1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution.
4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
7 // option. This file may not be copied, modified, or distributed
8 // except according to those terms.
10 use crate::reexport::*;
11 use crate::rustc::hir::def::Def;
12 use crate::rustc::hir::def_id;
13 use crate::rustc::hir::intravisit::{walk_block, walk_decl, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
14 use crate::rustc::hir::*;
15 use crate::rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
16 use crate::rustc::middle::region;
17 use crate::rustc::{declare_tool_lint, lint_array};
18 use if_chain::if_chain;
19 use itertools::Itertools;
20 // use crate::rustc::middle::region::CodeExtent;
21 use crate::consts::{constant, Constant};
22 use crate::rustc::middle::expr_use_visitor::*;
23 use crate::rustc::middle::mem_categorization::cmt_;
24 use crate::rustc::middle::mem_categorization::Categorization;
25 use crate::rustc::ty::subst::Subst;
26 use crate::rustc::ty::{self, Ty};
27 use crate::rustc_data_structures::fx::{FxHashMap, FxHashSet};
28 use crate::rustc_errors::Applicability;
29 use crate::syntax::ast;
30 use crate::syntax::source_map::Span;
31 use crate::syntax_pos::BytePos;
32 use crate::utils::usage::mutated_variables;
33 use crate::utils::{in_macro, sext, sugg};
34 use std::iter::{once, Iterator};
37 use crate::utils::paths;
39 get_enclosing_block, get_parent_expr, higher, is_integer_literal, is_refutable, last_path_segment,
40 match_trait_method, match_type, match_var, multispan_sugg, snippet, snippet_opt, snippet_with_applicability,
41 span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then, SpanlessEq,
44 /// **What it does:** Checks for for-loops that manually copy items between
45 /// slices that could be optimized by having a memcpy.
47 /// **Why is this bad?** It is not as fast as a memcpy.
49 /// **Known problems:** None.
53 /// for i in 0..src.len() {
54 /// dst[i + 64] = src[i];
57 declare_clippy_lint! {
60 "manually copying items between slices"
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 /// for i in 0..vec.len() {
74 /// println!("{}", vec[i]);
77 declare_clippy_lint! {
78 pub NEEDLESS_RANGE_LOOP,
80 "for-looping over a range of indices where an iterator over items would do"
83 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
84 /// suggests the latter.
86 /// **Why is this bad?** Readability.
88 /// **Known problems:** False negatives. We currently only warn on some known
93 /// // with `y` a `Vec` or slice:
94 /// for x in y.iter() {
98 /// can be rewritten to
104 declare_clippy_lint! {
105 pub EXPLICIT_ITER_LOOP,
107 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
110 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
111 /// suggests the latter.
113 /// **Why is this bad?** Readability.
115 /// **Known problems:** None
119 /// // with `y` a `Vec` or slice:
120 /// for x in y.into_iter() {
124 /// can be rewritten to
130 declare_clippy_lint! {
131 pub EXPLICIT_INTO_ITER_LOOP,
133 "for-looping over `_.into_iter()` when `_` would do"
136 /// **What it does:** Checks for loops on `x.next()`.
138 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
139 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
140 /// implements `IntoIterator`, so that possibly one value will be iterated,
141 /// leading to some hard to find bugs. No one will want to write such code
142 /// [except to win an Underhanded Rust
143 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
145 /// **Known problems:** None.
149 /// for x in y.next() {
153 declare_clippy_lint! {
156 "for-looping over `_.next()` which is probably not intended"
159 /// **What it does:** Checks for `for` loops over `Option` values.
161 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
164 /// **Known problems:** None.
168 /// for x in option {
175 /// if let Some(x) = option {
179 declare_clippy_lint! {
180 pub FOR_LOOP_OVER_OPTION,
182 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
185 /// **What it does:** Checks for `for` loops over `Result` values.
187 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
190 /// **Known problems:** None.
194 /// for x in result {
201 /// if let Ok(x) = result {
205 declare_clippy_lint! {
206 pub FOR_LOOP_OVER_RESULT,
208 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
211 /// **What it does:** Detects `loop + match` combinations that are easier
212 /// written as a `while let` loop.
214 /// **Why is this bad?** The `while let` loop is usually shorter and more
217 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
222 /// let x = match y {
226 /// // .. do something with x
228 /// // is easier written as
229 /// while let Some(x) = y {
230 /// // .. do something with x
233 declare_clippy_lint! {
236 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
239 /// **What it does:** Checks for using `collect()` on an iterator without using
242 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
243 /// iterator instead.
245 /// **Known problems:** None.
249 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
251 declare_clippy_lint! {
254 "`collect()`ing an iterator without using the result; this is usually better written as a for loop"
257 /// **What it does:** Checks for functions collecting an iterator when collect
260 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
261 /// when this allocation may not be needed.
263 /// **Known problems:**
268 /// let len = iterator.collect::<Vec<_>>().len();
270 /// let len = iterator.count();
272 declare_clippy_lint! {
273 pub NEEDLESS_COLLECT,
275 "collecting an iterator when collect is not needed"
278 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
279 /// are constant and `x` is greater or equal to `y`, unless the range is
280 /// reversed or has a negative `.step_by(_)`.
282 /// **Why is it bad?** Such loops will either be skipped or loop until
283 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
286 /// **Known problems:** The lint cannot catch loops over dynamically defined
287 /// ranges. Doing this would require simulating all possible inputs and code
288 /// paths through the program, which would be complex and error-prone.
292 /// for x in 5..10 - 5 {
294 /// } // oops, stray `-`
296 declare_clippy_lint! {
297 pub REVERSE_RANGE_LOOP,
299 "iteration over an empty range, such as `10..0` or `5..5`"
302 /// **What it does:** Checks `for` loops over slices with an explicit counter
303 /// and suggests the use of `.enumerate()`.
305 /// **Why is it bad?** Not only is the version using `.enumerate()` more
306 /// readable, the compiler is able to remove bounds checks which can lead to
307 /// faster code in some instances.
309 /// **Known problems:** None.
313 /// for i in 0..v.len() { foo(v[i]);
314 /// for i in 0..v.len() { bar(i, v[i]); }
316 declare_clippy_lint! {
317 pub EXPLICIT_COUNTER_LOOP,
319 "for-looping with an explicit counter when `_.enumerate()` would do"
322 /// **What it does:** Checks for empty `loop` expressions.
324 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
325 /// anything. Think of the environment and either block on something or at least
326 /// make the thread sleep for some microseconds.
328 /// **Known problems:** None.
334 declare_clippy_lint! {
337 "empty `loop {}`, which should block or sleep"
340 /// **What it does:** Checks for `while let` expressions on iterators.
342 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
343 /// the intent better.
345 /// **Known problems:** None.
349 /// while let Some(val) = iter() {
353 declare_clippy_lint! {
354 pub WHILE_LET_ON_ITERATOR,
356 "using a while-let loop instead of a for loop on an iterator"
359 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
360 /// ignoring either the keys or values.
362 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
363 /// can be used to express that don't need the values or keys.
365 /// **Known problems:** None.
369 /// for (k, _) in &map {
374 /// could be replaced by
377 /// for k in map.keys() {
381 declare_clippy_lint! {
384 "looping on a map using `iter` when `keys` or `values` would do"
387 /// **What it does:** Checks for loops that will always `break`, `return` or
388 /// `continue` an outer loop.
390 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
393 /// **Known problems:** None
402 declare_clippy_lint! {
405 "any loop that will always `break` or `return`"
408 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
410 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
412 /// **Known problems:** None
416 /// let mut foo = 42;
417 /// for i in 0..foo {
419 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
422 declare_clippy_lint! {
425 "for loop over a range where one of the bounds is a mutable variable"
428 /// **What it does:** Checks whether variables used within while loop condition
429 /// can be (and are) mutated in the body.
431 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
432 /// will lead to an infinite loop.
434 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
435 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
436 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
442 /// println!("let me loop forever!");
445 declare_clippy_lint! {
446 pub WHILE_IMMUTABLE_CONDITION,
448 "variables used within while expression are not mutated in the body"
451 #[derive(Copy, Clone)]
454 impl LintPass for Pass {
455 fn get_lints(&self) -> LintArray {
460 EXPLICIT_INTO_ITER_LOOP,
462 FOR_LOOP_OVER_RESULT,
463 FOR_LOOP_OVER_OPTION,
468 EXPLICIT_COUNTER_LOOP,
470 WHILE_LET_ON_ITERATOR,
474 WHILE_IMMUTABLE_CONDITION,
479 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
480 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
481 if let Some((pat, arg, body)) = higher::for_loop(expr) {
482 check_for_loop(cx, pat, arg, body, expr);
485 // check for never_loop
487 ExprKind::While(_, ref block, _) | ExprKind::Loop(ref block, _, _) => {
488 match never_loop_block(block, expr.id) {
489 NeverLoopResult::AlwaysBreak => {
490 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops")
492 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
498 // check for `loop { if let {} else break }` that could be `while let`
499 // (also matches an explicit "match" instead of "if let")
500 // (even if the "match" or "if let" is used for declaration)
501 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
502 // also check for empty `loop {}` statements
503 if block.stmts.is_empty() && block.expr.is_none() {
508 "empty `loop {}` detected. You may want to either use `panic!()` or add \
509 `std::thread::sleep(..);` to the loop body.",
513 // extract the expression from the first statement (if any) in a block
514 let inner_stmt_expr = extract_expr_from_first_stmt(block);
515 // or extract the first expression (if any) from the block
516 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
517 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
518 // ensure "if let" compatible match structure
520 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
522 && arms[0].pats.len() == 1
523 && arms[0].guard.is_none()
524 && arms[1].pats.len() == 1
525 && arms[1].guard.is_none()
526 && is_simple_break_expr(&arms[1].body)
528 if in_external_macro(cx.sess(), expr.span) {
532 // NOTE: we used to make build a body here instead of using
533 // ellipsis, this was removed because:
534 // 1) it was ugly with big bodies;
535 // 2) it was not indented properly;
536 // 3) it wasn’t very smart (see #675).
537 let mut applicability = Applicability::MachineApplicable;
542 "this loop could be written as a `while let` loop",
545 "while let {} = {} {{ .. }}",
546 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
547 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
558 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
559 let pat = &arms[0].pats[0].node;
561 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
562 &ExprKind::MethodCall(ref method_path, _, ref method_args),
563 ) = (pat, &match_expr.node)
565 let iter_expr = &method_args[0];
566 let lhs_constructor = last_path_segment(qpath);
567 if method_path.ident.name == "next"
568 && match_trait_method(cx, match_expr, &paths::ITERATOR)
569 && lhs_constructor.ident.name == "Some"
570 && (pat_args.is_empty()
571 || !is_refutable(cx, &pat_args[0])
572 && !is_iterator_used_after_while_let(cx, iter_expr)
573 && !is_nested(cx, expr, &method_args[0]))
575 let iterator = snippet(cx, method_args[0].span, "_");
576 let loop_var = if pat_args.is_empty() {
579 snippet(cx, pat_args[0].span, "_").into_owned()
583 WHILE_LET_ON_ITERATOR,
585 "this loop could be written as a `for` loop",
587 format!("for {} in {} {{ .. }}", loop_var, iterator),
588 Applicability::HasPlaceholders,
594 // check for while loops which conditions never change
595 if let ExprKind::While(ref cond, _, _) = expr.node {
596 check_infinite_loop(cx, cond, expr);
599 check_needless_collect(expr, cx);
602 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
603 if let StmtKind::Semi(ref expr, _) = stmt.node {
604 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
605 if args.len() == 1 && method.ident.name == "collect" && match_trait_method(cx, expr, &paths::ITERATOR) {
610 "you are collect()ing an iterator and throwing away the result. \
611 Consider using an explicit for loop to exhaust the iterator",
619 enum NeverLoopResult {
620 // A break/return always get triggered but not necessarily for the main loop.
622 // A continue may occur for the main loop.
627 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
629 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
630 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
634 // Combine two results for parts that are called in order.
635 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
637 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
638 NeverLoopResult::Otherwise => second,
642 // Combine two results where both parts are called but not necessarily in order.
643 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
644 match (left, right) {
645 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
646 NeverLoopResult::MayContinueMainLoop
648 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
649 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
653 // Combine two results where only one of the part may have been executed.
654 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
656 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
657 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
658 NeverLoopResult::MayContinueMainLoop
660 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
664 fn never_loop_block(block: &Block, main_loop_id: NodeId) -> NeverLoopResult {
665 let stmts = block.stmts.iter().map(stmt_to_expr);
666 let expr = once(block.expr.as_ref().map(|p| &**p));
667 let mut iter = stmts.chain(expr).filter_map(|e| e);
668 never_loop_expr_seq(&mut iter, main_loop_id)
671 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
673 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
674 StmtKind::Decl(ref d, ..) => decl_to_expr(d),
678 fn decl_to_expr(decl: &Decl) -> Option<&Expr> {
680 DeclKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
685 fn never_loop_expr(expr: &Expr, main_loop_id: NodeId) -> NeverLoopResult {
688 | ExprKind::Unary(_, ref e)
689 | ExprKind::Cast(ref e, _)
690 | ExprKind::Type(ref e, _)
691 | ExprKind::Field(ref e, _)
692 | ExprKind::AddrOf(_, ref e)
693 | ExprKind::Struct(_, _, Some(ref e))
694 | ExprKind::Repeat(ref e, _) => never_loop_expr(e, main_loop_id),
695 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
696 never_loop_expr_all(&mut es.iter(), main_loop_id)
698 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
699 ExprKind::Binary(_, ref e1, ref e2)
700 | ExprKind::Assign(ref e1, ref e2)
701 | ExprKind::AssignOp(_, ref e1, ref e2)
702 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
703 ExprKind::If(ref e, ref e2, ref e3) => {
704 let e1 = never_loop_expr(e, main_loop_id);
705 let e2 = never_loop_expr(e2, main_loop_id);
708 .map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
709 combine_seq(e1, combine_branches(e2, e3))
711 ExprKind::Loop(ref b, _, _) => {
712 // Break can come from the inner loop so remove them.
713 absorb_break(&never_loop_block(b, main_loop_id))
715 ExprKind::While(ref e, ref b, _) => {
716 let e = never_loop_expr(e, main_loop_id);
717 let result = never_loop_block(b, main_loop_id);
718 // Break can come from the inner loop so remove them.
719 combine_seq(e, absorb_break(&result))
721 ExprKind::Match(ref e, ref arms, _) => {
722 let e = never_loop_expr(e, main_loop_id);
726 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
730 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
731 ExprKind::Continue(d) => {
734 .expect("target id can only be missing in the presence of compilation errors");
735 if id == main_loop_id {
736 NeverLoopResult::MayContinueMainLoop
738 NeverLoopResult::AlwaysBreak
741 ExprKind::Break(_, _) => NeverLoopResult::AlwaysBreak,
742 ExprKind::Ret(ref e) => {
743 if let Some(ref e) = *e {
744 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
746 NeverLoopResult::AlwaysBreak
749 ExprKind::Struct(_, _, None)
751 | ExprKind::Closure(_, _, _, _, _)
752 | ExprKind::InlineAsm(_, _, _)
754 | ExprKind::Lit(_) => NeverLoopResult::Otherwise,
758 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
759 es.map(|e| never_loop_expr(e, main_loop_id))
760 .fold(NeverLoopResult::Otherwise, combine_seq)
763 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
764 es.map(|e| never_loop_expr(e, main_loop_id))
765 .fold(NeverLoopResult::Otherwise, combine_both)
768 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
769 e.map(|e| never_loop_expr(e, main_loop_id))
770 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
773 fn check_for_loop<'a, 'tcx>(
774 cx: &LateContext<'a, 'tcx>,
780 check_for_loop_range(cx, pat, arg, body, expr);
781 check_for_loop_reverse_range(cx, arg, expr);
782 check_for_loop_arg(cx, pat, arg, expr);
783 check_for_loop_explicit_counter(cx, arg, body, expr);
784 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
785 check_for_mut_range_bound(cx, arg, body);
786 detect_manual_memcpy(cx, pat, arg, body, expr);
789 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> bool {
791 if let ExprKind::Path(ref qpath) = expr.node;
792 if let QPath::Resolved(None, ref path) = *qpath;
793 if path.segments.len() == 1;
794 if let Def::Local(local_id) = cx.tables.qpath_def(qpath, expr.hir_id);
811 fn negative(s: String) -> Self {
812 Self { value: s, negate: true }
815 fn positive(s: String) -> Self {
823 struct FixedOffsetVar {
828 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
829 let is_slice = match ty.sty {
830 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
831 ty::Slice(..) | ty::Array(..) => true,
835 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
838 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> Option<FixedOffsetVar> {
839 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: ast::NodeId) -> Option<String> {
841 ExprKind::Lit(ref l) => match l.node {
842 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
845 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
850 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
851 let ty = cx.tables.expr_ty(seqexpr);
852 if !is_slice_like(cx, ty) {
856 let offset = match idx.node {
857 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
859 let offset_opt = if same_var(cx, lhs, var) {
860 extract_offset(cx, rhs, var)
861 } else if same_var(cx, rhs, var) {
862 extract_offset(cx, lhs, var)
867 offset_opt.map(Offset::positive)
869 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
872 ExprKind::Path(..) => {
873 if same_var(cx, idx, var) {
874 Some(Offset::positive("0".into()))
882 offset.map(|o| FixedOffsetVar {
883 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
891 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
892 cx: &LateContext<'a, 'tcx>,
895 ) -> Option<FixedOffsetVar> {
897 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
898 if method.ident.name == "clone";
900 if let Some(arg) = args.get(0);
902 return get_fixed_offset_var(cx, arg, var);
906 get_fixed_offset_var(cx, expr, var)
909 fn get_indexed_assignments<'a, 'tcx>(
910 cx: &LateContext<'a, 'tcx>,
913 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
914 fn get_assignment<'a, 'tcx>(
915 cx: &LateContext<'a, 'tcx>,
918 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
919 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
921 get_fixed_offset_var(cx, lhs, var),
922 fetch_cloned_fixed_offset_var(cx, rhs, var),
924 (Some(offset_left), Some(offset_right)) => {
925 // Source and destination must be different
926 if offset_left.var_name == offset_right.var_name {
929 Some((offset_left, offset_right))
939 if let ExprKind::Block(ref b, _) = body.node {
941 ref stmts, ref expr, ..
946 .map(|stmt| match stmt.node {
947 StmtKind::Decl(..) => None,
948 StmtKind::Expr(ref e, _node_id) | StmtKind::Semi(ref e, _node_id) => Some(get_assignment(cx, e, var)),
950 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
952 .collect::<Option<Vec<_>>>()
953 .unwrap_or_else(|| vec![])
955 get_assignment(cx, body, var).into_iter().collect()
959 /// Check for for loops that sequentially copy items from one slice-like
960 /// object to another.
961 fn detect_manual_memcpy<'a, 'tcx>(
962 cx: &LateContext<'a, 'tcx>,
968 if let Some(higher::Range {
972 }) = higher::range(cx, arg)
974 // the var must be a single name
975 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
976 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
977 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
978 ("0", _, "0", _) => "".into(),
979 ("0", _, x, false) | (x, false, "0", false) => x.into(),
980 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
981 (x, false, y, false) => format!("({} + {})", x, y),
982 (x, false, y, true) => {
986 format!("({} - {})", x, y)
989 (x, true, y, false) => {
993 format!("({} - {})", y, x)
996 (x, true, y, true) => format!("-({} + {})", x, y),
1000 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
1001 if let Some(end) = *end {
1003 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
1004 if method.ident.name == "len";
1005 if len_args.len() == 1;
1006 if let Some(arg) = len_args.get(0);
1007 if snippet(cx, arg.span, "??") == var_name;
1009 return if offset.negate {
1010 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
1017 let end_str = match limits {
1018 ast::RangeLimits::Closed => {
1019 let end = sugg::Sugg::hir(cx, end, "<count>");
1020 format!("{}", end + sugg::ONE)
1022 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1025 print_sum(&Offset::positive(end_str), &offset)
1031 // The only statements in the for loops can be indexed assignments from
1032 // indexed retrievals.
1033 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1035 let big_sugg = manual_copies
1037 .map(|(dst_var, src_var)| {
1038 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1039 let dst_offset = print_sum(&start_str, &dst_var.offset);
1040 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1041 let src_offset = print_sum(&start_str, &src_var.offset);
1042 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1043 let dst = if dst_offset == "" && dst_limit == "" {
1046 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1050 "{}.clone_from_slice(&{}[{}..{}])",
1051 dst, src_var.var_name, src_offset, src_limit
1056 if !big_sugg.is_empty() {
1061 "it looks like you're manually copying between slices",
1062 "try replacing the loop by",
1064 Applicability::Unspecified,
1071 /// Check for looping over a range and then indexing a sequence with it.
1072 /// The iteratee must be a range literal.
1073 fn check_for_loop_range<'a, 'tcx>(
1074 cx: &LateContext<'a, 'tcx>,
1080 if in_macro(expr.span) {
1084 if let Some(higher::Range {
1088 }) = higher::range(cx, arg)
1090 // the var must be a single name
1091 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1092 let mut visitor = VarVisitor {
1095 indexed_mut: FxHashSet::default(),
1096 indexed_indirectly: FxHashMap::default(),
1097 indexed_directly: FxHashMap::default(),
1098 referenced: FxHashSet::default(),
1100 prefer_mutable: false,
1102 walk_expr(&mut visitor, body);
1104 // linting condition: we only indexed one variable, and indexed it directly
1105 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1106 let (indexed, (indexed_extent, indexed_ty)) = visitor
1110 .expect("already checked that we have exactly 1 element");
1112 // ensure that the indexed variable was declared before the loop, see #601
1113 if let Some(indexed_extent) = indexed_extent {
1114 let parent_id = cx.tcx.hir.get_parent(expr.id);
1115 let parent_def_id = cx.tcx.hir.local_def_id(parent_id);
1116 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1117 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1118 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1123 // don't lint if the container that is indexed into is also used without
1125 if visitor.referenced.contains(&indexed) {
1129 let starts_at_zero = is_integer_literal(start, 0);
1131 let skip = if starts_at_zero {
1134 format!(".skip({})", snippet(cx, start.span, ".."))
1137 let mut end_is_start_plus_val = false;
1139 let take = if let Some(end) = *end {
1140 let mut take_expr = end;
1142 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1143 if let BinOpKind::Add = op.node {
1144 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1145 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1147 if start_equal_left {
1149 } else if start_equal_right {
1153 end_is_start_plus_val = start_equal_left | start_equal_right;
1157 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1161 ast::RangeLimits::Closed => {
1162 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1163 format!(".take({})", take_expr + sugg::ONE)
1165 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1172 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1173 ("mut ", "iter_mut")
1178 let take_is_empty = take.is_empty();
1179 let mut method_1 = take;
1180 let mut method_2 = skip;
1182 if end_is_start_plus_val {
1183 mem::swap(&mut method_1, &mut method_2);
1186 if visitor.nonindex {
1189 NEEDLESS_RANGE_LOOP,
1191 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1195 "consider using an iterator".to_string(),
1197 (pat.span, format!("({}, <item>)", ident.name)),
1200 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1207 let repl = if starts_at_zero && take_is_empty {
1208 format!("&{}{}", ref_mut, indexed)
1210 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1215 NEEDLESS_RANGE_LOOP,
1218 "the loop variable `{}` is only used to index `{}`.",
1224 "consider using an iterator".to_string(),
1225 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1235 fn is_len_call(expr: &Expr, var: Name) -> bool {
1237 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1238 if len_args.len() == 1;
1239 if method.ident.name == "len";
1240 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1241 if path.segments.len() == 1;
1242 if path.segments[0].ident.name == var;
1251 fn is_end_eq_array_len(cx: &LateContext<'_, '_>, end: &Expr, limits: ast::RangeLimits, indexed_ty: Ty<'_>) -> bool {
1253 if let ExprKind::Lit(ref lit) = end.node;
1254 if let ast::LitKind::Int(end_int, _) = lit.node;
1255 if let ty::TyKind::Array(_, arr_len_const) = indexed_ty.sty;
1256 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1258 return match limits {
1259 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1260 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1268 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1269 // if this for loop is iterating over a two-sided range...
1270 if let Some(higher::Range {
1274 }) = higher::range(cx, arg)
1276 // ...and both sides are compile-time constant integers...
1277 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1278 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1279 // ...and the start index is greater than the end index,
1280 // this loop will never run. This is often confusing for developers
1281 // who think that this will iterate from the larger value to the
1283 let ty = cx.tables.expr_ty(start);
1284 let (sup, eq) = match (start_idx, end_idx) {
1285 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1287 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1288 ty::Uint(_) => start_idx > end_idx,
1291 start_idx == end_idx,
1293 _ => (false, false),
1297 let start_snippet = snippet(cx, start.span, "_");
1298 let end_snippet = snippet(cx, end.span, "_");
1299 let dots = if limits == ast::RangeLimits::Closed {
1309 "this range is empty so this for loop will never run",
1311 db.span_suggestion_with_applicability(
1313 "consider using the following if you are attempting to iterate over this \
1316 "({end}{dots}{start}).rev()",
1319 start = start_snippet
1321 Applicability::MaybeIncorrect,
1325 } else if eq && limits != ast::RangeLimits::Closed {
1326 // if they are equal, it's also problematic - this loop
1332 "this range is empty so this for loop will never run",
1340 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1341 let mut applicability = Applicability::MachineApplicable;
1342 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1343 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1348 "it is more concise to loop over references to containers instead of using explicit \
1350 "to write this more concisely, try",
1351 format!("&{}{}", muta, object),
1356 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1357 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1358 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1359 // just the receiver, no arguments
1360 if args.len() == 1 {
1361 let method_name = &*method.ident.as_str();
1362 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1363 if method_name == "iter" || method_name == "iter_mut" {
1364 if is_ref_iterable_type(cx, &args[0]) {
1365 lint_iter_method(cx, args, arg, method_name);
1367 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1368 let def_id = cx.tables.type_dependent_defs()[arg.hir_id].def_id();
1369 let substs = cx.tables.node_substs(arg.hir_id);
1370 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1372 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1373 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1374 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1375 match cx.tables.expr_ty(&args[0]).sty {
1376 // If the length is greater than 32 no traits are implemented for array and
1377 // therefore we cannot use `&`.
1378 ty::TyKind::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1379 _ => lint_iter_method(cx, args, arg, method_name),
1382 let mut applicability = Applicability::MachineApplicable;
1383 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1386 EXPLICIT_INTO_ITER_LOOP,
1388 "it is more concise to loop over containers instead of using explicit \
1389 iteration methods`",
1390 "to write this more concisely, try",
1395 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1400 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1401 probably not what you want",
1403 next_loop_linted = true;
1407 if !next_loop_linted {
1408 check_arg_type(cx, pat, arg);
1412 /// Check for `for` loops over `Option`s and `Results`
1413 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1414 let ty = cx.tables.expr_ty(arg);
1415 if match_type(cx, ty, &paths::OPTION) {
1418 FOR_LOOP_OVER_OPTION,
1421 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1422 `if let` statement.",
1423 snippet(cx, arg.span, "_")
1426 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1427 snippet(cx, pat.span, "_"),
1428 snippet(cx, arg.span, "_")
1431 } else if match_type(cx, ty, &paths::RESULT) {
1434 FOR_LOOP_OVER_RESULT,
1437 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1438 `if let` statement.",
1439 snippet(cx, arg.span, "_")
1442 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1443 snippet(cx, pat.span, "_"),
1444 snippet(cx, arg.span, "_")
1450 fn check_for_loop_explicit_counter<'a, 'tcx>(
1451 cx: &LateContext<'a, 'tcx>,
1456 // Look for variables that are incremented once per loop iteration.
1457 let mut visitor = IncrementVisitor {
1459 states: FxHashMap::default(),
1463 walk_expr(&mut visitor, body);
1465 // For each candidate, check the parent block to see if
1466 // it's initialized to zero at the start of the loop.
1467 let map = &cx.tcx.hir;
1468 let parent_scope = map
1469 .get_enclosing_scope(expr.id)
1470 .and_then(|id| map.get_enclosing_scope(id));
1471 if let Some(parent_id) = parent_scope {
1472 if let Node::Block(block) = map.get(parent_id) {
1473 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1474 let mut visitor2 = InitializeVisitor {
1478 state: VarState::IncrOnce,
1483 walk_block(&mut visitor2, block);
1485 if visitor2.state == VarState::Warn {
1486 if let Some(name) = visitor2.name {
1489 EXPLICIT_COUNTER_LOOP,
1492 "the variable `{0}` is used as a loop counter. Consider using `for ({0}, \
1493 item) in {1}.enumerate()` or similar iterators",
1495 snippet(cx, arg.span, "_")
1505 /// Check for the `FOR_KV_MAP` lint.
1506 fn check_for_loop_over_map_kv<'a, 'tcx>(
1507 cx: &LateContext<'a, 'tcx>,
1513 let pat_span = pat.span;
1515 if let PatKind::Tuple(ref pat, _) = pat.node {
1517 let arg_span = arg.span;
1518 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1519 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1520 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1521 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1526 let mutbl = match mutbl {
1528 MutMutable => "_mut",
1530 let arg = match arg.node {
1531 ExprKind::AddrOf(_, ref expr) => &**expr,
1535 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1540 &format!("you seem to want to iterate on a map's {}s", kind),
1542 let map = sugg::Sugg::hir(cx, arg, "map");
1545 "use the corresponding method".into(),
1547 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1548 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1558 struct MutatePairDelegate {
1559 node_id_low: Option<NodeId>,
1560 node_id_high: Option<NodeId>,
1561 span_low: Option<Span>,
1562 span_high: Option<Span>,
1565 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1566 fn consume(&mut self, _: NodeId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1568 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1570 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1572 fn borrow(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1573 if let ty::BorrowKind::MutBorrow = bk {
1574 if let Categorization::Local(id) = cmt.cat {
1575 if Some(id) == self.node_id_low {
1576 self.span_low = Some(sp)
1578 if Some(id) == self.node_id_high {
1579 self.span_high = Some(sp)
1585 fn mutate(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1586 if let Categorization::Local(id) = cmt.cat {
1587 if Some(id) == self.node_id_low {
1588 self.span_low = Some(sp)
1590 if Some(id) == self.node_id_high {
1591 self.span_high = Some(sp)
1596 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1599 impl<'tcx> MutatePairDelegate {
1600 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1601 (self.span_low, self.span_high)
1605 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1606 if let Some(higher::Range {
1610 }) = higher::range(cx, arg)
1612 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1613 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1614 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1615 mut_warn_with_span(cx, span_low);
1616 mut_warn_with_span(cx, span_high);
1621 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1622 if let Some(sp) = span {
1627 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1632 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<NodeId> {
1634 if let ExprKind::Path(ref qpath) = bound.node;
1635 if let QPath::Resolved(None, _) = *qpath;
1637 let def = cx.tables.qpath_def(qpath, bound.hir_id);
1638 if let Def::Local(node_id) = def {
1639 let node_str = cx.tcx.hir.get(node_id);
1641 if let Node::Binding(pat) = node_str;
1642 if let PatKind::Binding(bind_ann, _, _, _) = pat.node;
1643 if let BindingAnnotation::Mutable = bind_ann;
1645 return Some(node_id);
1654 fn check_for_mutation(
1655 cx: &LateContext<'_, '_>,
1657 bound_ids: &[Option<NodeId>],
1658 ) -> (Option<Span>, Option<Span>) {
1659 let mut delegate = MutatePairDelegate {
1660 node_id_low: bound_ids[0],
1661 node_id_high: bound_ids[1],
1665 let def_id = def_id::DefId::local(body.hir_id.owner);
1666 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1667 ExprUseVisitor::new(&mut delegate, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).walk_expr(body);
1668 delegate.mutation_span()
1671 /// Return true if the pattern is a `PatWild` or an ident prefixed with `'_'`.
1672 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1674 PatKind::Wild => true,
1675 PatKind::Binding(_, _, ident, None) if ident.as_str().starts_with('_') => {
1676 let mut visitor = UsedVisitor {
1680 walk_expr(&mut visitor, body);
1687 struct UsedVisitor {
1688 var: ast::Name, // var to look for
1689 used: bool, // has the var been used otherwise?
1692 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1693 fn visit_expr(&mut self, expr: &'tcx Expr) {
1694 if match_var(expr, self.var) {
1697 walk_expr(self, expr);
1701 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1702 NestedVisitorMap::None
1706 struct LocalUsedVisitor<'a, 'tcx: 'a> {
1707 cx: &'a LateContext<'a, 'tcx>,
1712 impl<'a, 'tcx: 'a> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1713 fn visit_expr(&mut self, expr: &'tcx Expr) {
1714 if same_var(self.cx, expr, self.local) {
1717 walk_expr(self, expr);
1721 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1722 NestedVisitorMap::None
1726 struct VarVisitor<'a, 'tcx: 'a> {
1727 /// context reference
1728 cx: &'a LateContext<'a, 'tcx>,
1729 /// var name to look for as index
1731 /// indexed variables that are used mutably
1732 indexed_mut: FxHashSet<Name>,
1733 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1734 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1735 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1736 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1737 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1738 /// Any names that are used outside an index operation.
1739 /// Used to detect things like `&mut vec` used together with `vec[i]`
1740 referenced: FxHashSet<Name>,
1741 /// has the loop variable been used in expressions other than the index of
1744 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1745 /// takes `&mut self`
1746 prefer_mutable: bool,
1749 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1750 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1752 // the indexed container is referenced by a name
1753 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1754 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1755 if seqvar.segments.len() == 1;
1757 let index_used_directly = same_var(self.cx, idx, self.var);
1758 let indexed_indirectly = {
1759 let mut used_visitor = LocalUsedVisitor {
1764 walk_expr(&mut used_visitor, idx);
1768 if indexed_indirectly || index_used_directly {
1769 if self.prefer_mutable {
1770 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1772 let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
1774 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
1775 let hir_id = self.cx.tcx.hir.node_to_hir_id(node_id);
1777 let parent_id = self.cx.tcx.hir.get_parent(expr.id);
1778 let parent_def_id = self.cx.tcx.hir.local_def_id(parent_id);
1779 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1780 if indexed_indirectly {
1781 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1783 if index_used_directly {
1784 self.indexed_directly.insert(
1785 seqvar.segments[0].ident.name,
1786 (Some(extent), self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1789 return false; // no need to walk further *on the variable*
1791 Def::Static(..) | Def::Const(..) => {
1792 if indexed_indirectly {
1793 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1795 if index_used_directly {
1796 self.indexed_directly.insert(
1797 seqvar.segments[0].ident.name,
1798 (None, self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1801 return false; // no need to walk further *on the variable*
1812 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1813 fn visit_expr(&mut self, expr: &'tcx Expr) {
1816 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1817 if (meth.ident.name == "index" && match_trait_method(self.cx, expr, &paths::INDEX))
1818 || (meth.ident.name == "index_mut" && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1819 if !self.check(&args[1], &args[0], expr);
1825 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1826 if !self.check(idx, seqexpr, expr);
1831 // directly using a variable
1832 if let ExprKind::Path(ref qpath) = expr.node;
1833 if let QPath::Resolved(None, ref path) = *qpath;
1834 if path.segments.len() == 1;
1835 if let Def::Local(local_id) = self.cx.tables.qpath_def(qpath, expr.hir_id);
1837 if local_id == self.var {
1838 // we are not indexing anything, record that
1839 self.nonindex = true;
1841 // not the correct variable, but still a variable
1842 self.referenced.insert(path.segments[0].ident.name);
1846 let old = self.prefer_mutable;
1848 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1849 self.prefer_mutable = true;
1850 self.visit_expr(lhs);
1851 self.prefer_mutable = false;
1852 self.visit_expr(rhs);
1854 ExprKind::AddrOf(mutbl, ref expr) => {
1855 if mutbl == MutMutable {
1856 self.prefer_mutable = true;
1858 self.visit_expr(expr);
1860 ExprKind::Call(ref f, ref args) => {
1863 let ty = self.cx.tables.expr_ty_adjusted(expr);
1864 self.prefer_mutable = false;
1865 if let ty::Ref(_, _, mutbl) = ty.sty {
1866 if mutbl == MutMutable {
1867 self.prefer_mutable = true;
1870 self.visit_expr(expr);
1873 ExprKind::MethodCall(_, _, ref args) => {
1874 let def_id = self.cx.tables.type_dependent_defs()[expr.hir_id].def_id();
1875 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1876 self.prefer_mutable = false;
1877 if let ty::Ref(_, _, mutbl) = ty.sty {
1878 if mutbl == MutMutable {
1879 self.prefer_mutable = true;
1882 self.visit_expr(expr);
1885 _ => walk_expr(self, expr),
1887 self.prefer_mutable = old;
1889 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1890 NestedVisitorMap::None
1894 fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1895 let def_id = match var_def_id(cx, iter_expr) {
1897 None => return false,
1899 let mut visitor = VarUsedAfterLoopVisitor {
1902 iter_expr_id: iter_expr.id,
1903 past_while_let: false,
1904 var_used_after_while_let: false,
1906 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1907 walk_block(&mut visitor, enclosing_block);
1909 visitor.var_used_after_while_let
1912 struct VarUsedAfterLoopVisitor<'a, 'tcx: 'a> {
1913 cx: &'a LateContext<'a, 'tcx>,
1915 iter_expr_id: NodeId,
1916 past_while_let: bool,
1917 var_used_after_while_let: bool,
1920 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1921 fn visit_expr(&mut self, expr: &'tcx Expr) {
1922 if self.past_while_let {
1923 if Some(self.def_id) == var_def_id(self.cx, expr) {
1924 self.var_used_after_while_let = true;
1926 } else if self.iter_expr_id == expr.id {
1927 self.past_while_let = true;
1929 walk_expr(self, expr);
1931 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1932 NestedVisitorMap::None
1936 /// Return true if the type of expr is one that provides `IntoIterator` impls
1937 /// for `&T` and `&mut T`, such as `Vec`.
1939 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1940 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1941 // will allow further borrows afterwards
1942 let ty = cx.tables.expr_ty(e);
1943 is_iterable_array(ty, cx) ||
1944 match_type(cx, ty, &paths::VEC) ||
1945 match_type(cx, ty, &paths::LINKED_LIST) ||
1946 match_type(cx, ty, &paths::HASHMAP) ||
1947 match_type(cx, ty, &paths::HASHSET) ||
1948 match_type(cx, ty, &paths::VEC_DEQUE) ||
1949 match_type(cx, ty, &paths::BINARY_HEAP) ||
1950 match_type(cx, ty, &paths::BTREEMAP) ||
1951 match_type(cx, ty, &paths::BTREESET)
1954 fn is_iterable_array(ty: Ty<'_>, cx: &LateContext<'_, '_>) -> bool {
1955 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1957 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1962 /// If a block begins with a statement (possibly a `let` binding) and has an
1963 /// expression, return it.
1964 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1965 if block.stmts.is_empty() {
1968 if let StmtKind::Decl(ref decl, _) = block.stmts[0].node {
1969 if let DeclKind::Local(ref local) = decl.node {
1970 if let Some(ref expr) = local.init {
1983 /// If a block begins with an expression (with or without semicolon), return it.
1984 fn extract_first_expr(block: &Block) -> Option<&Expr> {
1986 Some(ref expr) if block.stmts.is_empty() => Some(expr),
1987 None if !block.stmts.is_empty() => match block.stmts[0].node {
1988 StmtKind::Expr(ref expr, _) | StmtKind::Semi(ref expr, _) => Some(expr),
1989 StmtKind::Decl(..) => None,
1995 /// Return true if expr contains a single break expr without destination label
1997 /// passed expression. The expression may be within a block.
1998 fn is_simple_break_expr(expr: &Expr) -> bool {
2000 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2001 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2002 Some(subexpr) => is_simple_break_expr(subexpr),
2009 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2010 // incremented exactly once in the loop body, and initialized to zero
2011 // at the start of the loop.
2012 #[derive(PartialEq)]
2014 Initial, // Not examined yet
2015 IncrOnce, // Incremented exactly once, may be a loop counter
2016 Declared, // Declared but not (yet) initialized to zero
2021 /// Scan a for loop for variables that are incremented exactly once.
2022 struct IncrementVisitor<'a, 'tcx: 'a> {
2023 cx: &'a LateContext<'a, 'tcx>, // context reference
2024 states: FxHashMap<NodeId, VarState>, // incremented variables
2025 depth: u32, // depth of conditional expressions
2029 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2030 fn visit_expr(&mut self, expr: &'tcx Expr) {
2035 // If node is a variable
2036 if let Some(def_id) = var_def_id(self.cx, expr) {
2037 if let Some(parent) = get_parent_expr(self.cx, expr) {
2038 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2041 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2042 if lhs.id == expr.id {
2043 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2044 *state = match *state {
2045 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2046 _ => VarState::DontWarn,
2049 // Assigned some other value
2050 *state = VarState::DontWarn;
2054 ExprKind::Assign(ref lhs, _) if lhs.id == expr.id => *state = VarState::DontWarn,
2055 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2059 } else if is_loop(expr) || is_conditional(expr) {
2061 walk_expr(self, expr);
2064 } else if let ExprKind::Continue(_) = expr.node {
2068 walk_expr(self, expr);
2070 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2071 NestedVisitorMap::None
2075 /// Check whether a variable is initialized to zero at the start of a loop.
2076 struct InitializeVisitor<'a, 'tcx: 'a> {
2077 cx: &'a LateContext<'a, 'tcx>, // context reference
2078 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2082 depth: u32, // depth of conditional expressions
2086 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2087 fn visit_decl(&mut self, decl: &'tcx Decl) {
2088 // Look for declarations of the variable
2089 if let DeclKind::Local(ref local) = decl.node {
2090 if local.pat.id == self.var_id {
2091 if let PatKind::Binding(_, _, ident, _) = local.pat.node {
2092 self.name = Some(ident.name);
2094 self.state = if let Some(ref init) = local.init {
2095 if is_integer_literal(init, 0) {
2106 walk_decl(self, decl);
2109 fn visit_expr(&mut self, expr: &'tcx Expr) {
2110 if self.state == VarState::DontWarn {
2113 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2114 self.past_loop = true;
2117 // No need to visit expressions before the variable is
2119 if self.state == VarState::IncrOnce {
2123 // If node is the desired variable, see how it's used
2124 if var_def_id(self.cx, expr) == Some(self.var_id) {
2125 if let Some(parent) = get_parent_expr(self.cx, expr) {
2127 ExprKind::AssignOp(_, ref lhs, _) if lhs.id == expr.id => {
2128 self.state = VarState::DontWarn;
2130 ExprKind::Assign(ref lhs, ref rhs) if lhs.id == expr.id => {
2131 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2137 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2143 self.state = VarState::DontWarn;
2146 } else if !self.past_loop && is_loop(expr) {
2147 self.state = VarState::DontWarn;
2149 } else if is_conditional(expr) {
2151 walk_expr(self, expr);
2155 walk_expr(self, expr);
2157 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2158 NestedVisitorMap::None
2162 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<NodeId> {
2163 if let ExprKind::Path(ref qpath) = expr.node {
2164 let path_res = cx.tables.qpath_def(qpath, expr.hir_id);
2165 if let Def::Local(node_id) = path_res {
2166 return Some(node_id);
2172 fn is_loop(expr: &Expr) -> bool {
2174 ExprKind::Loop(..) | ExprKind::While(..) => true,
2179 fn is_conditional(expr: &Expr) -> bool {
2181 ExprKind::If(..) | ExprKind::Match(..) => true,
2186 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2188 if let Some(loop_block) = get_enclosing_block(cx, match_expr.id);
2189 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(loop_block.id));
2191 return is_loop_nested(cx, loop_expr, iter_expr)
2197 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2198 let mut id = loop_expr.id;
2199 let iter_name = if let Some(name) = path_name(iter_expr) {
2205 let parent = cx.tcx.hir.get_parent_node(id);
2209 match cx.tcx.hir.find(parent) {
2210 Some(Node::Expr(expr)) => match expr.node {
2211 ExprKind::Loop(..) | ExprKind::While(..) => {
2216 Some(Node::Block(block)) => {
2217 let mut block_visitor = LoopNestVisitor {
2219 iterator: iter_name,
2222 walk_block(&mut block_visitor, block);
2223 if block_visitor.nesting == RuledOut {
2227 Some(Node::Stmt(_)) => (),
2236 #[derive(PartialEq, Eq)]
2238 Unknown, // no nesting detected yet
2239 RuledOut, // the iterator is initialized or assigned within scope
2240 LookFurther, // no nesting detected, no further walk required
2243 use self::Nesting::{LookFurther, RuledOut, Unknown};
2245 struct LoopNestVisitor {
2251 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2252 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2253 if stmt.node.id() == self.id {
2254 self.nesting = LookFurther;
2255 } else if self.nesting == Unknown {
2256 walk_stmt(self, stmt);
2260 fn visit_expr(&mut self, expr: &'tcx Expr) {
2261 if self.nesting != Unknown {
2264 if expr.id == self.id {
2265 self.nesting = LookFurther;
2269 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2270 if match_var(path, self.iterator) {
2271 self.nesting = RuledOut;
2274 _ => walk_expr(self, expr),
2278 fn visit_pat(&mut self, pat: &'tcx Pat) {
2279 if self.nesting != Unknown {
2282 if let PatKind::Binding(_, _, span_name, _) = pat.node {
2283 if self.iterator == span_name.name {
2284 self.nesting = RuledOut;
2291 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2292 NestedVisitorMap::None
2296 fn path_name(e: &Expr) -> Option<Name> {
2297 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2298 let segments = &path.segments;
2299 if segments.len() == 1 {
2300 return Some(segments[0].ident.name);
2306 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2307 if constant(cx, cx.tables, cond).is_some() {
2308 // A pure constant condition (e.g. while false) is not linted.
2312 let mut var_visitor = VarCollectorVisitor {
2314 ids: FxHashSet::default(),
2315 def_ids: FxHashMap::default(),
2318 var_visitor.visit_expr(cond);
2319 if var_visitor.skip {
2322 let used_in_condition = &var_visitor.ids;
2323 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2324 used_in_condition.is_disjoint(&used_mutably)
2328 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2329 if no_cond_variable_mutated && !mutable_static_in_cond {
2332 WHILE_IMMUTABLE_CONDITION,
2334 "Variable in the condition are not mutated in the loop body. \
2335 This either leads to an infinite or to a never running loop.",
2340 /// Collects the set of variables in an expression
2341 /// Stops analysis if a function call is found
2342 /// Note: In some cases such as `self`, there are no mutable annotation,
2343 /// All variables definition IDs are collected
2344 struct VarCollectorVisitor<'a, 'tcx: 'a> {
2345 cx: &'a LateContext<'a, 'tcx>,
2346 ids: FxHashSet<NodeId>,
2347 def_ids: FxHashMap<def_id::DefId, bool>,
2351 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2352 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2354 if let ExprKind::Path(ref qpath) = ex.node;
2355 if let QPath::Resolved(None, _) = *qpath;
2356 let def = self.cx.tables.qpath_def(qpath, ex.hir_id);
2359 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
2360 self.ids.insert(node_id);
2362 Def::Static(def_id, mutable) => {
2363 self.def_ids.insert(def_id, mutable);
2372 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2373 fn visit_expr(&mut self, ex: &'tcx Expr) {
2375 ExprKind::Path(_) => self.insert_def_id(ex),
2376 // If there is any function/method call… we just stop analysis
2377 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2379 _ => walk_expr(self, ex),
2383 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2384 NestedVisitorMap::None
2388 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2390 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2392 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2393 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2394 if chain_method.ident.name == "collect" && match_trait_method(cx, &args[0], &paths::ITERATOR);
2395 if let Some(ref generic_args) = chain_method.args;
2396 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2398 let ty = cx.tables.node_id_to_type(ty.hir_id);
2399 if match_type(cx, ty, &paths::VEC) ||
2400 match_type(cx, ty, &paths::VEC_DEQUE) ||
2401 match_type(cx, ty, &paths::BTREEMAP) ||
2402 match_type(cx, ty, &paths::HASHMAP) {
2403 if method.ident.name == "len" {
2404 let span = shorten_needless_collect_span(expr);
2405 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2406 db.span_suggestion_with_applicability(
2409 ".count()".to_string(),
2410 Applicability::MachineApplicable,
2414 if method.ident.name == "is_empty" {
2415 let span = shorten_needless_collect_span(expr);
2416 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2417 db.span_suggestion_with_applicability(
2420 ".next().is_none()".to_string(),
2421 Applicability::MachineApplicable,
2425 if method.ident.name == "contains" {
2426 let contains_arg = snippet(cx, args[1].span, "??");
2427 let span = shorten_needless_collect_span(expr);
2428 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2429 db.span_suggestion_with_applicability(
2433 ".any(|&x| x == {})",
2434 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2436 Applicability::MachineApplicable,
2445 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2447 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2448 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2450 return expr.span.with_lo(span.lo() - BytePos(1));