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)> {
950 fn get_start<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
951 starts.iter().find_map(|start| {
952 if same_var(cx, e, start.id) {
961 cx: &LateContext<'tcx>,
963 starts: &[Start<'tcx>],
964 ) -> Option<MinifyingSugg<'static>> {
966 ExprKind::Lit(l) => match l.node {
967 ast::LitKind::Int(x, _ty) => Some(MinifyingSugg::non_paren(x.to_string())),
970 ExprKind::Path(..) if get_start(cx, e, starts).is_none() => {
971 // `e` is always non paren as it's a `Path`
972 Some(MinifyingSugg::non_paren(snippet(cx, e.span, "???")))
979 ExprKind::Binary(op, lhs, rhs) => match op.node {
981 let offset_opt = get_start(cx, lhs, starts)
982 .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
983 .or_else(|| get_start(cx, rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
985 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
988 get_start(cx, lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
992 ExprKind::Path(..) => get_start(cx, idx, starts).map(|s| (s, Offset::empty())),
997 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
998 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1005 fn get_assignments<'a: 'c, 'tcx: 'c, 'c>(
1006 cx: &'a LateContext<'tcx>,
1007 stmts: &'tcx [Stmt<'tcx>],
1008 expr: Option<&'tcx Expr<'tcx>>,
1009 loop_counters: &'c [Start<'tcx>],
1010 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'c {
1013 .filter_map(move |stmt| match stmt.kind {
1014 StmtKind::Local(..) | StmtKind::Item(..) => None,
1015 StmtKind::Expr(e) | StmtKind::Semi(e) => if_chain! {
1016 if let ExprKind::AssignOp(_, var, _) = e.kind;
1017 // skip StartKind::Range
1018 if loop_counters.iter().skip(1).any(|counter| Some(counter.id) == var_def_id(cx, var));
1019 then { None } else { Some(e) }
1022 .chain(expr.into_iter())
1023 .map(get_assignment)
1026 fn get_loop_counters<'a, 'tcx>(
1027 cx: &'a LateContext<'tcx>,
1028 body: &'tcx Block<'tcx>,
1029 expr: &'tcx Expr<'_>,
1030 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1031 // Look for variables that are incremented once per loop iteration.
1032 let mut increment_visitor = IncrementVisitor::new(cx);
1033 walk_block(&mut increment_visitor, body);
1035 // For each candidate, check the parent block to see if
1036 // it's initialized to zero at the start of the loop.
1037 get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
1040 .filter_map(move |var_id| {
1041 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1042 walk_block(&mut initialize_visitor, block);
1044 initialize_visitor.get_result().map(|(_, initializer)| Start {
1046 kind: StartKind::Counter { initializer },
1053 fn build_manual_memcpy_suggestion<'tcx>(
1054 cx: &LateContext<'tcx>,
1057 limits: ast::RangeLimits,
1058 dst: &IndexExpr<'_>,
1059 src: &IndexExpr<'_>,
1061 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1062 if offset.as_str() == "0" {
1063 MinifyingSugg::non_paren("")
1070 |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| -> MinifyingSugg<'static> {
1072 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1073 if method.ident.name == sym!(len);
1074 if len_args.len() == 1;
1075 if let Some(arg) = len_args.get(0);
1076 if var_def_id(cx, arg) == var_def_id(cx, base);
1078 if sugg.as_str() == end_str {
1079 MinifyingSugg::non_paren("")
1085 ast::RangeLimits::Closed => {
1086 sugg + &MinifyingSugg::non_paren("1")
1088 ast::RangeLimits::HalfOpen => sugg,
1094 let start_str = MinifyingSugg::hir(cx, start, "");
1095 let end_str = MinifyingSugg::hir(cx, end, "");
1097 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1098 StartKind::Range => (
1099 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)),
1104 apply_offset(&end_str, &idx_expr.idx_offset),
1107 StartKind::Counter { initializer } => {
1108 let counter_start = MinifyingSugg::hir(cx, initializer, "");
1110 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)),
1115 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1121 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1122 let (src_offset, src_limit) = print_offset_and_limit(&src);
1124 let dst_base_str = snippet_opt(cx, dst.base.span).unwrap_or_else(|| "???".into());
1125 let src_base_str = snippet_opt(cx, src.base.span).unwrap_or_else(|| "???".into());
1127 let dst = if dst_offset.as_str() == "" && dst_limit.as_str() == "" {
1133 dst_offset.maybe_par(),
1134 dst_limit.maybe_par()
1139 "{}.clone_from_slice(&{}[{}..{}])",
1142 src_offset.maybe_par(),
1143 src_limit.maybe_par()
1147 /// Checks for for loops that sequentially copy items from one slice-like
1148 /// object to another.
1149 fn detect_manual_memcpy<'tcx>(
1150 cx: &LateContext<'tcx>,
1152 arg: &'tcx Expr<'_>,
1153 body: &'tcx Expr<'_>,
1154 expr: &'tcx Expr<'_>,
1156 if let Some(higher::Range {
1160 }) = higher::range(arg)
1162 // the var must be a single name
1163 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1164 let mut starts = vec![Start {
1166 kind: StartKind::Range,
1169 // This is one of few ways to return different iterators
1170 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1171 let mut iter_a = None;
1172 let mut iter_b = None;
1174 if let ExprKind::Block(block, _) = body.kind {
1175 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1176 starts.extend(loop_counters);
1178 iter_a = Some(get_assignments(cx, block.stmts, block.expr, &starts));
1180 iter_b = Some(get_assignment(body));
1183 // The only statements in the for loops can be indexed assignments from
1184 // indexed retrievals.
1185 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1187 let big_sugg = assignments
1189 o.and_then(|(lhs, rhs)| {
1190 let rhs = fetch_cloned_expr(rhs);
1192 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1193 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1194 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1195 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1196 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1197 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1199 // Source and destination must be different
1200 if var_def_id(cx, base_left) != var_def_id(cx, base_right);
1202 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1203 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1210 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1211 .collect::<Option<Vec<_>>>()
1212 .filter(|v| !v.is_empty())
1213 .map(|v| v.join("\n "));
1215 if let Some(big_sugg) = big_sugg {
1220 "it looks like you're manually copying between slices",
1221 "try replacing the loop by",
1223 Applicability::Unspecified,
1230 // Scans the body of the for loop and determines whether lint should be given
1231 struct SameItemPushVisitor<'a, 'tcx> {
1233 // this field holds the last vec push operation visited, which should be the only push seen
1234 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1235 cx: &'a LateContext<'tcx>,
1238 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1239 type Map = Map<'tcx>;
1241 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1243 // Non-determinism may occur ... don't give a lint
1244 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1245 ExprKind::Block(block, _) => self.visit_block(block),
1250 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1251 for stmt in b.stmts.iter() {
1252 self.visit_stmt(stmt);
1256 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1257 let vec_push_option = get_vec_push(self.cx, s);
1258 if vec_push_option.is_none() {
1259 // Current statement is not a push so visit inside
1261 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1265 // Current statement is a push ...check whether another
1266 // push had been previously done
1267 if self.vec_push.is_none() {
1268 self.vec_push = vec_push_option;
1270 // There are multiple pushes ... don't lint
1271 self.should_lint = false;
1276 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1277 NestedVisitorMap::None
1281 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1282 // the Vec being pushed into and the item being pushed
1283 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1285 // Extract method being called
1286 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1287 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1288 // Figure out the parameters for the method call
1289 if let Some(self_expr) = args.get(0);
1290 if let Some(pushed_item) = args.get(1);
1291 // Check that the method being called is push() on a Vec
1292 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym!(vec_type));
1293 if path.ident.name.as_str() == "push";
1295 return Some((self_expr, pushed_item))
1301 /// Detects for loop pushing the same item into a Vec
1302 fn detect_same_item_push<'tcx>(
1303 cx: &LateContext<'tcx>,
1306 body: &'tcx Expr<'_>,
1309 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1310 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1311 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1317 "it looks like the same item is being pushed into this Vec",
1320 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1321 item_str, vec_str, item_str
1326 if !matches!(pat.kind, PatKind::Wild) {
1330 // Determine whether it is safe to lint the body
1331 let mut same_item_push_visitor = SameItemPushVisitor {
1336 walk_expr(&mut same_item_push_visitor, body);
1337 if same_item_push_visitor.should_lint {
1338 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1339 let vec_ty = cx.typeck_results().expr_ty(vec);
1340 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1345 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1347 // Make sure that the push does not involve possibly mutating values
1348 match pushed_item.kind {
1349 ExprKind::Path(ref qpath) => {
1350 match qpath_res(cx, qpath, pushed_item.hir_id) {
1351 // immutable bindings that are initialized with literal or constant
1352 Res::Local(hir_id) => {
1354 let node = cx.tcx.hir().get(hir_id);
1355 if let Node::Binding(pat) = node;
1356 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1357 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1358 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1359 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1360 if let Some(init) = parent_let_expr.init;
1363 // immutable bindings that are initialized with literal
1364 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1365 // immutable bindings that are initialized with constant
1366 ExprKind::Path(ref path) => {
1367 if let Res::Def(DefKind::Const, ..) = qpath_res(cx, path, init.hir_id) {
1368 emit_lint(cx, vec, pushed_item);
1377 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1381 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1389 /// Checks for looping over a range and then indexing a sequence with it.
1390 /// The iteratee must be a range literal.
1391 #[allow(clippy::too_many_lines)]
1392 fn check_for_loop_range<'tcx>(
1393 cx: &LateContext<'tcx>,
1395 arg: &'tcx Expr<'_>,
1396 body: &'tcx Expr<'_>,
1397 expr: &'tcx Expr<'_>,
1399 if let Some(higher::Range {
1403 }) = higher::range(arg)
1405 // the var must be a single name
1406 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1407 let mut visitor = VarVisitor {
1410 indexed_mut: FxHashSet::default(),
1411 indexed_indirectly: FxHashMap::default(),
1412 indexed_directly: FxHashMap::default(),
1413 referenced: FxHashSet::default(),
1415 prefer_mutable: false,
1417 walk_expr(&mut visitor, body);
1419 // linting condition: we only indexed one variable, and indexed it directly
1420 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1421 let (indexed, (indexed_extent, indexed_ty)) = visitor
1425 .expect("already checked that we have exactly 1 element");
1427 // ensure that the indexed variable was declared before the loop, see #601
1428 if let Some(indexed_extent) = indexed_extent {
1429 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1430 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1431 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1432 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1433 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1438 // don't lint if the container that is indexed does not have .iter() method
1439 let has_iter = has_iter_method(cx, indexed_ty);
1440 if has_iter.is_none() {
1444 // don't lint if the container that is indexed into is also used without
1446 if visitor.referenced.contains(&indexed) {
1450 let starts_at_zero = is_integer_const(cx, start, 0);
1452 let skip = if starts_at_zero {
1455 format!(".skip({})", snippet(cx, start.span, ".."))
1458 let mut end_is_start_plus_val = false;
1460 let take = if let Some(end) = *end {
1461 let mut take_expr = end;
1463 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1464 if let BinOpKind::Add = op.node {
1465 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1466 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1468 if start_equal_left {
1470 } else if start_equal_right {
1474 end_is_start_plus_val = start_equal_left | start_equal_right;
1478 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1482 ast::RangeLimits::Closed => {
1483 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1484 format!(".take({})", take_expr + sugg::ONE)
1486 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1493 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1494 ("mut ", "iter_mut")
1499 let take_is_empty = take.is_empty();
1500 let mut method_1 = take;
1501 let mut method_2 = skip;
1503 if end_is_start_plus_val {
1504 mem::swap(&mut method_1, &mut method_2);
1507 if visitor.nonindex {
1510 NEEDLESS_RANGE_LOOP,
1512 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1516 "consider using an iterator",
1518 (pat.span, format!("({}, <item>)", ident.name)),
1521 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1528 let repl = if starts_at_zero && take_is_empty {
1529 format!("&{}{}", ref_mut, indexed)
1531 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1536 NEEDLESS_RANGE_LOOP,
1539 "the loop variable `{}` is only used to index `{}`.",
1545 "consider using an iterator",
1546 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1556 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1558 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1559 if len_args.len() == 1;
1560 if method.ident.name == sym!(len);
1561 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1562 if path.segments.len() == 1;
1563 if path.segments[0].ident.name == var;
1572 fn is_end_eq_array_len<'tcx>(
1573 cx: &LateContext<'tcx>,
1575 limits: ast::RangeLimits,
1576 indexed_ty: Ty<'tcx>,
1579 if let ExprKind::Lit(ref lit) = end.kind;
1580 if let ast::LitKind::Int(end_int, _) = lit.node;
1581 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1582 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1584 return match limits {
1585 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1586 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1594 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1595 let mut applicability = Applicability::MachineApplicable;
1596 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1597 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1602 "it is more concise to loop over references to containers instead of using explicit \
1604 "to write this more concisely, try",
1605 format!("&{}{}", muta, object),
1610 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1611 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1612 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1613 // just the receiver, no arguments
1614 if args.len() == 1 {
1615 let method_name = &*method.ident.as_str();
1616 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1617 if method_name == "iter" || method_name == "iter_mut" {
1618 if is_ref_iterable_type(cx, &args[0]) {
1619 lint_iter_method(cx, args, arg, method_name);
1621 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1622 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1623 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1624 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1625 let mut applicability = Applicability::MachineApplicable;
1626 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1629 EXPLICIT_INTO_ITER_LOOP,
1631 "it is more concise to loop over containers instead of using explicit \
1633 "to write this more concisely, try",
1638 let ref_receiver_ty = cx.tcx.mk_ref(
1639 cx.tcx.lifetimes.re_erased,
1642 mutbl: Mutability::Not,
1645 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1646 lint_iter_method(cx, args, arg, method_name)
1649 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1654 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1655 probably not what you want",
1657 next_loop_linted = true;
1661 if !next_loop_linted {
1662 check_arg_type(cx, pat, arg);
1666 /// Checks for `for` loops over `Option`s and `Result`s.
1667 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1668 let ty = cx.typeck_results().expr_ty(arg);
1669 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1672 FOR_LOOPS_OVER_FALLIBLES,
1675 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1676 `if let` statement.",
1677 snippet(cx, arg.span, "_")
1681 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1682 snippet(cx, pat.span, "_"),
1683 snippet(cx, arg.span, "_")
1686 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1689 FOR_LOOPS_OVER_FALLIBLES,
1692 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1693 `if let` statement.",
1694 snippet(cx, arg.span, "_")
1698 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1699 snippet(cx, pat.span, "_"),
1700 snippet(cx, arg.span, "_")
1706 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1707 // incremented exactly once in the loop body, and initialized to zero
1708 // at the start of the loop.
1709 fn check_for_loop_explicit_counter<'tcx>(
1710 cx: &LateContext<'tcx>,
1712 arg: &'tcx Expr<'_>,
1713 body: &'tcx Expr<'_>,
1714 expr: &'tcx Expr<'_>,
1716 // Look for variables that are incremented once per loop iteration.
1717 let mut increment_visitor = IncrementVisitor::new(cx);
1718 walk_expr(&mut increment_visitor, body);
1720 // For each candidate, check the parent block to see if
1721 // it's initialized to zero at the start of the loop.
1722 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1723 for id in increment_visitor.into_results() {
1724 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1725 walk_block(&mut initialize_visitor, block);
1728 if let Some((name, initializer)) = initialize_visitor.get_result();
1729 if is_integer_const(cx, initializer, 0);
1731 let mut applicability = Applicability::MachineApplicable;
1733 // for some reason this is the only way to get the `Span`
1734 // of the entire `for` loop
1735 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1743 EXPLICIT_COUNTER_LOOP,
1744 for_span.with_hi(arg.span.hi()),
1745 &format!("the variable `{}` is used as a loop counter.", name),
1748 "for ({}, {}) in {}.enumerate()",
1750 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1751 make_iterator_snippet(cx, arg, &mut applicability),
1761 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1762 /// actual `Iterator` that the loop uses.
1763 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1764 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1765 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1770 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1773 // (&x).into_iter() ==> x.iter()
1774 // (&mut x).into_iter() ==> x.iter_mut()
1776 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1777 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1779 let meth_name = match mutability {
1780 Mutability::Mut => "iter_mut",
1781 Mutability::Not => "iter",
1785 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1791 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1797 /// Checks for the `FOR_KV_MAP` lint.
1798 fn check_for_loop_over_map_kv<'tcx>(
1799 cx: &LateContext<'tcx>,
1801 arg: &'tcx Expr<'_>,
1802 body: &'tcx Expr<'_>,
1803 expr: &'tcx Expr<'_>,
1805 let pat_span = pat.span;
1807 if let PatKind::Tuple(ref pat, _) = pat.kind {
1809 let arg_span = arg.span;
1810 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1811 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1812 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1813 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1818 let mutbl = match mutbl {
1819 Mutability::Not => "",
1820 Mutability::Mut => "_mut",
1822 let arg = match arg.kind {
1823 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1827 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1832 &format!("you seem to want to iterate on a map's {}s", kind),
1834 let map = sugg::Sugg::hir(cx, arg, "map");
1837 "use the corresponding method",
1839 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1840 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1850 struct MutatePairDelegate<'a, 'tcx> {
1851 cx: &'a LateContext<'tcx>,
1852 hir_id_low: Option<HirId>,
1853 hir_id_high: Option<HirId>,
1854 span_low: Option<Span>,
1855 span_high: Option<Span>,
1858 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1859 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1861 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1862 if let ty::BorrowKind::MutBorrow = bk {
1863 if let PlaceBase::Local(id) = cmt.place.base {
1864 if Some(id) == self.hir_id_low {
1865 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1867 if Some(id) == self.hir_id_high {
1868 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1874 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>) {
1875 if let PlaceBase::Local(id) = cmt.place.base {
1876 if Some(id) == self.hir_id_low {
1877 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1879 if Some(id) == self.hir_id_high {
1880 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1886 impl MutatePairDelegate<'_, '_> {
1887 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1888 (self.span_low, self.span_high)
1892 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1893 if let Some(higher::Range {
1897 }) = higher::range(arg)
1899 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1900 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1901 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1902 mut_warn_with_span(cx, span_low);
1903 mut_warn_with_span(cx, span_high);
1908 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
1909 if let Some(sp) = span {
1914 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1919 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
1921 if let ExprKind::Path(ref qpath) = bound.kind;
1922 if let QPath::Resolved(None, _) = *qpath;
1924 let res = qpath_res(cx, qpath, bound.hir_id);
1925 if let Res::Local(hir_id) = res {
1926 let node_str = cx.tcx.hir().get(hir_id);
1928 if let Node::Binding(pat) = node_str;
1929 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1930 if let BindingAnnotation::Mutable = bind_ann;
1932 return Some(hir_id);
1941 fn check_for_mutation<'tcx>(
1942 cx: &LateContext<'tcx>,
1944 bound_ids: &[Option<HirId>],
1945 ) -> (Option<Span>, Option<Span>) {
1946 let mut delegate = MutatePairDelegate {
1948 hir_id_low: bound_ids[0],
1949 hir_id_high: bound_ids[1],
1953 let def_id = body.hir_id.owner.to_def_id();
1954 cx.tcx.infer_ctxt().enter(|infcx| {
1955 ExprUseVisitor::new(
1958 def_id.expect_local(),
1960 cx.typeck_results(),
1964 delegate.mutation_span()
1967 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1968 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
1970 PatKind::Wild => true,
1971 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
1976 struct LocalUsedVisitor<'a, 'tcx> {
1977 cx: &'a LateContext<'tcx>,
1982 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1983 type Map = Map<'tcx>;
1985 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1986 if same_var(self.cx, expr, self.local) {
1989 walk_expr(self, expr);
1993 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1994 NestedVisitorMap::None
1998 struct VarVisitor<'a, 'tcx> {
1999 /// context reference
2000 cx: &'a LateContext<'tcx>,
2001 /// var name to look for as index
2003 /// indexed variables that are used mutably
2004 indexed_mut: FxHashSet<Symbol>,
2005 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2006 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2007 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2008 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2009 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2010 /// Any names that are used outside an index operation.
2011 /// Used to detect things like `&mut vec` used together with `vec[i]`
2012 referenced: FxHashSet<Symbol>,
2013 /// has the loop variable been used in expressions other than the index of
2016 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2017 /// takes `&mut self`
2018 prefer_mutable: bool,
2021 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2022 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2024 // the indexed container is referenced by a name
2025 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2026 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2027 if seqvar.segments.len() == 1;
2029 let index_used_directly = same_var(self.cx, idx, self.var);
2030 let indexed_indirectly = {
2031 let mut used_visitor = LocalUsedVisitor {
2036 walk_expr(&mut used_visitor, idx);
2040 if indexed_indirectly || index_used_directly {
2041 if self.prefer_mutable {
2042 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2044 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
2046 Res::Local(hir_id) => {
2047 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2048 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2049 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2050 if indexed_indirectly {
2051 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2053 if index_used_directly {
2054 self.indexed_directly.insert(
2055 seqvar.segments[0].ident.name,
2056 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2059 return false; // no need to walk further *on the variable*
2061 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2062 if indexed_indirectly {
2063 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2065 if index_used_directly {
2066 self.indexed_directly.insert(
2067 seqvar.segments[0].ident.name,
2068 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2071 return false; // no need to walk further *on the variable*
2082 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2083 type Map = Map<'tcx>;
2085 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2088 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2089 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
2090 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2091 if !self.check(&args[1], &args[0], expr);
2097 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2098 if !self.check(idx, seqexpr, expr);
2103 // directly using a variable
2104 if let ExprKind::Path(ref qpath) = expr.kind;
2105 if let QPath::Resolved(None, ref path) = *qpath;
2106 if path.segments.len() == 1;
2108 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2109 if local_id == self.var {
2110 self.nonindex = true;
2112 // not the correct variable, but still a variable
2113 self.referenced.insert(path.segments[0].ident.name);
2119 let old = self.prefer_mutable;
2121 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2122 self.prefer_mutable = true;
2123 self.visit_expr(lhs);
2124 self.prefer_mutable = false;
2125 self.visit_expr(rhs);
2127 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2128 if mutbl == Mutability::Mut {
2129 self.prefer_mutable = true;
2131 self.visit_expr(expr);
2133 ExprKind::Call(ref f, args) => {
2136 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2137 self.prefer_mutable = false;
2138 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2139 if mutbl == Mutability::Mut {
2140 self.prefer_mutable = true;
2143 self.visit_expr(expr);
2146 ExprKind::MethodCall(_, _, args, _) => {
2147 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2148 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2149 self.prefer_mutable = false;
2150 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2151 if mutbl == Mutability::Mut {
2152 self.prefer_mutable = true;
2155 self.visit_expr(expr);
2158 ExprKind::Closure(_, _, body_id, ..) => {
2159 let body = self.cx.tcx.hir().body(body_id);
2160 self.visit_expr(&body.value);
2162 _ => walk_expr(self, expr),
2164 self.prefer_mutable = old;
2166 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2167 NestedVisitorMap::None
2171 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2172 let def_id = match var_def_id(cx, expr) {
2174 None => return false,
2176 if let Some(used_mutably) = mutated_variables(container, cx) {
2177 if used_mutably.contains(&def_id) {
2184 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2185 let def_id = match var_def_id(cx, iter_expr) {
2187 None => return false,
2189 let mut visitor = VarUsedAfterLoopVisitor {
2192 iter_expr_id: iter_expr.hir_id,
2193 past_while_let: false,
2194 var_used_after_while_let: false,
2196 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2197 walk_block(&mut visitor, enclosing_block);
2199 visitor.var_used_after_while_let
2202 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2203 cx: &'a LateContext<'tcx>,
2205 iter_expr_id: HirId,
2206 past_while_let: bool,
2207 var_used_after_while_let: bool,
2210 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2211 type Map = Map<'tcx>;
2213 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2214 if self.past_while_let {
2215 if Some(self.def_id) == var_def_id(self.cx, expr) {
2216 self.var_used_after_while_let = true;
2218 } else if self.iter_expr_id == expr.hir_id {
2219 self.past_while_let = true;
2221 walk_expr(self, expr);
2223 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2224 NestedVisitorMap::None
2228 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2229 /// for `&T` and `&mut T`, such as `Vec`.
2231 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2232 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2233 // will allow further borrows afterwards
2234 let ty = cx.typeck_results().expr_ty(e);
2235 is_iterable_array(ty, cx) ||
2236 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2237 match_type(cx, ty, &paths::LINKED_LIST) ||
2238 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2239 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2240 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2241 match_type(cx, ty, &paths::BINARY_HEAP) ||
2242 match_type(cx, ty, &paths::BTREEMAP) ||
2243 match_type(cx, ty, &paths::BTREESET)
2246 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2247 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2249 ty::Array(_, n) => n
2250 .try_eval_usize(cx.tcx, cx.param_env)
2251 .map_or(false, |val| (0..=32).contains(&val)),
2256 /// If a block begins with a statement (possibly a `let` binding) and has an
2257 /// expression, return it.
2258 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2259 if block.stmts.is_empty() {
2262 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2263 local.init //.map(|expr| expr)
2269 /// If a block begins with an expression (with or without semicolon), return it.
2270 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2272 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2273 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2274 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2275 StmtKind::Local(..) | StmtKind::Item(..) => None,
2281 /// Returns `true` if expr contains a single break expr without destination label
2283 /// passed expression. The expression may be within a block.
2284 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2286 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2287 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2292 #[derive(Debug, PartialEq)]
2293 enum IncrementVisitorVarState {
2294 Initial, // Not examined yet
2295 IncrOnce, // Incremented exactly once, may be a loop counter
2299 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2300 struct IncrementVisitor<'a, 'tcx> {
2301 cx: &'a LateContext<'tcx>, // context reference
2302 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2303 depth: u32, // depth of conditional expressions
2307 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2308 fn new(cx: &'a LateContext<'tcx>) -> Self {
2311 states: FxHashMap::default(),
2317 fn into_results(self) -> impl Iterator<Item = HirId> {
2318 self.states.into_iter().filter_map(|(id, state)| {
2319 if state == IncrementVisitorVarState::IncrOnce {
2328 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2329 type Map = Map<'tcx>;
2331 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2336 // If node is a variable
2337 if let Some(def_id) = var_def_id(self.cx, expr) {
2338 if let Some(parent) = get_parent_expr(self.cx, expr) {
2339 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2340 if *state == IncrementVisitorVarState::IncrOnce {
2341 *state = IncrementVisitorVarState::DontWarn;
2346 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2347 if lhs.hir_id == expr.hir_id {
2348 *state = if op.node == BinOpKind::Add
2349 && is_integer_const(self.cx, rhs, 1)
2350 && *state == IncrementVisitorVarState::Initial
2353 IncrementVisitorVarState::IncrOnce
2355 // Assigned some other value or assigned multiple times
2356 IncrementVisitorVarState::DontWarn
2360 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2361 *state = IncrementVisitorVarState::DontWarn
2363 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2364 *state = IncrementVisitorVarState::DontWarn
2370 walk_expr(self, expr);
2371 } else if is_loop(expr) || is_conditional(expr) {
2373 walk_expr(self, expr);
2375 } else if let ExprKind::Continue(_) = expr.kind {
2378 walk_expr(self, expr);
2381 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2382 NestedVisitorMap::None
2386 enum InitializeVisitorState<'hir> {
2387 Initial, // Not examined yet
2388 Declared(Symbol), // Declared but not (yet) initialized
2391 initializer: &'hir Expr<'hir>,
2396 /// Checks whether a variable is initialized at the start of a loop and not modified
2397 /// and used after the loop.
2398 struct InitializeVisitor<'a, 'tcx> {
2399 cx: &'a LateContext<'tcx>, // context reference
2400 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2402 state: InitializeVisitorState<'tcx>,
2403 depth: u32, // depth of conditional expressions
2407 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2408 fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2413 state: InitializeVisitorState::Initial,
2419 fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
2420 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2421 Some((name, initializer))
2428 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2429 type Map = Map<'tcx>;
2431 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2432 // Look for declarations of the variable
2434 if let StmtKind::Local(ref local) = stmt.kind;
2435 if local.pat.hir_id == self.var_id;
2436 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2438 self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
2439 InitializeVisitorState::Initialized {
2446 walk_stmt(self, stmt);
2449 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2450 if matches!(self.state, InitializeVisitorState::DontWarn) {
2453 if expr.hir_id == self.end_expr.hir_id {
2454 self.past_loop = true;
2457 // No need to visit expressions before the variable is
2459 if matches!(self.state, InitializeVisitorState::Initial) {
2463 // If node is the desired variable, see how it's used
2464 if var_def_id(self.cx, expr) == Some(self.var_id) {
2466 self.state = InitializeVisitorState::DontWarn;
2470 if let Some(parent) = get_parent_expr(self.cx, expr) {
2472 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2473 self.state = InitializeVisitorState::DontWarn;
2475 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2476 self.state = if_chain! {
2478 if let InitializeVisitorState::Declared(name)
2479 | InitializeVisitorState::Initialized { name, ..} = self.state;
2481 InitializeVisitorState::Initialized { initializer: rhs, name }
2483 InitializeVisitorState::DontWarn
2487 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2488 self.state = InitializeVisitorState::DontWarn
2494 walk_expr(self, expr);
2495 } else if !self.past_loop && is_loop(expr) {
2496 self.state = InitializeVisitorState::DontWarn;
2497 } else if is_conditional(expr) {
2499 walk_expr(self, expr);
2502 walk_expr(self, expr);
2506 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2507 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2511 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2512 if let ExprKind::Path(ref qpath) = expr.kind {
2513 let path_res = qpath_res(cx, qpath, expr.hir_id);
2514 if let Res::Local(hir_id) = path_res {
2515 return Some(hir_id);
2521 fn is_loop(expr: &Expr<'_>) -> bool {
2522 matches!(expr.kind, ExprKind::Loop(..))
2525 fn is_conditional(expr: &Expr<'_>) -> bool {
2526 matches!(expr.kind, ExprKind::Match(..))
2529 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2531 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2532 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2533 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2535 return is_loop_nested(cx, loop_expr, iter_expr)
2541 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2542 let mut id = loop_expr.hir_id;
2543 let iter_name = if let Some(name) = path_name(iter_expr) {
2549 let parent = cx.tcx.hir().get_parent_node(id);
2553 match cx.tcx.hir().find(parent) {
2554 Some(Node::Expr(expr)) => {
2555 if let ExprKind::Loop(..) = expr.kind {
2559 Some(Node::Block(block)) => {
2560 let mut block_visitor = LoopNestVisitor {
2562 iterator: iter_name,
2565 walk_block(&mut block_visitor, block);
2566 if block_visitor.nesting == RuledOut {
2570 Some(Node::Stmt(_)) => (),
2579 #[derive(PartialEq, Eq)]
2581 Unknown, // no nesting detected yet
2582 RuledOut, // the iterator is initialized or assigned within scope
2583 LookFurther, // no nesting detected, no further walk required
2586 use self::Nesting::{LookFurther, RuledOut, Unknown};
2588 struct LoopNestVisitor {
2594 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2595 type Map = Map<'tcx>;
2597 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2598 if stmt.hir_id == self.hir_id {
2599 self.nesting = LookFurther;
2600 } else if self.nesting == Unknown {
2601 walk_stmt(self, stmt);
2605 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2606 if self.nesting != Unknown {
2609 if expr.hir_id == self.hir_id {
2610 self.nesting = LookFurther;
2614 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2615 if match_var(path, self.iterator) {
2616 self.nesting = RuledOut;
2619 _ => walk_expr(self, expr),
2623 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2624 if self.nesting != Unknown {
2627 if let PatKind::Binding(.., span_name, _) = pat.kind {
2628 if self.iterator == span_name.name {
2629 self.nesting = RuledOut;
2636 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2637 NestedVisitorMap::None
2641 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2642 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2643 let segments = &path.segments;
2644 if segments.len() == 1 {
2645 return Some(segments[0].ident.name);
2651 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2652 if constant(cx, cx.typeck_results(), cond).is_some() {
2653 // A pure constant condition (e.g., `while false`) is not linted.
2657 let mut var_visitor = VarCollectorVisitor {
2659 ids: FxHashSet::default(),
2660 def_ids: FxHashMap::default(),
2663 var_visitor.visit_expr(cond);
2664 if var_visitor.skip {
2667 let used_in_condition = &var_visitor.ids;
2668 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2669 used_in_condition.is_disjoint(&used_mutably)
2673 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2675 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2676 has_break_or_return: false,
2678 has_break_or_return_visitor.visit_expr(expr);
2679 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2681 if no_cond_variable_mutated && !mutable_static_in_cond {
2684 WHILE_IMMUTABLE_CONDITION,
2686 "variables in the condition are not mutated in the loop body",
2688 diag.note("this may lead to an infinite or to a never running loop");
2690 if has_break_or_return {
2691 diag.note("this loop contains `return`s or `break`s");
2692 diag.help("rewrite it as `if cond { loop { } }`");
2699 struct HasBreakOrReturnVisitor {
2700 has_break_or_return: bool,
2703 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2704 type Map = Map<'tcx>;
2706 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2707 if self.has_break_or_return {
2712 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2713 self.has_break_or_return = true;
2719 walk_expr(self, expr);
2722 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2723 NestedVisitorMap::None
2727 /// Collects the set of variables in an expression
2728 /// Stops analysis if a function call is found
2729 /// Note: In some cases such as `self`, there are no mutable annotation,
2730 /// All variables definition IDs are collected
2731 struct VarCollectorVisitor<'a, 'tcx> {
2732 cx: &'a LateContext<'tcx>,
2733 ids: FxHashSet<HirId>,
2734 def_ids: FxHashMap<def_id::DefId, bool>,
2738 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2739 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2741 if let ExprKind::Path(ref qpath) = ex.kind;
2742 if let QPath::Resolved(None, _) = *qpath;
2743 let res = qpath_res(self.cx, qpath, ex.hir_id);
2746 Res::Local(hir_id) => {
2747 self.ids.insert(hir_id);
2749 Res::Def(DefKind::Static, def_id) => {
2750 let mutable = self.cx.tcx.is_mutable_static(def_id);
2751 self.def_ids.insert(def_id, mutable);
2760 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2761 type Map = Map<'tcx>;
2763 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2765 ExprKind::Path(_) => self.insert_def_id(ex),
2766 // If there is any function/method call… we just stop analysis
2767 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2769 _ => walk_expr(self, ex),
2773 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2774 NestedVisitorMap::None
2778 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2780 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2781 check_needless_collect_direct_usage(expr, cx);
2782 check_needless_collect_indirect_usage(expr, cx);
2784 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2786 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2787 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2788 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2789 if let Some(ref generic_args) = chain_method.args;
2790 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2792 let ty = cx.typeck_results().node_type(ty.hir_id);
2793 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2794 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2795 match_type(cx, ty, &paths::BTREEMAP) ||
2796 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2797 if method.ident.name == sym!(len) {
2798 let span = shorten_needless_collect_span(expr);
2803 NEEDLESS_COLLECT_MSG,
2805 "count()".to_string(),
2806 Applicability::MachineApplicable,
2809 if method.ident.name == sym!(is_empty) {
2810 let span = shorten_needless_collect_span(expr);
2815 NEEDLESS_COLLECT_MSG,
2817 "next().is_none()".to_string(),
2818 Applicability::MachineApplicable,
2821 if method.ident.name == sym!(contains) {
2822 let contains_arg = snippet(cx, args[1].span, "??");
2823 let span = shorten_needless_collect_span(expr);
2828 NEEDLESS_COLLECT_MSG,
2830 let (arg, pred) = contains_arg
2832 .map_or(("&x", &*contains_arg), |s| ("x", s));
2833 diag.span_suggestion(
2837 "any(|{}| x == {})",
2840 Applicability::MachineApplicable,
2850 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2851 if let ExprKind::Block(ref block, _) = expr.kind {
2852 for ref stmt in block.stmts {
2854 if let StmtKind::Local(
2855 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2856 init: Some(ref init_expr), .. }
2858 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2859 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2860 if let Some(ref generic_args) = method_name.args;
2861 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2862 if let ty = cx.typeck_results().node_type(ty.hir_id);
2863 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2864 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2865 match_type(cx, ty, &paths::LINKED_LIST);
2866 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2867 if iter_calls.len() == 1;
2869 // Suggest replacing iter_call with iter_replacement, and removing stmt
2870 let iter_call = &iter_calls[0];
2874 stmt.span.until(iter_call.span),
2875 NEEDLESS_COLLECT_MSG,
2877 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2878 diag.multipart_suggestion(
2879 iter_call.get_suggestion_text(),
2881 (stmt.span, String::new()),
2882 (iter_call.span, iter_replacement)
2884 Applicability::MachineApplicable,// MaybeIncorrect,
2894 struct IterFunction {
2895 func: IterFunctionKind,
2899 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2901 IterFunctionKind::IntoIter => String::new(),
2902 IterFunctionKind::Len => String::from(".count()"),
2903 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2904 IterFunctionKind::Contains(span) => format!(".any(|x| x == {})", snippet(cx, *span, "..")),
2907 fn get_suggestion_text(&self) -> &'static str {
2909 IterFunctionKind::IntoIter => {
2910 "Use the original Iterator instead of collecting it and then producing a new one"
2912 IterFunctionKind::Len => {
2913 "Take the original Iterator's count instead of collecting it and finding the length"
2915 IterFunctionKind::IsEmpty => {
2916 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
2918 IterFunctionKind::Contains(_) => {
2919 "Check if the original Iterator contains an element instead of collecting then checking"
2924 enum IterFunctionKind {
2931 struct IterFunctionVisitor {
2932 uses: Vec<IterFunction>,
2936 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
2937 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
2938 // Check function calls on our collection
2940 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
2941 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
2942 if let &[name] = &path.segments;
2943 if name.ident == self.target;
2945 let len = sym!(len);
2946 let is_empty = sym!(is_empty);
2947 let contains = sym!(contains);
2948 match method_name.ident.name {
2949 sym::into_iter => self.uses.push(
2950 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
2952 name if name == len => self.uses.push(
2953 IterFunction { func: IterFunctionKind::Len, span: expr.span }
2955 name if name == is_empty => self.uses.push(
2956 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
2958 name if name == contains => self.uses.push(
2959 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
2961 _ => self.seen_other = true,
2966 // Check if the collection is used for anything else
2968 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
2969 if let &[name] = &path.segments;
2970 if name.ident == self.target;
2972 self.seen_other = true;
2974 walk_expr(self, expr);
2979 type Map = Map<'tcx>;
2980 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2981 NestedVisitorMap::None
2985 /// Detect the occurences of calls to `iter` or `into_iter` for the
2986 /// given identifier
2987 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
2988 let mut visitor = IterFunctionVisitor {
2993 visitor.visit_block(block);
2994 if visitor.seen_other {
3001 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3003 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3004 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3006 return expr.span.with_lo(span.lo());