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_with_applicability, snippet_with_macro_callsite,
9 span_lint, 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 let is_manual_memcpy_triggered = detect_manual_memcpy(cx, pat, arg, body, expr);
772 if !is_manual_memcpy_triggered {
773 check_for_loop_range(cx, pat, arg, body, expr);
774 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
776 check_for_loop_arg(cx, pat, arg, expr);
777 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
778 check_for_mut_range_bound(cx, arg, body);
779 detect_same_item_push(cx, pat, arg, body, expr);
782 // this function assumes the given expression is a `for` loop.
783 fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
784 // for some reason this is the only way to get the `Span`
785 // of the entire `for` loop
786 if let ExprKind::Match(_, arms, _) = &expr.kind {
793 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
795 if let ExprKind::Path(qpath) = &expr.kind;
796 if let QPath::Resolved(None, path) = qpath;
797 if path.segments.len() == 1;
798 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
808 /// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
809 /// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
810 /// it exists for the convenience of the overloaded operators while normal functions can do the
813 struct MinifyingSugg<'a>(Sugg<'a>);
815 impl<'a> MinifyingSugg<'a> {
816 fn as_str(&self) -> &str {
817 let Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) = &self.0;
821 fn into_sugg(self) -> Sugg<'a> {
826 impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
827 fn from(sugg: Sugg<'a>) -> Self {
832 impl std::ops::Add for &MinifyingSugg<'static> {
833 type Output = MinifyingSugg<'static>;
834 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
835 match (self.as_str(), rhs.as_str()) {
836 ("0", _) => rhs.clone(),
837 (_, "0") => self.clone(),
838 (_, _) => (&self.0 + &rhs.0).into(),
843 impl std::ops::Sub for &MinifyingSugg<'static> {
844 type Output = MinifyingSugg<'static>;
845 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
846 match (self.as_str(), rhs.as_str()) {
847 (_, "0") => self.clone(),
848 ("0", _) => (-rhs.0.clone()).into(),
849 (x, y) if x == y => sugg::ZERO.into(),
850 (_, _) => (&self.0 - &rhs.0).into(),
855 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
856 type Output = MinifyingSugg<'static>;
857 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
858 match (self.as_str(), rhs.as_str()) {
859 ("0", _) => rhs.clone(),
861 (_, _) => (self.0 + &rhs.0).into(),
866 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
867 type Output = MinifyingSugg<'static>;
868 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
869 match (self.as_str(), rhs.as_str()) {
871 ("0", _) => (-rhs.0.clone()).into(),
872 (x, y) if x == y => sugg::ZERO.into(),
873 (_, _) => (self.0 - &rhs.0).into(),
878 /// a wrapper around `MinifyingSugg`, which carries a operator like currying
879 /// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
881 value: MinifyingSugg<'static>,
885 #[derive(Clone, Copy)]
892 fn negative(value: Sugg<'static>) -> Self {
895 sign: OffsetSign::Negative,
899 fn positive(value: Sugg<'static>) -> Self {
902 sign: OffsetSign::Positive,
907 Self::positive(sugg::ZERO)
911 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
913 OffsetSign::Positive => lhs + &rhs.value,
914 OffsetSign::Negative => lhs - &rhs.value,
918 #[derive(Debug, Clone, Copy)]
919 enum StartKind<'hir> {
921 Counter { initializer: &'hir Expr<'hir> },
924 struct IndexExpr<'hir> {
925 base: &'hir Expr<'hir>,
926 idx: StartKind<'hir>,
932 kind: StartKind<'hir>,
935 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
936 let is_slice = match ty.kind() {
937 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
938 ty::Slice(..) | ty::Array(..) => true,
942 is_slice || is_type_diagnostic_item(cx, ty, sym!(vec_type)) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
945 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
947 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
948 if method.ident.name == sym!(clone);
950 if let Some(arg) = args.get(0);
951 then { arg } else { expr }
955 fn get_details_from_idx<'tcx>(
956 cx: &LateContext<'tcx>,
958 starts: &[Start<'tcx>],
959 ) -> Option<(StartKind<'tcx>, Offset)> {
960 fn get_start<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
961 starts.iter().find_map(|start| {
962 if same_var(cx, e, start.id) {
970 fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
972 ExprKind::Lit(l) => match l.node {
973 ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
976 ExprKind::Path(..) if get_start(cx, e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
982 ExprKind::Binary(op, lhs, rhs) => match op.node {
984 let offset_opt = get_start(cx, lhs, starts)
985 .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
986 .or_else(|| get_start(cx, rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
988 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
991 get_start(cx, lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
995 ExprKind::Path(..) => get_start(cx, idx, starts).map(|s| (s, Offset::empty())),
1000 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1001 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1008 fn get_assignments<'a: 'c, 'tcx: 'c, 'c>(
1009 cx: &'a LateContext<'tcx>,
1010 Block { stmts, expr, .. }: &'tcx Block<'tcx>,
1011 loop_counters: &'c [Start<'tcx>],
1012 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'c {
1015 .filter_map(move |stmt| match stmt.kind {
1016 StmtKind::Local(..) | StmtKind::Item(..) => None,
1017 StmtKind::Expr(e) | StmtKind::Semi(e) => if_chain! {
1018 if let ExprKind::AssignOp(_, var, _) = e.kind;
1019 // skip StartKind::Range
1020 if loop_counters.iter().skip(1).any(|counter| Some(counter.id) == var_def_id(cx, var));
1021 then { None } else { Some(e) }
1024 .chain((*expr).into_iter())
1025 .map(get_assignment)
1028 fn get_loop_counters<'a, 'tcx>(
1029 cx: &'a LateContext<'tcx>,
1030 body: &'tcx Block<'tcx>,
1031 expr: &'tcx Expr<'_>,
1032 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1033 // Look for variables that are incremented once per loop iteration.
1034 let mut increment_visitor = IncrementVisitor::new(cx);
1035 walk_block(&mut increment_visitor, body);
1037 // For each candidate, check the parent block to see if
1038 // it's initialized to zero at the start of the loop.
1039 get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
1042 .filter_map(move |var_id| {
1043 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1044 walk_block(&mut initialize_visitor, block);
1046 initialize_visitor.get_result().map(|(_, initializer)| Start {
1048 kind: StartKind::Counter { initializer },
1055 fn build_manual_memcpy_suggestion<'tcx>(
1056 cx: &LateContext<'tcx>,
1059 limits: ast::RangeLimits,
1060 dst: &IndexExpr<'_>,
1061 src: &IndexExpr<'_>,
1063 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1064 if offset.as_str() == "0" {
1072 |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| -> MinifyingSugg<'static> {
1074 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1075 if method.ident.name == sym!(len);
1076 if len_args.len() == 1;
1077 if let Some(arg) = len_args.get(0);
1078 if var_def_id(cx, arg) == var_def_id(cx, base);
1080 if sugg.as_str() == end_str {
1087 ast::RangeLimits::Closed => {
1088 sugg + &sugg::ONE.into()
1090 ast::RangeLimits::HalfOpen => sugg,
1096 let start_str = Sugg::hir(cx, start, "").into();
1097 let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
1099 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1100 StartKind::Range => (
1101 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
1106 apply_offset(&end_str, &idx_expr.idx_offset),
1110 StartKind::Counter { initializer } => {
1111 let counter_start = Sugg::hir(cx, initializer, "").into();
1113 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
1118 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1125 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1126 let (src_offset, src_limit) = print_offset_and_limit(&src);
1128 let dst_base_str = snippet(cx, dst.base.span, "???");
1129 let src_base_str = snippet(cx, src.base.span, "???");
1131 let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
1137 dst_offset.maybe_par(),
1138 dst_limit.maybe_par()
1144 "{}.clone_from_slice(&{}[{}..{}]);",
1147 src_offset.maybe_par(),
1148 src_limit.maybe_par()
1152 /// Checks for for loops that sequentially copy items from one slice-like
1153 /// object to another.
1154 fn detect_manual_memcpy<'tcx>(
1155 cx: &LateContext<'tcx>,
1157 arg: &'tcx Expr<'_>,
1158 body: &'tcx Expr<'_>,
1159 expr: &'tcx Expr<'_>,
1161 if let Some(higher::Range {
1165 }) = higher::range(arg)
1167 // the var must be a single name
1168 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1169 let mut starts = vec![Start {
1171 kind: StartKind::Range,
1174 // This is one of few ways to return different iterators
1175 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1176 let mut iter_a = None;
1177 let mut iter_b = None;
1179 if let ExprKind::Block(block, _) = body.kind {
1180 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1181 starts.extend(loop_counters);
1183 iter_a = Some(get_assignments(cx, block, &starts));
1185 iter_b = Some(get_assignment(body));
1188 // The only statements in the for loops can be indexed assignments from
1189 // indexed retrievals.
1190 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1192 let big_sugg = assignments
1194 o.and_then(|(lhs, rhs)| {
1195 let rhs = fetch_cloned_expr(rhs);
1197 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1198 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1199 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1200 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1201 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1202 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1204 // Source and destination must be different
1205 if var_def_id(cx, base_left) != var_def_id(cx, base_right);
1207 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1208 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1215 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1216 .collect::<Option<Vec<_>>>()
1217 .filter(|v| !v.is_empty())
1218 .map(|v| v.join("\n "));
1220 if let Some(big_sugg) = big_sugg {
1224 get_span_of_entire_for_loop(expr),
1225 "it looks like you're manually copying between slices",
1226 "try replacing the loop by",
1228 Applicability::Unspecified,
1237 // Scans the body of the for loop and determines whether lint should be given
1238 struct SameItemPushVisitor<'a, 'tcx> {
1240 // this field holds the last vec push operation visited, which should be the only push seen
1241 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1242 cx: &'a LateContext<'tcx>,
1245 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1246 type Map = Map<'tcx>;
1248 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1250 // Non-determinism may occur ... don't give a lint
1251 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1252 ExprKind::Block(block, _) => self.visit_block(block),
1257 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1258 for stmt in b.stmts.iter() {
1259 self.visit_stmt(stmt);
1263 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1264 let vec_push_option = get_vec_push(self.cx, s);
1265 if vec_push_option.is_none() {
1266 // Current statement is not a push so visit inside
1268 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1272 // Current statement is a push ...check whether another
1273 // push had been previously done
1274 if self.vec_push.is_none() {
1275 self.vec_push = vec_push_option;
1277 // There are multiple pushes ... don't lint
1278 self.should_lint = false;
1283 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1284 NestedVisitorMap::None
1288 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1289 // the Vec being pushed into and the item being pushed
1290 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1292 // Extract method being called
1293 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1294 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1295 // Figure out the parameters for the method call
1296 if let Some(self_expr) = args.get(0);
1297 if let Some(pushed_item) = args.get(1);
1298 // Check that the method being called is push() on a Vec
1299 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym!(vec_type));
1300 if path.ident.name.as_str() == "push";
1302 return Some((self_expr, pushed_item))
1308 /// Detects for loop pushing the same item into a Vec
1309 fn detect_same_item_push<'tcx>(
1310 cx: &LateContext<'tcx>,
1313 body: &'tcx Expr<'_>,
1316 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1317 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1318 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1324 "it looks like the same item is being pushed into this Vec",
1327 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1328 item_str, vec_str, item_str
1333 if !matches!(pat.kind, PatKind::Wild) {
1337 // Determine whether it is safe to lint the body
1338 let mut same_item_push_visitor = SameItemPushVisitor {
1343 walk_expr(&mut same_item_push_visitor, body);
1344 if same_item_push_visitor.should_lint {
1345 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1346 let vec_ty = cx.typeck_results().expr_ty(vec);
1347 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1352 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1354 // Make sure that the push does not involve possibly mutating values
1355 match pushed_item.kind {
1356 ExprKind::Path(ref qpath) => {
1357 match qpath_res(cx, qpath, pushed_item.hir_id) {
1358 // immutable bindings that are initialized with literal or constant
1359 Res::Local(hir_id) => {
1361 let node = cx.tcx.hir().get(hir_id);
1362 if let Node::Binding(pat) = node;
1363 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1364 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1365 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1366 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1367 if let Some(init) = parent_let_expr.init;
1370 // immutable bindings that are initialized with literal
1371 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1372 // immutable bindings that are initialized with constant
1373 ExprKind::Path(ref path) => {
1374 if let Res::Def(DefKind::Const, ..) = qpath_res(cx, path, init.hir_id) {
1375 emit_lint(cx, vec, pushed_item);
1384 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1388 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1396 /// Checks for looping over a range and then indexing a sequence with it.
1397 /// The iteratee must be a range literal.
1398 #[allow(clippy::too_many_lines)]
1399 fn check_for_loop_range<'tcx>(
1400 cx: &LateContext<'tcx>,
1402 arg: &'tcx Expr<'_>,
1403 body: &'tcx Expr<'_>,
1404 expr: &'tcx Expr<'_>,
1406 if let Some(higher::Range {
1410 }) = higher::range(arg)
1412 // the var must be a single name
1413 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1414 let mut visitor = VarVisitor {
1417 indexed_mut: FxHashSet::default(),
1418 indexed_indirectly: FxHashMap::default(),
1419 indexed_directly: FxHashMap::default(),
1420 referenced: FxHashSet::default(),
1422 prefer_mutable: false,
1424 walk_expr(&mut visitor, body);
1426 // linting condition: we only indexed one variable, and indexed it directly
1427 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1428 let (indexed, (indexed_extent, indexed_ty)) = visitor
1432 .expect("already checked that we have exactly 1 element");
1434 // ensure that the indexed variable was declared before the loop, see #601
1435 if let Some(indexed_extent) = indexed_extent {
1436 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1437 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1438 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1439 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1440 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1445 // don't lint if the container that is indexed does not have .iter() method
1446 let has_iter = has_iter_method(cx, indexed_ty);
1447 if has_iter.is_none() {
1451 // don't lint if the container that is indexed into is also used without
1453 if visitor.referenced.contains(&indexed) {
1457 let starts_at_zero = is_integer_const(cx, start, 0);
1459 let skip = if starts_at_zero {
1462 format!(".skip({})", snippet(cx, start.span, ".."))
1465 let mut end_is_start_plus_val = false;
1467 let take = if let Some(end) = *end {
1468 let mut take_expr = end;
1470 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1471 if let BinOpKind::Add = op.node {
1472 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1473 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1475 if start_equal_left {
1477 } else if start_equal_right {
1481 end_is_start_plus_val = start_equal_left | start_equal_right;
1485 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1489 ast::RangeLimits::Closed => {
1490 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1491 format!(".take({})", take_expr + sugg::ONE)
1493 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1500 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1501 ("mut ", "iter_mut")
1506 let take_is_empty = take.is_empty();
1507 let mut method_1 = take;
1508 let mut method_2 = skip;
1510 if end_is_start_plus_val {
1511 mem::swap(&mut method_1, &mut method_2);
1514 if visitor.nonindex {
1517 NEEDLESS_RANGE_LOOP,
1519 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1523 "consider using an iterator",
1525 (pat.span, format!("({}, <item>)", ident.name)),
1528 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1535 let repl = if starts_at_zero && take_is_empty {
1536 format!("&{}{}", ref_mut, indexed)
1538 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1543 NEEDLESS_RANGE_LOOP,
1546 "the loop variable `{}` is only used to index `{}`.",
1552 "consider using an iterator",
1553 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1563 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1565 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1566 if len_args.len() == 1;
1567 if method.ident.name == sym!(len);
1568 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1569 if path.segments.len() == 1;
1570 if path.segments[0].ident.name == var;
1579 fn is_end_eq_array_len<'tcx>(
1580 cx: &LateContext<'tcx>,
1582 limits: ast::RangeLimits,
1583 indexed_ty: Ty<'tcx>,
1586 if let ExprKind::Lit(ref lit) = end.kind;
1587 if let ast::LitKind::Int(end_int, _) = lit.node;
1588 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1589 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1591 return match limits {
1592 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1593 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1601 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1602 let mut applicability = Applicability::MachineApplicable;
1603 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1604 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1609 "it is more concise to loop over references to containers instead of using explicit \
1611 "to write this more concisely, try",
1612 format!("&{}{}", muta, object),
1617 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1618 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1619 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1620 // just the receiver, no arguments
1621 if args.len() == 1 {
1622 let method_name = &*method.ident.as_str();
1623 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1624 if method_name == "iter" || method_name == "iter_mut" {
1625 if is_ref_iterable_type(cx, &args[0]) {
1626 lint_iter_method(cx, args, arg, method_name);
1628 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1629 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1630 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1631 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1632 let mut applicability = Applicability::MachineApplicable;
1633 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1636 EXPLICIT_INTO_ITER_LOOP,
1638 "it is more concise to loop over containers instead of using explicit \
1640 "to write this more concisely, try",
1645 let ref_receiver_ty = cx.tcx.mk_ref(
1646 cx.tcx.lifetimes.re_erased,
1649 mutbl: Mutability::Not,
1652 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1653 lint_iter_method(cx, args, arg, method_name)
1656 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1661 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1662 probably not what you want",
1664 next_loop_linted = true;
1668 if !next_loop_linted {
1669 check_arg_type(cx, pat, arg);
1673 /// Checks for `for` loops over `Option`s and `Result`s.
1674 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1675 let ty = cx.typeck_results().expr_ty(arg);
1676 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1679 FOR_LOOPS_OVER_FALLIBLES,
1682 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1683 `if let` statement.",
1684 snippet(cx, arg.span, "_")
1688 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1689 snippet(cx, pat.span, "_"),
1690 snippet(cx, arg.span, "_")
1693 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1696 FOR_LOOPS_OVER_FALLIBLES,
1699 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1700 `if let` statement.",
1701 snippet(cx, arg.span, "_")
1705 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1706 snippet(cx, pat.span, "_"),
1707 snippet(cx, arg.span, "_")
1713 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1714 // incremented exactly once in the loop body, and initialized to zero
1715 // at the start of the loop.
1716 fn check_for_loop_explicit_counter<'tcx>(
1717 cx: &LateContext<'tcx>,
1719 arg: &'tcx Expr<'_>,
1720 body: &'tcx Expr<'_>,
1721 expr: &'tcx Expr<'_>,
1723 // Look for variables that are incremented once per loop iteration.
1724 let mut increment_visitor = IncrementVisitor::new(cx);
1725 walk_expr(&mut increment_visitor, body);
1727 // For each candidate, check the parent block to see if
1728 // it's initialized to zero at the start of the loop.
1729 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1730 for id in increment_visitor.into_results() {
1731 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1732 walk_block(&mut initialize_visitor, block);
1735 if let Some((name, initializer)) = initialize_visitor.get_result();
1736 if is_integer_const(cx, initializer, 0);
1738 let mut applicability = Applicability::MachineApplicable;
1740 let for_span = get_span_of_entire_for_loop(expr);
1744 EXPLICIT_COUNTER_LOOP,
1745 for_span.with_hi(arg.span.hi()),
1746 &format!("the variable `{}` is used as a loop counter.", name),
1749 "for ({}, {}) in {}.enumerate()",
1751 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1752 make_iterator_snippet(cx, arg, &mut applicability),
1762 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1763 /// actual `Iterator` that the loop uses.
1764 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1765 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1766 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1771 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1774 // (&x).into_iter() ==> x.iter()
1775 // (&mut x).into_iter() ==> x.iter_mut()
1777 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1778 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1780 let meth_name = match mutability {
1781 Mutability::Mut => "iter_mut",
1782 Mutability::Not => "iter",
1786 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1792 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1798 /// Checks for the `FOR_KV_MAP` lint.
1799 fn check_for_loop_over_map_kv<'tcx>(
1800 cx: &LateContext<'tcx>,
1802 arg: &'tcx Expr<'_>,
1803 body: &'tcx Expr<'_>,
1804 expr: &'tcx Expr<'_>,
1806 let pat_span = pat.span;
1808 if let PatKind::Tuple(ref pat, _) = pat.kind {
1810 let arg_span = arg.span;
1811 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1812 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1813 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1814 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1819 let mutbl = match mutbl {
1820 Mutability::Not => "",
1821 Mutability::Mut => "_mut",
1823 let arg = match arg.kind {
1824 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1828 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1833 &format!("you seem to want to iterate on a map's {}s", kind),
1835 let map = sugg::Sugg::hir(cx, arg, "map");
1838 "use the corresponding method",
1840 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1841 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1851 struct MutatePairDelegate<'a, 'tcx> {
1852 cx: &'a LateContext<'tcx>,
1853 hir_id_low: Option<HirId>,
1854 hir_id_high: Option<HirId>,
1855 span_low: Option<Span>,
1856 span_high: Option<Span>,
1859 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1860 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1862 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1863 if let ty::BorrowKind::MutBorrow = bk {
1864 if let PlaceBase::Local(id) = cmt.place.base {
1865 if Some(id) == self.hir_id_low {
1866 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1868 if Some(id) == self.hir_id_high {
1869 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1875 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>) {
1876 if let PlaceBase::Local(id) = cmt.place.base {
1877 if Some(id) == self.hir_id_low {
1878 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1880 if Some(id) == self.hir_id_high {
1881 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1887 impl MutatePairDelegate<'_, '_> {
1888 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1889 (self.span_low, self.span_high)
1893 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1894 if let Some(higher::Range {
1898 }) = higher::range(arg)
1900 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1901 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1902 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1903 mut_warn_with_span(cx, span_low);
1904 mut_warn_with_span(cx, span_high);
1909 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
1910 if let Some(sp) = span {
1915 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1920 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
1922 if let ExprKind::Path(ref qpath) = bound.kind;
1923 if let QPath::Resolved(None, _) = *qpath;
1925 let res = qpath_res(cx, qpath, bound.hir_id);
1926 if let Res::Local(hir_id) = res {
1927 let node_str = cx.tcx.hir().get(hir_id);
1929 if let Node::Binding(pat) = node_str;
1930 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1931 if let BindingAnnotation::Mutable = bind_ann;
1933 return Some(hir_id);
1942 fn check_for_mutation<'tcx>(
1943 cx: &LateContext<'tcx>,
1945 bound_ids: &[Option<HirId>],
1946 ) -> (Option<Span>, Option<Span>) {
1947 let mut delegate = MutatePairDelegate {
1949 hir_id_low: bound_ids[0],
1950 hir_id_high: bound_ids[1],
1954 let def_id = body.hir_id.owner.to_def_id();
1955 cx.tcx.infer_ctxt().enter(|infcx| {
1956 ExprUseVisitor::new(
1959 def_id.expect_local(),
1961 cx.typeck_results(),
1965 delegate.mutation_span()
1968 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1969 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
1971 PatKind::Wild => true,
1972 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
1977 struct LocalUsedVisitor<'a, 'tcx> {
1978 cx: &'a LateContext<'tcx>,
1983 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1984 type Map = Map<'tcx>;
1986 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1987 if same_var(self.cx, expr, self.local) {
1990 walk_expr(self, expr);
1994 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1995 NestedVisitorMap::None
1999 struct VarVisitor<'a, 'tcx> {
2000 /// context reference
2001 cx: &'a LateContext<'tcx>,
2002 /// var name to look for as index
2004 /// indexed variables that are used mutably
2005 indexed_mut: FxHashSet<Symbol>,
2006 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2007 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2008 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2009 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2010 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2011 /// Any names that are used outside an index operation.
2012 /// Used to detect things like `&mut vec` used together with `vec[i]`
2013 referenced: FxHashSet<Symbol>,
2014 /// has the loop variable been used in expressions other than the index of
2017 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2018 /// takes `&mut self`
2019 prefer_mutable: bool,
2022 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2023 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2025 // the indexed container is referenced by a name
2026 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2027 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2028 if seqvar.segments.len() == 1;
2030 let index_used_directly = same_var(self.cx, idx, self.var);
2031 let indexed_indirectly = {
2032 let mut used_visitor = LocalUsedVisitor {
2037 walk_expr(&mut used_visitor, idx);
2041 if indexed_indirectly || index_used_directly {
2042 if self.prefer_mutable {
2043 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2045 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
2047 Res::Local(hir_id) => {
2048 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2049 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2050 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2051 if indexed_indirectly {
2052 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2054 if index_used_directly {
2055 self.indexed_directly.insert(
2056 seqvar.segments[0].ident.name,
2057 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2060 return false; // no need to walk further *on the variable*
2062 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2063 if indexed_indirectly {
2064 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2066 if index_used_directly {
2067 self.indexed_directly.insert(
2068 seqvar.segments[0].ident.name,
2069 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2072 return false; // no need to walk further *on the variable*
2083 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2084 type Map = Map<'tcx>;
2086 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2089 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2090 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
2091 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2092 if !self.check(&args[1], &args[0], expr);
2098 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2099 if !self.check(idx, seqexpr, expr);
2104 // directly using a variable
2105 if let ExprKind::Path(ref qpath) = expr.kind;
2106 if let QPath::Resolved(None, ref path) = *qpath;
2107 if path.segments.len() == 1;
2109 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2110 if local_id == self.var {
2111 self.nonindex = true;
2113 // not the correct variable, but still a variable
2114 self.referenced.insert(path.segments[0].ident.name);
2120 let old = self.prefer_mutable;
2122 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2123 self.prefer_mutable = true;
2124 self.visit_expr(lhs);
2125 self.prefer_mutable = false;
2126 self.visit_expr(rhs);
2128 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2129 if mutbl == Mutability::Mut {
2130 self.prefer_mutable = true;
2132 self.visit_expr(expr);
2134 ExprKind::Call(ref f, args) => {
2137 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2138 self.prefer_mutable = false;
2139 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2140 if mutbl == Mutability::Mut {
2141 self.prefer_mutable = true;
2144 self.visit_expr(expr);
2147 ExprKind::MethodCall(_, _, args, _) => {
2148 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2149 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2150 self.prefer_mutable = false;
2151 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2152 if mutbl == Mutability::Mut {
2153 self.prefer_mutable = true;
2156 self.visit_expr(expr);
2159 ExprKind::Closure(_, _, body_id, ..) => {
2160 let body = self.cx.tcx.hir().body(body_id);
2161 self.visit_expr(&body.value);
2163 _ => walk_expr(self, expr),
2165 self.prefer_mutable = old;
2167 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2168 NestedVisitorMap::None
2172 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2173 let def_id = match var_def_id(cx, expr) {
2175 None => return false,
2177 if let Some(used_mutably) = mutated_variables(container, cx) {
2178 if used_mutably.contains(&def_id) {
2185 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2186 let def_id = match var_def_id(cx, iter_expr) {
2188 None => return false,
2190 let mut visitor = VarUsedAfterLoopVisitor {
2193 iter_expr_id: iter_expr.hir_id,
2194 past_while_let: false,
2195 var_used_after_while_let: false,
2197 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2198 walk_block(&mut visitor, enclosing_block);
2200 visitor.var_used_after_while_let
2203 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2204 cx: &'a LateContext<'tcx>,
2206 iter_expr_id: HirId,
2207 past_while_let: bool,
2208 var_used_after_while_let: bool,
2211 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2212 type Map = Map<'tcx>;
2214 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2215 if self.past_while_let {
2216 if Some(self.def_id) == var_def_id(self.cx, expr) {
2217 self.var_used_after_while_let = true;
2219 } else if self.iter_expr_id == expr.hir_id {
2220 self.past_while_let = true;
2222 walk_expr(self, expr);
2224 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2225 NestedVisitorMap::None
2229 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2230 /// for `&T` and `&mut T`, such as `Vec`.
2232 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2233 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2234 // will allow further borrows afterwards
2235 let ty = cx.typeck_results().expr_ty(e);
2236 is_iterable_array(ty, cx) ||
2237 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2238 match_type(cx, ty, &paths::LINKED_LIST) ||
2239 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2240 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2241 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2242 match_type(cx, ty, &paths::BINARY_HEAP) ||
2243 match_type(cx, ty, &paths::BTREEMAP) ||
2244 match_type(cx, ty, &paths::BTREESET)
2247 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2248 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2250 ty::Array(_, n) => n
2251 .try_eval_usize(cx.tcx, cx.param_env)
2252 .map_or(false, |val| (0..=32).contains(&val)),
2257 /// If a block begins with a statement (possibly a `let` binding) and has an
2258 /// expression, return it.
2259 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2260 if block.stmts.is_empty() {
2263 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2264 local.init //.map(|expr| expr)
2270 /// If a block begins with an expression (with or without semicolon), return it.
2271 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2273 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2274 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2275 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2276 StmtKind::Local(..) | StmtKind::Item(..) => None,
2282 /// Returns `true` if expr contains a single break expr without destination label
2284 /// passed expression. The expression may be within a block.
2285 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2287 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2288 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2293 #[derive(Debug, PartialEq)]
2294 enum IncrementVisitorVarState {
2295 Initial, // Not examined yet
2296 IncrOnce, // Incremented exactly once, may be a loop counter
2300 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2301 struct IncrementVisitor<'a, 'tcx> {
2302 cx: &'a LateContext<'tcx>, // context reference
2303 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2304 depth: u32, // depth of conditional expressions
2308 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2309 fn new(cx: &'a LateContext<'tcx>) -> Self {
2312 states: FxHashMap::default(),
2318 fn into_results(self) -> impl Iterator<Item = HirId> {
2319 self.states.into_iter().filter_map(|(id, state)| {
2320 if state == IncrementVisitorVarState::IncrOnce {
2329 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2330 type Map = Map<'tcx>;
2332 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2337 // If node is a variable
2338 if let Some(def_id) = var_def_id(self.cx, expr) {
2339 if let Some(parent) = get_parent_expr(self.cx, expr) {
2340 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2341 if *state == IncrementVisitorVarState::IncrOnce {
2342 *state = IncrementVisitorVarState::DontWarn;
2347 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2348 if lhs.hir_id == expr.hir_id {
2349 *state = if op.node == BinOpKind::Add
2350 && is_integer_const(self.cx, rhs, 1)
2351 && *state == IncrementVisitorVarState::Initial
2354 IncrementVisitorVarState::IncrOnce
2356 // Assigned some other value or assigned multiple times
2357 IncrementVisitorVarState::DontWarn
2361 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2362 *state = IncrementVisitorVarState::DontWarn
2364 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2365 *state = IncrementVisitorVarState::DontWarn
2371 walk_expr(self, expr);
2372 } else if is_loop(expr) || is_conditional(expr) {
2374 walk_expr(self, expr);
2376 } else if let ExprKind::Continue(_) = expr.kind {
2379 walk_expr(self, expr);
2382 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2383 NestedVisitorMap::None
2387 enum InitializeVisitorState<'hir> {
2388 Initial, // Not examined yet
2389 Declared(Symbol), // Declared but not (yet) initialized
2392 initializer: &'hir Expr<'hir>,
2397 /// Checks whether a variable is initialized at the start of a loop and not modified
2398 /// and used after the loop.
2399 struct InitializeVisitor<'a, 'tcx> {
2400 cx: &'a LateContext<'tcx>, // context reference
2401 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2403 state: InitializeVisitorState<'tcx>,
2404 depth: u32, // depth of conditional expressions
2408 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2409 fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2414 state: InitializeVisitorState::Initial,
2420 fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
2421 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2422 Some((name, initializer))
2429 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2430 type Map = Map<'tcx>;
2432 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2433 // Look for declarations of the variable
2435 if let StmtKind::Local(ref local) = stmt.kind;
2436 if local.pat.hir_id == self.var_id;
2437 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2439 self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
2440 InitializeVisitorState::Initialized {
2447 walk_stmt(self, stmt);
2450 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2451 if matches!(self.state, InitializeVisitorState::DontWarn) {
2454 if expr.hir_id == self.end_expr.hir_id {
2455 self.past_loop = true;
2458 // No need to visit expressions before the variable is
2460 if matches!(self.state, InitializeVisitorState::Initial) {
2464 // If node is the desired variable, see how it's used
2465 if var_def_id(self.cx, expr) == Some(self.var_id) {
2467 self.state = InitializeVisitorState::DontWarn;
2471 if let Some(parent) = get_parent_expr(self.cx, expr) {
2473 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2474 self.state = InitializeVisitorState::DontWarn;
2476 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2477 self.state = if_chain! {
2479 if let InitializeVisitorState::Declared(name)
2480 | InitializeVisitorState::Initialized { name, ..} = self.state;
2482 InitializeVisitorState::Initialized { initializer: rhs, name }
2484 InitializeVisitorState::DontWarn
2488 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2489 self.state = InitializeVisitorState::DontWarn
2495 walk_expr(self, expr);
2496 } else if !self.past_loop && is_loop(expr) {
2497 self.state = InitializeVisitorState::DontWarn;
2498 } else if is_conditional(expr) {
2500 walk_expr(self, expr);
2503 walk_expr(self, expr);
2507 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2508 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2512 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2513 if let ExprKind::Path(ref qpath) = expr.kind {
2514 let path_res = qpath_res(cx, qpath, expr.hir_id);
2515 if let Res::Local(hir_id) = path_res {
2516 return Some(hir_id);
2522 fn is_loop(expr: &Expr<'_>) -> bool {
2523 matches!(expr.kind, ExprKind::Loop(..))
2526 fn is_conditional(expr: &Expr<'_>) -> bool {
2527 matches!(expr.kind, ExprKind::Match(..))
2530 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2532 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2533 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2534 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2536 return is_loop_nested(cx, loop_expr, iter_expr)
2542 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2543 let mut id = loop_expr.hir_id;
2544 let iter_name = if let Some(name) = path_name(iter_expr) {
2550 let parent = cx.tcx.hir().get_parent_node(id);
2554 match cx.tcx.hir().find(parent) {
2555 Some(Node::Expr(expr)) => {
2556 if let ExprKind::Loop(..) = expr.kind {
2560 Some(Node::Block(block)) => {
2561 let mut block_visitor = LoopNestVisitor {
2563 iterator: iter_name,
2566 walk_block(&mut block_visitor, block);
2567 if block_visitor.nesting == RuledOut {
2571 Some(Node::Stmt(_)) => (),
2580 #[derive(PartialEq, Eq)]
2582 Unknown, // no nesting detected yet
2583 RuledOut, // the iterator is initialized or assigned within scope
2584 LookFurther, // no nesting detected, no further walk required
2587 use self::Nesting::{LookFurther, RuledOut, Unknown};
2589 struct LoopNestVisitor {
2595 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2596 type Map = Map<'tcx>;
2598 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2599 if stmt.hir_id == self.hir_id {
2600 self.nesting = LookFurther;
2601 } else if self.nesting == Unknown {
2602 walk_stmt(self, stmt);
2606 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2607 if self.nesting != Unknown {
2610 if expr.hir_id == self.hir_id {
2611 self.nesting = LookFurther;
2615 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2616 if match_var(path, self.iterator) {
2617 self.nesting = RuledOut;
2620 _ => walk_expr(self, expr),
2624 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2625 if self.nesting != Unknown {
2628 if let PatKind::Binding(.., span_name, _) = pat.kind {
2629 if self.iterator == span_name.name {
2630 self.nesting = RuledOut;
2637 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2638 NestedVisitorMap::None
2642 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2643 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2644 let segments = &path.segments;
2645 if segments.len() == 1 {
2646 return Some(segments[0].ident.name);
2652 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2653 if constant(cx, cx.typeck_results(), cond).is_some() {
2654 // A pure constant condition (e.g., `while false`) is not linted.
2658 let mut var_visitor = VarCollectorVisitor {
2660 ids: FxHashSet::default(),
2661 def_ids: FxHashMap::default(),
2664 var_visitor.visit_expr(cond);
2665 if var_visitor.skip {
2668 let used_in_condition = &var_visitor.ids;
2669 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2670 used_in_condition.is_disjoint(&used_mutably)
2674 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2676 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2677 has_break_or_return: false,
2679 has_break_or_return_visitor.visit_expr(expr);
2680 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2682 if no_cond_variable_mutated && !mutable_static_in_cond {
2685 WHILE_IMMUTABLE_CONDITION,
2687 "variables in the condition are not mutated in the loop body",
2689 diag.note("this may lead to an infinite or to a never running loop");
2691 if has_break_or_return {
2692 diag.note("this loop contains `return`s or `break`s");
2693 diag.help("rewrite it as `if cond { loop { } }`");
2700 struct HasBreakOrReturnVisitor {
2701 has_break_or_return: bool,
2704 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2705 type Map = Map<'tcx>;
2707 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2708 if self.has_break_or_return {
2713 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2714 self.has_break_or_return = true;
2720 walk_expr(self, expr);
2723 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2724 NestedVisitorMap::None
2728 /// Collects the set of variables in an expression
2729 /// Stops analysis if a function call is found
2730 /// Note: In some cases such as `self`, there are no mutable annotation,
2731 /// All variables definition IDs are collected
2732 struct VarCollectorVisitor<'a, 'tcx> {
2733 cx: &'a LateContext<'tcx>,
2734 ids: FxHashSet<HirId>,
2735 def_ids: FxHashMap<def_id::DefId, bool>,
2739 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2740 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2742 if let ExprKind::Path(ref qpath) = ex.kind;
2743 if let QPath::Resolved(None, _) = *qpath;
2744 let res = qpath_res(self.cx, qpath, ex.hir_id);
2747 Res::Local(hir_id) => {
2748 self.ids.insert(hir_id);
2750 Res::Def(DefKind::Static, def_id) => {
2751 let mutable = self.cx.tcx.is_mutable_static(def_id);
2752 self.def_ids.insert(def_id, mutable);
2761 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2762 type Map = Map<'tcx>;
2764 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2766 ExprKind::Path(_) => self.insert_def_id(ex),
2767 // If there is any function/method call… we just stop analysis
2768 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2770 _ => walk_expr(self, ex),
2774 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2775 NestedVisitorMap::None
2779 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2781 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2782 check_needless_collect_direct_usage(expr, cx);
2783 check_needless_collect_indirect_usage(expr, cx);
2785 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2787 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2788 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2789 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2790 if let Some(ref generic_args) = chain_method.args;
2791 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2793 let ty = cx.typeck_results().node_type(ty.hir_id);
2794 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2795 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2796 match_type(cx, ty, &paths::BTREEMAP) ||
2797 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2798 if method.ident.name == sym!(len) {
2799 let span = shorten_needless_collect_span(expr);
2804 NEEDLESS_COLLECT_MSG,
2806 "count()".to_string(),
2807 Applicability::MachineApplicable,
2810 if method.ident.name == sym!(is_empty) {
2811 let span = shorten_needless_collect_span(expr);
2816 NEEDLESS_COLLECT_MSG,
2818 "next().is_none()".to_string(),
2819 Applicability::MachineApplicable,
2822 if method.ident.name == sym!(contains) {
2823 let contains_arg = snippet(cx, args[1].span, "??");
2824 let span = shorten_needless_collect_span(expr);
2829 NEEDLESS_COLLECT_MSG,
2831 let (arg, pred) = contains_arg
2833 .map_or(("&x", &*contains_arg), |s| ("x", s));
2834 diag.span_suggestion(
2838 "any(|{}| x == {})",
2841 Applicability::MachineApplicable,
2851 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2852 if let ExprKind::Block(ref block, _) = expr.kind {
2853 for ref stmt in block.stmts {
2855 if let StmtKind::Local(
2856 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2857 init: Some(ref init_expr), .. }
2859 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2860 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2861 if let Some(ref generic_args) = method_name.args;
2862 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2863 if let ty = cx.typeck_results().node_type(ty.hir_id);
2864 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2865 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2866 match_type(cx, ty, &paths::LINKED_LIST);
2867 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2868 if iter_calls.len() == 1;
2870 // Suggest replacing iter_call with iter_replacement, and removing stmt
2871 let iter_call = &iter_calls[0];
2875 stmt.span.until(iter_call.span),
2876 NEEDLESS_COLLECT_MSG,
2878 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2879 diag.multipart_suggestion(
2880 iter_call.get_suggestion_text(),
2882 (stmt.span, String::new()),
2883 (iter_call.span, iter_replacement)
2885 Applicability::MachineApplicable,// MaybeIncorrect,
2895 struct IterFunction {
2896 func: IterFunctionKind,
2900 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2902 IterFunctionKind::IntoIter => String::new(),
2903 IterFunctionKind::Len => String::from(".count()"),
2904 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2905 IterFunctionKind::Contains(span) => format!(".any(|x| x == {})", snippet(cx, *span, "..")),
2908 fn get_suggestion_text(&self) -> &'static str {
2910 IterFunctionKind::IntoIter => {
2911 "Use the original Iterator instead of collecting it and then producing a new one"
2913 IterFunctionKind::Len => {
2914 "Take the original Iterator's count instead of collecting it and finding the length"
2916 IterFunctionKind::IsEmpty => {
2917 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
2919 IterFunctionKind::Contains(_) => {
2920 "Check if the original Iterator contains an element instead of collecting then checking"
2925 enum IterFunctionKind {
2932 struct IterFunctionVisitor {
2933 uses: Vec<IterFunction>,
2937 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
2938 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
2939 // Check function calls on our collection
2941 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
2942 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
2943 if let &[name] = &path.segments;
2944 if name.ident == self.target;
2946 let len = sym!(len);
2947 let is_empty = sym!(is_empty);
2948 let contains = sym!(contains);
2949 match method_name.ident.name {
2950 sym::into_iter => self.uses.push(
2951 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
2953 name if name == len => self.uses.push(
2954 IterFunction { func: IterFunctionKind::Len, span: expr.span }
2956 name if name == is_empty => self.uses.push(
2957 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
2959 name if name == contains => self.uses.push(
2960 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
2962 _ => self.seen_other = true,
2967 // Check if the collection is used for anything else
2969 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
2970 if let &[name] = &path.segments;
2971 if name.ident == self.target;
2973 self.seen_other = true;
2975 walk_expr(self, expr);
2980 type Map = Map<'tcx>;
2981 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2982 NestedVisitorMap::None
2986 /// Detect the occurences of calls to `iter` or `into_iter` for the
2987 /// given identifier
2988 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
2989 let mut visitor = IterFunctionVisitor {
2994 visitor.visit_block(block);
2995 if visitor.seen_other {
3002 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3004 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3005 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3007 return expr.span.with_lo(span.lo());