1 use crate::reexport::*;
2 use if_chain::if_chain;
3 use itertools::Itertools;
4 use rustc::hir::def::{DefKind, Res};
5 use rustc::hir::def_id;
6 use rustc::hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
8 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
9 use rustc::middle::region;
10 use rustc::{declare_lint_pass, declare_tool_lint};
11 // use rustc::middle::region::CodeExtent;
12 use crate::consts::{constant, Constant};
13 use crate::utils::usage::mutated_variables;
14 use crate::utils::{in_macro_or_desugar, sext, sugg};
15 use rustc::middle::expr_use_visitor::*;
16 use rustc::middle::mem_categorization::cmt_;
17 use rustc::middle::mem_categorization::Categorization;
18 use rustc::ty::subst::Subst;
19 use rustc::ty::{self, Ty};
20 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
21 use rustc_errors::Applicability;
22 use std::iter::{once, Iterator};
25 use syntax::source_map::Span;
26 use syntax_pos::BytePos;
28 use crate::utils::paths;
30 get_enclosing_block, get_parent_expr, has_iter_method, higher, is_integer_literal, is_refutable, last_path_segment,
31 match_trait_method, match_type, match_var, multispan_sugg, snippet, snippet_opt, snippet_with_applicability,
32 span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then, SpanlessEq,
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 /// for i in 0..src.len() {
46 /// dst[i + 64] = src[i];
51 "manually copying items between slices"
54 declare_clippy_lint! {
55 /// **What it does:** Checks for looping over the range of `0..len` of some
56 /// collection just to get the values by index.
58 /// **Why is this bad?** Just iterating the collection itself makes the intent
59 /// more clear and is probably faster.
61 /// **Known problems:** None.
65 /// for i in 0..vec.len() {
66 /// println!("{}", vec[i]);
69 pub NEEDLESS_RANGE_LOOP,
71 "for-looping over a range of indices where an iterator over items would do"
74 declare_clippy_lint! {
75 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
76 /// suggests the latter.
78 /// **Why is this bad?** Readability.
80 /// **Known problems:** False negatives. We currently only warn on some known
85 /// // with `y` a `Vec` or slice:
86 /// for x in y.iter() {
90 /// can be rewritten to
96 pub EXPLICIT_ITER_LOOP,
98 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
101 declare_clippy_lint! {
102 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
103 /// suggests the latter.
105 /// **Why is this bad?** Readability.
107 /// **Known problems:** None
111 /// // with `y` a `Vec` or slice:
112 /// for x in y.into_iter() {
116 /// can be rewritten to
122 pub EXPLICIT_INTO_ITER_LOOP,
124 "for-looping over `_.into_iter()` when `_` would do"
127 declare_clippy_lint! {
128 /// **What it does:** Checks for loops on `x.next()`.
130 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
131 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
132 /// implements `IntoIterator`, so that possibly one value will be iterated,
133 /// leading to some hard to find bugs. No one will want to write such code
134 /// [except to win an Underhanded Rust
135 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
137 /// **Known problems:** None.
141 /// for x in y.next() {
147 "for-looping over `_.next()` which is probably not intended"
150 declare_clippy_lint! {
151 /// **What it does:** Checks for `for` loops over `Option` values.
153 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
156 /// **Known problems:** None.
160 /// for x in option {
167 /// if let Some(x) = option {
171 pub FOR_LOOP_OVER_OPTION,
173 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
176 declare_clippy_lint! {
177 /// **What it does:** Checks for `for` loops over `Result` values.
179 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
182 /// **Known problems:** None.
186 /// for x in result {
193 /// if let Ok(x) = result {
197 pub FOR_LOOP_OVER_RESULT,
199 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
202 declare_clippy_lint! {
203 /// **What it does:** Detects `loop + match` combinations that are easier
204 /// written as a `while let` loop.
206 /// **Why is this bad?** The `while let` loop is usually shorter and more
209 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
214 /// let x = match y {
218 /// // .. do something with x
220 /// // is easier written as
221 /// while let Some(x) = y {
222 /// // .. do something with x
227 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
230 declare_clippy_lint! {
231 /// **What it does:** Checks for using `collect()` on an iterator without using
234 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
235 /// iterator instead.
237 /// **Known problems:** None.
241 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
245 "`collect()`ing an iterator without using the result; this is usually better written as a for loop"
248 declare_clippy_lint! {
249 /// **What it does:** Checks for functions collecting an iterator when collect
252 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
253 /// when this allocation may not be needed.
255 /// **Known problems:**
260 /// let len = iterator.collect::<Vec<_>>().len();
262 /// let len = iterator.count();
264 pub NEEDLESS_COLLECT,
266 "collecting an iterator when collect is not needed"
269 declare_clippy_lint! {
270 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
271 /// are constant and `x` is greater or equal to `y`, unless the range is
272 /// reversed or has a negative `.step_by(_)`.
274 /// **Why is it bad?** Such loops will either be skipped or loop until
275 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
278 /// **Known problems:** The lint cannot catch loops over dynamically defined
279 /// ranges. Doing this would require simulating all possible inputs and code
280 /// paths through the program, which would be complex and error-prone.
284 /// for x in 5..10 - 5 {
286 /// } // oops, stray `-`
288 pub REVERSE_RANGE_LOOP,
290 "iteration over an empty range, such as `10..0` or `5..5`"
293 declare_clippy_lint! {
294 /// **What it does:** Checks `for` loops over slices with an explicit counter
295 /// and suggests the use of `.enumerate()`.
297 /// **Why is it bad?** Not only is the version using `.enumerate()` more
298 /// readable, the compiler is able to remove bounds checks which can lead to
299 /// faster code in some instances.
301 /// **Known problems:** None.
305 /// for i in 0..v.len() { foo(v[i]);
306 /// for i in 0..v.len() { bar(i, v[i]); }
308 pub EXPLICIT_COUNTER_LOOP,
310 "for-looping with an explicit counter when `_.enumerate()` would do"
313 declare_clippy_lint! {
314 /// **What it does:** Checks for empty `loop` expressions.
316 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
317 /// anything. Think of the environment and either block on something or at least
318 /// make the thread sleep for some microseconds.
320 /// **Known problems:** None.
328 "empty `loop {}`, which should block or sleep"
331 declare_clippy_lint! {
332 /// **What it does:** Checks for `while let` expressions on iterators.
334 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
335 /// the intent better.
337 /// **Known problems:** None.
341 /// while let Some(val) = iter() {
345 pub WHILE_LET_ON_ITERATOR,
347 "using a while-let loop instead of a for loop on an iterator"
350 declare_clippy_lint! {
351 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
352 /// ignoring either the keys or values.
354 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
355 /// can be used to express that don't need the values or keys.
357 /// **Known problems:** None.
361 /// for (k, _) in &map {
366 /// could be replaced by
369 /// for k in map.keys() {
375 "looping on a map using `iter` when `keys` or `values` would do"
378 declare_clippy_lint! {
379 /// **What it does:** Checks for loops that will always `break`, `return` or
380 /// `continue` an outer loop.
382 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
385 /// **Known problems:** None
396 "any loop that will always `break` or `return`"
399 declare_clippy_lint! {
400 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
402 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
404 /// **Known problems:** None
408 /// let mut foo = 42;
409 /// for i in 0..foo {
411 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
416 "for loop over a range where one of the bounds is a mutable variable"
419 declare_clippy_lint! {
420 /// **What it does:** Checks whether variables used within while loop condition
421 /// can be (and are) mutated in the body.
423 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
424 /// will lead to an infinite loop.
426 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
427 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
428 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
434 /// println!("let me loop forever!");
437 pub WHILE_IMMUTABLE_CONDITION,
439 "variables used within while expression are not mutated in the body"
442 declare_lint_pass!(Loops => [
446 EXPLICIT_INTO_ITER_LOOP,
448 FOR_LOOP_OVER_RESULT,
449 FOR_LOOP_OVER_OPTION,
454 EXPLICIT_COUNTER_LOOP,
456 WHILE_LET_ON_ITERATOR,
460 WHILE_IMMUTABLE_CONDITION,
463 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
464 #[allow(clippy::too_many_lines)]
465 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
466 // we don't want to check expanded macros
467 if in_macro_or_desugar(expr.span) {
471 if let Some((pat, arg, body)) = higher::for_loop(expr) {
472 check_for_loop(cx, pat, arg, body, expr);
475 // check for never_loop
477 ExprKind::While(_, ref block, _) | ExprKind::Loop(ref block, _, _) => {
478 match never_loop_block(block, expr.hir_id) {
479 NeverLoopResult::AlwaysBreak => {
480 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops")
482 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
488 // check for `loop { if let {} else break }` that could be `while let`
489 // (also matches an explicit "match" instead of "if let")
490 // (even if the "match" or "if let" is used for declaration)
491 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
492 // also check for empty `loop {}` statements
493 if block.stmts.is_empty() && block.expr.is_none() {
498 "empty `loop {}` detected. You may want to either use `panic!()` or add \
499 `std::thread::sleep(..);` to the loop body.",
503 // extract the expression from the first statement (if any) in a block
504 let inner_stmt_expr = extract_expr_from_first_stmt(block);
505 // or extract the first expression (if any) from the block
506 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
507 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
508 // ensure "if let" compatible match structure
510 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
512 && arms[0].pats.len() == 1
513 && arms[0].guard.is_none()
514 && arms[1].pats.len() == 1
515 && arms[1].guard.is_none()
516 && is_simple_break_expr(&arms[1].body)
518 if in_external_macro(cx.sess(), expr.span) {
522 // NOTE: we used to build a body here instead of using
523 // ellipsis, this was removed because:
524 // 1) it was ugly with big bodies;
525 // 2) it was not indented properly;
526 // 3) it wasn’t very smart (see #675).
527 let mut applicability = Applicability::HasPlaceholders;
532 "this loop could be written as a `while let` loop",
535 "while let {} = {} {{ .. }}",
536 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
537 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
548 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
549 let pat = &arms[0].pats[0].node;
551 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
552 &ExprKind::MethodCall(ref method_path, _, ref method_args),
553 ) = (pat, &match_expr.node)
555 let iter_expr = &method_args[0];
556 let lhs_constructor = last_path_segment(qpath);
557 if method_path.ident.name == "next"
558 && match_trait_method(cx, match_expr, &paths::ITERATOR)
559 && lhs_constructor.ident.name == "Some"
560 && (pat_args.is_empty()
561 || !is_refutable(cx, &pat_args[0])
562 && !is_used_inside(cx, iter_expr, &arms[0].body)
563 && !is_iterator_used_after_while_let(cx, iter_expr)
564 && !is_nested(cx, expr, &method_args[0]))
566 let iterator = snippet(cx, method_args[0].span, "_");
567 let loop_var = if pat_args.is_empty() {
570 snippet(cx, pat_args[0].span, "_").into_owned()
574 WHILE_LET_ON_ITERATOR,
576 "this loop could be written as a `for` loop",
578 format!("for {} in {} {{ .. }}", loop_var, iterator),
579 Applicability::HasPlaceholders,
585 // check for while loops which conditions never change
586 if let ExprKind::While(ref cond, _, _) = expr.node {
587 check_infinite_loop(cx, cond, expr);
590 check_needless_collect(expr, cx);
593 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
594 if let StmtKind::Semi(ref expr) = stmt.node {
595 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
596 if args.len() == 1 && method.ident.name == "collect" && match_trait_method(cx, expr, &paths::ITERATOR) {
601 "you are collect()ing an iterator and throwing away the result. \
602 Consider using an explicit for loop to exhaust the iterator",
610 enum NeverLoopResult {
611 // A break/return always get triggered but not necessarily for the main loop.
613 // A continue may occur for the main loop.
618 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
620 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
621 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
625 // Combine two results for parts that are called in order.
626 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
628 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
629 NeverLoopResult::Otherwise => second,
633 // Combine two results where both parts are called but not necessarily in order.
634 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
635 match (left, right) {
636 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
637 NeverLoopResult::MayContinueMainLoop
639 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
640 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
644 // Combine two results where only one of the part may have been executed.
645 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
647 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
648 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
649 NeverLoopResult::MayContinueMainLoop
651 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
655 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
656 let stmts = block.stmts.iter().map(stmt_to_expr);
657 let expr = once(block.expr.as_ref().map(|p| &**p));
658 let mut iter = stmts.chain(expr).filter_map(|e| e);
659 never_loop_expr_seq(&mut iter, main_loop_id)
662 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
664 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
665 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
670 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
673 | ExprKind::Unary(_, ref e)
674 | ExprKind::Cast(ref e, _)
675 | ExprKind::Type(ref e, _)
676 | ExprKind::Field(ref e, _)
677 | ExprKind::AddrOf(_, ref e)
678 | ExprKind::Struct(_, _, Some(ref e))
679 | ExprKind::Repeat(ref e, _)
680 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
681 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
682 never_loop_expr_all(&mut es.iter(), main_loop_id)
684 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
685 ExprKind::Binary(_, ref e1, ref e2)
686 | ExprKind::Assign(ref e1, ref e2)
687 | ExprKind::AssignOp(_, ref e1, ref e2)
688 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
689 ExprKind::Loop(ref b, _, _) => {
690 // Break can come from the inner loop so remove them.
691 absorb_break(&never_loop_block(b, main_loop_id))
693 ExprKind::While(ref e, ref b, _) => {
694 let e = never_loop_expr(e, main_loop_id);
695 let result = never_loop_block(b, main_loop_id);
696 // Break can come from the inner loop so remove them.
697 combine_seq(e, absorb_break(&result))
699 ExprKind::Match(ref e, ref arms, _) => {
700 let e = never_loop_expr(e, main_loop_id);
704 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
708 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
709 ExprKind::Continue(d) => {
712 .expect("target ID can only be missing in the presence of compilation errors");
713 if id == main_loop_id {
714 NeverLoopResult::MayContinueMainLoop
716 NeverLoopResult::AlwaysBreak
719 ExprKind::Break(_, _) => NeverLoopResult::AlwaysBreak,
720 ExprKind::Ret(ref e) => {
721 if let Some(ref e) = *e {
722 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
724 NeverLoopResult::AlwaysBreak
727 ExprKind::Struct(_, _, None)
729 | ExprKind::Closure(_, _, _, _, _)
730 | ExprKind::InlineAsm(_, _, _)
733 | ExprKind::Err => NeverLoopResult::Otherwise,
737 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
738 es.map(|e| never_loop_expr(e, main_loop_id))
739 .fold(NeverLoopResult::Otherwise, combine_seq)
742 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
743 es.map(|e| never_loop_expr(e, main_loop_id))
744 .fold(NeverLoopResult::Otherwise, combine_both)
747 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
748 e.map(|e| never_loop_expr(e, main_loop_id))
749 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
752 fn check_for_loop<'a, 'tcx>(
753 cx: &LateContext<'a, 'tcx>,
759 check_for_loop_range(cx, pat, arg, body, expr);
760 check_for_loop_reverse_range(cx, arg, expr);
761 check_for_loop_arg(cx, pat, arg, expr);
762 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
763 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
764 check_for_mut_range_bound(cx, arg, body);
765 detect_manual_memcpy(cx, pat, arg, body, expr);
768 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
770 if let ExprKind::Path(ref qpath) = expr.node;
771 if let QPath::Resolved(None, ref path) = *qpath;
772 if path.segments.len() == 1;
773 if let Res::Local(local_id) = cx.tables.qpath_res(qpath, expr.hir_id);
790 fn negative(s: String) -> Self {
791 Self { value: s, negate: true }
794 fn positive(s: String) -> Self {
802 struct FixedOffsetVar {
807 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
808 let is_slice = match ty.sty {
809 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
810 ty::Slice(..) | ty::Array(..) => true,
814 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
817 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
818 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
820 ExprKind::Lit(ref 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())),
829 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
830 let ty = cx.tables.expr_ty(seqexpr);
831 if !is_slice_like(cx, ty) {
835 let offset = match idx.node {
836 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
838 let offset_opt = if same_var(cx, lhs, var) {
839 extract_offset(cx, rhs, var)
840 } else if same_var(cx, rhs, var) {
841 extract_offset(cx, lhs, var)
846 offset_opt.map(Offset::positive)
848 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
851 ExprKind::Path(..) => {
852 if same_var(cx, idx, var) {
853 Some(Offset::positive("0".into()))
861 offset.map(|o| FixedOffsetVar {
862 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
870 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
871 cx: &LateContext<'a, 'tcx>,
874 ) -> Option<FixedOffsetVar> {
876 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
877 if method.ident.name == "clone";
879 if let Some(arg) = args.get(0);
881 return get_fixed_offset_var(cx, arg, var);
885 get_fixed_offset_var(cx, expr, var)
888 fn get_indexed_assignments<'a, 'tcx>(
889 cx: &LateContext<'a, 'tcx>,
892 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
893 fn get_assignment<'a, 'tcx>(
894 cx: &LateContext<'a, 'tcx>,
897 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
898 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
900 get_fixed_offset_var(cx, lhs, var),
901 fetch_cloned_fixed_offset_var(cx, rhs, var),
903 (Some(offset_left), Some(offset_right)) => {
904 // Source and destination must be different
905 if offset_left.var_name == offset_right.var_name {
908 Some((offset_left, offset_right))
918 if let ExprKind::Block(ref b, _) = body.node {
920 ref stmts, ref expr, ..
925 .map(|stmt| match stmt.node {
926 StmtKind::Local(..) | StmtKind::Item(..) => None,
927 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
929 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
931 .collect::<Option<Vec<_>>>()
932 .unwrap_or_else(|| vec![])
934 get_assignment(cx, body, var).into_iter().collect()
938 /// Checks for for loops that sequentially copy items from one slice-like
939 /// object to another.
940 fn detect_manual_memcpy<'a, 'tcx>(
941 cx: &LateContext<'a, 'tcx>,
947 if let Some(higher::Range {
951 }) = higher::range(cx, arg)
953 // the var must be a single name
954 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
955 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
956 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
957 ("0", _, "0", _) => "".into(),
958 ("0", _, x, false) | (x, false, "0", false) => x.into(),
959 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
960 (x, false, y, false) => format!("({} + {})", x, y),
961 (x, false, y, true) => {
965 format!("({} - {})", x, y)
968 (x, true, y, false) => {
972 format!("({} - {})", y, x)
975 (x, true, y, true) => format!("-({} + {})", x, y),
979 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
980 if let Some(end) = *end {
982 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
983 if method.ident.name == "len";
984 if len_args.len() == 1;
985 if let Some(arg) = len_args.get(0);
986 if snippet(cx, arg.span, "??") == var_name;
988 return if offset.negate {
989 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
996 let end_str = match limits {
997 ast::RangeLimits::Closed => {
998 let end = sugg::Sugg::hir(cx, end, "<count>");
999 format!("{}", end + sugg::ONE)
1001 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1004 print_sum(&Offset::positive(end_str), &offset)
1010 // The only statements in the for loops can be indexed assignments from
1011 // indexed retrievals.
1012 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1014 let big_sugg = manual_copies
1016 .map(|(dst_var, src_var)| {
1017 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1018 let dst_offset = print_sum(&start_str, &dst_var.offset);
1019 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1020 let src_offset = print_sum(&start_str, &src_var.offset);
1021 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1022 let dst = if dst_offset == "" && dst_limit == "" {
1025 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1029 "{}.clone_from_slice(&{}[{}..{}])",
1030 dst, src_var.var_name, src_offset, src_limit
1035 if !big_sugg.is_empty() {
1040 "it looks like you're manually copying between slices",
1041 "try replacing the loop by",
1043 Applicability::Unspecified,
1050 /// Checks for looping over a range and then indexing a sequence with it.
1051 /// The iteratee must be a range literal.
1052 #[allow(clippy::too_many_lines)]
1053 fn check_for_loop_range<'a, 'tcx>(
1054 cx: &LateContext<'a, 'tcx>,
1060 if in_macro_or_desugar(expr.span) {
1064 if let Some(higher::Range {
1068 }) = higher::range(cx, arg)
1070 // the var must be a single name
1071 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1072 let mut visitor = VarVisitor {
1075 indexed_mut: FxHashSet::default(),
1076 indexed_indirectly: FxHashMap::default(),
1077 indexed_directly: FxHashMap::default(),
1078 referenced: FxHashSet::default(),
1080 prefer_mutable: false,
1082 walk_expr(&mut visitor, body);
1084 // linting condition: we only indexed one variable, and indexed it directly
1085 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1086 let (indexed, (indexed_extent, indexed_ty)) = visitor
1090 .expect("already checked that we have exactly 1 element");
1092 // ensure that the indexed variable was declared before the loop, see #601
1093 if let Some(indexed_extent) = indexed_extent {
1094 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1095 let parent_def_id = cx.tcx.hir().local_def_id_from_hir_id(parent_id);
1096 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1097 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1098 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1103 // don't lint if the container that is indexed does not have .iter() method
1104 let has_iter = has_iter_method(cx, indexed_ty);
1105 if has_iter.is_none() {
1109 // don't lint if the container that is indexed into is also used without
1111 if visitor.referenced.contains(&indexed) {
1115 let starts_at_zero = is_integer_literal(start, 0);
1117 let skip = if starts_at_zero {
1120 format!(".skip({})", snippet(cx, start.span, ".."))
1123 let mut end_is_start_plus_val = false;
1125 let take = if let Some(end) = *end {
1126 let mut take_expr = end;
1128 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1129 if let BinOpKind::Add = op.node {
1130 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1131 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1133 if start_equal_left {
1135 } else if start_equal_right {
1139 end_is_start_plus_val = start_equal_left | start_equal_right;
1143 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1147 ast::RangeLimits::Closed => {
1148 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1149 format!(".take({})", take_expr + sugg::ONE)
1151 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1158 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1159 ("mut ", "iter_mut")
1164 let take_is_empty = take.is_empty();
1165 let mut method_1 = take;
1166 let mut method_2 = skip;
1168 if end_is_start_plus_val {
1169 mem::swap(&mut method_1, &mut method_2);
1172 if visitor.nonindex {
1175 NEEDLESS_RANGE_LOOP,
1177 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1181 "consider using an iterator".to_string(),
1183 (pat.span, format!("({}, <item>)", ident.name)),
1186 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1193 let repl = if starts_at_zero && take_is_empty {
1194 format!("&{}{}", ref_mut, indexed)
1196 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1201 NEEDLESS_RANGE_LOOP,
1204 "the loop variable `{}` is only used to index `{}`.",
1210 "consider using an iterator".to_string(),
1211 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1221 fn is_len_call(expr: &Expr, var: Name) -> bool {
1223 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1224 if len_args.len() == 1;
1225 if method.ident.name == "len";
1226 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1227 if path.segments.len() == 1;
1228 if path.segments[0].ident.name == var;
1237 fn is_end_eq_array_len(cx: &LateContext<'_, '_>, end: &Expr, limits: ast::RangeLimits, indexed_ty: Ty<'_>) -> bool {
1239 if let ExprKind::Lit(ref lit) = end.node;
1240 if let ast::LitKind::Int(end_int, _) = lit.node;
1241 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1242 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1244 return match limits {
1245 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1246 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1254 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1255 // if this for loop is iterating over a two-sided range...
1256 if let Some(higher::Range {
1260 }) = higher::range(cx, arg)
1262 // ...and both sides are compile-time constant integers...
1263 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1264 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1265 // ...and the start index is greater than the end index,
1266 // this loop will never run. This is often confusing for developers
1267 // who think that this will iterate from the larger value to the
1269 let ty = cx.tables.expr_ty(start);
1270 let (sup, eq) = match (start_idx, end_idx) {
1271 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1273 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1274 ty::Uint(_) => start_idx > end_idx,
1277 start_idx == end_idx,
1279 _ => (false, false),
1283 let start_snippet = snippet(cx, start.span, "_");
1284 let end_snippet = snippet(cx, end.span, "_");
1285 let dots = if limits == ast::RangeLimits::Closed {
1295 "this range is empty so this for loop will never run",
1299 "consider using the following if you are attempting to iterate over this \
1302 "({end}{dots}{start}).rev()",
1305 start = start_snippet
1307 Applicability::MaybeIncorrect,
1311 } else if eq && limits != ast::RangeLimits::Closed {
1312 // if they are equal, it's also problematic - this loop
1318 "this range is empty so this for loop will never run",
1326 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1327 let mut applicability = Applicability::MachineApplicable;
1328 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1329 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1334 "it is more concise to loop over references to containers instead of using explicit \
1336 "to write this more concisely, try",
1337 format!("&{}{}", muta, object),
1342 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1343 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1344 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1345 // just the receiver, no arguments
1346 if args.len() == 1 {
1347 let method_name = &*method.ident.as_str();
1348 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1349 if method_name == "iter" || method_name == "iter_mut" {
1350 if is_ref_iterable_type(cx, &args[0]) {
1351 lint_iter_method(cx, args, arg, method_name);
1353 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1354 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1355 let substs = cx.tables.node_substs(arg.hir_id);
1356 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1358 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1359 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1360 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1361 match cx.tables.expr_ty(&args[0]).sty {
1362 // If the length is greater than 32 no traits are implemented for array and
1363 // therefore we cannot use `&`.
1364 ty::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1365 _ => lint_iter_method(cx, args, arg, method_name),
1368 let mut applicability = Applicability::MachineApplicable;
1369 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1372 EXPLICIT_INTO_ITER_LOOP,
1374 "it is more concise to loop over containers instead of using explicit \
1375 iteration methods`",
1376 "to write this more concisely, try",
1381 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1386 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1387 probably not what you want",
1389 next_loop_linted = true;
1393 if !next_loop_linted {
1394 check_arg_type(cx, pat, arg);
1398 /// Checks for `for` loops over `Option`s and `Result`s.
1399 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1400 let ty = cx.tables.expr_ty(arg);
1401 if match_type(cx, ty, &paths::OPTION) {
1404 FOR_LOOP_OVER_OPTION,
1407 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1408 `if let` statement.",
1409 snippet(cx, arg.span, "_")
1412 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1413 snippet(cx, pat.span, "_"),
1414 snippet(cx, arg.span, "_")
1417 } else if match_type(cx, ty, &paths::RESULT) {
1420 FOR_LOOP_OVER_RESULT,
1423 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1424 `if let` statement.",
1425 snippet(cx, arg.span, "_")
1428 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1429 snippet(cx, pat.span, "_"),
1430 snippet(cx, arg.span, "_")
1436 fn check_for_loop_explicit_counter<'a, 'tcx>(
1437 cx: &LateContext<'a, 'tcx>,
1443 // Look for variables that are incremented once per loop iteration.
1444 let mut visitor = IncrementVisitor {
1446 states: FxHashMap::default(),
1450 walk_expr(&mut visitor, body);
1452 // For each candidate, check the parent block to see if
1453 // it's initialized to zero at the start of the loop.
1454 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1455 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1456 let mut visitor2 = InitializeVisitor {
1460 state: VarState::IncrOnce,
1465 walk_block(&mut visitor2, block);
1467 if visitor2.state == VarState::Warn {
1468 if let Some(name) = visitor2.name {
1469 let mut applicability = Applicability::MachineApplicable;
1472 EXPLICIT_COUNTER_LOOP,
1474 &format!("the variable `{}` is used as a loop counter.", name),
1477 "for ({}, {}) in {}.enumerate()",
1479 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1480 if higher::range(cx, arg).is_some() {
1483 snippet_with_applicability(cx, arg.span, "_", &mut applicability)
1488 sugg::Sugg::hir_with_applicability(cx, arg, "_", &mut applicability).maybe_par()
1500 /// Checks for the `FOR_KV_MAP` lint.
1501 fn check_for_loop_over_map_kv<'a, 'tcx>(
1502 cx: &LateContext<'a, 'tcx>,
1508 let pat_span = pat.span;
1510 if let PatKind::Tuple(ref pat, _) = pat.node {
1512 let arg_span = arg.span;
1513 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1514 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1515 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1516 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1521 let mutbl = match mutbl {
1523 MutMutable => "_mut",
1525 let arg = match arg.node {
1526 ExprKind::AddrOf(_, ref expr) => &**expr,
1530 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1535 &format!("you seem to want to iterate on a map's {}s", kind),
1537 let map = sugg::Sugg::hir(cx, arg, "map");
1540 "use the corresponding method".into(),
1542 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1543 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1553 struct MutatePairDelegate {
1554 hir_id_low: Option<HirId>,
1555 hir_id_high: Option<HirId>,
1556 span_low: Option<Span>,
1557 span_high: Option<Span>,
1560 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1561 fn consume(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1563 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1565 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1567 fn borrow(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1568 if let ty::BorrowKind::MutBorrow = bk {
1569 if let Categorization::Local(id) = cmt.cat {
1570 if Some(id) == self.hir_id_low {
1571 self.span_low = Some(sp)
1573 if Some(id) == self.hir_id_high {
1574 self.span_high = Some(sp)
1580 fn mutate(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1581 if let Categorization::Local(id) = cmt.cat {
1582 if Some(id) == self.hir_id_low {
1583 self.span_low = Some(sp)
1585 if Some(id) == self.hir_id_high {
1586 self.span_high = Some(sp)
1591 fn decl_without_init(&mut self, _: HirId, _: Span) {}
1594 impl<'tcx> MutatePairDelegate {
1595 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1596 (self.span_low, self.span_high)
1600 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1601 if let Some(higher::Range {
1605 }) = higher::range(cx, arg)
1607 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1608 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1609 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1610 mut_warn_with_span(cx, span_low);
1611 mut_warn_with_span(cx, span_high);
1616 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1617 if let Some(sp) = span {
1622 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1627 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1629 if let ExprKind::Path(ref qpath) = bound.node;
1630 if let QPath::Resolved(None, _) = *qpath;
1632 let res = cx.tables.qpath_res(qpath, bound.hir_id);
1633 if let Res::Local(node_id) = res {
1634 let node_str = cx.tcx.hir().get_by_hir_id(node_id);
1636 if let Node::Binding(pat) = node_str;
1637 if let PatKind::Binding(bind_ann, ..) = pat.node;
1638 if let BindingAnnotation::Mutable = bind_ann;
1640 return Some(node_id);
1649 fn check_for_mutation(
1650 cx: &LateContext<'_, '_>,
1652 bound_ids: &[Option<HirId>],
1653 ) -> (Option<Span>, Option<Span>) {
1654 let mut delegate = MutatePairDelegate {
1655 hir_id_low: bound_ids[0],
1656 hir_id_high: bound_ids[1],
1660 let def_id = def_id::DefId::local(body.hir_id.owner);
1661 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1662 ExprUseVisitor::new(&mut delegate, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).walk_expr(body);
1663 delegate.mutation_span()
1666 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1667 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1669 PatKind::Wild => true,
1670 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1671 let mut visitor = UsedVisitor {
1675 walk_expr(&mut visitor, body);
1682 struct UsedVisitor {
1683 var: ast::Name, // var to look for
1684 used: bool, // has the var been used otherwise?
1687 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1688 fn visit_expr(&mut self, expr: &'tcx Expr) {
1689 if match_var(expr, self.var) {
1692 walk_expr(self, expr);
1696 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1697 NestedVisitorMap::None
1701 struct LocalUsedVisitor<'a, 'tcx: 'a> {
1702 cx: &'a LateContext<'a, 'tcx>,
1707 impl<'a, 'tcx: 'a> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1708 fn visit_expr(&mut self, expr: &'tcx Expr) {
1709 if same_var(self.cx, expr, self.local) {
1712 walk_expr(self, expr);
1716 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1717 NestedVisitorMap::None
1721 struct VarVisitor<'a, 'tcx: 'a> {
1722 /// context reference
1723 cx: &'a LateContext<'a, 'tcx>,
1724 /// var name to look for as index
1726 /// indexed variables that are used mutably
1727 indexed_mut: FxHashSet<Name>,
1728 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1729 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1730 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1731 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1732 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1733 /// Any names that are used outside an index operation.
1734 /// Used to detect things like `&mut vec` used together with `vec[i]`
1735 referenced: FxHashSet<Name>,
1736 /// has the loop variable been used in expressions other than the index of
1739 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1740 /// takes `&mut self`
1741 prefer_mutable: bool,
1744 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1745 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1747 // the indexed container is referenced by a name
1748 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1749 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1750 if seqvar.segments.len() == 1;
1752 let index_used_directly = same_var(self.cx, idx, self.var);
1753 let indexed_indirectly = {
1754 let mut used_visitor = LocalUsedVisitor {
1759 walk_expr(&mut used_visitor, idx);
1763 if indexed_indirectly || index_used_directly {
1764 if self.prefer_mutable {
1765 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1767 let res = self.cx.tables.qpath_res(seqpath, seqexpr.hir_id);
1769 Res::Local(hir_id) | Res::Upvar(hir_id, ..) => {
1770 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1771 let parent_def_id = self.cx.tcx.hir().local_def_id_from_hir_id(parent_id);
1772 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1773 if indexed_indirectly {
1774 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1776 if index_used_directly {
1777 self.indexed_directly.insert(
1778 seqvar.segments[0].ident.name,
1779 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1782 return false; // no need to walk further *on the variable*
1784 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1785 if indexed_indirectly {
1786 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1788 if index_used_directly {
1789 self.indexed_directly.insert(
1790 seqvar.segments[0].ident.name,
1791 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1794 return false; // no need to walk further *on the variable*
1805 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1806 fn visit_expr(&mut self, expr: &'tcx Expr) {
1809 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1810 if (meth.ident.name == "index" && match_trait_method(self.cx, expr, &paths::INDEX))
1811 || (meth.ident.name == "index_mut" && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1812 if !self.check(&args[1], &args[0], expr);
1818 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1819 if !self.check(idx, seqexpr, expr);
1824 // directly using a variable
1825 if let ExprKind::Path(ref qpath) = expr.node;
1826 if let QPath::Resolved(None, ref path) = *qpath;
1827 if path.segments.len() == 1;
1829 match self.cx.tables.qpath_res(qpath, expr.hir_id) {
1830 Res::Upvar(local_id, ..) => {
1831 if local_id == self.var {
1832 // we are not indexing anything, record that
1833 self.nonindex = true;
1836 Res::Local(local_id) =>
1839 if local_id == self.var {
1840 self.nonindex = true;
1842 // not the correct variable, but still a variable
1843 self.referenced.insert(path.segments[0].ident.name);
1851 let old = self.prefer_mutable;
1853 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1854 self.prefer_mutable = true;
1855 self.visit_expr(lhs);
1856 self.prefer_mutable = false;
1857 self.visit_expr(rhs);
1859 ExprKind::AddrOf(mutbl, ref expr) => {
1860 if mutbl == MutMutable {
1861 self.prefer_mutable = true;
1863 self.visit_expr(expr);
1865 ExprKind::Call(ref f, ref args) => {
1868 let ty = self.cx.tables.expr_ty_adjusted(expr);
1869 self.prefer_mutable = false;
1870 if let ty::Ref(_, _, mutbl) = ty.sty {
1871 if mutbl == MutMutable {
1872 self.prefer_mutable = true;
1875 self.visit_expr(expr);
1878 ExprKind::MethodCall(_, _, ref args) => {
1879 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1880 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1881 self.prefer_mutable = false;
1882 if let ty::Ref(_, _, mutbl) = ty.sty {
1883 if mutbl == MutMutable {
1884 self.prefer_mutable = true;
1887 self.visit_expr(expr);
1890 ExprKind::Closure(_, _, body_id, ..) => {
1891 let body = self.cx.tcx.hir().body(body_id);
1892 self.visit_expr(&body.value);
1894 _ => walk_expr(self, expr),
1896 self.prefer_mutable = old;
1898 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1899 NestedVisitorMap::None
1903 fn is_used_inside<'a, 'tcx: 'a>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1904 let def_id = match var_def_id(cx, expr) {
1906 None => return false,
1908 if let Some(used_mutably) = mutated_variables(container, cx) {
1909 if used_mutably.contains(&def_id) {
1916 fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1917 let def_id = match var_def_id(cx, iter_expr) {
1919 None => return false,
1921 let mut visitor = VarUsedAfterLoopVisitor {
1924 iter_expr_id: iter_expr.hir_id,
1925 past_while_let: false,
1926 var_used_after_while_let: false,
1928 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1929 walk_block(&mut visitor, enclosing_block);
1931 visitor.var_used_after_while_let
1934 struct VarUsedAfterLoopVisitor<'a, 'tcx: 'a> {
1935 cx: &'a LateContext<'a, 'tcx>,
1937 iter_expr_id: HirId,
1938 past_while_let: bool,
1939 var_used_after_while_let: bool,
1942 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1943 fn visit_expr(&mut self, expr: &'tcx Expr) {
1944 if self.past_while_let {
1945 if Some(self.def_id) == var_def_id(self.cx, expr) {
1946 self.var_used_after_while_let = true;
1948 } else if self.iter_expr_id == expr.hir_id {
1949 self.past_while_let = true;
1951 walk_expr(self, expr);
1953 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1954 NestedVisitorMap::None
1958 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1959 /// for `&T` and `&mut T`, such as `Vec`.
1961 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1962 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1963 // will allow further borrows afterwards
1964 let ty = cx.tables.expr_ty(e);
1965 is_iterable_array(ty, cx) ||
1966 match_type(cx, ty, &paths::VEC) ||
1967 match_type(cx, ty, &paths::LINKED_LIST) ||
1968 match_type(cx, ty, &paths::HASHMAP) ||
1969 match_type(cx, ty, &paths::HASHSET) ||
1970 match_type(cx, ty, &paths::VEC_DEQUE) ||
1971 match_type(cx, ty, &paths::BINARY_HEAP) ||
1972 match_type(cx, ty, &paths::BTREEMAP) ||
1973 match_type(cx, ty, &paths::BTREESET)
1976 fn is_iterable_array(ty: Ty<'_>, cx: &LateContext<'_, '_>) -> bool {
1977 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1979 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1984 /// If a block begins with a statement (possibly a `let` binding) and has an
1985 /// expression, return it.
1986 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1987 if block.stmts.is_empty() {
1990 if let StmtKind::Local(ref local) = block.stmts[0].node {
1991 if let Some(ref expr) = local.init {
2001 /// If a block begins with an expression (with or without semicolon), return it.
2002 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2004 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2005 None if !block.stmts.is_empty() => match block.stmts[0].node {
2006 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2007 StmtKind::Local(..) | StmtKind::Item(..) => None,
2013 /// Returns `true` if expr contains a single break expr without destination label
2015 /// passed expression. The expression may be within a block.
2016 fn is_simple_break_expr(expr: &Expr) -> bool {
2018 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2019 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2020 Some(subexpr) => is_simple_break_expr(subexpr),
2027 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2028 // incremented exactly once in the loop body, and initialized to zero
2029 // at the start of the loop.
2030 #[derive(Debug, PartialEq)]
2032 Initial, // Not examined yet
2033 IncrOnce, // Incremented exactly once, may be a loop counter
2034 Declared, // Declared but not (yet) initialized to zero
2039 /// Scan a for loop for variables that are incremented exactly once.
2040 struct IncrementVisitor<'a, 'tcx: 'a> {
2041 cx: &'a LateContext<'a, 'tcx>, // context reference
2042 states: FxHashMap<HirId, VarState>, // incremented variables
2043 depth: u32, // depth of conditional expressions
2047 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2048 fn visit_expr(&mut self, expr: &'tcx Expr) {
2053 // If node is a variable
2054 if let Some(def_id) = var_def_id(self.cx, expr) {
2055 if let Some(parent) = get_parent_expr(self.cx, expr) {
2056 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2059 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2060 if lhs.hir_id == expr.hir_id {
2061 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2062 *state = match *state {
2063 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2064 _ => VarState::DontWarn,
2067 // Assigned some other value
2068 *state = VarState::DontWarn;
2072 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2073 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2077 } else if is_loop(expr) || is_conditional(expr) {
2079 walk_expr(self, expr);
2082 } else if let ExprKind::Continue(_) = expr.node {
2086 walk_expr(self, expr);
2088 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2089 NestedVisitorMap::None
2093 /// Checks whether a variable is initialized to zero at the start of a loop.
2094 struct InitializeVisitor<'a, 'tcx: 'a> {
2095 cx: &'a LateContext<'a, 'tcx>, // context reference
2096 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2100 depth: u32, // depth of conditional expressions
2104 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2105 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2106 // Look for declarations of the variable
2107 if let StmtKind::Local(ref local) = stmt.node {
2108 if local.pat.hir_id == self.var_id {
2109 if let PatKind::Binding(.., ident, _) = local.pat.node {
2110 self.name = Some(ident.name);
2112 self.state = if let Some(ref init) = local.init {
2113 if is_integer_literal(init, 0) {
2124 walk_stmt(self, stmt);
2127 fn visit_expr(&mut self, expr: &'tcx Expr) {
2128 if self.state == VarState::DontWarn {
2131 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2132 self.past_loop = true;
2135 // No need to visit expressions before the variable is
2137 if self.state == VarState::IncrOnce {
2141 // If node is the desired variable, see how it's used
2142 if var_def_id(self.cx, expr) == Some(self.var_id) {
2143 if let Some(parent) = get_parent_expr(self.cx, expr) {
2145 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2146 self.state = VarState::DontWarn;
2148 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2149 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2155 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2161 self.state = VarState::DontWarn;
2164 } else if !self.past_loop && is_loop(expr) {
2165 self.state = VarState::DontWarn;
2167 } else if is_conditional(expr) {
2169 walk_expr(self, expr);
2173 walk_expr(self, expr);
2175 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2176 NestedVisitorMap::None
2180 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2181 if let ExprKind::Path(ref qpath) = expr.node {
2182 let path_res = cx.tables.qpath_res(qpath, expr.hir_id);
2183 if let Res::Local(node_id) = path_res {
2184 return Some(node_id);
2190 fn is_loop(expr: &Expr) -> bool {
2192 ExprKind::Loop(..) | ExprKind::While(..) => true,
2197 fn is_conditional(expr: &Expr) -> bool {
2199 ExprKind::Match(..) => true,
2204 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2206 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2207 let parent_node = cx.tcx.hir().get_parent_node_by_hir_id(loop_block.hir_id);
2208 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find_by_hir_id(parent_node);
2210 return is_loop_nested(cx, loop_expr, iter_expr)
2216 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2217 let mut id = loop_expr.hir_id;
2218 let iter_name = if let Some(name) = path_name(iter_expr) {
2224 let parent = cx.tcx.hir().get_parent_node_by_hir_id(id);
2228 match cx.tcx.hir().find_by_hir_id(parent) {
2229 Some(Node::Expr(expr)) => match expr.node {
2230 ExprKind::Loop(..) | ExprKind::While(..) => {
2235 Some(Node::Block(block)) => {
2236 let mut block_visitor = LoopNestVisitor {
2238 iterator: iter_name,
2241 walk_block(&mut block_visitor, block);
2242 if block_visitor.nesting == RuledOut {
2246 Some(Node::Stmt(_)) => (),
2255 #[derive(PartialEq, Eq)]
2257 Unknown, // no nesting detected yet
2258 RuledOut, // the iterator is initialized or assigned within scope
2259 LookFurther, // no nesting detected, no further walk required
2262 use self::Nesting::{LookFurther, RuledOut, Unknown};
2264 struct LoopNestVisitor {
2270 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2271 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2272 if stmt.hir_id == self.hir_id {
2273 self.nesting = LookFurther;
2274 } else if self.nesting == Unknown {
2275 walk_stmt(self, stmt);
2279 fn visit_expr(&mut self, expr: &'tcx Expr) {
2280 if self.nesting != Unknown {
2283 if expr.hir_id == self.hir_id {
2284 self.nesting = LookFurther;
2288 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2289 if match_var(path, self.iterator) {
2290 self.nesting = RuledOut;
2293 _ => walk_expr(self, expr),
2297 fn visit_pat(&mut self, pat: &'tcx Pat) {
2298 if self.nesting != Unknown {
2301 if let PatKind::Binding(.., span_name, _) = pat.node {
2302 if self.iterator == span_name.name {
2303 self.nesting = RuledOut;
2310 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2311 NestedVisitorMap::None
2315 fn path_name(e: &Expr) -> Option<Name> {
2316 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2317 let segments = &path.segments;
2318 if segments.len() == 1 {
2319 return Some(segments[0].ident.name);
2325 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2326 if constant(cx, cx.tables, cond).is_some() {
2327 // A pure constant condition (e.g., `while false`) is not linted.
2331 let mut var_visitor = VarCollectorVisitor {
2333 ids: FxHashSet::default(),
2334 def_ids: FxHashMap::default(),
2337 var_visitor.visit_expr(cond);
2338 if var_visitor.skip {
2341 let used_in_condition = &var_visitor.ids;
2342 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2343 used_in_condition.is_disjoint(&used_mutably)
2347 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2348 if no_cond_variable_mutated && !mutable_static_in_cond {
2351 WHILE_IMMUTABLE_CONDITION,
2353 "Variable in the condition are not mutated in the loop body. \
2354 This either leads to an infinite or to a never running loop.",
2359 /// Collects the set of variables in an expression
2360 /// Stops analysis if a function call is found
2361 /// Note: In some cases such as `self`, there are no mutable annotation,
2362 /// All variables definition IDs are collected
2363 struct VarCollectorVisitor<'a, 'tcx: 'a> {
2364 cx: &'a LateContext<'a, 'tcx>,
2365 ids: FxHashSet<HirId>,
2366 def_ids: FxHashMap<def_id::DefId, bool>,
2370 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2371 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2373 if let ExprKind::Path(ref qpath) = ex.node;
2374 if let QPath::Resolved(None, _) = *qpath;
2375 let res = self.cx.tables.qpath_res(qpath, ex.hir_id);
2378 Res::Local(node_id) | Res::Upvar(node_id, ..) => {
2379 self.ids.insert(node_id);
2381 Res::Def(DefKind::Static, def_id) => {
2382 let mutable = self.cx.tcx.is_mutable_static(def_id);
2383 self.def_ids.insert(def_id, mutable);
2392 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2393 fn visit_expr(&mut self, ex: &'tcx Expr) {
2395 ExprKind::Path(_) => self.insert_def_id(ex),
2396 // If there is any function/method call… we just stop analysis
2397 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2399 _ => walk_expr(self, ex),
2403 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2404 NestedVisitorMap::None
2408 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2410 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2412 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2413 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2414 if chain_method.ident.name == "collect" && match_trait_method(cx, &args[0], &paths::ITERATOR);
2415 if let Some(ref generic_args) = chain_method.args;
2416 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2418 let ty = cx.tables.node_type(ty.hir_id);
2419 if match_type(cx, ty, &paths::VEC) ||
2420 match_type(cx, ty, &paths::VEC_DEQUE) ||
2421 match_type(cx, ty, &paths::BTREEMAP) ||
2422 match_type(cx, ty, &paths::HASHMAP) {
2423 if method.ident.name == "len" {
2424 let span = shorten_needless_collect_span(expr);
2425 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2429 ".count()".to_string(),
2430 Applicability::MachineApplicable,
2434 if method.ident.name == "is_empty" {
2435 let span = shorten_needless_collect_span(expr);
2436 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2440 ".next().is_none()".to_string(),
2441 Applicability::MachineApplicable,
2445 if method.ident.name == "contains" {
2446 let contains_arg = snippet(cx, args[1].span, "??");
2447 let span = shorten_needless_collect_span(expr);
2448 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2453 ".any(|&x| x == {})",
2454 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2456 Applicability::MachineApplicable,
2465 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2467 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2468 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2470 return expr.span.with_lo(span.lo() - BytePos(1));