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, span_lint,
9 span_lint_and_help, span_lint_and_sugg, span_lint_and_then, sugg, SpanlessEq,
11 use if_chain::if_chain;
13 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
14 use rustc_errors::Applicability;
15 use rustc_hir::def::{DefKind, Res};
16 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
18 def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, InlineAsmOperand,
19 Local, LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
21 use rustc_infer::infer::TyCtxtInferExt;
22 use rustc_lint::{LateContext, LateLintPass, LintContext};
23 use rustc_middle::hir::map::Map;
24 use rustc_middle::lint::in_external_macro;
25 use rustc_middle::middle::region;
26 use rustc_middle::ty::{self, Ty, TyS};
27 use rustc_session::{declare_lint_pass, declare_tool_lint};
28 use rustc_span::source_map::Span;
29 use rustc_span::symbol::{sym, Ident, Symbol};
30 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
31 use std::iter::{once, Iterator};
34 declare_clippy_lint! {
35 /// **What it does:** Checks for for-loops that manually copy items between
36 /// slices that could be optimized by having a memcpy.
38 /// **Why is this bad?** It is not as fast as a memcpy.
40 /// **Known problems:** None.
44 /// # let src = vec![1];
45 /// # let mut dst = vec![0; 65];
46 /// for i in 0..src.len() {
47 /// dst[i + 64] = src[i];
50 /// Could be written as:
52 /// # let src = vec![1];
53 /// # let mut dst = vec![0; 65];
54 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
58 "manually copying items between slices"
61 declare_clippy_lint! {
62 /// **What it does:** Checks for looping over the range of `0..len` of some
63 /// collection just to get the values by index.
65 /// **Why is this bad?** Just iterating the collection itself makes the intent
66 /// more clear and is probably faster.
68 /// **Known problems:** None.
72 /// let vec = vec!['a', 'b', 'c'];
73 /// for i in 0..vec.len() {
74 /// println!("{}", vec[i]);
77 /// Could be written as:
79 /// let vec = vec!['a', 'b', 'c'];
81 /// println!("{}", i);
84 pub NEEDLESS_RANGE_LOOP,
86 "for-looping over a range of indices where an iterator over items would do"
89 declare_clippy_lint! {
90 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
91 /// suggests the latter.
93 /// **Why is this bad?** Readability.
95 /// **Known problems:** False negatives. We currently only warn on some known
100 /// // with `y` a `Vec` or slice:
101 /// # let y = vec![1];
102 /// for x in y.iter() {
106 /// can be rewritten to
108 /// # let y = vec![1];
113 pub EXPLICIT_ITER_LOOP,
115 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
118 declare_clippy_lint! {
119 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
120 /// suggests the latter.
122 /// **Why is this bad?** Readability.
124 /// **Known problems:** None
128 /// # let y = vec![1];
129 /// // with `y` a `Vec` or slice:
130 /// for x in y.into_iter() {
134 /// can be rewritten to
136 /// # let y = vec![1];
141 pub EXPLICIT_INTO_ITER_LOOP,
143 "for-looping over `_.into_iter()` when `_` would do"
146 declare_clippy_lint! {
147 /// **What it does:** Checks for loops on `x.next()`.
149 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
150 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
151 /// implements `IntoIterator`, so that possibly one value will be iterated,
152 /// leading to some hard to find bugs. No one will want to write such code
153 /// [except to win an Underhanded Rust
154 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
156 /// **Known problems:** None.
160 /// for x in y.next() {
166 "for-looping over `_.next()` which is probably not intended"
169 declare_clippy_lint! {
170 /// **What it does:** Checks for `for` loops over `Option` or `Result` values.
172 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
175 /// **Known problems:** None.
179 /// # let opt = Some(1);
187 /// if let Some(x) = opt {
195 /// # let res: Result<i32, std::io::Error> = Ok(1);
203 /// if let Ok(x) = res {
207 pub FOR_LOOPS_OVER_FALLIBLES,
209 "for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
212 declare_clippy_lint! {
213 /// **What it does:** Detects `loop + match` combinations that are easier
214 /// written as a `while let` loop.
216 /// **Why is this bad?** The `while let` loop is usually shorter and more
219 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
223 /// # let y = Some(1);
225 /// let x = match y {
229 /// // .. do something with x
231 /// // is easier written as
232 /// while let Some(x) = y {
233 /// // .. do something with x
238 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
241 declare_clippy_lint! {
242 /// **What it does:** Checks for functions collecting an iterator when collect
245 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
246 /// when this allocation may not be needed.
248 /// **Known problems:**
253 /// # let iterator = vec![1].into_iter();
254 /// let len = iterator.clone().collect::<Vec<_>>().len();
256 /// let len = iterator.count();
258 pub NEEDLESS_COLLECT,
260 "collecting an iterator when collect is not needed"
263 declare_clippy_lint! {
264 /// **What it does:** Checks `for` loops over slices with an explicit counter
265 /// and suggests the use of `.enumerate()`.
267 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
268 /// declutters the code and may be faster in some instances.
270 /// **Known problems:** None.
274 /// # let v = vec![1];
275 /// # fn bar(bar: usize, baz: usize) {}
282 /// Could be written as
284 /// # let v = vec![1];
285 /// # fn bar(bar: usize, baz: usize) {}
286 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
288 pub EXPLICIT_COUNTER_LOOP,
290 "for-looping with an explicit counter when `_.enumerate()` would do"
293 declare_clippy_lint! {
294 /// **What it does:** Checks for empty `loop` expressions.
296 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
297 /// anything. Think of the environment and either block on something or at least
298 /// make the thread sleep for some microseconds.
300 /// **Known problems:** None.
308 "empty `loop {}`, which should block or sleep"
311 declare_clippy_lint! {
312 /// **What it does:** Checks for `while let` expressions on iterators.
314 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
315 /// the intent better.
317 /// **Known problems:** None.
321 /// while let Some(val) = iter() {
325 pub WHILE_LET_ON_ITERATOR,
327 "using a while-let loop instead of a for loop on an iterator"
330 declare_clippy_lint! {
331 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
332 /// ignoring either the keys or values.
334 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
335 /// can be used to express that don't need the values or keys.
337 /// **Known problems:** None.
341 /// for (k, _) in &map {
346 /// could be replaced by
349 /// for k in map.keys() {
355 "looping on a map using `iter` when `keys` or `values` would do"
358 declare_clippy_lint! {
359 /// **What it does:** Checks for loops that will always `break`, `return` or
360 /// `continue` an outer loop.
362 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
365 /// **Known problems:** None
376 "any loop that will always `break` or `return`"
379 declare_clippy_lint! {
380 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
382 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
384 /// **Known problems:** None
388 /// let mut foo = 42;
389 /// for i in 0..foo {
391 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
396 "for loop over a range where one of the bounds is a mutable variable"
399 declare_clippy_lint! {
400 /// **What it does:** Checks whether variables used within while loop condition
401 /// can be (and are) mutated in the body.
403 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
404 /// will lead to an infinite loop.
406 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
407 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
408 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
414 /// println!("let me loop forever!");
417 pub WHILE_IMMUTABLE_CONDITION,
419 "variables used within while expression are not mutated in the body"
422 declare_clippy_lint! {
423 /// **What it does:** Checks whether a for loop is being used to push a constant
424 /// value into a Vec.
426 /// **Why is this bad?** This kind of operation can be expressed more succinctly with
427 /// `vec![item;SIZE]` or `vec.resize(NEW_SIZE, item)` and using these alternatives may also
428 /// have better performance.
429 /// **Known problems:** None
435 /// let mut vec: Vec<u8> = Vec::new();
443 /// could be written as
447 /// let mut vec: Vec<u8> = vec![item1; 20];
448 /// vec.resize(20 + 30, item2);
452 "the same item is pushed inside of a for loop"
455 declare_lint_pass!(Loops => [
459 EXPLICIT_INTO_ITER_LOOP,
461 FOR_LOOPS_OVER_FALLIBLES,
464 EXPLICIT_COUNTER_LOOP,
466 WHILE_LET_ON_ITERATOR,
470 WHILE_IMMUTABLE_CONDITION,
474 impl<'tcx> LateLintPass<'tcx> for Loops {
475 #[allow(clippy::too_many_lines)]
476 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
477 if let Some((pat, arg, body)) = higher::for_loop(expr) {
478 // we don't want to check expanded macros
479 // this check is not at the top of the function
480 // since higher::for_loop expressions are marked as expansions
481 if body.span.from_expansion() {
484 check_for_loop(cx, pat, arg, body, expr);
487 // we don't want to check expanded macros
488 if expr.span.from_expansion() {
492 // check for never_loop
493 if let ExprKind::Loop(ref block, _, _) = expr.kind {
494 match never_loop_block(block, expr.hir_id) {
495 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
496 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
500 // check for `loop { if let {} else break }` that could be `while let`
501 // (also matches an explicit "match" instead of "if let")
502 // (even if the "match" or "if let" is used for declaration)
503 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
504 // also check for empty `loop {}` statements
505 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) {
510 "empty `loop {}` detected. You may want to either use `panic!()` or add \
511 `std::thread::sleep(..);` to the loop body.",
515 // extract the expression from the first statement (if any) in a block
516 let inner_stmt_expr = extract_expr_from_first_stmt(block);
517 // or extract the first expression (if any) from the block
518 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
519 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
520 // ensure "if let" compatible match structure
522 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
524 && arms[0].guard.is_none()
525 && arms[1].guard.is_none()
526 && is_simple_break_expr(&arms[1].body)
528 if in_external_macro(cx.sess(), expr.span) {
532 // NOTE: we used to build a body here instead of using
533 // ellipsis, this was removed because:
534 // 1) it was ugly with big bodies;
535 // 2) it was not indented properly;
536 // 3) it wasn’t very smart (see #675).
537 let mut applicability = Applicability::HasPlaceholders;
542 "this loop could be written as a `while let` loop",
545 "while let {} = {} {{ .. }}",
546 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
547 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
558 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
559 let pat = &arms[0].pat.kind;
561 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
562 &ExprKind::MethodCall(ref method_path, _, ref method_args, _),
563 ) = (pat, &match_expr.kind)
565 let iter_expr = &method_args[0];
567 // Don't lint when the iterator is recreated on every iteration
569 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
570 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
571 if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
577 let lhs_constructor = last_path_segment(qpath);
578 if method_path.ident.name == sym!(next)
579 && match_trait_method(cx, match_expr, &paths::ITERATOR)
580 && lhs_constructor.ident.name == sym!(Some)
581 && (pat_args.is_empty()
582 || !is_refutable(cx, &pat_args[0])
583 && !is_used_inside(cx, iter_expr, &arms[0].body)
584 && !is_iterator_used_after_while_let(cx, iter_expr)
585 && !is_nested(cx, expr, &method_args[0]))
587 let mut applicability = Applicability::MachineApplicable;
588 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
589 let loop_var = if pat_args.is_empty() {
592 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
596 WHILE_LET_ON_ITERATOR,
597 expr.span.with_hi(match_expr.span.hi()),
598 "this loop could be written as a `for` loop",
600 format!("for {} in {}", loop_var, iterator),
607 if let Some((cond, body)) = higher::while_loop(&expr) {
608 check_infinite_loop(cx, cond, body);
611 check_needless_collect(expr, cx);
615 enum NeverLoopResult {
616 // A break/return always get triggered but not necessarily for the main loop.
618 // A continue may occur for the main loop.
624 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
626 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
627 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
631 // Combine two results for parts that are called in order.
633 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
635 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
636 NeverLoopResult::Otherwise => second,
640 // Combine two results where both parts are called but not necessarily in order.
642 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
643 match (left, right) {
644 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
645 NeverLoopResult::MayContinueMainLoop
647 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
648 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
652 // Combine two results where only one of the part may have been executed.
654 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
656 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
657 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
658 NeverLoopResult::MayContinueMainLoop
660 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
664 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
665 let stmts = block.stmts.iter().map(stmt_to_expr);
666 let expr = once(block.expr.as_deref());
667 let mut iter = stmts.chain(expr).filter_map(|e| e);
668 never_loop_expr_seq(&mut iter, main_loop_id)
671 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
673 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
674 StmtKind::Local(ref local) => local.init.as_deref(),
679 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
682 | ExprKind::Unary(_, ref e)
683 | ExprKind::Cast(ref e, _)
684 | ExprKind::Type(ref e, _)
685 | ExprKind::Field(ref e, _)
686 | ExprKind::AddrOf(_, _, ref e)
687 | ExprKind::Struct(_, _, Some(ref e))
688 | ExprKind::Repeat(ref e, _)
689 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
690 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
691 never_loop_expr_all(&mut es.iter(), main_loop_id)
693 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
694 ExprKind::Binary(_, ref e1, ref e2)
695 | ExprKind::Assign(ref e1, ref e2, _)
696 | ExprKind::AssignOp(_, ref e1, ref e2)
697 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
698 ExprKind::Loop(ref b, _, _) => {
699 // Break can come from the inner loop so remove them.
700 absorb_break(&never_loop_block(b, main_loop_id))
702 ExprKind::Match(ref e, ref arms, _) => {
703 let e = never_loop_expr(e, main_loop_id);
707 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
711 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
712 ExprKind::Continue(d) => {
715 .expect("target ID can only be missing in the presence of compilation errors");
716 if id == main_loop_id {
717 NeverLoopResult::MayContinueMainLoop
719 NeverLoopResult::AlwaysBreak
722 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
723 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
725 ExprKind::InlineAsm(ref asm) => asm
729 InlineAsmOperand::In { expr, .. }
730 | InlineAsmOperand::InOut { expr, .. }
731 | InlineAsmOperand::Const { expr }
732 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
733 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
734 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
735 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
738 .fold(NeverLoopResult::Otherwise, combine_both),
739 ExprKind::Struct(_, _, None)
740 | ExprKind::Yield(_, _)
741 | ExprKind::Closure(_, _, _, _, _)
742 | ExprKind::LlvmInlineAsm(_)
745 | ExprKind::Err => NeverLoopResult::Otherwise,
749 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
750 es.map(|e| never_loop_expr(e, main_loop_id))
751 .fold(NeverLoopResult::Otherwise, combine_seq)
754 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
755 es.map(|e| never_loop_expr(e, main_loop_id))
756 .fold(NeverLoopResult::Otherwise, combine_both)
759 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
760 e.map(|e| never_loop_expr(e, main_loop_id))
761 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
764 fn check_for_loop<'tcx>(
765 cx: &LateContext<'tcx>,
768 body: &'tcx Expr<'_>,
769 expr: &'tcx Expr<'_>,
771 check_for_loop_range(cx, pat, arg, body, expr);
772 check_for_loop_arg(cx, pat, arg, expr);
773 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
774 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
775 check_for_mut_range_bound(cx, arg, body);
776 detect_manual_memcpy(cx, pat, arg, body, expr);
777 detect_same_item_push(cx, pat, arg, body, expr);
780 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
782 if let ExprKind::Path(qpath) = &expr.kind;
783 if let QPath::Resolved(None, path) = qpath;
784 if path.segments.len() == 1;
785 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
795 #[derive(Clone, Copy)]
807 fn negative(value: String) -> Self {
810 sign: OffsetSign::Negative,
814 fn positive(value: String) -> Self {
817 sign: OffsetSign::Positive,
822 struct FixedOffsetVar<'hir> {
823 var: &'hir Expr<'hir>,
827 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
828 let is_slice = match ty.kind {
829 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
830 ty::Slice(..) | ty::Array(..) => true,
834 is_slice || is_type_diagnostic_item(cx, ty, sym!(vec_type)) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
837 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
839 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
840 if method.ident.name == sym!(clone);
842 if let Some(arg) = args.get(0);
843 then { arg } else { expr }
847 fn get_offset<'tcx>(cx: &LateContext<'tcx>, idx: &Expr<'_>, var: HirId) -> Option<Offset> {
848 fn extract_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, var: HirId) -> Option<String> {
850 ExprKind::Lit(l) => match l.node {
851 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
854 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
860 ExprKind::Binary(op, lhs, rhs) => match op.node {
862 let offset_opt = if same_var(cx, lhs, var) {
863 extract_offset(cx, rhs, var)
864 } else if same_var(cx, rhs, var) {
865 extract_offset(cx, lhs, var)
870 offset_opt.map(Offset::positive)
872 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
875 ExprKind::Path(..) if same_var(cx, idx, var) => Some(Offset::positive("0".into())),
880 fn get_assignments<'tcx>(body: &'tcx Expr<'tcx>) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> {
881 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
882 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
889 // This is one of few ways to return different iterators
890 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
891 let mut iter_a = None;
892 let mut iter_b = None;
894 if let ExprKind::Block(b, _) = body.kind {
895 let Block { stmts, expr, .. } = *b;
899 .filter_map(|stmt| match stmt.kind {
900 StmtKind::Local(..) | StmtKind::Item(..) => None,
901 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
903 .chain(expr.into_iter())
907 iter_b = Some(get_assignment(body))
910 iter_a.into_iter().flatten().chain(iter_b.into_iter())
913 fn build_manual_memcpy_suggestion<'tcx>(
914 cx: &LateContext<'tcx>,
917 limits: ast::RangeLimits,
918 dst_var: FixedOffsetVar<'_>,
919 src_var: FixedOffsetVar<'_>,
921 fn print_sum(arg1: &str, arg2: &Offset) -> String {
922 match (arg1, &arg2.value[..], arg2.sign) {
923 ("0", "0", _) => "0".into(),
924 ("0", x, OffsetSign::Positive) | (x, "0", _) => x.into(),
925 ("0", x, OffsetSign::Negative) => format!("-{}", x),
926 (x, y, OffsetSign::Positive) => format!("({} + {})", x, y),
927 (x, y, OffsetSign::Negative) => {
931 format!("({} - {})", x, y)
937 fn print_offset(start_str: &str, inline_offset: &Offset) -> String {
938 let offset = print_sum(start_str, inline_offset);
939 if offset.as_str() == "0" {
946 let print_limit = |end: &Expr<'_>, offset: Offset, var: &Expr<'_>| {
948 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
949 if method.ident.name == sym!(len);
950 if len_args.len() == 1;
951 if let Some(arg) = len_args.get(0);
952 if var_def_id(cx, arg) == var_def_id(cx, var);
955 OffsetSign::Negative => format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value),
956 OffsetSign::Positive => "".into(),
959 let end_str = match limits {
960 ast::RangeLimits::Closed => {
961 let end = sugg::Sugg::hir(cx, end, "<count>");
962 format!("{}", end + sugg::ONE)
964 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
967 print_sum(&end_str, &offset)
972 let start_str = snippet(cx, start.span, "").to_string();
973 let dst_offset = print_offset(&start_str, &dst_var.offset);
974 let dst_limit = print_limit(end, dst_var.offset, dst_var.var);
975 let src_offset = print_offset(&start_str, &src_var.offset);
976 let src_limit = print_limit(end, src_var.offset, src_var.var);
978 let dst_var_name = snippet_opt(cx, dst_var.var.span).unwrap_or_else(|| "???".into());
979 let src_var_name = snippet_opt(cx, src_var.var.span).unwrap_or_else(|| "???".into());
981 let dst = if dst_offset == "" && dst_limit == "" {
984 format!("{}[{}..{}]", dst_var_name, dst_offset, dst_limit)
988 "{}.clone_from_slice(&{}[{}..{}])",
989 dst, src_var_name, src_offset, src_limit
992 /// Checks for for loops that sequentially copy items from one slice-like
993 /// object to another.
994 fn detect_manual_memcpy<'tcx>(
995 cx: &LateContext<'tcx>,
998 body: &'tcx Expr<'_>,
999 expr: &'tcx Expr<'_>,
1001 if let Some(higher::Range {
1005 }) = higher::range(cx, arg)
1007 // the var must be a single name
1008 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1009 // The only statements in the for loops can be indexed assignments from
1010 // indexed retrievals.
1011 let big_sugg = get_assignments(body)
1013 o.and_then(|(lhs, rhs)| {
1014 let rhs = fetch_cloned_expr(rhs);
1016 if let ExprKind::Index(seqexpr_left, idx_left) = lhs.kind;
1017 if let ExprKind::Index(seqexpr_right, idx_right) = rhs.kind;
1018 if is_slice_like(cx, cx.typeck_results().expr_ty(seqexpr_left))
1019 && is_slice_like(cx, cx.typeck_results().expr_ty(seqexpr_right));
1020 if let Some(offset_left) = get_offset(cx, &idx_left, canonical_id);
1021 if let Some(offset_right) = get_offset(cx, &idx_right, canonical_id);
1023 // Source and destination must be different
1024 if var_def_id(cx, seqexpr_left) != var_def_id(cx, seqexpr_right);
1026 Some((FixedOffsetVar { var: seqexpr_left, offset: offset_left },
1027 FixedOffsetVar { var: seqexpr_right, offset: offset_right }))
1034 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, dst, src)))
1035 .collect::<Option<Vec<_>>>()
1036 .filter(|v| !v.is_empty())
1037 .map(|v| v.join("\n "));
1039 if let Some(big_sugg) = big_sugg {
1044 "it looks like you're manually copying between slices",
1045 "try replacing the loop by",
1047 Applicability::Unspecified,
1054 // Delegate that traverses expression and detects mutable variables being used
1055 struct UsesMutableDelegate {
1056 found_mutable: bool,
1059 impl<'tcx> Delegate<'tcx> for UsesMutableDelegate {
1060 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1062 fn borrow(&mut self, _: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1063 // Mutable variable is found
1064 if let ty::BorrowKind::MutBorrow = bk {
1065 self.found_mutable = true;
1069 fn mutate(&mut self, _: &PlaceWithHirId<'tcx>) {}
1072 // Uses UsesMutableDelegate to find mutable variables in an expression expr
1073 fn has_mutable_variables<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
1074 let mut delegate = UsesMutableDelegate { found_mutable: false };
1075 let def_id = expr.hir_id.owner.to_def_id();
1076 cx.tcx.infer_ctxt().enter(|infcx| {
1077 ExprUseVisitor::new(
1080 def_id.expect_local(),
1082 cx.typeck_results(),
1086 delegate.found_mutable
1089 // Scans for the usage of the for loop pattern
1090 struct ForPatternVisitor<'a, 'tcx> {
1091 found_pattern: bool,
1092 // Pattern that we are searching for
1093 for_pattern: &'a Pat<'tcx>,
1094 cx: &'a LateContext<'tcx>,
1097 impl<'a, 'tcx> Visitor<'tcx> for ForPatternVisitor<'a, 'tcx> {
1098 type Map = Map<'tcx>;
1100 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1101 // Recursively explore an expression until a ExprKind::Path is found
1103 ExprKind::Array(expr_list) | ExprKind::MethodCall(_, _, expr_list, _) | ExprKind::Tup(expr_list) => {
1104 for expr in *expr_list {
1105 self.visit_expr(expr)
1108 ExprKind::Binary(_, lhs_expr, rhs_expr) => {
1109 self.visit_expr(lhs_expr);
1110 self.visit_expr(rhs_expr);
1113 | ExprKind::Unary(_, expr)
1114 | ExprKind::Cast(expr, _)
1115 | ExprKind::Type(expr, _)
1116 | ExprKind::AddrOf(_, _, expr)
1117 | ExprKind::Field(expr, _)
1118 | ExprKind::Struct(_, _, Some(expr)) => self.visit_expr(expr),
1120 // Exploration cannot continue ... calculate the hir_id of the current
1121 // expr assuming it is a Path
1122 if let Some(hir_id) = var_def_id(self.cx, &expr) {
1124 if hir_id == self.for_pattern.hir_id {
1125 self.found_pattern = true;
1127 // If the for loop pattern is a tuple, determine whether the current
1128 // expr is inside that tuple pattern
1129 if let PatKind::Tuple(pat_list, _) = &self.for_pattern.kind {
1130 let hir_id_list: Vec<HirId> = pat_list.iter().map(|p| p.hir_id).collect();
1131 if hir_id_list.contains(&hir_id) {
1132 self.found_pattern = true;
1140 // This is triggered by walk_expr() for the case of vec.push(pat)
1141 fn visit_qpath(&mut self, qpath: &'tcx QPath<'_>, _: HirId, _: Span) {
1143 if let QPath::Resolved(_, path) = qpath;
1144 if let Res::Local(hir_id) = &path.res;
1146 if *hir_id == self.for_pattern.hir_id{
1147 self.found_pattern = true;
1150 if let PatKind::Tuple(pat_list, _) = &self.for_pattern.kind {
1151 let hir_id_list: Vec<HirId> = pat_list.iter().map(|p| p.hir_id).collect();
1152 if hir_id_list.contains(&hir_id) {
1153 self.found_pattern = true;
1160 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1161 NestedVisitorMap::None
1165 // Scans the body of the for loop and determines whether lint should be given
1166 struct SameItemPushVisitor<'a, 'tcx> {
1168 // this field holds the last vec push operation visited, which should be the only push seen
1169 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1170 cx: &'a LateContext<'tcx>,
1173 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1174 type Map = Map<'tcx>;
1176 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1178 // Non-determinism may occur ... don't give a lint
1179 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1180 ExprKind::Block(block, _) => self.visit_block(block),
1185 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1186 for stmt in b.stmts.iter() {
1187 self.visit_stmt(stmt);
1191 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1192 let vec_push_option = get_vec_push(self.cx, s);
1193 if vec_push_option.is_none() {
1194 // Current statement is not a push so visit inside
1196 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1200 // Current statement is a push ...check whether another
1201 // push had been previously done
1202 if self.vec_push.is_none() {
1203 self.vec_push = vec_push_option;
1205 // There are multiple pushes ... don't lint
1206 self.should_lint = false;
1211 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1212 NestedVisitorMap::None
1216 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1217 // the Vec being pushed into and the item being pushed
1218 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1220 // Extract method being called
1221 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1222 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1223 // Figure out the parameters for the method call
1224 if let Some(self_expr) = args.get(0);
1225 if let Some(pushed_item) = args.get(1);
1226 // Check that the method being called is push() on a Vec
1227 if match_type(cx, cx.typeck_results().expr_ty(self_expr), &paths::VEC);
1228 if path.ident.name.as_str() == "push";
1230 return Some((self_expr, pushed_item))
1236 /// Detects for loop pushing the same item into a Vec
1237 fn detect_same_item_push<'tcx>(
1238 cx: &LateContext<'tcx>,
1241 body: &'tcx Expr<'_>,
1244 // Determine whether it is safe to lint the body
1245 let mut same_item_push_visitor = SameItemPushVisitor {
1250 walk_expr(&mut same_item_push_visitor, body);
1251 if same_item_push_visitor.should_lint {
1252 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1253 // Make sure that the push does not involve possibly mutating values
1254 if !has_mutable_variables(cx, pushed_item) {
1255 // Walk through the expression being pushed and make sure that it
1256 // does not contain the for loop pattern
1257 let mut for_pat_visitor = ForPatternVisitor {
1258 found_pattern: false,
1262 walk_expr(&mut for_pat_visitor, pushed_item);
1264 if !for_pat_visitor.found_pattern {
1265 let vec_str = snippet(cx, vec.span, "");
1266 let item_str = snippet(cx, pushed_item.span, "");
1272 "it looks like the same item is being pushed into this Vec",
1275 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1276 item_str, vec_str, item_str
1285 /// Checks for looping over a range and then indexing a sequence with it.
1286 /// The iteratee must be a range literal.
1287 #[allow(clippy::too_many_lines)]
1288 fn check_for_loop_range<'tcx>(
1289 cx: &LateContext<'tcx>,
1291 arg: &'tcx Expr<'_>,
1292 body: &'tcx Expr<'_>,
1293 expr: &'tcx Expr<'_>,
1295 if let Some(higher::Range {
1299 }) = higher::range(cx, arg)
1301 // the var must be a single name
1302 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1303 let mut visitor = VarVisitor {
1306 indexed_mut: FxHashSet::default(),
1307 indexed_indirectly: FxHashMap::default(),
1308 indexed_directly: FxHashMap::default(),
1309 referenced: FxHashSet::default(),
1311 prefer_mutable: false,
1313 walk_expr(&mut visitor, body);
1315 // linting condition: we only indexed one variable, and indexed it directly
1316 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1317 let (indexed, (indexed_extent, indexed_ty)) = visitor
1321 .expect("already checked that we have exactly 1 element");
1323 // ensure that the indexed variable was declared before the loop, see #601
1324 if let Some(indexed_extent) = indexed_extent {
1325 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1326 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1327 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1328 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1329 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1334 // don't lint if the container that is indexed does not have .iter() method
1335 let has_iter = has_iter_method(cx, indexed_ty);
1336 if has_iter.is_none() {
1340 // don't lint if the container that is indexed into is also used without
1342 if visitor.referenced.contains(&indexed) {
1346 let starts_at_zero = is_integer_const(cx, start, 0);
1348 let skip = if starts_at_zero {
1351 format!(".skip({})", snippet(cx, start.span, ".."))
1354 let mut end_is_start_plus_val = false;
1356 let take = if let Some(end) = *end {
1357 let mut take_expr = end;
1359 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1360 if let BinOpKind::Add = op.node {
1361 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1362 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1364 if start_equal_left {
1366 } else if start_equal_right {
1370 end_is_start_plus_val = start_equal_left | start_equal_right;
1374 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1378 ast::RangeLimits::Closed => {
1379 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1380 format!(".take({})", take_expr + sugg::ONE)
1382 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1389 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1390 ("mut ", "iter_mut")
1395 let take_is_empty = take.is_empty();
1396 let mut method_1 = take;
1397 let mut method_2 = skip;
1399 if end_is_start_plus_val {
1400 mem::swap(&mut method_1, &mut method_2);
1403 if visitor.nonindex {
1406 NEEDLESS_RANGE_LOOP,
1408 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1412 "consider using an iterator",
1414 (pat.span, format!("({}, <item>)", ident.name)),
1417 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1424 let repl = if starts_at_zero && take_is_empty {
1425 format!("&{}{}", ref_mut, indexed)
1427 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1432 NEEDLESS_RANGE_LOOP,
1435 "the loop variable `{}` is only used to index `{}`.",
1441 "consider using an iterator",
1442 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1452 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1454 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1455 if len_args.len() == 1;
1456 if method.ident.name == sym!(len);
1457 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1458 if path.segments.len() == 1;
1459 if path.segments[0].ident.name == var;
1468 fn is_end_eq_array_len<'tcx>(
1469 cx: &LateContext<'tcx>,
1471 limits: ast::RangeLimits,
1472 indexed_ty: Ty<'tcx>,
1475 if let ExprKind::Lit(ref lit) = end.kind;
1476 if let ast::LitKind::Int(end_int, _) = lit.node;
1477 if let ty::Array(_, arr_len_const) = indexed_ty.kind;
1478 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1480 return match limits {
1481 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1482 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1490 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1491 let mut applicability = Applicability::MachineApplicable;
1492 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1493 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1498 "it is more concise to loop over references to containers instead of using explicit \
1500 "to write this more concisely, try",
1501 format!("&{}{}", muta, object),
1506 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1507 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1508 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1509 // just the receiver, no arguments
1510 if args.len() == 1 {
1511 let method_name = &*method.ident.as_str();
1512 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1513 if method_name == "iter" || method_name == "iter_mut" {
1514 if is_ref_iterable_type(cx, &args[0]) {
1515 lint_iter_method(cx, args, arg, method_name);
1517 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1518 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1519 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1520 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1521 let mut applicability = Applicability::MachineApplicable;
1522 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1525 EXPLICIT_INTO_ITER_LOOP,
1527 "it is more concise to loop over containers instead of using explicit \
1529 "to write this more concisely, try",
1534 let ref_receiver_ty = cx.tcx.mk_ref(
1535 cx.tcx.lifetimes.re_erased,
1538 mutbl: Mutability::Not,
1541 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1542 lint_iter_method(cx, args, arg, method_name)
1545 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1550 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1551 probably not what you want",
1553 next_loop_linted = true;
1557 if !next_loop_linted {
1558 check_arg_type(cx, pat, arg);
1562 /// Checks for `for` loops over `Option`s and `Result`s.
1563 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1564 let ty = cx.typeck_results().expr_ty(arg);
1565 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1568 FOR_LOOPS_OVER_FALLIBLES,
1571 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1572 `if let` statement.",
1573 snippet(cx, arg.span, "_")
1577 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1578 snippet(cx, pat.span, "_"),
1579 snippet(cx, arg.span, "_")
1582 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1585 FOR_LOOPS_OVER_FALLIBLES,
1588 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1589 `if let` statement.",
1590 snippet(cx, arg.span, "_")
1594 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1595 snippet(cx, pat.span, "_"),
1596 snippet(cx, arg.span, "_")
1602 fn check_for_loop_explicit_counter<'tcx>(
1603 cx: &LateContext<'tcx>,
1605 arg: &'tcx Expr<'_>,
1606 body: &'tcx Expr<'_>,
1607 expr: &'tcx Expr<'_>,
1609 // Look for variables that are incremented once per loop iteration.
1610 let mut visitor = IncrementVisitor {
1612 states: FxHashMap::default(),
1616 walk_expr(&mut visitor, body);
1618 // For each candidate, check the parent block to see if
1619 // it's initialized to zero at the start of the loop.
1620 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1621 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1622 let mut visitor2 = InitializeVisitor {
1626 state: VarState::IncrOnce,
1631 walk_block(&mut visitor2, block);
1633 if visitor2.state == VarState::Warn {
1634 if let Some(name) = visitor2.name {
1635 let mut applicability = Applicability::MachineApplicable;
1637 // for some reason this is the only way to get the `Span`
1638 // of the entire `for` loop
1639 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1647 EXPLICIT_COUNTER_LOOP,
1648 for_span.with_hi(arg.span.hi()),
1649 &format!("the variable `{}` is used as a loop counter.", name),
1652 "for ({}, {}) in {}.enumerate()",
1654 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1655 make_iterator_snippet(cx, arg, &mut applicability),
1665 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1666 /// actual `Iterator` that the loop uses.
1667 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1668 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1669 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1674 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1677 // (&x).into_iter() ==> x.iter()
1678 // (&mut x).into_iter() ==> x.iter_mut()
1680 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1681 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1683 let meth_name = match mutability {
1684 Mutability::Mut => "iter_mut",
1685 Mutability::Not => "iter",
1689 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1695 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1701 /// Checks for the `FOR_KV_MAP` lint.
1702 fn check_for_loop_over_map_kv<'tcx>(
1703 cx: &LateContext<'tcx>,
1705 arg: &'tcx Expr<'_>,
1706 body: &'tcx Expr<'_>,
1707 expr: &'tcx Expr<'_>,
1709 let pat_span = pat.span;
1711 if let PatKind::Tuple(ref pat, _) = pat.kind {
1713 let arg_span = arg.span;
1714 let (new_pat_span, kind, ty, mutbl) = match cx.typeck_results().expr_ty(arg).kind {
1715 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1716 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1717 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1722 let mutbl = match mutbl {
1723 Mutability::Not => "",
1724 Mutability::Mut => "_mut",
1726 let arg = match arg.kind {
1727 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1731 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1736 &format!("you seem to want to iterate on a map's {}s", kind),
1738 let map = sugg::Sugg::hir(cx, arg, "map");
1741 "use the corresponding method",
1743 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1744 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1754 struct MutatePairDelegate<'a, 'tcx> {
1755 cx: &'a LateContext<'tcx>,
1756 hir_id_low: Option<HirId>,
1757 hir_id_high: Option<HirId>,
1758 span_low: Option<Span>,
1759 span_high: Option<Span>,
1762 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1763 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1765 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1766 if let ty::BorrowKind::MutBorrow = bk {
1767 if let PlaceBase::Local(id) = cmt.place.base {
1768 if Some(id) == self.hir_id_low {
1769 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1771 if Some(id) == self.hir_id_high {
1772 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1778 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>) {
1779 if let PlaceBase::Local(id) = cmt.place.base {
1780 if Some(id) == self.hir_id_low {
1781 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1783 if Some(id) == self.hir_id_high {
1784 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1790 impl MutatePairDelegate<'_, '_> {
1791 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1792 (self.span_low, self.span_high)
1796 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1797 if let Some(higher::Range {
1801 }) = higher::range(cx, arg)
1803 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1804 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1805 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1806 mut_warn_with_span(cx, span_low);
1807 mut_warn_with_span(cx, span_high);
1812 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
1813 if let Some(sp) = span {
1818 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1823 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
1825 if let ExprKind::Path(ref qpath) = bound.kind;
1826 if let QPath::Resolved(None, _) = *qpath;
1828 let res = qpath_res(cx, qpath, bound.hir_id);
1829 if let Res::Local(hir_id) = res {
1830 let node_str = cx.tcx.hir().get(hir_id);
1832 if let Node::Binding(pat) = node_str;
1833 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1834 if let BindingAnnotation::Mutable = bind_ann;
1836 return Some(hir_id);
1845 fn check_for_mutation<'tcx>(
1846 cx: &LateContext<'tcx>,
1848 bound_ids: &[Option<HirId>],
1849 ) -> (Option<Span>, Option<Span>) {
1850 let mut delegate = MutatePairDelegate {
1852 hir_id_low: bound_ids[0],
1853 hir_id_high: bound_ids[1],
1857 let def_id = body.hir_id.owner.to_def_id();
1858 cx.tcx.infer_ctxt().enter(|infcx| {
1859 ExprUseVisitor::new(
1862 def_id.expect_local(),
1864 cx.typeck_results(),
1868 delegate.mutation_span()
1871 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1872 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
1874 PatKind::Wild => true,
1875 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
1880 struct LocalUsedVisitor<'a, 'tcx> {
1881 cx: &'a LateContext<'tcx>,
1886 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1887 type Map = Map<'tcx>;
1889 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1890 if same_var(self.cx, expr, self.local) {
1893 walk_expr(self, expr);
1897 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1898 NestedVisitorMap::None
1902 struct VarVisitor<'a, 'tcx> {
1903 /// context reference
1904 cx: &'a LateContext<'tcx>,
1905 /// var name to look for as index
1907 /// indexed variables that are used mutably
1908 indexed_mut: FxHashSet<Symbol>,
1909 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1910 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
1911 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1912 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1913 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
1914 /// Any names that are used outside an index operation.
1915 /// Used to detect things like `&mut vec` used together with `vec[i]`
1916 referenced: FxHashSet<Symbol>,
1917 /// has the loop variable been used in expressions other than the index of
1920 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1921 /// takes `&mut self`
1922 prefer_mutable: bool,
1925 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1926 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
1928 // the indexed container is referenced by a name
1929 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
1930 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1931 if seqvar.segments.len() == 1;
1933 let index_used_directly = same_var(self.cx, idx, self.var);
1934 let indexed_indirectly = {
1935 let mut used_visitor = LocalUsedVisitor {
1940 walk_expr(&mut used_visitor, idx);
1944 if indexed_indirectly || index_used_directly {
1945 if self.prefer_mutable {
1946 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1948 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
1950 Res::Local(hir_id) => {
1951 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1952 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1953 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1954 if indexed_indirectly {
1955 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1957 if index_used_directly {
1958 self.indexed_directly.insert(
1959 seqvar.segments[0].ident.name,
1960 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
1963 return false; // no need to walk further *on the variable*
1965 Res::Def(DefKind::Static | DefKind::Const, ..) => {
1966 if indexed_indirectly {
1967 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1969 if index_used_directly {
1970 self.indexed_directly.insert(
1971 seqvar.segments[0].ident.name,
1972 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
1975 return false; // no need to walk further *on the variable*
1986 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1987 type Map = Map<'tcx>;
1989 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1992 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
1993 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1994 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1995 if !self.check(&args[1], &args[0], expr);
2001 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2002 if !self.check(idx, seqexpr, expr);
2007 // directly using a variable
2008 if let ExprKind::Path(ref qpath) = expr.kind;
2009 if let QPath::Resolved(None, ref path) = *qpath;
2010 if path.segments.len() == 1;
2012 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2013 if local_id == self.var {
2014 self.nonindex = true;
2016 // not the correct variable, but still a variable
2017 self.referenced.insert(path.segments[0].ident.name);
2023 let old = self.prefer_mutable;
2025 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2026 self.prefer_mutable = true;
2027 self.visit_expr(lhs);
2028 self.prefer_mutable = false;
2029 self.visit_expr(rhs);
2031 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2032 if mutbl == Mutability::Mut {
2033 self.prefer_mutable = true;
2035 self.visit_expr(expr);
2037 ExprKind::Call(ref f, args) => {
2040 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2041 self.prefer_mutable = false;
2042 if let ty::Ref(_, _, mutbl) = ty.kind {
2043 if mutbl == Mutability::Mut {
2044 self.prefer_mutable = true;
2047 self.visit_expr(expr);
2050 ExprKind::MethodCall(_, _, args, _) => {
2051 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2052 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2053 self.prefer_mutable = false;
2054 if let ty::Ref(_, _, mutbl) = ty.kind {
2055 if mutbl == Mutability::Mut {
2056 self.prefer_mutable = true;
2059 self.visit_expr(expr);
2062 ExprKind::Closure(_, _, body_id, ..) => {
2063 let body = self.cx.tcx.hir().body(body_id);
2064 self.visit_expr(&body.value);
2066 _ => walk_expr(self, expr),
2068 self.prefer_mutable = old;
2070 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2071 NestedVisitorMap::None
2075 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2076 let def_id = match var_def_id(cx, expr) {
2078 None => return false,
2080 if let Some(used_mutably) = mutated_variables(container, cx) {
2081 if used_mutably.contains(&def_id) {
2088 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2089 let def_id = match var_def_id(cx, iter_expr) {
2091 None => return false,
2093 let mut visitor = VarUsedAfterLoopVisitor {
2096 iter_expr_id: iter_expr.hir_id,
2097 past_while_let: false,
2098 var_used_after_while_let: false,
2100 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2101 walk_block(&mut visitor, enclosing_block);
2103 visitor.var_used_after_while_let
2106 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2107 cx: &'a LateContext<'tcx>,
2109 iter_expr_id: HirId,
2110 past_while_let: bool,
2111 var_used_after_while_let: bool,
2114 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2115 type Map = Map<'tcx>;
2117 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2118 if self.past_while_let {
2119 if Some(self.def_id) == var_def_id(self.cx, expr) {
2120 self.var_used_after_while_let = true;
2122 } else if self.iter_expr_id == expr.hir_id {
2123 self.past_while_let = true;
2125 walk_expr(self, expr);
2127 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2128 NestedVisitorMap::None
2132 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2133 /// for `&T` and `&mut T`, such as `Vec`.
2135 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2136 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2137 // will allow further borrows afterwards
2138 let ty = cx.typeck_results().expr_ty(e);
2139 is_iterable_array(ty, cx) ||
2140 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2141 match_type(cx, ty, &paths::LINKED_LIST) ||
2142 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2143 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2144 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2145 match_type(cx, ty, &paths::BINARY_HEAP) ||
2146 match_type(cx, ty, &paths::BTREEMAP) ||
2147 match_type(cx, ty, &paths::BTREESET)
2150 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2151 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2153 ty::Array(_, n) => n
2154 .try_eval_usize(cx.tcx, cx.param_env)
2155 .map_or(false, |val| (0..=32).contains(&val)),
2160 /// If a block begins with a statement (possibly a `let` binding) and has an
2161 /// expression, return it.
2162 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2163 if block.stmts.is_empty() {
2166 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2167 local.init //.map(|expr| expr)
2173 /// If a block begins with an expression (with or without semicolon), return it.
2174 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2176 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2177 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2178 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2179 StmtKind::Local(..) | StmtKind::Item(..) => None,
2185 /// Returns `true` if expr contains a single break expr without destination label
2187 /// passed expression. The expression may be within a block.
2188 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2190 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2191 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2196 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2197 // incremented exactly once in the loop body, and initialized to zero
2198 // at the start of the loop.
2199 #[derive(Debug, PartialEq)]
2201 Initial, // Not examined yet
2202 IncrOnce, // Incremented exactly once, may be a loop counter
2203 Declared, // Declared but not (yet) initialized to zero
2208 /// Scan a for loop for variables that are incremented exactly once.
2209 struct IncrementVisitor<'a, 'tcx> {
2210 cx: &'a LateContext<'tcx>, // context reference
2211 states: FxHashMap<HirId, VarState>, // incremented variables
2212 depth: u32, // depth of conditional expressions
2216 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2217 type Map = Map<'tcx>;
2219 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2224 // If node is a variable
2225 if let Some(def_id) = var_def_id(self.cx, expr) {
2226 if let Some(parent) = get_parent_expr(self.cx, expr) {
2227 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2230 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2231 if lhs.hir_id == expr.hir_id {
2232 if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) {
2233 *state = match *state {
2234 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2235 _ => VarState::DontWarn,
2238 // Assigned some other value
2239 *state = VarState::DontWarn;
2243 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2244 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2245 *state = VarState::DontWarn
2250 } else if is_loop(expr) || is_conditional(expr) {
2252 walk_expr(self, expr);
2255 } else if let ExprKind::Continue(_) = expr.kind {
2259 walk_expr(self, expr);
2261 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2262 NestedVisitorMap::None
2266 /// Checks whether a variable is initialized to zero at the start of a loop.
2267 struct InitializeVisitor<'a, 'tcx> {
2268 cx: &'a LateContext<'tcx>, // context reference
2269 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2272 name: Option<Symbol>,
2273 depth: u32, // depth of conditional expressions
2277 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2278 type Map = Map<'tcx>;
2280 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2281 // Look for declarations of the variable
2282 if let StmtKind::Local(ref local) = stmt.kind {
2283 if local.pat.hir_id == self.var_id {
2284 if let PatKind::Binding(.., ident, _) = local.pat.kind {
2285 self.name = Some(ident.name);
2287 self.state = local.init.as_ref().map_or(VarState::Declared, |init| {
2288 if is_integer_const(&self.cx, init, 0) {
2297 walk_stmt(self, stmt);
2300 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2301 if self.state == VarState::DontWarn {
2304 if expr.hir_id == self.end_expr.hir_id {
2305 self.past_loop = true;
2308 // No need to visit expressions before the variable is
2310 if self.state == VarState::IncrOnce {
2314 // If node is the desired variable, see how it's used
2315 if var_def_id(self.cx, expr) == Some(self.var_id) {
2316 if let Some(parent) = get_parent_expr(self.cx, expr) {
2318 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2319 self.state = VarState::DontWarn;
2321 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2322 self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 {
2328 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2329 self.state = VarState::DontWarn
2336 self.state = VarState::DontWarn;
2339 } else if !self.past_loop && is_loop(expr) {
2340 self.state = VarState::DontWarn;
2342 } else if is_conditional(expr) {
2344 walk_expr(self, expr);
2348 walk_expr(self, expr);
2351 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2352 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2356 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2357 if let ExprKind::Path(ref qpath) = expr.kind {
2358 let path_res = qpath_res(cx, qpath, expr.hir_id);
2359 if let Res::Local(hir_id) = path_res {
2360 return Some(hir_id);
2366 fn is_loop(expr: &Expr<'_>) -> bool {
2367 matches!(expr.kind, ExprKind::Loop(..))
2370 fn is_conditional(expr: &Expr<'_>) -> bool {
2371 matches!(expr.kind, ExprKind::Match(..))
2374 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2376 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2377 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2378 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2380 return is_loop_nested(cx, loop_expr, iter_expr)
2386 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2387 let mut id = loop_expr.hir_id;
2388 let iter_name = if let Some(name) = path_name(iter_expr) {
2394 let parent = cx.tcx.hir().get_parent_node(id);
2398 match cx.tcx.hir().find(parent) {
2399 Some(Node::Expr(expr)) => {
2400 if let ExprKind::Loop(..) = expr.kind {
2404 Some(Node::Block(block)) => {
2405 let mut block_visitor = LoopNestVisitor {
2407 iterator: iter_name,
2410 walk_block(&mut block_visitor, block);
2411 if block_visitor.nesting == RuledOut {
2415 Some(Node::Stmt(_)) => (),
2424 #[derive(PartialEq, Eq)]
2426 Unknown, // no nesting detected yet
2427 RuledOut, // the iterator is initialized or assigned within scope
2428 LookFurther, // no nesting detected, no further walk required
2431 use self::Nesting::{LookFurther, RuledOut, Unknown};
2433 struct LoopNestVisitor {
2439 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2440 type Map = Map<'tcx>;
2442 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2443 if stmt.hir_id == self.hir_id {
2444 self.nesting = LookFurther;
2445 } else if self.nesting == Unknown {
2446 walk_stmt(self, stmt);
2450 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2451 if self.nesting != Unknown {
2454 if expr.hir_id == self.hir_id {
2455 self.nesting = LookFurther;
2459 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2460 if match_var(path, self.iterator) {
2461 self.nesting = RuledOut;
2464 _ => walk_expr(self, expr),
2468 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2469 if self.nesting != Unknown {
2472 if let PatKind::Binding(.., span_name, _) = pat.kind {
2473 if self.iterator == span_name.name {
2474 self.nesting = RuledOut;
2481 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2482 NestedVisitorMap::None
2486 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2487 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2488 let segments = &path.segments;
2489 if segments.len() == 1 {
2490 return Some(segments[0].ident.name);
2496 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2497 if constant(cx, cx.typeck_results(), cond).is_some() {
2498 // A pure constant condition (e.g., `while false`) is not linted.
2502 let mut var_visitor = VarCollectorVisitor {
2504 ids: FxHashSet::default(),
2505 def_ids: FxHashMap::default(),
2508 var_visitor.visit_expr(cond);
2509 if var_visitor.skip {
2512 let used_in_condition = &var_visitor.ids;
2513 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2514 used_in_condition.is_disjoint(&used_mutably)
2518 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2520 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2521 has_break_or_return: false,
2523 has_break_or_return_visitor.visit_expr(expr);
2524 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2526 if no_cond_variable_mutated && !mutable_static_in_cond {
2529 WHILE_IMMUTABLE_CONDITION,
2531 "variables in the condition are not mutated in the loop body",
2533 diag.note("this may lead to an infinite or to a never running loop");
2535 if has_break_or_return {
2536 diag.note("this loop contains `return`s or `break`s");
2537 diag.help("rewrite it as `if cond { loop { } }`");
2544 struct HasBreakOrReturnVisitor {
2545 has_break_or_return: bool,
2548 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2549 type Map = Map<'tcx>;
2551 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2552 if self.has_break_or_return {
2557 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2558 self.has_break_or_return = true;
2564 walk_expr(self, expr);
2567 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2568 NestedVisitorMap::None
2572 /// Collects the set of variables in an expression
2573 /// Stops analysis if a function call is found
2574 /// Note: In some cases such as `self`, there are no mutable annotation,
2575 /// All variables definition IDs are collected
2576 struct VarCollectorVisitor<'a, 'tcx> {
2577 cx: &'a LateContext<'tcx>,
2578 ids: FxHashSet<HirId>,
2579 def_ids: FxHashMap<def_id::DefId, bool>,
2583 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2584 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2586 if let ExprKind::Path(ref qpath) = ex.kind;
2587 if let QPath::Resolved(None, _) = *qpath;
2588 let res = qpath_res(self.cx, qpath, ex.hir_id);
2591 Res::Local(hir_id) => {
2592 self.ids.insert(hir_id);
2594 Res::Def(DefKind::Static, def_id) => {
2595 let mutable = self.cx.tcx.is_mutable_static(def_id);
2596 self.def_ids.insert(def_id, mutable);
2605 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2606 type Map = Map<'tcx>;
2608 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2610 ExprKind::Path(_) => self.insert_def_id(ex),
2611 // If there is any function/method call… we just stop analysis
2612 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2614 _ => walk_expr(self, ex),
2618 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2619 NestedVisitorMap::None
2623 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2625 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2626 check_needless_collect_direct_usage(expr, cx);
2627 check_needless_collect_indirect_usage(expr, cx);
2629 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2631 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2632 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2633 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2634 if let Some(ref generic_args) = chain_method.args;
2635 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2637 let ty = cx.typeck_results().node_type(ty.hir_id);
2638 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2639 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2640 match_type(cx, ty, &paths::BTREEMAP) ||
2641 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2642 if method.ident.name == sym!(len) {
2643 let span = shorten_span(expr, sym!(collect));
2648 NEEDLESS_COLLECT_MSG,
2650 "count()".to_string(),
2651 Applicability::MachineApplicable,
2654 if method.ident.name == sym!(is_empty) {
2655 let span = shorten_span(expr, sym!(iter));
2660 NEEDLESS_COLLECT_MSG,
2662 "get(0).is_none()".to_string(),
2663 Applicability::MachineApplicable,
2666 if method.ident.name == sym!(contains) {
2667 let contains_arg = snippet(cx, args[1].span, "??");
2668 let span = shorten_span(expr, sym!(collect));
2673 NEEDLESS_COLLECT_MSG,
2675 let (arg, pred) = if contains_arg.starts_with('&') {
2676 ("x", &contains_arg[1..])
2678 ("&x", &*contains_arg)
2680 diag.span_suggestion(
2684 "any(|{}| x == {})",
2687 Applicability::MachineApplicable,
2697 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2698 if let ExprKind::Block(ref block, _) = expr.kind {
2699 for ref stmt in block.stmts {
2701 if let StmtKind::Local(
2702 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2703 init: Some(ref init_expr), .. }
2705 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2706 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2707 if let Some(ref generic_args) = method_name.args;
2708 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2709 if let ty = cx.typeck_results().node_type(ty.hir_id);
2710 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2711 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2712 match_type(cx, ty, &paths::LINKED_LIST);
2713 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2714 if iter_calls.len() == 1;
2716 // Suggest replacing iter_call with iter_replacement, and removing stmt
2717 let iter_call = &iter_calls[0];
2721 stmt.span.until(iter_call.span),
2722 NEEDLESS_COLLECT_MSG,
2724 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2725 diag.multipart_suggestion(
2726 iter_call.get_suggestion_text(),
2728 (stmt.span, String::new()),
2729 (iter_call.span, iter_replacement)
2731 Applicability::MachineApplicable,// MaybeIncorrect,
2741 struct IterFunction {
2742 func: IterFunctionKind,
2746 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2748 IterFunctionKind::IntoIter => String::new(),
2749 IterFunctionKind::Len => String::from(".count()"),
2750 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2751 IterFunctionKind::Contains(span) => format!(".any(|x| x == {})", snippet(cx, *span, "..")),
2754 fn get_suggestion_text(&self) -> &'static str {
2756 IterFunctionKind::IntoIter => {
2757 "Use the original Iterator instead of collecting it and then producing a new one"
2759 IterFunctionKind::Len => {
2760 "Take the original Iterator's count instead of collecting it and finding the length"
2762 IterFunctionKind::IsEmpty => {
2763 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
2765 IterFunctionKind::Contains(_) => {
2766 "Check if the original Iterator contains an element instead of collecting then checking"
2771 enum IterFunctionKind {
2778 struct IterFunctionVisitor {
2779 uses: Vec<IterFunction>,
2783 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
2784 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
2785 // Check function calls on our collection
2787 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
2788 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
2789 if let &[name] = &path.segments;
2790 if name.ident == self.target;
2792 let len = sym!(len);
2793 let is_empty = sym!(is_empty);
2794 let contains = sym!(contains);
2795 match method_name.ident.name {
2796 sym::into_iter => self.uses.push(
2797 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
2799 name if name == len => self.uses.push(
2800 IterFunction { func: IterFunctionKind::Len, span: expr.span }
2802 name if name == is_empty => self.uses.push(
2803 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
2805 name if name == contains => self.uses.push(
2806 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
2808 _ => self.seen_other = true,
2813 // Check if the collection is used for anything else
2815 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
2816 if let &[name] = &path.segments;
2817 if name.ident == self.target;
2819 self.seen_other = true;
2821 walk_expr(self, expr);
2826 type Map = Map<'tcx>;
2827 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2828 NestedVisitorMap::None
2832 /// Detect the occurences of calls to `iter` or `into_iter` for the
2833 /// given identifier
2834 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
2835 let mut visitor = IterFunctionVisitor {
2840 visitor.visit_block(block);
2841 if visitor.seen_other {
2848 fn shorten_span(expr: &Expr<'_>, target_fn_name: Symbol) -> Span {
2849 let mut current_expr = expr;
2850 while let ExprKind::MethodCall(ref path, ref span, ref args, _) = current_expr.kind {
2851 if path.ident.name == target_fn_name {
2852 return expr.span.with_lo(span.lo());
2854 current_expr = &args[0];