1 use crate::consts::constant;
2 use crate::reexport::Name;
3 use crate::utils::paths;
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, last_path_segment, match_trait_method, match_type, match_var,
8 multispan_sugg, snippet, snippet_opt, snippet_with_applicability, span_lint, span_lint_and_help,
9 span_lint_and_sugg, span_lint_and_then, SpanlessEq,
11 use crate::utils::{is_type_diagnostic_item, qpath_res, same_tys, sugg};
12 use if_chain::if_chain;
14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
15 use rustc_errors::Applicability;
16 use rustc_hir::def::{DefKind, Res};
17 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
19 def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, InlineAsmOperand,
20 LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
22 use rustc_infer::infer::TyCtxtInferExt;
23 use rustc_lint::{LateContext, LateLintPass, LintContext};
24 use rustc_middle::hir::map::Map;
25 use rustc_middle::lint::in_external_macro;
26 use rustc_middle::middle::region;
27 use rustc_middle::ty::{self, Ty};
28 use rustc_session::{declare_lint_pass, declare_tool_lint};
29 use rustc_span::source_map::Span;
30 use rustc_span::BytePos;
31 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase};
32 use std::iter::{once, Iterator};
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// # let src = vec![1];
46 /// # let mut dst = vec![0; 65];
47 /// for i in 0..src.len() {
48 /// dst[i + 64] = src[i];
51 /// Could be written as:
53 /// # let src = vec![1];
54 /// # let mut dst = vec![0; 65];
55 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
59 "manually copying items between slices"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for looping over the range of `0..len` of some
64 /// collection just to get the values by index.
66 /// **Why is this bad?** Just iterating the collection itself makes the intent
67 /// more clear and is probably faster.
69 /// **Known problems:** None.
73 /// let vec = vec!['a', 'b', 'c'];
74 /// for i in 0..vec.len() {
75 /// println!("{}", vec[i]);
78 /// Could be written as:
80 /// let vec = vec!['a', 'b', 'c'];
82 /// println!("{}", i);
85 pub NEEDLESS_RANGE_LOOP,
87 "for-looping over a range of indices where an iterator over items would do"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
92 /// suggests the latter.
94 /// **Why is this bad?** Readability.
96 /// **Known problems:** False negatives. We currently only warn on some known
101 /// // with `y` a `Vec` or slice:
102 /// # let y = vec![1];
103 /// for x in y.iter() {
107 /// can be rewritten to
109 /// # let y = vec![1];
114 pub EXPLICIT_ITER_LOOP,
116 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
121 /// suggests the latter.
123 /// **Why is this bad?** Readability.
125 /// **Known problems:** None
129 /// # let y = vec![1];
130 /// // with `y` a `Vec` or slice:
131 /// for x in y.into_iter() {
135 /// can be rewritten to
137 /// # let y = vec![1];
142 pub EXPLICIT_INTO_ITER_LOOP,
144 "for-looping over `_.into_iter()` when `_` would do"
147 declare_clippy_lint! {
148 /// **What it does:** Checks for loops on `x.next()`.
150 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
151 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
152 /// implements `IntoIterator`, so that possibly one value will be iterated,
153 /// leading to some hard to find bugs. No one will want to write such code
154 /// [except to win an Underhanded Rust
155 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
157 /// **Known problems:** None.
161 /// for x in y.next() {
167 "for-looping over `_.next()` which is probably not intended"
170 declare_clippy_lint! {
171 /// **What it does:** Checks for `for` loops over `Option` or `Result` values.
173 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
176 /// **Known problems:** None.
180 /// # let opt = Some(1);
188 /// if let Some(x) = opt {
196 /// # let res: Result<i32, std::io::Error> = Ok(1);
204 /// if let Ok(x) = res {
208 pub FOR_LOOPS_OVER_FALLIBLES,
210 "for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
213 declare_clippy_lint! {
214 /// **What it does:** Detects `loop + match` combinations that are easier
215 /// written as a `while let` loop.
217 /// **Why is this bad?** The `while let` loop is usually shorter and more
220 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
224 /// # let y = Some(1);
226 /// let x = match y {
230 /// // .. do something with x
232 /// // is easier written as
233 /// while let Some(x) = y {
234 /// // .. do something with x
239 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
242 declare_clippy_lint! {
243 /// **What it does:** Checks for functions collecting an iterator when collect
246 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
247 /// when this allocation may not be needed.
249 /// **Known problems:**
254 /// # let iterator = vec![1].into_iter();
255 /// let len = iterator.clone().collect::<Vec<_>>().len();
257 /// let len = iterator.count();
259 pub NEEDLESS_COLLECT,
261 "collecting an iterator when collect is not needed"
264 declare_clippy_lint! {
265 /// **What it does:** Checks `for` loops over slices with an explicit counter
266 /// and suggests the use of `.enumerate()`.
268 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
269 /// declutters the code and may be faster in some instances.
271 /// **Known problems:** None.
275 /// # let v = vec![1];
276 /// # fn bar(bar: usize, baz: usize) {}
283 /// Could be written as
285 /// # let v = vec![1];
286 /// # fn bar(bar: usize, baz: usize) {}
287 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
289 pub EXPLICIT_COUNTER_LOOP,
291 "for-looping with an explicit counter when `_.enumerate()` would do"
294 declare_clippy_lint! {
295 /// **What it does:** Checks for empty `loop` expressions.
297 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
298 /// anything. Think of the environment and either block on something or at least
299 /// make the thread sleep for some microseconds.
301 /// **Known problems:** None.
309 "empty `loop {}`, which should block or sleep"
312 declare_clippy_lint! {
313 /// **What it does:** Checks for `while let` expressions on iterators.
315 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
316 /// the intent better.
318 /// **Known problems:** None.
322 /// while let Some(val) = iter() {
326 pub WHILE_LET_ON_ITERATOR,
328 "using a while-let loop instead of a for loop on an iterator"
331 declare_clippy_lint! {
332 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
333 /// ignoring either the keys or values.
335 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
336 /// can be used to express that don't need the values or keys.
338 /// **Known problems:** None.
342 /// for (k, _) in &map {
347 /// could be replaced by
350 /// for k in map.keys() {
356 "looping on a map using `iter` when `keys` or `values` would do"
359 declare_clippy_lint! {
360 /// **What it does:** Checks for loops that will always `break`, `return` or
361 /// `continue` an outer loop.
363 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
366 /// **Known problems:** None
377 "any loop that will always `break` or `return`"
380 declare_clippy_lint! {
381 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
383 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
385 /// **Known problems:** None
389 /// let mut foo = 42;
390 /// for i in 0..foo {
392 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
397 "for loop over a range where one of the bounds is a mutable variable"
400 declare_clippy_lint! {
401 /// **What it does:** Checks whether variables used within while loop condition
402 /// can be (and are) mutated in the body.
404 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
405 /// will lead to an infinite loop.
407 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
408 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
409 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
415 /// println!("let me loop forever!");
418 pub WHILE_IMMUTABLE_CONDITION,
420 "variables used within while expression are not mutated in the body"
423 declare_lint_pass!(Loops => [
427 EXPLICIT_INTO_ITER_LOOP,
429 FOR_LOOPS_OVER_FALLIBLES,
432 EXPLICIT_COUNTER_LOOP,
434 WHILE_LET_ON_ITERATOR,
438 WHILE_IMMUTABLE_CONDITION,
441 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
442 #[allow(clippy::too_many_lines)]
443 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
444 if let Some((pat, arg, body)) = higher::for_loop(expr) {
445 // we don't want to check expanded macros
446 // this check is not at the top of the function
447 // since higher::for_loop expressions are marked as expansions
448 if body.span.from_expansion() {
451 check_for_loop(cx, pat, arg, body, expr);
454 // we don't want to check expanded macros
455 if expr.span.from_expansion() {
459 // check for never_loop
460 if let ExprKind::Loop(ref block, _, _) = expr.kind {
461 match never_loop_block(block, expr.hir_id) {
462 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
463 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
467 // check for `loop { if let {} else break }` that could be `while let`
468 // (also matches an explicit "match" instead of "if let")
469 // (even if the "match" or "if let" is used for declaration)
470 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
471 // also check for empty `loop {}` statements
472 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) {
477 "empty `loop {}` detected. You may want to either use `panic!()` or add \
478 `std::thread::sleep(..);` to the loop body.",
482 // extract the expression from the first statement (if any) in a block
483 let inner_stmt_expr = extract_expr_from_first_stmt(block);
484 // or extract the first expression (if any) from the block
485 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
486 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
487 // ensure "if let" compatible match structure
489 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
491 && arms[0].guard.is_none()
492 && arms[1].guard.is_none()
493 && is_simple_break_expr(&arms[1].body)
495 if in_external_macro(cx.sess(), expr.span) {
499 // NOTE: we used to build a body here instead of using
500 // ellipsis, this was removed because:
501 // 1) it was ugly with big bodies;
502 // 2) it was not indented properly;
503 // 3) it wasn’t very smart (see #675).
504 let mut applicability = Applicability::HasPlaceholders;
509 "this loop could be written as a `while let` loop",
512 "while let {} = {} {{ .. }}",
513 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
514 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
525 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
526 let pat = &arms[0].pat.kind;
528 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
529 &ExprKind::MethodCall(ref method_path, _, ref method_args),
530 ) = (pat, &match_expr.kind)
532 let iter_expr = &method_args[0];
534 // Don't lint when the iterator is recreated on every iteration
536 if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
537 if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
538 if implements_trait(cx, cx.tables.expr_ty(iter_expr), iter_def_id, &[]);
544 let lhs_constructor = last_path_segment(qpath);
545 if method_path.ident.name == sym!(next)
546 && match_trait_method(cx, match_expr, &paths::ITERATOR)
547 && lhs_constructor.ident.name == sym!(Some)
548 && (pat_args.is_empty()
549 || !is_refutable(cx, &pat_args[0])
550 && !is_used_inside(cx, iter_expr, &arms[0].body)
551 && !is_iterator_used_after_while_let(cx, iter_expr)
552 && !is_nested(cx, expr, &method_args[0]))
554 let mut applicability = Applicability::MachineApplicable;
555 let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
556 let loop_var = if pat_args.is_empty() {
559 snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
563 WHILE_LET_ON_ITERATOR,
564 expr.span.with_hi(match_expr.span.hi()),
565 "this loop could be written as a `for` loop",
567 format!("for {} in {}", loop_var, iterator),
574 if let Some((cond, body)) = higher::while_loop(&expr) {
575 check_infinite_loop(cx, cond, body);
578 check_needless_collect(expr, cx);
582 enum NeverLoopResult {
583 // A break/return always get triggered but not necessarily for the main loop.
585 // A continue may occur for the main loop.
591 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
593 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
594 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
598 // Combine two results for parts that are called in order.
600 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
602 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
603 NeverLoopResult::Otherwise => second,
607 // Combine two results where both parts are called but not necessarily in order.
609 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
610 match (left, right) {
611 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
612 NeverLoopResult::MayContinueMainLoop
614 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
615 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
619 // Combine two results where only one of the part may have been executed.
621 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
623 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
624 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
625 NeverLoopResult::MayContinueMainLoop
627 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
631 fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
632 let stmts = block.stmts.iter().map(stmt_to_expr);
633 let expr = once(block.expr.as_deref());
634 let mut iter = stmts.chain(expr).filter_map(|e| e);
635 never_loop_expr_seq(&mut iter, main_loop_id)
638 fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
640 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
641 StmtKind::Local(ref local) => local.init.as_deref(),
646 fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
649 | ExprKind::Unary(_, ref e)
650 | ExprKind::Cast(ref e, _)
651 | ExprKind::Type(ref e, _)
652 | ExprKind::Field(ref e, _)
653 | ExprKind::AddrOf(_, _, ref e)
654 | ExprKind::Struct(_, _, Some(ref e))
655 | ExprKind::Repeat(ref e, _)
656 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
657 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
658 never_loop_expr_all(&mut es.iter(), main_loop_id)
660 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
661 ExprKind::Binary(_, ref e1, ref e2)
662 | ExprKind::Assign(ref e1, ref e2, _)
663 | ExprKind::AssignOp(_, ref e1, ref e2)
664 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
665 ExprKind::Loop(ref b, _, _) => {
666 // Break can come from the inner loop so remove them.
667 absorb_break(&never_loop_block(b, main_loop_id))
669 ExprKind::Match(ref e, ref arms, _) => {
670 let e = never_loop_expr(e, main_loop_id);
674 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
678 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
679 ExprKind::Continue(d) => {
682 .expect("target ID can only be missing in the presence of compilation errors");
683 if id == main_loop_id {
684 NeverLoopResult::MayContinueMainLoop
686 NeverLoopResult::AlwaysBreak
689 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
690 if let Some(ref e) = *e {
691 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
693 NeverLoopResult::AlwaysBreak
696 ExprKind::InlineAsm(ref asm) => asm
700 InlineAsmOperand::In { expr, .. }
701 | InlineAsmOperand::InOut { expr, .. }
702 | InlineAsmOperand::Const { expr }
703 | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
704 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
705 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
706 never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
709 .fold(NeverLoopResult::Otherwise, combine_both),
710 ExprKind::Struct(_, _, None)
711 | ExprKind::Yield(_, _)
712 | ExprKind::Closure(_, _, _, _, _)
713 | ExprKind::LlvmInlineAsm(_)
716 | ExprKind::Err => NeverLoopResult::Otherwise,
720 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
721 es.map(|e| never_loop_expr(e, main_loop_id))
722 .fold(NeverLoopResult::Otherwise, combine_seq)
725 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
726 es.map(|e| never_loop_expr(e, main_loop_id))
727 .fold(NeverLoopResult::Otherwise, combine_both)
730 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
731 e.map(|e| never_loop_expr(e, main_loop_id))
732 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
735 fn check_for_loop<'a, 'tcx>(
736 cx: &LateContext<'a, 'tcx>,
739 body: &'tcx Expr<'_>,
740 expr: &'tcx Expr<'_>,
742 check_for_loop_range(cx, pat, arg, body, expr);
743 check_for_loop_arg(cx, pat, arg, expr);
744 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
745 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
746 check_for_mut_range_bound(cx, arg, body);
747 detect_manual_memcpy(cx, pat, arg, body, expr);
750 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId) -> bool {
752 if let ExprKind::Path(qpath) = &expr.kind;
753 if let QPath::Resolved(None, path) = qpath;
754 if path.segments.len() == 1;
755 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
765 #[derive(Clone, Copy)]
777 fn negative(value: String) -> Self {
780 sign: OffsetSign::Negative,
784 fn positive(value: String) -> Self {
787 sign: OffsetSign::Positive,
792 struct FixedOffsetVar<'hir> {
793 var: &'hir Expr<'hir>,
797 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
798 let is_slice = match ty.kind {
799 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
800 ty::Slice(..) | ty::Array(..) => true,
804 is_slice || is_type_diagnostic_item(cx, ty, sym!(vec_type)) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
807 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
809 if let ExprKind::MethodCall(method, _, args) = expr.kind;
810 if method.ident.name == sym!(clone);
812 if let Some(arg) = args.get(0);
813 then { arg } else { expr }
817 fn get_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, idx: &Expr<'_>, var: HirId) -> Option<Offset> {
818 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr<'_>, var: HirId) -> Option<String> {
820 ExprKind::Lit(l) => match l.node {
821 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
824 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
830 ExprKind::Binary(op, lhs, rhs) => match op.node {
832 let offset_opt = if same_var(cx, lhs, var) {
833 extract_offset(cx, rhs, var)
834 } else if same_var(cx, rhs, var) {
835 extract_offset(cx, lhs, var)
840 offset_opt.map(Offset::positive)
842 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
845 ExprKind::Path(..) if same_var(cx, idx, var) => Some(Offset::positive("0".into())),
850 fn get_assignments<'tcx>(body: &'tcx Expr<'tcx>) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> {
851 fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
852 if let ExprKind::Assign(lhs, rhs, _) = e.kind {
859 // This is one of few ways to return different iterators
860 // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
861 let mut iter_a = None;
862 let mut iter_b = None;
864 if let ExprKind::Block(b, _) = body.kind {
865 let Block { stmts, expr, .. } = *b;
869 .filter_map(|stmt| match stmt.kind {
870 StmtKind::Local(..) | StmtKind::Item(..) => None,
871 StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
873 .chain(expr.into_iter())
877 iter_b = Some(get_assignment(body))
880 iter_a.into_iter().flatten().chain(iter_b.into_iter())
883 fn build_manual_memcpy_suggestion<'a, 'tcx>(
884 cx: &LateContext<'a, 'tcx>,
887 limits: ast::RangeLimits,
888 dst_var: FixedOffsetVar<'_>,
889 src_var: FixedOffsetVar<'_>,
891 fn print_sum(arg1: &str, arg2: &Offset) -> String {
892 match (arg1, &arg2.value[..], arg2.sign) {
893 ("0", "0", _) => "0".into(),
894 ("0", x, OffsetSign::Positive) | (x, "0", _) => x.into(),
895 ("0", x, OffsetSign::Negative) => format!("-{}", x),
896 (x, y, OffsetSign::Positive) => format!("({} + {})", x, y),
897 (x, y, OffsetSign::Negative) => {
901 format!("({} - {})", x, y)
907 fn print_offset(start_str: &str, inline_offset: &Offset) -> String {
908 let offset = print_sum(start_str, inline_offset);
909 if offset.as_str() == "0" {
916 let print_limit = |end: &Expr<'_>, offset: Offset, var: &Expr<'_>| {
918 if let ExprKind::MethodCall(method, _, len_args) = end.kind;
919 if method.ident.name == sym!(len);
920 if len_args.len() == 1;
921 if let Some(arg) = len_args.get(0);
922 if var_def_id(cx, arg) == var_def_id(cx, var);
925 OffsetSign::Negative => format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value),
926 OffsetSign::Positive => "".into(),
929 let end_str = match limits {
930 ast::RangeLimits::Closed => {
931 let end = sugg::Sugg::hir(cx, end, "<count>");
932 format!("{}", end + sugg::ONE)
934 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
937 print_sum(&end_str, &offset)
942 let start_str = snippet(cx, start.span, "").to_string();
943 let dst_offset = print_offset(&start_str, &dst_var.offset);
944 let dst_limit = print_limit(end, dst_var.offset, dst_var.var);
945 let src_offset = print_offset(&start_str, &src_var.offset);
946 let src_limit = print_limit(end, src_var.offset, src_var.var);
948 let dst_var_name = snippet_opt(cx, dst_var.var.span).unwrap_or_else(|| "???".into());
949 let src_var_name = snippet_opt(cx, src_var.var.span).unwrap_or_else(|| "???".into());
951 let dst = if dst_offset == "" && dst_limit == "" {
954 format!("{}[{}..{}]", dst_var_name, dst_offset, dst_limit)
958 "{}.clone_from_slice(&{}[{}..{}])",
959 dst, src_var_name, src_offset, src_limit
962 /// Checks for for loops that sequentially copy items from one slice-like
963 /// object to another.
964 fn detect_manual_memcpy<'a, 'tcx>(
965 cx: &LateContext<'a, 'tcx>,
968 body: &'tcx Expr<'_>,
969 expr: &'tcx Expr<'_>,
971 if let Some(higher::Range {
975 }) = higher::range(cx, arg)
977 // the var must be a single name
978 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
979 // The only statements in the for loops can be indexed assignments from
980 // indexed retrievals.
981 let big_sugg = get_assignments(body)
983 o.and_then(|(lhs, rhs)| {
984 let rhs = fetch_cloned_expr(rhs);
986 if let ExprKind::Index(seqexpr_left, idx_left) = lhs.kind;
987 if let ExprKind::Index(seqexpr_right, idx_right) = rhs.kind;
988 if is_slice_like(cx, cx.tables.expr_ty(seqexpr_left))
989 && is_slice_like(cx, cx.tables.expr_ty(seqexpr_right));
990 if let Some(offset_left) = get_offset(cx, &idx_left, canonical_id);
991 if let Some(offset_right) = get_offset(cx, &idx_right, canonical_id);
993 // Source and destination must be different
994 if var_def_id(cx, seqexpr_left) != var_def_id(cx, seqexpr_right);
996 Some((FixedOffsetVar { var: seqexpr_left, offset: offset_left },
997 FixedOffsetVar { var: seqexpr_right, offset: offset_right }))
1004 .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, dst, src)))
1005 .collect::<Option<Vec<_>>>()
1006 .filter(|v| !v.is_empty())
1007 .map(|v| v.join("\n "));
1009 if let Some(big_sugg) = big_sugg {
1014 "it looks like you're manually copying between slices",
1015 "try replacing the loop by",
1017 Applicability::Unspecified,
1024 /// Checks for looping over a range and then indexing a sequence with it.
1025 /// The iteratee must be a range literal.
1026 #[allow(clippy::too_many_lines)]
1027 fn check_for_loop_range<'a, 'tcx>(
1028 cx: &LateContext<'a, 'tcx>,
1030 arg: &'tcx Expr<'_>,
1031 body: &'tcx Expr<'_>,
1032 expr: &'tcx Expr<'_>,
1034 if let Some(higher::Range {
1038 }) = higher::range(cx, arg)
1040 // the var must be a single name
1041 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1042 let mut visitor = VarVisitor {
1045 indexed_mut: FxHashSet::default(),
1046 indexed_indirectly: FxHashMap::default(),
1047 indexed_directly: FxHashMap::default(),
1048 referenced: FxHashSet::default(),
1050 prefer_mutable: false,
1052 walk_expr(&mut visitor, body);
1054 // linting condition: we only indexed one variable, and indexed it directly
1055 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1056 let (indexed, (indexed_extent, indexed_ty)) = visitor
1060 .expect("already checked that we have exactly 1 element");
1062 // ensure that the indexed variable was declared before the loop, see #601
1063 if let Some(indexed_extent) = indexed_extent {
1064 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1065 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1066 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1067 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1068 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1073 // don't lint if the container that is indexed does not have .iter() method
1074 let has_iter = has_iter_method(cx, indexed_ty);
1075 if has_iter.is_none() {
1079 // don't lint if the container that is indexed into is also used without
1081 if visitor.referenced.contains(&indexed) {
1085 let starts_at_zero = is_integer_const(cx, start, 0);
1087 let skip = if starts_at_zero {
1090 format!(".skip({})", snippet(cx, start.span, ".."))
1093 let mut end_is_start_plus_val = false;
1095 let take = if let Some(end) = *end {
1096 let mut take_expr = end;
1098 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1099 if let BinOpKind::Add = op.node {
1100 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1101 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1103 if start_equal_left {
1105 } else if start_equal_right {
1109 end_is_start_plus_val = start_equal_left | start_equal_right;
1113 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1117 ast::RangeLimits::Closed => {
1118 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1119 format!(".take({})", take_expr + sugg::ONE)
1121 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1128 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1129 ("mut ", "iter_mut")
1134 let take_is_empty = take.is_empty();
1135 let mut method_1 = take;
1136 let mut method_2 = skip;
1138 if end_is_start_plus_val {
1139 mem::swap(&mut method_1, &mut method_2);
1142 if visitor.nonindex {
1145 NEEDLESS_RANGE_LOOP,
1147 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1151 "consider using an iterator",
1153 (pat.span, format!("({}, <item>)", ident.name)),
1156 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1163 let repl = if starts_at_zero && take_is_empty {
1164 format!("&{}{}", ref_mut, indexed)
1166 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1171 NEEDLESS_RANGE_LOOP,
1174 "the loop variable `{}` is only used to index `{}`.",
1180 "consider using an iterator",
1181 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1191 fn is_len_call(expr: &Expr<'_>, var: Name) -> bool {
1193 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.kind;
1194 if len_args.len() == 1;
1195 if method.ident.name == sym!(len);
1196 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1197 if path.segments.len() == 1;
1198 if path.segments[0].ident.name == var;
1207 fn is_end_eq_array_len<'tcx>(
1208 cx: &LateContext<'_, 'tcx>,
1210 limits: ast::RangeLimits,
1211 indexed_ty: Ty<'tcx>,
1214 if let ExprKind::Lit(ref lit) = end.kind;
1215 if let ast::LitKind::Int(end_int, _) = lit.node;
1216 if let ty::Array(_, arr_len_const) = indexed_ty.kind;
1217 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1219 return match limits {
1220 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1221 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1229 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
1230 let mut applicability = Applicability::MachineApplicable;
1231 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1232 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1237 "it is more concise to loop over references to containers instead of using explicit \
1239 "to write this more concisely, try",
1240 format!("&{}{}", muta, object),
1245 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
1246 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1247 if let ExprKind::MethodCall(ref method, _, ref args) = arg.kind {
1248 // just the receiver, no arguments
1249 if args.len() == 1 {
1250 let method_name = &*method.ident.as_str();
1251 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1252 if method_name == "iter" || method_name == "iter_mut" {
1253 if is_ref_iterable_type(cx, &args[0]) {
1254 lint_iter_method(cx, args, arg, method_name);
1256 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1257 let receiver_ty = cx.tables.expr_ty(&args[0]);
1258 let receiver_ty_adjusted = cx.tables.expr_ty_adjusted(&args[0]);
1259 if same_tys(cx, receiver_ty, receiver_ty_adjusted) {
1260 let mut applicability = Applicability::MachineApplicable;
1261 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1264 EXPLICIT_INTO_ITER_LOOP,
1266 "it is more concise to loop over containers instead of using explicit \
1268 "to write this more concisely, try",
1273 let ref_receiver_ty = cx.tcx.mk_ref(
1274 cx.tcx.lifetimes.re_erased,
1277 mutbl: Mutability::Not,
1280 if same_tys(cx, receiver_ty_adjusted, ref_receiver_ty) {
1281 lint_iter_method(cx, args, arg, method_name)
1284 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1289 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1290 probably not what you want",
1292 next_loop_linted = true;
1296 if !next_loop_linted {
1297 check_arg_type(cx, pat, arg);
1301 /// Checks for `for` loops over `Option`s and `Result`s.
1302 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat<'_>, arg: &Expr<'_>) {
1303 let ty = cx.tables.expr_ty(arg);
1304 if is_type_diagnostic_item(cx, ty, sym!(option_type)) {
1307 FOR_LOOPS_OVER_FALLIBLES,
1310 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1311 `if let` statement.",
1312 snippet(cx, arg.span, "_")
1316 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1317 snippet(cx, pat.span, "_"),
1318 snippet(cx, arg.span, "_")
1321 } else if is_type_diagnostic_item(cx, ty, sym!(result_type)) {
1324 FOR_LOOPS_OVER_FALLIBLES,
1327 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1328 `if let` statement.",
1329 snippet(cx, arg.span, "_")
1333 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1334 snippet(cx, pat.span, "_"),
1335 snippet(cx, arg.span, "_")
1341 fn check_for_loop_explicit_counter<'a, 'tcx>(
1342 cx: &LateContext<'a, 'tcx>,
1344 arg: &'tcx Expr<'_>,
1345 body: &'tcx Expr<'_>,
1346 expr: &'tcx Expr<'_>,
1348 // Look for variables that are incremented once per loop iteration.
1349 let mut visitor = IncrementVisitor {
1351 states: FxHashMap::default(),
1355 walk_expr(&mut visitor, body);
1357 // For each candidate, check the parent block to see if
1358 // it's initialized to zero at the start of the loop.
1359 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1360 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1361 let mut visitor2 = InitializeVisitor {
1365 state: VarState::IncrOnce,
1370 walk_block(&mut visitor2, block);
1372 if visitor2.state == VarState::Warn {
1373 if let Some(name) = visitor2.name {
1374 let mut applicability = Applicability::MachineApplicable;
1376 // for some reason this is the only way to get the `Span`
1377 // of the entire `for` loop
1378 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1386 EXPLICIT_COUNTER_LOOP,
1387 for_span.with_hi(arg.span.hi()),
1388 &format!("the variable `{}` is used as a loop counter.", name),
1391 "for ({}, {}) in {}.enumerate()",
1393 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1394 make_iterator_snippet(cx, arg, &mut applicability),
1404 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1405 /// actual `Iterator` that the loop uses.
1406 fn make_iterator_snippet(cx: &LateContext<'_, '_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
1407 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR)
1408 .map_or(false, |id| implements_trait(cx, cx.tables.expr_ty(arg), id, &[]));
1412 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1415 // (&x).into_iter() ==> x.iter()
1416 // (&mut x).into_iter() ==> x.iter_mut()
1418 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1419 if has_iter_method(cx, cx.tables.expr_ty(&arg_inner)).is_some() =>
1421 let meth_name = match mutability {
1422 Mutability::Mut => "iter_mut",
1423 Mutability::Not => "iter",
1427 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1433 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1439 /// Checks for the `FOR_KV_MAP` lint.
1440 fn check_for_loop_over_map_kv<'a, 'tcx>(
1441 cx: &LateContext<'a, 'tcx>,
1443 arg: &'tcx Expr<'_>,
1444 body: &'tcx Expr<'_>,
1445 expr: &'tcx Expr<'_>,
1447 let pat_span = pat.span;
1449 if let PatKind::Tuple(ref pat, _) = pat.kind {
1451 let arg_span = arg.span;
1452 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).kind {
1453 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1454 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1455 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1460 let mutbl = match mutbl {
1461 Mutability::Not => "",
1462 Mutability::Mut => "_mut",
1464 let arg = match arg.kind {
1465 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1469 if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
1474 &format!("you seem to want to iterate on a map's {}s", kind),
1476 let map = sugg::Sugg::hir(cx, arg, "map");
1479 "use the corresponding method",
1481 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1482 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1492 struct MutatePairDelegate {
1493 hir_id_low: Option<HirId>,
1494 hir_id_high: Option<HirId>,
1495 span_low: Option<Span>,
1496 span_high: Option<Span>,
1499 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1500 fn consume(&mut self, _: &Place<'tcx>, _: ConsumeMode) {}
1502 fn borrow(&mut self, cmt: &Place<'tcx>, bk: ty::BorrowKind) {
1503 if let ty::BorrowKind::MutBorrow = bk {
1504 if let PlaceBase::Local(id) = cmt.base {
1505 if Some(id) == self.hir_id_low {
1506 self.span_low = Some(cmt.span)
1508 if Some(id) == self.hir_id_high {
1509 self.span_high = Some(cmt.span)
1515 fn mutate(&mut self, cmt: &Place<'tcx>) {
1516 if let PlaceBase::Local(id) = cmt.base {
1517 if Some(id) == self.hir_id_low {
1518 self.span_low = Some(cmt.span)
1520 if Some(id) == self.hir_id_high {
1521 self.span_high = Some(cmt.span)
1527 impl<'tcx> MutatePairDelegate {
1528 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1529 (self.span_low, self.span_high)
1533 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr<'_>, body: &Expr<'_>) {
1534 if let Some(higher::Range {
1538 }) = higher::range(cx, arg)
1540 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1541 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1542 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1543 mut_warn_with_span(cx, span_low);
1544 mut_warn_with_span(cx, span_high);
1549 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1550 if let Some(sp) = span {
1555 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1560 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr<'_>) -> Option<HirId> {
1562 if let ExprKind::Path(ref qpath) = bound.kind;
1563 if let QPath::Resolved(None, _) = *qpath;
1565 let res = qpath_res(cx, qpath, bound.hir_id);
1566 if let Res::Local(hir_id) = res {
1567 let node_str = cx.tcx.hir().get(hir_id);
1569 if let Node::Binding(pat) = node_str;
1570 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1571 if let BindingAnnotation::Mutable = bind_ann;
1573 return Some(hir_id);
1582 fn check_for_mutation(
1583 cx: &LateContext<'_, '_>,
1585 bound_ids: &[Option<HirId>],
1586 ) -> (Option<Span>, Option<Span>) {
1587 let mut delegate = MutatePairDelegate {
1588 hir_id_low: bound_ids[0],
1589 hir_id_high: bound_ids[1],
1593 let def_id = body.hir_id.owner.to_def_id();
1594 cx.tcx.infer_ctxt().enter(|infcx| {
1595 ExprUseVisitor::new(&mut delegate, &infcx, def_id.expect_local(), cx.param_env, cx.tables).walk_expr(body);
1597 delegate.mutation_span()
1600 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1601 fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
1603 PatKind::Wild => true,
1604 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body),
1609 struct LocalUsedVisitor<'a, 'tcx> {
1610 cx: &'a LateContext<'a, 'tcx>,
1615 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1616 type Map = Map<'tcx>;
1618 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1619 if same_var(self.cx, expr, self.local) {
1622 walk_expr(self, expr);
1626 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1627 NestedVisitorMap::None
1631 struct VarVisitor<'a, 'tcx> {
1632 /// context reference
1633 cx: &'a LateContext<'a, 'tcx>,
1634 /// var name to look for as index
1636 /// indexed variables that are used mutably
1637 indexed_mut: FxHashSet<Name>,
1638 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1639 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1640 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1641 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1642 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1643 /// Any names that are used outside an index operation.
1644 /// Used to detect things like `&mut vec` used together with `vec[i]`
1645 referenced: FxHashSet<Name>,
1646 /// has the loop variable been used in expressions other than the index of
1649 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1650 /// takes `&mut self`
1651 prefer_mutable: bool,
1654 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1655 fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
1657 // the indexed container is referenced by a name
1658 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
1659 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1660 if seqvar.segments.len() == 1;
1662 let index_used_directly = same_var(self.cx, idx, self.var);
1663 let indexed_indirectly = {
1664 let mut used_visitor = LocalUsedVisitor {
1669 walk_expr(&mut used_visitor, idx);
1673 if indexed_indirectly || index_used_directly {
1674 if self.prefer_mutable {
1675 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1677 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
1679 Res::Local(hir_id) => {
1680 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1681 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1682 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1683 if indexed_indirectly {
1684 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1686 if index_used_directly {
1687 self.indexed_directly.insert(
1688 seqvar.segments[0].ident.name,
1689 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1692 return false; // no need to walk further *on the variable*
1694 Res::Def(DefKind::Static | DefKind::Const, ..) => {
1695 if indexed_indirectly {
1696 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1698 if index_used_directly {
1699 self.indexed_directly.insert(
1700 seqvar.segments[0].ident.name,
1701 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1704 return false; // no need to walk further *on the variable*
1715 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1716 type Map = Map<'tcx>;
1718 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1721 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.kind;
1722 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1723 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1724 if !self.check(&args[1], &args[0], expr);
1730 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
1731 if !self.check(idx, seqexpr, expr);
1736 // directly using a variable
1737 if let ExprKind::Path(ref qpath) = expr.kind;
1738 if let QPath::Resolved(None, ref path) = *qpath;
1739 if path.segments.len() == 1;
1741 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
1742 if local_id == self.var {
1743 self.nonindex = true;
1745 // not the correct variable, but still a variable
1746 self.referenced.insert(path.segments[0].ident.name);
1752 let old = self.prefer_mutable;
1754 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
1755 self.prefer_mutable = true;
1756 self.visit_expr(lhs);
1757 self.prefer_mutable = false;
1758 self.visit_expr(rhs);
1760 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
1761 if mutbl == Mutability::Mut {
1762 self.prefer_mutable = true;
1764 self.visit_expr(expr);
1766 ExprKind::Call(ref f, args) => {
1769 let ty = self.cx.tables.expr_ty_adjusted(expr);
1770 self.prefer_mutable = false;
1771 if let ty::Ref(_, _, mutbl) = ty.kind {
1772 if mutbl == Mutability::Mut {
1773 self.prefer_mutable = true;
1776 self.visit_expr(expr);
1779 ExprKind::MethodCall(_, _, args) => {
1780 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1781 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1782 self.prefer_mutable = false;
1783 if let ty::Ref(_, _, mutbl) = ty.kind {
1784 if mutbl == Mutability::Mut {
1785 self.prefer_mutable = true;
1788 self.visit_expr(expr);
1791 ExprKind::Closure(_, _, body_id, ..) => {
1792 let body = self.cx.tcx.hir().body(body_id);
1793 self.visit_expr(&body.value);
1795 _ => walk_expr(self, expr),
1797 self.prefer_mutable = old;
1799 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1800 NestedVisitorMap::None
1804 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
1805 let def_id = match var_def_id(cx, expr) {
1807 None => return false,
1809 if let Some(used_mutably) = mutated_variables(container, cx) {
1810 if used_mutably.contains(&def_id) {
1817 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
1818 let def_id = match var_def_id(cx, iter_expr) {
1820 None => return false,
1822 let mut visitor = VarUsedAfterLoopVisitor {
1825 iter_expr_id: iter_expr.hir_id,
1826 past_while_let: false,
1827 var_used_after_while_let: false,
1829 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1830 walk_block(&mut visitor, enclosing_block);
1832 visitor.var_used_after_while_let
1835 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1836 cx: &'a LateContext<'a, 'tcx>,
1838 iter_expr_id: HirId,
1839 past_while_let: bool,
1840 var_used_after_while_let: bool,
1843 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1844 type Map = Map<'tcx>;
1846 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1847 if self.past_while_let {
1848 if Some(self.def_id) == var_def_id(self.cx, expr) {
1849 self.var_used_after_while_let = true;
1851 } else if self.iter_expr_id == expr.hir_id {
1852 self.past_while_let = true;
1854 walk_expr(self, expr);
1856 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1857 NestedVisitorMap::None
1861 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1862 /// for `&T` and `&mut T`, such as `Vec`.
1864 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr<'_>) -> bool {
1865 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1866 // will allow further borrows afterwards
1867 let ty = cx.tables.expr_ty(e);
1868 is_iterable_array(ty, cx) ||
1869 is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
1870 match_type(cx, ty, &paths::LINKED_LIST) ||
1871 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
1872 is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
1873 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
1874 match_type(cx, ty, &paths::BINARY_HEAP) ||
1875 match_type(cx, ty, &paths::BTREEMAP) ||
1876 match_type(cx, ty, &paths::BTREESET)
1879 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1880 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1882 ty::Array(_, n) => {
1883 if let Some(val) = n.try_eval_usize(cx.tcx, cx.param_env) {
1884 (0..=32).contains(&val)
1893 /// If a block begins with a statement (possibly a `let` binding) and has an
1894 /// expression, return it.
1895 fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
1896 if block.stmts.is_empty() {
1899 if let StmtKind::Local(ref local) = block.stmts[0].kind {
1900 if let Some(expr) = local.init {
1910 /// If a block begins with an expression (with or without semicolon), return it.
1911 fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
1913 Some(ref expr) if block.stmts.is_empty() => Some(expr),
1914 None if !block.stmts.is_empty() => match block.stmts[0].kind {
1915 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
1916 StmtKind::Local(..) | StmtKind::Item(..) => None,
1922 /// Returns `true` if expr contains a single break expr without destination label
1924 /// passed expression. The expression may be within a block.
1925 fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
1927 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
1928 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
1933 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1934 // incremented exactly once in the loop body, and initialized to zero
1935 // at the start of the loop.
1936 #[derive(Debug, PartialEq)]
1938 Initial, // Not examined yet
1939 IncrOnce, // Incremented exactly once, may be a loop counter
1940 Declared, // Declared but not (yet) initialized to zero
1945 /// Scan a for loop for variables that are incremented exactly once.
1946 struct IncrementVisitor<'a, 'tcx> {
1947 cx: &'a LateContext<'a, 'tcx>, // context reference
1948 states: FxHashMap<HirId, VarState>, // incremented variables
1949 depth: u32, // depth of conditional expressions
1953 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
1954 type Map = Map<'tcx>;
1956 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
1961 // If node is a variable
1962 if let Some(def_id) = var_def_id(self.cx, expr) {
1963 if let Some(parent) = get_parent_expr(self.cx, expr) {
1964 let state = self.states.entry(def_id).or_insert(VarState::Initial);
1967 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
1968 if lhs.hir_id == expr.hir_id {
1969 if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) {
1970 *state = match *state {
1971 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
1972 _ => VarState::DontWarn,
1975 // Assigned some other value
1976 *state = VarState::DontWarn;
1980 ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
1981 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
1982 *state = VarState::DontWarn
1987 } else if is_loop(expr) || is_conditional(expr) {
1989 walk_expr(self, expr);
1992 } else if let ExprKind::Continue(_) = expr.kind {
1996 walk_expr(self, expr);
1998 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1999 NestedVisitorMap::None
2003 /// Checks whether a variable is initialized to zero at the start of a loop.
2004 struct InitializeVisitor<'a, 'tcx> {
2005 cx: &'a LateContext<'a, 'tcx>, // context reference
2006 end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
2010 depth: u32, // depth of conditional expressions
2014 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2015 type Map = Map<'tcx>;
2017 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2018 // Look for declarations of the variable
2019 if let StmtKind::Local(ref local) = stmt.kind {
2020 if local.pat.hir_id == self.var_id {
2021 if let PatKind::Binding(.., ident, _) = local.pat.kind {
2022 self.name = Some(ident.name);
2024 self.state = if let Some(ref init) = local.init {
2025 if is_integer_const(&self.cx, init, 0) {
2036 walk_stmt(self, stmt);
2039 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2040 if self.state == VarState::DontWarn {
2043 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2044 self.past_loop = true;
2047 // No need to visit expressions before the variable is
2049 if self.state == VarState::IncrOnce {
2053 // If node is the desired variable, see how it's used
2054 if var_def_id(self.cx, expr) == Some(self.var_id) {
2055 if let Some(parent) = get_parent_expr(self.cx, expr) {
2057 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2058 self.state = VarState::DontWarn;
2060 ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
2061 self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 {
2067 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2068 self.state = VarState::DontWarn
2075 self.state = VarState::DontWarn;
2078 } else if !self.past_loop && is_loop(expr) {
2079 self.state = VarState::DontWarn;
2081 } else if is_conditional(expr) {
2083 walk_expr(self, expr);
2087 walk_expr(self, expr);
2090 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2091 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2095 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> Option<HirId> {
2096 if let ExprKind::Path(ref qpath) = expr.kind {
2097 let path_res = qpath_res(cx, qpath, expr.hir_id);
2098 if let Res::Local(hir_id) = path_res {
2099 return Some(hir_id);
2105 fn is_loop(expr: &Expr<'_>) -> bool {
2107 ExprKind::Loop(..) => true,
2112 fn is_conditional(expr: &Expr<'_>) -> bool {
2114 ExprKind::Match(..) => true,
2119 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2121 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2122 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2123 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2125 return is_loop_nested(cx, loop_expr, iter_expr)
2131 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
2132 let mut id = loop_expr.hir_id;
2133 let iter_name = if let Some(name) = path_name(iter_expr) {
2139 let parent = cx.tcx.hir().get_parent_node(id);
2143 match cx.tcx.hir().find(parent) {
2144 Some(Node::Expr(expr)) => {
2145 if let ExprKind::Loop(..) = expr.kind {
2149 Some(Node::Block(block)) => {
2150 let mut block_visitor = LoopNestVisitor {
2152 iterator: iter_name,
2155 walk_block(&mut block_visitor, block);
2156 if block_visitor.nesting == RuledOut {
2160 Some(Node::Stmt(_)) => (),
2169 #[derive(PartialEq, Eq)]
2171 Unknown, // no nesting detected yet
2172 RuledOut, // the iterator is initialized or assigned within scope
2173 LookFurther, // no nesting detected, no further walk required
2176 use self::Nesting::{LookFurther, RuledOut, Unknown};
2178 struct LoopNestVisitor {
2184 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2185 type Map = Map<'tcx>;
2187 fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
2188 if stmt.hir_id == self.hir_id {
2189 self.nesting = LookFurther;
2190 } else if self.nesting == Unknown {
2191 walk_stmt(self, stmt);
2195 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2196 if self.nesting != Unknown {
2199 if expr.hir_id == self.hir_id {
2200 self.nesting = LookFurther;
2204 ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
2205 if match_var(path, self.iterator) {
2206 self.nesting = RuledOut;
2209 _ => walk_expr(self, expr),
2213 fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
2214 if self.nesting != Unknown {
2217 if let PatKind::Binding(.., span_name, _) = pat.kind {
2218 if self.iterator == span_name.name {
2219 self.nesting = RuledOut;
2226 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2227 NestedVisitorMap::None
2231 fn path_name(e: &Expr<'_>) -> Option<Name> {
2232 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2233 let segments = &path.segments;
2234 if segments.len() == 1 {
2235 return Some(segments[0].ident.name);
2241 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
2242 if constant(cx, cx.tables, cond).is_some() {
2243 // A pure constant condition (e.g., `while false`) is not linted.
2247 let mut var_visitor = VarCollectorVisitor {
2249 ids: FxHashSet::default(),
2250 def_ids: FxHashMap::default(),
2253 var_visitor.visit_expr(cond);
2254 if var_visitor.skip {
2257 let used_in_condition = &var_visitor.ids;
2258 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2259 used_in_condition.is_disjoint(&used_mutably)
2263 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2265 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2266 has_break_or_return: false,
2268 has_break_or_return_visitor.visit_expr(expr);
2269 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2271 if no_cond_variable_mutated && !mutable_static_in_cond {
2274 WHILE_IMMUTABLE_CONDITION,
2276 "variables in the condition are not mutated in the loop body",
2278 diag.note("this may lead to an infinite or to a never running loop");
2280 if has_break_or_return {
2281 diag.note("this loop contains `return`s or `break`s");
2282 diag.help("rewrite it as `if cond { loop { } }`");
2289 struct HasBreakOrReturnVisitor {
2290 has_break_or_return: bool,
2293 impl<'a, 'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2294 type Map = Map<'tcx>;
2296 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
2297 if self.has_break_or_return {
2302 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2303 self.has_break_or_return = true;
2309 walk_expr(self, expr);
2312 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2313 NestedVisitorMap::None
2317 /// Collects the set of variables in an expression
2318 /// Stops analysis if a function call is found
2319 /// Note: In some cases such as `self`, there are no mutable annotation,
2320 /// All variables definition IDs are collected
2321 struct VarCollectorVisitor<'a, 'tcx> {
2322 cx: &'a LateContext<'a, 'tcx>,
2323 ids: FxHashSet<HirId>,
2324 def_ids: FxHashMap<def_id::DefId, bool>,
2328 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2329 fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
2331 if let ExprKind::Path(ref qpath) = ex.kind;
2332 if let QPath::Resolved(None, _) = *qpath;
2333 let res = qpath_res(self.cx, qpath, ex.hir_id);
2336 Res::Local(hir_id) => {
2337 self.ids.insert(hir_id);
2339 Res::Def(DefKind::Static, def_id) => {
2340 let mutable = self.cx.tcx.is_mutable_static(def_id);
2341 self.def_ids.insert(def_id, mutable);
2350 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2351 type Map = Map<'tcx>;
2353 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
2355 ExprKind::Path(_) => self.insert_def_id(ex),
2356 // If there is any function/method call… we just stop analysis
2357 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2359 _ => walk_expr(self, ex),
2363 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2364 NestedVisitorMap::None
2368 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2370 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'a, 'tcx>) {
2372 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
2373 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].kind;
2374 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2375 if let Some(ref generic_args) = chain_method.args;
2376 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2378 let ty = cx.tables.node_type(ty.hir_id);
2379 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) ||
2380 is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
2381 match_type(cx, ty, &paths::BTREEMAP) ||
2382 is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
2383 if method.ident.name == sym!(len) {
2384 let span = shorten_needless_collect_span(expr);
2389 NEEDLESS_COLLECT_MSG,
2391 ".count()".to_string(),
2392 Applicability::MachineApplicable,
2395 if method.ident.name == sym!(is_empty) {
2396 let span = shorten_needless_collect_span(expr);
2401 NEEDLESS_COLLECT_MSG,
2403 ".next().is_none()".to_string(),
2404 Applicability::MachineApplicable,
2407 if method.ident.name == sym!(contains) {
2408 let contains_arg = snippet(cx, args[1].span, "??");
2409 let span = shorten_needless_collect_span(expr);
2414 NEEDLESS_COLLECT_MSG,
2416 let (arg, pred) = if contains_arg.starts_with('&') {
2417 ("x", &contains_arg[1..])
2419 ("&x", &*contains_arg)
2421 diag.span_suggestion(
2425 ".any(|{}| x == {})",
2428 Applicability::MachineApplicable,
2438 fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
2440 if let ExprKind::MethodCall(_, _, ref args) = expr.kind;
2441 if let ExprKind::MethodCall(_, ref span, _) = args[0].kind;
2443 return expr.span.with_lo(span.lo() - BytePos(1));