1 use crate::consts::constant;
2 use crate::utils::paths;
3 use crate::utils::sugg::Sugg;
4 use crate::utils::usage::{is_unused, mutated_variables};
6 contains_name, get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
7 indent_of, is_integer_const, is_no_std_crate, is_refutable, is_type_diagnostic_item, last_path_segment,
8 match_trait_method, match_type, match_var, multispan_sugg, qpath_res, single_segment_path, snippet,
9 snippet_with_applicability, snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_sugg,
10 span_lint_and_then, sugg, SpanlessEq,
12 use if_chain::if_chain;
14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
15 use rustc_errors::Applicability;
16 use rustc_hir::def::{DefKind, Res};
17 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
19 def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, InlineAsmOperand,
20 Local, LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
22 use rustc_infer::infer::TyCtxtInferExt;
23 use rustc_lint::{LateContext, LateLintPass, LintContext};
24 use rustc_middle::hir::map::Map;
25 use rustc_middle::lint::in_external_macro;
26 use rustc_middle::middle::region;
27 use rustc_middle::ty::{self, Ty, TyS};
28 use rustc_session::{declare_lint_pass, declare_tool_lint};
29 use rustc_span::source_map::Span;
30 use rustc_span::symbol::{sym, Ident, Symbol};
31 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
32 use std::iter::{once, Iterator};
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// # let src = vec![1];
46 /// # let mut dst = vec![0; 65];
47 /// for i in 0..src.len() {
48 /// dst[i + 64] = src[i];
51 /// Could be written as:
53 /// # let src = vec![1];
54 /// # let mut dst = vec![0; 65];
55 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
59 "manually copying items between slices"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for looping over the range of `0..len` of some
64 /// collection just to get the values by index.
66 /// **Why is this bad?** Just iterating the collection itself makes the intent
67 /// more clear and is probably faster.
69 /// **Known problems:** None.
73 /// let vec = vec!['a', 'b', 'c'];
74 /// for i in 0..vec.len() {
75 /// println!("{}", vec[i]);
78 /// Could be written as:
80 /// let vec = vec!['a', 'b', 'c'];
82 /// println!("{}", i);
85 pub NEEDLESS_RANGE_LOOP,
87 "for-looping over a range of indices where an iterator over items would do"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
92 /// suggests the latter.
94 /// **Why is this bad?** Readability.
96 /// **Known problems:** False negatives. We currently only warn on some known
101 /// // with `y` a `Vec` or slice:
102 /// # let y = vec![1];
103 /// for x in y.iter() {
107 /// can be rewritten to
109 /// # let y = vec![1];
114 pub EXPLICIT_ITER_LOOP,
116 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
121 /// suggests the latter.
123 /// **Why is this bad?** Readability.
125 /// **Known problems:** None
129 /// # let y = vec![1];
130 /// // with `y` a `Vec` or slice:
131 /// for x in y.into_iter() {
135 /// can be rewritten to
137 /// # let y = vec![1];
142 pub EXPLICIT_INTO_ITER_LOOP,
144 "for-looping over `_.into_iter()` when `_` would do"
147 declare_clippy_lint! {
148 /// **What it does:** Checks for loops on `x.next()`.
150 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
151 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
152 /// implements `IntoIterator`, so that possibly one value will be iterated,
153 /// leading to some hard to find bugs. No one will want to write such code
154 /// [except to win an Underhanded Rust
155 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
157 /// **Known problems:** None.
161 /// for x in y.next() {
167 "for-looping over `_.next()` which is probably not intended"
170 declare_clippy_lint! {
171 /// **What it does:** Checks for `for` loops over `Option` or `Result` values.
173 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
176 /// **Known problems:** None.
180 /// # let opt = Some(1);
188 /// if let Some(x) = opt {
196 /// # let res: Result<i32, std::io::Error> = Ok(1);
204 /// if let Ok(x) = res {
208 pub FOR_LOOPS_OVER_FALLIBLES,
210 "for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
213 declare_clippy_lint! {
214 /// **What it does:** Detects `loop + match` combinations that are easier
215 /// written as a `while let` loop.
217 /// **Why is this bad?** The `while let` loop is usually shorter and more
220 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
224 /// # let y = Some(1);
226 /// let x = match y {
230 /// // .. do something with x
232 /// // is easier written as
233 /// while let Some(x) = y {
234 /// // .. do something with x
239 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
242 declare_clippy_lint! {
243 /// **What it does:** Checks for functions collecting an iterator when collect
246 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
247 /// when this allocation may not be needed.
249 /// **Known problems:**
254 /// # let iterator = vec![1].into_iter();
255 /// let len = iterator.clone().collect::<Vec<_>>().len();
257 /// let len = iterator.count();
259 pub NEEDLESS_COLLECT,
261 "collecting an iterator when collect is not needed"
264 declare_clippy_lint! {
265 /// **What it does:** Checks `for` loops over slices with an explicit counter
266 /// and suggests the use of `.enumerate()`.
268 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
269 /// declutters the code and may be faster in some instances.
271 /// **Known problems:** None.
275 /// # let v = vec![1];
276 /// # fn bar(bar: usize, baz: usize) {}
283 /// Could be written as
285 /// # let v = vec![1];
286 /// # fn bar(bar: usize, baz: usize) {}
287 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
289 pub EXPLICIT_COUNTER_LOOP,
291 "for-looping with an explicit counter when `_.enumerate()` would do"
294 declare_clippy_lint! {
295 /// **What it does:** Checks for empty `loop` expressions.
297 /// **Why is this bad?** 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_clippy_lint! {
457 /// **What it does:** Checks whether a for loop has a single element.
459 /// **Why is this bad?** There is no reason to have a loop of a
461 /// **Known problems:** None
466 /// for item in &[item1] {
467 /// println!("{}", item);
470 /// could be written as
473 /// let item = &item1;
474 /// println!("{}", item);
476 pub SINGLE_ELEMENT_LOOP,
478 "there is no reason to have a single element loop"
481 declare_lint_pass!(Loops => [
485 EXPLICIT_INTO_ITER_LOOP,
487 FOR_LOOPS_OVER_FALLIBLES,
490 EXPLICIT_COUNTER_LOOP,
492 WHILE_LET_ON_ITERATOR,
496 WHILE_IMMUTABLE_CONDITION,
501 impl<'tcx> LateLintPass<'tcx> for Loops {
502 #[allow(clippy::too_many_lines)]
503 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
504 if let Some((pat, arg, body)) = higher::for_loop(expr) {
505 // we don't want to check expanded macros
506 // this check is not at the top of the function
507 // since higher::for_loop expressions are marked as expansions
508 if body.span.from_expansion() {
511 check_for_loop(cx, pat, arg, body, expr);
514 // we don't want to check expanded macros
515 if expr.span.from_expansion() {
519 // check for never_loop
520 if let ExprKind::Loop(ref block, _, _) = expr.kind {
521 match never_loop_block(block, expr.hir_id) {
522 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
523 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
527 // check for `loop { if let {} else break }` that could be `while let`
528 // (also matches an explicit "match" instead of "if let")
529 // (even if the "match" or "if let" is used for declaration)
530 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
531 // also check for empty `loop {}` statements
532 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) {
537 "empty `loop {}` detected. You may want to either use `panic!()` or add \
538 `std::thread::sleep(..);` to the loop body.",
542 // extract the expression from the first statement (if any) in a block
543 let inner_stmt_expr = extract_expr_from_first_stmt(block);
544 // or extract the first expression (if any) from the block
545 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
546 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
547 // ensure "if let" compatible match structure
549 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
551 && arms[0].guard.is_none()
552 && arms[1].guard.is_none()
553 && is_simple_break_expr(&arms[1].body)
555 if in_external_macro(cx.sess(), expr.span) {
559 // NOTE: we used to build a body here instead of using
560 // ellipsis, this was removed because:
561 // 1) it was ugly with big bodies;
562 // 2) it was not indented properly;
563 // 3) it wasn’t very smart (see #675).
564 let mut applicability = Applicability::HasPlaceholders;
569 "this loop could be written as a `while let` loop",
572 "while let {} = {} {{ .. }}",
573 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
574 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
585 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
586 let pat = &arms[0].pat.kind;
588 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
589 &ExprKind::MethodCall(ref method_path, _, ref method_args, _),
590 ) = (pat, &match_expr.kind)
592 let iter_expr = &method_args[0];
594 // Don't lint when the iterator is recreated on every iteration
596 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
597 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
598 if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
604 let lhs_constructor = last_path_segment(qpath);
605 if method_path.ident.name == sym!(next)
606 && match_trait_method(cx, match_expr, &paths::ITERATOR)
607 && lhs_constructor.ident.name == sym!(Some)
608 && (pat_args.is_empty()
609 || !is_refutable(cx, &pat_args[0])
610 && !is_used_inside(cx, iter_expr, &arms[0].body)
611 && !is_iterator_used_after_while_let(cx, iter_expr)
612 && !is_nested(cx, expr, &method_args[0]))
614 let mut applicability = Applicability::MachineApplicable;
615 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
616 let loop_var = if pat_args.is_empty() {
619 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
623 WHILE_LET_ON_ITERATOR,
624 expr.span.with_hi(match_expr.span.hi()),
625 "this loop could be written as a `for` loop",
627 format!("for {} in {}", loop_var, iterator),
634 if let Some((cond, body)) = higher::while_loop(&expr) {
635 check_infinite_loop(cx, cond, body);
638 check_needless_collect(expr, cx);
642 enum NeverLoopResult {
643 // A break/return always get triggered but not necessarily for the main loop.
645 // A continue may occur for the main loop.
651 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
653 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
654 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
658 // Combine two results for parts that are called in order.
660 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
662 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
663 NeverLoopResult::Otherwise => second,
667 // Combine two results where both parts are called but not necessarily in order.
669 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
670 match (left, right) {
671 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
672 NeverLoopResult::MayContinueMainLoop
674 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
675 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
679 // Combine two results where only one of the part may have been executed.
681 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
683 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
684 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
685 NeverLoopResult::MayContinueMainLoop
687 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
691 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
692 let stmts = block.stmts.iter().map(stmt_to_expr);
693 let expr = once(block.expr.as_deref());
694 let mut iter = stmts.chain(expr).filter_map(|e| e);
695 never_loop_expr_seq(&mut iter, main_loop_id)
698 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
700 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
701 StmtKind::Local(ref local) => local.init.as_deref(),
706 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
709 | ExprKind::Unary(_, ref e)
710 | ExprKind::Cast(ref e, _)
711 | ExprKind::Type(ref e, _)
712 | ExprKind::Field(ref e, _)
713 | ExprKind::AddrOf(_, _, ref e)
714 | ExprKind::Struct(_, _, Some(ref e))
715 | ExprKind::Repeat(ref e, _)
716 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
717 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
718 never_loop_expr_all(&mut es.iter(), main_loop_id)
720 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
721 ExprKind::Binary(_, ref e1, ref e2)
722 | ExprKind::Assign(ref e1, ref e2, _)
723 | ExprKind::AssignOp(_, ref e1, ref e2)
724 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
725 ExprKind::Loop(ref b, _, _) => {
726 // Break can come from the inner loop so remove them.
727 absorb_break(&never_loop_block(b, main_loop_id))
729 ExprKind::Match(ref e, ref arms, _) => {
730 let e = never_loop_expr(e, main_loop_id);
734 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
738 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
739 ExprKind::Continue(d) => {
742 .expect("target ID can only be missing in the presence of compilation errors");
743 if id == main_loop_id {
744 NeverLoopResult::MayContinueMainLoop
746 NeverLoopResult::AlwaysBreak
749 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
750 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
752 ExprKind::InlineAsm(ref asm) => asm
756 InlineAsmOperand::In { expr, .. }
757 | InlineAsmOperand::InOut { expr, .. }
758 | InlineAsmOperand::Const { expr }
759 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
760 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
761 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
762 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
765 .fold(NeverLoopResult::Otherwise, combine_both),
766 ExprKind::Struct(_, _, None)
767 | ExprKind::Yield(_, _)
768 | ExprKind::Closure(_, _, _, _, _)
769 | ExprKind::LlvmInlineAsm(_)
771 | ExprKind::ConstBlock(_)
773 | ExprKind::Err => NeverLoopResult::Otherwise,
777 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
778 es.map(|e| never_loop_expr(e, main_loop_id))
779 .fold(NeverLoopResult::Otherwise, combine_seq)
782 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
783 es.map(|e| never_loop_expr(e, main_loop_id))
784 .fold(NeverLoopResult::Otherwise, combine_both)
787 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
788 e.map(|e| never_loop_expr(e, main_loop_id))
789 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
792 fn check_for_loop<'tcx>(
793 cx: &LateContext<'tcx>,
796 body: &'tcx Expr<'_>,
797 expr: &'tcx Expr<'_>,
799 let is_manual_memcpy_triggered = detect_manual_memcpy(cx, pat, arg, body, expr);
800 if !is_manual_memcpy_triggered {
801 check_for_loop_range(cx, pat, arg, body, expr);
802 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
804 check_for_loop_arg(cx, pat, arg, expr);
805 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
806 check_for_mut_range_bound(cx, arg, body);
807 check_for_single_element_loop(cx, pat, arg, body, expr);
808 detect_same_item_push(cx, pat, arg, body, expr);
811 // this function assumes the given expression is a `for` loop.
812 fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
813 // for some reason this is the only way to get the `Span`
814 // of the entire `for` loop
815 if let ExprKind::Match(_, arms, _) = &expr.kind {
822 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
824 if let ExprKind::Path(qpath) = &expr.kind;
825 if let QPath::Resolved(None, path) = qpath;
826 if path.segments.len() == 1;
827 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
837 /// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
838 /// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
839 /// it exists for the convenience of the overloaded operators while normal functions can do the
842 struct MinifyingSugg<'a>(Sugg<'a>);
844 impl<'a> MinifyingSugg<'a> {
845 fn as_str(&self) -> &str {
846 let Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) = &self.0;
850 fn into_sugg(self) -> Sugg<'a> {
855 impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
856 fn from(sugg: Sugg<'a>) -> Self {
861 impl std::ops::Add for &MinifyingSugg<'static> {
862 type Output = MinifyingSugg<'static>;
863 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
864 match (self.as_str(), rhs.as_str()) {
865 ("0", _) => rhs.clone(),
866 (_, "0") => self.clone(),
867 (_, _) => (&self.0 + &rhs.0).into(),
872 impl std::ops::Sub for &MinifyingSugg<'static> {
873 type Output = MinifyingSugg<'static>;
874 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
875 match (self.as_str(), rhs.as_str()) {
876 (_, "0") => self.clone(),
877 ("0", _) => (-rhs.0.clone()).into(),
878 (x, y) if x == y => sugg::ZERO.into(),
879 (_, _) => (&self.0 - &rhs.0).into(),
884 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
885 type Output = MinifyingSugg<'static>;
886 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
887 match (self.as_str(), rhs.as_str()) {
888 ("0", _) => rhs.clone(),
890 (_, _) => (self.0 + &rhs.0).into(),
895 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
896 type Output = MinifyingSugg<'static>;
897 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
898 match (self.as_str(), rhs.as_str()) {
900 ("0", _) => (-rhs.0.clone()).into(),
901 (x, y) if x == y => sugg::ZERO.into(),
902 (_, _) => (self.0 - &rhs.0).into(),
907 /// a wrapper around `MinifyingSugg`, which carries a operator like currying
908 /// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
910 value: MinifyingSugg<'static>,
914 #[derive(Clone, Copy)]
921 fn negative(value: Sugg<'static>) -> Self {
924 sign: OffsetSign::Negative,
928 fn positive(value: Sugg<'static>) -> Self {
931 sign: OffsetSign::Positive,
936 Self::positive(sugg::ZERO)
940 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
942 OffsetSign::Positive => lhs + &rhs.value,
943 OffsetSign::Negative => lhs - &rhs.value,
947 #[derive(Debug, Clone, Copy)]
948 enum StartKind<'hir> {
950 Counter { initializer: &'hir Expr<'hir> },
953 struct IndexExpr<'hir> {
954 base: &'hir Expr<'hir>,
955 idx: StartKind<'hir>,
961 kind: StartKind<'hir>,
964 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
965 let is_slice = match ty.kind() {
966 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
967 ty::Slice(..) | ty::Array(..) => true,
971 is_slice || is_type_diagnostic_item(cx, ty, sym!(vec_type)) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
974 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
976 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
977 if method.ident.name == sym!(clone);
979 if let Some(arg) = args.get(0);
980 then { arg } else { expr }
984 fn get_details_from_idx<'tcx>(
985 cx: &LateContext<'tcx>,
987 starts: &[Start<'tcx>],
988 ) -> Option<(StartKind<'tcx>, Offset)> {
989 fn get_start<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
990 starts.iter().find_map(|start| {
991 if same_var(cx, e, start.id) {
999 fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
1001 ExprKind::Lit(l) => match l.node {
1002 ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
1005 ExprKind::Path(..) if get_start(cx, e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
1011 ExprKind::Binary(op, lhs, rhs) => match op.node {
1013 let offset_opt = get_start(cx, lhs, starts)
1014 .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
1015 .or_else(|| get_start(cx, rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
1017 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
1020 get_start(cx, lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
1024 ExprKind::Path(..) => get_start(cx, idx, starts).map(|s| (s, Offset::empty())),
1029 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1030 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1037 /// Get assignments from the given block.
1038 /// The returned iterator yields `None` if no assignment expressions are there,
1039 /// filtering out the increments of the given whitelisted loop counters;
1040 /// because its job is to make sure there's nothing other than assignments and the increments.
1041 fn get_assignments<'a: 'c, 'tcx: 'c, 'c>(
1042 cx: &'a LateContext<'tcx>,
1043 Block { stmts, expr, .. }: &'tcx Block<'tcx>,
1044 loop_counters: &'c [Start<'tcx>],
1045 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'c {
1046 // As the `filter` and `map` below do different things, I think putting together
1047 // just increases complexity. (cc #3188 and #4193)
1048 #[allow(clippy::filter_map)]
1051 .filter_map(move |stmt| match stmt.kind {
1052 StmtKind::Local(..) | StmtKind::Item(..) => None,
1053 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
1055 .chain((*expr).into_iter())
1057 if let ExprKind::AssignOp(_, place, _) = e.kind {
1060 // skip the first item which should be `StartKind::Range`
1061 // this makes it possible to use the slice with `StartKind::Range` in the same iterator loop.
1063 .any(|counter| same_var(cx, place, counter.id))
1068 .map(get_assignment)
1071 fn get_loop_counters<'a, 'tcx>(
1072 cx: &'a LateContext<'tcx>,
1073 body: &'tcx Block<'tcx>,
1074 expr: &'tcx Expr<'_>,
1075 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1076 // Look for variables that are incremented once per loop iteration.
1077 let mut increment_visitor = IncrementVisitor::new(cx);
1078 walk_block(&mut increment_visitor, body);
1080 // For each candidate, check the parent block to see if
1081 // it's initialized to zero at the start of the loop.
1082 get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
1085 .filter_map(move |var_id| {
1086 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1087 walk_block(&mut initialize_visitor, block);
1089 initialize_visitor.get_result().map(|(_, initializer)| Start {
1091 kind: StartKind::Counter { initializer },
1098 fn build_manual_memcpy_suggestion<'tcx>(
1099 cx: &LateContext<'tcx>,
1102 limits: ast::RangeLimits,
1103 dst: &IndexExpr<'_>,
1104 src: &IndexExpr<'_>,
1106 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1107 if offset.as_str() == "0" {
1114 let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
1116 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1117 if method.ident.name == sym!(len);
1118 if len_args.len() == 1;
1119 if let Some(arg) = len_args.get(0);
1120 if var_def_id(cx, arg) == var_def_id(cx, base);
1122 if sugg.as_str() == end_str {
1129 ast::RangeLimits::Closed => {
1130 sugg + &sugg::ONE.into()
1132 ast::RangeLimits::HalfOpen => sugg,
1138 let start_str = Sugg::hir(cx, start, "").into();
1139 let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
1141 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1142 StartKind::Range => (
1143 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
1148 apply_offset(&end_str, &idx_expr.idx_offset),
1152 StartKind::Counter { initializer } => {
1153 let counter_start = Sugg::hir(cx, initializer, "").into();
1155 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
1160 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1167 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1168 let (src_offset, src_limit) = print_offset_and_limit(&src);
1170 let dst_base_str = snippet(cx, dst.base.span, "???");
1171 let src_base_str = snippet(cx, src.base.span, "???");
1173 let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
1179 dst_offset.maybe_par(),
1180 dst_limit.maybe_par()
1186 "{}.clone_from_slice(&{}[{}..{}]);",
1189 src_offset.maybe_par(),
1190 src_limit.maybe_par()
1194 /// Checks for for loops that sequentially copy items from one slice-like
1195 /// object to another.
1196 fn detect_manual_memcpy<'tcx>(
1197 cx: &LateContext<'tcx>,
1199 arg: &'tcx Expr<'_>,
1200 body: &'tcx Expr<'_>,
1201 expr: &'tcx Expr<'_>,
1203 if let Some(higher::Range {
1207 }) = higher::range(arg)
1209 // the var must be a single name
1210 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1211 let mut starts = vec![Start {
1213 kind: StartKind::Range,
1216 // This is one of few ways to return different iterators
1217 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1218 let mut iter_a = None;
1219 let mut iter_b = None;
1221 if let ExprKind::Block(block, _) = body.kind {
1222 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1223 starts.extend(loop_counters);
1225 iter_a = Some(get_assignments(cx, block, &starts));
1227 iter_b = Some(get_assignment(body));
1230 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1232 let big_sugg = assignments
1233 // The only statements in the for loops can be indexed assignments from
1234 // indexed retrievals (except increments of loop counters).
1236 o.and_then(|(lhs, rhs)| {
1237 let rhs = fetch_cloned_expr(rhs);
1239 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1240 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1241 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1242 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1243 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1244 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1246 // Source and destination must be different
1247 if var_def_id(cx, base_left) != var_def_id(cx, base_right);
1249 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1250 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1257 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1258 .collect::<Option<Vec<_>>>()
1259 .filter(|v| !v.is_empty())
1260 .map(|v| v.join("\n "));
1262 if let Some(big_sugg) = big_sugg {
1266 get_span_of_entire_for_loop(expr),
1267 "it looks like you're manually copying between slices",
1268 "try replacing the loop by",
1270 Applicability::Unspecified,
1279 // Scans the body of the for loop and determines whether lint should be given
1280 struct SameItemPushVisitor<'a, 'tcx> {
1282 // this field holds the last vec push operation visited, which should be the only push seen
1283 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1284 cx: &'a LateContext<'tcx>,
1287 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1288 type Map = Map<'tcx>;
1290 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1292 // Non-determinism may occur ... don't give a lint
1293 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1294 ExprKind::Block(block, _) => self.visit_block(block),
1299 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1300 for stmt in b.stmts.iter() {
1301 self.visit_stmt(stmt);
1305 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1306 let vec_push_option = get_vec_push(self.cx, s);
1307 if vec_push_option.is_none() {
1308 // Current statement is not a push so visit inside
1310 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1314 // Current statement is a push ...check whether another
1315 // push had been previously done
1316 if self.vec_push.is_none() {
1317 self.vec_push = vec_push_option;
1319 // There are multiple pushes ... don't lint
1320 self.should_lint = false;
1325 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1326 NestedVisitorMap::None
1330 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1331 // the Vec being pushed into and the item being pushed
1332 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1334 // Extract method being called
1335 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1336 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1337 // Figure out the parameters for the method call
1338 if let Some(self_expr) = args.get(0);
1339 if let Some(pushed_item) = args.get(1);
1340 // Check that the method being called is push() on a Vec
1341 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym!(vec_type));
1342 if path.ident.name.as_str() == "push";
1344 return Some((self_expr, pushed_item))
1350 /// Detects for loop pushing the same item into a Vec
1351 fn detect_same_item_push<'tcx>(
1352 cx: &LateContext<'tcx>,
1355 body: &'tcx Expr<'_>,
1358 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1359 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1360 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1366 "it looks like the same item is being pushed into this Vec",
1369 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1370 item_str, vec_str, item_str
1375 if !matches!(pat.kind, PatKind::Wild) {
1379 // Determine whether it is safe to lint the body
1380 let mut same_item_push_visitor = SameItemPushVisitor {
1385 walk_expr(&mut same_item_push_visitor, body);
1386 if same_item_push_visitor.should_lint {
1387 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1388 let vec_ty = cx.typeck_results().expr_ty(vec);
1389 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1394 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1396 // Make sure that the push does not involve possibly mutating values
1397 match pushed_item.kind {
1398 ExprKind::Path(ref qpath) => {
1399 match qpath_res(cx, qpath, pushed_item.hir_id) {
1400 // immutable bindings that are initialized with literal or constant
1401 Res::Local(hir_id) => {
1403 let node = cx.tcx.hir().get(hir_id);
1404 if let Node::Binding(pat) = node;
1405 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1406 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1407 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1408 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1409 if let Some(init) = parent_let_expr.init;
1412 // immutable bindings that are initialized with literal
1413 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1414 // immutable bindings that are initialized with constant
1415 ExprKind::Path(ref path) => {
1416 if let Res::Def(DefKind::Const, ..) = qpath_res(cx, path, init.hir_id) {
1417 emit_lint(cx, vec, pushed_item);
1426 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1430 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1438 /// Checks for looping over a range and then indexing a sequence with it.
1439 /// The iteratee must be a range literal.
1440 #[allow(clippy::too_many_lines)]
1441 fn check_for_loop_range<'tcx>(
1442 cx: &LateContext<'tcx>,
1444 arg: &'tcx Expr<'_>,
1445 body: &'tcx Expr<'_>,
1446 expr: &'tcx Expr<'_>,
1448 if let Some(higher::Range {
1452 }) = higher::range(arg)
1454 // the var must be a single name
1455 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1456 let mut visitor = VarVisitor {
1459 indexed_mut: FxHashSet::default(),
1460 indexed_indirectly: FxHashMap::default(),
1461 indexed_directly: FxHashMap::default(),
1462 referenced: FxHashSet::default(),
1464 prefer_mutable: false,
1466 walk_expr(&mut visitor, body);
1468 // linting condition: we only indexed one variable, and indexed it directly
1469 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1470 let (indexed, (indexed_extent, indexed_ty)) = visitor
1474 .expect("already checked that we have exactly 1 element");
1476 // ensure that the indexed variable was declared before the loop, see #601
1477 if let Some(indexed_extent) = indexed_extent {
1478 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1479 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1480 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1481 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1482 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1487 // don't lint if the container that is indexed does not have .iter() method
1488 let has_iter = has_iter_method(cx, indexed_ty);
1489 if has_iter.is_none() {
1493 // don't lint if the container that is indexed into is also used without
1495 if visitor.referenced.contains(&indexed) {
1499 let starts_at_zero = is_integer_const(cx, start, 0);
1501 let skip = if starts_at_zero {
1503 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
1506 format!(".skip({})", snippet(cx, start.span, ".."))
1509 let mut end_is_start_plus_val = false;
1511 let take = if let Some(end) = *end {
1512 let mut take_expr = end;
1514 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1515 if let BinOpKind::Add = op.node {
1516 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1517 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1519 if start_equal_left {
1521 } else if start_equal_right {
1525 end_is_start_plus_val = start_equal_left | start_equal_right;
1529 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1531 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
1535 ast::RangeLimits::Closed => {
1536 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1537 format!(".take({})", take_expr + sugg::ONE)
1539 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1546 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1547 ("mut ", "iter_mut")
1552 let take_is_empty = take.is_empty();
1553 let mut method_1 = take;
1554 let mut method_2 = skip;
1556 if end_is_start_plus_val {
1557 mem::swap(&mut method_1, &mut method_2);
1560 if visitor.nonindex {
1563 NEEDLESS_RANGE_LOOP,
1565 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1569 "consider using an iterator",
1571 (pat.span, format!("({}, <item>)", ident.name)),
1574 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1581 let repl = if starts_at_zero && take_is_empty {
1582 format!("&{}{}", ref_mut, indexed)
1584 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1589 NEEDLESS_RANGE_LOOP,
1592 "the loop variable `{}` is only used to index `{}`.",
1598 "consider using an iterator",
1599 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1609 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1611 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1612 if len_args.len() == 1;
1613 if method.ident.name == sym!(len);
1614 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1615 if path.segments.len() == 1;
1616 if path.segments[0].ident.name == var;
1625 fn is_end_eq_array_len<'tcx>(
1626 cx: &LateContext<'tcx>,
1628 limits: ast::RangeLimits,
1629 indexed_ty: Ty<'tcx>,
1632 if let ExprKind::Lit(ref lit) = end.kind;
1633 if let ast::LitKind::Int(end_int, _) = lit.node;
1634 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1635 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1637 return match limits {
1638 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1639 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1647 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1648 let mut applicability = Applicability::MachineApplicable;
1649 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1650 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1655 "it is more concise to loop over references to containers instead of using explicit \
1657 "to write this more concisely, try",
1658 format!("&{}{}", muta, object),
1663 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1664 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1665 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1666 // just the receiver, no arguments
1667 if args.len() == 1 {
1668 let method_name = &*method.ident.as_str();
1669 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1670 if method_name == "iter" || method_name == "iter_mut" {
1671 if is_ref_iterable_type(cx, &args[0]) {
1672 lint_iter_method(cx, args, arg, method_name);
1674 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1675 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1676 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1677 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1678 let mut applicability = Applicability::MachineApplicable;
1679 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1682 EXPLICIT_INTO_ITER_LOOP,
1684 "it is more concise to loop over containers instead of using explicit \
1686 "to write this more concisely, try",
1691 let ref_receiver_ty = cx.tcx.mk_ref(
1692 cx.tcx.lifetimes.re_erased,
1695 mutbl: Mutability::Not,
1698 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1699 lint_iter_method(cx, args, arg, method_name)
1702 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1707 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1708 probably not what you want",
1710 next_loop_linted = true;
1714 if !next_loop_linted {
1715 check_arg_type(cx, pat, arg);
1719 /// Checks for `for` loops over `Option`s and `Result`s.
1720 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1721 let ty = cx.typeck_results().expr_ty(arg);
1722 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1725 FOR_LOOPS_OVER_FALLIBLES,
1728 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1729 `if let` statement.",
1730 snippet(cx, arg.span, "_")
1734 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1735 snippet(cx, pat.span, "_"),
1736 snippet(cx, arg.span, "_")
1739 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1742 FOR_LOOPS_OVER_FALLIBLES,
1745 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1746 `if let` statement.",
1747 snippet(cx, arg.span, "_")
1751 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1752 snippet(cx, pat.span, "_"),
1753 snippet(cx, arg.span, "_")
1759 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1760 // incremented exactly once in the loop body, and initialized to zero
1761 // at the start of the loop.
1762 fn check_for_loop_explicit_counter<'tcx>(
1763 cx: &LateContext<'tcx>,
1765 arg: &'tcx Expr<'_>,
1766 body: &'tcx Expr<'_>,
1767 expr: &'tcx Expr<'_>,
1769 // Look for variables that are incremented once per loop iteration.
1770 let mut increment_visitor = IncrementVisitor::new(cx);
1771 walk_expr(&mut increment_visitor, body);
1773 // For each candidate, check the parent block to see if
1774 // it's initialized to zero at the start of the loop.
1775 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1776 for id in increment_visitor.into_results() {
1777 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1778 walk_block(&mut initialize_visitor, block);
1781 if let Some((name, initializer)) = initialize_visitor.get_result();
1782 if is_integer_const(cx, initializer, 0);
1784 let mut applicability = Applicability::MachineApplicable;
1786 let for_span = get_span_of_entire_for_loop(expr);
1790 EXPLICIT_COUNTER_LOOP,
1791 for_span.with_hi(arg.span.hi()),
1792 &format!("the variable `{}` is used as a loop counter.", name),
1795 "for ({}, {}) in {}.enumerate()",
1797 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1798 make_iterator_snippet(cx, arg, &mut applicability),
1808 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1809 /// actual `Iterator` that the loop uses.
1810 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1811 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1812 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1817 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1820 // (&x).into_iter() ==> x.iter()
1821 // (&mut x).into_iter() ==> x.iter_mut()
1823 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1824 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1826 let meth_name = match mutability {
1827 Mutability::Mut => "iter_mut",
1828 Mutability::Not => "iter",
1832 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1838 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1844 /// Checks for the `FOR_KV_MAP` lint.
1845 fn check_for_loop_over_map_kv<'tcx>(
1846 cx: &LateContext<'tcx>,
1848 arg: &'tcx Expr<'_>,
1849 body: &'tcx Expr<'_>,
1850 expr: &'tcx Expr<'_>,
1852 let pat_span = pat.span;
1854 if let PatKind::Tuple(ref pat, _) = pat.kind {
1856 let arg_span = arg.span;
1857 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1858 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1859 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1860 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1865 let mutbl = match mutbl {
1866 Mutability::Not => "",
1867 Mutability::Mut => "_mut",
1869 let arg = match arg.kind {
1870 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1874 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1879 &format!("you seem to want to iterate on a map's {}s", kind),
1881 let map = sugg::Sugg::hir(cx, arg, "map");
1884 "use the corresponding method",
1886 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1887 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1897 fn check_for_single_element_loop<'tcx>(
1898 cx: &LateContext<'tcx>,
1900 arg: &'tcx Expr<'_>,
1901 body: &'tcx Expr<'_>,
1902 expr: &'tcx Expr<'_>,
1905 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg_expr) = arg.kind;
1906 if let PatKind::Binding(.., target, _) = pat.kind;
1907 if let ExprKind::Array(ref arg_expr_list) = arg_expr.kind;
1908 if let [arg_expression] = arg_expr_list;
1909 if let ExprKind::Path(ref list_item) = arg_expression.kind;
1910 if let Some(list_item_name) = single_segment_path(list_item).map(|ps| ps.ident.name);
1911 if let ExprKind::Block(ref block, _) = body.kind;
1912 if !block.stmts.is_empty();
1915 let for_span = get_span_of_entire_for_loop(expr);
1916 let mut block_str = snippet(cx, block.span, "..").into_owned();
1917 block_str.remove(0);
1923 SINGLE_ELEMENT_LOOP,
1925 "for loop over a single element",
1927 format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),
1928 Applicability::MachineApplicable
1934 struct MutatePairDelegate<'a, 'tcx> {
1935 cx: &'a LateContext<'tcx>,
1936 hir_id_low: Option<HirId>,
1937 hir_id_high: Option<HirId>,
1938 span_low: Option<Span>,
1939 span_high: Option<Span>,
1942 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1943 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1945 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1946 if let ty::BorrowKind::MutBorrow = bk {
1947 if let PlaceBase::Local(id) = cmt.place.base {
1948 if Some(id) == self.hir_id_low {
1949 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1951 if Some(id) == self.hir_id_high {
1952 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1958 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>) {
1959 if let PlaceBase::Local(id) = cmt.place.base {
1960 if Some(id) == self.hir_id_low {
1961 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1963 if Some(id) == self.hir_id_high {
1964 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1970 impl MutatePairDelegate<'_, '_> {
1971 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1972 (self.span_low, self.span_high)
1976 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1977 if let Some(higher::Range {
1981 }) = higher::range(arg)
1983 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1984 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1985 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1986 mut_warn_with_span(cx, span_low);
1987 mut_warn_with_span(cx, span_high);
1992 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
1993 if let Some(sp) = span {
1998 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
2003 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
2005 if let ExprKind::Path(ref qpath) = bound.kind;
2006 if let QPath::Resolved(None, _) = *qpath;
2008 let res = qpath_res(cx, qpath, bound.hir_id);
2009 if let Res::Local(hir_id) = res {
2010 let node_str = cx.tcx.hir().get(hir_id);
2012 if let Node::Binding(pat) = node_str;
2013 if let PatKind::Binding(bind_ann, ..) = pat.kind;
2014 if let BindingAnnotation::Mutable = bind_ann;
2016 return Some(hir_id);
2025 fn check_for_mutation<'tcx>(
2026 cx: &LateContext<'tcx>,
2028 bound_ids: &[Option<HirId>],
2029 ) -> (Option<Span>, Option<Span>) {
2030 let mut delegate = MutatePairDelegate {
2032 hir_id_low: bound_ids[0],
2033 hir_id_high: bound_ids[1],
2037 let def_id = body.hir_id.owner.to_def_id();
2038 cx.tcx.infer_ctxt().enter(|infcx| {
2039 ExprUseVisitor::new(
2042 def_id.expect_local(),
2044 cx.typeck_results(),
2048 delegate.mutation_span()
2051 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
2052 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
2054 PatKind::Wild => true,
2055 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
2060 struct LocalUsedVisitor<'a, 'tcx> {
2061 cx: &'a LateContext<'tcx>,
2066 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
2067 type Map = Map<'tcx>;
2069 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2070 if same_var(self.cx, expr, self.local) {
2073 walk_expr(self, expr);
2077 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2078 NestedVisitorMap::None
2082 struct VarVisitor<'a, 'tcx> {
2083 /// context reference
2084 cx: &'a LateContext<'tcx>,
2085 /// var name to look for as index
2087 /// indexed variables that are used mutably
2088 indexed_mut: FxHashSet<Symbol>,
2089 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2090 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2091 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2092 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2093 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2094 /// Any names that are used outside an index operation.
2095 /// Used to detect things like `&mut vec` used together with `vec[i]`
2096 referenced: FxHashSet<Symbol>,
2097 /// has the loop variable been used in expressions other than the index of
2100 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2101 /// takes `&mut self`
2102 prefer_mutable: bool,
2105 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2106 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2108 // the indexed container is referenced by a name
2109 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2110 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2111 if seqvar.segments.len() == 1;
2113 let index_used_directly = same_var(self.cx, idx, self.var);
2114 let indexed_indirectly = {
2115 let mut used_visitor = LocalUsedVisitor {
2120 walk_expr(&mut used_visitor, idx);
2124 if indexed_indirectly || index_used_directly {
2125 if self.prefer_mutable {
2126 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2128 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
2130 Res::Local(hir_id) => {
2131 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2132 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2133 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2134 if indexed_indirectly {
2135 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2137 if index_used_directly {
2138 self.indexed_directly.insert(
2139 seqvar.segments[0].ident.name,
2140 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2143 return false; // no need to walk further *on the variable*
2145 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2146 if indexed_indirectly {
2147 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2149 if index_used_directly {
2150 self.indexed_directly.insert(
2151 seqvar.segments[0].ident.name,
2152 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2155 return false; // no need to walk further *on the variable*
2166 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2167 type Map = Map<'tcx>;
2169 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2172 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2173 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
2174 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2175 if !self.check(&args[1], &args[0], expr);
2181 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2182 if !self.check(idx, seqexpr, expr);
2187 // directly using a variable
2188 if let ExprKind::Path(ref qpath) = expr.kind;
2189 if let QPath::Resolved(None, ref path) = *qpath;
2190 if path.segments.len() == 1;
2192 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2193 if local_id == self.var {
2194 self.nonindex = true;
2196 // not the correct variable, but still a variable
2197 self.referenced.insert(path.segments[0].ident.name);
2203 let old = self.prefer_mutable;
2205 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2206 self.prefer_mutable = true;
2207 self.visit_expr(lhs);
2208 self.prefer_mutable = false;
2209 self.visit_expr(rhs);
2211 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2212 if mutbl == Mutability::Mut {
2213 self.prefer_mutable = true;
2215 self.visit_expr(expr);
2217 ExprKind::Call(ref f, args) => {
2220 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2221 self.prefer_mutable = false;
2222 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2223 if mutbl == Mutability::Mut {
2224 self.prefer_mutable = true;
2227 self.visit_expr(expr);
2230 ExprKind::MethodCall(_, _, args, _) => {
2231 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2232 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2233 self.prefer_mutable = false;
2234 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2235 if mutbl == Mutability::Mut {
2236 self.prefer_mutable = true;
2239 self.visit_expr(expr);
2242 ExprKind::Closure(_, _, body_id, ..) => {
2243 let body = self.cx.tcx.hir().body(body_id);
2244 self.visit_expr(&body.value);
2246 _ => walk_expr(self, expr),
2248 self.prefer_mutable = old;
2250 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2251 NestedVisitorMap::None
2255 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2256 let def_id = match var_def_id(cx, expr) {
2258 None => return false,
2260 if let Some(used_mutably) = mutated_variables(container, cx) {
2261 if used_mutably.contains(&def_id) {
2268 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2269 let def_id = match var_def_id(cx, iter_expr) {
2271 None => return false,
2273 let mut visitor = VarUsedAfterLoopVisitor {
2276 iter_expr_id: iter_expr.hir_id,
2277 past_while_let: false,
2278 var_used_after_while_let: false,
2280 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2281 walk_block(&mut visitor, enclosing_block);
2283 visitor.var_used_after_while_let
2286 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2287 cx: &'a LateContext<'tcx>,
2289 iter_expr_id: HirId,
2290 past_while_let: bool,
2291 var_used_after_while_let: bool,
2294 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2295 type Map = Map<'tcx>;
2297 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2298 if self.past_while_let {
2299 if Some(self.def_id) == var_def_id(self.cx, expr) {
2300 self.var_used_after_while_let = true;
2302 } else if self.iter_expr_id == expr.hir_id {
2303 self.past_while_let = true;
2305 walk_expr(self, expr);
2307 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2308 NestedVisitorMap::None
2312 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2313 /// for `&T` and `&mut T`, such as `Vec`.
2315 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2316 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2317 // will allow further borrows afterwards
2318 let ty = cx.typeck_results().expr_ty(e);
2319 is_iterable_array(ty, cx) ||
2320 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2321 match_type(cx, ty, &paths::LINKED_LIST) ||
2322 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2323 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2324 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2325 match_type(cx, ty, &paths::BINARY_HEAP) ||
2326 match_type(cx, ty, &paths::BTREEMAP) ||
2327 match_type(cx, ty, &paths::BTREESET)
2330 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2331 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2333 ty::Array(_, n) => n
2334 .try_eval_usize(cx.tcx, cx.param_env)
2335 .map_or(false, |val| (0..=32).contains(&val)),
2340 /// If a block begins with a statement (possibly a `let` binding) and has an
2341 /// expression, return it.
2342 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2343 if block.stmts.is_empty() {
2346 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2347 local.init //.map(|expr| expr)
2353 /// If a block begins with an expression (with or without semicolon), return it.
2354 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2356 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2357 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2358 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2359 StmtKind::Local(..) | StmtKind::Item(..) => None,
2365 /// Returns `true` if expr contains a single break expr without destination label
2367 /// passed expression. The expression may be within a block.
2368 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2370 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2371 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2376 #[derive(Debug, PartialEq)]
2377 enum IncrementVisitorVarState {
2378 Initial, // Not examined yet
2379 IncrOnce, // Incremented exactly once, may be a loop counter
2383 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2384 struct IncrementVisitor<'a, 'tcx> {
2385 cx: &'a LateContext<'tcx>, // context reference
2386 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2387 depth: u32, // depth of conditional expressions
2391 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2392 fn new(cx: &'a LateContext<'tcx>) -> Self {
2395 states: FxHashMap::default(),
2401 fn into_results(self) -> impl Iterator<Item = HirId> {
2402 self.states.into_iter().filter_map(|(id, state)| {
2403 if state == IncrementVisitorVarState::IncrOnce {
2412 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2413 type Map = Map<'tcx>;
2415 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2420 // If node is a variable
2421 if let Some(def_id) = var_def_id(self.cx, expr) {
2422 if let Some(parent) = get_parent_expr(self.cx, expr) {
2423 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2424 if *state == IncrementVisitorVarState::IncrOnce {
2425 *state = IncrementVisitorVarState::DontWarn;
2430 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2431 if lhs.hir_id == expr.hir_id {
2432 *state = if op.node == BinOpKind::Add
2433 && is_integer_const(self.cx, rhs, 1)
2434 && *state == IncrementVisitorVarState::Initial
2437 IncrementVisitorVarState::IncrOnce
2439 // Assigned some other value or assigned multiple times
2440 IncrementVisitorVarState::DontWarn
2444 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2445 *state = IncrementVisitorVarState::DontWarn
2447 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2448 *state = IncrementVisitorVarState::DontWarn
2454 walk_expr(self, expr);
2455 } else if is_loop(expr) || is_conditional(expr) {
2457 walk_expr(self, expr);
2459 } else if let ExprKind::Continue(_) = expr.kind {
2462 walk_expr(self, expr);
2465 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2466 NestedVisitorMap::None
2470 enum InitializeVisitorState<'hir> {
2471 Initial, // Not examined yet
2472 Declared(Symbol), // Declared but not (yet) initialized
2475 initializer: &'hir Expr<'hir>,
2480 /// Checks whether a variable is initialized at the start of a loop and not modified
2481 /// and used after the loop.
2482 struct InitializeVisitor<'a, 'tcx> {
2483 cx: &'a LateContext<'tcx>, // context reference
2484 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2486 state: InitializeVisitorState<'tcx>,
2487 depth: u32, // depth of conditional expressions
2491 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2492 fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2497 state: InitializeVisitorState::Initial,
2503 fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
2504 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2505 Some((name, initializer))
2512 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2513 type Map = Map<'tcx>;
2515 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2516 // Look for declarations of the variable
2518 if let StmtKind::Local(ref local) = stmt.kind;
2519 if local.pat.hir_id == self.var_id;
2520 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2522 self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
2523 InitializeVisitorState::Initialized {
2530 walk_stmt(self, stmt);
2533 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2534 if matches!(self.state, InitializeVisitorState::DontWarn) {
2537 if expr.hir_id == self.end_expr.hir_id {
2538 self.past_loop = true;
2541 // No need to visit expressions before the variable is
2543 if matches!(self.state, InitializeVisitorState::Initial) {
2547 // If node is the desired variable, see how it's used
2548 if var_def_id(self.cx, expr) == Some(self.var_id) {
2550 self.state = InitializeVisitorState::DontWarn;
2554 if let Some(parent) = get_parent_expr(self.cx, expr) {
2556 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2557 self.state = InitializeVisitorState::DontWarn;
2559 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2560 self.state = if_chain! {
2562 if let InitializeVisitorState::Declared(name)
2563 | InitializeVisitorState::Initialized { name, ..} = self.state;
2565 InitializeVisitorState::Initialized { initializer: rhs, name }
2567 InitializeVisitorState::DontWarn
2571 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2572 self.state = InitializeVisitorState::DontWarn
2578 walk_expr(self, expr);
2579 } else if !self.past_loop && is_loop(expr) {
2580 self.state = InitializeVisitorState::DontWarn;
2581 } else if is_conditional(expr) {
2583 walk_expr(self, expr);
2586 walk_expr(self, expr);
2590 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2591 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2595 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2596 if let ExprKind::Path(ref qpath) = expr.kind {
2597 let path_res = qpath_res(cx, qpath, expr.hir_id);
2598 if let Res::Local(hir_id) = path_res {
2599 return Some(hir_id);
2605 fn is_loop(expr: &Expr<'_>) -> bool {
2606 matches!(expr.kind, ExprKind::Loop(..))
2609 fn is_conditional(expr: &Expr<'_>) -> bool {
2610 matches!(expr.kind, ExprKind::Match(..))
2613 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2615 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2616 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2617 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2619 return is_loop_nested(cx, loop_expr, iter_expr)
2625 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2626 let mut id = loop_expr.hir_id;
2627 let iter_name = if let Some(name) = path_name(iter_expr) {
2633 let parent = cx.tcx.hir().get_parent_node(id);
2637 match cx.tcx.hir().find(parent) {
2638 Some(Node::Expr(expr)) => {
2639 if let ExprKind::Loop(..) = expr.kind {
2643 Some(Node::Block(block)) => {
2644 let mut block_visitor = LoopNestVisitor {
2646 iterator: iter_name,
2649 walk_block(&mut block_visitor, block);
2650 if block_visitor.nesting == RuledOut {
2654 Some(Node::Stmt(_)) => (),
2663 #[derive(PartialEq, Eq)]
2665 Unknown, // no nesting detected yet
2666 RuledOut, // the iterator is initialized or assigned within scope
2667 LookFurther, // no nesting detected, no further walk required
2670 use self::Nesting::{LookFurther, RuledOut, Unknown};
2672 struct LoopNestVisitor {
2678 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2679 type Map = Map<'tcx>;
2681 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2682 if stmt.hir_id == self.hir_id {
2683 self.nesting = LookFurther;
2684 } else if self.nesting == Unknown {
2685 walk_stmt(self, stmt);
2689 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2690 if self.nesting != Unknown {
2693 if expr.hir_id == self.hir_id {
2694 self.nesting = LookFurther;
2698 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2699 if match_var(path, self.iterator) {
2700 self.nesting = RuledOut;
2703 _ => walk_expr(self, expr),
2707 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2708 if self.nesting != Unknown {
2711 if let PatKind::Binding(.., span_name, _) = pat.kind {
2712 if self.iterator == span_name.name {
2713 self.nesting = RuledOut;
2720 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2721 NestedVisitorMap::None
2725 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2726 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2727 let segments = &path.segments;
2728 if segments.len() == 1 {
2729 return Some(segments[0].ident.name);
2735 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2736 if constant(cx, cx.typeck_results(), cond).is_some() {
2737 // A pure constant condition (e.g., `while false`) is not linted.
2741 let mut var_visitor = VarCollectorVisitor {
2743 ids: FxHashSet::default(),
2744 def_ids: FxHashMap::default(),
2747 var_visitor.visit_expr(cond);
2748 if var_visitor.skip {
2751 let used_in_condition = &var_visitor.ids;
2752 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2753 used_in_condition.is_disjoint(&used_mutably)
2757 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2759 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2760 has_break_or_return: false,
2762 has_break_or_return_visitor.visit_expr(expr);
2763 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2765 if no_cond_variable_mutated && !mutable_static_in_cond {
2768 WHILE_IMMUTABLE_CONDITION,
2770 "variables in the condition are not mutated in the loop body",
2772 diag.note("this may lead to an infinite or to a never running loop");
2774 if has_break_or_return {
2775 diag.note("this loop contains `return`s or `break`s");
2776 diag.help("rewrite it as `if cond { loop { } }`");
2783 struct HasBreakOrReturnVisitor {
2784 has_break_or_return: bool,
2787 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2788 type Map = Map<'tcx>;
2790 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2791 if self.has_break_or_return {
2796 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2797 self.has_break_or_return = true;
2803 walk_expr(self, expr);
2806 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2807 NestedVisitorMap::None
2811 /// Collects the set of variables in an expression
2812 /// Stops analysis if a function call is found
2813 /// Note: In some cases such as `self`, there are no mutable annotation,
2814 /// All variables definition IDs are collected
2815 struct VarCollectorVisitor<'a, 'tcx> {
2816 cx: &'a LateContext<'tcx>,
2817 ids: FxHashSet<HirId>,
2818 def_ids: FxHashMap<def_id::DefId, bool>,
2822 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2823 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2825 if let ExprKind::Path(ref qpath) = ex.kind;
2826 if let QPath::Resolved(None, _) = *qpath;
2827 let res = qpath_res(self.cx, qpath, ex.hir_id);
2830 Res::Local(hir_id) => {
2831 self.ids.insert(hir_id);
2833 Res::Def(DefKind::Static, def_id) => {
2834 let mutable = self.cx.tcx.is_mutable_static(def_id);
2835 self.def_ids.insert(def_id, mutable);
2844 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2845 type Map = Map<'tcx>;
2847 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2849 ExprKind::Path(_) => self.insert_def_id(ex),
2850 // If there is any function/method call… we just stop analysis
2851 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2853 _ => walk_expr(self, ex),
2857 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2858 NestedVisitorMap::None
2862 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2864 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2865 check_needless_collect_direct_usage(expr, cx);
2866 check_needless_collect_indirect_usage(expr, cx);
2868 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2870 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2871 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2872 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2873 if let Some(ref generic_args) = chain_method.args;
2874 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2876 let ty = cx.typeck_results().node_type(ty.hir_id);
2877 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2878 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2879 match_type(cx, ty, &paths::BTREEMAP) ||
2880 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2881 if method.ident.name == sym!(len) {
2882 let span = shorten_needless_collect_span(expr);
2887 NEEDLESS_COLLECT_MSG,
2889 "count()".to_string(),
2890 Applicability::MachineApplicable,
2893 if method.ident.name == sym!(is_empty) {
2894 let span = shorten_needless_collect_span(expr);
2899 NEEDLESS_COLLECT_MSG,
2901 "next().is_none()".to_string(),
2902 Applicability::MachineApplicable,
2905 if method.ident.name == sym!(contains) {
2906 let contains_arg = snippet(cx, args[1].span, "??");
2907 let span = shorten_needless_collect_span(expr);
2912 NEEDLESS_COLLECT_MSG,
2914 let (arg, pred) = contains_arg
2916 .map_or(("&x", &*contains_arg), |s| ("x", s));
2917 diag.span_suggestion(
2921 "any(|{}| x == {})",
2924 Applicability::MachineApplicable,
2934 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2935 if let ExprKind::Block(ref block, _) = expr.kind {
2936 for ref stmt in block.stmts {
2938 if let StmtKind::Local(
2939 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2940 init: Some(ref init_expr), .. }
2942 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2943 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2944 if let Some(ref generic_args) = method_name.args;
2945 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2946 if let ty = cx.typeck_results().node_type(ty.hir_id);
2947 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2948 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2949 match_type(cx, ty, &paths::LINKED_LIST);
2950 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2951 if iter_calls.len() == 1;
2953 // Suggest replacing iter_call with iter_replacement, and removing stmt
2954 let iter_call = &iter_calls[0];
2958 stmt.span.until(iter_call.span),
2959 NEEDLESS_COLLECT_MSG,
2961 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2962 diag.multipart_suggestion(
2963 iter_call.get_suggestion_text(),
2965 (stmt.span, String::new()),
2966 (iter_call.span, iter_replacement)
2968 Applicability::MachineApplicable,// MaybeIncorrect,
2978 struct IterFunction {
2979 func: IterFunctionKind,
2983 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2985 IterFunctionKind::IntoIter => String::new(),
2986 IterFunctionKind::Len => String::from(".count()"),
2987 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2988 IterFunctionKind::Contains(span) => format!(".any(|x| x == {})", snippet(cx, *span, "..")),
2991 fn get_suggestion_text(&self) -> &'static str {
2993 IterFunctionKind::IntoIter => {
2994 "Use the original Iterator instead of collecting it and then producing a new one"
2996 IterFunctionKind::Len => {
2997 "Take the original Iterator's count instead of collecting it and finding the length"
2999 IterFunctionKind::IsEmpty => {
3000 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
3002 IterFunctionKind::Contains(_) => {
3003 "Check if the original Iterator contains an element instead of collecting then checking"
3008 enum IterFunctionKind {
3015 struct IterFunctionVisitor {
3016 uses: Vec<IterFunction>,
3020 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
3021 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
3022 // Check function calls on our collection
3024 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
3025 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
3026 if let &[name] = &path.segments;
3027 if name.ident == self.target;
3029 let len = sym!(len);
3030 let is_empty = sym!(is_empty);
3031 let contains = sym!(contains);
3032 match method_name.ident.name {
3033 sym::into_iter => self.uses.push(
3034 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
3036 name if name == len => self.uses.push(
3037 IterFunction { func: IterFunctionKind::Len, span: expr.span }
3039 name if name == is_empty => self.uses.push(
3040 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
3042 name if name == contains => self.uses.push(
3043 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
3045 _ => self.seen_other = true,
3050 // Check if the collection is used for anything else
3052 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
3053 if let &[name] = &path.segments;
3054 if name.ident == self.target;
3056 self.seen_other = true;
3058 walk_expr(self, expr);
3063 type Map = Map<'tcx>;
3064 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3065 NestedVisitorMap::None
3069 /// Detect the occurences of calls to `iter` or `into_iter` for the
3070 /// given identifier
3071 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
3072 let mut visitor = IterFunctionVisitor {
3077 visitor.visit_block(block);
3078 if visitor.seen_other {
3085 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3087 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3088 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3090 return expr.span.with_lo(span.lo());