1 use crate::consts::constant;
2 use crate::utils::sugg::Sugg;
3 use crate::utils::usage::mutated_variables;
4 use crate::utils::visitors::LocalUsedVisitor;
6 contains_name, get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
7 indent_of, is_in_panic_handler, is_integer_const, is_no_std_crate, is_ok_ctor, is_refutable, is_some_ctor,
8 is_type_diagnostic_item, last_path_segment, match_trait_method, match_type, multispan_sugg, path_to_local,
9 path_to_local_id, paths, single_segment_path, snippet, snippet_with_applicability, snippet_with_macro_callsite,
10 span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then, sugg, SpanlessEq,
12 use if_chain::if_chain;
14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
15 use rustc_errors::Applicability;
16 use rustc_hir::def::{DefKind, Res};
17 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
19 def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, InlineAsmOperand,
20 Local, LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
22 use rustc_infer::infer::TyCtxtInferExt;
23 use rustc_lint::{LateContext, LateLintPass, LintContext};
24 use rustc_middle::hir::map::Map;
25 use rustc_middle::lint::in_external_macro;
26 use rustc_middle::middle::region;
27 use rustc_middle::ty::{self, Ty, TyS};
28 use rustc_session::{declare_lint_pass, declare_tool_lint};
29 use rustc_span::source_map::Span;
30 use rustc_span::symbol::{sym, Ident, Symbol};
31 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
32 use std::iter::{once, Iterator};
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// # let src = vec![1];
46 /// # let mut dst = vec![0; 65];
47 /// for i in 0..src.len() {
48 /// dst[i + 64] = src[i];
51 /// Could be written as:
53 /// # let src = vec![1];
54 /// # let mut dst = vec![0; 65];
55 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
59 "manually copying items between slices"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for looping over the range of `0..len` of some
64 /// collection just to get the values by index.
66 /// **Why is this bad?** Just iterating the collection itself makes the intent
67 /// more clear and is probably faster.
69 /// **Known problems:** None.
73 /// let vec = vec!['a', 'b', 'c'];
74 /// for i in 0..vec.len() {
75 /// println!("{}", vec[i]);
78 /// Could be written as:
80 /// let vec = vec!['a', 'b', 'c'];
82 /// println!("{}", i);
85 pub NEEDLESS_RANGE_LOOP,
87 "for-looping over a range of indices where an iterator over items would do"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
92 /// suggests the latter.
94 /// **Why is this bad?** Readability.
96 /// **Known problems:** False negatives. We currently only warn on some known
101 /// // with `y` a `Vec` or slice:
102 /// # let y = vec![1];
103 /// for x in y.iter() {
107 /// can be rewritten to
109 /// # let y = vec![1];
114 pub EXPLICIT_ITER_LOOP,
116 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
121 /// suggests the latter.
123 /// **Why is this bad?** Readability.
125 /// **Known problems:** None
129 /// # let y = vec![1];
130 /// // with `y` a `Vec` or slice:
131 /// for x in y.into_iter() {
135 /// can be rewritten to
137 /// # let y = vec![1];
142 pub EXPLICIT_INTO_ITER_LOOP,
144 "for-looping over `_.into_iter()` when `_` would do"
147 declare_clippy_lint! {
148 /// **What it does:** Checks for loops on `x.next()`.
150 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
151 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
152 /// implements `IntoIterator`, so that possibly one value will be iterated,
153 /// leading to some hard to find bugs. No one will want to write such code
154 /// [except to win an Underhanded Rust
155 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
157 /// **Known problems:** None.
161 /// for x in y.next() {
167 "for-looping over `_.next()` which is probably not intended"
170 declare_clippy_lint! {
171 /// **What it does:** Checks for `for` loops over `Option` or `Result` values.
173 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
176 /// **Known problems:** None.
180 /// # let opt = Some(1);
188 /// if let Some(x) = opt {
196 /// # let res: Result<i32, std::io::Error> = Ok(1);
204 /// if let Ok(x) = res {
208 pub FOR_LOOPS_OVER_FALLIBLES,
210 "for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
213 declare_clippy_lint! {
214 /// **What it does:** Detects `loop + match` combinations that are easier
215 /// written as a `while let` loop.
217 /// **Why is this bad?** The `while let` loop is usually shorter and more
220 /// **Known problems:** Sometimes the wrong binding is displayed ([#383](https://github.com/rust-lang/rust-clippy/issues/383)).
224 /// # let y = Some(1);
226 /// let x = match y {
230 /// // .. do something with x
232 /// // is easier written as
233 /// while let Some(x) = y {
234 /// // .. do something with x
239 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
242 declare_clippy_lint! {
243 /// **What it does:** Checks for functions collecting an iterator when collect
246 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
247 /// when this allocation may not be needed.
249 /// **Known problems:**
254 /// # let iterator = vec![1].into_iter();
255 /// let len = iterator.clone().collect::<Vec<_>>().len();
257 /// let len = iterator.count();
259 pub NEEDLESS_COLLECT,
261 "collecting an iterator when collect is not needed"
264 declare_clippy_lint! {
265 /// **What it does:** Checks `for` loops over slices with an explicit counter
266 /// and suggests the use of `.enumerate()`.
268 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
269 /// declutters the code and may be faster in some instances.
271 /// **Known problems:** None.
275 /// # let v = vec![1];
276 /// # fn bar(bar: usize, baz: usize) {}
283 /// Could be written as
285 /// # let v = vec![1];
286 /// # fn bar(bar: usize, baz: usize) {}
287 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
289 pub EXPLICIT_COUNTER_LOOP,
291 "for-looping with an explicit counter when `_.enumerate()` would do"
294 declare_clippy_lint! {
295 /// **What it does:** Checks for empty `loop` expressions.
297 /// **Why is this bad?** These busy loops burn CPU cycles without doing
298 /// anything. It is _almost always_ a better idea to `panic!` than to have
301 /// If panicking isn't possible, think of the environment and either:
302 /// - block on something
303 /// - sleep the thread for some microseconds
304 /// - yield or pause the thread
306 /// For `std` targets, this can be done with
307 /// [`std::thread::sleep`](https://doc.rust-lang.org/std/thread/fn.sleep.html)
308 /// or [`std::thread::yield_now`](https://doc.rust-lang.org/std/thread/fn.yield_now.html).
310 /// For `no_std` targets, doing this is more complicated, especially because
311 /// `#[panic_handler]`s can't panic. To stop/pause the thread, you will
312 /// probably need to invoke some target-specific intrinsic. Examples include:
313 /// - [`x86_64::instructions::hlt`](https://docs.rs/x86_64/0.12.2/x86_64/instructions/fn.hlt.html)
314 /// - [`cortex_m::asm::wfi`](https://docs.rs/cortex-m/0.6.3/cortex_m/asm/fn.wfi.html)
316 /// **Known problems:** None.
324 "empty `loop {}`, which should block or sleep"
327 declare_clippy_lint! {
328 /// **What it does:** Checks for `while let` expressions on iterators.
330 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
331 /// the intent better.
333 /// **Known problems:** None.
337 /// while let Some(val) = iter() {
341 pub WHILE_LET_ON_ITERATOR,
343 "using a `while let` loop instead of a for loop on an iterator"
346 declare_clippy_lint! {
347 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
348 /// ignoring either the keys or values.
350 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
351 /// can be used to express that don't need the values or keys.
353 /// **Known problems:** None.
357 /// for (k, _) in &map {
362 /// could be replaced by
365 /// for k in map.keys() {
371 "looping on a map using `iter` when `keys` or `values` would do"
374 declare_clippy_lint! {
375 /// **What it does:** Checks for loops that will always `break`, `return` or
376 /// `continue` an outer loop.
378 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
381 /// **Known problems:** None
392 "any loop that will always `break` or `return`"
395 declare_clippy_lint! {
396 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
398 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
400 /// **Known problems:** None
404 /// let mut foo = 42;
405 /// for i in 0..foo {
407 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
412 "for loop over a range where one of the bounds is a mutable variable"
415 declare_clippy_lint! {
416 /// **What it does:** Checks whether variables used within while loop condition
417 /// can be (and are) mutated in the body.
419 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
420 /// will lead to an infinite loop.
422 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
423 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
424 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
430 /// println!("let me loop forever!");
433 pub WHILE_IMMUTABLE_CONDITION,
435 "variables used within while expression are not mutated in the body"
438 declare_clippy_lint! {
439 /// **What it does:** Checks whether a for loop is being used to push a constant
440 /// value into a Vec.
442 /// **Why is this bad?** This kind of operation can be expressed more succinctly with
443 /// `vec![item;SIZE]` or `vec.resize(NEW_SIZE, item)` and using these alternatives may also
444 /// have better performance.
445 /// **Known problems:** None
451 /// let mut vec: Vec<u8> = Vec::new();
459 /// could be written as
463 /// let mut vec: Vec<u8> = vec![item1; 20];
464 /// vec.resize(20 + 30, item2);
468 "the same item is pushed inside of a for loop"
471 declare_clippy_lint! {
472 /// **What it does:** Checks whether a for loop has a single element.
474 /// **Why is this bad?** There is no reason to have a loop of a
476 /// **Known problems:** None
481 /// for item in &[item1] {
482 /// println!("{}", item);
485 /// could be written as
488 /// let item = &item1;
489 /// println!("{}", item);
491 pub SINGLE_ELEMENT_LOOP,
493 "there is no reason to have a single element loop"
496 declare_clippy_lint! {
497 /// **What it does:** Check for unnecessary `if let` usage in a for loop
498 /// where only the `Some` or `Ok` variant of the iterator element is used.
500 /// **Why is this bad?** It is verbose and can be simplified
501 /// by first calling the `flatten` method on the `Iterator`.
503 /// **Known problems:** None.
508 /// let x = vec![Some(1), Some(2), Some(3)];
510 /// if let Some(n) = n {
511 /// println!("{}", n);
517 /// let x = vec![Some(1), Some(2), Some(3)];
518 /// for n in x.into_iter().flatten() {
519 /// println!("{}", n);
524 "for loops over `Option`s or `Result`s with a single expression can be simplified"
527 declare_lint_pass!(Loops => [
532 EXPLICIT_INTO_ITER_LOOP,
534 FOR_LOOPS_OVER_FALLIBLES,
537 EXPLICIT_COUNTER_LOOP,
539 WHILE_LET_ON_ITERATOR,
543 WHILE_IMMUTABLE_CONDITION,
548 impl<'tcx> LateLintPass<'tcx> for Loops {
549 #[allow(clippy::too_many_lines)]
550 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
551 if let Some((pat, arg, body, span)) = higher::for_loop(expr) {
552 // we don't want to check expanded macros
553 // this check is not at the top of the function
554 // since higher::for_loop expressions are marked as expansions
555 if body.span.from_expansion() {
558 check_for_loop(cx, pat, arg, body, expr, span);
561 // we don't want to check expanded macros
562 if expr.span.from_expansion() {
566 // check for never_loop
567 if let ExprKind::Loop(ref block, _, _, _) = expr.kind {
568 match never_loop_block(block, expr.hir_id) {
569 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
570 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
574 // check for `loop { if let {} else break }` that could be `while let`
575 // (also matches an explicit "match" instead of "if let")
576 // (even if the "match" or "if let" is used for declaration)
577 if let ExprKind::Loop(ref block, _, LoopSource::Loop, _) = expr.kind {
578 // also check for empty `loop {}` statements, skipping those in #[panic_handler]
579 if block.stmts.is_empty() && block.expr.is_none() && !is_in_panic_handler(cx, expr) {
580 let msg = "empty `loop {}` wastes CPU cycles";
581 let help = if is_no_std_crate(cx.tcx.hir().krate()) {
582 "you should either use `panic!()` or add a call pausing or sleeping the thread to the loop body"
584 "you should either use `panic!()` or add `std::thread::sleep(..);` to the loop body"
586 span_lint_and_help(cx, EMPTY_LOOP, expr.span, msg, None, help);
589 // extract the expression from the first statement (if any) in a block
590 let inner_stmt_expr = extract_expr_from_first_stmt(block);
591 // or extract the first expression (if any) from the block
592 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
593 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
594 // ensure "if let" compatible match structure
596 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
598 && arms[0].guard.is_none()
599 && arms[1].guard.is_none()
600 && is_simple_break_expr(&arms[1].body)
602 if in_external_macro(cx.sess(), expr.span) {
606 // NOTE: we used to build a body here instead of using
607 // ellipsis, this was removed because:
608 // 1) it was ugly with big bodies;
609 // 2) it was not indented properly;
610 // 3) it wasn’t very smart (see #675).
611 let mut applicability = Applicability::HasPlaceholders;
616 "this loop could be written as a `while let` loop",
619 "while let {} = {} {{ .. }}",
620 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
621 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
632 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
633 let pat = &arms[0].pat.kind;
635 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
636 &ExprKind::MethodCall(ref method_path, _, ref method_args, _),
637 ) = (pat, &match_expr.kind)
639 let iter_expr = &method_args[0];
641 // Don't lint when the iterator is recreated on every iteration
643 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
644 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
645 if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
651 let lhs_constructor = last_path_segment(qpath);
652 if method_path.ident.name == sym::next
653 && match_trait_method(cx, match_expr, &paths::ITERATOR)
654 && lhs_constructor.ident.name == sym::Some
655 && (pat_args.is_empty()
656 || !is_refutable(cx, &pat_args[0])
657 && !is_used_inside(cx, iter_expr, &arms[0].body)
658 && !is_iterator_used_after_while_let(cx, iter_expr)
659 && !is_nested(cx, expr, &method_args[0]))
661 let mut applicability = Applicability::MachineApplicable;
662 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
663 let loop_var = if pat_args.is_empty() {
666 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
670 WHILE_LET_ON_ITERATOR,
671 expr.span.with_hi(match_expr.span.hi()),
672 "this loop could be written as a `for` loop",
674 format!("for {} in {}", loop_var, iterator),
681 if let Some((cond, body)) = higher::while_loop(&expr) {
682 check_infinite_loop(cx, cond, body);
685 check_needless_collect(expr, cx);
689 enum NeverLoopResult {
690 // A break/return always get triggered but not necessarily for the main loop.
692 // A continue may occur for the main loop.
698 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
700 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
701 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
705 // Combine two results for parts that are called in order.
707 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
709 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
710 NeverLoopResult::Otherwise => second,
714 // Combine two results where both parts are called but not necessarily in order.
716 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
717 match (left, right) {
718 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
719 NeverLoopResult::MayContinueMainLoop
721 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
722 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
726 // Combine two results where only one of the part may have been executed.
728 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
730 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
731 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
732 NeverLoopResult::MayContinueMainLoop
734 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
738 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
739 let stmts = block.stmts.iter().map(stmt_to_expr);
740 let expr = once(block.expr.as_deref());
741 let mut iter = stmts.chain(expr).flatten();
742 never_loop_expr_seq(&mut iter, main_loop_id)
745 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
747 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
748 StmtKind::Local(ref local) => local.init.as_deref(),
753 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
756 | ExprKind::Unary(_, ref e)
757 | ExprKind::Cast(ref e, _)
758 | ExprKind::Type(ref e, _)
759 | ExprKind::Field(ref e, _)
760 | ExprKind::AddrOf(_, _, ref e)
761 | ExprKind::Struct(_, _, Some(ref e))
762 | ExprKind::Repeat(ref e, _)
763 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
764 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
765 never_loop_expr_all(&mut es.iter(), main_loop_id)
767 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
768 ExprKind::Binary(_, ref e1, ref e2)
769 | ExprKind::Assign(ref e1, ref e2, _)
770 | ExprKind::AssignOp(_, ref e1, ref e2)
771 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
772 ExprKind::Loop(ref b, _, _, _) => {
773 // Break can come from the inner loop so remove them.
774 absorb_break(&never_loop_block(b, main_loop_id))
776 ExprKind::If(ref e, ref e2, ref e3) => {
777 let e1 = never_loop_expr(e, main_loop_id);
778 let e2 = never_loop_expr(e2, main_loop_id);
781 .map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
782 combine_seq(e1, combine_branches(e2, e3))
784 ExprKind::Match(ref e, ref arms, _) => {
785 let e = never_loop_expr(e, main_loop_id);
789 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
793 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
794 ExprKind::Continue(d) => {
797 .expect("target ID can only be missing in the presence of compilation errors");
798 if id == main_loop_id {
799 NeverLoopResult::MayContinueMainLoop
801 NeverLoopResult::AlwaysBreak
804 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
805 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
807 ExprKind::InlineAsm(ref asm) => asm
810 .map(|(o, _)| match o {
811 InlineAsmOperand::In { expr, .. }
812 | InlineAsmOperand::InOut { expr, .. }
813 | InlineAsmOperand::Const { expr }
814 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
815 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
816 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
817 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
820 .fold(NeverLoopResult::Otherwise, combine_both),
821 ExprKind::Struct(_, _, None)
822 | ExprKind::Yield(_, _)
823 | ExprKind::Closure(_, _, _, _, _)
824 | ExprKind::LlvmInlineAsm(_)
826 | ExprKind::ConstBlock(_)
828 | ExprKind::Err => NeverLoopResult::Otherwise,
832 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
833 es.map(|e| never_loop_expr(e, main_loop_id))
834 .fold(NeverLoopResult::Otherwise, combine_seq)
837 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
838 es.map(|e| never_loop_expr(e, main_loop_id))
839 .fold(NeverLoopResult::Otherwise, combine_both)
842 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
843 e.map(|e| never_loop_expr(e, main_loop_id))
844 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
847 fn check_for_loop<'tcx>(
848 cx: &LateContext<'tcx>,
851 body: &'tcx Expr<'_>,
852 expr: &'tcx Expr<'_>,
855 let is_manual_memcpy_triggered = detect_manual_memcpy(cx, pat, arg, body, expr);
856 if !is_manual_memcpy_triggered {
857 check_for_loop_range(cx, pat, arg, body, expr);
858 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
860 check_for_loop_arg(cx, pat, arg, expr);
861 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
862 check_for_mut_range_bound(cx, arg, body);
863 check_for_single_element_loop(cx, pat, arg, body, expr);
864 detect_same_item_push(cx, pat, arg, body, expr);
865 check_manual_flatten(cx, pat, arg, body, span);
868 // this function assumes the given expression is a `for` loop.
869 fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
870 // for some reason this is the only way to get the `Span`
871 // of the entire `for` loop
872 if let ExprKind::Match(_, arms, _) = &expr.kind {
879 /// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
880 /// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
881 /// it exists for the convenience of the overloaded operators while normal functions can do the
884 struct MinifyingSugg<'a>(Sugg<'a>);
886 impl<'a> MinifyingSugg<'a> {
887 fn as_str(&self) -> &str {
888 let Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) = &self.0;
892 fn into_sugg(self) -> Sugg<'a> {
897 impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
898 fn from(sugg: Sugg<'a>) -> Self {
903 impl std::ops::Add for &MinifyingSugg<'static> {
904 type Output = MinifyingSugg<'static>;
905 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
906 match (self.as_str(), rhs.as_str()) {
907 ("0", _) => rhs.clone(),
908 (_, "0") => self.clone(),
909 (_, _) => (&self.0 + &rhs.0).into(),
914 impl std::ops::Sub for &MinifyingSugg<'static> {
915 type Output = MinifyingSugg<'static>;
916 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
917 match (self.as_str(), rhs.as_str()) {
918 (_, "0") => self.clone(),
919 ("0", _) => (-rhs.0.clone()).into(),
920 (x, y) if x == y => sugg::ZERO.into(),
921 (_, _) => (&self.0 - &rhs.0).into(),
926 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
927 type Output = MinifyingSugg<'static>;
928 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
929 match (self.as_str(), rhs.as_str()) {
930 ("0", _) => rhs.clone(),
932 (_, _) => (self.0 + &rhs.0).into(),
937 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
938 type Output = MinifyingSugg<'static>;
939 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
940 match (self.as_str(), rhs.as_str()) {
942 ("0", _) => (-rhs.0.clone()).into(),
943 (x, y) if x == y => sugg::ZERO.into(),
944 (_, _) => (self.0 - &rhs.0).into(),
949 /// a wrapper around `MinifyingSugg`, which carries a operator like currying
950 /// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
952 value: MinifyingSugg<'static>,
956 #[derive(Clone, Copy)]
963 fn negative(value: Sugg<'static>) -> Self {
966 sign: OffsetSign::Negative,
970 fn positive(value: Sugg<'static>) -> Self {
973 sign: OffsetSign::Positive,
978 Self::positive(sugg::ZERO)
982 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
984 OffsetSign::Positive => lhs + &rhs.value,
985 OffsetSign::Negative => lhs - &rhs.value,
989 #[derive(Debug, Clone, Copy)]
990 enum StartKind<'hir> {
992 Counter { initializer: &'hir Expr<'hir> },
995 struct IndexExpr<'hir> {
996 base: &'hir Expr<'hir>,
997 idx: StartKind<'hir>,
1001 struct Start<'hir> {
1003 kind: StartKind<'hir>,
1006 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
1007 let is_slice = match ty.kind() {
1008 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
1009 ty::Slice(..) | ty::Array(..) => true,
1013 is_slice || is_type_diagnostic_item(cx, ty, sym::vec_type) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
1016 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
1018 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
1019 if method.ident.name == sym::clone;
1021 if let Some(arg) = args.get(0);
1022 then { arg } else { expr }
1026 fn get_details_from_idx<'tcx>(
1027 cx: &LateContext<'tcx>,
1029 starts: &[Start<'tcx>],
1030 ) -> Option<(StartKind<'tcx>, Offset)> {
1031 fn get_start<'tcx>(e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
1032 let id = path_to_local(e)?;
1033 starts.iter().find(|start| start.id == id).map(|start| start.kind)
1036 fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
1038 ExprKind::Lit(l) => match l.node {
1039 ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
1042 ExprKind::Path(..) if get_start(e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
1048 ExprKind::Binary(op, lhs, rhs) => match op.node {
1050 let offset_opt = get_start(lhs, starts)
1051 .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
1052 .or_else(|| get_start(rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
1054 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
1057 get_start(lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
1061 ExprKind::Path(..) => get_start(idx, starts).map(|s| (s, Offset::empty())),
1066 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1067 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1074 /// Get assignments from the given block.
1075 /// The returned iterator yields `None` if no assignment expressions are there,
1076 /// filtering out the increments of the given whitelisted loop counters;
1077 /// because its job is to make sure there's nothing other than assignments and the increments.
1078 fn get_assignments<'a, 'tcx>(
1079 Block { stmts, expr, .. }: &'tcx Block<'tcx>,
1080 loop_counters: &'a [Start<'tcx>],
1081 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'a {
1082 // As the `filter` and `map` below do different things, I think putting together
1083 // just increases complexity. (cc #3188 and #4193)
1086 .filter_map(move |stmt| match stmt.kind {
1087 StmtKind::Local(..) | StmtKind::Item(..) => None,
1088 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
1090 .chain((*expr).into_iter())
1092 if let ExprKind::AssignOp(_, place, _) = e.kind {
1093 path_to_local(place).map_or(false, |id| {
1096 // skip the first item which should be `StartKind::Range`
1097 // this makes it possible to use the slice with `StartKind::Range` in the same iterator loop.
1099 .any(|counter| counter.id == id)
1105 .map(get_assignment)
1108 fn get_loop_counters<'a, 'tcx>(
1109 cx: &'a LateContext<'tcx>,
1110 body: &'tcx Block<'tcx>,
1111 expr: &'tcx Expr<'_>,
1112 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1113 // Look for variables that are incremented once per loop iteration.
1114 let mut increment_visitor = IncrementVisitor::new(cx);
1115 walk_block(&mut increment_visitor, body);
1117 // For each candidate, check the parent block to see if
1118 // it's initialized to zero at the start of the loop.
1119 get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
1122 .filter_map(move |var_id| {
1123 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1124 walk_block(&mut initialize_visitor, block);
1126 initialize_visitor.get_result().map(|(_, initializer)| Start {
1128 kind: StartKind::Counter { initializer },
1135 fn build_manual_memcpy_suggestion<'tcx>(
1136 cx: &LateContext<'tcx>,
1139 limits: ast::RangeLimits,
1140 dst: &IndexExpr<'_>,
1141 src: &IndexExpr<'_>,
1143 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1144 if offset.as_str() == "0" {
1151 let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
1153 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1154 if method.ident.name == sym!(len);
1155 if len_args.len() == 1;
1156 if let Some(arg) = len_args.get(0);
1157 if path_to_local(arg) == path_to_local(base);
1159 if sugg.as_str() == end_str {
1166 ast::RangeLimits::Closed => {
1167 sugg + &sugg::ONE.into()
1169 ast::RangeLimits::HalfOpen => sugg,
1175 let start_str = Sugg::hir(cx, start, "").into();
1176 let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
1178 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1179 StartKind::Range => (
1180 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
1185 apply_offset(&end_str, &idx_expr.idx_offset),
1189 StartKind::Counter { initializer } => {
1190 let counter_start = Sugg::hir(cx, initializer, "").into();
1192 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
1197 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1204 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1205 let (src_offset, src_limit) = print_offset_and_limit(&src);
1207 let dst_base_str = snippet(cx, dst.base.span, "???");
1208 let src_base_str = snippet(cx, src.base.span, "???");
1210 let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
1216 dst_offset.maybe_par(),
1217 dst_limit.maybe_par()
1223 "{}.clone_from_slice(&{}[{}..{}]);",
1226 src_offset.maybe_par(),
1227 src_limit.maybe_par()
1231 /// Checks for for loops that sequentially copy items from one slice-like
1232 /// object to another.
1233 fn detect_manual_memcpy<'tcx>(
1234 cx: &LateContext<'tcx>,
1236 arg: &'tcx Expr<'_>,
1237 body: &'tcx Expr<'_>,
1238 expr: &'tcx Expr<'_>,
1240 if let Some(higher::Range {
1244 }) = higher::range(arg)
1246 // the var must be a single name
1247 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1248 let mut starts = vec![Start {
1250 kind: StartKind::Range,
1253 // This is one of few ways to return different iterators
1254 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1255 let mut iter_a = None;
1256 let mut iter_b = None;
1258 if let ExprKind::Block(block, _) = body.kind {
1259 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1260 starts.extend(loop_counters);
1262 iter_a = Some(get_assignments(block, &starts));
1264 iter_b = Some(get_assignment(body));
1267 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1269 let big_sugg = assignments
1270 // The only statements in the for loops can be indexed assignments from
1271 // indexed retrievals (except increments of loop counters).
1273 o.and_then(|(lhs, rhs)| {
1274 let rhs = fetch_cloned_expr(rhs);
1276 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1277 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1278 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1279 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1280 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1281 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1283 // Source and destination must be different
1284 if path_to_local(base_left) != path_to_local(base_right);
1286 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1287 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1294 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1295 .collect::<Option<Vec<_>>>()
1296 .filter(|v| !v.is_empty())
1297 .map(|v| v.join("\n "));
1299 if let Some(big_sugg) = big_sugg {
1303 get_span_of_entire_for_loop(expr),
1304 "it looks like you're manually copying between slices",
1305 "try replacing the loop by",
1307 Applicability::Unspecified,
1316 // Scans the body of the for loop and determines whether lint should be given
1317 struct SameItemPushVisitor<'a, 'tcx> {
1319 // this field holds the last vec push operation visited, which should be the only push seen
1320 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1321 cx: &'a LateContext<'tcx>,
1324 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1325 type Map = Map<'tcx>;
1327 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1329 // Non-determinism may occur ... don't give a lint
1330 ExprKind::Loop(..) | ExprKind::Match(..) => self.should_lint = false,
1331 ExprKind::Block(block, _) => self.visit_block(block),
1336 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1337 for stmt in b.stmts.iter() {
1338 self.visit_stmt(stmt);
1342 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1343 let vec_push_option = get_vec_push(self.cx, s);
1344 if vec_push_option.is_none() {
1345 // Current statement is not a push so visit inside
1347 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1351 // Current statement is a push ...check whether another
1352 // push had been previously done
1353 if self.vec_push.is_none() {
1354 self.vec_push = vec_push_option;
1356 // There are multiple pushes ... don't lint
1357 self.should_lint = false;
1362 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1363 NestedVisitorMap::None
1367 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1368 // the Vec being pushed into and the item being pushed
1369 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1371 // Extract method being called
1372 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1373 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1374 // Figure out the parameters for the method call
1375 if let Some(self_expr) = args.get(0);
1376 if let Some(pushed_item) = args.get(1);
1377 // Check that the method being called is push() on a Vec
1378 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::vec_type);
1379 if path.ident.name.as_str() == "push";
1381 return Some((self_expr, pushed_item))
1387 /// Detects for loop pushing the same item into a Vec
1388 fn detect_same_item_push<'tcx>(
1389 cx: &LateContext<'tcx>,
1392 body: &'tcx Expr<'_>,
1395 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1396 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1397 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1403 "it looks like the same item is being pushed into this Vec",
1406 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1407 item_str, vec_str, item_str
1412 if !matches!(pat.kind, PatKind::Wild) {
1416 // Determine whether it is safe to lint the body
1417 let mut same_item_push_visitor = SameItemPushVisitor {
1422 walk_expr(&mut same_item_push_visitor, body);
1423 if same_item_push_visitor.should_lint {
1424 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1425 let vec_ty = cx.typeck_results().expr_ty(vec);
1426 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1431 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1433 // Make sure that the push does not involve possibly mutating values
1434 match pushed_item.kind {
1435 ExprKind::Path(ref qpath) => {
1436 match cx.qpath_res(qpath, pushed_item.hir_id) {
1437 // immutable bindings that are initialized with literal or constant
1438 Res::Local(hir_id) => {
1440 let node = cx.tcx.hir().get(hir_id);
1441 if let Node::Binding(pat) = node;
1442 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1443 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1444 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1445 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1446 if let Some(init) = parent_let_expr.init;
1449 // immutable bindings that are initialized with literal
1450 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1451 // immutable bindings that are initialized with constant
1452 ExprKind::Path(ref path) => {
1453 if let Res::Def(DefKind::Const, ..) = cx.qpath_res(path, init.hir_id) {
1454 emit_lint(cx, vec, pushed_item);
1463 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1467 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1475 /// Checks for looping over a range and then indexing a sequence with it.
1476 /// The iteratee must be a range literal.
1477 #[allow(clippy::too_many_lines)]
1478 fn check_for_loop_range<'tcx>(
1479 cx: &LateContext<'tcx>,
1481 arg: &'tcx Expr<'_>,
1482 body: &'tcx Expr<'_>,
1483 expr: &'tcx Expr<'_>,
1485 if let Some(higher::Range {
1489 }) = higher::range(arg)
1491 // the var must be a single name
1492 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1493 let mut visitor = VarVisitor {
1496 indexed_mut: FxHashSet::default(),
1497 indexed_indirectly: FxHashMap::default(),
1498 indexed_directly: FxHashMap::default(),
1499 referenced: FxHashSet::default(),
1501 prefer_mutable: false,
1503 walk_expr(&mut visitor, body);
1505 // linting condition: we only indexed one variable, and indexed it directly
1506 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1507 let (indexed, (indexed_extent, indexed_ty)) = visitor
1511 .expect("already checked that we have exactly 1 element");
1513 // ensure that the indexed variable was declared before the loop, see #601
1514 if let Some(indexed_extent) = indexed_extent {
1515 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1516 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1517 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1518 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1519 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1524 // don't lint if the container that is indexed does not have .iter() method
1525 let has_iter = has_iter_method(cx, indexed_ty);
1526 if has_iter.is_none() {
1530 // don't lint if the container that is indexed into is also used without
1532 if visitor.referenced.contains(&indexed) {
1536 let starts_at_zero = is_integer_const(cx, start, 0);
1538 let skip = if starts_at_zero {
1540 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
1543 format!(".skip({})", snippet(cx, start.span, ".."))
1546 let mut end_is_start_plus_val = false;
1548 let take = if let Some(end) = *end {
1549 let mut take_expr = end;
1551 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1552 if let BinOpKind::Add = op.node {
1553 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1554 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1556 if start_equal_left {
1558 } else if start_equal_right {
1562 end_is_start_plus_val = start_equal_left | start_equal_right;
1566 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1568 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
1572 ast::RangeLimits::Closed => {
1573 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1574 format!(".take({})", take_expr + sugg::ONE)
1576 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1583 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1584 ("mut ", "iter_mut")
1589 let take_is_empty = take.is_empty();
1590 let mut method_1 = take;
1591 let mut method_2 = skip;
1593 if end_is_start_plus_val {
1594 mem::swap(&mut method_1, &mut method_2);
1597 if visitor.nonindex {
1600 NEEDLESS_RANGE_LOOP,
1602 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1606 "consider using an iterator",
1608 (pat.span, format!("({}, <item>)", ident.name)),
1611 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1618 let repl = if starts_at_zero && take_is_empty {
1619 format!("&{}{}", ref_mut, indexed)
1621 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1626 NEEDLESS_RANGE_LOOP,
1629 "the loop variable `{}` is only used to index `{}`.",
1635 "consider using an iterator",
1636 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1646 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1648 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1649 if len_args.len() == 1;
1650 if method.ident.name == sym!(len);
1651 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1652 if path.segments.len() == 1;
1653 if path.segments[0].ident.name == var;
1662 fn is_end_eq_array_len<'tcx>(
1663 cx: &LateContext<'tcx>,
1665 limits: ast::RangeLimits,
1666 indexed_ty: Ty<'tcx>,
1669 if let ExprKind::Lit(ref lit) = end.kind;
1670 if let ast::LitKind::Int(end_int, _) = lit.node;
1671 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1672 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1674 return match limits {
1675 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1676 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1684 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1685 let mut applicability = Applicability::MachineApplicable;
1686 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1687 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1692 "it is more concise to loop over references to containers instead of using explicit \
1694 "to write this more concisely, try",
1695 format!("&{}{}", muta, object),
1700 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1701 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1702 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1703 // just the receiver, no arguments
1704 if args.len() == 1 {
1705 let method_name = &*method.ident.as_str();
1706 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1707 if method_name == "iter" || method_name == "iter_mut" {
1708 if is_ref_iterable_type(cx, &args[0]) {
1709 lint_iter_method(cx, args, arg, method_name);
1711 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1712 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1713 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1714 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1715 let mut applicability = Applicability::MachineApplicable;
1716 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1719 EXPLICIT_INTO_ITER_LOOP,
1721 "it is more concise to loop over containers instead of using explicit \
1723 "to write this more concisely, try",
1728 let ref_receiver_ty = cx.tcx.mk_ref(
1729 cx.tcx.lifetimes.re_erased,
1732 mutbl: Mutability::Not,
1735 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1736 lint_iter_method(cx, args, arg, method_name)
1739 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1744 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1745 probably not what you want",
1747 next_loop_linted = true;
1751 if !next_loop_linted {
1752 check_arg_type(cx, pat, arg);
1756 /// Checks for `for` loops over `Option`s and `Result`s.
1757 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1758 let ty = cx.typeck_results().expr_ty(arg);
1759 if is_type_diagnostic_item(cx, ty, sym::option_type) {
1762 FOR_LOOPS_OVER_FALLIBLES,
1765 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1766 `if let` statement.",
1767 snippet(cx, arg.span, "_")
1771 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1772 snippet(cx, pat.span, "_"),
1773 snippet(cx, arg.span, "_")
1776 } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
1779 FOR_LOOPS_OVER_FALLIBLES,
1782 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1783 `if let` statement.",
1784 snippet(cx, arg.span, "_")
1788 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1789 snippet(cx, pat.span, "_"),
1790 snippet(cx, arg.span, "_")
1796 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1797 // incremented exactly once in the loop body, and initialized to zero
1798 // at the start of the loop.
1799 fn check_for_loop_explicit_counter<'tcx>(
1800 cx: &LateContext<'tcx>,
1802 arg: &'tcx Expr<'_>,
1803 body: &'tcx Expr<'_>,
1804 expr: &'tcx Expr<'_>,
1806 // Look for variables that are incremented once per loop iteration.
1807 let mut increment_visitor = IncrementVisitor::new(cx);
1808 walk_expr(&mut increment_visitor, body);
1810 // For each candidate, check the parent block to see if
1811 // it's initialized to zero at the start of the loop.
1812 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1813 for id in increment_visitor.into_results() {
1814 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1815 walk_block(&mut initialize_visitor, block);
1818 if let Some((name, initializer)) = initialize_visitor.get_result();
1819 if is_integer_const(cx, initializer, 0);
1821 let mut applicability = Applicability::MachineApplicable;
1823 let for_span = get_span_of_entire_for_loop(expr);
1827 EXPLICIT_COUNTER_LOOP,
1828 for_span.with_hi(arg.span.hi()),
1829 &format!("the variable `{}` is used as a loop counter.", name),
1832 "for ({}, {}) in {}.enumerate()",
1834 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1835 make_iterator_snippet(cx, arg, &mut applicability),
1845 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1846 /// actual `Iterator` that the loop uses.
1847 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1848 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1849 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1854 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1857 // (&x).into_iter() ==> x.iter()
1858 // (&mut x).into_iter() ==> x.iter_mut()
1860 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1861 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1863 let meth_name = match mutability {
1864 Mutability::Mut => "iter_mut",
1865 Mutability::Not => "iter",
1869 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1875 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1881 /// Checks for the `FOR_KV_MAP` lint.
1882 fn check_for_loop_over_map_kv<'tcx>(
1883 cx: &LateContext<'tcx>,
1885 arg: &'tcx Expr<'_>,
1886 body: &'tcx Expr<'_>,
1887 expr: &'tcx Expr<'_>,
1889 let pat_span = pat.span;
1891 if let PatKind::Tuple(ref pat, _) = pat.kind {
1893 let arg_span = arg.span;
1894 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1895 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1896 (key, _) if pat_is_wild(cx, key, body) => (pat[1].span, "value", ty, mutbl),
1897 (_, value) if pat_is_wild(cx, value, body) => (pat[0].span, "key", ty, Mutability::Not),
1902 let mutbl = match mutbl {
1903 Mutability::Not => "",
1904 Mutability::Mut => "_mut",
1906 let arg = match arg.kind {
1907 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1911 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1916 &format!("you seem to want to iterate on a map's {}s", kind),
1918 let map = sugg::Sugg::hir(cx, arg, "map");
1921 "use the corresponding method",
1923 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1924 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1934 fn check_for_single_element_loop<'tcx>(
1935 cx: &LateContext<'tcx>,
1937 arg: &'tcx Expr<'_>,
1938 body: &'tcx Expr<'_>,
1939 expr: &'tcx Expr<'_>,
1942 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg_expr) = arg.kind;
1943 if let PatKind::Binding(.., target, _) = pat.kind;
1944 if let ExprKind::Array([arg_expression]) = arg_expr.kind;
1945 if let ExprKind::Path(ref list_item) = arg_expression.kind;
1946 if let Some(list_item_name) = single_segment_path(list_item).map(|ps| ps.ident.name);
1947 if let ExprKind::Block(ref block, _) = body.kind;
1948 if !block.stmts.is_empty();
1951 let for_span = get_span_of_entire_for_loop(expr);
1952 let mut block_str = snippet(cx, block.span, "..").into_owned();
1953 block_str.remove(0);
1959 SINGLE_ELEMENT_LOOP,
1961 "for loop over a single element",
1963 format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),
1964 Applicability::MachineApplicable
1970 /// Check for unnecessary `if let` usage in a for loop where only the `Some` or `Ok` variant of the
1971 /// iterator element is used.
1972 fn check_manual_flatten<'tcx>(
1973 cx: &LateContext<'tcx>,
1975 arg: &'tcx Expr<'_>,
1976 body: &'tcx Expr<'_>,
1979 if let ExprKind::Block(ref block, _) = body.kind {
1980 // Ensure the `if let` statement is the only expression or statement in the for-loop
1981 let inner_expr = if block.stmts.len() == 1 && block.expr.is_none() {
1982 let match_stmt = &block.stmts[0];
1983 if let StmtKind::Semi(inner_expr) = match_stmt.kind {
1988 } else if block.stmts.is_empty() {
1995 if let Some(inner_expr) = inner_expr;
1996 if let ExprKind::Match(
1997 ref match_expr, ref match_arms, MatchSource::IfLetDesugar{ contains_else_clause: false }
1998 ) = inner_expr.kind;
1999 // Ensure match_expr in `if let` statement is the same as the pat from the for-loop
2000 if let PatKind::Binding(_, pat_hir_id, _, _) = pat.kind;
2001 if path_to_local_id(match_expr, pat_hir_id);
2002 // Ensure the `if let` statement is for the `Some` variant of `Option` or the `Ok` variant of `Result`
2003 if let PatKind::TupleStruct(QPath::Resolved(None, path), _, _) = match_arms[0].pat.kind;
2004 let some_ctor = is_some_ctor(cx, path.res);
2005 let ok_ctor = is_ok_ctor(cx, path.res);
2006 if some_ctor || ok_ctor;
2007 let if_let_type = if some_ctor { "Some" } else { "Ok" };
2010 // Prepare the error message
2011 let msg = format!("unnecessary `if let` since only the `{}` variant of the iterator element is used", if_let_type);
2013 // Prepare the help message
2014 let mut applicability = Applicability::MaybeIncorrect;
2015 let arg_snippet = make_iterator_snippet(cx, arg, &mut applicability);
2023 let sugg = format!("{}.flatten()", arg_snippet);
2024 diag.span_suggestion(
2028 Applicability::MaybeIncorrect,
2032 "...and remove the `if let` statement in the for loop",
2041 struct MutatePairDelegate<'a, 'tcx> {
2042 cx: &'a LateContext<'tcx>,
2043 hir_id_low: Option<HirId>,
2044 hir_id_high: Option<HirId>,
2045 span_low: Option<Span>,
2046 span_high: Option<Span>,
2049 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
2050 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: HirId, _: ConsumeMode) {}
2052 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId, bk: ty::BorrowKind) {
2053 if let ty::BorrowKind::MutBorrow = bk {
2054 if let PlaceBase::Local(id) = cmt.place.base {
2055 if Some(id) == self.hir_id_low {
2056 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
2058 if Some(id) == self.hir_id_high {
2059 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
2065 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId) {
2066 if let PlaceBase::Local(id) = cmt.place.base {
2067 if Some(id) == self.hir_id_low {
2068 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
2070 if Some(id) == self.hir_id_high {
2071 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
2077 impl MutatePairDelegate<'_, '_> {
2078 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
2079 (self.span_low, self.span_high)
2083 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
2084 if let Some(higher::Range {
2088 }) = higher::range(arg)
2090 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
2091 if mut_ids[0].is_some() || mut_ids[1].is_some() {
2092 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
2093 mut_warn_with_span(cx, span_low);
2094 mut_warn_with_span(cx, span_high);
2099 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
2100 if let Some(sp) = span {
2105 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
2110 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
2112 if let Some(hir_id) = path_to_local(bound);
2113 if let Node::Binding(pat) = cx.tcx.hir().get(hir_id);
2114 if let PatKind::Binding(BindingAnnotation::Mutable, ..) = pat.kind;
2116 return Some(hir_id);
2122 fn check_for_mutation<'tcx>(
2123 cx: &LateContext<'tcx>,
2125 bound_ids: &[Option<HirId>],
2126 ) -> (Option<Span>, Option<Span>) {
2127 let mut delegate = MutatePairDelegate {
2129 hir_id_low: bound_ids[0],
2130 hir_id_high: bound_ids[1],
2134 cx.tcx.infer_ctxt().enter(|infcx| {
2135 ExprUseVisitor::new(
2140 cx.typeck_results(),
2144 delegate.mutation_span()
2147 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
2148 fn pat_is_wild<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
2150 PatKind::Wild => true,
2151 PatKind::Binding(_, id, ident, None) if ident.as_str().starts_with('_') => {
2152 !LocalUsedVisitor::new(cx, id).check_expr(body)
2158 struct VarVisitor<'a, 'tcx> {
2159 /// context reference
2160 cx: &'a LateContext<'tcx>,
2161 /// var name to look for as index
2163 /// indexed variables that are used mutably
2164 indexed_mut: FxHashSet<Symbol>,
2165 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2166 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2167 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2168 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2169 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2170 /// Any names that are used outside an index operation.
2171 /// Used to detect things like `&mut vec` used together with `vec[i]`
2172 referenced: FxHashSet<Symbol>,
2173 /// has the loop variable been used in expressions other than the index of
2176 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2177 /// takes `&mut self`
2178 prefer_mutable: bool,
2181 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2182 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2184 // the indexed container is referenced by a name
2185 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2186 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2187 if seqvar.segments.len() == 1;
2189 let index_used_directly = path_to_local_id(idx, self.var);
2190 let indexed_indirectly = {
2191 let mut used_visitor = LocalUsedVisitor::new(self.cx, self.var);
2192 walk_expr(&mut used_visitor, idx);
2196 if indexed_indirectly || index_used_directly {
2197 if self.prefer_mutable {
2198 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2200 let res = self.cx.qpath_res(seqpath, seqexpr.hir_id);
2202 Res::Local(hir_id) => {
2203 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2204 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2205 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2206 if indexed_indirectly {
2207 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2209 if index_used_directly {
2210 self.indexed_directly.insert(
2211 seqvar.segments[0].ident.name,
2212 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2215 return false; // no need to walk further *on the variable*
2217 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2218 if indexed_indirectly {
2219 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2221 if index_used_directly {
2222 self.indexed_directly.insert(
2223 seqvar.segments[0].ident.name,
2224 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2227 return false; // no need to walk further *on the variable*
2238 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2239 type Map = Map<'tcx>;
2241 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2244 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2245 if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX))
2246 || (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2247 if !self.check(&args[1], &args[0], expr);
2253 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2254 if !self.check(idx, seqexpr, expr);
2259 // directly using a variable
2260 if let ExprKind::Path(QPath::Resolved(None, path)) = expr.kind;
2261 if let Res::Local(local_id) = path.res;
2263 if local_id == self.var {
2264 self.nonindex = true;
2266 // not the correct variable, but still a variable
2267 self.referenced.insert(path.segments[0].ident.name);
2272 let old = self.prefer_mutable;
2274 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2275 self.prefer_mutable = true;
2276 self.visit_expr(lhs);
2277 self.prefer_mutable = false;
2278 self.visit_expr(rhs);
2280 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2281 if mutbl == Mutability::Mut {
2282 self.prefer_mutable = true;
2284 self.visit_expr(expr);
2286 ExprKind::Call(ref f, args) => {
2289 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2290 self.prefer_mutable = false;
2291 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2292 if mutbl == Mutability::Mut {
2293 self.prefer_mutable = true;
2296 self.visit_expr(expr);
2299 ExprKind::MethodCall(_, _, args, _) => {
2300 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2301 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2302 self.prefer_mutable = false;
2303 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2304 if mutbl == Mutability::Mut {
2305 self.prefer_mutable = true;
2308 self.visit_expr(expr);
2311 ExprKind::Closure(_, _, body_id, ..) => {
2312 let body = self.cx.tcx.hir().body(body_id);
2313 self.visit_expr(&body.value);
2315 _ => walk_expr(self, expr),
2317 self.prefer_mutable = old;
2319 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2320 NestedVisitorMap::None
2324 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2325 let def_id = match path_to_local(expr) {
2327 None => return false,
2329 if let Some(used_mutably) = mutated_variables(container, cx) {
2330 if used_mutably.contains(&def_id) {
2337 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2338 let def_id = match path_to_local(iter_expr) {
2340 None => return false,
2342 let mut visitor = VarUsedAfterLoopVisitor {
2344 iter_expr_id: iter_expr.hir_id,
2345 past_while_let: false,
2346 var_used_after_while_let: false,
2348 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2349 walk_block(&mut visitor, enclosing_block);
2351 visitor.var_used_after_while_let
2354 struct VarUsedAfterLoopVisitor {
2356 iter_expr_id: HirId,
2357 past_while_let: bool,
2358 var_used_after_while_let: bool,
2361 impl<'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor {
2362 type Map = Map<'tcx>;
2364 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2365 if self.past_while_let {
2366 if path_to_local_id(expr, self.def_id) {
2367 self.var_used_after_while_let = true;
2369 } else if self.iter_expr_id == expr.hir_id {
2370 self.past_while_let = true;
2372 walk_expr(self, expr);
2374 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2375 NestedVisitorMap::None
2379 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2380 /// for `&T` and `&mut T`, such as `Vec`.
2382 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2383 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2384 // will allow further borrows afterwards
2385 let ty = cx.typeck_results().expr_ty(e);
2386 is_iterable_array(ty, cx) ||
2387 is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2388 match_type(cx, ty, &paths::LINKED_LIST) ||
2389 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2390 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2391 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2392 match_type(cx, ty, &paths::BINARY_HEAP) ||
2393 match_type(cx, ty, &paths::BTREEMAP) ||
2394 match_type(cx, ty, &paths::BTREESET)
2397 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2398 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2400 ty::Array(_, n) => n
2401 .try_eval_usize(cx.tcx, cx.param_env)
2402 .map_or(false, |val| (0..=32).contains(&val)),
2407 /// If a block begins with a statement (possibly a `let` binding) and has an
2408 /// expression, return it.
2409 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2410 if block.stmts.is_empty() {
2413 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2414 local.init //.map(|expr| expr)
2420 /// If a block begins with an expression (with or without semicolon), return it.
2421 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2423 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2424 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2425 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2426 StmtKind::Local(..) | StmtKind::Item(..) => None,
2432 /// Returns `true` if expr contains a single break expr without destination label
2434 /// passed expression. The expression may be within a block.
2435 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2437 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2438 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2443 #[derive(Debug, PartialEq)]
2444 enum IncrementVisitorVarState {
2445 Initial, // Not examined yet
2446 IncrOnce, // Incremented exactly once, may be a loop counter
2450 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2451 struct IncrementVisitor<'a, 'tcx> {
2452 cx: &'a LateContext<'tcx>, // context reference
2453 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2454 depth: u32, // depth of conditional expressions
2458 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2459 fn new(cx: &'a LateContext<'tcx>) -> Self {
2462 states: FxHashMap::default(),
2468 fn into_results(self) -> impl Iterator<Item = HirId> {
2469 self.states.into_iter().filter_map(|(id, state)| {
2470 if state == IncrementVisitorVarState::IncrOnce {
2479 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2480 type Map = Map<'tcx>;
2482 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2487 // If node is a variable
2488 if let Some(def_id) = path_to_local(expr) {
2489 if let Some(parent) = get_parent_expr(self.cx, expr) {
2490 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2491 if *state == IncrementVisitorVarState::IncrOnce {
2492 *state = IncrementVisitorVarState::DontWarn;
2497 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2498 if lhs.hir_id == expr.hir_id {
2499 *state = if op.node == BinOpKind::Add
2500 && is_integer_const(self.cx, rhs, 1)
2501 && *state == IncrementVisitorVarState::Initial
2504 IncrementVisitorVarState::IncrOnce
2506 // Assigned some other value or assigned multiple times
2507 IncrementVisitorVarState::DontWarn
2511 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2512 *state = IncrementVisitorVarState::DontWarn
2514 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2515 *state = IncrementVisitorVarState::DontWarn
2521 walk_expr(self, expr);
2522 } else if is_loop(expr) || is_conditional(expr) {
2524 walk_expr(self, expr);
2526 } else if let ExprKind::Continue(_) = expr.kind {
2529 walk_expr(self, expr);
2532 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2533 NestedVisitorMap::None
2537 enum InitializeVisitorState<'hir> {
2538 Initial, // Not examined yet
2539 Declared(Symbol), // Declared but not (yet) initialized
2542 initializer: &'hir Expr<'hir>,
2547 /// Checks whether a variable is initialized at the start of a loop and not modified
2548 /// and used after the loop.
2549 struct InitializeVisitor<'a, 'tcx> {
2550 cx: &'a LateContext<'tcx>, // context reference
2551 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2553 state: InitializeVisitorState<'tcx>,
2554 depth: u32, // depth of conditional expressions
2558 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2559 fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2564 state: InitializeVisitorState::Initial,
2570 fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
2571 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2572 Some((name, initializer))
2579 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2580 type Map = Map<'tcx>;
2582 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2583 // Look for declarations of the variable
2585 if let StmtKind::Local(ref local) = stmt.kind;
2586 if local.pat.hir_id == self.var_id;
2587 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2589 self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
2590 InitializeVisitorState::Initialized {
2597 walk_stmt(self, stmt);
2600 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2601 if matches!(self.state, InitializeVisitorState::DontWarn) {
2604 if expr.hir_id == self.end_expr.hir_id {
2605 self.past_loop = true;
2608 // No need to visit expressions before the variable is
2610 if matches!(self.state, InitializeVisitorState::Initial) {
2614 // If node is the desired variable, see how it's used
2615 if path_to_local_id(expr, self.var_id) {
2617 self.state = InitializeVisitorState::DontWarn;
2621 if let Some(parent) = get_parent_expr(self.cx, expr) {
2623 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2624 self.state = InitializeVisitorState::DontWarn;
2626 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2627 self.state = if_chain! {
2629 if let InitializeVisitorState::Declared(name)
2630 | InitializeVisitorState::Initialized { name, ..} = self.state;
2632 InitializeVisitorState::Initialized { initializer: rhs, name }
2634 InitializeVisitorState::DontWarn
2638 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2639 self.state = InitializeVisitorState::DontWarn
2645 walk_expr(self, expr);
2646 } else if !self.past_loop && is_loop(expr) {
2647 self.state = InitializeVisitorState::DontWarn;
2648 } else if is_conditional(expr) {
2650 walk_expr(self, expr);
2653 walk_expr(self, expr);
2657 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2658 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2662 fn is_loop(expr: &Expr<'_>) -> bool {
2663 matches!(expr.kind, ExprKind::Loop(..))
2666 fn is_conditional(expr: &Expr<'_>) -> bool {
2667 matches!(expr.kind, ExprKind::If(..) | ExprKind::Match(..))
2670 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2672 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2673 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2674 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2676 return is_loop_nested(cx, loop_expr, iter_expr)
2682 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2683 let mut id = loop_expr.hir_id;
2684 let iter_id = if let Some(id) = path_to_local(iter_expr) {
2690 let parent = cx.tcx.hir().get_parent_node(id);
2694 match cx.tcx.hir().find(parent) {
2695 Some(Node::Expr(expr)) => {
2696 if let ExprKind::Loop(..) = expr.kind {
2700 Some(Node::Block(block)) => {
2701 let mut block_visitor = LoopNestVisitor {
2706 walk_block(&mut block_visitor, block);
2707 if block_visitor.nesting == RuledOut {
2711 Some(Node::Stmt(_)) => (),
2720 #[derive(PartialEq, Eq)]
2722 Unknown, // no nesting detected yet
2723 RuledOut, // the iterator is initialized or assigned within scope
2724 LookFurther, // no nesting detected, no further walk required
2727 use self::Nesting::{LookFurther, RuledOut, Unknown};
2729 struct LoopNestVisitor {
2735 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2736 type Map = Map<'tcx>;
2738 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2739 if stmt.hir_id == self.hir_id {
2740 self.nesting = LookFurther;
2741 } else if self.nesting == Unknown {
2742 walk_stmt(self, stmt);
2746 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2747 if self.nesting != Unknown {
2750 if expr.hir_id == self.hir_id {
2751 self.nesting = LookFurther;
2755 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2756 if path_to_local_id(path, self.iterator) {
2757 self.nesting = RuledOut;
2760 _ => walk_expr(self, expr),
2764 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2765 if self.nesting != Unknown {
2768 if let PatKind::Binding(_, id, ..) = pat.kind {
2769 if id == self.iterator {
2770 self.nesting = RuledOut;
2777 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2778 NestedVisitorMap::None
2782 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2783 if constant(cx, cx.typeck_results(), cond).is_some() {
2784 // A pure constant condition (e.g., `while false`) is not linted.
2788 let mut var_visitor = VarCollectorVisitor {
2790 ids: FxHashSet::default(),
2791 def_ids: FxHashMap::default(),
2794 var_visitor.visit_expr(cond);
2795 if var_visitor.skip {
2798 let used_in_condition = &var_visitor.ids;
2799 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2800 used_in_condition.is_disjoint(&used_mutably)
2804 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2806 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2807 has_break_or_return: false,
2809 has_break_or_return_visitor.visit_expr(expr);
2810 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2812 if no_cond_variable_mutated && !mutable_static_in_cond {
2815 WHILE_IMMUTABLE_CONDITION,
2817 "variables in the condition are not mutated in the loop body",
2819 diag.note("this may lead to an infinite or to a never running loop");
2821 if has_break_or_return {
2822 diag.note("this loop contains `return`s or `break`s");
2823 diag.help("rewrite it as `if cond { loop { } }`");
2830 struct HasBreakOrReturnVisitor {
2831 has_break_or_return: bool,
2834 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2835 type Map = Map<'tcx>;
2837 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2838 if self.has_break_or_return {
2843 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2844 self.has_break_or_return = true;
2850 walk_expr(self, expr);
2853 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2854 NestedVisitorMap::None
2858 /// Collects the set of variables in an expression
2859 /// Stops analysis if a function call is found
2860 /// Note: In some cases such as `self`, there are no mutable annotation,
2861 /// All variables definition IDs are collected
2862 struct VarCollectorVisitor<'a, 'tcx> {
2863 cx: &'a LateContext<'tcx>,
2864 ids: FxHashSet<HirId>,
2865 def_ids: FxHashMap<def_id::DefId, bool>,
2869 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2870 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2872 if let ExprKind::Path(ref qpath) = ex.kind;
2873 if let QPath::Resolved(None, _) = *qpath;
2874 let res = self.cx.qpath_res(qpath, ex.hir_id);
2877 Res::Local(hir_id) => {
2878 self.ids.insert(hir_id);
2880 Res::Def(DefKind::Static, def_id) => {
2881 let mutable = self.cx.tcx.is_mutable_static(def_id);
2882 self.def_ids.insert(def_id, mutable);
2891 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2892 type Map = Map<'tcx>;
2894 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2896 ExprKind::Path(_) => self.insert_def_id(ex),
2897 // If there is any function/method call… we just stop analysis
2898 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2900 _ => walk_expr(self, ex),
2904 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2905 NestedVisitorMap::None
2909 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2911 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2912 check_needless_collect_direct_usage(expr, cx);
2913 check_needless_collect_indirect_usage(expr, cx);
2915 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2917 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2918 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2919 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2920 if let Some(ref generic_args) = chain_method.args;
2921 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2923 let ty = cx.typeck_results().node_type(ty.hir_id);
2924 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2925 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2926 match_type(cx, ty, &paths::BTREEMAP) ||
2927 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2928 if method.ident.name == sym!(len) {
2929 let span = shorten_needless_collect_span(expr);
2934 NEEDLESS_COLLECT_MSG,
2936 "count()".to_string(),
2937 Applicability::MachineApplicable,
2940 if method.ident.name == sym!(is_empty) {
2941 let span = shorten_needless_collect_span(expr);
2946 NEEDLESS_COLLECT_MSG,
2948 "next().is_none()".to_string(),
2949 Applicability::MachineApplicable,
2952 if method.ident.name == sym!(contains) {
2953 let contains_arg = snippet(cx, args[1].span, "??");
2954 let span = shorten_needless_collect_span(expr);
2959 NEEDLESS_COLLECT_MSG,
2961 let (arg, pred) = contains_arg
2963 .map_or(("&x", &*contains_arg), |s| ("x", s));
2964 diag.span_suggestion(
2968 "any(|{}| x == {})",
2971 Applicability::MachineApplicable,
2981 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2982 if let ExprKind::Block(ref block, _) = expr.kind {
2983 for ref stmt in block.stmts {
2985 if let StmtKind::Local(
2986 Local { pat: Pat { hir_id: pat_id, kind: PatKind::Binding(_, _, ident, .. ), .. },
2987 init: Some(ref init_expr), .. }
2989 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2990 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2991 if let Some(ref generic_args) = method_name.args;
2992 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2993 if let ty = cx.typeck_results().node_type(ty.hir_id);
2994 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2995 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2996 match_type(cx, ty, &paths::LINKED_LIST);
2997 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2998 if iter_calls.len() == 1;
3000 let mut used_count_visitor = UsedCountVisitor {
3005 walk_block(&mut used_count_visitor, block);
3006 if used_count_visitor.count > 1 {
3010 // Suggest replacing iter_call with iter_replacement, and removing stmt
3011 let iter_call = &iter_calls[0];
3015 stmt.span.until(iter_call.span),
3016 NEEDLESS_COLLECT_MSG,
3018 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
3019 diag.multipart_suggestion(
3020 iter_call.get_suggestion_text(),
3022 (stmt.span, String::new()),
3023 (iter_call.span, iter_replacement)
3025 Applicability::MachineApplicable,// MaybeIncorrect,
3035 struct IterFunction {
3036 func: IterFunctionKind,
3040 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
3042 IterFunctionKind::IntoIter => String::new(),
3043 IterFunctionKind::Len => String::from(".count()"),
3044 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
3045 IterFunctionKind::Contains(span) => {
3046 let s = snippet(cx, *span, "..");
3047 if let Some(stripped) = s.strip_prefix('&') {
3048 format!(".any(|x| x == {})", stripped)
3050 format!(".any(|x| x == *{})", s)
3055 fn get_suggestion_text(&self) -> &'static str {
3057 IterFunctionKind::IntoIter => {
3058 "Use the original Iterator instead of collecting it and then producing a new one"
3060 IterFunctionKind::Len => {
3061 "Take the original Iterator's count instead of collecting it and finding the length"
3063 IterFunctionKind::IsEmpty => {
3064 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
3066 IterFunctionKind::Contains(_) => {
3067 "Check if the original Iterator contains an element instead of collecting then checking"
3072 enum IterFunctionKind {
3079 struct IterFunctionVisitor {
3080 uses: Vec<IterFunction>,
3084 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
3085 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
3086 // Check function calls on our collection
3088 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
3089 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
3090 if let &[name] = &path.segments;
3091 if name.ident == self.target;
3093 let len = sym!(len);
3094 let is_empty = sym!(is_empty);
3095 let contains = sym!(contains);
3096 match method_name.ident.name {
3097 sym::into_iter => self.uses.push(
3098 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
3100 name if name == len => self.uses.push(
3101 IterFunction { func: IterFunctionKind::Len, span: expr.span }
3103 name if name == is_empty => self.uses.push(
3104 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
3106 name if name == contains => self.uses.push(
3107 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
3109 _ => self.seen_other = true,
3114 // Check if the collection is used for anything else
3116 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
3117 if let &[name] = &path.segments;
3118 if name.ident == self.target;
3120 self.seen_other = true;
3122 walk_expr(self, expr);
3127 type Map = Map<'tcx>;
3128 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3129 NestedVisitorMap::None
3133 struct UsedCountVisitor<'a, 'tcx> {
3134 cx: &'a LateContext<'tcx>,
3139 impl<'a, 'tcx> Visitor<'tcx> for UsedCountVisitor<'a, 'tcx> {
3140 type Map = Map<'tcx>;
3142 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
3143 if path_to_local_id(expr, self.id) {
3146 walk_expr(self, expr);
3150 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3151 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
3155 /// Detect the occurrences of calls to `iter` or `into_iter` for the
3156 /// given identifier
3157 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
3158 let mut visitor = IterFunctionVisitor {
3163 visitor.visit_block(block);
3164 if visitor.seen_other {
3171 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3173 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3174 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3176 return expr.span.with_lo(span.lo());