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 // we don't want to check expanded macros
482 if in_macro(expr.span) {
486 if let Some((pat, arg, body)) = higher::for_loop(expr) {
487 check_for_loop(cx, pat, arg, body, expr);
490 // check for never_loop
492 ExprKind::While(_, ref block, _) | ExprKind::Loop(ref block, _, _) => {
493 match never_loop_block(block, expr.id) {
494 NeverLoopResult::AlwaysBreak => {
495 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops")
497 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
503 // check for `loop { if let {} else break }` that could be `while let`
504 // (also matches an explicit "match" instead of "if let")
505 // (even if the "match" or "if let" is used for declaration)
506 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
507 // also check for empty `loop {}` statements
508 if block.stmts.is_empty() && block.expr.is_none() {
513 "empty `loop {}` detected. You may want to either use `panic!()` or add \
514 `std::thread::sleep(..);` to the loop body.",
518 // extract the expression from the first statement (if any) in a block
519 let inner_stmt_expr = extract_expr_from_first_stmt(block);
520 // or extract the first expression (if any) from the block
521 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
522 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
523 // ensure "if let" compatible match structure
525 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
527 && arms[0].pats.len() == 1
528 && arms[0].guard.is_none()
529 && arms[1].pats.len() == 1
530 && arms[1].guard.is_none()
531 && is_simple_break_expr(&arms[1].body)
533 if in_external_macro(cx.sess(), expr.span) {
537 // NOTE: we used to make build a body here instead of using
538 // ellipsis, this was removed because:
539 // 1) it was ugly with big bodies;
540 // 2) it was not indented properly;
541 // 3) it wasn’t very smart (see #675).
542 let mut applicability = Applicability::MachineApplicable;
547 "this loop could be written as a `while let` loop",
550 "while let {} = {} {{ .. }}",
551 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
552 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
563 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
564 let pat = &arms[0].pats[0].node;
566 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
567 &ExprKind::MethodCall(ref method_path, _, ref method_args),
568 ) = (pat, &match_expr.node)
570 let iter_expr = &method_args[0];
571 let lhs_constructor = last_path_segment(qpath);
572 if method_path.ident.name == "next"
573 && match_trait_method(cx, match_expr, &paths::ITERATOR)
574 && lhs_constructor.ident.name == "Some"
575 && (pat_args.is_empty()
576 || !is_refutable(cx, &pat_args[0])
577 && !is_iterator_used_after_while_let(cx, iter_expr)
578 && !is_nested(cx, expr, &method_args[0]))
580 let iterator = snippet(cx, method_args[0].span, "_");
581 let loop_var = if pat_args.is_empty() {
584 snippet(cx, pat_args[0].span, "_").into_owned()
588 WHILE_LET_ON_ITERATOR,
590 "this loop could be written as a `for` loop",
592 format!("for {} in {} {{ .. }}", loop_var, iterator),
593 Applicability::HasPlaceholders,
599 // check for while loops which conditions never change
600 if let ExprKind::While(ref cond, _, _) = expr.node {
601 check_infinite_loop(cx, cond, expr);
604 check_needless_collect(expr, cx);
607 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
608 if let StmtKind::Semi(ref expr, _) = stmt.node {
609 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
610 if args.len() == 1 && method.ident.name == "collect" && match_trait_method(cx, expr, &paths::ITERATOR) {
615 "you are collect()ing an iterator and throwing away the result. \
616 Consider using an explicit for loop to exhaust the iterator",
624 enum NeverLoopResult {
625 // A break/return always get triggered but not necessarily for the main loop.
627 // A continue may occur for the main loop.
632 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
634 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
635 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
639 // Combine two results for parts that are called in order.
640 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
642 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
643 NeverLoopResult::Otherwise => second,
647 // Combine two results where both parts are called but not necessarily in order.
648 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
649 match (left, right) {
650 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
651 NeverLoopResult::MayContinueMainLoop
653 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
654 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
658 // Combine two results where only one of the part may have been executed.
659 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
661 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
662 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
663 NeverLoopResult::MayContinueMainLoop
665 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
669 fn never_loop_block(block: &Block, main_loop_id: NodeId) -> NeverLoopResult {
670 let stmts = block.stmts.iter().map(stmt_to_expr);
671 let expr = once(block.expr.as_ref().map(|p| &**p));
672 let mut iter = stmts.chain(expr).filter_map(|e| e);
673 never_loop_expr_seq(&mut iter, main_loop_id)
676 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
678 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
679 StmtKind::Decl(ref d, ..) => decl_to_expr(d),
683 fn decl_to_expr(decl: &Decl) -> Option<&Expr> {
685 DeclKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
690 fn never_loop_expr(expr: &Expr, main_loop_id: NodeId) -> NeverLoopResult {
693 | ExprKind::Unary(_, ref e)
694 | ExprKind::Cast(ref e, _)
695 | ExprKind::Type(ref e, _)
696 | ExprKind::Field(ref e, _)
697 | ExprKind::AddrOf(_, ref e)
698 | ExprKind::Struct(_, _, Some(ref e))
699 | ExprKind::Repeat(ref e, _) => never_loop_expr(e, main_loop_id),
700 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
701 never_loop_expr_all(&mut es.iter(), main_loop_id)
703 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
704 ExprKind::Binary(_, ref e1, ref e2)
705 | ExprKind::Assign(ref e1, ref e2)
706 | ExprKind::AssignOp(_, ref e1, ref e2)
707 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
708 ExprKind::If(ref e, ref e2, ref e3) => {
709 let e1 = never_loop_expr(e, main_loop_id);
710 let e2 = never_loop_expr(e2, main_loop_id);
713 .map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
714 combine_seq(e1, combine_branches(e2, e3))
716 ExprKind::Loop(ref b, _, _) => {
717 // Break can come from the inner loop so remove them.
718 absorb_break(&never_loop_block(b, main_loop_id))
720 ExprKind::While(ref e, ref b, _) => {
721 let e = never_loop_expr(e, main_loop_id);
722 let result = never_loop_block(b, main_loop_id);
723 // Break can come from the inner loop so remove them.
724 combine_seq(e, absorb_break(&result))
726 ExprKind::Match(ref e, ref arms, _) => {
727 let e = never_loop_expr(e, main_loop_id);
731 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
735 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
736 ExprKind::Continue(d) => {
739 .expect("target id can only be missing in the presence of compilation errors");
740 if id == main_loop_id {
741 NeverLoopResult::MayContinueMainLoop
743 NeverLoopResult::AlwaysBreak
746 ExprKind::Break(_, _) => NeverLoopResult::AlwaysBreak,
747 ExprKind::Ret(ref e) => {
748 if let Some(ref e) = *e {
749 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
751 NeverLoopResult::AlwaysBreak
754 ExprKind::Struct(_, _, None)
756 | ExprKind::Closure(_, _, _, _, _)
757 | ExprKind::InlineAsm(_, _, _)
760 | ExprKind::Err => NeverLoopResult::Otherwise,
764 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
765 es.map(|e| never_loop_expr(e, main_loop_id))
766 .fold(NeverLoopResult::Otherwise, combine_seq)
769 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
770 es.map(|e| never_loop_expr(e, main_loop_id))
771 .fold(NeverLoopResult::Otherwise, combine_both)
774 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
775 e.map(|e| never_loop_expr(e, main_loop_id))
776 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
779 fn check_for_loop<'a, 'tcx>(
780 cx: &LateContext<'a, 'tcx>,
786 check_for_loop_range(cx, pat, arg, body, expr);
787 check_for_loop_reverse_range(cx, arg, expr);
788 check_for_loop_arg(cx, pat, arg, expr);
789 check_for_loop_explicit_counter(cx, arg, body, expr);
790 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
791 check_for_mut_range_bound(cx, arg, body);
792 detect_manual_memcpy(cx, pat, arg, body, expr);
795 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> bool {
797 if let ExprKind::Path(ref qpath) = expr.node;
798 if let QPath::Resolved(None, ref path) = *qpath;
799 if path.segments.len() == 1;
800 if let Def::Local(local_id) = cx.tables.qpath_def(qpath, expr.hir_id);
817 fn negative(s: String) -> Self {
818 Self { value: s, negate: true }
821 fn positive(s: String) -> Self {
829 struct FixedOffsetVar {
834 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
835 let is_slice = match ty.sty {
836 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
837 ty::Slice(..) | ty::Array(..) => true,
841 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
844 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> Option<FixedOffsetVar> {
845 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: ast::NodeId) -> Option<String> {
847 ExprKind::Lit(ref l) => match l.node {
848 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
851 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
856 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
857 let ty = cx.tables.expr_ty(seqexpr);
858 if !is_slice_like(cx, ty) {
862 let offset = match idx.node {
863 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
865 let offset_opt = if same_var(cx, lhs, var) {
866 extract_offset(cx, rhs, var)
867 } else if same_var(cx, rhs, var) {
868 extract_offset(cx, lhs, var)
873 offset_opt.map(Offset::positive)
875 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
878 ExprKind::Path(..) => {
879 if same_var(cx, idx, var) {
880 Some(Offset::positive("0".into()))
888 offset.map(|o| FixedOffsetVar {
889 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
897 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
898 cx: &LateContext<'a, 'tcx>,
901 ) -> Option<FixedOffsetVar> {
903 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
904 if method.ident.name == "clone";
906 if let Some(arg) = args.get(0);
908 return get_fixed_offset_var(cx, arg, var);
912 get_fixed_offset_var(cx, expr, var)
915 fn get_indexed_assignments<'a, 'tcx>(
916 cx: &LateContext<'a, 'tcx>,
919 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
920 fn get_assignment<'a, 'tcx>(
921 cx: &LateContext<'a, 'tcx>,
924 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
925 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
927 get_fixed_offset_var(cx, lhs, var),
928 fetch_cloned_fixed_offset_var(cx, rhs, var),
930 (Some(offset_left), Some(offset_right)) => {
931 // Source and destination must be different
932 if offset_left.var_name == offset_right.var_name {
935 Some((offset_left, offset_right))
945 if let ExprKind::Block(ref b, _) = body.node {
947 ref stmts, ref expr, ..
952 .map(|stmt| match stmt.node {
953 StmtKind::Decl(..) => None,
954 StmtKind::Expr(ref e, _node_id) | StmtKind::Semi(ref e, _node_id) => Some(get_assignment(cx, e, var)),
956 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
958 .collect::<Option<Vec<_>>>()
959 .unwrap_or_else(|| vec![])
961 get_assignment(cx, body, var).into_iter().collect()
965 /// Check for for loops that sequentially copy items from one slice-like
966 /// object to another.
967 fn detect_manual_memcpy<'a, 'tcx>(
968 cx: &LateContext<'a, 'tcx>,
974 if let Some(higher::Range {
978 }) = higher::range(cx, arg)
980 // the var must be a single name
981 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
982 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
983 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
984 ("0", _, "0", _) => "".into(),
985 ("0", _, x, false) | (x, false, "0", false) => x.into(),
986 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
987 (x, false, y, false) => format!("({} + {})", x, y),
988 (x, false, y, true) => {
992 format!("({} - {})", x, y)
995 (x, true, y, false) => {
999 format!("({} - {})", y, x)
1002 (x, true, y, true) => format!("-({} + {})", x, y),
1006 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
1007 if let Some(end) = *end {
1009 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
1010 if method.ident.name == "len";
1011 if len_args.len() == 1;
1012 if let Some(arg) = len_args.get(0);
1013 if snippet(cx, arg.span, "??") == var_name;
1015 return if offset.negate {
1016 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
1023 let end_str = match limits {
1024 ast::RangeLimits::Closed => {
1025 let end = sugg::Sugg::hir(cx, end, "<count>");
1026 format!("{}", end + sugg::ONE)
1028 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1031 print_sum(&Offset::positive(end_str), &offset)
1037 // The only statements in the for loops can be indexed assignments from
1038 // indexed retrievals.
1039 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1041 let big_sugg = manual_copies
1043 .map(|(dst_var, src_var)| {
1044 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1045 let dst_offset = print_sum(&start_str, &dst_var.offset);
1046 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1047 let src_offset = print_sum(&start_str, &src_var.offset);
1048 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1049 let dst = if dst_offset == "" && dst_limit == "" {
1052 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1056 "{}.clone_from_slice(&{}[{}..{}])",
1057 dst, src_var.var_name, src_offset, src_limit
1062 if !big_sugg.is_empty() {
1067 "it looks like you're manually copying between slices",
1068 "try replacing the loop by",
1070 Applicability::Unspecified,
1077 /// Check for looping over a range and then indexing a sequence with it.
1078 /// The iteratee must be a range literal.
1079 fn check_for_loop_range<'a, 'tcx>(
1080 cx: &LateContext<'a, 'tcx>,
1086 if in_macro(expr.span) {
1090 if let Some(higher::Range {
1094 }) = higher::range(cx, arg)
1096 // the var must be a single name
1097 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1098 let mut visitor = VarVisitor {
1101 indexed_mut: FxHashSet::default(),
1102 indexed_indirectly: FxHashMap::default(),
1103 indexed_directly: FxHashMap::default(),
1104 referenced: FxHashSet::default(),
1106 prefer_mutable: false,
1108 walk_expr(&mut visitor, body);
1110 // linting condition: we only indexed one variable, and indexed it directly
1111 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1112 let (indexed, (indexed_extent, indexed_ty)) = visitor
1116 .expect("already checked that we have exactly 1 element");
1118 // ensure that the indexed variable was declared before the loop, see #601
1119 if let Some(indexed_extent) = indexed_extent {
1120 let parent_id = cx.tcx.hir().get_parent(expr.id);
1121 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1122 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1123 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1124 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1129 // don't lint if the container that is indexed into is also used without
1131 if visitor.referenced.contains(&indexed) {
1135 let starts_at_zero = is_integer_literal(start, 0);
1137 let skip = if starts_at_zero {
1140 format!(".skip({})", snippet(cx, start.span, ".."))
1143 let mut end_is_start_plus_val = false;
1145 let take = if let Some(end) = *end {
1146 let mut take_expr = end;
1148 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1149 if let BinOpKind::Add = op.node {
1150 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1151 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1153 if start_equal_left {
1155 } else if start_equal_right {
1159 end_is_start_plus_val = start_equal_left | start_equal_right;
1163 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1167 ast::RangeLimits::Closed => {
1168 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1169 format!(".take({})", take_expr + sugg::ONE)
1171 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1178 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1179 ("mut ", "iter_mut")
1184 let take_is_empty = take.is_empty();
1185 let mut method_1 = take;
1186 let mut method_2 = skip;
1188 if end_is_start_plus_val {
1189 mem::swap(&mut method_1, &mut method_2);
1192 if visitor.nonindex {
1195 NEEDLESS_RANGE_LOOP,
1197 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1201 "consider using an iterator".to_string(),
1203 (pat.span, format!("({}, <item>)", ident.name)),
1206 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1213 let repl = if starts_at_zero && take_is_empty {
1214 format!("&{}{}", ref_mut, indexed)
1216 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1221 NEEDLESS_RANGE_LOOP,
1224 "the loop variable `{}` is only used to index `{}`.",
1230 "consider using an iterator".to_string(),
1231 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1241 fn is_len_call(expr: &Expr, var: Name) -> bool {
1243 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1244 if len_args.len() == 1;
1245 if method.ident.name == "len";
1246 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1247 if path.segments.len() == 1;
1248 if path.segments[0].ident.name == var;
1257 fn is_end_eq_array_len(cx: &LateContext<'_, '_>, end: &Expr, limits: ast::RangeLimits, indexed_ty: Ty<'_>) -> bool {
1259 if let ExprKind::Lit(ref lit) = end.node;
1260 if let ast::LitKind::Int(end_int, _) = lit.node;
1261 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1262 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1264 return match limits {
1265 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1266 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1274 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1275 // if this for loop is iterating over a two-sided range...
1276 if let Some(higher::Range {
1280 }) = higher::range(cx, arg)
1282 // ...and both sides are compile-time constant integers...
1283 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1284 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1285 // ...and the start index is greater than the end index,
1286 // this loop will never run. This is often confusing for developers
1287 // who think that this will iterate from the larger value to the
1289 let ty = cx.tables.expr_ty(start);
1290 let (sup, eq) = match (start_idx, end_idx) {
1291 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1293 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1294 ty::Uint(_) => start_idx > end_idx,
1297 start_idx == end_idx,
1299 _ => (false, false),
1303 let start_snippet = snippet(cx, start.span, "_");
1304 let end_snippet = snippet(cx, end.span, "_");
1305 let dots = if limits == ast::RangeLimits::Closed {
1315 "this range is empty so this for loop will never run",
1317 db.span_suggestion_with_applicability(
1319 "consider using the following if you are attempting to iterate over this \
1322 "({end}{dots}{start}).rev()",
1325 start = start_snippet
1327 Applicability::MaybeIncorrect,
1331 } else if eq && limits != ast::RangeLimits::Closed {
1332 // if they are equal, it's also problematic - this loop
1338 "this range is empty so this for loop will never run",
1346 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1347 let mut applicability = Applicability::MachineApplicable;
1348 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1349 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1354 "it is more concise to loop over references to containers instead of using explicit \
1356 "to write this more concisely, try",
1357 format!("&{}{}", muta, object),
1362 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1363 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1364 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1365 // just the receiver, no arguments
1366 if args.len() == 1 {
1367 let method_name = &*method.ident.as_str();
1368 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1369 if method_name == "iter" || method_name == "iter_mut" {
1370 if is_ref_iterable_type(cx, &args[0]) {
1371 lint_iter_method(cx, args, arg, method_name);
1373 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1374 let def_id = cx.tables.type_dependent_defs()[arg.hir_id].def_id();
1375 let substs = cx.tables.node_substs(arg.hir_id);
1376 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1378 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1379 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1380 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1381 match cx.tables.expr_ty(&args[0]).sty {
1382 // If the length is greater than 32 no traits are implemented for array and
1383 // therefore we cannot use `&`.
1384 ty::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1385 _ => lint_iter_method(cx, args, arg, method_name),
1388 let mut applicability = Applicability::MachineApplicable;
1389 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1392 EXPLICIT_INTO_ITER_LOOP,
1394 "it is more concise to loop over containers instead of using explicit \
1395 iteration methods`",
1396 "to write this more concisely, try",
1401 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1406 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1407 probably not what you want",
1409 next_loop_linted = true;
1413 if !next_loop_linted {
1414 check_arg_type(cx, pat, arg);
1418 /// Check for `for` loops over `Option`s and `Results`
1419 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1420 let ty = cx.tables.expr_ty(arg);
1421 if match_type(cx, ty, &paths::OPTION) {
1424 FOR_LOOP_OVER_OPTION,
1427 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1428 `if let` statement.",
1429 snippet(cx, arg.span, "_")
1432 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1433 snippet(cx, pat.span, "_"),
1434 snippet(cx, arg.span, "_")
1437 } else if match_type(cx, ty, &paths::RESULT) {
1440 FOR_LOOP_OVER_RESULT,
1443 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1444 `if let` statement.",
1445 snippet(cx, arg.span, "_")
1448 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1449 snippet(cx, pat.span, "_"),
1450 snippet(cx, arg.span, "_")
1456 fn check_for_loop_explicit_counter<'a, 'tcx>(
1457 cx: &LateContext<'a, 'tcx>,
1462 // Look for variables that are incremented once per loop iteration.
1463 let mut visitor = IncrementVisitor {
1465 states: FxHashMap::default(),
1469 walk_expr(&mut visitor, body);
1471 // For each candidate, check the parent block to see if
1472 // it's initialized to zero at the start of the loop.
1473 let map = &cx.tcx.hir();
1474 let parent_scope = map
1475 .get_enclosing_scope(expr.id)
1476 .and_then(|id| map.get_enclosing_scope(id));
1477 if let Some(parent_id) = parent_scope {
1478 if let Node::Block(block) = map.get(parent_id) {
1479 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1480 let mut visitor2 = InitializeVisitor {
1484 state: VarState::IncrOnce,
1489 walk_block(&mut visitor2, block);
1491 if visitor2.state == VarState::Warn {
1492 if let Some(name) = visitor2.name {
1495 EXPLICIT_COUNTER_LOOP,
1498 "the variable `{0}` is used as a loop counter. Consider using `for ({0}, \
1499 item) in {1}.enumerate()` or similar iterators",
1501 snippet(cx, arg.span, "_")
1511 /// Check for the `FOR_KV_MAP` lint.
1512 fn check_for_loop_over_map_kv<'a, 'tcx>(
1513 cx: &LateContext<'a, 'tcx>,
1519 let pat_span = pat.span;
1521 if let PatKind::Tuple(ref pat, _) = pat.node {
1523 let arg_span = arg.span;
1524 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1525 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1526 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1527 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1532 let mutbl = match mutbl {
1534 MutMutable => "_mut",
1536 let arg = match arg.node {
1537 ExprKind::AddrOf(_, ref expr) => &**expr,
1541 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1546 &format!("you seem to want to iterate on a map's {}s", kind),
1548 let map = sugg::Sugg::hir(cx, arg, "map");
1551 "use the corresponding method".into(),
1553 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1554 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1564 struct MutatePairDelegate {
1565 node_id_low: Option<NodeId>,
1566 node_id_high: Option<NodeId>,
1567 span_low: Option<Span>,
1568 span_high: Option<Span>,
1571 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1572 fn consume(&mut self, _: NodeId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1574 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1576 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1578 fn borrow(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1579 if let ty::BorrowKind::MutBorrow = bk {
1580 if let Categorization::Local(id) = cmt.cat {
1581 if Some(id) == self.node_id_low {
1582 self.span_low = Some(sp)
1584 if Some(id) == self.node_id_high {
1585 self.span_high = Some(sp)
1591 fn mutate(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1592 if let Categorization::Local(id) = cmt.cat {
1593 if Some(id) == self.node_id_low {
1594 self.span_low = Some(sp)
1596 if Some(id) == self.node_id_high {
1597 self.span_high = Some(sp)
1602 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1605 impl<'tcx> MutatePairDelegate {
1606 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1607 (self.span_low, self.span_high)
1611 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1612 if let Some(higher::Range {
1616 }) = higher::range(cx, arg)
1618 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1619 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1620 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1621 mut_warn_with_span(cx, span_low);
1622 mut_warn_with_span(cx, span_high);
1627 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1628 if let Some(sp) = span {
1633 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1638 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<NodeId> {
1640 if let ExprKind::Path(ref qpath) = bound.node;
1641 if let QPath::Resolved(None, _) = *qpath;
1643 let def = cx.tables.qpath_def(qpath, bound.hir_id);
1644 if let Def::Local(node_id) = def {
1645 let node_str = cx.tcx.hir().get(node_id);
1647 if let Node::Binding(pat) = node_str;
1648 if let PatKind::Binding(bind_ann, _, _, _) = pat.node;
1649 if let BindingAnnotation::Mutable = bind_ann;
1651 return Some(node_id);
1660 fn check_for_mutation(
1661 cx: &LateContext<'_, '_>,
1663 bound_ids: &[Option<NodeId>],
1664 ) -> (Option<Span>, Option<Span>) {
1665 let mut delegate = MutatePairDelegate {
1666 node_id_low: bound_ids[0],
1667 node_id_high: bound_ids[1],
1671 let def_id = def_id::DefId::local(body.hir_id.owner);
1672 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1673 ExprUseVisitor::new(&mut delegate, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).walk_expr(body);
1674 delegate.mutation_span()
1677 /// Return true if the pattern is a `PatWild` or an ident prefixed with `'_'`.
1678 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1680 PatKind::Wild => true,
1681 PatKind::Binding(_, _, ident, None) if ident.as_str().starts_with('_') => {
1682 let mut visitor = UsedVisitor {
1686 walk_expr(&mut visitor, body);
1693 struct UsedVisitor {
1694 var: ast::Name, // var to look for
1695 used: bool, // has the var been used otherwise?
1698 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1699 fn visit_expr(&mut self, expr: &'tcx Expr) {
1700 if match_var(expr, self.var) {
1703 walk_expr(self, expr);
1707 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1708 NestedVisitorMap::None
1712 struct LocalUsedVisitor<'a, 'tcx: 'a> {
1713 cx: &'a LateContext<'a, 'tcx>,
1718 impl<'a, 'tcx: 'a> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1719 fn visit_expr(&mut self, expr: &'tcx Expr) {
1720 if same_var(self.cx, expr, self.local) {
1723 walk_expr(self, expr);
1727 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1728 NestedVisitorMap::None
1732 struct VarVisitor<'a, 'tcx: 'a> {
1733 /// context reference
1734 cx: &'a LateContext<'a, 'tcx>,
1735 /// var name to look for as index
1737 /// indexed variables that are used mutably
1738 indexed_mut: FxHashSet<Name>,
1739 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1740 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1741 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1742 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1743 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1744 /// Any names that are used outside an index operation.
1745 /// Used to detect things like `&mut vec` used together with `vec[i]`
1746 referenced: FxHashSet<Name>,
1747 /// has the loop variable been used in expressions other than the index of
1750 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1751 /// takes `&mut self`
1752 prefer_mutable: bool,
1755 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1756 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1758 // the indexed container is referenced by a name
1759 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1760 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1761 if seqvar.segments.len() == 1;
1763 let index_used_directly = same_var(self.cx, idx, self.var);
1764 let indexed_indirectly = {
1765 let mut used_visitor = LocalUsedVisitor {
1770 walk_expr(&mut used_visitor, idx);
1774 if indexed_indirectly || index_used_directly {
1775 if self.prefer_mutable {
1776 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1778 let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
1780 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
1781 let hir_id = self.cx.tcx.hir().node_to_hir_id(node_id);
1783 let parent_id = self.cx.tcx.hir().get_parent(expr.id);
1784 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1785 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1786 if indexed_indirectly {
1787 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1789 if index_used_directly {
1790 self.indexed_directly.insert(
1791 seqvar.segments[0].ident.name,
1792 (Some(extent), self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1795 return false; // no need to walk further *on the variable*
1797 Def::Static(..) | Def::Const(..) => {
1798 if indexed_indirectly {
1799 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1801 if index_used_directly {
1802 self.indexed_directly.insert(
1803 seqvar.segments[0].ident.name,
1804 (None, self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1807 return false; // no need to walk further *on the variable*
1818 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1819 fn visit_expr(&mut self, expr: &'tcx Expr) {
1822 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1823 if (meth.ident.name == "index" && match_trait_method(self.cx, expr, &paths::INDEX))
1824 || (meth.ident.name == "index_mut" && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1825 if !self.check(&args[1], &args[0], expr);
1831 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1832 if !self.check(idx, seqexpr, expr);
1837 // directly using a variable
1838 if let ExprKind::Path(ref qpath) = expr.node;
1839 if let QPath::Resolved(None, ref path) = *qpath;
1840 if path.segments.len() == 1;
1841 if let Def::Local(local_id) = self.cx.tables.qpath_def(qpath, expr.hir_id);
1843 if local_id == self.var {
1844 // we are not indexing anything, record that
1845 self.nonindex = true;
1847 // not the correct variable, but still a variable
1848 self.referenced.insert(path.segments[0].ident.name);
1852 let old = self.prefer_mutable;
1854 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1855 self.prefer_mutable = true;
1856 self.visit_expr(lhs);
1857 self.prefer_mutable = false;
1858 self.visit_expr(rhs);
1860 ExprKind::AddrOf(mutbl, ref expr) => {
1861 if mutbl == MutMutable {
1862 self.prefer_mutable = true;
1864 self.visit_expr(expr);
1866 ExprKind::Call(ref f, ref args) => {
1869 let ty = self.cx.tables.expr_ty_adjusted(expr);
1870 self.prefer_mutable = false;
1871 if let ty::Ref(_, _, mutbl) = ty.sty {
1872 if mutbl == MutMutable {
1873 self.prefer_mutable = true;
1876 self.visit_expr(expr);
1879 ExprKind::MethodCall(_, _, ref args) => {
1880 let def_id = self.cx.tables.type_dependent_defs()[expr.hir_id].def_id();
1881 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1882 self.prefer_mutable = false;
1883 if let ty::Ref(_, _, mutbl) = ty.sty {
1884 if mutbl == MutMutable {
1885 self.prefer_mutable = true;
1888 self.visit_expr(expr);
1891 _ => walk_expr(self, expr),
1893 self.prefer_mutable = old;
1895 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1896 NestedVisitorMap::None
1900 fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1901 let def_id = match var_def_id(cx, iter_expr) {
1903 None => return false,
1905 let mut visitor = VarUsedAfterLoopVisitor {
1908 iter_expr_id: iter_expr.id,
1909 past_while_let: false,
1910 var_used_after_while_let: false,
1912 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1913 walk_block(&mut visitor, enclosing_block);
1915 visitor.var_used_after_while_let
1918 struct VarUsedAfterLoopVisitor<'a, 'tcx: 'a> {
1919 cx: &'a LateContext<'a, 'tcx>,
1921 iter_expr_id: NodeId,
1922 past_while_let: bool,
1923 var_used_after_while_let: bool,
1926 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1927 fn visit_expr(&mut self, expr: &'tcx Expr) {
1928 if self.past_while_let {
1929 if Some(self.def_id) == var_def_id(self.cx, expr) {
1930 self.var_used_after_while_let = true;
1932 } else if self.iter_expr_id == expr.id {
1933 self.past_while_let = true;
1935 walk_expr(self, expr);
1937 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1938 NestedVisitorMap::None
1942 /// Return true if the type of expr is one that provides `IntoIterator` impls
1943 /// for `&T` and `&mut T`, such as `Vec`.
1945 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1946 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1947 // will allow further borrows afterwards
1948 let ty = cx.tables.expr_ty(e);
1949 is_iterable_array(ty, cx) ||
1950 match_type(cx, ty, &paths::VEC) ||
1951 match_type(cx, ty, &paths::LINKED_LIST) ||
1952 match_type(cx, ty, &paths::HASHMAP) ||
1953 match_type(cx, ty, &paths::HASHSET) ||
1954 match_type(cx, ty, &paths::VEC_DEQUE) ||
1955 match_type(cx, ty, &paths::BINARY_HEAP) ||
1956 match_type(cx, ty, &paths::BTREEMAP) ||
1957 match_type(cx, ty, &paths::BTREESET)
1960 fn is_iterable_array(ty: Ty<'_>, cx: &LateContext<'_, '_>) -> bool {
1961 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1963 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1968 /// If a block begins with a statement (possibly a `let` binding) and has an
1969 /// expression, return it.
1970 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1971 if block.stmts.is_empty() {
1974 if let StmtKind::Decl(ref decl, _) = block.stmts[0].node {
1975 if let DeclKind::Local(ref local) = decl.node {
1976 if let Some(ref expr) = local.init {
1989 /// If a block begins with an expression (with or without semicolon), return it.
1990 fn extract_first_expr(block: &Block) -> Option<&Expr> {
1992 Some(ref expr) if block.stmts.is_empty() => Some(expr),
1993 None if !block.stmts.is_empty() => match block.stmts[0].node {
1994 StmtKind::Expr(ref expr, _) | StmtKind::Semi(ref expr, _) => Some(expr),
1995 StmtKind::Decl(..) => None,
2001 /// Return true if expr contains a single break expr without destination label
2003 /// passed expression. The expression may be within a block.
2004 fn is_simple_break_expr(expr: &Expr) -> bool {
2006 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2007 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2008 Some(subexpr) => is_simple_break_expr(subexpr),
2015 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2016 // incremented exactly once in the loop body, and initialized to zero
2017 // at the start of the loop.
2018 #[derive(PartialEq)]
2020 Initial, // Not examined yet
2021 IncrOnce, // Incremented exactly once, may be a loop counter
2022 Declared, // Declared but not (yet) initialized to zero
2027 /// Scan a for loop for variables that are incremented exactly once.
2028 struct IncrementVisitor<'a, 'tcx: 'a> {
2029 cx: &'a LateContext<'a, 'tcx>, // context reference
2030 states: FxHashMap<NodeId, VarState>, // incremented variables
2031 depth: u32, // depth of conditional expressions
2035 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2036 fn visit_expr(&mut self, expr: &'tcx Expr) {
2041 // If node is a variable
2042 if let Some(def_id) = var_def_id(self.cx, expr) {
2043 if let Some(parent) = get_parent_expr(self.cx, expr) {
2044 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2047 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2048 if lhs.id == expr.id {
2049 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2050 *state = match *state {
2051 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2052 _ => VarState::DontWarn,
2055 // Assigned some other value
2056 *state = VarState::DontWarn;
2060 ExprKind::Assign(ref lhs, _) if lhs.id == expr.id => *state = VarState::DontWarn,
2061 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2065 } else if is_loop(expr) || is_conditional(expr) {
2067 walk_expr(self, expr);
2070 } else if let ExprKind::Continue(_) = expr.node {
2074 walk_expr(self, expr);
2076 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2077 NestedVisitorMap::None
2081 /// Check whether a variable is initialized to zero at the start of a loop.
2082 struct InitializeVisitor<'a, 'tcx: 'a> {
2083 cx: &'a LateContext<'a, 'tcx>, // context reference
2084 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2088 depth: u32, // depth of conditional expressions
2092 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2093 fn visit_decl(&mut self, decl: &'tcx Decl) {
2094 // Look for declarations of the variable
2095 if let DeclKind::Local(ref local) = decl.node {
2096 if local.pat.id == self.var_id {
2097 if let PatKind::Binding(_, _, ident, _) = local.pat.node {
2098 self.name = Some(ident.name);
2100 self.state = if let Some(ref init) = local.init {
2101 if is_integer_literal(init, 0) {
2112 walk_decl(self, decl);
2115 fn visit_expr(&mut self, expr: &'tcx Expr) {
2116 if self.state == VarState::DontWarn {
2119 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2120 self.past_loop = true;
2123 // No need to visit expressions before the variable is
2125 if self.state == VarState::IncrOnce {
2129 // If node is the desired variable, see how it's used
2130 if var_def_id(self.cx, expr) == Some(self.var_id) {
2131 if let Some(parent) = get_parent_expr(self.cx, expr) {
2133 ExprKind::AssignOp(_, ref lhs, _) if lhs.id == expr.id => {
2134 self.state = VarState::DontWarn;
2136 ExprKind::Assign(ref lhs, ref rhs) if lhs.id == expr.id => {
2137 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2143 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2149 self.state = VarState::DontWarn;
2152 } else if !self.past_loop && is_loop(expr) {
2153 self.state = VarState::DontWarn;
2155 } else if is_conditional(expr) {
2157 walk_expr(self, expr);
2161 walk_expr(self, expr);
2163 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2164 NestedVisitorMap::None
2168 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<NodeId> {
2169 if let ExprKind::Path(ref qpath) = expr.node {
2170 let path_res = cx.tables.qpath_def(qpath, expr.hir_id);
2171 if let Def::Local(node_id) = path_res {
2172 return Some(node_id);
2178 fn is_loop(expr: &Expr) -> bool {
2180 ExprKind::Loop(..) | ExprKind::While(..) => true,
2185 fn is_conditional(expr: &Expr) -> bool {
2187 ExprKind::If(..) | ExprKind::Match(..) => true,
2192 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2194 if let Some(loop_block) = get_enclosing_block(cx, match_expr.id);
2195 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(loop_block.id));
2197 return is_loop_nested(cx, loop_expr, iter_expr)
2203 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2204 let mut id = loop_expr.id;
2205 let iter_name = if let Some(name) = path_name(iter_expr) {
2211 let parent = cx.tcx.hir().get_parent_node(id);
2215 match cx.tcx.hir().find(parent) {
2216 Some(Node::Expr(expr)) => match expr.node {
2217 ExprKind::Loop(..) | ExprKind::While(..) => {
2222 Some(Node::Block(block)) => {
2223 let mut block_visitor = LoopNestVisitor {
2225 iterator: iter_name,
2228 walk_block(&mut block_visitor, block);
2229 if block_visitor.nesting == RuledOut {
2233 Some(Node::Stmt(_)) => (),
2242 #[derive(PartialEq, Eq)]
2244 Unknown, // no nesting detected yet
2245 RuledOut, // the iterator is initialized or assigned within scope
2246 LookFurther, // no nesting detected, no further walk required
2249 use self::Nesting::{LookFurther, RuledOut, Unknown};
2251 struct LoopNestVisitor {
2257 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2258 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2259 if stmt.node.id() == self.id {
2260 self.nesting = LookFurther;
2261 } else if self.nesting == Unknown {
2262 walk_stmt(self, stmt);
2266 fn visit_expr(&mut self, expr: &'tcx Expr) {
2267 if self.nesting != Unknown {
2270 if expr.id == self.id {
2271 self.nesting = LookFurther;
2275 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2276 if match_var(path, self.iterator) {
2277 self.nesting = RuledOut;
2280 _ => walk_expr(self, expr),
2284 fn visit_pat(&mut self, pat: &'tcx Pat) {
2285 if self.nesting != Unknown {
2288 if let PatKind::Binding(_, _, span_name, _) = pat.node {
2289 if self.iterator == span_name.name {
2290 self.nesting = RuledOut;
2297 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2298 NestedVisitorMap::None
2302 fn path_name(e: &Expr) -> Option<Name> {
2303 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2304 let segments = &path.segments;
2305 if segments.len() == 1 {
2306 return Some(segments[0].ident.name);
2312 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2313 if constant(cx, cx.tables, cond).is_some() {
2314 // A pure constant condition (e.g. while false) is not linted.
2318 let mut var_visitor = VarCollectorVisitor {
2320 ids: FxHashSet::default(),
2321 def_ids: FxHashMap::default(),
2324 var_visitor.visit_expr(cond);
2325 if var_visitor.skip {
2328 let used_in_condition = &var_visitor.ids;
2329 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2330 used_in_condition.is_disjoint(&used_mutably)
2334 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2335 if no_cond_variable_mutated && !mutable_static_in_cond {
2338 WHILE_IMMUTABLE_CONDITION,
2340 "Variable in the condition are not mutated in the loop body. \
2341 This either leads to an infinite or to a never running loop.",
2346 /// Collects the set of variables in an expression
2347 /// Stops analysis if a function call is found
2348 /// Note: In some cases such as `self`, there are no mutable annotation,
2349 /// All variables definition IDs are collected
2350 struct VarCollectorVisitor<'a, 'tcx: 'a> {
2351 cx: &'a LateContext<'a, 'tcx>,
2352 ids: FxHashSet<NodeId>,
2353 def_ids: FxHashMap<def_id::DefId, bool>,
2357 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2358 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2360 if let ExprKind::Path(ref qpath) = ex.node;
2361 if let QPath::Resolved(None, _) = *qpath;
2362 let def = self.cx.tables.qpath_def(qpath, ex.hir_id);
2365 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
2366 self.ids.insert(node_id);
2368 Def::Static(def_id, mutable) => {
2369 self.def_ids.insert(def_id, mutable);
2378 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2379 fn visit_expr(&mut self, ex: &'tcx Expr) {
2381 ExprKind::Path(_) => self.insert_def_id(ex),
2382 // If there is any function/method call… we just stop analysis
2383 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2385 _ => walk_expr(self, ex),
2389 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2390 NestedVisitorMap::None
2394 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2396 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2398 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2399 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2400 if chain_method.ident.name == "collect" && match_trait_method(cx, &args[0], &paths::ITERATOR);
2401 if let Some(ref generic_args) = chain_method.args;
2402 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2404 let ty = cx.tables.node_id_to_type(ty.hir_id);
2405 if match_type(cx, ty, &paths::VEC) ||
2406 match_type(cx, ty, &paths::VEC_DEQUE) ||
2407 match_type(cx, ty, &paths::BTREEMAP) ||
2408 match_type(cx, ty, &paths::HASHMAP) {
2409 if method.ident.name == "len" {
2410 let span = shorten_needless_collect_span(expr);
2411 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2412 db.span_suggestion_with_applicability(
2415 ".count()".to_string(),
2416 Applicability::MachineApplicable,
2420 if method.ident.name == "is_empty" {
2421 let span = shorten_needless_collect_span(expr);
2422 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2423 db.span_suggestion_with_applicability(
2426 ".next().is_none()".to_string(),
2427 Applicability::MachineApplicable,
2431 if method.ident.name == "contains" {
2432 let contains_arg = snippet(cx, args[1].span, "??");
2433 let span = shorten_needless_collect_span(expr);
2434 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2435 db.span_suggestion_with_applicability(
2439 ".any(|&x| x == {})",
2440 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2442 Applicability::MachineApplicable,
2451 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2453 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2454 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2456 return expr.span.with_lo(span.lo() - BytePos(1));