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 get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
7 is_integer_const, is_no_std_crate, is_refutable, is_type_diagnostic_item, last_path_segment, match_trait_method,
8 match_type, match_var, multispan_sugg, qpath_res, snippet, snippet_opt, snippet_with_applicability,
9 snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then, sugg,
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?** Those busy loops burn CPU cycles without doing
298 /// anything. Think of the environment and either block on something or at least
299 /// make the thread sleep for some microseconds.
301 /// **Known problems:** None.
309 "empty `loop {}`, which should block or sleep"
312 declare_clippy_lint! {
313 /// **What it does:** Checks for `while let` expressions on iterators.
315 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
316 /// the intent better.
318 /// **Known problems:** None.
322 /// while let Some(val) = iter() {
326 pub WHILE_LET_ON_ITERATOR,
328 "using a while-let loop instead of a for loop on an iterator"
331 declare_clippy_lint! {
332 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
333 /// ignoring either the keys or values.
335 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
336 /// can be used to express that don't need the values or keys.
338 /// **Known problems:** None.
342 /// for (k, _) in &map {
347 /// could be replaced by
350 /// for k in map.keys() {
356 "looping on a map using `iter` when `keys` or `values` would do"
359 declare_clippy_lint! {
360 /// **What it does:** Checks for loops that will always `break`, `return` or
361 /// `continue` an outer loop.
363 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
366 /// **Known problems:** None
377 "any loop that will always `break` or `return`"
380 declare_clippy_lint! {
381 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
383 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
385 /// **Known problems:** None
389 /// let mut foo = 42;
390 /// for i in 0..foo {
392 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
397 "for loop over a range where one of the bounds is a mutable variable"
400 declare_clippy_lint! {
401 /// **What it does:** Checks whether variables used within while loop condition
402 /// can be (and are) mutated in the body.
404 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
405 /// will lead to an infinite loop.
407 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
408 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
409 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
415 /// println!("let me loop forever!");
418 pub WHILE_IMMUTABLE_CONDITION,
420 "variables used within while expression are not mutated in the body"
423 declare_clippy_lint! {
424 /// **What it does:** Checks whether a for loop is being used to push a constant
425 /// value into a Vec.
427 /// **Why is this bad?** This kind of operation can be expressed more succinctly with
428 /// `vec![item;SIZE]` or `vec.resize(NEW_SIZE, item)` and using these alternatives may also
429 /// have better performance.
430 /// **Known problems:** None
436 /// let mut vec: Vec<u8> = Vec::new();
444 /// could be written as
448 /// let mut vec: Vec<u8> = vec![item1; 20];
449 /// vec.resize(20 + 30, item2);
453 "the same item is pushed inside of a for loop"
456 declare_lint_pass!(Loops => [
460 EXPLICIT_INTO_ITER_LOOP,
462 FOR_LOOPS_OVER_FALLIBLES,
465 EXPLICIT_COUNTER_LOOP,
467 WHILE_LET_ON_ITERATOR,
471 WHILE_IMMUTABLE_CONDITION,
475 impl<'tcx> LateLintPass<'tcx> for Loops {
476 #[allow(clippy::too_many_lines)]
477 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
478 if let Some((pat, arg, body)) = higher::for_loop(expr) {
479 // we don't want to check expanded macros
480 // this check is not at the top of the function
481 // since higher::for_loop expressions are marked as expansions
482 if body.span.from_expansion() {
485 check_for_loop(cx, pat, arg, body, expr);
488 // we don't want to check expanded macros
489 if expr.span.from_expansion() {
493 // check for never_loop
494 if let ExprKind::Loop(ref block, _, _) = expr.kind {
495 match never_loop_block(block, expr.hir_id) {
496 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
497 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
501 // check for `loop { if let {} else break }` that could be `while let`
502 // (also matches an explicit "match" instead of "if let")
503 // (even if the "match" or "if let" is used for declaration)
504 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
505 // also check for empty `loop {}` statements
506 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) {
511 "empty `loop {}` detected. You may want to either use `panic!()` or add \
512 `std::thread::sleep(..);` to the loop body.",
516 // extract the expression from the first statement (if any) in a block
517 let inner_stmt_expr = extract_expr_from_first_stmt(block);
518 // or extract the first expression (if any) from the block
519 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
520 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
521 // ensure "if let" compatible match structure
523 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
525 && arms[0].guard.is_none()
526 && arms[1].guard.is_none()
527 && is_simple_break_expr(&arms[1].body)
529 if in_external_macro(cx.sess(), expr.span) {
533 // NOTE: we used to build a body here instead of using
534 // ellipsis, this was removed because:
535 // 1) it was ugly with big bodies;
536 // 2) it was not indented properly;
537 // 3) it wasn’t very smart (see #675).
538 let mut applicability = Applicability::HasPlaceholders;
543 "this loop could be written as a `while let` loop",
546 "while let {} = {} {{ .. }}",
547 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
548 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
559 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
560 let pat = &arms[0].pat.kind;
562 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
563 &ExprKind::MethodCall(ref method_path, _, ref method_args, _),
564 ) = (pat, &match_expr.kind)
566 let iter_expr = &method_args[0];
568 // Don't lint when the iterator is recreated on every iteration
570 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
571 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
572 if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
578 let lhs_constructor = last_path_segment(qpath);
579 if method_path.ident.name == sym!(next)
580 && match_trait_method(cx, match_expr, &paths::ITERATOR)
581 && lhs_constructor.ident.name == sym!(Some)
582 && (pat_args.is_empty()
583 || !is_refutable(cx, &pat_args[0])
584 && !is_used_inside(cx, iter_expr, &arms[0].body)
585 && !is_iterator_used_after_while_let(cx, iter_expr)
586 && !is_nested(cx, expr, &method_args[0]))
588 let mut applicability = Applicability::MachineApplicable;
589 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
590 let loop_var = if pat_args.is_empty() {
593 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
597 WHILE_LET_ON_ITERATOR,
598 expr.span.with_hi(match_expr.span.hi()),
599 "this loop could be written as a `for` loop",
601 format!("for {} in {}", loop_var, iterator),
608 if let Some((cond, body)) = higher::while_loop(&expr) {
609 check_infinite_loop(cx, cond, body);
612 check_needless_collect(expr, cx);
616 enum NeverLoopResult {
617 // A break/return always get triggered but not necessarily for the main loop.
619 // A continue may occur for the main loop.
625 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
627 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
628 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
632 // Combine two results for parts that are called in order.
634 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
636 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
637 NeverLoopResult::Otherwise => second,
641 // Combine two results where both parts are called but not necessarily in order.
643 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
644 match (left, right) {
645 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
646 NeverLoopResult::MayContinueMainLoop
648 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
649 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
653 // Combine two results where only one of the part may have been executed.
655 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
657 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
658 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
659 NeverLoopResult::MayContinueMainLoop
661 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
665 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
666 let stmts = block.stmts.iter().map(stmt_to_expr);
667 let expr = once(block.expr.as_deref());
668 let mut iter = stmts.chain(expr).filter_map(|e| e);
669 never_loop_expr_seq(&mut iter, main_loop_id)
672 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
674 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
675 StmtKind::Local(ref local) => local.init.as_deref(),
680 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
683 | ExprKind::Unary(_, ref e)
684 | ExprKind::Cast(ref e, _)
685 | ExprKind::Type(ref e, _)
686 | ExprKind::Field(ref e, _)
687 | ExprKind::AddrOf(_, _, ref e)
688 | ExprKind::Struct(_, _, Some(ref e))
689 | ExprKind::Repeat(ref e, _)
690 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
691 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
692 never_loop_expr_all(&mut es.iter(), main_loop_id)
694 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
695 ExprKind::Binary(_, ref e1, ref e2)
696 | ExprKind::Assign(ref e1, ref e2, _)
697 | ExprKind::AssignOp(_, ref e1, ref e2)
698 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
699 ExprKind::Loop(ref b, _, _) => {
700 // Break can come from the inner loop so remove them.
701 absorb_break(&never_loop_block(b, main_loop_id))
703 ExprKind::Match(ref e, ref arms, _) => {
704 let e = never_loop_expr(e, main_loop_id);
708 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
712 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
713 ExprKind::Continue(d) => {
716 .expect("target ID can only be missing in the presence of compilation errors");
717 if id == main_loop_id {
718 NeverLoopResult::MayContinueMainLoop
720 NeverLoopResult::AlwaysBreak
723 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
724 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
726 ExprKind::InlineAsm(ref asm) => asm
730 InlineAsmOperand::In { expr, .. }
731 | InlineAsmOperand::InOut { expr, .. }
732 | InlineAsmOperand::Const { expr }
733 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
734 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
735 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
736 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
739 .fold(NeverLoopResult::Otherwise, combine_both),
740 ExprKind::Struct(_, _, None)
741 | ExprKind::Yield(_, _)
742 | ExprKind::Closure(_, _, _, _, _)
743 | ExprKind::LlvmInlineAsm(_)
746 | ExprKind::Err => NeverLoopResult::Otherwise,
750 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
751 es.map(|e| never_loop_expr(e, main_loop_id))
752 .fold(NeverLoopResult::Otherwise, combine_seq)
755 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
756 es.map(|e| never_loop_expr(e, main_loop_id))
757 .fold(NeverLoopResult::Otherwise, combine_both)
760 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
761 e.map(|e| never_loop_expr(e, main_loop_id))
762 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
765 fn check_for_loop<'tcx>(
766 cx: &LateContext<'tcx>,
769 body: &'tcx Expr<'_>,
770 expr: &'tcx Expr<'_>,
772 check_for_loop_range(cx, pat, arg, body, expr);
773 check_for_loop_arg(cx, pat, arg, expr);
774 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
775 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
776 check_for_mut_range_bound(cx, arg, body);
777 detect_manual_memcpy(cx, pat, arg, body, expr);
778 detect_same_item_push(cx, pat, arg, body, expr);
781 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
783 if let ExprKind::Path(qpath) = &expr.kind;
784 if let QPath::Resolved(None, path) = qpath;
785 if path.segments.len() == 1;
786 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
796 #[derive(Clone, Copy)]
803 value: MinifyingSugg<'static>,
808 fn negative(value: MinifyingSugg<'static>) -> Self {
811 sign: OffsetSign::Negative,
815 fn positive(value: MinifyingSugg<'static>) -> Self {
818 sign: OffsetSign::Positive,
823 Self::positive(MinifyingSugg::non_paren("0"))
827 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
829 OffsetSign::Positive => lhs + &rhs.value,
830 OffsetSign::Negative => lhs - &rhs.value,
835 struct MinifyingSugg<'a>(sugg::Sugg<'a>);
837 impl std::fmt::Display for MinifyingSugg<'_> {
838 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
839 std::fmt::Display::fmt(&self.0, f)
843 impl<'a> MinifyingSugg<'a> {
844 fn as_str(&self) -> &str {
845 let sugg::Sugg::NonParen(s) | sugg::Sugg::MaybeParen(s) | sugg::Sugg::BinOp(_, s) = &self.0;
849 fn hir(cx: &LateContext<'_, '_>, expr: &Expr<'_>, default: &'a str) -> Self {
850 Self(sugg::Sugg::hir(cx, expr, default))
853 fn maybe_par(self) -> Self {
854 Self(self.0.maybe_par())
857 fn non_paren(str: impl Into<std::borrow::Cow<'a, str>>) -> Self {
858 Self(sugg::Sugg::NonParen(str.into()))
862 impl std::ops::Add for &MinifyingSugg<'static> {
863 type Output = MinifyingSugg<'static>;
864 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
865 match (self.as_str(), rhs.as_str()) {
866 ("0", _) => rhs.clone(),
867 (_, "0") => self.clone(),
868 (_, _) => MinifyingSugg(&self.0 + &rhs.0),
873 impl std::ops::Sub for &MinifyingSugg<'static> {
874 type Output = MinifyingSugg<'static>;
875 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
876 match (self.as_str(), rhs.as_str()) {
877 (_, "0") => self.clone(),
878 ("0", _) => MinifyingSugg(-(rhs.0.clone())),
879 (x, y) if x == y => MinifyingSugg::non_paren("0"),
880 (_, _) => MinifyingSugg(&self.0 - &rhs.0),
885 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
886 type Output = MinifyingSugg<'static>;
887 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
888 match (self.as_str(), rhs.as_str()) {
889 ("0", _) => rhs.clone(),
891 (_, _) => MinifyingSugg(self.0 + &rhs.0),
896 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
897 type Output = MinifyingSugg<'static>;
898 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
899 match (self.as_str(), rhs.as_str()) {
901 ("0", _) => MinifyingSugg(-(rhs.0.clone())),
902 (x, y) if x == y => MinifyingSugg::non_paren("0"),
903 (_, _) => MinifyingSugg(self.0 - &rhs.0),
908 #[derive(Debug, Clone, Copy)]
909 enum StartKind<'hir> {
911 Counter { initializer: &'hir Expr<'hir> },
914 struct IndexExpr<'hir> {
915 base: &'hir Expr<'hir>,
916 idx: StartKind<'hir>,
922 kind: StartKind<'hir>,
925 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
926 let is_slice = match ty.kind() {
927 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
928 ty::Slice(..) | ty::Array(..) => true,
932 is_slice || is_type_diagnostic_item(cx, ty, sym!(vec_type)) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
935 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
937 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
938 if method.ident.name == sym!(clone);
940 if let Some(arg) = args.get(0);
941 then { arg } else { expr }
945 fn get_details_from_idx<'tcx>(
946 cx: &LateContext<'tcx>,
948 starts: &[Start<'tcx>],
949 ) -> Option<(StartKind<'tcx>, Offset)> {
951 cx: &LateContext<'tcx>,
953 starts: &[Start<'tcx>],
954 ) -> Option<StartKind<'tcx>> {
955 starts.iter().find_map(|start| {
956 if same_var(cx, e, start.id) {
965 cx: &LateContext<'tcx>,
967 starts: &[Start<'tcx>],
968 ) -> Option<MinifyingSugg<'static>> {
970 ExprKind::Lit(l) => match l.node {
971 ast::LitKind::Int(x, _ty) => Some(MinifyingSugg::non_paren(x.to_string())),
974 ExprKind::Path(..) if get_start(cx, e, starts).is_none() => {
975 // `e` is always non paren as it's a `Path`
976 Some(MinifyingSugg::non_paren(snippet(cx, e.span, "???")))
983 ExprKind::Binary(op, lhs, rhs) => match op.node {
985 let offset_opt = if let Some(s) = get_start(cx, lhs, starts) {
986 get_offset(cx, rhs, starts).map(|o| (s, o))
987 } else if let Some(s) = get_start(cx, rhs, starts) {
988 get_offset(cx, lhs, starts).map(|o| (s, o))
993 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
996 get_start(cx, lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
1000 ExprKind::Path(..) => get_start(cx, idx, starts).map(|s| (s, Offset::empty())),
1005 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1006 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1013 fn get_assignments<'a: 'c, 'tcx: 'c, 'c>(
1014 cx: &'a LateContext<'a, 'tcx>,
1015 stmts: &'tcx [Stmt<'tcx>],
1016 expr: Option<&'tcx Expr<'tcx>>,
1017 loop_counters: &'c [Start<'tcx>],
1018 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'c {
1021 .filter_map(move |stmt| match stmt.kind {
1022 StmtKind::Local(..) | StmtKind::Item(..) => None,
1023 StmtKind::Expr(e) | StmtKind::Semi(e) => if_chain! {
1024 if let ExprKind::AssignOp(_, var, _) = e.kind;
1025 // skip StartKind::Range
1026 if loop_counters.iter().skip(1).any(|counter| Some(counter.id) == var_def_id(cx, var));
1027 then { None } else { Some(e) }
1030 .chain(expr.into_iter())
1031 .map(get_assignment)
1034 fn get_loop_counters<'a, 'tcx>(
1035 cx: &'a LateContext<'a, 'tcx>,
1036 body: &'tcx Block<'tcx>,
1037 expr: &'tcx Expr<'_>,
1038 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1039 // Look for variables that are incremented once per loop iteration.
1040 let mut increment_visitor = IncrementVisitor::new(cx);
1041 walk_block(&mut increment_visitor, body);
1043 // For each candidate, check the parent block to see if
1044 // it's initialized to zero at the start of the loop.
1045 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1048 .filter_map(move |var_id| {
1049 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1050 walk_block(&mut initialize_visitor, block);
1052 initialize_visitor.get_result().map(|(_, initializer)| Start {
1054 kind: StartKind::Counter { initializer },
1063 fn build_manual_memcpy_suggestion<'tcx>(
1064 cx: &LateContext<'tcx>,
1067 limits: ast::RangeLimits,
1068 dst: &IndexExpr<'_>,
1069 src: &IndexExpr<'_>,
1071 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1072 if offset.as_str() == "0" {
1073 MinifyingSugg::non_paren("")
1080 |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| -> MinifyingSugg<'static> {
1082 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1083 if method.ident.name == sym!(len);
1084 if len_args.len() == 1;
1085 if let Some(arg) = len_args.get(0);
1086 if var_def_id(cx, arg) == var_def_id(cx, base);
1088 if sugg.as_str() == end_str {
1089 MinifyingSugg::non_paren("")
1095 ast::RangeLimits::Closed => {
1096 sugg + &MinifyingSugg::non_paren("1")
1098 ast::RangeLimits::HalfOpen => sugg,
1104 let start_str = MinifyingSugg::hir(cx, start, "");
1105 let end_str = MinifyingSugg::hir(cx, end, "");
1107 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1108 StartKind::Range => (
1109 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)),
1114 apply_offset(&end_str, &idx_expr.idx_offset),
1117 StartKind::Counter { initializer } => {
1118 let counter_start = MinifyingSugg::hir(cx, initializer, "");
1120 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)),
1125 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1131 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1132 let (src_offset, src_limit) = print_offset_and_limit(&src);
1134 let dst_base_str = snippet_opt(cx, dst.base.span).unwrap_or_else(|| "???".into());
1135 let src_base_str = snippet_opt(cx, src.base.span).unwrap_or_else(|| "???".into());
1137 let dst = if dst_offset.as_str() == "" && dst_limit.as_str() == "" {
1143 dst_offset.maybe_par(),
1144 dst_limit.maybe_par()
1149 "{}.clone_from_slice(&{}[{}..{}])",
1152 src_offset.maybe_par(),
1153 src_limit.maybe_par()
1157 /// Checks for for loops that sequentially copy items from one slice-like
1158 /// object to another.
1159 fn detect_manual_memcpy<'tcx>(
1160 cx: &LateContext<'tcx>,
1162 arg: &'tcx Expr<'_>,
1163 body: &'tcx Expr<'_>,
1164 expr: &'tcx Expr<'_>,
1166 if let Some(higher::Range {
1170 }) = higher::range(arg)
1172 // the var must be a single name
1173 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1174 let mut starts = vec![Start {
1176 kind: StartKind::Range,
1179 // This is one of few ways to return different iterators
1180 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1181 let mut iter_a = None;
1182 let mut iter_b = None;
1184 if let ExprKind::Block(block, _) = body.kind {
1185 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1186 starts.extend(loop_counters);
1188 iter_a = Some(get_assignments(cx, block.stmts, block.expr, &starts));
1190 iter_b = Some(get_assignment(body));
1193 // The only statements in the for loops can be indexed assignments from
1194 // indexed retrievals.
1195 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1197 let big_sugg = assignments
1199 o.and_then(|(lhs, rhs)| {
1200 let rhs = fetch_cloned_expr(rhs);
1202 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1203 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1204 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1205 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1206 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1207 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1209 // Source and destination must be different
1210 if var_def_id(cx, base_left) != var_def_id(cx, base_right);
1212 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1213 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1220 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1221 .collect::<Option<Vec<_>>>()
1222 .filter(|v| !v.is_empty())
1223 .map(|v| v.join("\n "));
1225 if let Some(big_sugg) = big_sugg {
1230 "it looks like you're manually copying between slices",
1231 "try replacing the loop by",
1233 Applicability::Unspecified,
1240 // Scans the body of the for loop and determines whether lint should be given
1241 struct SameItemPushVisitor<'a, 'tcx> {
1243 // this field holds the last vec push operation visited, which should be the only push seen
1244 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1245 cx: &'a LateContext<'tcx>,
1248 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1249 type Map = Map<'tcx>;
1251 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1253 // Non-determinism may occur ... don't give a lint
1254 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1255 ExprKind::Block(block, _) => self.visit_block(block),
1260 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1261 for stmt in b.stmts.iter() {
1262 self.visit_stmt(stmt);
1266 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1267 let vec_push_option = get_vec_push(self.cx, s);
1268 if vec_push_option.is_none() {
1269 // Current statement is not a push so visit inside
1271 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1275 // Current statement is a push ...check whether another
1276 // push had been previously done
1277 if self.vec_push.is_none() {
1278 self.vec_push = vec_push_option;
1280 // There are multiple pushes ... don't lint
1281 self.should_lint = false;
1286 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1287 NestedVisitorMap::None
1291 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1292 // the Vec being pushed into and the item being pushed
1293 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1295 // Extract method being called
1296 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1297 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1298 // Figure out the parameters for the method call
1299 if let Some(self_expr) = args.get(0);
1300 if let Some(pushed_item) = args.get(1);
1301 // Check that the method being called is push() on a Vec
1302 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym!(vec_type));
1303 if path.ident.name.as_str() == "push";
1305 return Some((self_expr, pushed_item))
1311 /// Detects for loop pushing the same item into a Vec
1312 fn detect_same_item_push<'tcx>(
1313 cx: &LateContext<'tcx>,
1316 body: &'tcx Expr<'_>,
1319 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1320 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1321 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1327 "it looks like the same item is being pushed into this Vec",
1330 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1331 item_str, vec_str, item_str
1336 if !matches!(pat.kind, PatKind::Wild) {
1340 // Determine whether it is safe to lint the body
1341 let mut same_item_push_visitor = SameItemPushVisitor {
1346 walk_expr(&mut same_item_push_visitor, body);
1347 if same_item_push_visitor.should_lint {
1348 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1349 let vec_ty = cx.typeck_results().expr_ty(vec);
1350 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1355 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1357 // Make sure that the push does not involve possibly mutating values
1358 match pushed_item.kind {
1359 ExprKind::Path(ref qpath) => {
1360 match qpath_res(cx, qpath, pushed_item.hir_id) {
1361 // immutable bindings that are initialized with literal or constant
1362 Res::Local(hir_id) => {
1364 let node = cx.tcx.hir().get(hir_id);
1365 if let Node::Binding(pat) = node;
1366 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1367 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1368 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1369 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1370 if let Some(init) = parent_let_expr.init;
1373 // immutable bindings that are initialized with literal
1374 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1375 // immutable bindings that are initialized with constant
1376 ExprKind::Path(ref path) => {
1377 if let Res::Def(DefKind::Const, ..) = qpath_res(cx, path, init.hir_id) {
1378 emit_lint(cx, vec, pushed_item);
1387 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1391 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1399 /// Checks for looping over a range and then indexing a sequence with it.
1400 /// The iteratee must be a range literal.
1401 #[allow(clippy::too_many_lines)]
1402 fn check_for_loop_range<'tcx>(
1403 cx: &LateContext<'tcx>,
1405 arg: &'tcx Expr<'_>,
1406 body: &'tcx Expr<'_>,
1407 expr: &'tcx Expr<'_>,
1409 if let Some(higher::Range {
1413 }) = higher::range(arg)
1415 // the var must be a single name
1416 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1417 let mut visitor = VarVisitor {
1420 indexed_mut: FxHashSet::default(),
1421 indexed_indirectly: FxHashMap::default(),
1422 indexed_directly: FxHashMap::default(),
1423 referenced: FxHashSet::default(),
1425 prefer_mutable: false,
1427 walk_expr(&mut visitor, body);
1429 // linting condition: we only indexed one variable, and indexed it directly
1430 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1431 let (indexed, (indexed_extent, indexed_ty)) = visitor
1435 .expect("already checked that we have exactly 1 element");
1437 // ensure that the indexed variable was declared before the loop, see #601
1438 if let Some(indexed_extent) = indexed_extent {
1439 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1440 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1441 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1442 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1443 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1448 // don't lint if the container that is indexed does not have .iter() method
1449 let has_iter = has_iter_method(cx, indexed_ty);
1450 if has_iter.is_none() {
1454 // don't lint if the container that is indexed into is also used without
1456 if visitor.referenced.contains(&indexed) {
1460 let starts_at_zero = is_integer_const(cx, start, 0);
1462 let skip = if starts_at_zero {
1465 format!(".skip({})", snippet(cx, start.span, ".."))
1468 let mut end_is_start_plus_val = false;
1470 let take = if let Some(end) = *end {
1471 let mut take_expr = end;
1473 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1474 if let BinOpKind::Add = op.node {
1475 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1476 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1478 if start_equal_left {
1480 } else if start_equal_right {
1484 end_is_start_plus_val = start_equal_left | start_equal_right;
1488 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1492 ast::RangeLimits::Closed => {
1493 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1494 format!(".take({})", take_expr + sugg::ONE)
1496 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1503 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1504 ("mut ", "iter_mut")
1509 let take_is_empty = take.is_empty();
1510 let mut method_1 = take;
1511 let mut method_2 = skip;
1513 if end_is_start_plus_val {
1514 mem::swap(&mut method_1, &mut method_2);
1517 if visitor.nonindex {
1520 NEEDLESS_RANGE_LOOP,
1522 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1526 "consider using an iterator",
1528 (pat.span, format!("({}, <item>)", ident.name)),
1531 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1538 let repl = if starts_at_zero && take_is_empty {
1539 format!("&{}{}", ref_mut, indexed)
1541 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1546 NEEDLESS_RANGE_LOOP,
1549 "the loop variable `{}` is only used to index `{}`.",
1555 "consider using an iterator",
1556 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1566 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1568 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1569 if len_args.len() == 1;
1570 if method.ident.name == sym!(len);
1571 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1572 if path.segments.len() == 1;
1573 if path.segments[0].ident.name == var;
1582 fn is_end_eq_array_len<'tcx>(
1583 cx: &LateContext<'tcx>,
1585 limits: ast::RangeLimits,
1586 indexed_ty: Ty<'tcx>,
1589 if let ExprKind::Lit(ref lit) = end.kind;
1590 if let ast::LitKind::Int(end_int, _) = lit.node;
1591 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1592 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1594 return match limits {
1595 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1596 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1604 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1605 let mut applicability = Applicability::MachineApplicable;
1606 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1607 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1612 "it is more concise to loop over references to containers instead of using explicit \
1614 "to write this more concisely, try",
1615 format!("&{}{}", muta, object),
1620 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1621 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1622 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1623 // just the receiver, no arguments
1624 if args.len() == 1 {
1625 let method_name = &*method.ident.as_str();
1626 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1627 if method_name == "iter" || method_name == "iter_mut" {
1628 if is_ref_iterable_type(cx, &args[0]) {
1629 lint_iter_method(cx, args, arg, method_name);
1631 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1632 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1633 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1634 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1635 let mut applicability = Applicability::MachineApplicable;
1636 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1639 EXPLICIT_INTO_ITER_LOOP,
1641 "it is more concise to loop over containers instead of using explicit \
1643 "to write this more concisely, try",
1648 let ref_receiver_ty = cx.tcx.mk_ref(
1649 cx.tcx.lifetimes.re_erased,
1652 mutbl: Mutability::Not,
1655 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1656 lint_iter_method(cx, args, arg, method_name)
1659 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1664 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1665 probably not what you want",
1667 next_loop_linted = true;
1671 if !next_loop_linted {
1672 check_arg_type(cx, pat, arg);
1676 /// Checks for `for` loops over `Option`s and `Result`s.
1677 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1678 let ty = cx.typeck_results().expr_ty(arg);
1679 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1682 FOR_LOOPS_OVER_FALLIBLES,
1685 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1686 `if let` statement.",
1687 snippet(cx, arg.span, "_")
1691 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1692 snippet(cx, pat.span, "_"),
1693 snippet(cx, arg.span, "_")
1696 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1699 FOR_LOOPS_OVER_FALLIBLES,
1702 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1703 `if let` statement.",
1704 snippet(cx, arg.span, "_")
1708 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1709 snippet(cx, pat.span, "_"),
1710 snippet(cx, arg.span, "_")
1716 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1717 // incremented exactly once in the loop body, and initialized to zero
1718 // at the start of the loop.
1719 fn check_for_loop_explicit_counter<'tcx>(
1720 cx: &LateContext<'tcx>,
1722 arg: &'tcx Expr<'_>,
1723 body: &'tcx Expr<'_>,
1724 expr: &'tcx Expr<'_>,
1726 // Look for variables that are incremented once per loop iteration.
1727 let mut increment_visitor = IncrementVisitor::new(cx);
1728 walk_expr(&mut increment_visitor, body);
1730 // For each candidate, check the parent block to see if
1731 // it's initialized to zero at the start of the loop.
1732 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1733 for id in increment_visitor.into_results() {
1734 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1735 walk_block(&mut initialize_visitor, block);
1738 if let Some((name, initializer)) = initialize_visitor.get_result();
1739 if is_integer_const(cx, initializer, 0);
1741 let mut applicability = Applicability::MachineApplicable;
1743 // for some reason this is the only way to get the `Span`
1744 // of the entire `for` loop
1745 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1753 EXPLICIT_COUNTER_LOOP,
1754 for_span.with_hi(arg.span.hi()),
1755 &format!("the variable `{}` is used as a loop counter.", name),
1758 "for ({}, {}) in {}.enumerate()",
1760 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1761 make_iterator_snippet(cx, arg, &mut applicability),
1771 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1772 /// actual `Iterator` that the loop uses.
1773 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1774 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1775 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1780 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1783 // (&x).into_iter() ==> x.iter()
1784 // (&mut x).into_iter() ==> x.iter_mut()
1786 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1787 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1789 let meth_name = match mutability {
1790 Mutability::Mut => "iter_mut",
1791 Mutability::Not => "iter",
1795 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1801 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1807 /// Checks for the `FOR_KV_MAP` lint.
1808 fn check_for_loop_over_map_kv<'tcx>(
1809 cx: &LateContext<'tcx>,
1811 arg: &'tcx Expr<'_>,
1812 body: &'tcx Expr<'_>,
1813 expr: &'tcx Expr<'_>,
1815 let pat_span = pat.span;
1817 if let PatKind::Tuple(ref pat, _) = pat.kind {
1819 let arg_span = arg.span;
1820 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1821 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1822 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1823 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1828 let mutbl = match mutbl {
1829 Mutability::Not => "",
1830 Mutability::Mut => "_mut",
1832 let arg = match arg.kind {
1833 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1837 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1842 &format!("you seem to want to iterate on a map's {}s", kind),
1844 let map = sugg::Sugg::hir(cx, arg, "map");
1847 "use the corresponding method",
1849 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1850 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1860 struct MutatePairDelegate<'a, 'tcx> {
1861 cx: &'a LateContext<'tcx>,
1862 hir_id_low: Option<HirId>,
1863 hir_id_high: Option<HirId>,
1864 span_low: Option<Span>,
1865 span_high: Option<Span>,
1868 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1869 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1871 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1872 if let ty::BorrowKind::MutBorrow = bk {
1873 if let PlaceBase::Local(id) = cmt.place.base {
1874 if Some(id) == self.hir_id_low {
1875 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1877 if Some(id) == self.hir_id_high {
1878 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1884 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>) {
1885 if let PlaceBase::Local(id) = cmt.place.base {
1886 if Some(id) == self.hir_id_low {
1887 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1889 if Some(id) == self.hir_id_high {
1890 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1896 impl MutatePairDelegate<'_, '_> {
1897 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1898 (self.span_low, self.span_high)
1902 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1903 if let Some(higher::Range {
1907 }) = higher::range(arg)
1909 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1910 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1911 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1912 mut_warn_with_span(cx, span_low);
1913 mut_warn_with_span(cx, span_high);
1918 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
1919 if let Some(sp) = span {
1924 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1929 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
1931 if let ExprKind::Path(ref qpath) = bound.kind;
1932 if let QPath::Resolved(None, _) = *qpath;
1934 let res = qpath_res(cx, qpath, bound.hir_id);
1935 if let Res::Local(hir_id) = res {
1936 let node_str = cx.tcx.hir().get(hir_id);
1938 if let Node::Binding(pat) = node_str;
1939 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1940 if let BindingAnnotation::Mutable = bind_ann;
1942 return Some(hir_id);
1951 fn check_for_mutation<'tcx>(
1952 cx: &LateContext<'tcx>,
1954 bound_ids: &[Option<HirId>],
1955 ) -> (Option<Span>, Option<Span>) {
1956 let mut delegate = MutatePairDelegate {
1958 hir_id_low: bound_ids[0],
1959 hir_id_high: bound_ids[1],
1963 let def_id = body.hir_id.owner.to_def_id();
1964 cx.tcx.infer_ctxt().enter(|infcx| {
1965 ExprUseVisitor::new(
1968 def_id.expect_local(),
1970 cx.typeck_results(),
1974 delegate.mutation_span()
1977 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1978 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
1980 PatKind::Wild => true,
1981 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
1986 struct LocalUsedVisitor<'a, 'tcx> {
1987 cx: &'a LateContext<'tcx>,
1992 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1993 type Map = Map<'tcx>;
1995 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1996 if same_var(self.cx, expr, self.local) {
1999 walk_expr(self, expr);
2003 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2004 NestedVisitorMap::None
2008 struct VarVisitor<'a, 'tcx> {
2009 /// context reference
2010 cx: &'a LateContext<'tcx>,
2011 /// var name to look for as index
2013 /// indexed variables that are used mutably
2014 indexed_mut: FxHashSet<Symbol>,
2015 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2016 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2017 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2018 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2019 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2020 /// Any names that are used outside an index operation.
2021 /// Used to detect things like `&mut vec` used together with `vec[i]`
2022 referenced: FxHashSet<Symbol>,
2023 /// has the loop variable been used in expressions other than the index of
2026 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2027 /// takes `&mut self`
2028 prefer_mutable: bool,
2031 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2032 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2034 // the indexed container is referenced by a name
2035 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2036 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2037 if seqvar.segments.len() == 1;
2039 let index_used_directly = same_var(self.cx, idx, self.var);
2040 let indexed_indirectly = {
2041 let mut used_visitor = LocalUsedVisitor {
2046 walk_expr(&mut used_visitor, idx);
2050 if indexed_indirectly || index_used_directly {
2051 if self.prefer_mutable {
2052 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2054 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
2056 Res::Local(hir_id) => {
2057 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2058 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2059 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2060 if indexed_indirectly {
2061 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2063 if index_used_directly {
2064 self.indexed_directly.insert(
2065 seqvar.segments[0].ident.name,
2066 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2069 return false; // no need to walk further *on the variable*
2071 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2072 if indexed_indirectly {
2073 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2075 if index_used_directly {
2076 self.indexed_directly.insert(
2077 seqvar.segments[0].ident.name,
2078 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2081 return false; // no need to walk further *on the variable*
2092 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2093 type Map = Map<'tcx>;
2095 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2098 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2099 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
2100 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2101 if !self.check(&args[1], &args[0], expr);
2107 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2108 if !self.check(idx, seqexpr, expr);
2113 // directly using a variable
2114 if let ExprKind::Path(ref qpath) = expr.kind;
2115 if let QPath::Resolved(None, ref path) = *qpath;
2116 if path.segments.len() == 1;
2118 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2119 if local_id == self.var {
2120 self.nonindex = true;
2122 // not the correct variable, but still a variable
2123 self.referenced.insert(path.segments[0].ident.name);
2129 let old = self.prefer_mutable;
2131 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2132 self.prefer_mutable = true;
2133 self.visit_expr(lhs);
2134 self.prefer_mutable = false;
2135 self.visit_expr(rhs);
2137 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2138 if mutbl == Mutability::Mut {
2139 self.prefer_mutable = true;
2141 self.visit_expr(expr);
2143 ExprKind::Call(ref f, args) => {
2146 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2147 self.prefer_mutable = false;
2148 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2149 if mutbl == Mutability::Mut {
2150 self.prefer_mutable = true;
2153 self.visit_expr(expr);
2156 ExprKind::MethodCall(_, _, args, _) => {
2157 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2158 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2159 self.prefer_mutable = false;
2160 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2161 if mutbl == Mutability::Mut {
2162 self.prefer_mutable = true;
2165 self.visit_expr(expr);
2168 ExprKind::Closure(_, _, body_id, ..) => {
2169 let body = self.cx.tcx.hir().body(body_id);
2170 self.visit_expr(&body.value);
2172 _ => walk_expr(self, expr),
2174 self.prefer_mutable = old;
2176 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2177 NestedVisitorMap::None
2181 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2182 let def_id = match var_def_id(cx, expr) {
2184 None => return false,
2186 if let Some(used_mutably) = mutated_variables(container, cx) {
2187 if used_mutably.contains(&def_id) {
2194 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2195 let def_id = match var_def_id(cx, iter_expr) {
2197 None => return false,
2199 let mut visitor = VarUsedAfterLoopVisitor {
2202 iter_expr_id: iter_expr.hir_id,
2203 past_while_let: false,
2204 var_used_after_while_let: false,
2206 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2207 walk_block(&mut visitor, enclosing_block);
2209 visitor.var_used_after_while_let
2212 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2213 cx: &'a LateContext<'tcx>,
2215 iter_expr_id: HirId,
2216 past_while_let: bool,
2217 var_used_after_while_let: bool,
2220 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2221 type Map = Map<'tcx>;
2223 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2224 if self.past_while_let {
2225 if Some(self.def_id) == var_def_id(self.cx, expr) {
2226 self.var_used_after_while_let = true;
2228 } else if self.iter_expr_id == expr.hir_id {
2229 self.past_while_let = true;
2231 walk_expr(self, expr);
2233 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2234 NestedVisitorMap::None
2238 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2239 /// for `&T` and `&mut T`, such as `Vec`.
2241 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2242 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2243 // will allow further borrows afterwards
2244 let ty = cx.typeck_results().expr_ty(e);
2245 is_iterable_array(ty, cx) ||
2246 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2247 match_type(cx, ty, &paths::LINKED_LIST) ||
2248 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2249 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2250 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2251 match_type(cx, ty, &paths::BINARY_HEAP) ||
2252 match_type(cx, ty, &paths::BTREEMAP) ||
2253 match_type(cx, ty, &paths::BTREESET)
2256 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2257 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2259 ty::Array(_, n) => n
2260 .try_eval_usize(cx.tcx, cx.param_env)
2261 .map_or(false, |val| (0..=32).contains(&val)),
2266 /// If a block begins with a statement (possibly a `let` binding) and has an
2267 /// expression, return it.
2268 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2269 if block.stmts.is_empty() {
2272 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2273 local.init //.map(|expr| expr)
2279 /// If a block begins with an expression (with or without semicolon), return it.
2280 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2282 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2283 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2284 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2285 StmtKind::Local(..) | StmtKind::Item(..) => None,
2291 /// Returns `true` if expr contains a single break expr without destination label
2293 /// passed expression. The expression may be within a block.
2294 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2296 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2297 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2302 #[derive(Debug, PartialEq)]
2303 enum IncrementVisitorVarState {
2304 Initial, // Not examined yet
2305 IncrOnce, // Incremented exactly once, may be a loop counter
2309 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2310 struct IncrementVisitor<'a, 'tcx> {
2311 cx: &'a LateContext<'tcx>, // context reference
2312 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2313 depth: u32, // depth of conditional expressions
2317 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2318 fn new(cx: &'a LateContext<'a, 'tcx>) -> Self {
2321 states: FxHashMap::default(),
2327 fn into_results(self) -> impl Iterator<Item = HirId> {
2328 self.states.into_iter().filter_map(|(id, state)| {
2329 if state == IncrementVisitorVarState::IncrOnce {
2338 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2339 type Map = Map<'tcx>;
2341 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2346 // If node is a variable
2347 if let Some(def_id) = var_def_id(self.cx, expr) {
2348 if let Some(parent) = get_parent_expr(self.cx, expr) {
2349 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2350 if *state == IncrementVisitorVarState::IncrOnce {
2351 *state = IncrementVisitorVarState::DontWarn;
2356 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2357 if lhs.hir_id == expr.hir_id {
2358 *state = if op.node == BinOpKind::Add
2359 && is_integer_const(self.cx, rhs, 1)
2360 && *state == IncrementVisitorVarState::Initial
2363 IncrementVisitorVarState::IncrOnce
2365 // Assigned some other value or assigned multiple times
2366 IncrementVisitorVarState::DontWarn
2370 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2371 *state = IncrementVisitorVarState::DontWarn
2373 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2374 *state = IncrementVisitorVarState::DontWarn
2380 walk_expr(self, expr);
2381 } else if is_loop(expr) || is_conditional(expr) {
2383 walk_expr(self, expr);
2385 } else if let ExprKind::Continue(_) = expr.kind {
2388 walk_expr(self, expr);
2391 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2392 NestedVisitorMap::None
2396 enum InitializeVisitorState<'hir> {
2397 Initial, // Not examined yet
2398 Declared(Symbol), // Declared but not (yet) initialized
2399 Initialized { name: Symbol, initializer: &'hir Expr<'hir> },
2403 /// Checks whether a variable is initialized at the start of a loop and not modified
2404 /// and used after the loop.
2405 struct InitializeVisitor<'a, 'tcx> {
2406 cx: &'a LateContext<'tcx>, // context reference
2407 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2409 state: InitializeVisitorState<'tcx>,
2410 depth: u32, // depth of conditional expressions
2414 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2415 fn new(cx: &'a LateContext<'a, 'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2420 state: InitializeVisitorState::Initial,
2426 fn get_result(&self) -> Option<(Name, &'tcx Expr<'tcx>)> {
2427 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2428 Some((name, initializer))
2435 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2436 type Map = Map<'tcx>;
2438 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2439 // Look for declarations of the variable
2441 if let StmtKind::Local(ref local) = stmt.kind;
2442 if local.pat.hir_id == self.var_id;
2443 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2445 self.state = if let Some(ref init) = local.init {
2446 InitializeVisitorState::Initialized {
2451 InitializeVisitorState::Declared(ident.name)
2455 walk_stmt(self, stmt);
2458 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2459 if matches!(self.state, InitializeVisitorState::DontWarn) {
2462 if expr.hir_id == self.end_expr.hir_id {
2463 self.past_loop = true;
2466 // No need to visit expressions before the variable is
2468 if matches!(self.state, InitializeVisitorState::Initial) {
2472 // If node is the desired variable, see how it's used
2473 if var_def_id(self.cx, expr) == Some(self.var_id) {
2475 self.state = InitializeVisitorState::DontWarn;
2479 if let Some(parent) = get_parent_expr(self.cx, expr) {
2481 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2482 self.state = InitializeVisitorState::DontWarn;
2484 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2485 self.state = if_chain! {
2487 if let InitializeVisitorState::Declared(name)
2488 | InitializeVisitorState::Initialized { name, ..} = self.state;
2490 InitializeVisitorState::Initialized { initializer: rhs, name }
2492 InitializeVisitorState::DontWarn
2496 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2497 self.state = InitializeVisitorState::DontWarn
2503 walk_expr(self, expr);
2504 } else if !self.past_loop && is_loop(expr) {
2505 self.state = InitializeVisitorState::DontWarn;
2506 } else if is_conditional(expr) {
2508 walk_expr(self, expr);
2511 walk_expr(self, expr);
2515 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2516 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2520 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2521 if let ExprKind::Path(ref qpath) = expr.kind {
2522 let path_res = qpath_res(cx, qpath, expr.hir_id);
2523 if let Res::Local(hir_id) = path_res {
2524 return Some(hir_id);
2530 fn is_loop(expr: &Expr<'_>) -> bool {
2531 matches!(expr.kind, ExprKind::Loop(..))
2534 fn is_conditional(expr: &Expr<'_>) -> bool {
2535 matches!(expr.kind, ExprKind::Match(..))
2538 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2540 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2541 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2542 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2544 return is_loop_nested(cx, loop_expr, iter_expr)
2550 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2551 let mut id = loop_expr.hir_id;
2552 let iter_name = if let Some(name) = path_name(iter_expr) {
2558 let parent = cx.tcx.hir().get_parent_node(id);
2562 match cx.tcx.hir().find(parent) {
2563 Some(Node::Expr(expr)) => {
2564 if let ExprKind::Loop(..) = expr.kind {
2568 Some(Node::Block(block)) => {
2569 let mut block_visitor = LoopNestVisitor {
2571 iterator: iter_name,
2574 walk_block(&mut block_visitor, block);
2575 if block_visitor.nesting == RuledOut {
2579 Some(Node::Stmt(_)) => (),
2588 #[derive(PartialEq, Eq)]
2590 Unknown, // no nesting detected yet
2591 RuledOut, // the iterator is initialized or assigned within scope
2592 LookFurther, // no nesting detected, no further walk required
2595 use self::Nesting::{LookFurther, RuledOut, Unknown};
2597 struct LoopNestVisitor {
2603 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2604 type Map = Map<'tcx>;
2606 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2607 if stmt.hir_id == self.hir_id {
2608 self.nesting = LookFurther;
2609 } else if self.nesting == Unknown {
2610 walk_stmt(self, stmt);
2614 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2615 if self.nesting != Unknown {
2618 if expr.hir_id == self.hir_id {
2619 self.nesting = LookFurther;
2623 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2624 if match_var(path, self.iterator) {
2625 self.nesting = RuledOut;
2628 _ => walk_expr(self, expr),
2632 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2633 if self.nesting != Unknown {
2636 if let PatKind::Binding(.., span_name, _) = pat.kind {
2637 if self.iterator == span_name.name {
2638 self.nesting = RuledOut;
2645 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2646 NestedVisitorMap::None
2650 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2651 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2652 let segments = &path.segments;
2653 if segments.len() == 1 {
2654 return Some(segments[0].ident.name);
2660 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2661 if constant(cx, cx.typeck_results(), cond).is_some() {
2662 // A pure constant condition (e.g., `while false`) is not linted.
2666 let mut var_visitor = VarCollectorVisitor {
2668 ids: FxHashSet::default(),
2669 def_ids: FxHashMap::default(),
2672 var_visitor.visit_expr(cond);
2673 if var_visitor.skip {
2676 let used_in_condition = &var_visitor.ids;
2677 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2678 used_in_condition.is_disjoint(&used_mutably)
2682 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2684 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2685 has_break_or_return: false,
2687 has_break_or_return_visitor.visit_expr(expr);
2688 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2690 if no_cond_variable_mutated && !mutable_static_in_cond {
2693 WHILE_IMMUTABLE_CONDITION,
2695 "variables in the condition are not mutated in the loop body",
2697 diag.note("this may lead to an infinite or to a never running loop");
2699 if has_break_or_return {
2700 diag.note("this loop contains `return`s or `break`s");
2701 diag.help("rewrite it as `if cond { loop { } }`");
2708 struct HasBreakOrReturnVisitor {
2709 has_break_or_return: bool,
2712 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2713 type Map = Map<'tcx>;
2715 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2716 if self.has_break_or_return {
2721 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2722 self.has_break_or_return = true;
2728 walk_expr(self, expr);
2731 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2732 NestedVisitorMap::None
2736 /// Collects the set of variables in an expression
2737 /// Stops analysis if a function call is found
2738 /// Note: In some cases such as `self`, there are no mutable annotation,
2739 /// All variables definition IDs are collected
2740 struct VarCollectorVisitor<'a, 'tcx> {
2741 cx: &'a LateContext<'tcx>,
2742 ids: FxHashSet<HirId>,
2743 def_ids: FxHashMap<def_id::DefId, bool>,
2747 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2748 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2750 if let ExprKind::Path(ref qpath) = ex.kind;
2751 if let QPath::Resolved(None, _) = *qpath;
2752 let res = qpath_res(self.cx, qpath, ex.hir_id);
2755 Res::Local(hir_id) => {
2756 self.ids.insert(hir_id);
2758 Res::Def(DefKind::Static, def_id) => {
2759 let mutable = self.cx.tcx.is_mutable_static(def_id);
2760 self.def_ids.insert(def_id, mutable);
2769 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2770 type Map = Map<'tcx>;
2772 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2774 ExprKind::Path(_) => self.insert_def_id(ex),
2775 // If there is any function/method call… we just stop analysis
2776 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2778 _ => walk_expr(self, ex),
2782 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2783 NestedVisitorMap::None
2787 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2789 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2790 check_needless_collect_direct_usage(expr, cx);
2791 check_needless_collect_indirect_usage(expr, cx);
2793 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2795 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2796 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2797 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2798 if let Some(ref generic_args) = chain_method.args;
2799 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2801 let ty = cx.typeck_results().node_type(ty.hir_id);
2802 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2803 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2804 match_type(cx, ty, &paths::BTREEMAP) ||
2805 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2806 if method.ident.name == sym!(len) {
2807 let span = shorten_needless_collect_span(expr);
2812 NEEDLESS_COLLECT_MSG,
2814 "count()".to_string(),
2815 Applicability::MachineApplicable,
2818 if method.ident.name == sym!(is_empty) {
2819 let span = shorten_needless_collect_span(expr);
2824 NEEDLESS_COLLECT_MSG,
2826 "next().is_none()".to_string(),
2827 Applicability::MachineApplicable,
2830 if method.ident.name == sym!(contains) {
2831 let contains_arg = snippet(cx, args[1].span, "??");
2832 let span = shorten_needless_collect_span(expr);
2837 NEEDLESS_COLLECT_MSG,
2839 let (arg, pred) = contains_arg
2841 .map_or(("&x", &*contains_arg), |s| ("x", s));
2842 diag.span_suggestion(
2846 "any(|{}| x == {})",
2849 Applicability::MachineApplicable,
2859 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2860 if let ExprKind::Block(ref block, _) = expr.kind {
2861 for ref stmt in block.stmts {
2863 if let StmtKind::Local(
2864 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2865 init: Some(ref init_expr), .. }
2867 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2868 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2869 if let Some(ref generic_args) = method_name.args;
2870 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2871 if let ty = cx.typeck_results().node_type(ty.hir_id);
2872 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2873 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2874 match_type(cx, ty, &paths::LINKED_LIST);
2875 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2876 if iter_calls.len() == 1;
2878 // Suggest replacing iter_call with iter_replacement, and removing stmt
2879 let iter_call = &iter_calls[0];
2883 stmt.span.until(iter_call.span),
2884 NEEDLESS_COLLECT_MSG,
2886 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2887 diag.multipart_suggestion(
2888 iter_call.get_suggestion_text(),
2890 (stmt.span, String::new()),
2891 (iter_call.span, iter_replacement)
2893 Applicability::MachineApplicable,// MaybeIncorrect,
2903 struct IterFunction {
2904 func: IterFunctionKind,
2908 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2910 IterFunctionKind::IntoIter => String::new(),
2911 IterFunctionKind::Len => String::from(".count()"),
2912 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2913 IterFunctionKind::Contains(span) => format!(".any(|x| x == {})", snippet(cx, *span, "..")),
2916 fn get_suggestion_text(&self) -> &'static str {
2918 IterFunctionKind::IntoIter => {
2919 "Use the original Iterator instead of collecting it and then producing a new one"
2921 IterFunctionKind::Len => {
2922 "Take the original Iterator's count instead of collecting it and finding the length"
2924 IterFunctionKind::IsEmpty => {
2925 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
2927 IterFunctionKind::Contains(_) => {
2928 "Check if the original Iterator contains an element instead of collecting then checking"
2933 enum IterFunctionKind {
2940 struct IterFunctionVisitor {
2941 uses: Vec<IterFunction>,
2945 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
2946 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
2947 // Check function calls on our collection
2949 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
2950 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
2951 if let &[name] = &path.segments;
2952 if name.ident == self.target;
2954 let len = sym!(len);
2955 let is_empty = sym!(is_empty);
2956 let contains = sym!(contains);
2957 match method_name.ident.name {
2958 sym::into_iter => self.uses.push(
2959 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
2961 name if name == len => self.uses.push(
2962 IterFunction { func: IterFunctionKind::Len, span: expr.span }
2964 name if name == is_empty => self.uses.push(
2965 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
2967 name if name == contains => self.uses.push(
2968 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
2970 _ => self.seen_other = true,
2975 // Check if the collection is used for anything else
2977 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
2978 if let &[name] = &path.segments;
2979 if name.ident == self.target;
2981 self.seen_other = true;
2983 walk_expr(self, expr);
2988 type Map = Map<'tcx>;
2989 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2990 NestedVisitorMap::None
2994 /// Detect the occurences of calls to `iter` or `into_iter` for the
2995 /// given identifier
2996 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
2997 let mut visitor = IterFunctionVisitor {
3002 visitor.visit_block(block);
3003 if visitor.seen_other {
3010 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3012 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3013 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3015 return expr.span.with_lo(span.lo());