1 use crate::consts::constant;
2 use crate::utils::paths;
3 use crate::utils::sugg::Sugg;
4 use crate::utils::usage::{is_unused, mutated_variables};
6 contains_name, get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
7 indent_of, is_integer_const, is_no_std_crate, is_refutable, is_type_diagnostic_item, last_path_segment,
8 match_trait_method, match_type, match_var, multispan_sugg, qpath_res, single_segment_path, snippet,
9 snippet_with_applicability, snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_sugg,
10 span_lint_and_then, sugg, SpanlessEq,
12 use if_chain::if_chain;
14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
15 use rustc_errors::Applicability;
16 use rustc_hir::def::{DefKind, Res};
17 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
19 def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, InlineAsmOperand,
20 Local, LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
22 use rustc_infer::infer::TyCtxtInferExt;
23 use rustc_lint::{LateContext, LateLintPass, LintContext};
24 use rustc_middle::hir::map::Map;
25 use rustc_middle::lint::in_external_macro;
26 use rustc_middle::middle::region;
27 use rustc_middle::ty::{self, Ty, TyS};
28 use rustc_session::{declare_lint_pass, declare_tool_lint};
29 use rustc_span::source_map::Span;
30 use rustc_span::symbol::{sym, Ident, Symbol};
31 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
32 use std::iter::{once, Iterator};
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// # let src = vec![1];
46 /// # let mut dst = vec![0; 65];
47 /// for i in 0..src.len() {
48 /// dst[i + 64] = src[i];
51 /// Could be written as:
53 /// # let src = vec![1];
54 /// # let mut dst = vec![0; 65];
55 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
59 "manually copying items between slices"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for looping over the range of `0..len` of some
64 /// collection just to get the values by index.
66 /// **Why is this bad?** Just iterating the collection itself makes the intent
67 /// more clear and is probably faster.
69 /// **Known problems:** None.
73 /// let vec = vec!['a', 'b', 'c'];
74 /// for i in 0..vec.len() {
75 /// println!("{}", vec[i]);
78 /// Could be written as:
80 /// let vec = vec!['a', 'b', 'c'];
82 /// println!("{}", i);
85 pub NEEDLESS_RANGE_LOOP,
87 "for-looping over a range of indices where an iterator over items would do"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
92 /// suggests the latter.
94 /// **Why is this bad?** Readability.
96 /// **Known problems:** False negatives. We currently only warn on some known
101 /// // with `y` a `Vec` or slice:
102 /// # let y = vec![1];
103 /// for x in y.iter() {
107 /// can be rewritten to
109 /// # let y = vec![1];
114 pub EXPLICIT_ITER_LOOP,
116 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
121 /// suggests the latter.
123 /// **Why is this bad?** Readability.
125 /// **Known problems:** None
129 /// # let y = vec![1];
130 /// // with `y` a `Vec` or slice:
131 /// for x in y.into_iter() {
135 /// can be rewritten to
137 /// # let y = vec![1];
142 pub EXPLICIT_INTO_ITER_LOOP,
144 "for-looping over `_.into_iter()` when `_` would do"
147 declare_clippy_lint! {
148 /// **What it does:** Checks for loops on `x.next()`.
150 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
151 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
152 /// implements `IntoIterator`, so that possibly one value will be iterated,
153 /// leading to some hard to find bugs. No one will want to write such code
154 /// [except to win an Underhanded Rust
155 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
157 /// **Known problems:** None.
161 /// for x in y.next() {
167 "for-looping over `_.next()` which is probably not intended"
170 declare_clippy_lint! {
171 /// **What it does:** Checks for `for` loops over `Option` or `Result` values.
173 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
176 /// **Known problems:** None.
180 /// # let opt = Some(1);
188 /// if let Some(x) = opt {
196 /// # let res: Result<i32, std::io::Error> = Ok(1);
204 /// if let Ok(x) = res {
208 pub FOR_LOOPS_OVER_FALLIBLES,
210 "for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
213 declare_clippy_lint! {
214 /// **What it does:** Detects `loop + match` combinations that are easier
215 /// written as a `while let` loop.
217 /// **Why is this bad?** The `while let` loop is usually shorter and more
220 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
224 /// # let y = Some(1);
226 /// let x = match y {
230 /// // .. do something with x
232 /// // is easier written as
233 /// while let Some(x) = y {
234 /// // .. do something with x
239 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
242 declare_clippy_lint! {
243 /// **What it does:** Checks for functions collecting an iterator when collect
246 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
247 /// when this allocation may not be needed.
249 /// **Known problems:**
254 /// # let iterator = vec![1].into_iter();
255 /// let len = iterator.clone().collect::<Vec<_>>().len();
257 /// let len = iterator.count();
259 pub NEEDLESS_COLLECT,
261 "collecting an iterator when collect is not needed"
264 declare_clippy_lint! {
265 /// **What it does:** Checks `for` loops over slices with an explicit counter
266 /// and suggests the use of `.enumerate()`.
268 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
269 /// declutters the code and may be faster in some instances.
271 /// **Known problems:** None.
275 /// # let v = vec![1];
276 /// # fn bar(bar: usize, baz: usize) {}
283 /// Could be written as
285 /// # let v = vec![1];
286 /// # fn bar(bar: usize, baz: usize) {}
287 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
289 pub EXPLICIT_COUNTER_LOOP,
291 "for-looping with an explicit counter when `_.enumerate()` would do"
294 declare_clippy_lint! {
295 /// **What it does:** Checks for empty `loop` expressions.
297 /// **Why is this bad?** 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_lint_pass!(Loops => [
500 EXPLICIT_INTO_ITER_LOOP,
502 FOR_LOOPS_OVER_FALLIBLES,
505 EXPLICIT_COUNTER_LOOP,
507 WHILE_LET_ON_ITERATOR,
511 WHILE_IMMUTABLE_CONDITION,
516 impl<'tcx> LateLintPass<'tcx> for Loops {
517 #[allow(clippy::too_many_lines)]
518 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
519 if let Some((pat, arg, body)) = higher::for_loop(expr) {
520 // we don't want to check expanded macros
521 // this check is not at the top of the function
522 // since higher::for_loop expressions are marked as expansions
523 if body.span.from_expansion() {
526 check_for_loop(cx, pat, arg, body, expr);
529 // we don't want to check expanded macros
530 if expr.span.from_expansion() {
534 // check for never_loop
535 if let ExprKind::Loop(ref block, _, _) = expr.kind {
536 match never_loop_block(block, expr.hir_id) {
537 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
538 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
542 // check for `loop { if let {} else break }` that could be `while let`
543 // (also matches an explicit "match" instead of "if let")
544 // (even if the "match" or "if let" is used for declaration)
545 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
546 // also check for empty `loop {}` statements
547 // TODO(issue #6161): Enable for no_std crates (outside of #[panic_handler])
548 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) {
553 "empty `loop {}` wastes CPU cycles",
555 "You should either use `panic!()` or add `std::thread::sleep(..);` to the loop body.",
559 // extract the expression from the first statement (if any) in a block
560 let inner_stmt_expr = extract_expr_from_first_stmt(block);
561 // or extract the first expression (if any) from the block
562 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
563 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
564 // ensure "if let" compatible match structure
566 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
568 && arms[0].guard.is_none()
569 && arms[1].guard.is_none()
570 && is_simple_break_expr(&arms[1].body)
572 if in_external_macro(cx.sess(), expr.span) {
576 // NOTE: we used to build a body here instead of using
577 // ellipsis, this was removed because:
578 // 1) it was ugly with big bodies;
579 // 2) it was not indented properly;
580 // 3) it wasn’t very smart (see #675).
581 let mut applicability = Applicability::HasPlaceholders;
586 "this loop could be written as a `while let` loop",
589 "while let {} = {} {{ .. }}",
590 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
591 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
602 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
603 let pat = &arms[0].pat.kind;
605 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
606 &ExprKind::MethodCall(ref method_path, _, ref method_args, _),
607 ) = (pat, &match_expr.kind)
609 let iter_expr = &method_args[0];
611 // Don't lint when the iterator is recreated on every iteration
613 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
614 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
615 if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
621 let lhs_constructor = last_path_segment(qpath);
622 if method_path.ident.name == sym::next
623 && match_trait_method(cx, match_expr, &paths::ITERATOR)
624 && lhs_constructor.ident.name == sym::Some
625 && (pat_args.is_empty()
626 || !is_refutable(cx, &pat_args[0])
627 && !is_used_inside(cx, iter_expr, &arms[0].body)
628 && !is_iterator_used_after_while_let(cx, iter_expr)
629 && !is_nested(cx, expr, &method_args[0]))
631 let mut applicability = Applicability::MachineApplicable;
632 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
633 let loop_var = if pat_args.is_empty() {
636 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
640 WHILE_LET_ON_ITERATOR,
641 expr.span.with_hi(match_expr.span.hi()),
642 "this loop could be written as a `for` loop",
644 format!("for {} in {}", loop_var, iterator),
651 if let Some((cond, body)) = higher::while_loop(&expr) {
652 check_infinite_loop(cx, cond, body);
655 check_needless_collect(expr, cx);
659 enum NeverLoopResult {
660 // A break/return always get triggered but not necessarily for the main loop.
662 // A continue may occur for the main loop.
668 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
670 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
671 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
675 // Combine two results for parts that are called in order.
677 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
679 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
680 NeverLoopResult::Otherwise => second,
684 // Combine two results where both parts are called but not necessarily in order.
686 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
687 match (left, right) {
688 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
689 NeverLoopResult::MayContinueMainLoop
691 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
692 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
696 // Combine two results where only one of the part may have been executed.
698 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
700 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
701 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
702 NeverLoopResult::MayContinueMainLoop
704 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
708 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
709 let stmts = block.stmts.iter().map(stmt_to_expr);
710 let expr = once(block.expr.as_deref());
711 let mut iter = stmts.chain(expr).filter_map(|e| e);
712 never_loop_expr_seq(&mut iter, main_loop_id)
715 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
717 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
718 StmtKind::Local(ref local) => local.init.as_deref(),
723 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
726 | ExprKind::Unary(_, ref e)
727 | ExprKind::Cast(ref e, _)
728 | ExprKind::Type(ref e, _)
729 | ExprKind::Field(ref e, _)
730 | ExprKind::AddrOf(_, _, ref e)
731 | ExprKind::Struct(_, _, Some(ref e))
732 | ExprKind::Repeat(ref e, _)
733 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
734 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
735 never_loop_expr_all(&mut es.iter(), main_loop_id)
737 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
738 ExprKind::Binary(_, ref e1, ref e2)
739 | ExprKind::Assign(ref e1, ref e2, _)
740 | ExprKind::AssignOp(_, ref e1, ref e2)
741 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
742 ExprKind::Loop(ref b, _, _) => {
743 // Break can come from the inner loop so remove them.
744 absorb_break(&never_loop_block(b, main_loop_id))
746 ExprKind::Match(ref e, ref arms, _) => {
747 let e = never_loop_expr(e, main_loop_id);
751 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
755 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
756 ExprKind::Continue(d) => {
759 .expect("target ID can only be missing in the presence of compilation errors");
760 if id == main_loop_id {
761 NeverLoopResult::MayContinueMainLoop
763 NeverLoopResult::AlwaysBreak
766 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
767 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
769 ExprKind::InlineAsm(ref asm) => asm
773 InlineAsmOperand::In { expr, .. }
774 | InlineAsmOperand::InOut { expr, .. }
775 | InlineAsmOperand::Const { expr }
776 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
777 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
778 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
779 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
782 .fold(NeverLoopResult::Otherwise, combine_both),
783 ExprKind::Struct(_, _, None)
784 | ExprKind::Yield(_, _)
785 | ExprKind::Closure(_, _, _, _, _)
786 | ExprKind::LlvmInlineAsm(_)
788 | ExprKind::ConstBlock(_)
790 | ExprKind::Err => NeverLoopResult::Otherwise,
794 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
795 es.map(|e| never_loop_expr(e, main_loop_id))
796 .fold(NeverLoopResult::Otherwise, combine_seq)
799 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
800 es.map(|e| never_loop_expr(e, main_loop_id))
801 .fold(NeverLoopResult::Otherwise, combine_both)
804 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
805 e.map(|e| never_loop_expr(e, main_loop_id))
806 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
809 fn check_for_loop<'tcx>(
810 cx: &LateContext<'tcx>,
813 body: &'tcx Expr<'_>,
814 expr: &'tcx Expr<'_>,
816 let is_manual_memcpy_triggered = detect_manual_memcpy(cx, pat, arg, body, expr);
817 if !is_manual_memcpy_triggered {
818 check_for_loop_range(cx, pat, arg, body, expr);
819 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
821 check_for_loop_arg(cx, pat, arg, expr);
822 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
823 check_for_mut_range_bound(cx, arg, body);
824 check_for_single_element_loop(cx, pat, arg, body, expr);
825 detect_same_item_push(cx, pat, arg, body, expr);
828 // this function assumes the given expression is a `for` loop.
829 fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
830 // for some reason this is the only way to get the `Span`
831 // of the entire `for` loop
832 if let ExprKind::Match(_, arms, _) = &expr.kind {
839 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
841 if let ExprKind::Path(qpath) = &expr.kind;
842 if let QPath::Resolved(None, path) = qpath;
843 if path.segments.len() == 1;
844 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
854 /// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
855 /// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
856 /// it exists for the convenience of the overloaded operators while normal functions can do the
859 struct MinifyingSugg<'a>(Sugg<'a>);
861 impl<'a> MinifyingSugg<'a> {
862 fn as_str(&self) -> &str {
863 let Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) = &self.0;
867 fn into_sugg(self) -> Sugg<'a> {
872 impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
873 fn from(sugg: Sugg<'a>) -> Self {
878 impl std::ops::Add for &MinifyingSugg<'static> {
879 type Output = MinifyingSugg<'static>;
880 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
881 match (self.as_str(), rhs.as_str()) {
882 ("0", _) => rhs.clone(),
883 (_, "0") => self.clone(),
884 (_, _) => (&self.0 + &rhs.0).into(),
889 impl std::ops::Sub for &MinifyingSugg<'static> {
890 type Output = MinifyingSugg<'static>;
891 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
892 match (self.as_str(), rhs.as_str()) {
893 (_, "0") => self.clone(),
894 ("0", _) => (-rhs.0.clone()).into(),
895 (x, y) if x == y => sugg::ZERO.into(),
896 (_, _) => (&self.0 - &rhs.0).into(),
901 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
902 type Output = MinifyingSugg<'static>;
903 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
904 match (self.as_str(), rhs.as_str()) {
905 ("0", _) => rhs.clone(),
907 (_, _) => (self.0 + &rhs.0).into(),
912 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
913 type Output = MinifyingSugg<'static>;
914 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
915 match (self.as_str(), rhs.as_str()) {
917 ("0", _) => (-rhs.0.clone()).into(),
918 (x, y) if x == y => sugg::ZERO.into(),
919 (_, _) => (self.0 - &rhs.0).into(),
924 /// a wrapper around `MinifyingSugg`, which carries a operator like currying
925 /// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
927 value: MinifyingSugg<'static>,
931 #[derive(Clone, Copy)]
938 fn negative(value: Sugg<'static>) -> Self {
941 sign: OffsetSign::Negative,
945 fn positive(value: Sugg<'static>) -> Self {
948 sign: OffsetSign::Positive,
953 Self::positive(sugg::ZERO)
957 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
959 OffsetSign::Positive => lhs + &rhs.value,
960 OffsetSign::Negative => lhs - &rhs.value,
964 #[derive(Debug, Clone, Copy)]
965 enum StartKind<'hir> {
967 Counter { initializer: &'hir Expr<'hir> },
970 struct IndexExpr<'hir> {
971 base: &'hir Expr<'hir>,
972 idx: StartKind<'hir>,
978 kind: StartKind<'hir>,
981 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
982 let is_slice = match ty.kind() {
983 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
984 ty::Slice(..) | ty::Array(..) => true,
988 is_slice || is_type_diagnostic_item(cx, ty, sym::vec_type) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
991 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
993 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
994 if method.ident.name == sym::clone;
996 if let Some(arg) = args.get(0);
997 then { arg } else { expr }
1001 fn get_details_from_idx<'tcx>(
1002 cx: &LateContext<'tcx>,
1004 starts: &[Start<'tcx>],
1005 ) -> Option<(StartKind<'tcx>, Offset)> {
1006 fn get_start<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
1007 starts.iter().find_map(|start| {
1008 if same_var(cx, e, start.id) {
1016 fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
1018 ExprKind::Lit(l) => match l.node {
1019 ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
1022 ExprKind::Path(..) if get_start(cx, e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
1028 ExprKind::Binary(op, lhs, rhs) => match op.node {
1030 let offset_opt = get_start(cx, lhs, starts)
1031 .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
1032 .or_else(|| get_start(cx, rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
1034 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
1037 get_start(cx, lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
1041 ExprKind::Path(..) => get_start(cx, idx, starts).map(|s| (s, Offset::empty())),
1046 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1047 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1054 /// Get assignments from the given block.
1055 /// The returned iterator yields `None` if no assignment expressions are there,
1056 /// filtering out the increments of the given whitelisted loop counters;
1057 /// because its job is to make sure there's nothing other than assignments and the increments.
1058 fn get_assignments<'a: 'c, 'tcx: 'c, 'c>(
1059 cx: &'a LateContext<'tcx>,
1060 Block { stmts, expr, .. }: &'tcx Block<'tcx>,
1061 loop_counters: &'c [Start<'tcx>],
1062 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'c {
1063 // As the `filter` and `map` below do different things, I think putting together
1064 // just increases complexity. (cc #3188 and #4193)
1065 #[allow(clippy::filter_map)]
1068 .filter_map(move |stmt| match stmt.kind {
1069 StmtKind::Local(..) | StmtKind::Item(..) => None,
1070 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
1072 .chain((*expr).into_iter())
1074 if let ExprKind::AssignOp(_, place, _) = e.kind {
1077 // skip the first item which should be `StartKind::Range`
1078 // this makes it possible to use the slice with `StartKind::Range` in the same iterator loop.
1080 .any(|counter| same_var(cx, place, counter.id))
1085 .map(get_assignment)
1088 fn get_loop_counters<'a, 'tcx>(
1089 cx: &'a LateContext<'tcx>,
1090 body: &'tcx Block<'tcx>,
1091 expr: &'tcx Expr<'_>,
1092 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1093 // Look for variables that are incremented once per loop iteration.
1094 let mut increment_visitor = IncrementVisitor::new(cx);
1095 walk_block(&mut increment_visitor, body);
1097 // For each candidate, check the parent block to see if
1098 // it's initialized to zero at the start of the loop.
1099 get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
1102 .filter_map(move |var_id| {
1103 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1104 walk_block(&mut initialize_visitor, block);
1106 initialize_visitor.get_result().map(|(_, initializer)| Start {
1108 kind: StartKind::Counter { initializer },
1115 fn build_manual_memcpy_suggestion<'tcx>(
1116 cx: &LateContext<'tcx>,
1119 limits: ast::RangeLimits,
1120 dst: &IndexExpr<'_>,
1121 src: &IndexExpr<'_>,
1123 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1124 if offset.as_str() == "0" {
1131 let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
1133 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1134 if method.ident.name == sym!(len);
1135 if len_args.len() == 1;
1136 if let Some(arg) = len_args.get(0);
1137 if var_def_id(cx, arg) == var_def_id(cx, base);
1139 if sugg.as_str() == end_str {
1146 ast::RangeLimits::Closed => {
1147 sugg + &sugg::ONE.into()
1149 ast::RangeLimits::HalfOpen => sugg,
1155 let start_str = Sugg::hir(cx, start, "").into();
1156 let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
1158 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1159 StartKind::Range => (
1160 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
1165 apply_offset(&end_str, &idx_expr.idx_offset),
1169 StartKind::Counter { initializer } => {
1170 let counter_start = Sugg::hir(cx, initializer, "").into();
1172 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
1177 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1184 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1185 let (src_offset, src_limit) = print_offset_and_limit(&src);
1187 let dst_base_str = snippet(cx, dst.base.span, "???");
1188 let src_base_str = snippet(cx, src.base.span, "???");
1190 let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
1196 dst_offset.maybe_par(),
1197 dst_limit.maybe_par()
1203 "{}.clone_from_slice(&{}[{}..{}]);",
1206 src_offset.maybe_par(),
1207 src_limit.maybe_par()
1211 /// Checks for for loops that sequentially copy items from one slice-like
1212 /// object to another.
1213 fn detect_manual_memcpy<'tcx>(
1214 cx: &LateContext<'tcx>,
1216 arg: &'tcx Expr<'_>,
1217 body: &'tcx Expr<'_>,
1218 expr: &'tcx Expr<'_>,
1220 if let Some(higher::Range {
1224 }) = higher::range(arg)
1226 // the var must be a single name
1227 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1228 let mut starts = vec![Start {
1230 kind: StartKind::Range,
1233 // This is one of few ways to return different iterators
1234 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1235 let mut iter_a = None;
1236 let mut iter_b = None;
1238 if let ExprKind::Block(block, _) = body.kind {
1239 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1240 starts.extend(loop_counters);
1242 iter_a = Some(get_assignments(cx, block, &starts));
1244 iter_b = Some(get_assignment(body));
1247 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1249 let big_sugg = assignments
1250 // The only statements in the for loops can be indexed assignments from
1251 // indexed retrievals (except increments of loop counters).
1253 o.and_then(|(lhs, rhs)| {
1254 let rhs = fetch_cloned_expr(rhs);
1256 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1257 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1258 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1259 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1260 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1261 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1263 // Source and destination must be different
1264 if var_def_id(cx, base_left) != var_def_id(cx, base_right);
1266 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1267 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1274 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1275 .collect::<Option<Vec<_>>>()
1276 .filter(|v| !v.is_empty())
1277 .map(|v| v.join("\n "));
1279 if let Some(big_sugg) = big_sugg {
1283 get_span_of_entire_for_loop(expr),
1284 "it looks like you're manually copying between slices",
1285 "try replacing the loop by",
1287 Applicability::Unspecified,
1296 // Scans the body of the for loop and determines whether lint should be given
1297 struct SameItemPushVisitor<'a, 'tcx> {
1299 // this field holds the last vec push operation visited, which should be the only push seen
1300 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1301 cx: &'a LateContext<'tcx>,
1304 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1305 type Map = Map<'tcx>;
1307 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1309 // Non-determinism may occur ... don't give a lint
1310 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1311 ExprKind::Block(block, _) => self.visit_block(block),
1316 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1317 for stmt in b.stmts.iter() {
1318 self.visit_stmt(stmt);
1322 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1323 let vec_push_option = get_vec_push(self.cx, s);
1324 if vec_push_option.is_none() {
1325 // Current statement is not a push so visit inside
1327 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1331 // Current statement is a push ...check whether another
1332 // push had been previously done
1333 if self.vec_push.is_none() {
1334 self.vec_push = vec_push_option;
1336 // There are multiple pushes ... don't lint
1337 self.should_lint = false;
1342 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1343 NestedVisitorMap::None
1347 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1348 // the Vec being pushed into and the item being pushed
1349 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1351 // Extract method being called
1352 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1353 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1354 // Figure out the parameters for the method call
1355 if let Some(self_expr) = args.get(0);
1356 if let Some(pushed_item) = args.get(1);
1357 // Check that the method being called is push() on a Vec
1358 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::vec_type);
1359 if path.ident.name.as_str() == "push";
1361 return Some((self_expr, pushed_item))
1367 /// Detects for loop pushing the same item into a Vec
1368 fn detect_same_item_push<'tcx>(
1369 cx: &LateContext<'tcx>,
1372 body: &'tcx Expr<'_>,
1375 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1376 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1377 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1383 "it looks like the same item is being pushed into this Vec",
1386 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1387 item_str, vec_str, item_str
1392 if !matches!(pat.kind, PatKind::Wild) {
1396 // Determine whether it is safe to lint the body
1397 let mut same_item_push_visitor = SameItemPushVisitor {
1402 walk_expr(&mut same_item_push_visitor, body);
1403 if same_item_push_visitor.should_lint {
1404 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1405 let vec_ty = cx.typeck_results().expr_ty(vec);
1406 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1411 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1413 // Make sure that the push does not involve possibly mutating values
1414 match pushed_item.kind {
1415 ExprKind::Path(ref qpath) => {
1416 match qpath_res(cx, qpath, pushed_item.hir_id) {
1417 // immutable bindings that are initialized with literal or constant
1418 Res::Local(hir_id) => {
1420 let node = cx.tcx.hir().get(hir_id);
1421 if let Node::Binding(pat) = node;
1422 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1423 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1424 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1425 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1426 if let Some(init) = parent_let_expr.init;
1429 // immutable bindings that are initialized with literal
1430 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1431 // immutable bindings that are initialized with constant
1432 ExprKind::Path(ref path) => {
1433 if let Res::Def(DefKind::Const, ..) = qpath_res(cx, path, init.hir_id) {
1434 emit_lint(cx, vec, pushed_item);
1443 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1447 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1455 /// Checks for looping over a range and then indexing a sequence with it.
1456 /// The iteratee must be a range literal.
1457 #[allow(clippy::too_many_lines)]
1458 fn check_for_loop_range<'tcx>(
1459 cx: &LateContext<'tcx>,
1461 arg: &'tcx Expr<'_>,
1462 body: &'tcx Expr<'_>,
1463 expr: &'tcx Expr<'_>,
1465 if let Some(higher::Range {
1469 }) = higher::range(arg)
1471 // the var must be a single name
1472 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1473 let mut visitor = VarVisitor {
1476 indexed_mut: FxHashSet::default(),
1477 indexed_indirectly: FxHashMap::default(),
1478 indexed_directly: FxHashMap::default(),
1479 referenced: FxHashSet::default(),
1481 prefer_mutable: false,
1483 walk_expr(&mut visitor, body);
1485 // linting condition: we only indexed one variable, and indexed it directly
1486 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1487 let (indexed, (indexed_extent, indexed_ty)) = visitor
1491 .expect("already checked that we have exactly 1 element");
1493 // ensure that the indexed variable was declared before the loop, see #601
1494 if let Some(indexed_extent) = indexed_extent {
1495 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1496 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1497 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1498 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1499 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1504 // don't lint if the container that is indexed does not have .iter() method
1505 let has_iter = has_iter_method(cx, indexed_ty);
1506 if has_iter.is_none() {
1510 // don't lint if the container that is indexed into is also used without
1512 if visitor.referenced.contains(&indexed) {
1516 let starts_at_zero = is_integer_const(cx, start, 0);
1518 let skip = if starts_at_zero {
1520 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
1523 format!(".skip({})", snippet(cx, start.span, ".."))
1526 let mut end_is_start_plus_val = false;
1528 let take = if let Some(end) = *end {
1529 let mut take_expr = end;
1531 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1532 if let BinOpKind::Add = op.node {
1533 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1534 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1536 if start_equal_left {
1538 } else if start_equal_right {
1542 end_is_start_plus_val = start_equal_left | start_equal_right;
1546 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1548 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
1552 ast::RangeLimits::Closed => {
1553 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1554 format!(".take({})", take_expr + sugg::ONE)
1556 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1563 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1564 ("mut ", "iter_mut")
1569 let take_is_empty = take.is_empty();
1570 let mut method_1 = take;
1571 let mut method_2 = skip;
1573 if end_is_start_plus_val {
1574 mem::swap(&mut method_1, &mut method_2);
1577 if visitor.nonindex {
1580 NEEDLESS_RANGE_LOOP,
1582 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1586 "consider using an iterator",
1588 (pat.span, format!("({}, <item>)", ident.name)),
1591 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1598 let repl = if starts_at_zero && take_is_empty {
1599 format!("&{}{}", ref_mut, indexed)
1601 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1606 NEEDLESS_RANGE_LOOP,
1609 "the loop variable `{}` is only used to index `{}`.",
1615 "consider using an iterator",
1616 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1626 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1628 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1629 if len_args.len() == 1;
1630 if method.ident.name == sym!(len);
1631 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1632 if path.segments.len() == 1;
1633 if path.segments[0].ident.name == var;
1642 fn is_end_eq_array_len<'tcx>(
1643 cx: &LateContext<'tcx>,
1645 limits: ast::RangeLimits,
1646 indexed_ty: Ty<'tcx>,
1649 if let ExprKind::Lit(ref lit) = end.kind;
1650 if let ast::LitKind::Int(end_int, _) = lit.node;
1651 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1652 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1654 return match limits {
1655 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1656 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1664 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1665 let mut applicability = Applicability::MachineApplicable;
1666 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1667 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1672 "it is more concise to loop over references to containers instead of using explicit \
1674 "to write this more concisely, try",
1675 format!("&{}{}", muta, object),
1680 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1681 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1682 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1683 // just the receiver, no arguments
1684 if args.len() == 1 {
1685 let method_name = &*method.ident.as_str();
1686 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1687 if method_name == "iter" || method_name == "iter_mut" {
1688 if is_ref_iterable_type(cx, &args[0]) {
1689 lint_iter_method(cx, args, arg, method_name);
1691 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1692 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1693 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1694 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1695 let mut applicability = Applicability::MachineApplicable;
1696 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1699 EXPLICIT_INTO_ITER_LOOP,
1701 "it is more concise to loop over containers instead of using explicit \
1703 "to write this more concisely, try",
1708 let ref_receiver_ty = cx.tcx.mk_ref(
1709 cx.tcx.lifetimes.re_erased,
1712 mutbl: Mutability::Not,
1715 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1716 lint_iter_method(cx, args, arg, method_name)
1719 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1724 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1725 probably not what you want",
1727 next_loop_linted = true;
1731 if !next_loop_linted {
1732 check_arg_type(cx, pat, arg);
1736 /// Checks for `for` loops over `Option`s and `Result`s.
1737 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1738 let ty = cx.typeck_results().expr_ty(arg);
1739 if is_type_diagnostic_item(cx, ty, sym::option_type) {
1742 FOR_LOOPS_OVER_FALLIBLES,
1745 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1746 `if let` statement.",
1747 snippet(cx, arg.span, "_")
1751 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1752 snippet(cx, pat.span, "_"),
1753 snippet(cx, arg.span, "_")
1756 } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
1759 FOR_LOOPS_OVER_FALLIBLES,
1762 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1763 `if let` statement.",
1764 snippet(cx, arg.span, "_")
1768 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1769 snippet(cx, pat.span, "_"),
1770 snippet(cx, arg.span, "_")
1776 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1777 // incremented exactly once in the loop body, and initialized to zero
1778 // at the start of the loop.
1779 fn check_for_loop_explicit_counter<'tcx>(
1780 cx: &LateContext<'tcx>,
1782 arg: &'tcx Expr<'_>,
1783 body: &'tcx Expr<'_>,
1784 expr: &'tcx Expr<'_>,
1786 // Look for variables that are incremented once per loop iteration.
1787 let mut increment_visitor = IncrementVisitor::new(cx);
1788 walk_expr(&mut increment_visitor, body);
1790 // For each candidate, check the parent block to see if
1791 // it's initialized to zero at the start of the loop.
1792 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1793 for id in increment_visitor.into_results() {
1794 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1795 walk_block(&mut initialize_visitor, block);
1798 if let Some((name, initializer)) = initialize_visitor.get_result();
1799 if is_integer_const(cx, initializer, 0);
1801 let mut applicability = Applicability::MachineApplicable;
1803 let for_span = get_span_of_entire_for_loop(expr);
1807 EXPLICIT_COUNTER_LOOP,
1808 for_span.with_hi(arg.span.hi()),
1809 &format!("the variable `{}` is used as a loop counter.", name),
1812 "for ({}, {}) in {}.enumerate()",
1814 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1815 make_iterator_snippet(cx, arg, &mut applicability),
1825 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1826 /// actual `Iterator` that the loop uses.
1827 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1828 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1829 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1834 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1837 // (&x).into_iter() ==> x.iter()
1838 // (&mut x).into_iter() ==> x.iter_mut()
1840 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1841 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1843 let meth_name = match mutability {
1844 Mutability::Mut => "iter_mut",
1845 Mutability::Not => "iter",
1849 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1855 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1861 /// Checks for the `FOR_KV_MAP` lint.
1862 fn check_for_loop_over_map_kv<'tcx>(
1863 cx: &LateContext<'tcx>,
1865 arg: &'tcx Expr<'_>,
1866 body: &'tcx Expr<'_>,
1867 expr: &'tcx Expr<'_>,
1869 let pat_span = pat.span;
1871 if let PatKind::Tuple(ref pat, _) = pat.kind {
1873 let arg_span = arg.span;
1874 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1875 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1876 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1877 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1882 let mutbl = match mutbl {
1883 Mutability::Not => "",
1884 Mutability::Mut => "_mut",
1886 let arg = match arg.kind {
1887 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1891 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1896 &format!("you seem to want to iterate on a map's {}s", kind),
1898 let map = sugg::Sugg::hir(cx, arg, "map");
1901 "use the corresponding method",
1903 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1904 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1914 fn check_for_single_element_loop<'tcx>(
1915 cx: &LateContext<'tcx>,
1917 arg: &'tcx Expr<'_>,
1918 body: &'tcx Expr<'_>,
1919 expr: &'tcx Expr<'_>,
1922 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg_expr) = arg.kind;
1923 if let PatKind::Binding(.., target, _) = pat.kind;
1924 if let ExprKind::Array(ref arg_expr_list) = arg_expr.kind;
1925 if let [arg_expression] = arg_expr_list;
1926 if let ExprKind::Path(ref list_item) = arg_expression.kind;
1927 if let Some(list_item_name) = single_segment_path(list_item).map(|ps| ps.ident.name);
1928 if let ExprKind::Block(ref block, _) = body.kind;
1929 if !block.stmts.is_empty();
1932 let for_span = get_span_of_entire_for_loop(expr);
1933 let mut block_str = snippet(cx, block.span, "..").into_owned();
1934 block_str.remove(0);
1940 SINGLE_ELEMENT_LOOP,
1942 "for loop over a single element",
1944 format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),
1945 Applicability::MachineApplicable
1951 struct MutatePairDelegate<'a, 'tcx> {
1952 cx: &'a LateContext<'tcx>,
1953 hir_id_low: Option<HirId>,
1954 hir_id_high: Option<HirId>,
1955 span_low: Option<Span>,
1956 span_high: Option<Span>,
1959 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1960 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: HirId, _: ConsumeMode) {}
1962 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId, bk: ty::BorrowKind) {
1963 if let ty::BorrowKind::MutBorrow = bk {
1964 if let PlaceBase::Local(id) = cmt.place.base {
1965 if Some(id) == self.hir_id_low {
1966 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
1968 if Some(id) == self.hir_id_high {
1969 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
1975 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId) {
1976 if let PlaceBase::Local(id) = cmt.place.base {
1977 if Some(id) == self.hir_id_low {
1978 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
1980 if Some(id) == self.hir_id_high {
1981 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
1987 impl MutatePairDelegate<'_, '_> {
1988 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1989 (self.span_low, self.span_high)
1993 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1994 if let Some(higher::Range {
1998 }) = higher::range(arg)
2000 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
2001 if mut_ids[0].is_some() || mut_ids[1].is_some() {
2002 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
2003 mut_warn_with_span(cx, span_low);
2004 mut_warn_with_span(cx, span_high);
2009 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
2010 if let Some(sp) = span {
2015 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
2020 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
2022 if let ExprKind::Path(ref qpath) = bound.kind;
2023 if let QPath::Resolved(None, _) = *qpath;
2025 let res = qpath_res(cx, qpath, bound.hir_id);
2026 if let Res::Local(hir_id) = res {
2027 let node_str = cx.tcx.hir().get(hir_id);
2029 if let Node::Binding(pat) = node_str;
2030 if let PatKind::Binding(bind_ann, ..) = pat.kind;
2031 if let BindingAnnotation::Mutable = bind_ann;
2033 return Some(hir_id);
2042 fn check_for_mutation<'tcx>(
2043 cx: &LateContext<'tcx>,
2045 bound_ids: &[Option<HirId>],
2046 ) -> (Option<Span>, Option<Span>) {
2047 let mut delegate = MutatePairDelegate {
2049 hir_id_low: bound_ids[0],
2050 hir_id_high: bound_ids[1],
2054 cx.tcx.infer_ctxt().enter(|infcx| {
2055 ExprUseVisitor::new(
2060 cx.typeck_results(),
2064 delegate.mutation_span()
2067 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
2068 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
2070 PatKind::Wild => true,
2071 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
2076 struct LocalUsedVisitor<'a, 'tcx> {
2077 cx: &'a LateContext<'tcx>,
2082 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
2083 type Map = Map<'tcx>;
2085 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2086 if same_var(self.cx, expr, self.local) {
2089 walk_expr(self, expr);
2093 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2094 NestedVisitorMap::None
2098 struct VarVisitor<'a, 'tcx> {
2099 /// context reference
2100 cx: &'a LateContext<'tcx>,
2101 /// var name to look for as index
2103 /// indexed variables that are used mutably
2104 indexed_mut: FxHashSet<Symbol>,
2105 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2106 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2107 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2108 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2109 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2110 /// Any names that are used outside an index operation.
2111 /// Used to detect things like `&mut vec` used together with `vec[i]`
2112 referenced: FxHashSet<Symbol>,
2113 /// has the loop variable been used in expressions other than the index of
2116 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2117 /// takes `&mut self`
2118 prefer_mutable: bool,
2121 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2122 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2124 // the indexed container is referenced by a name
2125 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2126 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2127 if seqvar.segments.len() == 1;
2129 let index_used_directly = same_var(self.cx, idx, self.var);
2130 let indexed_indirectly = {
2131 let mut used_visitor = LocalUsedVisitor {
2136 walk_expr(&mut used_visitor, idx);
2140 if indexed_indirectly || index_used_directly {
2141 if self.prefer_mutable {
2142 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2144 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
2146 Res::Local(hir_id) => {
2147 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2148 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2149 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2150 if indexed_indirectly {
2151 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2153 if index_used_directly {
2154 self.indexed_directly.insert(
2155 seqvar.segments[0].ident.name,
2156 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2159 return false; // no need to walk further *on the variable*
2161 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2162 if indexed_indirectly {
2163 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2165 if index_used_directly {
2166 self.indexed_directly.insert(
2167 seqvar.segments[0].ident.name,
2168 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2171 return false; // no need to walk further *on the variable*
2182 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2183 type Map = Map<'tcx>;
2185 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2188 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2189 if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX))
2190 || (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2191 if !self.check(&args[1], &args[0], expr);
2197 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2198 if !self.check(idx, seqexpr, expr);
2203 // directly using a variable
2204 if let ExprKind::Path(ref qpath) = expr.kind;
2205 if let QPath::Resolved(None, ref path) = *qpath;
2206 if path.segments.len() == 1;
2208 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2209 if local_id == self.var {
2210 self.nonindex = true;
2212 // not the correct variable, but still a variable
2213 self.referenced.insert(path.segments[0].ident.name);
2219 let old = self.prefer_mutable;
2221 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2222 self.prefer_mutable = true;
2223 self.visit_expr(lhs);
2224 self.prefer_mutable = false;
2225 self.visit_expr(rhs);
2227 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2228 if mutbl == Mutability::Mut {
2229 self.prefer_mutable = true;
2231 self.visit_expr(expr);
2233 ExprKind::Call(ref f, args) => {
2236 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2237 self.prefer_mutable = false;
2238 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2239 if mutbl == Mutability::Mut {
2240 self.prefer_mutable = true;
2243 self.visit_expr(expr);
2246 ExprKind::MethodCall(_, _, args, _) => {
2247 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2248 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2249 self.prefer_mutable = false;
2250 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2251 if mutbl == Mutability::Mut {
2252 self.prefer_mutable = true;
2255 self.visit_expr(expr);
2258 ExprKind::Closure(_, _, body_id, ..) => {
2259 let body = self.cx.tcx.hir().body(body_id);
2260 self.visit_expr(&body.value);
2262 _ => walk_expr(self, expr),
2264 self.prefer_mutable = old;
2266 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2267 NestedVisitorMap::None
2271 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2272 let def_id = match var_def_id(cx, expr) {
2274 None => return false,
2276 if let Some(used_mutably) = mutated_variables(container, cx) {
2277 if used_mutably.contains(&def_id) {
2284 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2285 let def_id = match var_def_id(cx, iter_expr) {
2287 None => return false,
2289 let mut visitor = VarUsedAfterLoopVisitor {
2292 iter_expr_id: iter_expr.hir_id,
2293 past_while_let: false,
2294 var_used_after_while_let: false,
2296 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2297 walk_block(&mut visitor, enclosing_block);
2299 visitor.var_used_after_while_let
2302 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2303 cx: &'a LateContext<'tcx>,
2305 iter_expr_id: HirId,
2306 past_while_let: bool,
2307 var_used_after_while_let: bool,
2310 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2311 type Map = Map<'tcx>;
2313 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2314 if self.past_while_let {
2315 if Some(self.def_id) == var_def_id(self.cx, expr) {
2316 self.var_used_after_while_let = true;
2318 } else if self.iter_expr_id == expr.hir_id {
2319 self.past_while_let = true;
2321 walk_expr(self, expr);
2323 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2324 NestedVisitorMap::None
2328 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2329 /// for `&T` and `&mut T`, such as `Vec`.
2331 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2332 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2333 // will allow further borrows afterwards
2334 let ty = cx.typeck_results().expr_ty(e);
2335 is_iterable_array(ty, cx) ||
2336 is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2337 match_type(cx, ty, &paths::LINKED_LIST) ||
2338 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2339 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2340 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2341 match_type(cx, ty, &paths::BINARY_HEAP) ||
2342 match_type(cx, ty, &paths::BTREEMAP) ||
2343 match_type(cx, ty, &paths::BTREESET)
2346 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2347 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2349 ty::Array(_, n) => n
2350 .try_eval_usize(cx.tcx, cx.param_env)
2351 .map_or(false, |val| (0..=32).contains(&val)),
2356 /// If a block begins with a statement (possibly a `let` binding) and has an
2357 /// expression, return it.
2358 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2359 if block.stmts.is_empty() {
2362 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2363 local.init //.map(|expr| expr)
2369 /// If a block begins with an expression (with or without semicolon), return it.
2370 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2372 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2373 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2374 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2375 StmtKind::Local(..) | StmtKind::Item(..) => None,
2381 /// Returns `true` if expr contains a single break expr without destination label
2383 /// passed expression. The expression may be within a block.
2384 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2386 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2387 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2392 #[derive(Debug, PartialEq)]
2393 enum IncrementVisitorVarState {
2394 Initial, // Not examined yet
2395 IncrOnce, // Incremented exactly once, may be a loop counter
2399 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2400 struct IncrementVisitor<'a, 'tcx> {
2401 cx: &'a LateContext<'tcx>, // context reference
2402 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2403 depth: u32, // depth of conditional expressions
2407 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2408 fn new(cx: &'a LateContext<'tcx>) -> Self {
2411 states: FxHashMap::default(),
2417 fn into_results(self) -> impl Iterator<Item = HirId> {
2418 self.states.into_iter().filter_map(|(id, state)| {
2419 if state == IncrementVisitorVarState::IncrOnce {
2428 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2429 type Map = Map<'tcx>;
2431 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2436 // If node is a variable
2437 if let Some(def_id) = var_def_id(self.cx, expr) {
2438 if let Some(parent) = get_parent_expr(self.cx, expr) {
2439 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2440 if *state == IncrementVisitorVarState::IncrOnce {
2441 *state = IncrementVisitorVarState::DontWarn;
2446 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2447 if lhs.hir_id == expr.hir_id {
2448 *state = if op.node == BinOpKind::Add
2449 && is_integer_const(self.cx, rhs, 1)
2450 && *state == IncrementVisitorVarState::Initial
2453 IncrementVisitorVarState::IncrOnce
2455 // Assigned some other value or assigned multiple times
2456 IncrementVisitorVarState::DontWarn
2460 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2461 *state = IncrementVisitorVarState::DontWarn
2463 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2464 *state = IncrementVisitorVarState::DontWarn
2470 walk_expr(self, expr);
2471 } else if is_loop(expr) || is_conditional(expr) {
2473 walk_expr(self, expr);
2475 } else if let ExprKind::Continue(_) = expr.kind {
2478 walk_expr(self, expr);
2481 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2482 NestedVisitorMap::None
2486 enum InitializeVisitorState<'hir> {
2487 Initial, // Not examined yet
2488 Declared(Symbol), // Declared but not (yet) initialized
2491 initializer: &'hir Expr<'hir>,
2496 /// Checks whether a variable is initialized at the start of a loop and not modified
2497 /// and used after the loop.
2498 struct InitializeVisitor<'a, 'tcx> {
2499 cx: &'a LateContext<'tcx>, // context reference
2500 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2502 state: InitializeVisitorState<'tcx>,
2503 depth: u32, // depth of conditional expressions
2507 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2508 fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2513 state: InitializeVisitorState::Initial,
2519 fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
2520 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2521 Some((name, initializer))
2528 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2529 type Map = Map<'tcx>;
2531 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2532 // Look for declarations of the variable
2534 if let StmtKind::Local(ref local) = stmt.kind;
2535 if local.pat.hir_id == self.var_id;
2536 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2538 self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
2539 InitializeVisitorState::Initialized {
2546 walk_stmt(self, stmt);
2549 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2550 if matches!(self.state, InitializeVisitorState::DontWarn) {
2553 if expr.hir_id == self.end_expr.hir_id {
2554 self.past_loop = true;
2557 // No need to visit expressions before the variable is
2559 if matches!(self.state, InitializeVisitorState::Initial) {
2563 // If node is the desired variable, see how it's used
2564 if var_def_id(self.cx, expr) == Some(self.var_id) {
2566 self.state = InitializeVisitorState::DontWarn;
2570 if let Some(parent) = get_parent_expr(self.cx, expr) {
2572 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2573 self.state = InitializeVisitorState::DontWarn;
2575 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2576 self.state = if_chain! {
2578 if let InitializeVisitorState::Declared(name)
2579 | InitializeVisitorState::Initialized { name, ..} = self.state;
2581 InitializeVisitorState::Initialized { initializer: rhs, name }
2583 InitializeVisitorState::DontWarn
2587 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2588 self.state = InitializeVisitorState::DontWarn
2594 walk_expr(self, expr);
2595 } else if !self.past_loop && is_loop(expr) {
2596 self.state = InitializeVisitorState::DontWarn;
2597 } else if is_conditional(expr) {
2599 walk_expr(self, expr);
2602 walk_expr(self, expr);
2606 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2607 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2611 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2612 if let ExprKind::Path(ref qpath) = expr.kind {
2613 let path_res = qpath_res(cx, qpath, expr.hir_id);
2614 if let Res::Local(hir_id) = path_res {
2615 return Some(hir_id);
2621 fn is_loop(expr: &Expr<'_>) -> bool {
2622 matches!(expr.kind, ExprKind::Loop(..))
2625 fn is_conditional(expr: &Expr<'_>) -> bool {
2626 matches!(expr.kind, ExprKind::Match(..))
2629 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2631 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2632 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2633 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2635 return is_loop_nested(cx, loop_expr, iter_expr)
2641 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2642 let mut id = loop_expr.hir_id;
2643 let iter_name = if let Some(name) = path_name(iter_expr) {
2649 let parent = cx.tcx.hir().get_parent_node(id);
2653 match cx.tcx.hir().find(parent) {
2654 Some(Node::Expr(expr)) => {
2655 if let ExprKind::Loop(..) = expr.kind {
2659 Some(Node::Block(block)) => {
2660 let mut block_visitor = LoopNestVisitor {
2662 iterator: iter_name,
2665 walk_block(&mut block_visitor, block);
2666 if block_visitor.nesting == RuledOut {
2670 Some(Node::Stmt(_)) => (),
2679 #[derive(PartialEq, Eq)]
2681 Unknown, // no nesting detected yet
2682 RuledOut, // the iterator is initialized or assigned within scope
2683 LookFurther, // no nesting detected, no further walk required
2686 use self::Nesting::{LookFurther, RuledOut, Unknown};
2688 struct LoopNestVisitor {
2694 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2695 type Map = Map<'tcx>;
2697 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2698 if stmt.hir_id == self.hir_id {
2699 self.nesting = LookFurther;
2700 } else if self.nesting == Unknown {
2701 walk_stmt(self, stmt);
2705 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2706 if self.nesting != Unknown {
2709 if expr.hir_id == self.hir_id {
2710 self.nesting = LookFurther;
2714 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2715 if match_var(path, self.iterator) {
2716 self.nesting = RuledOut;
2719 _ => walk_expr(self, expr),
2723 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2724 if self.nesting != Unknown {
2727 if let PatKind::Binding(.., span_name, _) = pat.kind {
2728 if self.iterator == span_name.name {
2729 self.nesting = RuledOut;
2736 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2737 NestedVisitorMap::None
2741 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2742 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2743 let segments = &path.segments;
2744 if segments.len() == 1 {
2745 return Some(segments[0].ident.name);
2751 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2752 if constant(cx, cx.typeck_results(), cond).is_some() {
2753 // A pure constant condition (e.g., `while false`) is not linted.
2757 let mut var_visitor = VarCollectorVisitor {
2759 ids: FxHashSet::default(),
2760 def_ids: FxHashMap::default(),
2763 var_visitor.visit_expr(cond);
2764 if var_visitor.skip {
2767 let used_in_condition = &var_visitor.ids;
2768 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2769 used_in_condition.is_disjoint(&used_mutably)
2773 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2775 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2776 has_break_or_return: false,
2778 has_break_or_return_visitor.visit_expr(expr);
2779 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2781 if no_cond_variable_mutated && !mutable_static_in_cond {
2784 WHILE_IMMUTABLE_CONDITION,
2786 "variables in the condition are not mutated in the loop body",
2788 diag.note("this may lead to an infinite or to a never running loop");
2790 if has_break_or_return {
2791 diag.note("this loop contains `return`s or `break`s");
2792 diag.help("rewrite it as `if cond { loop { } }`");
2799 struct HasBreakOrReturnVisitor {
2800 has_break_or_return: bool,
2803 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2804 type Map = Map<'tcx>;
2806 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2807 if self.has_break_or_return {
2812 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2813 self.has_break_or_return = true;
2819 walk_expr(self, expr);
2822 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2823 NestedVisitorMap::None
2827 /// Collects the set of variables in an expression
2828 /// Stops analysis if a function call is found
2829 /// Note: In some cases such as `self`, there are no mutable annotation,
2830 /// All variables definition IDs are collected
2831 struct VarCollectorVisitor<'a, 'tcx> {
2832 cx: &'a LateContext<'tcx>,
2833 ids: FxHashSet<HirId>,
2834 def_ids: FxHashMap<def_id::DefId, bool>,
2838 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2839 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2841 if let ExprKind::Path(ref qpath) = ex.kind;
2842 if let QPath::Resolved(None, _) = *qpath;
2843 let res = qpath_res(self.cx, qpath, ex.hir_id);
2846 Res::Local(hir_id) => {
2847 self.ids.insert(hir_id);
2849 Res::Def(DefKind::Static, def_id) => {
2850 let mutable = self.cx.tcx.is_mutable_static(def_id);
2851 self.def_ids.insert(def_id, mutable);
2860 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2861 type Map = Map<'tcx>;
2863 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2865 ExprKind::Path(_) => self.insert_def_id(ex),
2866 // If there is any function/method call… we just stop analysis
2867 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2869 _ => walk_expr(self, ex),
2873 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2874 NestedVisitorMap::None
2878 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2880 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2881 check_needless_collect_direct_usage(expr, cx);
2882 check_needless_collect_indirect_usage(expr, cx);
2884 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2886 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2887 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2888 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2889 if let Some(ref generic_args) = chain_method.args;
2890 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2892 let ty = cx.typeck_results().node_type(ty.hir_id);
2893 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2894 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2895 match_type(cx, ty, &paths::BTREEMAP) ||
2896 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2897 if method.ident.name == sym!(len) {
2898 let span = shorten_needless_collect_span(expr);
2903 NEEDLESS_COLLECT_MSG,
2905 "count()".to_string(),
2906 Applicability::MachineApplicable,
2909 if method.ident.name == sym!(is_empty) {
2910 let span = shorten_needless_collect_span(expr);
2915 NEEDLESS_COLLECT_MSG,
2917 "next().is_none()".to_string(),
2918 Applicability::MachineApplicable,
2921 if method.ident.name == sym!(contains) {
2922 let contains_arg = snippet(cx, args[1].span, "??");
2923 let span = shorten_needless_collect_span(expr);
2928 NEEDLESS_COLLECT_MSG,
2930 let (arg, pred) = contains_arg
2932 .map_or(("&x", &*contains_arg), |s| ("x", s));
2933 diag.span_suggestion(
2937 "any(|{}| x == {})",
2940 Applicability::MachineApplicable,
2950 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2951 if let ExprKind::Block(ref block, _) = expr.kind {
2952 for ref stmt in block.stmts {
2954 if let StmtKind::Local(
2955 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2956 init: Some(ref init_expr), .. }
2958 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2959 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2960 if let Some(ref generic_args) = method_name.args;
2961 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2962 if let ty = cx.typeck_results().node_type(ty.hir_id);
2963 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2964 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2965 match_type(cx, ty, &paths::LINKED_LIST);
2966 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2967 if iter_calls.len() == 1;
2969 // Suggest replacing iter_call with iter_replacement, and removing stmt
2970 let iter_call = &iter_calls[0];
2974 stmt.span.until(iter_call.span),
2975 NEEDLESS_COLLECT_MSG,
2977 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2978 diag.multipart_suggestion(
2979 iter_call.get_suggestion_text(),
2981 (stmt.span, String::new()),
2982 (iter_call.span, iter_replacement)
2984 Applicability::MachineApplicable,// MaybeIncorrect,
2994 struct IterFunction {
2995 func: IterFunctionKind,
2999 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
3001 IterFunctionKind::IntoIter => String::new(),
3002 IterFunctionKind::Len => String::from(".count()"),
3003 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
3004 IterFunctionKind::Contains(span) => {
3005 let s = snippet(cx, *span, "..");
3006 if let Some(stripped) = s.strip_prefix('&') {
3007 format!(".any(|x| x == {})", stripped)
3009 format!(".any(|x| x == *{})", s)
3014 fn get_suggestion_text(&self) -> &'static str {
3016 IterFunctionKind::IntoIter => {
3017 "Use the original Iterator instead of collecting it and then producing a new one"
3019 IterFunctionKind::Len => {
3020 "Take the original Iterator's count instead of collecting it and finding the length"
3022 IterFunctionKind::IsEmpty => {
3023 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
3025 IterFunctionKind::Contains(_) => {
3026 "Check if the original Iterator contains an element instead of collecting then checking"
3031 enum IterFunctionKind {
3038 struct IterFunctionVisitor {
3039 uses: Vec<IterFunction>,
3043 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
3044 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
3045 // Check function calls on our collection
3047 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
3048 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
3049 if let &[name] = &path.segments;
3050 if name.ident == self.target;
3052 let len = sym!(len);
3053 let is_empty = sym!(is_empty);
3054 let contains = sym!(contains);
3055 match method_name.ident.name {
3056 sym::into_iter => self.uses.push(
3057 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
3059 name if name == len => self.uses.push(
3060 IterFunction { func: IterFunctionKind::Len, span: expr.span }
3062 name if name == is_empty => self.uses.push(
3063 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
3065 name if name == contains => self.uses.push(
3066 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
3068 _ => self.seen_other = true,
3073 // Check if the collection is used for anything else
3075 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
3076 if let &[name] = &path.segments;
3077 if name.ident == self.target;
3079 self.seen_other = true;
3081 walk_expr(self, expr);
3086 type Map = Map<'tcx>;
3087 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3088 NestedVisitorMap::None
3092 /// Detect the occurences of calls to `iter` or `into_iter` for the
3093 /// given identifier
3094 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
3095 let mut visitor = IterFunctionVisitor {
3100 visitor.visit_block(block);
3101 if visitor.seen_other {
3108 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3110 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3111 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3113 return expr.span.with_lo(span.lo());