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_in_panic_handler, is_integer_const, is_no_std_crate, is_refutable, is_type_diagnostic_item,
8 last_path_segment, match_trait_method, match_type, match_var, multispan_sugg, qpath_res, single_segment_path,
9 snippet, snippet_with_applicability, snippet_with_macro_callsite, span_lint, span_lint_and_help,
10 span_lint_and_sugg, span_lint_and_then, sugg, SpanlessEq,
12 use if_chain::if_chain;
14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
15 use rustc_errors::Applicability;
16 use rustc_hir::def::{DefKind, Res};
17 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
19 def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, InlineAsmOperand,
20 Local, LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
22 use rustc_infer::infer::TyCtxtInferExt;
23 use rustc_lint::{LateContext, LateLintPass, LintContext};
24 use rustc_middle::hir::map::Map;
25 use rustc_middle::lint::in_external_macro;
26 use rustc_middle::middle::region;
27 use rustc_middle::ty::{self, Ty, TyS};
28 use rustc_session::{declare_lint_pass, declare_tool_lint};
29 use rustc_span::source_map::Span;
30 use rustc_span::symbol::{sym, Ident, Symbol};
31 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
32 use std::iter::{once, Iterator};
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// # let src = vec![1];
46 /// # let mut dst = vec![0; 65];
47 /// for i in 0..src.len() {
48 /// dst[i + 64] = src[i];
51 /// Could be written as:
53 /// # let src = vec![1];
54 /// # let mut dst = vec![0; 65];
55 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
59 "manually copying items between slices"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for looping over the range of `0..len` of some
64 /// collection just to get the values by index.
66 /// **Why is this bad?** Just iterating the collection itself makes the intent
67 /// more clear and is probably faster.
69 /// **Known problems:** None.
73 /// let vec = vec!['a', 'b', 'c'];
74 /// for i in 0..vec.len() {
75 /// println!("{}", vec[i]);
78 /// Could be written as:
80 /// let vec = vec!['a', 'b', 'c'];
82 /// println!("{}", i);
85 pub NEEDLESS_RANGE_LOOP,
87 "for-looping over a range of indices where an iterator over items would do"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
92 /// suggests the latter.
94 /// **Why is this bad?** Readability.
96 /// **Known problems:** False negatives. We currently only warn on some known
101 /// // with `y` a `Vec` or slice:
102 /// # let y = vec![1];
103 /// for x in y.iter() {
107 /// can be rewritten to
109 /// # let y = vec![1];
114 pub EXPLICIT_ITER_LOOP,
116 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
121 /// suggests the latter.
123 /// **Why is this bad?** Readability.
125 /// **Known problems:** None
129 /// # let y = vec![1];
130 /// // with `y` a `Vec` or slice:
131 /// for x in y.into_iter() {
135 /// can be rewritten to
137 /// # let y = vec![1];
142 pub EXPLICIT_INTO_ITER_LOOP,
144 "for-looping over `_.into_iter()` when `_` would do"
147 declare_clippy_lint! {
148 /// **What it does:** Checks for loops on `x.next()`.
150 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
151 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
152 /// implements `IntoIterator`, so that possibly one value will be iterated,
153 /// leading to some hard to find bugs. No one will want to write such code
154 /// [except to win an Underhanded Rust
155 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
157 /// **Known problems:** None.
161 /// for x in y.next() {
167 "for-looping over `_.next()` which is probably not intended"
170 declare_clippy_lint! {
171 /// **What it does:** Checks for `for` loops over `Option` or `Result` values.
173 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
176 /// **Known problems:** None.
180 /// # let opt = Some(1);
188 /// if let Some(x) = opt {
196 /// # let res: Result<i32, std::io::Error> = Ok(1);
204 /// if let Ok(x) = res {
208 pub FOR_LOOPS_OVER_FALLIBLES,
210 "for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
213 declare_clippy_lint! {
214 /// **What it does:** Detects `loop + match` combinations that are easier
215 /// written as a `while let` loop.
217 /// **Why is this bad?** The `while let` loop is usually shorter and more
220 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
224 /// # let y = Some(1);
226 /// let x = match y {
230 /// // .. do something with x
232 /// // is easier written as
233 /// while let Some(x) = y {
234 /// // .. do something with x
239 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
242 declare_clippy_lint! {
243 /// **What it does:** Checks for functions collecting an iterator when collect
246 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
247 /// when this allocation may not be needed.
249 /// **Known problems:**
254 /// # let iterator = vec![1].into_iter();
255 /// let len = iterator.clone().collect::<Vec<_>>().len();
257 /// let len = iterator.count();
259 pub NEEDLESS_COLLECT,
261 "collecting an iterator when collect is not needed"
264 declare_clippy_lint! {
265 /// **What it does:** Checks `for` loops over slices with an explicit counter
266 /// and suggests the use of `.enumerate()`.
268 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
269 /// declutters the code and may be faster in some instances.
271 /// **Known problems:** None.
275 /// # let v = vec![1];
276 /// # fn bar(bar: usize, baz: usize) {}
283 /// Could be written as
285 /// # let v = vec![1];
286 /// # fn bar(bar: usize, baz: usize) {}
287 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
289 pub EXPLICIT_COUNTER_LOOP,
291 "for-looping with an explicit counter when `_.enumerate()` would do"
294 declare_clippy_lint! {
295 /// **What it does:** Checks for empty `loop` expressions.
297 /// **Why is this bad?** 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, skipping those in #[panic_handler]
547 if block.stmts.is_empty() && block.expr.is_none() && !is_in_panic_handler(cx, expr) {
548 let msg = "empty `loop {}` wastes CPU cycles";
549 let help = if is_no_std_crate(cx.tcx.hir().krate()) {
550 "you should either use `panic!()` or add a call pausing or sleeping the thread to the loop body"
552 "you should either use `panic!()` or add `std::thread::sleep(..);` to the loop body"
554 span_lint_and_help(cx, EMPTY_LOOP, expr.span, msg, None, help);
557 // extract the expression from the first statement (if any) in a block
558 let inner_stmt_expr = extract_expr_from_first_stmt(block);
559 // or extract the first expression (if any) from the block
560 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
561 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
562 // ensure "if let" compatible match structure
564 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
566 && arms[0].guard.is_none()
567 && arms[1].guard.is_none()
568 && is_simple_break_expr(&arms[1].body)
570 if in_external_macro(cx.sess(), expr.span) {
574 // NOTE: we used to build a body here instead of using
575 // ellipsis, this was removed because:
576 // 1) it was ugly with big bodies;
577 // 2) it was not indented properly;
578 // 3) it wasn’t very smart (see #675).
579 let mut applicability = Applicability::HasPlaceholders;
584 "this loop could be written as a `while let` loop",
587 "while let {} = {} {{ .. }}",
588 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
589 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
600 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
601 let pat = &arms[0].pat.kind;
603 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
604 &ExprKind::MethodCall(ref method_path, _, ref method_args, _),
605 ) = (pat, &match_expr.kind)
607 let iter_expr = &method_args[0];
609 // Don't lint when the iterator is recreated on every iteration
611 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
612 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
613 if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
619 let lhs_constructor = last_path_segment(qpath);
620 if method_path.ident.name == sym::next
621 && match_trait_method(cx, match_expr, &paths::ITERATOR)
622 && lhs_constructor.ident.name == sym::Some
623 && (pat_args.is_empty()
624 || !is_refutable(cx, &pat_args[0])
625 && !is_used_inside(cx, iter_expr, &arms[0].body)
626 && !is_iterator_used_after_while_let(cx, iter_expr)
627 && !is_nested(cx, expr, &method_args[0]))
629 let mut applicability = Applicability::MachineApplicable;
630 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
631 let loop_var = if pat_args.is_empty() {
634 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
638 WHILE_LET_ON_ITERATOR,
639 expr.span.with_hi(match_expr.span.hi()),
640 "this loop could be written as a `for` loop",
642 format!("for {} in {}", loop_var, iterator),
649 if let Some((cond, body)) = higher::while_loop(&expr) {
650 check_infinite_loop(cx, cond, body);
653 check_needless_collect(expr, cx);
657 enum NeverLoopResult {
658 // A break/return always get triggered but not necessarily for the main loop.
660 // A continue may occur for the main loop.
666 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
668 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
669 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
673 // Combine two results for parts that are called in order.
675 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
677 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
678 NeverLoopResult::Otherwise => second,
682 // Combine two results where both parts are called but not necessarily in order.
684 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
685 match (left, right) {
686 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
687 NeverLoopResult::MayContinueMainLoop
689 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
690 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
694 // Combine two results where only one of the part may have been executed.
696 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
698 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
699 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
700 NeverLoopResult::MayContinueMainLoop
702 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
706 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
707 let stmts = block.stmts.iter().map(stmt_to_expr);
708 let expr = once(block.expr.as_deref());
709 let mut iter = stmts.chain(expr).filter_map(|e| e);
710 never_loop_expr_seq(&mut iter, main_loop_id)
713 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
715 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
716 StmtKind::Local(ref local) => local.init.as_deref(),
721 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
724 | ExprKind::Unary(_, ref e)
725 | ExprKind::Cast(ref e, _)
726 | ExprKind::Type(ref e, _)
727 | ExprKind::Field(ref e, _)
728 | ExprKind::AddrOf(_, _, ref e)
729 | ExprKind::Struct(_, _, Some(ref e))
730 | ExprKind::Repeat(ref e, _)
731 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
732 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
733 never_loop_expr_all(&mut es.iter(), main_loop_id)
735 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
736 ExprKind::Binary(_, ref e1, ref e2)
737 | ExprKind::Assign(ref e1, ref e2, _)
738 | ExprKind::AssignOp(_, ref e1, ref e2)
739 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
740 ExprKind::Loop(ref b, _, _) => {
741 // Break can come from the inner loop so remove them.
742 absorb_break(&never_loop_block(b, main_loop_id))
744 ExprKind::Match(ref e, ref arms, _) => {
745 let e = never_loop_expr(e, main_loop_id);
749 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
753 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
754 ExprKind::Continue(d) => {
757 .expect("target ID can only be missing in the presence of compilation errors");
758 if id == main_loop_id {
759 NeverLoopResult::MayContinueMainLoop
761 NeverLoopResult::AlwaysBreak
764 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
765 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
767 ExprKind::InlineAsm(ref asm) => asm
771 InlineAsmOperand::In { expr, .. }
772 | InlineAsmOperand::InOut { expr, .. }
773 | InlineAsmOperand::Const { expr }
774 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
775 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
776 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
777 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
780 .fold(NeverLoopResult::Otherwise, combine_both),
781 ExprKind::Struct(_, _, None)
782 | ExprKind::Yield(_, _)
783 | ExprKind::Closure(_, _, _, _, _)
784 | ExprKind::LlvmInlineAsm(_)
786 | ExprKind::ConstBlock(_)
788 | ExprKind::Err => NeverLoopResult::Otherwise,
792 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
793 es.map(|e| never_loop_expr(e, main_loop_id))
794 .fold(NeverLoopResult::Otherwise, combine_seq)
797 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
798 es.map(|e| never_loop_expr(e, main_loop_id))
799 .fold(NeverLoopResult::Otherwise, combine_both)
802 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
803 e.map(|e| never_loop_expr(e, main_loop_id))
804 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
807 fn check_for_loop<'tcx>(
808 cx: &LateContext<'tcx>,
811 body: &'tcx Expr<'_>,
812 expr: &'tcx Expr<'_>,
814 let is_manual_memcpy_triggered = detect_manual_memcpy(cx, pat, arg, body, expr);
815 if !is_manual_memcpy_triggered {
816 check_for_loop_range(cx, pat, arg, body, expr);
817 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
819 check_for_loop_arg(cx, pat, arg, expr);
820 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
821 check_for_mut_range_bound(cx, arg, body);
822 check_for_single_element_loop(cx, pat, arg, body, expr);
823 detect_same_item_push(cx, pat, arg, body, expr);
826 // this function assumes the given expression is a `for` loop.
827 fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
828 // for some reason this is the only way to get the `Span`
829 // of the entire `for` loop
830 if let ExprKind::Match(_, arms, _) = &expr.kind {
837 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
839 if let ExprKind::Path(qpath) = &expr.kind;
840 if let QPath::Resolved(None, path) = qpath;
841 if path.segments.len() == 1;
842 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
852 /// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
853 /// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
854 /// it exists for the convenience of the overloaded operators while normal functions can do the
857 struct MinifyingSugg<'a>(Sugg<'a>);
859 impl<'a> MinifyingSugg<'a> {
860 fn as_str(&self) -> &str {
861 let Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) = &self.0;
865 fn into_sugg(self) -> Sugg<'a> {
870 impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
871 fn from(sugg: Sugg<'a>) -> Self {
876 impl std::ops::Add for &MinifyingSugg<'static> {
877 type Output = MinifyingSugg<'static>;
878 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
879 match (self.as_str(), rhs.as_str()) {
880 ("0", _) => rhs.clone(),
881 (_, "0") => self.clone(),
882 (_, _) => (&self.0 + &rhs.0).into(),
887 impl std::ops::Sub for &MinifyingSugg<'static> {
888 type Output = MinifyingSugg<'static>;
889 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
890 match (self.as_str(), rhs.as_str()) {
891 (_, "0") => self.clone(),
892 ("0", _) => (-rhs.0.clone()).into(),
893 (x, y) if x == y => sugg::ZERO.into(),
894 (_, _) => (&self.0 - &rhs.0).into(),
899 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
900 type Output = MinifyingSugg<'static>;
901 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
902 match (self.as_str(), rhs.as_str()) {
903 ("0", _) => rhs.clone(),
905 (_, _) => (self.0 + &rhs.0).into(),
910 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
911 type Output = MinifyingSugg<'static>;
912 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
913 match (self.as_str(), rhs.as_str()) {
915 ("0", _) => (-rhs.0.clone()).into(),
916 (x, y) if x == y => sugg::ZERO.into(),
917 (_, _) => (self.0 - &rhs.0).into(),
922 /// a wrapper around `MinifyingSugg`, which carries a operator like currying
923 /// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
925 value: MinifyingSugg<'static>,
929 #[derive(Clone, Copy)]
936 fn negative(value: Sugg<'static>) -> Self {
939 sign: OffsetSign::Negative,
943 fn positive(value: Sugg<'static>) -> Self {
946 sign: OffsetSign::Positive,
951 Self::positive(sugg::ZERO)
955 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
957 OffsetSign::Positive => lhs + &rhs.value,
958 OffsetSign::Negative => lhs - &rhs.value,
962 #[derive(Debug, Clone, Copy)]
963 enum StartKind<'hir> {
965 Counter { initializer: &'hir Expr<'hir> },
968 struct IndexExpr<'hir> {
969 base: &'hir Expr<'hir>,
970 idx: StartKind<'hir>,
976 kind: StartKind<'hir>,
979 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
980 let is_slice = match ty.kind() {
981 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
982 ty::Slice(..) | ty::Array(..) => true,
986 is_slice || is_type_diagnostic_item(cx, ty, sym::vec_type) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
989 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
991 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
992 if method.ident.name == sym::clone;
994 if let Some(arg) = args.get(0);
995 then { arg } else { expr }
999 fn get_details_from_idx<'tcx>(
1000 cx: &LateContext<'tcx>,
1002 starts: &[Start<'tcx>],
1003 ) -> Option<(StartKind<'tcx>, Offset)> {
1004 fn get_start<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
1005 starts.iter().find_map(|start| {
1006 if same_var(cx, e, start.id) {
1014 fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
1016 ExprKind::Lit(l) => match l.node {
1017 ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
1020 ExprKind::Path(..) if get_start(cx, e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
1026 ExprKind::Binary(op, lhs, rhs) => match op.node {
1028 let offset_opt = get_start(cx, lhs, starts)
1029 .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
1030 .or_else(|| get_start(cx, rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
1032 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
1035 get_start(cx, lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
1039 ExprKind::Path(..) => get_start(cx, idx, starts).map(|s| (s, Offset::empty())),
1044 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1045 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1052 /// Get assignments from the given block.
1053 /// The returned iterator yields `None` if no assignment expressions are there,
1054 /// filtering out the increments of the given whitelisted loop counters;
1055 /// because its job is to make sure there's nothing other than assignments and the increments.
1056 fn get_assignments<'a: 'c, 'tcx: 'c, 'c>(
1057 cx: &'a LateContext<'tcx>,
1058 Block { stmts, expr, .. }: &'tcx Block<'tcx>,
1059 loop_counters: &'c [Start<'tcx>],
1060 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'c {
1061 // As the `filter` and `map` below do different things, I think putting together
1062 // just increases complexity. (cc #3188 and #4193)
1063 #[allow(clippy::filter_map)]
1066 .filter_map(move |stmt| match stmt.kind {
1067 StmtKind::Local(..) | StmtKind::Item(..) => None,
1068 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
1070 .chain((*expr).into_iter())
1072 if let ExprKind::AssignOp(_, place, _) = e.kind {
1075 // skip the first item which should be `StartKind::Range`
1076 // this makes it possible to use the slice with `StartKind::Range` in the same iterator loop.
1078 .any(|counter| same_var(cx, place, counter.id))
1083 .map(get_assignment)
1086 fn get_loop_counters<'a, 'tcx>(
1087 cx: &'a LateContext<'tcx>,
1088 body: &'tcx Block<'tcx>,
1089 expr: &'tcx Expr<'_>,
1090 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1091 // Look for variables that are incremented once per loop iteration.
1092 let mut increment_visitor = IncrementVisitor::new(cx);
1093 walk_block(&mut increment_visitor, body);
1095 // For each candidate, check the parent block to see if
1096 // it's initialized to zero at the start of the loop.
1097 get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
1100 .filter_map(move |var_id| {
1101 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1102 walk_block(&mut initialize_visitor, block);
1104 initialize_visitor.get_result().map(|(_, initializer)| Start {
1106 kind: StartKind::Counter { initializer },
1113 fn build_manual_memcpy_suggestion<'tcx>(
1114 cx: &LateContext<'tcx>,
1117 limits: ast::RangeLimits,
1118 dst: &IndexExpr<'_>,
1119 src: &IndexExpr<'_>,
1121 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1122 if offset.as_str() == "0" {
1129 let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
1131 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1132 if method.ident.name == sym!(len);
1133 if len_args.len() == 1;
1134 if let Some(arg) = len_args.get(0);
1135 if var_def_id(cx, arg) == var_def_id(cx, base);
1137 if sugg.as_str() == end_str {
1144 ast::RangeLimits::Closed => {
1145 sugg + &sugg::ONE.into()
1147 ast::RangeLimits::HalfOpen => sugg,
1153 let start_str = Sugg::hir(cx, start, "").into();
1154 let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
1156 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1157 StartKind::Range => (
1158 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
1163 apply_offset(&end_str, &idx_expr.idx_offset),
1167 StartKind::Counter { initializer } => {
1168 let counter_start = Sugg::hir(cx, initializer, "").into();
1170 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
1175 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1182 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1183 let (src_offset, src_limit) = print_offset_and_limit(&src);
1185 let dst_base_str = snippet(cx, dst.base.span, "???");
1186 let src_base_str = snippet(cx, src.base.span, "???");
1188 let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
1194 dst_offset.maybe_par(),
1195 dst_limit.maybe_par()
1201 "{}.clone_from_slice(&{}[{}..{}]);",
1204 src_offset.maybe_par(),
1205 src_limit.maybe_par()
1209 /// Checks for for loops that sequentially copy items from one slice-like
1210 /// object to another.
1211 fn detect_manual_memcpy<'tcx>(
1212 cx: &LateContext<'tcx>,
1214 arg: &'tcx Expr<'_>,
1215 body: &'tcx Expr<'_>,
1216 expr: &'tcx Expr<'_>,
1218 if let Some(higher::Range {
1222 }) = higher::range(arg)
1224 // the var must be a single name
1225 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1226 let mut starts = vec![Start {
1228 kind: StartKind::Range,
1231 // This is one of few ways to return different iterators
1232 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1233 let mut iter_a = None;
1234 let mut iter_b = None;
1236 if let ExprKind::Block(block, _) = body.kind {
1237 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1238 starts.extend(loop_counters);
1240 iter_a = Some(get_assignments(cx, block, &starts));
1242 iter_b = Some(get_assignment(body));
1245 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1247 let big_sugg = assignments
1248 // The only statements in the for loops can be indexed assignments from
1249 // indexed retrievals (except increments of loop counters).
1251 o.and_then(|(lhs, rhs)| {
1252 let rhs = fetch_cloned_expr(rhs);
1254 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1255 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1256 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1257 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1258 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1259 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1261 // Source and destination must be different
1262 if var_def_id(cx, base_left) != var_def_id(cx, base_right);
1264 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1265 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1272 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1273 .collect::<Option<Vec<_>>>()
1274 .filter(|v| !v.is_empty())
1275 .map(|v| v.join("\n "));
1277 if let Some(big_sugg) = big_sugg {
1281 get_span_of_entire_for_loop(expr),
1282 "it looks like you're manually copying between slices",
1283 "try replacing the loop by",
1285 Applicability::Unspecified,
1294 // Scans the body of the for loop and determines whether lint should be given
1295 struct SameItemPushVisitor<'a, 'tcx> {
1297 // this field holds the last vec push operation visited, which should be the only push seen
1298 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1299 cx: &'a LateContext<'tcx>,
1302 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1303 type Map = Map<'tcx>;
1305 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1307 // Non-determinism may occur ... don't give a lint
1308 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1309 ExprKind::Block(block, _) => self.visit_block(block),
1314 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1315 for stmt in b.stmts.iter() {
1316 self.visit_stmt(stmt);
1320 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1321 let vec_push_option = get_vec_push(self.cx, s);
1322 if vec_push_option.is_none() {
1323 // Current statement is not a push so visit inside
1325 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1329 // Current statement is a push ...check whether another
1330 // push had been previously done
1331 if self.vec_push.is_none() {
1332 self.vec_push = vec_push_option;
1334 // There are multiple pushes ... don't lint
1335 self.should_lint = false;
1340 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1341 NestedVisitorMap::None
1345 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1346 // the Vec being pushed into and the item being pushed
1347 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1349 // Extract method being called
1350 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1351 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1352 // Figure out the parameters for the method call
1353 if let Some(self_expr) = args.get(0);
1354 if let Some(pushed_item) = args.get(1);
1355 // Check that the method being called is push() on a Vec
1356 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::vec_type);
1357 if path.ident.name.as_str() == "push";
1359 return Some((self_expr, pushed_item))
1365 /// Detects for loop pushing the same item into a Vec
1366 fn detect_same_item_push<'tcx>(
1367 cx: &LateContext<'tcx>,
1370 body: &'tcx Expr<'_>,
1373 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1374 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1375 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1381 "it looks like the same item is being pushed into this Vec",
1384 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1385 item_str, vec_str, item_str
1390 if !matches!(pat.kind, PatKind::Wild) {
1394 // Determine whether it is safe to lint the body
1395 let mut same_item_push_visitor = SameItemPushVisitor {
1400 walk_expr(&mut same_item_push_visitor, body);
1401 if same_item_push_visitor.should_lint {
1402 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1403 let vec_ty = cx.typeck_results().expr_ty(vec);
1404 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1409 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1411 // Make sure that the push does not involve possibly mutating values
1412 match pushed_item.kind {
1413 ExprKind::Path(ref qpath) => {
1414 match qpath_res(cx, qpath, pushed_item.hir_id) {
1415 // immutable bindings that are initialized with literal or constant
1416 Res::Local(hir_id) => {
1418 let node = cx.tcx.hir().get(hir_id);
1419 if let Node::Binding(pat) = node;
1420 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1421 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1422 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1423 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1424 if let Some(init) = parent_let_expr.init;
1427 // immutable bindings that are initialized with literal
1428 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1429 // immutable bindings that are initialized with constant
1430 ExprKind::Path(ref path) => {
1431 if let Res::Def(DefKind::Const, ..) = qpath_res(cx, path, init.hir_id) {
1432 emit_lint(cx, vec, pushed_item);
1441 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1445 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1453 /// Checks for looping over a range and then indexing a sequence with it.
1454 /// The iteratee must be a range literal.
1455 #[allow(clippy::too_many_lines)]
1456 fn check_for_loop_range<'tcx>(
1457 cx: &LateContext<'tcx>,
1459 arg: &'tcx Expr<'_>,
1460 body: &'tcx Expr<'_>,
1461 expr: &'tcx Expr<'_>,
1463 if let Some(higher::Range {
1467 }) = higher::range(arg)
1469 // the var must be a single name
1470 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1471 let mut visitor = VarVisitor {
1474 indexed_mut: FxHashSet::default(),
1475 indexed_indirectly: FxHashMap::default(),
1476 indexed_directly: FxHashMap::default(),
1477 referenced: FxHashSet::default(),
1479 prefer_mutable: false,
1481 walk_expr(&mut visitor, body);
1483 // linting condition: we only indexed one variable, and indexed it directly
1484 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1485 let (indexed, (indexed_extent, indexed_ty)) = visitor
1489 .expect("already checked that we have exactly 1 element");
1491 // ensure that the indexed variable was declared before the loop, see #601
1492 if let Some(indexed_extent) = indexed_extent {
1493 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1494 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1495 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1496 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1497 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1502 // don't lint if the container that is indexed does not have .iter() method
1503 let has_iter = has_iter_method(cx, indexed_ty);
1504 if has_iter.is_none() {
1508 // don't lint if the container that is indexed into is also used without
1510 if visitor.referenced.contains(&indexed) {
1514 let starts_at_zero = is_integer_const(cx, start, 0);
1516 let skip = if starts_at_zero {
1518 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
1521 format!(".skip({})", snippet(cx, start.span, ".."))
1524 let mut end_is_start_plus_val = false;
1526 let take = if let Some(end) = *end {
1527 let mut take_expr = end;
1529 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1530 if let BinOpKind::Add = op.node {
1531 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1532 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1534 if start_equal_left {
1536 } else if start_equal_right {
1540 end_is_start_plus_val = start_equal_left | start_equal_right;
1544 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1546 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
1550 ast::RangeLimits::Closed => {
1551 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1552 format!(".take({})", take_expr + sugg::ONE)
1554 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1561 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1562 ("mut ", "iter_mut")
1567 let take_is_empty = take.is_empty();
1568 let mut method_1 = take;
1569 let mut method_2 = skip;
1571 if end_is_start_plus_val {
1572 mem::swap(&mut method_1, &mut method_2);
1575 if visitor.nonindex {
1578 NEEDLESS_RANGE_LOOP,
1580 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1584 "consider using an iterator",
1586 (pat.span, format!("({}, <item>)", ident.name)),
1589 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1596 let repl = if starts_at_zero && take_is_empty {
1597 format!("&{}{}", ref_mut, indexed)
1599 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1604 NEEDLESS_RANGE_LOOP,
1607 "the loop variable `{}` is only used to index `{}`.",
1613 "consider using an iterator",
1614 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1624 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1626 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1627 if len_args.len() == 1;
1628 if method.ident.name == sym!(len);
1629 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1630 if path.segments.len() == 1;
1631 if path.segments[0].ident.name == var;
1640 fn is_end_eq_array_len<'tcx>(
1641 cx: &LateContext<'tcx>,
1643 limits: ast::RangeLimits,
1644 indexed_ty: Ty<'tcx>,
1647 if let ExprKind::Lit(ref lit) = end.kind;
1648 if let ast::LitKind::Int(end_int, _) = lit.node;
1649 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1650 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1652 return match limits {
1653 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1654 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1662 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1663 let mut applicability = Applicability::MachineApplicable;
1664 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1665 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1670 "it is more concise to loop over references to containers instead of using explicit \
1672 "to write this more concisely, try",
1673 format!("&{}{}", muta, object),
1678 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1679 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1680 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1681 // just the receiver, no arguments
1682 if args.len() == 1 {
1683 let method_name = &*method.ident.as_str();
1684 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1685 if method_name == "iter" || method_name == "iter_mut" {
1686 if is_ref_iterable_type(cx, &args[0]) {
1687 lint_iter_method(cx, args, arg, method_name);
1689 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1690 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1691 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1692 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1693 let mut applicability = Applicability::MachineApplicable;
1694 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1697 EXPLICIT_INTO_ITER_LOOP,
1699 "it is more concise to loop over containers instead of using explicit \
1701 "to write this more concisely, try",
1706 let ref_receiver_ty = cx.tcx.mk_ref(
1707 cx.tcx.lifetimes.re_erased,
1710 mutbl: Mutability::Not,
1713 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1714 lint_iter_method(cx, args, arg, method_name)
1717 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1722 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1723 probably not what you want",
1725 next_loop_linted = true;
1729 if !next_loop_linted {
1730 check_arg_type(cx, pat, arg);
1734 /// Checks for `for` loops over `Option`s and `Result`s.
1735 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1736 let ty = cx.typeck_results().expr_ty(arg);
1737 if is_type_diagnostic_item(cx, ty, sym::option_type) {
1740 FOR_LOOPS_OVER_FALLIBLES,
1743 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1744 `if let` statement.",
1745 snippet(cx, arg.span, "_")
1749 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1750 snippet(cx, pat.span, "_"),
1751 snippet(cx, arg.span, "_")
1754 } else if is_type_diagnostic_item(cx, ty, sym::result_type) {
1757 FOR_LOOPS_OVER_FALLIBLES,
1760 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1761 `if let` statement.",
1762 snippet(cx, arg.span, "_")
1766 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1767 snippet(cx, pat.span, "_"),
1768 snippet(cx, arg.span, "_")
1774 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1775 // incremented exactly once in the loop body, and initialized to zero
1776 // at the start of the loop.
1777 fn check_for_loop_explicit_counter<'tcx>(
1778 cx: &LateContext<'tcx>,
1780 arg: &'tcx Expr<'_>,
1781 body: &'tcx Expr<'_>,
1782 expr: &'tcx Expr<'_>,
1784 // Look for variables that are incremented once per loop iteration.
1785 let mut increment_visitor = IncrementVisitor::new(cx);
1786 walk_expr(&mut increment_visitor, body);
1788 // For each candidate, check the parent block to see if
1789 // it's initialized to zero at the start of the loop.
1790 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1791 for id in increment_visitor.into_results() {
1792 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1793 walk_block(&mut initialize_visitor, block);
1796 if let Some((name, initializer)) = initialize_visitor.get_result();
1797 if is_integer_const(cx, initializer, 0);
1799 let mut applicability = Applicability::MachineApplicable;
1801 let for_span = get_span_of_entire_for_loop(expr);
1805 EXPLICIT_COUNTER_LOOP,
1806 for_span.with_hi(arg.span.hi()),
1807 &format!("the variable `{}` is used as a loop counter.", name),
1810 "for ({}, {}) in {}.enumerate()",
1812 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1813 make_iterator_snippet(cx, arg, &mut applicability),
1823 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1824 /// actual `Iterator` that the loop uses.
1825 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1826 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1827 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1832 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1835 // (&x).into_iter() ==> x.iter()
1836 // (&mut x).into_iter() ==> x.iter_mut()
1838 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1839 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1841 let meth_name = match mutability {
1842 Mutability::Mut => "iter_mut",
1843 Mutability::Not => "iter",
1847 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1853 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1859 /// Checks for the `FOR_KV_MAP` lint.
1860 fn check_for_loop_over_map_kv<'tcx>(
1861 cx: &LateContext<'tcx>,
1863 arg: &'tcx Expr<'_>,
1864 body: &'tcx Expr<'_>,
1865 expr: &'tcx Expr<'_>,
1867 let pat_span = pat.span;
1869 if let PatKind::Tuple(ref pat, _) = pat.kind {
1871 let arg_span = arg.span;
1872 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1873 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1874 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1875 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1880 let mutbl = match mutbl {
1881 Mutability::Not => "",
1882 Mutability::Mut => "_mut",
1884 let arg = match arg.kind {
1885 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1889 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1894 &format!("you seem to want to iterate on a map's {}s", kind),
1896 let map = sugg::Sugg::hir(cx, arg, "map");
1899 "use the corresponding method",
1901 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1902 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1912 fn check_for_single_element_loop<'tcx>(
1913 cx: &LateContext<'tcx>,
1915 arg: &'tcx Expr<'_>,
1916 body: &'tcx Expr<'_>,
1917 expr: &'tcx Expr<'_>,
1920 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg_expr) = arg.kind;
1921 if let PatKind::Binding(.., target, _) = pat.kind;
1922 if let ExprKind::Array(ref arg_expr_list) = arg_expr.kind;
1923 if let [arg_expression] = arg_expr_list;
1924 if let ExprKind::Path(ref list_item) = arg_expression.kind;
1925 if let Some(list_item_name) = single_segment_path(list_item).map(|ps| ps.ident.name);
1926 if let ExprKind::Block(ref block, _) = body.kind;
1927 if !block.stmts.is_empty();
1930 let for_span = get_span_of_entire_for_loop(expr);
1931 let mut block_str = snippet(cx, block.span, "..").into_owned();
1932 block_str.remove(0);
1938 SINGLE_ELEMENT_LOOP,
1940 "for loop over a single element",
1942 format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),
1943 Applicability::MachineApplicable
1949 struct MutatePairDelegate<'a, 'tcx> {
1950 cx: &'a LateContext<'tcx>,
1951 hir_id_low: Option<HirId>,
1952 hir_id_high: Option<HirId>,
1953 span_low: Option<Span>,
1954 span_high: Option<Span>,
1957 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1958 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: HirId, _: ConsumeMode) {}
1960 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId, bk: ty::BorrowKind) {
1961 if let ty::BorrowKind::MutBorrow = bk {
1962 if let PlaceBase::Local(id) = cmt.place.base {
1963 if Some(id) == self.hir_id_low {
1964 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
1966 if Some(id) == self.hir_id_high {
1967 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
1973 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId) {
1974 if let PlaceBase::Local(id) = cmt.place.base {
1975 if Some(id) == self.hir_id_low {
1976 self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
1978 if Some(id) == self.hir_id_high {
1979 self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
1985 impl MutatePairDelegate<'_, '_> {
1986 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1987 (self.span_low, self.span_high)
1991 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1992 if let Some(higher::Range {
1996 }) = higher::range(arg)
1998 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1999 if mut_ids[0].is_some() || mut_ids[1].is_some() {
2000 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
2001 mut_warn_with_span(cx, span_low);
2002 mut_warn_with_span(cx, span_high);
2007 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
2008 if let Some(sp) = span {
2013 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
2018 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
2020 if let ExprKind::Path(ref qpath) = bound.kind;
2021 if let QPath::Resolved(None, _) = *qpath;
2023 let res = qpath_res(cx, qpath, bound.hir_id);
2024 if let Res::Local(hir_id) = res {
2025 let node_str = cx.tcx.hir().get(hir_id);
2027 if let Node::Binding(pat) = node_str;
2028 if let PatKind::Binding(bind_ann, ..) = pat.kind;
2029 if let BindingAnnotation::Mutable = bind_ann;
2031 return Some(hir_id);
2040 fn check_for_mutation<'tcx>(
2041 cx: &LateContext<'tcx>,
2043 bound_ids: &[Option<HirId>],
2044 ) -> (Option<Span>, Option<Span>) {
2045 let mut delegate = MutatePairDelegate {
2047 hir_id_low: bound_ids[0],
2048 hir_id_high: bound_ids[1],
2052 cx.tcx.infer_ctxt().enter(|infcx| {
2053 ExprUseVisitor::new(
2058 cx.typeck_results(),
2062 delegate.mutation_span()
2065 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
2066 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
2068 PatKind::Wild => true,
2069 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
2074 struct LocalUsedVisitor<'a, 'tcx> {
2075 cx: &'a LateContext<'tcx>,
2080 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
2081 type Map = Map<'tcx>;
2083 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2084 if same_var(self.cx, expr, self.local) {
2087 walk_expr(self, expr);
2091 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2092 NestedVisitorMap::None
2096 struct VarVisitor<'a, 'tcx> {
2097 /// context reference
2098 cx: &'a LateContext<'tcx>,
2099 /// var name to look for as index
2101 /// indexed variables that are used mutably
2102 indexed_mut: FxHashSet<Symbol>,
2103 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2104 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2105 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2106 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2107 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2108 /// Any names that are used outside an index operation.
2109 /// Used to detect things like `&mut vec` used together with `vec[i]`
2110 referenced: FxHashSet<Symbol>,
2111 /// has the loop variable been used in expressions other than the index of
2114 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2115 /// takes `&mut self`
2116 prefer_mutable: bool,
2119 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2120 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2122 // the indexed container is referenced by a name
2123 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2124 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2125 if seqvar.segments.len() == 1;
2127 let index_used_directly = same_var(self.cx, idx, self.var);
2128 let indexed_indirectly = {
2129 let mut used_visitor = LocalUsedVisitor {
2134 walk_expr(&mut used_visitor, idx);
2138 if indexed_indirectly || index_used_directly {
2139 if self.prefer_mutable {
2140 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2142 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
2144 Res::Local(hir_id) => {
2145 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2146 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2147 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2148 if indexed_indirectly {
2149 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2151 if index_used_directly {
2152 self.indexed_directly.insert(
2153 seqvar.segments[0].ident.name,
2154 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2157 return false; // no need to walk further *on the variable*
2159 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2160 if indexed_indirectly {
2161 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2163 if index_used_directly {
2164 self.indexed_directly.insert(
2165 seqvar.segments[0].ident.name,
2166 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2169 return false; // no need to walk further *on the variable*
2180 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2181 type Map = Map<'tcx>;
2183 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2186 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2187 if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX))
2188 || (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2189 if !self.check(&args[1], &args[0], expr);
2195 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2196 if !self.check(idx, seqexpr, expr);
2201 // directly using a variable
2202 if let ExprKind::Path(ref qpath) = expr.kind;
2203 if let QPath::Resolved(None, ref path) = *qpath;
2204 if path.segments.len() == 1;
2206 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2207 if local_id == self.var {
2208 self.nonindex = true;
2210 // not the correct variable, but still a variable
2211 self.referenced.insert(path.segments[0].ident.name);
2217 let old = self.prefer_mutable;
2219 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2220 self.prefer_mutable = true;
2221 self.visit_expr(lhs);
2222 self.prefer_mutable = false;
2223 self.visit_expr(rhs);
2225 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2226 if mutbl == Mutability::Mut {
2227 self.prefer_mutable = true;
2229 self.visit_expr(expr);
2231 ExprKind::Call(ref f, args) => {
2234 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2235 self.prefer_mutable = false;
2236 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2237 if mutbl == Mutability::Mut {
2238 self.prefer_mutable = true;
2241 self.visit_expr(expr);
2244 ExprKind::MethodCall(_, _, args, _) => {
2245 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2246 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2247 self.prefer_mutable = false;
2248 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2249 if mutbl == Mutability::Mut {
2250 self.prefer_mutable = true;
2253 self.visit_expr(expr);
2256 ExprKind::Closure(_, _, body_id, ..) => {
2257 let body = self.cx.tcx.hir().body(body_id);
2258 self.visit_expr(&body.value);
2260 _ => walk_expr(self, expr),
2262 self.prefer_mutable = old;
2264 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2265 NestedVisitorMap::None
2269 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2270 let def_id = match var_def_id(cx, expr) {
2272 None => return false,
2274 if let Some(used_mutably) = mutated_variables(container, cx) {
2275 if used_mutably.contains(&def_id) {
2282 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2283 let def_id = match var_def_id(cx, iter_expr) {
2285 None => return false,
2287 let mut visitor = VarUsedAfterLoopVisitor {
2290 iter_expr_id: iter_expr.hir_id,
2291 past_while_let: false,
2292 var_used_after_while_let: false,
2294 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2295 walk_block(&mut visitor, enclosing_block);
2297 visitor.var_used_after_while_let
2300 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2301 cx: &'a LateContext<'tcx>,
2303 iter_expr_id: HirId,
2304 past_while_let: bool,
2305 var_used_after_while_let: bool,
2308 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2309 type Map = Map<'tcx>;
2311 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2312 if self.past_while_let {
2313 if Some(self.def_id) == var_def_id(self.cx, expr) {
2314 self.var_used_after_while_let = true;
2316 } else if self.iter_expr_id == expr.hir_id {
2317 self.past_while_let = true;
2319 walk_expr(self, expr);
2321 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2322 NestedVisitorMap::None
2326 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2327 /// for `&T` and `&mut T`, such as `Vec`.
2329 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2330 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2331 // will allow further borrows afterwards
2332 let ty = cx.typeck_results().expr_ty(e);
2333 is_iterable_array(ty, cx) ||
2334 is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2335 match_type(cx, ty, &paths::LINKED_LIST) ||
2336 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2337 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2338 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2339 match_type(cx, ty, &paths::BINARY_HEAP) ||
2340 match_type(cx, ty, &paths::BTREEMAP) ||
2341 match_type(cx, ty, &paths::BTREESET)
2344 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2345 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2347 ty::Array(_, n) => n
2348 .try_eval_usize(cx.tcx, cx.param_env)
2349 .map_or(false, |val| (0..=32).contains(&val)),
2354 /// If a block begins with a statement (possibly a `let` binding) and has an
2355 /// expression, return it.
2356 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2357 if block.stmts.is_empty() {
2360 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2361 local.init //.map(|expr| expr)
2367 /// If a block begins with an expression (with or without semicolon), return it.
2368 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2370 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2371 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2372 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2373 StmtKind::Local(..) | StmtKind::Item(..) => None,
2379 /// Returns `true` if expr contains a single break expr without destination label
2381 /// passed expression. The expression may be within a block.
2382 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2384 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2385 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2390 #[derive(Debug, PartialEq)]
2391 enum IncrementVisitorVarState {
2392 Initial, // Not examined yet
2393 IncrOnce, // Incremented exactly once, may be a loop counter
2397 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2398 struct IncrementVisitor<'a, 'tcx> {
2399 cx: &'a LateContext<'tcx>, // context reference
2400 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2401 depth: u32, // depth of conditional expressions
2405 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2406 fn new(cx: &'a LateContext<'tcx>) -> Self {
2409 states: FxHashMap::default(),
2415 fn into_results(self) -> impl Iterator<Item = HirId> {
2416 self.states.into_iter().filter_map(|(id, state)| {
2417 if state == IncrementVisitorVarState::IncrOnce {
2426 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2427 type Map = Map<'tcx>;
2429 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2434 // If node is a variable
2435 if let Some(def_id) = var_def_id(self.cx, expr) {
2436 if let Some(parent) = get_parent_expr(self.cx, expr) {
2437 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2438 if *state == IncrementVisitorVarState::IncrOnce {
2439 *state = IncrementVisitorVarState::DontWarn;
2444 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2445 if lhs.hir_id == expr.hir_id {
2446 *state = if op.node == BinOpKind::Add
2447 && is_integer_const(self.cx, rhs, 1)
2448 && *state == IncrementVisitorVarState::Initial
2451 IncrementVisitorVarState::IncrOnce
2453 // Assigned some other value or assigned multiple times
2454 IncrementVisitorVarState::DontWarn
2458 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2459 *state = IncrementVisitorVarState::DontWarn
2461 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2462 *state = IncrementVisitorVarState::DontWarn
2468 walk_expr(self, expr);
2469 } else if is_loop(expr) || is_conditional(expr) {
2471 walk_expr(self, expr);
2473 } else if let ExprKind::Continue(_) = expr.kind {
2476 walk_expr(self, expr);
2479 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2480 NestedVisitorMap::None
2484 enum InitializeVisitorState<'hir> {
2485 Initial, // Not examined yet
2486 Declared(Symbol), // Declared but not (yet) initialized
2489 initializer: &'hir Expr<'hir>,
2494 /// Checks whether a variable is initialized at the start of a loop and not modified
2495 /// and used after the loop.
2496 struct InitializeVisitor<'a, 'tcx> {
2497 cx: &'a LateContext<'tcx>, // context reference
2498 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2500 state: InitializeVisitorState<'tcx>,
2501 depth: u32, // depth of conditional expressions
2505 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2506 fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2511 state: InitializeVisitorState::Initial,
2517 fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
2518 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2519 Some((name, initializer))
2526 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2527 type Map = Map<'tcx>;
2529 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2530 // Look for declarations of the variable
2532 if let StmtKind::Local(ref local) = stmt.kind;
2533 if local.pat.hir_id == self.var_id;
2534 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2536 self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
2537 InitializeVisitorState::Initialized {
2544 walk_stmt(self, stmt);
2547 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2548 if matches!(self.state, InitializeVisitorState::DontWarn) {
2551 if expr.hir_id == self.end_expr.hir_id {
2552 self.past_loop = true;
2555 // No need to visit expressions before the variable is
2557 if matches!(self.state, InitializeVisitorState::Initial) {
2561 // If node is the desired variable, see how it's used
2562 if var_def_id(self.cx, expr) == Some(self.var_id) {
2564 self.state = InitializeVisitorState::DontWarn;
2568 if let Some(parent) = get_parent_expr(self.cx, expr) {
2570 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2571 self.state = InitializeVisitorState::DontWarn;
2573 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2574 self.state = if_chain! {
2576 if let InitializeVisitorState::Declared(name)
2577 | InitializeVisitorState::Initialized { name, ..} = self.state;
2579 InitializeVisitorState::Initialized { initializer: rhs, name }
2581 InitializeVisitorState::DontWarn
2585 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2586 self.state = InitializeVisitorState::DontWarn
2592 walk_expr(self, expr);
2593 } else if !self.past_loop && is_loop(expr) {
2594 self.state = InitializeVisitorState::DontWarn;
2595 } else if is_conditional(expr) {
2597 walk_expr(self, expr);
2600 walk_expr(self, expr);
2604 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2605 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2609 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2610 if let ExprKind::Path(ref qpath) = expr.kind {
2611 let path_res = qpath_res(cx, qpath, expr.hir_id);
2612 if let Res::Local(hir_id) = path_res {
2613 return Some(hir_id);
2619 fn is_loop(expr: &Expr<'_>) -> bool {
2620 matches!(expr.kind, ExprKind::Loop(..))
2623 fn is_conditional(expr: &Expr<'_>) -> bool {
2624 matches!(expr.kind, ExprKind::Match(..))
2627 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2629 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2630 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2631 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2633 return is_loop_nested(cx, loop_expr, iter_expr)
2639 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2640 let mut id = loop_expr.hir_id;
2641 let iter_name = if let Some(name) = path_name(iter_expr) {
2647 let parent = cx.tcx.hir().get_parent_node(id);
2651 match cx.tcx.hir().find(parent) {
2652 Some(Node::Expr(expr)) => {
2653 if let ExprKind::Loop(..) = expr.kind {
2657 Some(Node::Block(block)) => {
2658 let mut block_visitor = LoopNestVisitor {
2660 iterator: iter_name,
2663 walk_block(&mut block_visitor, block);
2664 if block_visitor.nesting == RuledOut {
2668 Some(Node::Stmt(_)) => (),
2677 #[derive(PartialEq, Eq)]
2679 Unknown, // no nesting detected yet
2680 RuledOut, // the iterator is initialized or assigned within scope
2681 LookFurther, // no nesting detected, no further walk required
2684 use self::Nesting::{LookFurther, RuledOut, Unknown};
2686 struct LoopNestVisitor {
2692 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2693 type Map = Map<'tcx>;
2695 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2696 if stmt.hir_id == self.hir_id {
2697 self.nesting = LookFurther;
2698 } else if self.nesting == Unknown {
2699 walk_stmt(self, stmt);
2703 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2704 if self.nesting != Unknown {
2707 if expr.hir_id == self.hir_id {
2708 self.nesting = LookFurther;
2712 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2713 if match_var(path, self.iterator) {
2714 self.nesting = RuledOut;
2717 _ => walk_expr(self, expr),
2721 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2722 if self.nesting != Unknown {
2725 if let PatKind::Binding(.., span_name, _) = pat.kind {
2726 if self.iterator == span_name.name {
2727 self.nesting = RuledOut;
2734 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2735 NestedVisitorMap::None
2739 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2740 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2741 let segments = &path.segments;
2742 if segments.len() == 1 {
2743 return Some(segments[0].ident.name);
2749 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2750 if constant(cx, cx.typeck_results(), cond).is_some() {
2751 // A pure constant condition (e.g., `while false`) is not linted.
2755 let mut var_visitor = VarCollectorVisitor {
2757 ids: FxHashSet::default(),
2758 def_ids: FxHashMap::default(),
2761 var_visitor.visit_expr(cond);
2762 if var_visitor.skip {
2765 let used_in_condition = &var_visitor.ids;
2766 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2767 used_in_condition.is_disjoint(&used_mutably)
2771 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2773 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2774 has_break_or_return: false,
2776 has_break_or_return_visitor.visit_expr(expr);
2777 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2779 if no_cond_variable_mutated && !mutable_static_in_cond {
2782 WHILE_IMMUTABLE_CONDITION,
2784 "variables in the condition are not mutated in the loop body",
2786 diag.note("this may lead to an infinite or to a never running loop");
2788 if has_break_or_return {
2789 diag.note("this loop contains `return`s or `break`s");
2790 diag.help("rewrite it as `if cond { loop { } }`");
2797 struct HasBreakOrReturnVisitor {
2798 has_break_or_return: bool,
2801 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2802 type Map = Map<'tcx>;
2804 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2805 if self.has_break_or_return {
2810 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2811 self.has_break_or_return = true;
2817 walk_expr(self, expr);
2820 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2821 NestedVisitorMap::None
2825 /// Collects the set of variables in an expression
2826 /// Stops analysis if a function call is found
2827 /// Note: In some cases such as `self`, there are no mutable annotation,
2828 /// All variables definition IDs are collected
2829 struct VarCollectorVisitor<'a, 'tcx> {
2830 cx: &'a LateContext<'tcx>,
2831 ids: FxHashSet<HirId>,
2832 def_ids: FxHashMap<def_id::DefId, bool>,
2836 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2837 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2839 if let ExprKind::Path(ref qpath) = ex.kind;
2840 if let QPath::Resolved(None, _) = *qpath;
2841 let res = qpath_res(self.cx, qpath, ex.hir_id);
2844 Res::Local(hir_id) => {
2845 self.ids.insert(hir_id);
2847 Res::Def(DefKind::Static, def_id) => {
2848 let mutable = self.cx.tcx.is_mutable_static(def_id);
2849 self.def_ids.insert(def_id, mutable);
2858 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2859 type Map = Map<'tcx>;
2861 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2863 ExprKind::Path(_) => self.insert_def_id(ex),
2864 // If there is any function/method call… we just stop analysis
2865 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2867 _ => walk_expr(self, ex),
2871 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2872 NestedVisitorMap::None
2876 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2878 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2879 check_needless_collect_direct_usage(expr, cx);
2880 check_needless_collect_indirect_usage(expr, cx);
2882 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2884 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2885 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2886 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2887 if let Some(ref generic_args) = chain_method.args;
2888 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2890 let ty = cx.typeck_results().node_type(ty.hir_id);
2891 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2892 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2893 match_type(cx, ty, &paths::BTREEMAP) ||
2894 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2895 if method.ident.name == sym!(len) {
2896 let span = shorten_needless_collect_span(expr);
2901 NEEDLESS_COLLECT_MSG,
2903 "count()".to_string(),
2904 Applicability::MachineApplicable,
2907 if method.ident.name == sym!(is_empty) {
2908 let span = shorten_needless_collect_span(expr);
2913 NEEDLESS_COLLECT_MSG,
2915 "next().is_none()".to_string(),
2916 Applicability::MachineApplicable,
2919 if method.ident.name == sym!(contains) {
2920 let contains_arg = snippet(cx, args[1].span, "??");
2921 let span = shorten_needless_collect_span(expr);
2926 NEEDLESS_COLLECT_MSG,
2928 let (arg, pred) = contains_arg
2930 .map_or(("&x", &*contains_arg), |s| ("x", s));
2931 diag.span_suggestion(
2935 "any(|{}| x == {})",
2938 Applicability::MachineApplicable,
2948 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2949 if let ExprKind::Block(ref block, _) = expr.kind {
2950 for ref stmt in block.stmts {
2952 if let StmtKind::Local(
2953 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2954 init: Some(ref init_expr), .. }
2956 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2957 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2958 if let Some(ref generic_args) = method_name.args;
2959 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2960 if let ty = cx.typeck_results().node_type(ty.hir_id);
2961 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2962 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2963 match_type(cx, ty, &paths::LINKED_LIST);
2964 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2965 if iter_calls.len() == 1;
2967 // Suggest replacing iter_call with iter_replacement, and removing stmt
2968 let iter_call = &iter_calls[0];
2972 stmt.span.until(iter_call.span),
2973 NEEDLESS_COLLECT_MSG,
2975 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2976 diag.multipart_suggestion(
2977 iter_call.get_suggestion_text(),
2979 (stmt.span, String::new()),
2980 (iter_call.span, iter_replacement)
2982 Applicability::MachineApplicable,// MaybeIncorrect,
2992 struct IterFunction {
2993 func: IterFunctionKind,
2997 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2999 IterFunctionKind::IntoIter => String::new(),
3000 IterFunctionKind::Len => String::from(".count()"),
3001 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
3002 IterFunctionKind::Contains(span) => {
3003 let s = snippet(cx, *span, "..");
3004 if let Some(stripped) = s.strip_prefix('&') {
3005 format!(".any(|x| x == {})", stripped)
3007 format!(".any(|x| x == *{})", s)
3012 fn get_suggestion_text(&self) -> &'static str {
3014 IterFunctionKind::IntoIter => {
3015 "Use the original Iterator instead of collecting it and then producing a new one"
3017 IterFunctionKind::Len => {
3018 "Take the original Iterator's count instead of collecting it and finding the length"
3020 IterFunctionKind::IsEmpty => {
3021 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
3023 IterFunctionKind::Contains(_) => {
3024 "Check if the original Iterator contains an element instead of collecting then checking"
3029 enum IterFunctionKind {
3036 struct IterFunctionVisitor {
3037 uses: Vec<IterFunction>,
3041 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
3042 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
3043 // Check function calls on our collection
3045 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
3046 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
3047 if let &[name] = &path.segments;
3048 if name.ident == self.target;
3050 let len = sym!(len);
3051 let is_empty = sym!(is_empty);
3052 let contains = sym!(contains);
3053 match method_name.ident.name {
3054 sym::into_iter => self.uses.push(
3055 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
3057 name if name == len => self.uses.push(
3058 IterFunction { func: IterFunctionKind::Len, span: expr.span }
3060 name if name == is_empty => self.uses.push(
3061 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
3063 name if name == contains => self.uses.push(
3064 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
3066 _ => self.seen_other = true,
3071 // Check if the collection is used for anything else
3073 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
3074 if let &[name] = &path.segments;
3075 if name.ident == self.target;
3077 self.seen_other = true;
3079 walk_expr(self, expr);
3084 type Map = Map<'tcx>;
3085 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3086 NestedVisitorMap::None
3090 /// Detect the occurrences of calls to `iter` or `into_iter` for the
3091 /// given identifier
3092 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
3093 let mut visitor = IterFunctionVisitor {
3098 visitor.visit_block(block);
3099 if visitor.seen_other {
3106 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3108 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3109 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3111 return expr.span.with_lo(span.lo());