcx Expr<'_>,
1783 expr: &'tcx Expr<'_>,
1785 // Look for variables that are incremented once per loop iteration.
1786 let mut increment_visitor = IncrementVisitor::new(cx);
1787 walk_expr(&mut increment_visitor, body);
1789 // For each candidate, check the parent block to see if
1790 // it's initialized to zero at the start of the loop.
1791 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1792 for id in increment_visitor.into_results() {
1793 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1794 walk_block(&mut initialize_visitor, block);
1797 if let Some((name, initializer)) = initialize_visitor.get_result();
1798 if is_integer_const(cx, initializer, 0);
1800 let mut applicability = Applicability::MachineApplicable;
1802 let for_span = get_span_of_entire_for_loop(expr);
1806 EXPLICIT_COUNTER_LOOP,
1807 for_span.with_hi(arg.span.hi()),
1808 &format!("the variable `{}` is used as a loop counter.", name),
1811 "for ({}, {}) in {}.enumerate()",
1813 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1814 make_iterator_snippet(cx, arg, &mut applicability),
1824 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1825 /// actual `Iterator` that the loop uses.
1826 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1827 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1828 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1833 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1836 // (&x).into_iter() ==> x.iter()
1837 // (&mut x).into_iter() ==> x.iter_mut()
1839 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1840 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1842 let meth_name = match mutability {
1843 Mutability::Mut => "iter_mut",
1844 Mutability::Not => "iter",
1848 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1854 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1860 /// Checks for the `FOR_KV_MAP` lint.
1861 fn check_for_loop_over_map_kv<'tcx>(
1862 cx: &LateContext<'tcx>,
1864 arg: &'tcx Expr<'_>,
1865 body: &'tcx Expr<'_>,
1866 expr: &'tcx Expr<'_>,
1868 let pat_span = pat.span;
1870 if let PatKind::Tuple(ref pat, _) = pat.kind {
1872 let arg_span = arg.span;
1873 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1874 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1875 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1876 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1881 let mutbl = match mutbl {
1882 Mutability::Not => "",
1883 Mutability::Mut => "_mut",
1885 let arg = match arg.kind {
1886 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1890 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1895 &format!("you seem to want to iterate on a map's {}s", kind),
1897 let map = sugg::Sugg::hir(cx, arg, "map");
1900 "use the corresponding method",
1902 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1903 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1913 fn check_for_single_element_loop<'tcx>(
1914 cx: &LateContext<'tcx>,
1916 arg: &'tcx Expr<'_>,
1917 body: &'tcx Expr<'_>,
1918 expr: &'tcx Expr<'_>,
1921 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg_expr) = arg.kind;
1922 if let PatKind::Binding(.., target, _) = pat.kind;
1923 if let ExprKind::Array([arg_expression]) = arg_expr.kind;
1924 if let ExprKind::Path(ref list_item) = arg_expression.kind;
1925 if let Some(list_item_name) = single_segment_path(list_item).map(|ps| ps.ident.name);
1926 if let ExprKind::Block(ref block, _) = body.kind;
1927 if !block.stmts.is_empty();
1930 let for_span = get_span_of_entire_for_loop(expr);
1931 let mut block_str = snippet(cx, block.span, "..").into_owned();
1932 block_str.remove(0);
1938 SINGLE_ELEMENT_LOOP,
1940 "for loop over a single element",
1942 format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),
1943 Applicability::MachineApplicable
1949 struct MutatePairDelegate<'a, 'tcx> {
1950 cx: &'a LateContext<'tcx>,
1951 hir_id_low: Option<HirId>,
1952 hir_id_high: Option<HirId>,
1953 span_low: Option<Span>,
1954 span_high: Option<Span>,
1957 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1958 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: HirId, _: ConsumeMode) {}
1960 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId, bk: ty::BorrowKind) {
1961 if let ty::BorrowKind::MutBorrow = bk {
1962 if let PlaceBase::Local(id) = cmt.place.base {
1963 if Some(id) == self.hir_id_low {
1964 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
1966 if Some(id) == self.hir_id_high {
1967 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
1973 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId) {
1974 if let PlaceBase::Local(id) = cmt.place.base {
1975 if Some(id) == self.hir_id_low {
1976 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
1978 if Some(id) == self.hir_id_high {
1979 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
1985 impl MutatePairDelegate<'_, '_> {
1986 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1987 (self.span_low, self.span_high)
1991 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1992 if let Some(higher::Range {
1996 }) = higher::range(arg)
1998 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1999 if mut_ids[0].is_some() || mut_ids[1].is_some() {
2000 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
2001 mut_warn_with_span(cx, span_low);
2002 mut_warn_with_span(cx, span_high);
2007 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
2008 if let Some(sp) = span {
2013 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
2018 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
2020 if let ExprKind::Path(ref qpath) = bound.kind;
2021 if let QPath::Resolved(None, _) = *qpath;
2023 let res = qpath_res(cx, qpath, bound.hir_id);
2024 if let Res::Local(hir_id) = res {
2025 let node_str = cx.tcx.hir().get(hir_id);
2027 if let Node::Binding(pat) = node_str;
2028 if let PatKind::Binding(BindingAnnotation::Mutable, ..) = pat.kind;
2030 return Some(hir_id);
2039 fn check_for_mutation<'tcx>(
2040 cx: &LateContext<'tcx>,
2042 bound_ids: &[Option<HirId>],
2043 ) -> (Option<Span>, Option<Span>) {
2044 let mut delegate = MutatePairDelegate {
2046 hir_id_low: bound_ids[0],
2047 hir_id_high: bound_ids[1],
2051 cx.tcx.infer_ctxt().enter(|infcx| {
2052 ExprUseVisitor::new(
2057 cx.typeck_results(),
2061 delegate.mutation_span()
2064 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
2065 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
2067 PatKind::Wild => true,
2068 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
2073 struct VarVisitor<'a, 'tcx> {
2074 /// context reference
2075 cx: &'a LateContext<'tcx>,
2076 /// var name to look for as index
2078 /// indexed variables that are used mutably
2079 indexed_mut: FxHashSet<Symbol>,
2080 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2081 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2082 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2083 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2084 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2085 /// Any names that are used outside an index operation.
2086 /// Used to detect things like `&mut vec` used together with `vec[i]`
2087 referenced: FxHashSet<Symbol>,
2088 /// has the loop variable been used in expressions other than the index of
2091 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2092 /// takes `&mut self`
2093 prefer_mutable: bool,
2096 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2097 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2099 // the indexed container is referenced by a name
2100 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2101 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2102 if seqvar.segments.len() == 1;
2104 let index_used_directly = same_var(self.cx, idx, self.var);
2105 let indexed_indirectly = {
2106 let mut used_visitor = LocalUsedVisitor::new(self.var);
2107 walk_expr(&mut used_visitor, idx);
2111 if indexed_indirectly || index_used_directly {
2112 if self.prefer_mutable {
2113 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2115 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
2117 Res::Local(hir_id) => {
2118 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2119 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2120 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2121 if indexed_indirectly {
2122 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2124 if index_used_directly {
2125 self.indexed_directly.insert(
2126 seqvar.segments[0].ident.name,
2127 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2130 return false; // no need to walk further *on the variable*
2132 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2133 if indexed_indirectly {
2134 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2136 if index_used_directly {
2137 self.indexed_directly.insert(
2138 seqvar.segments[0].ident.name,
2139 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2142 return false; // no need to walk further *on the variable*
2153 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2154 type Map = Map<'tcx>;
2156 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2159 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2160 if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX))
2161 || (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2162 if !self.check(&args[1], &args[0], expr);
2168 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2169 if !self.check(idx, seqexpr, expr);
2174 // directly using a variable
2175 if let ExprKind::Path(ref qpath) = expr.kind;
2176 if let QPath::Resolved(None, ref path) = *qpath;
2177 if path.segments.len() == 1;
2179 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2180 if local_id == self.var {
2181 self.nonindex = true;
2183 // not the correct variable, but still a variable
2184 self.referenced.insert(path.segments[0].ident.name);
2190 let old = self.prefer_mutable;
2192 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2193 self.prefer_mutable = true;
2194 self.visit_expr(lhs);
2195 self.prefer_mutable = false;
2196 self.visit_expr(rhs);
2198 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2199 if mutbl == Mutability::Mut {
2200 self.prefer_mutable = true;
2202 self.visit_expr(expr);
2204 ExprKind::Call(ref f, args) => {
2207 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2208 self.prefer_mutable = false;
2209 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2210 if mutbl == Mutability::Mut {
2211 self.prefer_mutable = true;
2214 self.visit_expr(expr);
2217 ExprKind::MethodCall(_, _, args, _) => {
2218 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2219 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2220 self.prefer_mutable = false;
2221 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2222 if mutbl == Mutability::Mut {
2223 self.prefer_mutable = true;
2226 self.visit_expr(expr);
2229 ExprKind::Closure(_, _, body_id, ..) => {
2230 let body = self.cx.tcx.hir().body(body_id);
2231 self.visit_expr(&body.value);
2233 _ => walk_expr(self, expr),
2235 self.prefer_mutable = old;
2237 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2238 NestedVisitorMap::None
2242 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2243 let def_id = match var_def_id(cx, expr) {
2245 None => return false,
2247 if let Some(used_mutably) = mutated_variables(container, cx) {
2248 if used_mutably.contains(&def_id) {
2255 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2256 let def_id = match var_def_id(cx, iter_expr) {
2258 None => return false,
2260 let mut visitor = VarUsedAfterLoopVisitor {
2263 iter_expr_id: iter_expr.hir_id,
2264 past_while_let: false,
2265 var_used_after_while_let: false,
2267 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2268 walk_block(&mut visitor, enclosing_block);
2270 visitor.var_used_after_while_let
2273 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2274 cx: &'a LateContext<'tcx>,
2276 iter_expr_id: HirId,
2277 past_while_let: bool,
2278 var_used_after_while_let: bool,
2281 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2282 type Map = Map<'tcx>;
2284 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2285 if self.past_while_let {
2286 if Some(self.def_id) == var_def_id(self.cx, expr) {
2287 self.var_used_after_while_let = true;
2289 } else if self.iter_expr_id == expr.hir_id {
2290 self.past_while_let = true;
2292 walk_expr(self, expr);
2294 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2295 NestedVisitorMap::None
2299 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2300 /// for `&T` and `&mut T`, such as `Vec`.
2302 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2303 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2304 // will allow further borrows afterwards
2305 let ty = cx.typeck_results().expr_ty(e);
2306 is_iterable_array(ty, cx) ||
2307 is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2308 match_type(cx, ty, &paths::LINKED_LIST) ||
2309 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2310 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2311 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2312 match_type(cx, ty, &paths::BINARY_HEAP) ||
2313 match_type(cx, ty, &paths::BTREEMAP) ||
2314 match_type(cx, ty, &paths::BTREESET)
2317 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2318 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2320 ty::Array(_, n) => n
2321 .try_eval_usize(cx.tcx, cx.param_env)
2322 .map_or(false, |val| (0..=32).contains(&val)),
2327 /// If a block begins with a statement (possibly a `let` binding) and has an
2328 /// expression, return it.
2329 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2330 if block.stmts.is_empty() {
2333 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2334 local.init //.map(|expr| expr)
2340 /// If a block begins with an expression (with or without semicolon), return it.
2341 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2343 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2344 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2345 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2346 StmtKind::Local(..) | StmtKind::Item(..) => None,
2352 /// Returns `true` if expr contains a single break expr without destination label
2354 /// passed expression. The expression may be within a block.
2355 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2357 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2358 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2363 #[derive(Debug, PartialEq)]
2364 enum IncrementVisitorVarState {
2365 Initial, // Not examined yet
2366 IncrOnce, // Incremented exactly once, may be a loop counter
2370 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2371 struct IncrementVisitor<'a, 'tcx> {
2372 cx: &'a LateContext<'tcx>, // context reference
2373 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2374 depth: u32, // depth of conditional expressions
2378 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2379 fn new(cx: &'a LateContext<'tcx>) -> Self {
2382 states: FxHashMap::default(),
2388 fn into_results(self) -> impl Iterator<Item = HirId> {
2389 self.states.into_iter().filter_map(|(id, state)| {
2390 if state == IncrementVisitorVarState::IncrOnce {
2399 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2400 type Map = Map<'tcx>;
2402 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2407 // If node is a variable
2408 if let Some(def_id) = var_def_id(self.cx, expr) {
2409 if let Some(parent) = get_parent_expr(self.cx, expr) {
2410 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2411 if *state == IncrementVisitorVarState::IncrOnce {
2412 *state = IncrementVisitorVarState::DontWarn;
2417 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2418 if lhs.hir_id == expr.hir_id {
2419 *state = if op.node == BinOpKind::Add
2420 && is_integer_const(self.cx, rhs, 1)
2421 && *state == IncrementVisitorVarState::Initial
2424 IncrementVisitorVarState::IncrOnce
2426 // Assigned some other value or assigned multiple times
2427 IncrementVisitorVarState::DontWarn
2431 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2432 *state = IncrementVisitorVarState::DontWarn
2434 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2435 *state = IncrementVisitorVarState::DontWarn
2441 walk_expr(self, expr);
2442 } else if is_loop(expr) || is_conditional(expr) {
2444 walk_expr(self, expr);
2446 } else if let ExprKind::Continue(_) = expr.kind {
2449 walk_expr(self, expr);
2452 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2453 NestedVisitorMap::None
2457 enum InitializeVisitorState<'hir> {
2458 Initial, // Not examined yet
2459 Declared(Symbol), // Declared but not (yet) initialized
2462 initializer: &'hir Expr<'hir>,
2467 /// Checks whether a variable is initialized at the start of a loop and not modified
2468 /// and used after the loop.
2469 struct InitializeVisitor<'a, 'tcx> {
2470 cx: &'a LateContext<'tcx>, // context reference
2471 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2473 state: InitializeVisitorState<'tcx>,
2474 depth: u32, // depth of conditional expressions
2478 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2479 fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2484 state: InitializeVisitorState::Initial,
2490 fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
2491 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2492 Some((name, initializer))
2499 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2500 type Map = Map<'tcx>;
2502 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2503 // Look for declarations of the variable
2505 if let StmtKind::Local(ref local) = stmt.kind;
2506 if local.pat.hir_id == self.var_id;
2507 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2509 self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
2510 InitializeVisitorState::Initialized {
2517 walk_stmt(self, stmt);
2520 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2521 if matches!(self.state, InitializeVisitorState::DontWarn) {
2524 if expr.hir_id == self.end_expr.hir_id {
2525 self.past_loop = true;
2528 // No need to visit expressions before the variable is
2530 if matches!(self.state, InitializeVisitorState::Initial) {
2534 // If node is the desired variable, see how it's used
2535 if var_def_id(self.cx, expr) == Some(self.var_id) {
2537 self.state = InitializeVisitorState::DontWarn;
2541 if let Some(parent) = get_parent_expr(self.cx, expr) {
2543 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2544 self.state = InitializeVisitorState::DontWarn;
2546 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2547 self.state = if_chain! {
2549 if let InitializeVisitorState::Declared(name)
2550 | InitializeVisitorState::Initialized { name, ..} = self.state;
2552 InitializeVisitorState::Initialized { initializer: rhs, name }
2554 InitializeVisitorState::DontWarn
2558 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2559 self.state = InitializeVisitorState::DontWarn
2565 walk_expr(self, expr);
2566 } else if !self.past_loop && is_loop(expr) {
2567 self.state = InitializeVisitorState::DontWarn;
2568 } else if is_conditional(expr) {
2570 walk_expr(self, expr);
2573 walk_expr(self, expr);
2577 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2578 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2582 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2583 if let ExprKind::Path(ref qpath) = expr.kind {
2584 let path_res = qpath_res(cx, qpath, expr.hir_id);
2585 if let Res::Local(hir_id) = path_res {
2586 return Some(hir_id);
2592 fn is_loop(expr: &Expr<'_>) -> bool {
2593 matches!(expr.kind, ExprKind::Loop(..))
2596 fn is_conditional(expr: &Expr<'_>) -> bool {
2597 matches!(expr.kind, ExprKind::Match(..))
2600 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2602 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2603 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2604 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2606 return is_loop_nested(cx, loop_expr, iter_expr)
2612 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2613 let mut id = loop_expr.hir_id;
2614 let iter_name = if let Some(name) = path_name(iter_expr) {
2620 let parent = cx.tcx.hir().get_parent_node(id);
2624 match cx.tcx.hir().find(parent) {
2625 Some(Node::Expr(expr)) => {
2626 if let ExprKind::Loop(..) = expr.kind {
2630 Some(Node::Block(block)) => {
2631 let mut block_visitor = LoopNestVisitor {
2633 iterator: iter_name,
2636 walk_block(&mut block_visitor, block);
2637 if block_visitor.nesting == RuledOut {
2641 Some(Node::Stmt(_)) => (),
2650 #[derive(PartialEq, Eq)]
2652 Unknown, // no nesting detected yet
2653 RuledOut, // the iterator is initialized or assigned within scope
2654 LookFurther, // no nesting detected, no further walk required
2657 use self::Nesting::{LookFurther, RuledOut, Unknown};
2659 struct LoopNestVisitor {
2665 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2666 type Map = Map<'tcx>;
2668 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2669 if stmt.hir_id == self.hir_id {
2670 self.nesting = LookFurther;
2671 } else if self.nesting == Unknown {
2672 walk_stmt(self, stmt);
2676 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2677 if self.nesting != Unknown {
2680 if expr.hir_id == self.hir_id {
2681 self.nesting = LookFurther;
2685 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2686 if match_var(path, self.iterator) {
2687 self.nesting = RuledOut;
2690 _ => walk_expr(self, expr),
2694 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2695 if self.nesting != Unknown {
2698 if let PatKind::Binding(.., span_name, _) = pat.kind {
2699 if self.iterator == span_name.name {
2700 self.nesting = RuledOut;
2707 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2708 NestedVisitorMap::None
2712 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2713 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2714 let segments = &path.segments;
2715 if segments.len() == 1 {
2716 return Some(segments[0].ident.name);
2722 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2723 if constant(cx, cx.typeck_results(), cond).is_some() {
2724 // A pure constant condition (e.g., `while false`) is not linted.
2728 let mut var_visitor = VarCollectorVisitor {
2730 ids: FxHashSet::default(),
2731 def_ids: FxHashMap::default(),
2734 var_visitor.visit_expr(cond);
2735 if var_visitor.skip {
2738 let used_in_condition = &var_visitor.ids;
2739 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2740 used_in_condition.is_disjoint(&used_mutably)
2744 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2746 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2747 has_break_or_return: false,
2749 has_break_or_return_visitor.visit_expr(expr);
2750 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2752 if no_cond_variable_mutated && !mutable_static_in_cond {
2755 WHILE_IMMUTABLE_CONDITION,
2757 "variables in the condition are not mutated in the loop body",
2759 diag.note("this may lead to an infinite or to a never running loop");
2761 if has_break_or_return {
2762 diag.note("this loop contains `return`s or `break`s");
2763 diag.help("rewrite it as `if cond { loop { } }`");
2770 struct HasBreakOrReturnVisitor {
2771 has_break_or_return: bool,
2774 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2775 type Map = Map<'tcx>;
2777 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2778 if self.has_break_or_return {
2783 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2784 self.has_break_or_return = true;
2790 walk_expr(self, expr);
2793 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2794 NestedVisitorMap::None
2798 /// Collects the set of variables in an expression
2799 /// Stops analysis if a function call is found
2800 /// Note: In some cases such as `self`, there are no mutable annotation,
2801 /// All variables definition IDs are collected
2802 struct VarCollectorVisitor<'a, 'tcx> {
2803 cx: &'a LateContext<'tcx>,
2804 ids: FxHashSet<HirId>,
2805 def_ids: FxHashMap<def_id::DefId, bool>,
2809 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2810 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2812 if let ExprKind::Path(ref qpath) = ex.kind;
2813 if let QPath::Resolved(None, _) = *qpath;
2814 let res = qpath_res(self.cx, qpath, ex.hir_id);
2817 Res::Local(hir_id) => {
2818 self.ids.insert(hir_id);
2820 Res::Def(DefKind::Static, def_id) => {
2821 let mutable = self.cx.tcx.is_mutable_static(def_id);
2822 self.def_ids.insert(def_id, mutable);
2831 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2832 type Map = Map<'tcx>;
2834 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2836 ExprKind::Path(_) => self.insert_def_id(ex),
2837 // If there is any function/method call… we just stop analysis
2838 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2840 _ => walk_expr(self, ex),
2844 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2845 NestedVisitorMap::None
2849 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2851 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2852 check_needless_collect_direct_usage(expr, cx);
2853 check_needless_collect_indirect_usage(expr, cx);
2855 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2857 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2858 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2859 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2860 if let Some(ref generic_args) = chain_method.args;
2861 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2863 let ty = cx.typeck_results().node_type(ty.hir_id);
2864 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2865 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2866 match_type(cx, ty, &paths::BTREEMAP) ||
2867 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2868 if method.ident.name == sym!(len) {
2869 let span = shorten_needless_collect_span(expr);
2874 NEEDLESS_COLLECT_MSG,
2876 "count()".to_string(),
2877 Applicability::MachineApplicable,
2880 if method.ident.name == sym!(is_empty) {
2881 let span = shorten_needless_collect_span(expr);
2886 NEEDLESS_COLLECT_MSG,
2888 "next().is_none()".to_string(),
2889 Applicability::MachineApplicable,
2892 if method.ident.name == sym!(contains) {
2893 let contains_arg = snippet(cx, args[1].span, "??");
2894 let span = shorten_needless_collect_span(expr);
2899 NEEDLESS_COLLECT_MSG,
2901 let (arg, pred) = contains_arg
2903 .map_or(("&x", &*contains_arg), |s| ("x", s));
2904 diag.span_suggestion(
2908 "any(|{}| x == {})",
2911 Applicability::MachineApplicable,
2921 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2922 if let ExprKind::Block(ref block, _) = expr.kind {
2923 for ref stmt in block.stmts {
2925 if let StmtKind::Local(
2926 Local { pat: Pat { hir_id: pat_id, kind: PatKind::Binding(_, _, ident, .. ), .. },
2927 init: Some(ref init_expr), .. }
2929 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2930 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2931 if let Some(ref generic_args) = method_name.args;
2932 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2933 if let ty = cx.typeck_results().node_type(ty.hir_id);
2934 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2935 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2936 match_type(cx, ty, &paths::LINKED_LIST);
2937 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2938 if iter_calls.len() == 1;
2940 let mut used_count_visitor = UsedCountVisitor {
2945 walk_block(&mut used_count_visitor, block);
2946 if used_count_visitor.count > 1 {
2950 // Suggest replacing iter_call with iter_replacement, and removing stmt
2951 let iter_call = &iter_calls[0];
2955 stmt.span.until(iter_call.span),
2956 NEEDLESS_COLLECT_MSG,
2958 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2959 diag.multipart_suggestion(
2960 iter_call.get_suggestion_text(),
2962 (stmt.span, String::new()),
2963 (iter_call.span, iter_replacement)
2965 Applicability::MachineApplicable,// MaybeIncorrect,
2975 struct IterFunction {
2976 func: IterFunctionKind,
2980 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2982 IterFunctionKind::IntoIter => String::new(),
2983 IterFunctionKind::Len => String::from(".count()"),
2984 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2985 IterFunctionKind::Contains(span) => {
2986 let s = snippet(cx, *span, "..");
2987 if let Some(stripped) = s.strip_prefix('&') {
2988 format!(".any(|x| x == {})", stripped)
2990 format!(".any(|x| x == *{})", s)
2995 fn get_suggestion_text(&self) -> &'static str {
2997 IterFunctionKind::IntoIter => {
2998 "Use the original Iterator instead of collecting it and then producing a new one"
3000 IterFunctionKind::Len => {
3001 "Take the original Iterator's count instead of collecting it and finding the length"
3003 IterFunctionKind::IsEmpty => {
3004 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
3006 IterFunctionKind::Contains(_) => {
3007 "Check if the original Iterator contains an element instead of collecting then checking"
3012 enum IterFunctionKind {
3019 struct IterFunctionVisitor {
3020 uses: Vec<IterFunction>,
3024 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
3025 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
3026 // Check function calls on our collection
3028 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
3029 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
3030 if let &[name] = &path.segments;
3031 if name.ident == self.target;
3033 let len = sym!(len);
3034 let is_empty = sym!(is_empty);
3035 let contains = sym!(contains);
3036 match method_name.ident.name {
3037 sym::into_iter => self.uses.push(
3038 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
3040 name if name == len => self.uses.push(
3041 IterFunction { func: IterFunctionKind::Len, span: expr.span }
3043 name if name == is_empty => self.uses.push(
3044 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
3046 name if name == contains => self.uses.push(
3047 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
3049 _ => self.seen_other = true,
3054 // Check if the collection is used for anything else
3056 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
3057 if let &[name] = &path.segments;
3058 if name.ident == self.target;
3060 self.seen_other = true;
3062 walk_expr(self, expr);
3067 type Map = Map<'tcx>;
3068 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3069 NestedVisitorMap::None
3073 struct UsedCountVisitor<'a, 'tcx> {
3074 cx: &'a LateContext<'tcx>,
3079 impl<'a, 'tcx> Visitor<'tcx> for UsedCountVisitor<'a, 'tcx> {
3080 type Map = Map<'tcx>;
3082 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
3083 if same_var(self.cx, expr, self.id) {
3086 walk_expr(self, expr);
3090 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3091 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
3095 /// Detect the occurrences of calls to `iter` or `into_iter` for the
3096 /// given identifier
3097 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
3098 let mut visitor = IterFunctionVisitor {
3103 visitor.visit_block(block);
3104 if visitor.seen_other {
3111 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3113 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3114 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3116 return expr.span.with_lo(span.lo());