1 use crate::consts::constant;
2 use crate::utils::paths;
3 use crate::utils::sugg::Sugg;
4 use crate::utils::usage::{is_unused, mutated_variables};
6 contains_name, get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
7 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?** These busy loops burn CPU cycles without doing
297 /// anything. It is _almost always_ a better idea to `panic!` than to have
300 /// If panicking isn't possible, think of the environment and either:
301 /// - block on something
302 /// - sleep the thread for some microseconds
303 /// - yield or pause the thread
305 /// For `std` targets, this can be done with
306 /// [`std::thread::sleep`](https://doc.rust-lang.org/std/thread/fn.sleep.html)
307 /// or [`std::thread::yield_now`](https://doc.rust-lang.org/std/thread/fn.yield_now.html).
309 /// For `no_std` targets, doing this is more complicated, especially because
310 /// `#[panic_handler]`s can't panic. To stop/pause the thread, you will
311 /// probably need to invoke some target-specific intrinsic. Examples include:
312 /// - [`x86_64::instructions::hlt`](https://docs.rs/x86_64/0.12.2/x86_64/instructions/fn.hlt.html)
313 /// - [`cortex_m::asm::wfi`](https://docs.rs/cortex-m/0.6.3/cortex_m/asm/fn.wfi.html)
315 /// **Known problems:** None.
323 "empty `loop {}`, which should block or sleep"
326 declare_clippy_lint! {
327 /// **What it does:** Checks for `while let` expressions on iterators.
329 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
330 /// the intent better.
332 /// **Known problems:** None.
336 /// while let Some(val) = iter() {
340 pub WHILE_LET_ON_ITERATOR,
342 "using a while-let loop instead of a for loop on an iterator"
345 declare_clippy_lint! {
346 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
347 /// ignoring either the keys or values.
349 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
350 /// can be used to express that don't need the values or keys.
352 /// **Known problems:** None.
356 /// for (k, _) in &map {
361 /// could be replaced by
364 /// for k in map.keys() {
370 "looping on a map using `iter` when `keys` or `values` would do"
373 declare_clippy_lint! {
374 /// **What it does:** Checks for loops that will always `break`, `return` or
375 /// `continue` an outer loop.
377 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
380 /// **Known problems:** None
391 "any loop that will always `break` or `return`"
394 declare_clippy_lint! {
395 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
397 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
399 /// **Known problems:** None
403 /// let mut foo = 42;
404 /// for i in 0..foo {
406 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
411 "for loop over a range where one of the bounds is a mutable variable"
414 declare_clippy_lint! {
415 /// **What it does:** Checks whether variables used within while loop condition
416 /// can be (and are) mutated in the body.
418 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
419 /// will lead to an infinite loop.
421 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
422 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
423 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
429 /// println!("let me loop forever!");
432 pub WHILE_IMMUTABLE_CONDITION,
434 "variables used within while expression are not mutated in the body"
437 declare_clippy_lint! {
438 /// **What it does:** Checks whether a for loop is being used to push a constant
439 /// value into a Vec.
441 /// **Why is this bad?** This kind of operation can be expressed more succinctly with
442 /// `vec![item;SIZE]` or `vec.resize(NEW_SIZE, item)` and using these alternatives may also
443 /// have better performance.
444 /// **Known problems:** None
450 /// let mut vec: Vec<u8> = Vec::new();
458 /// could be written as
462 /// let mut vec: Vec<u8> = vec![item1; 20];
463 /// vec.resize(20 + 30, item2);
467 "the same item is pushed inside of a for loop"
470 declare_lint_pass!(Loops => [
474 EXPLICIT_INTO_ITER_LOOP,
476 FOR_LOOPS_OVER_FALLIBLES,
479 EXPLICIT_COUNTER_LOOP,
481 WHILE_LET_ON_ITERATOR,
485 WHILE_IMMUTABLE_CONDITION,
489 impl<'tcx> LateLintPass<'tcx> for Loops {
490 #[allow(clippy::too_many_lines)]
491 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
492 if let Some((pat, arg, body)) = higher::for_loop(expr) {
493 // we don't want to check expanded macros
494 // this check is not at the top of the function
495 // since higher::for_loop expressions are marked as expansions
496 if body.span.from_expansion() {
499 check_for_loop(cx, pat, arg, body, expr);
502 // we don't want to check expanded macros
503 if expr.span.from_expansion() {
507 // check for never_loop
508 if let ExprKind::Loop(ref block, _, _) = expr.kind {
509 match never_loop_block(block, expr.hir_id) {
510 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
511 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
515 // check for `loop { if let {} else break }` that could be `while let`
516 // (also matches an explicit "match" instead of "if let")
517 // (even if the "match" or "if let" is used for declaration)
518 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
519 // also check for empty `loop {}` statements
520 // TODO(issue #6161): Enable for no_std crates (outside of #[panic_handler])
521 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) {
526 "empty `loop {}` wastes CPU cycles",
528 "You should either use `panic!()` or add `std::thread::sleep(..);` to the loop body.",
532 // extract the expression from the first statement (if any) in a block
533 let inner_stmt_expr = extract_expr_from_first_stmt(block);
534 // or extract the first expression (if any) from the block
535 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
536 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
537 // ensure "if let" compatible match structure
539 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
541 && arms[0].guard.is_none()
542 && arms[1].guard.is_none()
543 && is_simple_break_expr(&arms[1].body)
545 if in_external_macro(cx.sess(), expr.span) {
549 // NOTE: we used to build a body here instead of using
550 // ellipsis, this was removed because:
551 // 1) it was ugly with big bodies;
552 // 2) it was not indented properly;
553 // 3) it wasn’t very smart (see #675).
554 let mut applicability = Applicability::HasPlaceholders;
559 "this loop could be written as a `while let` loop",
562 "while let {} = {} {{ .. }}",
563 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
564 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
575 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
576 let pat = &arms[0].pat.kind;
578 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
579 &ExprKind::MethodCall(ref method_path, _, ref method_args, _),
580 ) = (pat, &match_expr.kind)
582 let iter_expr = &method_args[0];
584 // Don't lint when the iterator is recreated on every iteration
586 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
587 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
588 if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
594 let lhs_constructor = last_path_segment(qpath);
595 if method_path.ident.name == sym!(next)
596 && match_trait_method(cx, match_expr, &paths::ITERATOR)
597 && lhs_constructor.ident.name == sym!(Some)
598 && (pat_args.is_empty()
599 || !is_refutable(cx, &pat_args[0])
600 && !is_used_inside(cx, iter_expr, &arms[0].body)
601 && !is_iterator_used_after_while_let(cx, iter_expr)
602 && !is_nested(cx, expr, &method_args[0]))
604 let mut applicability = Applicability::MachineApplicable;
605 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
606 let loop_var = if pat_args.is_empty() {
609 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
613 WHILE_LET_ON_ITERATOR,
614 expr.span.with_hi(match_expr.span.hi()),
615 "this loop could be written as a `for` loop",
617 format!("for {} in {}", loop_var, iterator),
624 if let Some((cond, body)) = higher::while_loop(&expr) {
625 check_infinite_loop(cx, cond, body);
628 check_needless_collect(expr, cx);
632 enum NeverLoopResult {
633 // A break/return always get triggered but not necessarily for the main loop.
635 // A continue may occur for the main loop.
641 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
643 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
644 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
648 // Combine two results for parts that are called in order.
650 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
652 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
653 NeverLoopResult::Otherwise => second,
657 // Combine two results where both parts are called but not necessarily in order.
659 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
660 match (left, right) {
661 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
662 NeverLoopResult::MayContinueMainLoop
664 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
665 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
669 // Combine two results where only one of the part may have been executed.
671 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
673 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
674 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
675 NeverLoopResult::MayContinueMainLoop
677 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
681 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
682 let stmts = block.stmts.iter().map(stmt_to_expr);
683 let expr = once(block.expr.as_deref());
684 let mut iter = stmts.chain(expr).filter_map(|e| e);
685 never_loop_expr_seq(&mut iter, main_loop_id)
688 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
690 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
691 StmtKind::Local(ref local) => local.init.as_deref(),
696 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
699 | ExprKind::Unary(_, ref e)
700 | ExprKind::Cast(ref e, _)
701 | ExprKind::Type(ref e, _)
702 | ExprKind::Field(ref e, _)
703 | ExprKind::AddrOf(_, _, ref e)
704 | ExprKind::Struct(_, _, Some(ref e))
705 | ExprKind::Repeat(ref e, _)
706 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
707 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
708 never_loop_expr_all(&mut es.iter(), main_loop_id)
710 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
711 ExprKind::Binary(_, ref e1, ref e2)
712 | ExprKind::Assign(ref e1, ref e2, _)
713 | ExprKind::AssignOp(_, ref e1, ref e2)
714 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
715 ExprKind::Loop(ref b, _, _) => {
716 // Break can come from the inner loop so remove them.
717 absorb_break(&never_loop_block(b, main_loop_id))
719 ExprKind::Match(ref e, ref arms, _) => {
720 let e = never_loop_expr(e, main_loop_id);
724 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
728 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
729 ExprKind::Continue(d) => {
732 .expect("target ID can only be missing in the presence of compilation errors");
733 if id == main_loop_id {
734 NeverLoopResult::MayContinueMainLoop
736 NeverLoopResult::AlwaysBreak
739 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
740 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
742 ExprKind::InlineAsm(ref asm) => asm
746 InlineAsmOperand::In { expr, .. }
747 | InlineAsmOperand::InOut { expr, .. }
748 | InlineAsmOperand::Const { expr }
749 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
750 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
751 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
752 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
755 .fold(NeverLoopResult::Otherwise, combine_both),
756 ExprKind::Struct(_, _, None)
757 | ExprKind::Yield(_, _)
758 | ExprKind::Closure(_, _, _, _, _)
759 | ExprKind::LlvmInlineAsm(_)
761 | ExprKind::ConstBlock(_)
763 | ExprKind::Err => NeverLoopResult::Otherwise,
767 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
768 es.map(|e| never_loop_expr(e, main_loop_id))
769 .fold(NeverLoopResult::Otherwise, combine_seq)
772 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
773 es.map(|e| never_loop_expr(e, main_loop_id))
774 .fold(NeverLoopResult::Otherwise, combine_both)
777 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
778 e.map(|e| never_loop_expr(e, main_loop_id))
779 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
782 fn check_for_loop<'tcx>(
783 cx: &LateContext<'tcx>,
786 body: &'tcx Expr<'_>,
787 expr: &'tcx Expr<'_>,
789 let is_manual_memcpy_triggered = detect_manual_memcpy(cx, pat, arg, body, expr);
790 if !is_manual_memcpy_triggered {
791 check_for_loop_range(cx, pat, arg, body, expr);
792 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
794 check_for_loop_arg(cx, pat, arg, expr);
795 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
796 check_for_mut_range_bound(cx, arg, body);
797 detect_same_item_push(cx, pat, arg, body, expr);
800 // this function assumes the given expression is a `for` loop.
801 fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
802 // for some reason this is the only way to get the `Span`
803 // of the entire `for` loop
804 if let ExprKind::Match(_, arms, _) = &expr.kind {
811 fn same_var<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
813 if let ExprKind::Path(qpath) = &expr.kind;
814 if let QPath::Resolved(None, path) = qpath;
815 if path.segments.len() == 1;
816 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
826 /// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
827 /// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
828 /// it exists for the convenience of the overloaded operators while normal functions can do the
831 struct MinifyingSugg<'a>(Sugg<'a>);
833 impl<'a> MinifyingSugg<'a> {
834 fn as_str(&self) -> &str {
835 let Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) = &self.0;
839 fn into_sugg(self) -> Sugg<'a> {
844 impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
845 fn from(sugg: Sugg<'a>) -> Self {
850 impl std::ops::Add for &MinifyingSugg<'static> {
851 type Output = MinifyingSugg<'static>;
852 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
853 match (self.as_str(), rhs.as_str()) {
854 ("0", _) => rhs.clone(),
855 (_, "0") => self.clone(),
856 (_, _) => (&self.0 + &rhs.0).into(),
861 impl std::ops::Sub for &MinifyingSugg<'static> {
862 type Output = MinifyingSugg<'static>;
863 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
864 match (self.as_str(), rhs.as_str()) {
865 (_, "0") => self.clone(),
866 ("0", _) => (-rhs.0.clone()).into(),
867 (x, y) if x == y => sugg::ZERO.into(),
868 (_, _) => (&self.0 - &rhs.0).into(),
873 impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
874 type Output = MinifyingSugg<'static>;
875 fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
876 match (self.as_str(), rhs.as_str()) {
877 ("0", _) => rhs.clone(),
879 (_, _) => (self.0 + &rhs.0).into(),
884 impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
885 type Output = MinifyingSugg<'static>;
886 fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
887 match (self.as_str(), rhs.as_str()) {
889 ("0", _) => (-rhs.0.clone()).into(),
890 (x, y) if x == y => sugg::ZERO.into(),
891 (_, _) => (self.0 - &rhs.0).into(),
896 /// a wrapper around `MinifyingSugg`, which carries a operator like currying
897 /// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
899 value: MinifyingSugg<'static>,
903 #[derive(Clone, Copy)]
910 fn negative(value: Sugg<'static>) -> Self {
913 sign: OffsetSign::Negative,
917 fn positive(value: Sugg<'static>) -> Self {
920 sign: OffsetSign::Positive,
925 Self::positive(sugg::ZERO)
929 fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
931 OffsetSign::Positive => lhs + &rhs.value,
932 OffsetSign::Negative => lhs - &rhs.value,
936 #[derive(Debug, Clone, Copy)]
937 enum StartKind<'hir> {
939 Counter { initializer: &'hir Expr<'hir> },
942 struct IndexExpr<'hir> {
943 base: &'hir Expr<'hir>,
944 idx: StartKind<'hir>,
950 kind: StartKind<'hir>,
953 fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
954 let is_slice = match ty.kind() {
955 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
956 ty::Slice(..) | ty::Array(..) => true,
960 is_slice || is_type_diagnostic_item(cx, ty, sym!(vec_type)) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
963 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
965 if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
966 if method.ident.name == sym!(clone);
968 if let Some(arg) = args.get(0);
969 then { arg } else { expr }
973 fn get_details_from_idx<'tcx>(
974 cx: &LateContext<'tcx>,
976 starts: &[Start<'tcx>],
977 ) -> Option<(StartKind<'tcx>, Offset)> {
978 fn get_start<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
979 starts.iter().find_map(|start| {
980 if same_var(cx, e, start.id) {
988 fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
990 ExprKind::Lit(l) => match l.node {
991 ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
994 ExprKind::Path(..) if get_start(cx, e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
1000 ExprKind::Binary(op, lhs, rhs) => match op.node {
1002 let offset_opt = get_start(cx, lhs, starts)
1003 .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
1004 .or_else(|| get_start(cx, rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
1006 offset_opt.map(|(s, o)| (s, Offset::positive(o)))
1009 get_start(cx, lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
1013 ExprKind::Path(..) => get_start(cx, idx, starts).map(|s| (s, Offset::empty())),
1018 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1019 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
1026 /// Get assignments from the given block.
1027 /// The returned iterator yields `None` if no assignment expressions are there,
1028 /// filtering out the increments of the given whitelisted loop counters;
1029 /// because its job is to make sure there's nothing other than assignments and the increments.
1030 fn get_assignments<'a: 'c, 'tcx: 'c, 'c>(
1031 cx: &'a LateContext<'tcx>,
1032 Block { stmts, expr, .. }: &'tcx Block<'tcx>,
1033 loop_counters: &'c [Start<'tcx>],
1034 ) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'c {
1035 // As the `filter` and `map` below do different things, I think putting together
1036 // just increases complexity. (cc #3188 and #4193)
1037 #[allow(clippy::filter_map)]
1040 .filter_map(move |stmt| match stmt.kind {
1041 StmtKind::Local(..) | StmtKind::Item(..) => None,
1042 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
1044 .chain((*expr).into_iter())
1046 if let ExprKind::AssignOp(_, place, _) = e.kind {
1049 // skip the first item which should be `StartKind::Range`
1050 // this makes it possible to use the slice with `StartKind::Range` in the same iterator loop.
1052 .any(|counter| same_var(cx, place, counter.id))
1057 .map(get_assignment)
1060 fn get_loop_counters<'a, 'tcx>(
1061 cx: &'a LateContext<'tcx>,
1062 body: &'tcx Block<'tcx>,
1063 expr: &'tcx Expr<'_>,
1064 ) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
1065 // Look for variables that are incremented once per loop iteration.
1066 let mut increment_visitor = IncrementVisitor::new(cx);
1067 walk_block(&mut increment_visitor, body);
1069 // For each candidate, check the parent block to see if
1070 // it's initialized to zero at the start of the loop.
1071 get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
1074 .filter_map(move |var_id| {
1075 let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
1076 walk_block(&mut initialize_visitor, block);
1078 initialize_visitor.get_result().map(|(_, initializer)| Start {
1080 kind: StartKind::Counter { initializer },
1087 fn build_manual_memcpy_suggestion<'tcx>(
1088 cx: &LateContext<'tcx>,
1091 limits: ast::RangeLimits,
1092 dst: &IndexExpr<'_>,
1093 src: &IndexExpr<'_>,
1095 fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
1096 if offset.as_str() == "0" {
1103 let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
1105 if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
1106 if method.ident.name == sym!(len);
1107 if len_args.len() == 1;
1108 if let Some(arg) = len_args.get(0);
1109 if var_def_id(cx, arg) == var_def_id(cx, base);
1111 if sugg.as_str() == end_str {
1118 ast::RangeLimits::Closed => {
1119 sugg + &sugg::ONE.into()
1121 ast::RangeLimits::HalfOpen => sugg,
1127 let start_str = Sugg::hir(cx, start, "").into();
1128 let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
1130 let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
1131 StartKind::Range => (
1132 print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
1137 apply_offset(&end_str, &idx_expr.idx_offset),
1141 StartKind::Counter { initializer } => {
1142 let counter_start = Sugg::hir(cx, initializer, "").into();
1144 print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
1149 apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
1156 let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
1157 let (src_offset, src_limit) = print_offset_and_limit(&src);
1159 let dst_base_str = snippet(cx, dst.base.span, "???");
1160 let src_base_str = snippet(cx, src.base.span, "???");
1162 let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
1168 dst_offset.maybe_par(),
1169 dst_limit.maybe_par()
1175 "{}.clone_from_slice(&{}[{}..{}]);",
1178 src_offset.maybe_par(),
1179 src_limit.maybe_par()
1183 /// Checks for for loops that sequentially copy items from one slice-like
1184 /// object to another.
1185 fn detect_manual_memcpy<'tcx>(
1186 cx: &LateContext<'tcx>,
1188 arg: &'tcx Expr<'_>,
1189 body: &'tcx Expr<'_>,
1190 expr: &'tcx Expr<'_>,
1192 if let Some(higher::Range {
1196 }) = higher::range(arg)
1198 // the var must be a single name
1199 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
1200 let mut starts = vec![Start {
1202 kind: StartKind::Range,
1205 // This is one of few ways to return different iterators
1206 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
1207 let mut iter_a = None;
1208 let mut iter_b = None;
1210 if let ExprKind::Block(block, _) = body.kind {
1211 if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
1212 starts.extend(loop_counters);
1214 iter_a = Some(get_assignments(cx, block, &starts));
1216 iter_b = Some(get_assignment(body));
1219 let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
1221 let big_sugg = assignments
1222 // The only statements in the for loops can be indexed assignments from
1223 // indexed retrievals (except increments of loop counters).
1225 o.and_then(|(lhs, rhs)| {
1226 let rhs = fetch_cloned_expr(rhs);
1228 if let ExprKind::Index(base_left, idx_left) = lhs.kind;
1229 if let ExprKind::Index(base_right, idx_right) = rhs.kind;
1230 if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
1231 && is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
1232 if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
1233 if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
1235 // Source and destination must be different
1236 if var_def_id(cx, base_left) != var_def_id(cx, base_right);
1238 Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
1239 IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
1246 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
1247 .collect::<Option<Vec<_>>>()
1248 .filter(|v| !v.is_empty())
1249 .map(|v| v.join("\n "));
1251 if let Some(big_sugg) = big_sugg {
1255 get_span_of_entire_for_loop(expr),
1256 "it looks like you're manually copying between slices",
1257 "try replacing the loop by",
1259 Applicability::Unspecified,
1268 // Scans the body of the for loop and determines whether lint should be given
1269 struct SameItemPushVisitor<'a, 'tcx> {
1271 // this field holds the last vec push operation visited, which should be the only push seen
1272 vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
1273 cx: &'a LateContext<'tcx>,
1276 impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
1277 type Map = Map<'tcx>;
1279 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1281 // Non-determinism may occur ... don't give a lint
1282 ExprKind::Loop(_, _, _) | ExprKind::Match(_, _, _) => self.should_lint = false,
1283 ExprKind::Block(block, _) => self.visit_block(block),
1288 fn visit_block(&mut self, b: &'tcx Block<'_>) {
1289 for stmt in b.stmts.iter() {
1290 self.visit_stmt(stmt);
1294 fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
1295 let vec_push_option = get_vec_push(self.cx, s);
1296 if vec_push_option.is_none() {
1297 // Current statement is not a push so visit inside
1299 StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
1303 // Current statement is a push ...check whether another
1304 // push had been previously done
1305 if self.vec_push.is_none() {
1306 self.vec_push = vec_push_option;
1308 // There are multiple pushes ... don't lint
1309 self.should_lint = false;
1314 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1315 NestedVisitorMap::None
1319 // Given some statement, determine if that statement is a push on a Vec. If it is, return
1320 // the Vec being pushed into and the item being pushed
1321 fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
1323 // Extract method being called
1324 if let StmtKind::Semi(semi_stmt) = &stmt.kind;
1325 if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
1326 // Figure out the parameters for the method call
1327 if let Some(self_expr) = args.get(0);
1328 if let Some(pushed_item) = args.get(1);
1329 // Check that the method being called is push() on a Vec
1330 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym!(vec_type));
1331 if path.ident.name.as_str() == "push";
1333 return Some((self_expr, pushed_item))
1339 /// Detects for loop pushing the same item into a Vec
1340 fn detect_same_item_push<'tcx>(
1341 cx: &LateContext<'tcx>,
1344 body: &'tcx Expr<'_>,
1347 fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
1348 let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
1349 let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
1355 "it looks like the same item is being pushed into this Vec",
1358 "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
1359 item_str, vec_str, item_str
1364 if !matches!(pat.kind, PatKind::Wild) {
1368 // Determine whether it is safe to lint the body
1369 let mut same_item_push_visitor = SameItemPushVisitor {
1374 walk_expr(&mut same_item_push_visitor, body);
1375 if same_item_push_visitor.should_lint {
1376 if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
1377 let vec_ty = cx.typeck_results().expr_ty(vec);
1378 let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
1383 .map_or(false, |id| implements_trait(cx, ty, id, &[]))
1385 // Make sure that the push does not involve possibly mutating values
1386 match pushed_item.kind {
1387 ExprKind::Path(ref qpath) => {
1388 match qpath_res(cx, qpath, pushed_item.hir_id) {
1389 // immutable bindings that are initialized with literal or constant
1390 Res::Local(hir_id) => {
1392 let node = cx.tcx.hir().get(hir_id);
1393 if let Node::Binding(pat) = node;
1394 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1395 if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
1396 let parent_node = cx.tcx.hir().get_parent_node(hir_id);
1397 if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
1398 if let Some(init) = parent_let_expr.init;
1401 // immutable bindings that are initialized with literal
1402 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1403 // immutable bindings that are initialized with constant
1404 ExprKind::Path(ref path) => {
1405 if let Res::Def(DefKind::Const, ..) = qpath_res(cx, path, init.hir_id) {
1406 emit_lint(cx, vec, pushed_item);
1415 Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
1419 ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
1427 /// Checks for looping over a range and then indexing a sequence with it.
1428 /// The iteratee must be a range literal.
1429 #[allow(clippy::too_many_lines)]
1430 fn check_for_loop_range<'tcx>(
1431 cx: &LateContext<'tcx>,
1433 arg: &'tcx Expr<'_>,
1434 body: &'tcx Expr<'_>,
1435 expr: &'tcx Expr<'_>,
1437 if let Some(higher::Range {
1441 }) = higher::range(arg)
1443 // the var must be a single name
1444 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1445 let mut visitor = VarVisitor {
1448 indexed_mut: FxHashSet::default(),
1449 indexed_indirectly: FxHashMap::default(),
1450 indexed_directly: FxHashMap::default(),
1451 referenced: FxHashSet::default(),
1453 prefer_mutable: false,
1455 walk_expr(&mut visitor, body);
1457 // linting condition: we only indexed one variable, and indexed it directly
1458 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1459 let (indexed, (indexed_extent, indexed_ty)) = visitor
1463 .expect("already checked that we have exactly 1 element");
1465 // ensure that the indexed variable was declared before the loop, see #601
1466 if let Some(indexed_extent) = indexed_extent {
1467 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1468 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1469 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1470 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1471 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1476 // don't lint if the container that is indexed does not have .iter() method
1477 let has_iter = has_iter_method(cx, indexed_ty);
1478 if has_iter.is_none() {
1482 // don't lint if the container that is indexed into is also used without
1484 if visitor.referenced.contains(&indexed) {
1488 let starts_at_zero = is_integer_const(cx, start, 0);
1490 let skip = if starts_at_zero {
1492 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
1495 format!(".skip({})", snippet(cx, start.span, ".."))
1498 let mut end_is_start_plus_val = false;
1500 let take = if let Some(end) = *end {
1501 let mut take_expr = end;
1503 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1504 if let BinOpKind::Add = op.node {
1505 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1506 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1508 if start_equal_left {
1510 } else if start_equal_right {
1514 end_is_start_plus_val = start_equal_left | start_equal_right;
1518 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1520 } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
1524 ast::RangeLimits::Closed => {
1525 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1526 format!(".take({})", take_expr + sugg::ONE)
1528 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1535 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1536 ("mut ", "iter_mut")
1541 let take_is_empty = take.is_empty();
1542 let mut method_1 = take;
1543 let mut method_2 = skip;
1545 if end_is_start_plus_val {
1546 mem::swap(&mut method_1, &mut method_2);
1549 if visitor.nonindex {
1552 NEEDLESS_RANGE_LOOP,
1554 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1558 "consider using an iterator",
1560 (pat.span, format!("({}, <item>)", ident.name)),
1563 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1570 let repl = if starts_at_zero && take_is_empty {
1571 format!("&{}{}", ref_mut, indexed)
1573 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1578 NEEDLESS_RANGE_LOOP,
1581 "the loop variable `{}` is only used to index `{}`.",
1587 "consider using an iterator",
1588 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1598 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
1600 if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
1601 if len_args.len() == 1;
1602 if method.ident.name == sym!(len);
1603 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1604 if path.segments.len() == 1;
1605 if path.segments[0].ident.name == var;
1614 fn is_end_eq_array_len<'tcx>(
1615 cx: &LateContext<'tcx>,
1617 limits: ast::RangeLimits,
1618 indexed_ty: Ty<'tcx>,
1621 if let ExprKind::Lit(ref lit) = end.kind;
1622 if let ast::LitKind::Int(end_int, _) = lit.node;
1623 if let ty::Array(_, arr_len_const) = indexed_ty.kind();
1624 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1626 return match limits {
1627 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1628 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1636 fn lint_iter_method(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1637 let mut applicability = Applicability::MachineApplicable;
1638 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1639 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1644 "it is more concise to loop over references to containers instead of using explicit \
1646 "to write this more concisely, try",
1647 format!("&{}{}", muta, object),
1652 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1653 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1654 if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
1655 // just the receiver, no arguments
1656 if args.len() == 1 {
1657 let method_name = &*method.ident.as_str();
1658 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1659 if method_name == "iter" || method_name == "iter_mut" {
1660 if is_ref_iterable_type(cx, &args[0]) {
1661 lint_iter_method(cx, args, arg, method_name);
1663 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1664 let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
1665 let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
1666 if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
1667 let mut applicability = Applicability::MachineApplicable;
1668 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1671 EXPLICIT_INTO_ITER_LOOP,
1673 "it is more concise to loop over containers instead of using explicit \
1675 "to write this more concisely, try",
1680 let ref_receiver_ty = cx.tcx.mk_ref(
1681 cx.tcx.lifetimes.re_erased,
1684 mutbl: Mutability::Not,
1687 if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
1688 lint_iter_method(cx, args, arg, method_name)
1691 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1696 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1697 probably not what you want",
1699 next_loop_linted = true;
1703 if !next_loop_linted {
1704 check_arg_type(cx, pat, arg);
1708 /// Checks for `for` loops over `Option`s and `Result`s.
1709 fn check_arg_type(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1710 let ty = cx.typeck_results().expr_ty(arg);
1711 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1714 FOR_LOOPS_OVER_FALLIBLES,
1717 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1718 `if let` statement.",
1719 snippet(cx, arg.span, "_")
1723 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1724 snippet(cx, pat.span, "_"),
1725 snippet(cx, arg.span, "_")
1728 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1731 FOR_LOOPS_OVER_FALLIBLES,
1734 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1735 `if let` statement.",
1736 snippet(cx, arg.span, "_")
1740 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1741 snippet(cx, pat.span, "_"),
1742 snippet(cx, arg.span, "_")
1748 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1749 // incremented exactly once in the loop body, and initialized to zero
1750 // at the start of the loop.
1751 fn check_for_loop_explicit_counter<'tcx>(
1752 cx: &LateContext<'tcx>,
1754 arg: &'tcx Expr<'_>,
1755 body: &'tcx Expr<'_>,
1756 expr: &'tcx Expr<'_>,
1758 // Look for variables that are incremented once per loop iteration.
1759 let mut increment_visitor = IncrementVisitor::new(cx);
1760 walk_expr(&mut increment_visitor, body);
1762 // For each candidate, check the parent block to see if
1763 // it's initialized to zero at the start of the loop.
1764 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1765 for id in increment_visitor.into_results() {
1766 let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
1767 walk_block(&mut initialize_visitor, block);
1770 if let Some((name, initializer)) = initialize_visitor.get_result();
1771 if is_integer_const(cx, initializer, 0);
1773 let mut applicability = Applicability::MachineApplicable;
1775 let for_span = get_span_of_entire_for_loop(expr);
1779 EXPLICIT_COUNTER_LOOP,
1780 for_span.with_hi(arg.span.hi()),
1781 &format!("the variable `{}` is used as a loop counter.", name),
1784 "for ({}, {}) in {}.enumerate()",
1786 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1787 make_iterator_snippet(cx, arg, &mut applicability),
1797 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1798 /// actual `Iterator` that the loop uses.
1799 fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1800 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
1801 implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
1806 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1809 // (&x).into_iter() ==> x.iter()
1810 // (&mut x).into_iter() ==> x.iter_mut()
1812 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1813 if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
1815 let meth_name = match mutability {
1816 Mutability::Mut => "iter_mut",
1817 Mutability::Not => "iter",
1821 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1827 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1833 /// Checks for the `FOR_KV_MAP` lint.
1834 fn check_for_loop_over_map_kv<'tcx>(
1835 cx: &LateContext<'tcx>,
1837 arg: &'tcx Expr<'_>,
1838 body: &'tcx Expr<'_>,
1839 expr: &'tcx Expr<'_>,
1841 let pat_span = pat.span;
1843 if let PatKind::Tuple(ref pat, _) = pat.kind {
1845 let arg_span = arg.span;
1846 let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
1847 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1848 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1849 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1854 let mutbl = match mutbl {
1855 Mutability::Not => "",
1856 Mutability::Mut => "_mut",
1858 let arg = match arg.kind {
1859 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1863 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1868 &format!("you seem to want to iterate on a map's {}s", kind),
1870 let map = sugg::Sugg::hir(cx, arg, "map");
1873 "use the corresponding method",
1875 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1876 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1886 struct MutatePairDelegate<'a, 'tcx> {
1887 cx: &'a LateContext<'tcx>,
1888 hir_id_low: Option<HirId>,
1889 hir_id_high: Option<HirId>,
1890 span_low: Option<Span>,
1891 span_high: Option<Span>,
1894 impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
1895 fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: ConsumeMode) {}
1897 fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, bk: ty::BorrowKind) {
1898 if let ty::BorrowKind::MutBorrow = bk {
1899 if let PlaceBase::Local(id) = cmt.place.base {
1900 if Some(id) == self.hir_id_low {
1901 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1903 if Some(id) == self.hir_id_high {
1904 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1910 fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>) {
1911 if let PlaceBase::Local(id) = cmt.place.base {
1912 if Some(id) == self.hir_id_low {
1913 self.span_low = Some(self.cx.tcx.hir().span(cmt.hir_id))
1915 if Some(id) == self.hir_id_high {
1916 self.span_high = Some(self.cx.tcx.hir().span(cmt.hir_id))
1922 impl MutatePairDelegate<'_, '_> {
1923 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1924 (self.span_low, self.span_high)
1928 fn check_for_mut_range_bound(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
1929 if let Some(higher::Range {
1933 }) = higher::range(arg)
1935 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1936 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1937 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1938 mut_warn_with_span(cx, span_low);
1939 mut_warn_with_span(cx, span_high);
1944 fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
1945 if let Some(sp) = span {
1950 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1955 fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
1957 if let ExprKind::Path(ref qpath) = bound.kind;
1958 if let QPath::Resolved(None, _) = *qpath;
1960 let res = qpath_res(cx, qpath, bound.hir_id);
1961 if let Res::Local(hir_id) = res {
1962 let node_str = cx.tcx.hir().get(hir_id);
1964 if let Node::Binding(pat) = node_str;
1965 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1966 if let BindingAnnotation::Mutable = bind_ann;
1968 return Some(hir_id);
1977 fn check_for_mutation<'tcx>(
1978 cx: &LateContext<'tcx>,
1980 bound_ids: &[Option<HirId>],
1981 ) -> (Option<Span>, Option<Span>) {
1982 let mut delegate = MutatePairDelegate {
1984 hir_id_low: bound_ids[0],
1985 hir_id_high: bound_ids[1],
1989 let def_id = body.hir_id.owner.to_def_id();
1990 cx.tcx.infer_ctxt().enter(|infcx| {
1991 ExprUseVisitor::new(
1994 def_id.expect_local(),
1996 cx.typeck_results(),
2000 delegate.mutation_span()
2003 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
2004 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
2006 PatKind::Wild => true,
2007 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
2012 struct LocalUsedVisitor<'a, 'tcx> {
2013 cx: &'a LateContext<'tcx>,
2018 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
2019 type Map = Map<'tcx>;
2021 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2022 if same_var(self.cx, expr, self.local) {
2025 walk_expr(self, expr);
2029 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2030 NestedVisitorMap::None
2034 struct VarVisitor<'a, 'tcx> {
2035 /// context reference
2036 cx: &'a LateContext<'tcx>,
2037 /// var name to look for as index
2039 /// indexed variables that are used mutably
2040 indexed_mut: FxHashSet<Symbol>,
2041 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
2042 indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
2043 /// subset of `indexed` of vars that are indexed directly: `v[i]`
2044 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
2045 indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
2046 /// Any names that are used outside an index operation.
2047 /// Used to detect things like `&mut vec` used together with `vec[i]`
2048 referenced: FxHashSet<Symbol>,
2049 /// has the loop variable been used in expressions other than the index of
2052 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
2053 /// takes `&mut self`
2054 prefer_mutable: bool,
2057 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
2058 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
2060 // the indexed container is referenced by a name
2061 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
2062 if let QPath::Resolved(None, ref seqvar) = *seqpath;
2063 if seqvar.segments.len() == 1;
2065 let index_used_directly = same_var(self.cx, idx, self.var);
2066 let indexed_indirectly = {
2067 let mut used_visitor = LocalUsedVisitor {
2072 walk_expr(&mut used_visitor, idx);
2076 if indexed_indirectly || index_used_directly {
2077 if self.prefer_mutable {
2078 self.indexed_mut.insert(seqvar.segments[0].ident.name);
2080 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
2082 Res::Local(hir_id) => {
2083 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
2084 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
2085 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
2086 if indexed_indirectly {
2087 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
2089 if index_used_directly {
2090 self.indexed_directly.insert(
2091 seqvar.segments[0].ident.name,
2092 (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
2095 return false; // no need to walk further *on the variable*
2097 Res::Def(DefKind::Static | DefKind::Const, ..) => {
2098 if indexed_indirectly {
2099 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
2101 if index_used_directly {
2102 self.indexed_directly.insert(
2103 seqvar.segments[0].ident.name,
2104 (None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
2107 return false; // no need to walk further *on the variable*
2118 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
2119 type Map = Map<'tcx>;
2121 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2124 if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
2125 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
2126 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
2127 if !self.check(&args[1], &args[0], expr);
2133 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
2134 if !self.check(idx, seqexpr, expr);
2139 // directly using a variable
2140 if let ExprKind::Path(ref qpath) = expr.kind;
2141 if let QPath::Resolved(None, ref path) = *qpath;
2142 if path.segments.len() == 1;
2144 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
2145 if local_id == self.var {
2146 self.nonindex = true;
2148 // not the correct variable, but still a variable
2149 self.referenced.insert(path.segments[0].ident.name);
2155 let old = self.prefer_mutable;
2157 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
2158 self.prefer_mutable = true;
2159 self.visit_expr(lhs);
2160 self.prefer_mutable = false;
2161 self.visit_expr(rhs);
2163 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
2164 if mutbl == Mutability::Mut {
2165 self.prefer_mutable = true;
2167 self.visit_expr(expr);
2169 ExprKind::Call(ref f, args) => {
2172 let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
2173 self.prefer_mutable = false;
2174 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2175 if mutbl == Mutability::Mut {
2176 self.prefer_mutable = true;
2179 self.visit_expr(expr);
2182 ExprKind::MethodCall(_, _, args, _) => {
2183 let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
2184 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
2185 self.prefer_mutable = false;
2186 if let ty::Ref(_, _, mutbl) = *ty.kind() {
2187 if mutbl == Mutability::Mut {
2188 self.prefer_mutable = true;
2191 self.visit_expr(expr);
2194 ExprKind::Closure(_, _, body_id, ..) => {
2195 let body = self.cx.tcx.hir().body(body_id);
2196 self.visit_expr(&body.value);
2198 _ => walk_expr(self, expr),
2200 self.prefer_mutable = old;
2202 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2203 NestedVisitorMap::None
2207 fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
2208 let def_id = match var_def_id(cx, expr) {
2210 None => return false,
2212 if let Some(used_mutably) = mutated_variables(container, cx) {
2213 if used_mutably.contains(&def_id) {
2220 fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
2221 let def_id = match var_def_id(cx, iter_expr) {
2223 None => return false,
2225 let mut visitor = VarUsedAfterLoopVisitor {
2228 iter_expr_id: iter_expr.hir_id,
2229 past_while_let: false,
2230 var_used_after_while_let: false,
2232 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
2233 walk_block(&mut visitor, enclosing_block);
2235 visitor.var_used_after_while_let
2238 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
2239 cx: &'a LateContext<'tcx>,
2241 iter_expr_id: HirId,
2242 past_while_let: bool,
2243 var_used_after_while_let: bool,
2246 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
2247 type Map = Map<'tcx>;
2249 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2250 if self.past_while_let {
2251 if Some(self.def_id) == var_def_id(self.cx, expr) {
2252 self.var_used_after_while_let = true;
2254 } else if self.iter_expr_id == expr.hir_id {
2255 self.past_while_let = true;
2257 walk_expr(self, expr);
2259 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2260 NestedVisitorMap::None
2264 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
2265 /// for `&T` and `&mut T`, such as `Vec`.
2267 fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
2268 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
2269 // will allow further borrows afterwards
2270 let ty = cx.typeck_results().expr_ty(e);
2271 is_iterable_array(ty, cx) ||
2272 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2273 match_type(cx, ty, &paths::LINKED_LIST) ||
2274 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
2275 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
2276 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2277 match_type(cx, ty, &paths::BINARY_HEAP) ||
2278 match_type(cx, ty, &paths::BTREEMAP) ||
2279 match_type(cx, ty, &paths::BTREESET)
2282 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
2283 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2285 ty::Array(_, n) => n
2286 .try_eval_usize(cx.tcx, cx.param_env)
2287 .map_or(false, |val| (0..=32).contains(&val)),
2292 /// If a block begins with a statement (possibly a `let` binding) and has an
2293 /// expression, return it.
2294 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2295 if block.stmts.is_empty() {
2298 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2299 local.init //.map(|expr| expr)
2305 /// If a block begins with an expression (with or without semicolon), return it.
2306 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
2308 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2309 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2310 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2311 StmtKind::Local(..) | StmtKind::Item(..) => None,
2317 /// Returns `true` if expr contains a single break expr without destination label
2319 /// passed expression. The expression may be within a block.
2320 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
2322 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2323 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2328 #[derive(Debug, PartialEq)]
2329 enum IncrementVisitorVarState {
2330 Initial, // Not examined yet
2331 IncrOnce, // Incremented exactly once, may be a loop counter
2335 /// Scan a for loop for variables that are incremented exactly once and not used after that.
2336 struct IncrementVisitor<'a, 'tcx> {
2337 cx: &'a LateContext<'tcx>, // context reference
2338 states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
2339 depth: u32, // depth of conditional expressions
2343 impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
2344 fn new(cx: &'a LateContext<'tcx>) -> Self {
2347 states: FxHashMap::default(),
2353 fn into_results(self) -> impl Iterator<Item = HirId> {
2354 self.states.into_iter().filter_map(|(id, state)| {
2355 if state == IncrementVisitorVarState::IncrOnce {
2364 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2365 type Map = Map<'tcx>;
2367 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2372 // If node is a variable
2373 if let Some(def_id) = var_def_id(self.cx, expr) {
2374 if let Some(parent) = get_parent_expr(self.cx, expr) {
2375 let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
2376 if *state == IncrementVisitorVarState::IncrOnce {
2377 *state = IncrementVisitorVarState::DontWarn;
2382 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2383 if lhs.hir_id == expr.hir_id {
2384 *state = if op.node == BinOpKind::Add
2385 && is_integer_const(self.cx, rhs, 1)
2386 && *state == IncrementVisitorVarState::Initial
2389 IncrementVisitorVarState::IncrOnce
2391 // Assigned some other value or assigned multiple times
2392 IncrementVisitorVarState::DontWarn
2396 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
2397 *state = IncrementVisitorVarState::DontWarn
2399 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2400 *state = IncrementVisitorVarState::DontWarn
2406 walk_expr(self, expr);
2407 } else if is_loop(expr) || is_conditional(expr) {
2409 walk_expr(self, expr);
2411 } else if let ExprKind::Continue(_) = expr.kind {
2414 walk_expr(self, expr);
2417 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2418 NestedVisitorMap::None
2422 enum InitializeVisitorState<'hir> {
2423 Initial, // Not examined yet
2424 Declared(Symbol), // Declared but not (yet) initialized
2427 initializer: &'hir Expr<'hir>,
2432 /// Checks whether a variable is initialized at the start of a loop and not modified
2433 /// and used after the loop.
2434 struct InitializeVisitor<'a, 'tcx> {
2435 cx: &'a LateContext<'tcx>, // context reference
2436 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2438 state: InitializeVisitorState<'tcx>,
2439 depth: u32, // depth of conditional expressions
2443 impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
2444 fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
2449 state: InitializeVisitorState::Initial,
2455 fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
2456 if let InitializeVisitorState::Initialized { name, initializer } = self.state {
2457 Some((name, initializer))
2464 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2465 type Map = Map<'tcx>;
2467 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2468 // Look for declarations of the variable
2470 if let StmtKind::Local(ref local) = stmt.kind;
2471 if local.pat.hir_id == self.var_id;
2472 if let PatKind::Binding(.., ident, _) = local.pat.kind;
2474 self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
2475 InitializeVisitorState::Initialized {
2482 walk_stmt(self, stmt);
2485 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2486 if matches!(self.state, InitializeVisitorState::DontWarn) {
2489 if expr.hir_id == self.end_expr.hir_id {
2490 self.past_loop = true;
2493 // No need to visit expressions before the variable is
2495 if matches!(self.state, InitializeVisitorState::Initial) {
2499 // If node is the desired variable, see how it's used
2500 if var_def_id(self.cx, expr) == Some(self.var_id) {
2502 self.state = InitializeVisitorState::DontWarn;
2506 if let Some(parent) = get_parent_expr(self.cx, expr) {
2508 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2509 self.state = InitializeVisitorState::DontWarn;
2511 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2512 self.state = if_chain! {
2514 if let InitializeVisitorState::Declared(name)
2515 | InitializeVisitorState::Initialized { name, ..} = self.state;
2517 InitializeVisitorState::Initialized { initializer: rhs, name }
2519 InitializeVisitorState::DontWarn
2523 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2524 self.state = InitializeVisitorState::DontWarn
2530 walk_expr(self, expr);
2531 } else if !self.past_loop && is_loop(expr) {
2532 self.state = InitializeVisitorState::DontWarn;
2533 } else if is_conditional(expr) {
2535 walk_expr(self, expr);
2538 walk_expr(self, expr);
2542 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2543 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2547 fn var_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<HirId> {
2548 if let ExprKind::Path(ref qpath) = expr.kind {
2549 let path_res = qpath_res(cx, qpath, expr.hir_id);
2550 if let Res::Local(hir_id) = path_res {
2551 return Some(hir_id);
2557 fn is_loop(expr: &Expr<'_>) -> bool {
2558 matches!(expr.kind, ExprKind::Loop(..))
2561 fn is_conditional(expr: &Expr<'_>) -> bool {
2562 matches!(expr.kind, ExprKind::Match(..))
2565 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2567 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2568 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2569 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2571 return is_loop_nested(cx, loop_expr, iter_expr)
2577 fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2578 let mut id = loop_expr.hir_id;
2579 let iter_name = if let Some(name) = path_name(iter_expr) {
2585 let parent = cx.tcx.hir().get_parent_node(id);
2589 match cx.tcx.hir().find(parent) {
2590 Some(Node::Expr(expr)) => {
2591 if let ExprKind::Loop(..) = expr.kind {
2595 Some(Node::Block(block)) => {
2596 let mut block_visitor = LoopNestVisitor {
2598 iterator: iter_name,
2601 walk_block(&mut block_visitor, block);
2602 if block_visitor.nesting == RuledOut {
2606 Some(Node::Stmt(_)) => (),
2615 #[derive(PartialEq, Eq)]
2617 Unknown, // no nesting detected yet
2618 RuledOut, // the iterator is initialized or assigned within scope
2619 LookFurther, // no nesting detected, no further walk required
2622 use self::Nesting::{LookFurther, RuledOut, Unknown};
2624 struct LoopNestVisitor {
2630 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2631 type Map = Map<'tcx>;
2633 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2634 if stmt.hir_id == self.hir_id {
2635 self.nesting = LookFurther;
2636 } else if self.nesting == Unknown {
2637 walk_stmt(self, stmt);
2641 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2642 if self.nesting != Unknown {
2645 if expr.hir_id == self.hir_id {
2646 self.nesting = LookFurther;
2650 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2651 if match_var(path, self.iterator) {
2652 self.nesting = RuledOut;
2655 _ => walk_expr(self, expr),
2659 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2660 if self.nesting != Unknown {
2663 if let PatKind::Binding(.., span_name, _) = pat.kind {
2664 if self.iterator == span_name.name {
2665 self.nesting = RuledOut;
2672 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2673 NestedVisitorMap::None
2677 fn path_name(e: &Expr<'_>) -> Option<Symbol> {
2678 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2679 let segments = &path.segments;
2680 if segments.len() == 1 {
2681 return Some(segments[0].ident.name);
2687 fn check_infinite_loop<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2688 if constant(cx, cx.typeck_results(), cond).is_some() {
2689 // A pure constant condition (e.g., `while false`) is not linted.
2693 let mut var_visitor = VarCollectorVisitor {
2695 ids: FxHashSet::default(),
2696 def_ids: FxHashMap::default(),
2699 var_visitor.visit_expr(cond);
2700 if var_visitor.skip {
2703 let used_in_condition = &var_visitor.ids;
2704 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2705 used_in_condition.is_disjoint(&used_mutably)
2709 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2711 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2712 has_break_or_return: false,
2714 has_break_or_return_visitor.visit_expr(expr);
2715 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2717 if no_cond_variable_mutated && !mutable_static_in_cond {
2720 WHILE_IMMUTABLE_CONDITION,
2722 "variables in the condition are not mutated in the loop body",
2724 diag.note("this may lead to an infinite or to a never running loop");
2726 if has_break_or_return {
2727 diag.note("this loop contains `return`s or `break`s");
2728 diag.help("rewrite it as `if cond { loop { } }`");
2735 struct HasBreakOrReturnVisitor {
2736 has_break_or_return: bool,
2739 impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2740 type Map = Map<'tcx>;
2742 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2743 if self.has_break_or_return {
2748 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2749 self.has_break_or_return = true;
2755 walk_expr(self, expr);
2758 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2759 NestedVisitorMap::None
2763 /// Collects the set of variables in an expression
2764 /// Stops analysis if a function call is found
2765 /// Note: In some cases such as `self`, there are no mutable annotation,
2766 /// All variables definition IDs are collected
2767 struct VarCollectorVisitor<'a, 'tcx> {
2768 cx: &'a LateContext<'tcx>,
2769 ids: FxHashSet<HirId>,
2770 def_ids: FxHashMap<def_id::DefId, bool>,
2774 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2775 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2777 if let ExprKind::Path(ref qpath) = ex.kind;
2778 if let QPath::Resolved(None, _) = *qpath;
2779 let res = qpath_res(self.cx, qpath, ex.hir_id);
2782 Res::Local(hir_id) => {
2783 self.ids.insert(hir_id);
2785 Res::Def(DefKind::Static, def_id) => {
2786 let mutable = self.cx.tcx.is_mutable_static(def_id);
2787 self.def_ids.insert(def_id, mutable);
2796 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2797 type Map = Map<'tcx>;
2799 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2801 ExprKind::Path(_) => self.insert_def_id(ex),
2802 // If there is any function/method call… we just stop analysis
2803 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2805 _ => walk_expr(self, ex),
2809 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2810 NestedVisitorMap::None
2814 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2816 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2817 check_needless_collect_direct_usage(expr, cx);
2818 check_needless_collect_indirect_usage(expr, cx);
2820 fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2822 if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
2823 if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
2824 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2825 if let Some(ref generic_args) = chain_method.args;
2826 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2828 let ty = cx.typeck_results().node_type(ty.hir_id);
2829 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2830 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2831 match_type(cx, ty, &paths::BTREEMAP) ||
2832 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2833 if method.ident.name == sym!(len) {
2834 let span = shorten_needless_collect_span(expr);
2839 NEEDLESS_COLLECT_MSG,
2841 "count()".to_string(),
2842 Applicability::MachineApplicable,
2845 if method.ident.name == sym!(is_empty) {
2846 let span = shorten_needless_collect_span(expr);
2851 NEEDLESS_COLLECT_MSG,
2853 "next().is_none()".to_string(),
2854 Applicability::MachineApplicable,
2857 if method.ident.name == sym!(contains) {
2858 let contains_arg = snippet(cx, args[1].span, "??");
2859 let span = shorten_needless_collect_span(expr);
2864 NEEDLESS_COLLECT_MSG,
2866 let (arg, pred) = contains_arg
2868 .map_or(("&x", &*contains_arg), |s| ("x", s));
2869 diag.span_suggestion(
2873 "any(|{}| x == {})",
2876 Applicability::MachineApplicable,
2886 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
2887 if let ExprKind::Block(ref block, _) = expr.kind {
2888 for ref stmt in block.stmts {
2890 if let StmtKind::Local(
2891 Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
2892 init: Some(ref init_expr), .. }
2894 if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
2895 if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
2896 if let Some(ref generic_args) = method_name.args;
2897 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2898 if let ty = cx.typeck_results().node_type(ty.hir_id);
2899 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
2900 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2901 match_type(cx, ty, &paths::LINKED_LIST);
2902 if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
2903 if iter_calls.len() == 1;
2905 // Suggest replacing iter_call with iter_replacement, and removing stmt
2906 let iter_call = &iter_calls[0];
2910 stmt.span.until(iter_call.span),
2911 NEEDLESS_COLLECT_MSG,
2913 let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
2914 diag.multipart_suggestion(
2915 iter_call.get_suggestion_text(),
2917 (stmt.span, String::new()),
2918 (iter_call.span, iter_replacement)
2920 Applicability::MachineApplicable,// MaybeIncorrect,
2930 struct IterFunction {
2931 func: IterFunctionKind,
2935 fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
2937 IterFunctionKind::IntoIter => String::new(),
2938 IterFunctionKind::Len => String::from(".count()"),
2939 IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
2940 IterFunctionKind::Contains(span) => format!(".any(|x| x == {})", snippet(cx, *span, "..")),
2943 fn get_suggestion_text(&self) -> &'static str {
2945 IterFunctionKind::IntoIter => {
2946 "Use the original Iterator instead of collecting it and then producing a new one"
2948 IterFunctionKind::Len => {
2949 "Take the original Iterator's count instead of collecting it and finding the length"
2951 IterFunctionKind::IsEmpty => {
2952 "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
2954 IterFunctionKind::Contains(_) => {
2955 "Check if the original Iterator contains an element instead of collecting then checking"
2960 enum IterFunctionKind {
2967 struct IterFunctionVisitor {
2968 uses: Vec<IterFunction>,
2972 impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
2973 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
2974 // Check function calls on our collection
2976 if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
2977 if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
2978 if let &[name] = &path.segments;
2979 if name.ident == self.target;
2981 let len = sym!(len);
2982 let is_empty = sym!(is_empty);
2983 let contains = sym!(contains);
2984 match method_name.ident.name {
2985 sym::into_iter => self.uses.push(
2986 IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
2988 name if name == len => self.uses.push(
2989 IterFunction { func: IterFunctionKind::Len, span: expr.span }
2991 name if name == is_empty => self.uses.push(
2992 IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
2994 name if name == contains => self.uses.push(
2995 IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
2997 _ => self.seen_other = true,
3002 // Check if the collection is used for anything else
3004 if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
3005 if let &[name] = &path.segments;
3006 if name.ident == self.target;
3008 self.seen_other = true;
3010 walk_expr(self, expr);
3015 type Map = Map<'tcx>;
3016 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3017 NestedVisitorMap::None
3021 /// Detect the occurences of calls to `iter` or `into_iter` for the
3022 /// given identifier
3023 fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
3024 let mut visitor = IterFunctionVisitor {
3029 visitor.visit_block(block);
3030 if visitor.seen_other {
3037 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
3039 if let ExprKind::MethodCall(.., args, _) = &expr.kind;
3040 if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
3042 return expr.span.with_lo(span.lo());