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, single_segment_path, snippet,
10 snippet_with_applicability, snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_sugg,
11 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::If(ref e, ref e2, ref e3) => {
746 let e1 = never_loop_expr(e, main_loop_id);
747 let e2 = never_loop_expr(e2, main_loop_id);
750 .map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
751 combine_seq(e1, combine_branches(e2, e3))
753 ExprKind::Match(ref e, ref arms, _) => {
754 let e = never_loop_expr(e, main_loop_id);
758 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
762 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
763 ExprKind::Continue(d) => {
766 .expect("target ID can only be missing in the presence of compilation errors");
767 if id == main_loop_id {
768 NeverLoopResult::MayContinueMainLoop
770 NeverLoopResult::AlwaysBreak
773 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
774 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
776 ExprKind::InlineAsm(ref asm) => asm
779 .map(|(o, _)| match o {
780 InlineAsmOperand::In { expr, .. }
781 | InlineAsmOperand::InOut { expr, .. }
782 | InlineAsmOperand::Const { expr }
783 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
784 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
785 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
786 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
789 .fold(NeverLoopResult::Otherwise, combine_both),
790 ExprKind::Struct(_, _, None)
791 | ExprKind::Yield(_, _)
792 | ExprKind::Closure(_, _, _, _, _)
793 | ExprKind::LlvmInlineAsm(_)
795 | ExprKind::ConstBlock(_)
797 | ExprKind::Err => NeverLoopResult::Otherwise,
801 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
802 es.map(|e| never_loop_expr(e, main_loop_id))
803 .fold(NeverLoopResult::Otherwise, combine_seq)
806 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
807 es.map(|e| never_loop_expr(e, main_loop_id))
808 .fold(NeverLoopResult::Otherwise, combine_both)
811 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
812 e.map(|e| never_loop_expr(e, main_loop_id))
813 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
816 fn check_for_loop<'tcx>(
817 cx: &LateContext<'tcx>,
820 body: &'tcx Expr<'_>,
821 expr: &'tcx Expr<'_>,
823 let is_manual_memcpy_triggered = detect_manual_memcpy(cx, pat, arg, body, expr);
824 if !is_manual_memcpy_triggered {
825 check_for_loop_range(cx, pat, arg, body, expr);
826 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
828 check_for_loop_arg(cx, pat, arg, expr);
829 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
830 check_for_mut_range_bound(cx, arg, body);
831 check_for_single_element_loop(cx, pat, arg, body, expr);
832 detect_same_item_push(cx, pat, arg, body, expr);
835 // this function assumes the given expression is a `for` loop.
836 fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
837 // for some reason this is the only way to get the `Span`
838 // of the entire `for` loop
839 if let ExprKind::Match(_, arms, _) = &expr.kind {
846 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
848 if let ExprKind::Path(qpath) = &expr.kind;
849 if let QPath::Resolved(None, path) = qpath;
850 if path.segments.len() == 1;
851 if let Res::Local(local_id) = cx.qpath_res(qpath, expr.hir_id);
861 /// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
862 /// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
863 /// it exists for the convenience of the overloaded operators while normal functions can do the
866 struct MinifyingSugg<'a>(Sugg<'a>);
868 impl<'a> MinifyingSugg<'a> {
869 fn as_str(&self) -> &str {
870 let Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) = &self.0;
874 fn into_sugg(self) -> Sugg<'a> {
879 impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
880 fn from(sugg: Sugg<'a>) -> Self {
885 impl std::ops::Add for &MinifyingSugg<'static> {
886 type Output = MinifyingSugg<'static>;
887 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
888 match (self.as_str(), rhs.as_str()) {
889 ("0", _) => rhs.clone(),
890 (_, "0") => self.clone(),
891 (_, _) => (&self.0 + &rhs.0).into(),
896 impl std::ops::Sub for &MinifyingSugg<'static> {
897 type Output = MinifyingSugg<'static>;
898 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
899 match (self.as_str(), rhs.as_str()) {
900 (_, "0") => self.clone(),
901 ("0", _) => (-rhs.0.clone()).into(),
902 (x, y) if x == y => sugg::ZERO.into(),
903 (_, _) => (&self.0 - &rhs.0).into(),
908 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
909 type Output = MinifyingSugg<'static>;
910 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
911 match (self.as_str(), rhs.as_str()) {
912 ("0", _) => rhs.clone(),
914 (_, _) => (self.0 + &rhs.0).into(),
919 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
920 type Output = MinifyingSugg<'static>;
921 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
922 match (self.as_str(), rhs.as_str()) {
924 ("0", _) => (-rhs.0.clone()).into(),
925 (x, y) if x == y => sugg::ZERO.into(),
926 (_, _) => (self.0 - &rhs.0).into(),
931 /// a wrapper around `MinifyingSugg`, which carries a operator like currying
932 /// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
934 value: MinifyingSugg<'static>,
938 #[derive(Clone, Copy)]
945 fn negative(value: Sugg<'static>) -> Self {
948 sign: OffsetSign::Negative,
952 fn positive(value: Sugg<'static>) -> Self {
955 sign: OffsetSign::Positive,
960 Self::positive(sugg::ZERO)
964 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
966 OffsetSign::Positive => lhs + &rhs.value,
967 OffsetSign::Negative => lhs - &rhs.value,
971 #[derive(Debug, Clone, Copy)]
972 enum StartKind<'hir> {
974 Counter { initializer: &'hir Expr<'hir> },
977 struct IndexExpr<'hir> {
978 base: &'hir Expr<'hir>,
979 idx: StartKind<'hir>,
985 kind: StartKind<'hir>,
988 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
989 let is_slice = match ty.kind() {
990 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
991 ty::Slice(..) | ty::Array(..) => true,
995 is_slice || is_type_diagnostic_item(cx, ty, sym::vec_type) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
998 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
1000 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
1001 if method.ident.name == sym::clone;
1003 if let Some(arg) = args.get(0);
1004 then { arg } else { expr }
1008 fn get_details_from_idx<'tcx>(
1009 cx: &LateContext<'tcx>,
1011 starts: &[Start<'tcx>],
1012 ) -> Option<(StartKind<'tcx>, Offset)> {
1013 fn get_start<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
1014 starts.iter().find_map(|start| {
1015 if same_var(cx, e, start.id) {
1023 fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
1025 ExprKind::Lit(l) => match l.node {
1026 ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
1029 ExprKind::Path(..) if get_start(cx, e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
1035 ExprKind::Binary(op, lhs, rhs) => match op.node {
1037 let offset_opt = get_start(cx, lhs, starts)
1038 .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
1039 .or_else(|| get_start(cx, rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
1041 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
1044 get_start(cx, lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
1048 ExprKind::Path(..) => get_start(cx, idx, starts).map(|s| (s, Offset::empty())),
1053 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1054 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1061 /// Get assignments from the given block.
1062 /// The returned iterator yields `None` if no assignment expressions are there,
1063 /// filtering out the increments of the given whitelisted loop counters;
1064 /// because its job is to make sure there's nothing other than assignments and the increments.
1065 fn get_assignments<'a: 'c, 'tcx: 'c, 'c>(
1066 cx: &'a LateContext<'tcx>,
1067 Block { stmts, expr, .. }: &'tcx Block<'tcx>,
1068 loop_counters: &'c [Start<'tcx>],
1069 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'c {
1070 // As the `filter` and `map` below do different things, I think putting together
1071 // just increases complexity. (cc #3188 and #4193)
1074 .filter_map(move |stmt| match stmt.kind {
1075 StmtKind::Local(..) | StmtKind::Item(..) => None,
1076 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
1078 .chain((*expr).into_iter())
1080 if let ExprKind::AssignOp(_, place, _) = e.kind {
1083 // skip the first item which should be `StartKind::Range`
1084 // this makes it possible to use the slice with `StartKind::Range` in the same iterator loop.
1086 .any(|counter| same_var(cx, place, counter.id))
1091 .map(get_assignment)
1094 fn get_loop_counters<'a, 'tcx>(
1095 cx: &'a LateContext<'tcx>,
1096 body: &'tcx Block<'tcx>,
1097 expr: &'tcx Expr<'_>,
1098 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1099 // Look for variables that are incremented once per loop iteration.
1100 let mut increment_visitor = IncrementVisitor::new(cx);
1101 walk_block(&mut increment_visitor, body);
1103 // For each candidate, check the parent block to see if
1104 // it's initialized to zero at the start of the loop.
1105 get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
1108 .filter_map(move |var_id| {
1109 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1110 walk_block(&mut initialize_visitor, block);
1112 initialize_visitor.get_result().map(|(_, initializer)| Start {
1114 kind: StartKind::Counter { initializer },
1121 fn build_manual_memcpy_suggestion<'tcx>(
1122 cx: &LateContext<'tcx>,
1125 limits: ast::RangeLimits,
1126 dst: &IndexExpr<'_>,
1127 src: &IndexExpr<'_>,
1129 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1130 if offset.as_str() == "0" {
1137 let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
1139 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1140 if method.ident.name == sym!(len);
1141 if len_args.len() == 1;
1142 if let Some(arg) = len_args.get(0);
1143 if var_def_id(cx, arg) == var_def_id(cx, base);
1145 if sugg.as_str() == end_str {
1152 ast::RangeLimits::Closed => {
1153 sugg + &sugg::ONE.into()
1155 ast::RangeLimits::HalfOpen => sugg,
1161 let start_str = Sugg::hir(cx, start, "").into();
1162 let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
1164 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1165 StartKind::Range => (
1166 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
1171 apply_offset(&end_str, &idx_expr.idx_offset),
1175 StartKind::Counter { initializer } => {
1176 let counter_start = Sugg::hir(cx, initializer, "").into();
1178 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
1183 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1190 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1191 let (src_offset, src_limit) = print_offset_and_limit(&src);
1193 let dst_base_str = snippet(cx, dst.base.span, "???");
1194 let src_base_str = snippet(cx, src.base.span, "???");
1196 let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
1202 dst_offset.maybe_par(),
1203 dst_limit.maybe_par()
1209 "{}.clone_from_slice(&{}[{}..{}]);",
1212 src_offset.maybe_par(),
1213 src_limit.maybe_par()
1217 /// Checks for for loops that sequentially copy items from one slice-like
1218 /// object to another.
1219 fn detect_manual_memcpy<'tcx>(
1220 cx: &LateContext<'tcx>,
1222 arg: &'tcx Expr<'_>,
1223 body: &'tcx Expr<'_>,
1224 expr: &'tcx Expr<'_>,
1226 if let Some(higher::Range {
1230 }) = higher::range(arg)
1232 // the var must be a single name
1233 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1234 let mut starts = vec![Start {
1236 kind: StartKind::Range,
1239 // This is one of few ways to return different iterators
1240 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1241 let mut iter_a = None;
1242 let mut iter_b = None;
1244 if let ExprKind::Block(block, _) = body.kind {
1245 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1246 starts.extend(loop_counters);
1248 iter_a = Some(get_assignments(cx, block, &starts));
1250 iter_b = Some(get_assignment(body));
1253 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1255 let big_sugg = assignments
1256 // The only statements in the for loops can be indexed assignments from
1257 // indexed retrievals (except increments of loop counters).
1259 o.and_then(|(lhs, rhs)| {
1260 let rhs = fetch_cloned_expr(rhs);
1262 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1263 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1264 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1265 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1266 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1267 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1269 // Source and destination must be different
1270 if var_def_id(cx, base_left) != var_def_id(cx, base_right);
1272 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1273 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1280 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1281 .collect::<Option<Vec<_>>>()
1282 .filter(|v| !v.is_empty())
1283 .map(|v| v.join("\n "));
1285 if let Some(big_sugg) = big_sugg {
1289 get_span_of_entire_for_loop(expr),
1290 "it looks like you're manually copying between slices",
1291 "try replacing the loop by",
1293 Applicability::Unspecified,
1302 // Scans the body of the for loop and determines whether lint should be given
1303 struct SameItemPushVisitor<'a, 'tcx> {
1305 // this field holds the last vec push operation visited, which should be the only push seen
1306 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1307 cx: &'a LateContext<'tcx>,
1310 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1311 type Map = Map<'tcx>;
1313 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1315 // Non-determinism may occur ... don't give a lint
1316 ExprKind::Loop(..) | ExprKind::Match(..) => self.should_lint = false,
1317 ExprKind::Block(block, _) => self.visit_block(block),
1322 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1323 for stmt in b.stmts.iter() {
1324 self.visit_stmt(stmt);
1328 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1329 let vec_push_option = get_vec_push(self.cx, s);
1330 if vec_push_option.is_none() {
1331 // Current statement is not a push so visit inside
1333 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1337 // Current statement is a push ...check whether another
1338 // push had been previously done
1339 if self.vec_push.is_none() {
1340 self.vec_push = vec_push_option;
1342 // There are multiple pushes ... don't lint
1343 self.should_lint = false;
1348 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1349 NestedVisitorMap::None
1353 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1354 // the Vec being pushed into and the item being pushed
1355 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1357 // Extract method being called
1358 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1359 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1360 // Figure out the parameters for the method call
1361 if let Some(self_expr) = args.get(0);
1362 if let Some(pushed_item) = args.get(1);
1363 // Check that the method being called is push() on a Vec
1364 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::vec_type);
1365 if path.ident.name.as_str() == "push";
1367 return Some((self_expr, pushed_item))
1373 /// Detects for loop pushing the same item into a Vec
1374 fn detect_same_item_push<'tcx>(
1375 cx: &LateContext<'tcx>,
1378 body: &'tcx Expr<'_>,
1381 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1382 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1383 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1389 "it looks like the same item is being pushed into this Vec",
1392 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1393 item_str, vec_str, item_str
1398 if !matches!(pat.kind, PatKind::Wild) {
1402 // Determine whether it is safe to lint the body
1403 let mut same_item_push_visitor = SameItemPushVisitor {
1408 walk_expr(&mut same_item_push_visitor, body);
1409 if same_item_push_visitor.should_lint {
1410 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1411 let vec_ty = cx.typeck_results().expr_ty(vec);
1412 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1417 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1419 // Make sure that the push does not involve possibly mutating values
1420 match pushed_item.kind {
1421 ExprKind::Path(ref qpath) => {
1422 match cx.qpath_res(qpath, pushed_item.hir_id) {
1423 // immutable bindings that are initialized with literal or constant
1424 Res::Local(hir_id) => {
1426 let node = cx.tcx.hir().get(hir_id);
1427 if let Node::Binding(pat) = node;
1428 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1429 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1430 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1431 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1432 if let Some(init) = parent_let_expr.init;
1435 // immutable bindings that are initialized with literal
1436 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1437 // immutable bindings that are initialized with constant
1438 ExprKind::Path(ref path) => {
1439 if let Res::Def(DefKind::Const, ..) = cx.qpath_res(path, init.hir_id) {
1440 emit_lint(cx, vec, pushed_item);
1449 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1453 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1461 /// Checks for looping over a range and then indexing a sequence with it.
1462 /// The iteratee must be a range literal.
1463 #[allow(clippy::too_many_lines)]
1464 fn check_for_loop_range<'tcx>(
1465 cx: &LateContext<'tcx>,
1467 arg: &'tcx Expr<'_>,
1468 body: &'tcx Expr<'_>,
1469 expr: &'tcx Expr<'_>,
1471 if let Some(higher::Range {
1475 }) = higher::range(arg)
1477 // the var must be a single name
1478 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1479 let mut visitor = VarVisitor {
1482 indexed_mut: FxHashSet::default(),
1483 indexed_indirectly: FxHashMap::default(),
1484 indexed_directly: FxHashMap::default(),
1485 referenced: FxHashSet::default(),
1487 prefer_mutable: false,
1489 walk_expr(&mut visitor, body);
1491 // linting condition: we only indexed one variable, and indexed it directly
1492 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1493 let (indexed, (indexed_extent, indexed_ty)) = visitor
1497 .expect("already checked that we have exactly 1 element");
1499 // ensure that the indexed variable was declared before the loop, see #601
1500 if let Some(indexed_extent) = indexed_extent {
1501 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1502 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1503 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1504 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1505 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1510 // don't lint if the container that is indexed does not have .iter() method
1511 let has_iter = has_iter_method(cx, indexed_ty);
1512 if has_iter.is_none() {
1516 // don't lint if the container that is indexed into is also used without
1518 if visitor.referenced.contains(&indexed) {
1522 let starts_at_zero = is_integer_const(cx, start, 0);
1524 let skip = if starts_at_zero {
1526 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
1529 format!(".skip({})", snippet(cx, start.span, ".."))
1532 let mut end_is_start_plus_val = false;
1534 let take = if let Some(end) = *end {
1535 let mut take_expr = end;
1537 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1538 if let BinOpKind::Add = op.node {
1539 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1540 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1542 if start_equal_left {
1544 } else if start_equal_right {
1548 end_is_start_plus_val = start_equal_left | start_equal_right;
1552 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1554 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
1558 ast::RangeLimits::Closed => {
1559 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1560 format!(".take({})", take_expr + sugg::ONE)
1562 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1569 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1570 ("mut ", "iter_mut")
1575 let take_is_empty = take.is_empty();
1576 let mut method_1 = take;
1577 let mut method_2 = skip;
1579 if end_is_start_plus_val {
1580 mem::swap(&mut method_1, &mut method_2);
1583 if visitor.nonindex {
1586 NEEDLESS_RANGE_LOOP,
1588 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1592 "consider using an iterator",
1594 (pat.span, format!("({}, <item>)", ident.name)),
1597 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1604 let repl = if starts_at_zero && take_is_empty {
1605 format!("&{}{}", ref_mut, indexed)
1607 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1612 NEEDLESS_RANGE_LOOP,
1615 "the loop variable `{}` is only used to index `{}`.",
1621 "consider using an iterator",
1622 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1632 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1634 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1635 if len_args.len() == 1;
1636 if method.ident.name == sym!(len);
1637 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1638 if path.segments.len() == 1;
1639 if path.segments[0].ident.name == var;
1648 fn is_end_eq_array_len<'tcx>(
1649 cx: &LateContext<'tcx>,
1651 limits: ast::RangeLimits,
1652 indexed_ty: Ty<'tcx>,
1655 if let ExprKind::Lit(ref lit) = end.kind;
1656 if let ast::LitKind::Int(end_int, _) = lit.node;
1657 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1658 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1660 return match limits {
1661 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1662 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1670 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1671 let mut applicability = Applicability::MachineApplicable;
1672 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1673 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1678 "it is more concise to loop over references to containers instead of using explicit \
1680 "to write this more concisely, try",
1681 format!("&{}{}", muta, object),
1686 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1687 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1688 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1689 // just the receiver, no arguments
1690 if args.len() == 1 {
1691 let method_name = &*method.ident.as_str();
1692 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1693 if method_name == "iter" || method_name == "iter_mut" {
1694 if is_ref_iterable_type(cx, &args[0]) {
1695 lint_iter_method(cx, args, arg, method_name);
1697 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1698 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1699 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1700 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1701 let mut applicability = Applicability::MachineApplicable;
1702 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1705 EXPLICIT_INTO_ITER_LOOP,
1707 "it is more concise to loop over containers instead of using explicit \
1709 "to write this more concisely, try",
1714 let ref_receiver_ty = cx.tcx.mk_ref(
1715 cx.tcx.lifetimes.re_erased,
1718 mutbl: Mutability::Not,
1721 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1722 lint_iter_method(cx, args, arg, method_name)
1725 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1730 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1731 probably not what you want",
1733 next_loop_linted = true;
1737 if !next_loop_linted {
1738 check_arg_type(cx, pat, arg);
1742 /// Checks for `for` loops over `Option`s and `Result`s.
1743 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1744 let ty = cx.typeck_results().expr_ty(arg);
1745 if is_type_diagnostic_item(cx, ty, sym::option_type) {
1748 FOR_LOOPS_OVER_FALLIBLES,
1751 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1752 `if let` statement.",
1753 snippet(cx, arg.span, "_")
1757 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1758 snippet(cx, pat.span, "_"),
1759 snippet(cx, arg.span, "_")
1762 } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
1765 FOR_LOOPS_OVER_FALLIBLES,
1768 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1769 `if let` statement.",
1770 snippet(cx, arg.span, "_")
1774 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1775 snippet(cx, pat.span, "_"),
1776 snippet(cx, arg.span, "_")
1782 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1783 // incremented exactly once in the loop body, and initialized to zero
1784 // at the start of the loop.
1785 fn check_for_loop_explicit_counter<'tcx>(
1786 cx: &LateContext<'tcx>,
1788 arg: &'tcx Expr<'_>,
1789 body: &'tcx Expr<'_>,
1790 expr: &'tcx Expr<'_>,
1792 // Look for variables that are incremented once per loop iteration.
1793 let mut increment_visitor = IncrementVisitor::new(cx);
1794 walk_expr(&mut increment_visitor, body);
1796 // For each candidate, check the parent block to see if
1797 // it's initialized to zero at the start of the loop.
1798 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1799 for id in increment_visitor.into_results() {
1800 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1801 walk_block(&mut initialize_visitor, block);
1804 if let Some((name, initializer)) = initialize_visitor.get_result();
1805 if is_integer_const(cx, initializer, 0);
1807 let mut applicability = Applicability::MachineApplicable;
1809 let for_span = get_span_of_entire_for_loop(expr);
1813 EXPLICIT_COUNTER_LOOP,
1814 for_span.with_hi(arg.span.hi()),
1815 &format!("the variable `{}` is used as a loop counter.", name),
1818 "for ({}, {}) in {}.enumerate()",
1820 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1821 make_iterator_snippet(cx, arg, &mut applicability),
1831 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1832 /// actual `Iterator` that the loop uses.
1833 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1834 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1835 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1840 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1843 // (&x).into_iter() ==> x.iter()
1844 // (&mut x).into_iter() ==> x.iter_mut()
1846 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1847 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1849 let meth_name = match mutability {
1850 Mutability::Mut => "iter_mut",
1851 Mutability::Not => "iter",
1855 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1861 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1867 /// Checks for the `FOR_KV_MAP` lint.
1868 fn check_for_loop_over_map_kv<'tcx>(
1869 cx: &LateContext<'tcx>,
1871 arg: &'tcx Expr<'_>,
1872 body: &'tcx Expr<'_>,
1873 expr: &'tcx Expr<'_>,
1875 let pat_span = pat.span;
1877 if let PatKind::Tuple(ref pat, _) = pat.kind {
1879 let arg_span = arg.span;
1880 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1881 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1882 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1883 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1888 let mutbl = match mutbl {
1889 Mutability::Not => "",
1890 Mutability::Mut => "_mut",
1892 let arg = match arg.kind {
1893 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1897 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1902 &format!("you seem to want to iterate on a map's {}s", kind),
1904 let map = sugg::Sugg::hir(cx, arg, "map");
1907 "use the corresponding method",
1909 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1910 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1920 fn check_for_single_element_loop<'tcx>(
1921 cx: &LateContext<'tcx>,
1923 arg: &'tcx Expr<'_>,
1924 body: &'tcx Expr<'_>,
1925 expr: &'tcx Expr<'_>,
1928 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg_expr) = arg.kind;
1929 if let PatKind::Binding(.., target, _) = pat.kind;
1930 if let ExprKind::Array([arg_expression]) = arg_expr.kind;
1931 if let ExprKind::Path(ref list_item) = arg_expression.kind;
1932 if let Some(list_item_name) = single_segment_path(list_item).map(|ps| ps.ident.name);
1933 if let ExprKind::Block(ref block, _) = body.kind;
1934 if !block.stmts.is_empty();
1937 let for_span = get_span_of_entire_for_loop(expr);
1938 let mut block_str = snippet(cx, block.span, "..").into_owned();
1939 block_str.remove(0);
1945 SINGLE_ELEMENT_LOOP,
1947 "for loop over a single element",
1949 format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),
1950 Applicability::MachineApplicable
1956 struct MutatePairDelegate<'a, 'tcx> {
1957 cx: &'a LateContext<'tcx>,
1958 hir_id_low: Option<HirId>,
1959 hir_id_high: Option<HirId>,
1960 span_low: Option<Span>,
1961 span_high: Option<Span>,
1964 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1965 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: HirId, _: ConsumeMode) {}
1967 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId, bk: ty::BorrowKind) {
1968 if let ty::BorrowKind::MutBorrow = bk {
1969 if let PlaceBase::Local(id) = cmt.place.base {
1970 if Some(id) == self.hir_id_low {
1971 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
1973 if Some(id) == self.hir_id_high {
1974 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
1980 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId) {
1981 if let PlaceBase::Local(id) = cmt.place.base {
1982 if Some(id) == self.hir_id_low {
1983 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
1985 if Some(id) == self.hir_id_high {
1986 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
1992 impl MutatePairDelegate<'_, '_> {
1993 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1994 (self.span_low, self.span_high)
1998 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1999 if let Some(higher::Range {
2003 }) = higher::range(arg)
2005 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
2006 if mut_ids[0].is_some() || mut_ids[1].is_some() {
2007 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
2008 mut_warn_with_span(cx, span_low);
2009 mut_warn_with_span(cx, span_high);
2014 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
2015 if let Some(sp) = span {
2020 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
2025 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
2027 if let ExprKind::Path(ref qpath) = bound.kind;
2028 if let QPath::Resolved(None, _) = *qpath;
2030 let res = cx.qpath_res(qpath, bound.hir_id);
2031 if let Res::Local(hir_id) = res {
2032 let node_str = cx.tcx.hir().get(hir_id);
2034 if let Node::Binding(pat) = node_str;
2035 if let PatKind::Binding(BindingAnnotation::Mutable, ..) = pat.kind;
2037 return Some(hir_id);
2046 fn check_for_mutation<'tcx>(
2047 cx: &LateContext<'tcx>,
2049 bound_ids: &[Option<HirId>],
2050 ) -> (Option<Span>, Option<Span>) {
2051 let mut delegate = MutatePairDelegate {
2053 hir_id_low: bound_ids[0],
2054 hir_id_high: bound_ids[1],
2058 cx.tcx.infer_ctxt().enter(|infcx| {
2059 ExprUseVisitor::new(
2064 cx.typeck_results(),
2068 delegate.mutation_span()
2071 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
2072 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
2074 PatKind::Wild => true,
2075 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
2080 struct VarVisitor<'a, 'tcx> {
2081 /// context reference
2082 cx: &'a LateContext<'tcx>,
2083 /// var name to look for as index
2085 /// indexed variables that are used mutably
2086 indexed_mut: FxHashSet<Symbol>,
2087 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2088 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2089 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2090 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2091 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2092 /// Any names that are used outside an index operation.
2093 /// Used to detect things like `&mut vec` used together with `vec[i]`
2094 referenced: FxHashSet<Symbol>,
2095 /// has the loop variable been used in expressions other than the index of
2098 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2099 /// takes `&mut self`
2100 prefer_mutable: bool,
2103 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2104 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2106 // the indexed container is referenced by a name
2107 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2108 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2109 if seqvar.segments.len() == 1;
2111 let index_used_directly = same_var(self.cx, idx, self.var);
2112 let indexed_indirectly = {
2113 let mut used_visitor = LocalUsedVisitor::new(self.var);
2114 walk_expr(&mut used_visitor, idx);
2118 if indexed_indirectly || index_used_directly {
2119 if self.prefer_mutable {
2120 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2122 let res = self.cx.qpath_res(seqpath, seqexpr.hir_id);
2124 Res::Local(hir_id) => {
2125 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2126 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2127 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2128 if indexed_indirectly {
2129 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2131 if index_used_directly {
2132 self.indexed_directly.insert(
2133 seqvar.segments[0].ident.name,
2134 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2137 return false; // no need to walk further *on the variable*
2139 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2140 if indexed_indirectly {
2141 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2143 if index_used_directly {
2144 self.indexed_directly.insert(
2145 seqvar.segments[0].ident.name,
2146 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2149 return false; // no need to walk further *on the variable*
2160 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2161 type Map = Map<'tcx>;
2163 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2166 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2167 if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX))
2168 || (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2169 if !self.check(&args[1], &args[0], expr);
2175 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2176 if !self.check(idx, seqexpr, expr);
2181 // directly using a variable
2182 if let ExprKind::Path(ref qpath) = expr.kind;
2183 if let QPath::Resolved(None, ref path) = *qpath;
2184 if path.segments.len() == 1;
2186 if let Res::Local(local_id) = self.cx.qpath_res(qpath, expr.hir_id) {
2187 if local_id == self.var {
2188 self.nonindex = true;
2190 // not the correct variable, but still a variable
2191 self.referenced.insert(path.segments[0].ident.name);
2197 let old = self.prefer_mutable;
2199 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2200 self.prefer_mutable = true;
2201 self.visit_expr(lhs);
2202 self.prefer_mutable = false;
2203 self.visit_expr(rhs);
2205 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2206 if mutbl == Mutability::Mut {
2207 self.prefer_mutable = true;
2209 self.visit_expr(expr);
2211 ExprKind::Call(ref f, args) => {
2214 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2215 self.prefer_mutable = false;
2216 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2217 if mutbl == Mutability::Mut {
2218 self.prefer_mutable = true;
2221 self.visit_expr(expr);
2224 ExprKind::MethodCall(_, _, args, _) => {
2225 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2226 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2227 self.prefer_mutable = false;
2228 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2229 if mutbl == Mutability::Mut {
2230 self.prefer_mutable = true;
2233 self.visit_expr(expr);
2236 ExprKind::Closure(_, _, body_id, ..) => {
2237 let body = self.cx.tcx.hir().body(body_id);
2238 self.visit_expr(&body.value);
2240 _ => walk_expr(self, expr),
2242 self.prefer_mutable = old;
2244 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2245 NestedVisitorMap::None
2249 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2250 let def_id = match var_def_id(cx, expr) {
2252 None => return false,
2254 if let Some(used_mutably) = mutated_variables(container, cx) {
2255 if used_mutably.contains(&def_id) {
2262 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2263 let def_id = match var_def_id(cx, iter_expr) {
2265 None => return false,
2267 let mut visitor = VarUsedAfterLoopVisitor {
2270 iter_expr_id: iter_expr.hir_id,
2271 past_while_let: false,
2272 var_used_after_while_let: false,
2274 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2275 walk_block(&mut visitor, enclosing_block);
2277 visitor.var_used_after_while_let
2280 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2281 cx: &'a LateContext<'tcx>,
2283 iter_expr_id: HirId,
2284 past_while_let: bool,
2285 var_used_after_while_let: bool,
2288 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2289 type Map = Map<'tcx>;
2291 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2292 if self.past_while_let {
2293 if Some(self.def_id) == var_def_id(self.cx, expr) {
2294 self.var_used_after_while_let = true;
2296 } else if self.iter_expr_id == expr.hir_id {
2297 self.past_while_let = true;
2299 walk_expr(self, expr);
2301 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2302 NestedVisitorMap::None
2306 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2307 /// for `&T` and `&mut T`, such as `Vec`.
2309 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2310 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2311 // will allow further borrows afterwards
2312 let ty = cx.typeck_results().expr_ty(e);
2313 is_iterable_array(ty, cx) ||
2314 is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2315 match_type(cx, ty, &paths::LINKED_LIST) ||
2316 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2317 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2318 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2319 match_type(cx, ty, &paths::BINARY_HEAP) ||
2320 match_type(cx, ty, &paths::BTREEMAP) ||
2321 match_type(cx, ty, &paths::BTREESET)
2324 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2325 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2327 ty::Array(_, n) => n
2328 .try_eval_usize(cx.tcx, cx.param_env)
2329 .map_or(false, |val| (0..=32).contains(&val)),
2334 /// If a block begins with a statement (possibly a `let` binding) and has an
2335 /// expression, return it.
2336 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2337 if block.stmts.is_empty() {
2340 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2341 local.init //.map(|expr| expr)
2347 /// If a block begins with an expression (with or without semicolon), return it.
2348 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2350 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2351 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2352 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2353 StmtKind::Local(..) | StmtKind::Item(..) => None,
2359 /// Returns `true` if expr contains a single break expr without destination label
2361 /// passed expression. The expression may be within a block.
2362 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2364 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2365 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2370 #[derive(Debug, PartialEq)]
2371 enum IncrementVisitorVarState {
2372 Initial, // Not examined yet
2373 IncrOnce, // Incremented exactly once, may be a loop counter
2377 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2378 struct IncrementVisitor<'a, 'tcx> {
2379 cx: &'a LateContext<'tcx>, // context reference
2380 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2381 depth: u32, // depth of conditional expressions
2385 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2386 fn new(cx: &'a LateContext<'tcx>) -> Self {
2389 states: FxHashMap::default(),
2395 fn into_results(self) -> impl Iterator<Item = HirId> {
2396 self.states.into_iter().filter_map(|(id, state)| {
2397 if state == IncrementVisitorVarState::IncrOnce {
2406 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2407 type Map = Map<'tcx>;
2409 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2414 // If node is a variable
2415 if let Some(def_id) = var_def_id(self.cx, expr) {
2416 if let Some(parent) = get_parent_expr(self.cx, expr) {
2417 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2418 if *state == IncrementVisitorVarState::IncrOnce {
2419 *state = IncrementVisitorVarState::DontWarn;
2424 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2425 if lhs.hir_id == expr.hir_id {
2426 *state = if op.node == BinOpKind::Add
2427 && is_integer_const(self.cx, rhs, 1)
2428 && *state == IncrementVisitorVarState::Initial
2431 IncrementVisitorVarState::IncrOnce
2433 // Assigned some other value or assigned multiple times
2434 IncrementVisitorVarState::DontWarn
2438 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2439 *state = IncrementVisitorVarState::DontWarn
2441 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2442 *state = IncrementVisitorVarState::DontWarn
2448 walk_expr(self, expr);
2449 } else if is_loop(expr) || is_conditional(expr) {
2451 walk_expr(self, expr);
2453 } else if let ExprKind::Continue(_) = expr.kind {
2456 walk_expr(self, expr);
2459 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2460 NestedVisitorMap::None
2464 enum InitializeVisitorState<'hir> {
2465 Initial, // Not examined yet
2466 Declared(Symbol), // Declared but not (yet) initialized
2469 initializer: &'hir Expr<'hir>,
2474 /// Checks whether a variable is initialized at the start of a loop and not modified
2475 /// and used after the loop.
2476 struct InitializeVisitor<'a, 'tcx> {
2477 cx: &'a LateContext<'tcx>, // context reference
2478 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2480 state: InitializeVisitorState<'tcx>,
2481 depth: u32, // depth of conditional expressions
2485 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2486 fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2491 state: InitializeVisitorState::Initial,
2497 fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
2498 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2499 Some((name, initializer))
2506 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2507 type Map = Map<'tcx>;
2509 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2510 // Look for declarations of the variable
2512 if let StmtKind::Local(ref local) = stmt.kind;
2513 if local.pat.hir_id == self.var_id;
2514 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2516 self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
2517 InitializeVisitorState::Initialized {
2524 walk_stmt(self, stmt);
2527 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2528 if matches!(self.state, InitializeVisitorState::DontWarn) {
2531 if expr.hir_id == self.end_expr.hir_id {
2532 self.past_loop = true;
2535 // No need to visit expressions before the variable is
2537 if matches!(self.state, InitializeVisitorState::Initial) {
2541 // If node is the desired variable, see how it's used
2542 if var_def_id(self.cx, expr) == Some(self.var_id) {
2544 self.state = InitializeVisitorState::DontWarn;
2548 if let Some(parent) = get_parent_expr(self.cx, expr) {
2550 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2551 self.state = InitializeVisitorState::DontWarn;
2553 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2554 self.state = if_chain! {
2556 if let InitializeVisitorState::Declared(name)
2557 | InitializeVisitorState::Initialized { name, ..} = self.state;
2559 InitializeVisitorState::Initialized { initializer: rhs, name }
2561 InitializeVisitorState::DontWarn
2565 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2566 self.state = InitializeVisitorState::DontWarn
2572 walk_expr(self, expr);
2573 } else if !self.past_loop && is_loop(expr) {
2574 self.state = InitializeVisitorState::DontWarn;
2575 } else if is_conditional(expr) {
2577 walk_expr(self, expr);
2580 walk_expr(self, expr);
2584 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2585 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2589 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2590 if let ExprKind::Path(ref qpath) = expr.kind {
2591 let path_res = cx.qpath_res(qpath, expr.hir_id);
2592 if let Res::Local(hir_id) = path_res {
2593 return Some(hir_id);
2599 fn is_loop(expr: &Expr<'_>) -> bool {
2600 matches!(expr.kind, ExprKind::Loop(..))
2603 fn is_conditional(expr: &Expr<'_>) -> bool {
2604 matches!(expr.kind, ExprKind::If(..) | ExprKind::Match(..))
2607 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2609 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2610 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2611 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2613 return is_loop_nested(cx, loop_expr, iter_expr)
2619 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2620 let mut id = loop_expr.hir_id;
2621 let iter_name = if let Some(name) = path_name(iter_expr) {
2627 let parent = cx.tcx.hir().get_parent_node(id);
2631 match cx.tcx.hir().find(parent) {
2632 Some(Node::Expr(expr)) => {
2633 if let ExprKind::Loop(..) = expr.kind {
2637 Some(Node::Block(block)) => {
2638 let mut block_visitor = LoopNestVisitor {
2640 iterator: iter_name,
2643 walk_block(&mut block_visitor, block);
2644 if block_visitor.nesting == RuledOut {
2648 Some(Node::Stmt(_)) => (),
2657 #[derive(PartialEq, Eq)]
2659 Unknown, // no nesting detected yet
2660 RuledOut, // the iterator is initialized or assigned within scope
2661 LookFurther, // no nesting detected, no further walk required
2664 use self::Nesting::{LookFurther, RuledOut, Unknown};
2666 struct LoopNestVisitor {
2672 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2673 type Map = Map<'tcx>;
2675 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2676 if stmt.hir_id == self.hir_id {
2677 self.nesting = LookFurther;
2678 } else if self.nesting == Unknown {
2679 walk_stmt(self, stmt);
2683 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2684 if self.nesting != Unknown {
2687 if expr.hir_id == self.hir_id {
2688 self.nesting = LookFurther;
2692 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2693 if match_var(path, self.iterator) {
2694 self.nesting = RuledOut;
2697 _ => walk_expr(self, expr),
2701 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2702 if self.nesting != Unknown {
2705 if let PatKind::Binding(.., span_name, _) = pat.kind {
2706 if self.iterator == span_name.name {
2707 self.nesting = RuledOut;
2714 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2715 NestedVisitorMap::None
2719 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2720 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2721 let segments = &path.segments;
2722 if segments.len() == 1 {
2723 return Some(segments[0].ident.name);
2729 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2730 if constant(cx, cx.typeck_results(), cond).is_some() {
2731 // A pure constant condition (e.g., `while false`) is not linted.
2735 let mut var_visitor = VarCollectorVisitor {
2737 ids: FxHashSet::default(),
2738 def_ids: FxHashMap::default(),
2741 var_visitor.visit_expr(cond);
2742 if var_visitor.skip {
2745 let used_in_condition = &var_visitor.ids;
2746 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2747 used_in_condition.is_disjoint(&used_mutably)
2751 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2753 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2754 has_break_or_return: false,
2756 has_break_or_return_visitor.visit_expr(expr);
2757 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2759 if no_cond_variable_mutated && !mutable_static_in_cond {
2762 WHILE_IMMUTABLE_CONDITION,
2764 "variables in the condition are not mutated in the loop body",
2766 diag.note("this may lead to an infinite or to a never running loop");
2768 if has_break_or_return {
2769 diag.note("this loop contains `return`s or `break`s");
2770 diag.help("rewrite it as `if cond { loop { } }`");
2777 struct HasBreakOrReturnVisitor {
2778 has_break_or_return: bool,
2781 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2782 type Map = Map<'tcx>;
2784 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2785 if self.has_break_or_return {
2790 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2791 self.has_break_or_return = true;
2797 walk_expr(self, expr);
2800 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2801 NestedVisitorMap::None
2805 /// Collects the set of variables in an expression
2806 /// Stops analysis if a function call is found
2807 /// Note: In some cases such as `self`, there are no mutable annotation,
2808 /// All variables definition IDs are collected
2809 struct VarCollectorVisitor<'a, 'tcx> {
2810 cx: &'a LateContext<'tcx>,
2811 ids: FxHashSet<HirId>,
2812 def_ids: FxHashMap<def_id::DefId, bool>,
2816 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2817 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2819 if let ExprKind::Path(ref qpath) = ex.kind;
2820 if let QPath::Resolved(None, _) = *qpath;
2821 let res = self.cx.qpath_res(qpath, ex.hir_id);
2824 Res::Local(hir_id) => {
2825 self.ids.insert(hir_id);
2827 Res::Def(DefKind::Static, def_id) => {
2828 let mutable = self.cx.tcx.is_mutable_static(def_id);
2829 self.def_ids.insert(def_id, mutable);
2838 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2839 type Map = Map<'tcx>;
2841 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2843 ExprKind::Path(_) => self.insert_def_id(ex),
2844 // If there is any function/method call… we just stop analysis
2845 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2847 _ => walk_expr(self, ex),
2851 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2852 NestedVisitorMap::None
2856 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2858 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2859 check_needless_collect_direct_usage(expr, cx);
2860 check_needless_collect_indirect_usage(expr, cx);
2862 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2864 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2865 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2866 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2867 if let Some(ref generic_args) = chain_method.args;
2868 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2870 let ty = cx.typeck_results().node_type(ty.hir_id);
2871 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2872 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2873 match_type(cx, ty, &paths::BTREEMAP) ||
2874 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2875 if method.ident.name == sym!(len) {
2876 let span = shorten_needless_collect_span(expr);
2881 NEEDLESS_COLLECT_MSG,
2883 "count()".to_string(),
2884 Applicability::MachineApplicable,
2887 if method.ident.name == sym!(is_empty) {
2888 let span = shorten_needless_collect_span(expr);
2893 NEEDLESS_COLLECT_MSG,
2895 "next().is_none()".to_string(),
2896 Applicability::MachineApplicable,
2899 if method.ident.name == sym!(contains) {
2900 let contains_arg = snippet(cx, args[1].span, "??");
2901 let span = shorten_needless_collect_span(expr);
2906 NEEDLESS_COLLECT_MSG,
2908 let (arg, pred) = contains_arg
2910 .map_or(("&x", &*contains_arg), |s| ("x", s));
2911 diag.span_suggestion(
2915 "any(|{}| x == {})",
2918 Applicability::MachineApplicable,
2928 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2929 if let ExprKind::Block(ref block, _) = expr.kind {
2930 for ref stmt in block.stmts {
2932 if let StmtKind::Local(
2933 Local { pat: Pat { hir_id: pat_id, kind: PatKind::Binding(_, _, ident, .. ), .. },
2934 init: Some(ref init_expr), .. }
2936 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2937 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2938 if let Some(ref generic_args) = method_name.args;
2939 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2940 if let ty = cx.typeck_results().node_type(ty.hir_id);
2941 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2942 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2943 match_type(cx, ty, &paths::LINKED_LIST);
2944 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2945 if iter_calls.len() == 1;
2947 let mut used_count_visitor = UsedCountVisitor {
2952 walk_block(&mut used_count_visitor, block);
2953 if used_count_visitor.count > 1 {
2957 // Suggest replacing iter_call with iter_replacement, and removing stmt
2958 let iter_call = &iter_calls[0];
2962 stmt.span.until(iter_call.span),
2963 NEEDLESS_COLLECT_MSG,
2965 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2966 diag.multipart_suggestion(
2967 iter_call.get_suggestion_text(),
2969 (stmt.span, String::new()),
2970 (iter_call.span, iter_replacement)
2972 Applicability::MachineApplicable,// MaybeIncorrect,
2982 struct IterFunction {
2983 func: IterFunctionKind,
2987 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2989 IterFunctionKind::IntoIter => String::new(),
2990 IterFunctionKind::Len => String::from(".count()"),
2991 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2992 IterFunctionKind::Contains(span) => {
2993 let s = snippet(cx, *span, "..");
2994 if let Some(stripped) = s.strip_prefix('&') {
2995 format!(".any(|x| x == {})", stripped)
2997 format!(".any(|x| x == *{})", s)
3002 fn get_suggestion_text(&self) -> &'static str {
3004 IterFunctionKind::IntoIter => {
3005 "Use the original Iterator instead of collecting it and then producing a new one"
3007 IterFunctionKind::Len => {
3008 "Take the original Iterator's count instead of collecting it and finding the length"
3010 IterFunctionKind::IsEmpty => {
3011 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
3013 IterFunctionKind::Contains(_) => {
3014 "Check if the original Iterator contains an element instead of collecting then checking"
3019 enum IterFunctionKind {
3026 struct IterFunctionVisitor {
3027 uses: Vec<IterFunction>,
3031 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
3032 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
3033 // Check function calls on our collection
3035 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
3036 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
3037 if let &[name] = &path.segments;
3038 if name.ident == self.target;
3040 let len = sym!(len);
3041 let is_empty = sym!(is_empty);
3042 let contains = sym!(contains);
3043 match method_name.ident.name {
3044 sym::into_iter => self.uses.push(
3045 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
3047 name if name == len => self.uses.push(
3048 IterFunction { func: IterFunctionKind::Len, span: expr.span }
3050 name if name == is_empty => self.uses.push(
3051 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
3053 name if name == contains => self.uses.push(
3054 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
3056 _ => self.seen_other = true,
3061 // Check if the collection is used for anything else
3063 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
3064 if let &[name] = &path.segments;
3065 if name.ident == self.target;
3067 self.seen_other = true;
3069 walk_expr(self, expr);
3074 type Map = Map<'tcx>;
3075 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3076 NestedVisitorMap::None
3080 struct UsedCountVisitor<'a, 'tcx> {
3081 cx: &'a LateContext<'tcx>,
3086 impl<'a, 'tcx> Visitor<'tcx> for UsedCountVisitor<'a, 'tcx> {
3087 type Map = Map<'tcx>;
3089 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
3090 if same_var(self.cx, expr, self.id) {
3093 walk_expr(self, expr);
3097 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3098 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
3102 /// Detect the occurrences of calls to `iter` or `into_iter` for the
3103 /// given identifier
3104 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
3105 let mut visitor = IterFunctionVisitor {
3110 visitor.visit_block(block);
3111 if visitor.seen_other {
3118 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3120 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3121 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3123 return expr.span.with_lo(span.lo());