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.
11 use itertools::Itertools;
12 use crate::reexport::*;
13 use crate::rustc::hir::*;
14 use crate::rustc::hir::def::Def;
15 use crate::rustc::hir::def_id;
16 use crate::rustc::hir::intravisit::{walk_block, walk_decl, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
17 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass, in_external_macro, LintContext};
18 use crate::rustc::{declare_tool_lint, lint_array};
19 use if_chain::if_chain;
20 use crate::rustc::middle::region;
21 // use crate::rustc::middle::region::CodeExtent;
22 use crate::rustc::middle::expr_use_visitor::*;
23 use crate::rustc::middle::mem_categorization::Categorization;
24 use crate::rustc::middle::mem_categorization::cmt_;
25 use crate::rustc::ty::{self, Ty};
26 use crate::rustc::ty::subst::Subst;
27 use crate::rustc_errors::Applicability;
28 use crate::rustc_data_structures::fx::{FxHashMap, FxHashSet};
29 use std::iter::{once, Iterator};
31 use crate::syntax::ast;
32 use crate::syntax::source_map::Span;
33 use crate::syntax_pos::BytePos;
34 use crate::utils::{in_macro, sugg, sext};
35 use crate::utils::usage::mutated_variables;
36 use crate::consts::{constant, Constant};
38 use crate::utils::paths;
40 get_enclosing_block, get_parent_expr, higher, is_integer_literal, is_refutable, last_path_segment,
41 match_trait_method, match_type, match_var, multispan_sugg, snippet, snippet_opt, snippet_with_applicability,
42 span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then, SpanlessEq,
45 /// **What it does:** Checks for for-loops that manually copy items between
46 /// slices that could be optimized by having a memcpy.
48 /// **Why is this bad?** It is not as fast as a memcpy.
50 /// **Known problems:** None.
54 /// for i in 0..src.len() {
55 /// dst[i + 64] = src[i];
58 declare_clippy_lint! {
61 "manually copying items between slices"
64 /// **What it does:** Checks for looping over the range of `0..len` of some
65 /// collection just to get the values by index.
67 /// **Why is this bad?** Just iterating the collection itself makes the intent
68 /// more clear and is probably faster.
70 /// **Known problems:** None.
74 /// for i in 0..vec.len() {
75 /// println!("{}", vec[i]);
78 declare_clippy_lint! {
79 pub NEEDLESS_RANGE_LOOP,
81 "for-looping over a range of indices where an iterator over items would do"
84 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
85 /// suggests the latter.
87 /// **Why is this bad?** Readability.
89 /// **Known problems:** False negatives. We currently only warn on some known
94 /// // with `y` a `Vec` or slice:
95 /// for x in y.iter() { .. }
97 /// can be rewritten to
99 /// for x in &y { .. }
101 declare_clippy_lint! {
102 pub EXPLICIT_ITER_LOOP,
104 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
107 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
108 /// suggests the latter.
110 /// **Why is this bad?** Readability.
112 /// **Known problems:** None
116 /// // with `y` a `Vec` or slice:
117 /// for x in y.into_iter() { .. }
119 /// can be rewritten to
121 /// for x in y { .. }
123 declare_clippy_lint! {
124 pub EXPLICIT_INTO_ITER_LOOP,
126 "for-looping over `_.into_iter()` when `_` would do"
129 /// **What it does:** Checks for loops on `x.next()`.
131 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
132 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
133 /// implements `IntoIterator`, so that possibly one value will be iterated,
134 /// leading to some hard to find bugs. No one will want to write such code
135 /// [except to win an Underhanded Rust
136 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
138 /// **Known problems:** None.
142 /// for x in y.next() { .. }
144 declare_clippy_lint! {
147 "for-looping over `_.next()` which is probably not intended"
150 /// **What it does:** Checks for `for` loops over `Option` values.
152 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
155 /// **Known problems:** None.
159 /// for x in option { .. }
164 /// if let Some(x) = option { .. }
166 declare_clippy_lint! {
167 pub FOR_LOOP_OVER_OPTION,
169 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
172 /// **What it does:** Checks for `for` loops over `Result` values.
174 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
177 /// **Known problems:** None.
181 /// for x in result { .. }
186 /// if let Ok(x) = result { .. }
188 declare_clippy_lint! {
189 pub FOR_LOOP_OVER_RESULT,
191 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
194 /// **What it does:** Detects `loop + match` combinations that are easier
195 /// written as a `while let` loop.
197 /// **Why is this bad?** The `while let` loop is usually shorter and more
200 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
205 /// let x = match y {
209 /// // .. do something with x
211 /// // is easier written as
212 /// while let Some(x) = y {
213 /// // .. do something with x
216 declare_clippy_lint! {
219 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
222 /// **What it does:** Checks for using `collect()` on an iterator without using
225 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
226 /// iterator instead.
228 /// **Known problems:** None.
232 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
234 declare_clippy_lint! {
237 "`collect()`ing an iterator without using the result; this is usually better \
238 written as a for loop"
241 /// **What it does:** Checks for functions collecting an iterator when collect
244 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
245 /// when this allocation may not be needed.
247 /// **Known problems:**
252 /// let len = iterator.collect::<Vec<_>>().len();
254 /// let len = iterator.count();
256 declare_clippy_lint! {
257 pub NEEDLESS_COLLECT,
259 "collecting an iterator when collect is not needed"
262 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
263 /// are constant and `x` is greater or equal to `y`, unless the range is
264 /// reversed or has a negative `.step_by(_)`.
266 /// **Why is it bad?** Such loops will either be skipped or loop until
267 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
270 /// **Known problems:** The lint cannot catch loops over dynamically defined
271 /// ranges. Doing this would require simulating all possible inputs and code
272 /// paths through the program, which would be complex and error-prone.
276 /// for x in 5..10-5 { .. } // oops, stray `-`
278 declare_clippy_lint! {
279 pub REVERSE_RANGE_LOOP,
281 "iteration over an empty range, such as `10..0` or `5..5`"
284 /// **What it does:** Checks `for` loops over slices with an explicit counter
285 /// and suggests the use of `.enumerate()`.
287 /// **Why is it bad?** Not only is the version using `.enumerate()` more
288 /// readable, the compiler is able to remove bounds checks which can lead to
289 /// faster code in some instances.
291 /// **Known problems:** None.
295 /// for i in 0..v.len() { foo(v[i]);
296 /// for i in 0..v.len() { bar(i, v[i]); }
298 declare_clippy_lint! {
299 pub EXPLICIT_COUNTER_LOOP,
301 "for-looping with an explicit counter when `_.enumerate()` would do"
304 /// **What it does:** Checks for empty `loop` expressions.
306 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
307 /// anything. Think of the environment and either block on something or at least
308 /// make the thread sleep for some microseconds.
310 /// **Known problems:** None.
316 declare_clippy_lint! {
319 "empty `loop {}`, which should block or sleep"
322 /// **What it does:** Checks for `while let` expressions on iterators.
324 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
325 /// the intent better.
327 /// **Known problems:** None.
331 /// while let Some(val) = iter() { .. }
333 declare_clippy_lint! {
334 pub WHILE_LET_ON_ITERATOR,
336 "using a while-let loop instead of a for loop on an iterator"
339 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
340 /// ignoring either the keys or values.
342 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
343 /// can be used to express that don't need the values or keys.
345 /// **Known problems:** None.
349 /// for (k, _) in &map { .. }
352 /// could be replaced by
355 /// for k in map.keys() { .. }
357 declare_clippy_lint! {
360 "looping on a map using `iter` when `keys` or `values` would do"
363 /// **What it does:** Checks for loops that will always `break`, `return` or
364 /// `continue` an outer loop.
366 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
369 /// **Known problems:** None
373 /// loop { ..; break; }
375 declare_clippy_lint! {
378 "any loop that will always `break` or `return`"
381 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
383 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
385 /// **Known problems:** None
389 /// let mut foo = 42;
390 /// for i in 0..foo {
392 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
395 declare_clippy_lint! {
398 "for loop over a range where one of the bounds is a mutable variable"
401 /// **What it does:** Checks whether variables used within while loop condition
402 /// can be (and are) mutated in the body.
404 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
405 /// will lead to an infinite loop.
407 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
408 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
409 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
415 /// println!("let me loop forever!");
418 declare_clippy_lint! {
419 pub WHILE_IMMUTABLE_CONDITION,
421 "variables used within while expression are not mutated in the body"
424 #[derive(Copy, Clone)]
427 impl LintPass for Pass {
428 fn get_lints(&self) -> LintArray {
433 EXPLICIT_INTO_ITER_LOOP,
435 FOR_LOOP_OVER_RESULT,
436 FOR_LOOP_OVER_OPTION,
441 EXPLICIT_COUNTER_LOOP,
443 WHILE_LET_ON_ITERATOR,
447 WHILE_IMMUTABLE_CONDITION,
452 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
453 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
454 if let Some((pat, arg, body)) = higher::for_loop(expr) {
455 check_for_loop(cx, pat, arg, body, expr);
458 // check for never_loop
460 ExprKind::While(_, ref block, _) | ExprKind::Loop(ref block, _, _) => {
461 match never_loop_block(block, expr.id) {
462 NeverLoopResult::AlwaysBreak =>
463 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
464 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
470 // check for `loop { if let {} else break }` that could be `while let`
471 // (also matches an explicit "match" instead of "if let")
472 // (even if the "match" or "if let" is used for declaration)
473 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
474 // also check for empty `loop {}` statements
475 if block.stmts.is_empty() && block.expr.is_none() {
480 "empty `loop {}` detected. You may want to either use `panic!()` or add \
481 `std::thread::sleep(..);` to the loop body.",
485 // extract the expression from the first statement (if any) in a block
486 let inner_stmt_expr = extract_expr_from_first_stmt(block);
487 // or extract the first expression (if any) from the block
488 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
489 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
490 // ensure "if let" compatible match structure
492 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
493 if arms.len() == 2 && arms[0].pats.len() == 1 && arms[0].guard.is_none()
494 && arms[1].pats.len() == 1 && arms[1].guard.is_none()
495 && is_simple_break_expr(&arms[1].body)
497 if in_external_macro(cx.sess(), expr.span) {
501 // NOTE: we used to make build a body here instead of using
502 // ellipsis, this was removed because:
503 // 1) it was ugly with big bodies;
504 // 2) it was not indented properly;
505 // 3) it wasn’t very smart (see #675).
506 let mut applicability = Applicability::MachineApplicable;
511 "this loop could be written as a `while let` loop",
514 "while let {} = {} {{ .. }}",
515 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
516 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
527 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
528 let pat = &arms[0].pats[0].node;
530 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
531 &ExprKind::MethodCall(ref method_path, _, ref method_args),
532 ) = (pat, &match_expr.node)
534 let iter_expr = &method_args[0];
535 let lhs_constructor = last_path_segment(qpath);
536 if method_path.ident.name == "next" && match_trait_method(cx, match_expr, &paths::ITERATOR)
537 && lhs_constructor.ident.name == "Some" && (
539 || !is_refutable(cx, &pat_args[0])
540 && !is_iterator_used_after_while_let(cx, iter_expr)
541 && !is_nested(cx, expr, &method_args[0]))
543 let iterator = snippet(cx, method_args[0].span, "_");
544 let loop_var = if pat_args.is_empty() {
547 snippet(cx, pat_args[0].span, "_").into_owned()
551 WHILE_LET_ON_ITERATOR,
553 "this loop could be written as a `for` loop",
555 format!("for {} in {} {{ .. }}", loop_var, iterator),
556 Applicability::HasPlaceholders,
562 // check for while loops which conditions never change
563 if let ExprKind::While(ref cond, _, _) = expr.node {
564 check_infinite_loop(cx, cond, expr);
567 check_needless_collect(expr, cx);
570 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
571 if let StmtKind::Semi(ref expr, _) = stmt.node {
572 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
573 if args.len() == 1 && method.ident.name == "collect" && match_trait_method(cx, expr, &paths::ITERATOR) {
578 "you are collect()ing an iterator and throwing away the result. \
579 Consider using an explicit for loop to exhaust the iterator",
587 enum NeverLoopResult {
588 // A break/return always get triggered but not necessarily for the main loop.
590 // A continue may occur for the main loop.
595 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
597 NeverLoopResult::AlwaysBreak |
598 NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
599 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
603 // Combine two results for parts that are called in order.
604 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
606 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
607 NeverLoopResult::Otherwise => second,
611 // Combine two results where both parts are called but not necessarily in order.
612 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
613 match (left, right) {
614 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) =>
615 NeverLoopResult::MayContinueMainLoop,
616 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) =>
617 NeverLoopResult::AlwaysBreak,
618 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) =>
619 NeverLoopResult::Otherwise,
623 // Combine two results where only one of the part may have been executed.
624 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
626 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) =>
627 NeverLoopResult::AlwaysBreak,
628 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) =>
629 NeverLoopResult::MayContinueMainLoop,
630 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) =>
631 NeverLoopResult::Otherwise,
635 fn never_loop_block(block: &Block, main_loop_id: NodeId) -> NeverLoopResult {
636 let stmts = block.stmts.iter().map(stmt_to_expr);
637 let expr = once(block.expr.as_ref().map(|p| &**p));
638 let mut iter = stmts.chain(expr).filter_map(|e| e);
639 never_loop_expr_seq(&mut iter, main_loop_id)
642 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
644 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
645 StmtKind::Decl(ref d, ..) => decl_to_expr(d),
649 fn decl_to_expr(decl: &Decl) -> Option<&Expr> {
651 DeclKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
656 fn never_loop_expr(expr: &Expr, main_loop_id: NodeId) -> NeverLoopResult {
658 ExprKind::Box(ref e) |
659 ExprKind::Unary(_, ref e) |
660 ExprKind::Cast(ref e, _) |
661 ExprKind::Type(ref e, _) |
662 ExprKind::Field(ref e, _) |
663 ExprKind::AddrOf(_, ref e) |
664 ExprKind::Struct(_, _, Some(ref e)) |
665 ExprKind::Repeat(ref e, _) => never_loop_expr(e, main_loop_id),
666 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
667 never_loop_expr_all(&mut es.iter(), main_loop_id)
669 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
670 ExprKind::Binary(_, ref e1, ref e2) |
671 ExprKind::Assign(ref e1, ref e2) |
672 ExprKind::AssignOp(_, ref e1, ref e2) |
673 ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
674 ExprKind::If(ref e, ref e2, ref e3) => {
675 let e1 = never_loop_expr(e, main_loop_id);
676 let e2 = never_loop_expr(e2, main_loop_id);
677 let e3 = e3.as_ref().map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
678 combine_seq(e1, combine_branches(e2, e3))
680 ExprKind::Loop(ref b, _, _) => {
681 // Break can come from the inner loop so remove them.
682 absorb_break(&never_loop_block(b, main_loop_id))
684 ExprKind::While(ref e, ref b, _) => {
685 let e = never_loop_expr(e, main_loop_id);
686 let result = never_loop_block(b, main_loop_id);
687 // Break can come from the inner loop so remove them.
688 combine_seq(e, absorb_break(&result))
690 ExprKind::Match(ref e, ref arms, _) => {
691 let e = never_loop_expr(e, main_loop_id);
695 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
699 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
700 ExprKind::Continue(d) => {
702 .expect("target id can only be missing in the presence of compilation errors");
703 if id == main_loop_id {
704 NeverLoopResult::MayContinueMainLoop
706 NeverLoopResult::AlwaysBreak
709 ExprKind::Break(_, _) => {
710 NeverLoopResult::AlwaysBreak
712 ExprKind::Ret(ref e) => {
713 if let Some(ref e) = *e {
714 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
716 NeverLoopResult::AlwaysBreak
719 ExprKind::Struct(_, _, None) |
721 ExprKind::Closure(_, _, _, _, _) |
722 ExprKind::InlineAsm(_, _, _) |
724 ExprKind::Lit(_) => NeverLoopResult::Otherwise,
728 fn never_loop_expr_seq<'a, T: Iterator<Item=&'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
729 es.map(|e| never_loop_expr(e, main_loop_id))
730 .fold(NeverLoopResult::Otherwise, combine_seq)
733 fn never_loop_expr_all<'a, T: Iterator<Item=&'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
734 es.map(|e| never_loop_expr(e, main_loop_id))
735 .fold(NeverLoopResult::Otherwise, combine_both)
738 fn never_loop_expr_branch<'a, T: Iterator<Item=&'a Expr>>(e: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
739 e.map(|e| never_loop_expr(e, main_loop_id))
740 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
743 fn check_for_loop<'a, 'tcx>(
744 cx: &LateContext<'a, 'tcx>,
750 check_for_loop_range(cx, pat, arg, body, expr);
751 check_for_loop_reverse_range(cx, arg, expr);
752 check_for_loop_arg(cx, pat, arg, expr);
753 check_for_loop_explicit_counter(cx, arg, body, expr);
754 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
755 check_for_mut_range_bound(cx, arg, body);
756 detect_manual_memcpy(cx, pat, arg, body, expr);
759 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> bool {
761 if let ExprKind::Path(ref qpath) = expr.node;
762 if let QPath::Resolved(None, ref path) = *qpath;
763 if path.segments.len() == 1;
764 if let Def::Local(local_id) = cx.tables.qpath_def(qpath, expr.hir_id);
781 fn negative(s: String) -> Self {
788 fn positive(s: String) -> Self {
796 struct FixedOffsetVar {
801 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
802 let is_slice = match ty.sty {
803 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
804 ty::Slice(..) | ty::Array(..) => true,
808 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
811 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> Option<FixedOffsetVar> {
812 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: ast::NodeId) -> Option<String> {
814 ExprKind::Lit(ref l) => match l.node {
815 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
818 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
823 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
824 let ty = cx.tables.expr_ty(seqexpr);
825 if !is_slice_like(cx, ty) {
829 let offset = match idx.node {
830 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
832 let offset_opt = if same_var(cx, lhs, var) {
833 extract_offset(cx, rhs, var)
834 } else if same_var(cx, rhs, var) {
835 extract_offset(cx, lhs, var)
840 offset_opt.map(Offset::positive)
842 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
845 ExprKind::Path(..) => if same_var(cx, idx, var) {
846 Some(Offset::positive("0".into()))
855 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
864 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
865 cx: &LateContext<'a, 'tcx>,
868 ) -> Option<FixedOffsetVar> {
870 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
871 if method.ident.name == "clone";
873 if let Some(arg) = args.get(0);
875 return get_fixed_offset_var(cx, arg, var);
879 get_fixed_offset_var(cx, expr, var)
882 fn get_indexed_assignments<'a, 'tcx>(
883 cx: &LateContext<'a, 'tcx>,
886 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
887 fn get_assignment<'a, 'tcx>(
888 cx: &LateContext<'a, 'tcx>,
891 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
892 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
893 match (get_fixed_offset_var(cx, lhs, var), fetch_cloned_fixed_offset_var(cx, rhs, var)) {
894 (Some(offset_left), Some(offset_right)) => {
895 // Source and destination must be different
896 if offset_left.var_name == offset_right.var_name {
899 Some((offset_left, offset_right))
909 if let ExprKind::Block(ref b, _) = body.node {
918 .map(|stmt| match stmt.node {
919 StmtKind::Decl(..) => None,
920 StmtKind::Expr(ref e, _node_id) | StmtKind::Semi(ref e, _node_id) => Some(get_assignment(cx, e, var)),
925 .map(|e| Some(get_assignment(cx, &*e, var))),
928 .collect::<Option<Vec<_>>>()
929 .unwrap_or_else(|| vec![])
931 get_assignment(cx, body, var).into_iter().collect()
935 /// Check for for loops that sequentially copy items from one slice-like
936 /// object to another.
937 fn detect_manual_memcpy<'a, 'tcx>(
938 cx: &LateContext<'a, 'tcx>,
944 if let Some(higher::Range {
948 }) = higher::range(cx, arg)
950 // the var must be a single name
951 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
952 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
953 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
954 ("0", _, "0", _) => "".into(),
955 ("0", _, x, false) | (x, false, "0", false) => x.into(),
956 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
957 (x, false, y, false) => format!("({} + {})", x, y),
958 (x, false, y, true) => {
962 format!("({} - {})", x, y)
965 (x, true, y, false) => {
969 format!("({} - {})", y, x)
972 (x, true, y, true) => format!("-({} + {})", x, y),
976 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| if let Some(end) = *end {
978 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
979 if method.ident.name == "len";
980 if len_args.len() == 1;
981 if let Some(arg) = len_args.get(0);
982 if snippet(cx, arg.span, "??") == var_name;
984 return if offset.negate {
985 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
992 let end_str = match limits {
993 ast::RangeLimits::Closed => {
994 let end = sugg::Sugg::hir(cx, end, "<count>");
995 format!("{}", end + sugg::ONE)
997 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1000 print_sum(&Offset::positive(end_str), &offset)
1005 // The only statements in the for loops can be indexed assignments from
1006 // indexed retrievals.
1007 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1009 let big_sugg = manual_copies
1011 .map(|(dst_var, src_var)| {
1012 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1013 let dst_offset = print_sum(&start_str, &dst_var.offset);
1014 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1015 let src_offset = print_sum(&start_str, &src_var.offset);
1016 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1017 let dst = if dst_offset == "" && dst_limit == "" {
1020 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1023 format!("{}.clone_from_slice(&{}[{}..{}])", dst, src_var.var_name, src_offset, src_limit)
1027 if !big_sugg.is_empty() {
1032 "it looks like you're manually copying between slices",
1033 "try replacing the loop by",
1035 Applicability::Unspecified,
1042 /// Check for looping over a range and then indexing a sequence with it.
1043 /// The iteratee must be a range literal.
1044 fn check_for_loop_range<'a, 'tcx>(
1045 cx: &LateContext<'a, 'tcx>,
1051 if in_macro(expr.span) {
1055 if let Some(higher::Range {
1059 }) = higher::range(cx, arg)
1061 // the var must be a single name
1062 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1063 let mut visitor = VarVisitor {
1066 indexed_mut: FxHashSet::default(),
1067 indexed_indirectly: FxHashMap::default(),
1068 indexed_directly: FxHashMap::default(),
1069 referenced: FxHashSet::default(),
1071 prefer_mutable: false,
1073 walk_expr(&mut visitor, body);
1075 // linting condition: we only indexed one variable, and indexed it directly
1076 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1077 let (indexed, (indexed_extent, indexed_ty)) = visitor
1081 .expect("already checked that we have exactly 1 element");
1083 // ensure that the indexed variable was declared before the loop, see #601
1084 if let Some(indexed_extent) = indexed_extent {
1085 let parent_id = cx.tcx.hir.get_parent(expr.id);
1086 let parent_def_id = cx.tcx.hir.local_def_id(parent_id);
1087 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1088 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1089 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1094 // don't lint if the container that is indexed into is also used without
1096 if visitor.referenced.contains(&indexed) {
1100 let starts_at_zero = is_integer_literal(start, 0);
1102 let skip = if starts_at_zero {
1105 format!(".skip({})", snippet(cx, start.span, ".."))
1108 let mut end_is_start_plus_val = false;
1110 let take = if let Some(end) = *end {
1111 let mut take_expr = end;
1113 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1114 if let BinOpKind::Add = op.node {
1115 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1116 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1118 if start_equal_left {
1120 } else if start_equal_right {
1124 end_is_start_plus_val = start_equal_left | start_equal_right;
1128 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1132 ast::RangeLimits::Closed => {
1133 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1134 format!(".take({})", take_expr + sugg::ONE)
1136 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1143 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1144 ("mut ", "iter_mut")
1149 let take_is_empty = take.is_empty();
1150 let mut method_1 = take;
1151 let mut method_2 = skip;
1153 if end_is_start_plus_val {
1154 mem::swap(&mut method_1, &mut method_2);
1157 if visitor.nonindex {
1160 NEEDLESS_RANGE_LOOP,
1162 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1166 "consider using an iterator".to_string(),
1168 (pat.span, format!("({}, <item>)", ident.name)),
1169 (arg.span, format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2)),
1175 let repl = if starts_at_zero && take_is_empty {
1176 format!("&{}{}", ref_mut, indexed)
1178 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1183 NEEDLESS_RANGE_LOOP,
1185 &format!("the loop variable `{}` is only used to index `{}`.", ident.name, indexed),
1189 "consider using an iterator".to_string(),
1190 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1200 fn is_len_call(expr: &Expr, var: Name) -> bool {
1202 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1203 if len_args.len() == 1;
1204 if method.ident.name == "len";
1205 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1206 if path.segments.len() == 1;
1207 if path.segments[0].ident.name == var;
1216 fn is_end_eq_array_len(
1217 cx: &LateContext<'_, '_>,
1219 limits: ast::RangeLimits,
1223 if let ExprKind::Lit(ref lit) = end.node;
1224 if let ast::LitKind::Int(end_int, _) = lit.node;
1225 if let ty::TyKind::Array(_, arr_len_const) = indexed_ty.sty;
1226 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1228 return match limits {
1229 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1230 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1238 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1239 // if this for loop is iterating over a two-sided range...
1240 if let Some(higher::Range {
1244 }) = higher::range(cx, arg)
1246 // ...and both sides are compile-time constant integers...
1247 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1248 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1249 // ...and the start index is greater than the end index,
1250 // this loop will never run. This is often confusing for developers
1251 // who think that this will iterate from the larger value to the
1253 let ty = cx.tables.expr_ty(start);
1254 let (sup, eq) = match (start_idx, end_idx) {
1256 Constant::Int(start_idx),
1257 Constant::Int(end_idx),
1258 ) => (match ty.sty {
1259 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1260 ty::Uint(_) => start_idx > end_idx,
1262 }, start_idx == end_idx),
1263 _ => (false, false),
1267 let start_snippet = snippet(cx, start.span, "_");
1268 let end_snippet = snippet(cx, end.span, "_");
1269 let dots = if limits == ast::RangeLimits::Closed {
1279 "this range is empty so this for loop will never run",
1281 db.span_suggestion_with_applicability(
1283 "consider using the following if you are attempting to iterate over this \
1286 "({end}{dots}{start}).rev()",
1289 start = start_snippet
1291 Applicability::MaybeIncorrect,
1295 } else if eq && limits != ast::RangeLimits::Closed {
1296 // if they are equal, it's also problematic - this loop
1302 "this range is empty so this for loop will never run",
1310 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1311 let mut applicability = Applicability::MachineApplicable;
1312 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1313 let muta = if method_name == "iter_mut" {
1322 "it is more concise to loop over references to containers instead of using explicit \
1324 "to write this more concisely, try",
1325 format!("&{}{}", muta, object),
1330 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1331 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1332 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1333 // just the receiver, no arguments
1334 if args.len() == 1 {
1335 let method_name = &*method.ident.as_str();
1336 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1337 if method_name == "iter" || method_name == "iter_mut" {
1338 if is_ref_iterable_type(cx, &args[0]) {
1339 lint_iter_method(cx, args, arg, method_name);
1341 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1342 let def_id = cx.tables.type_dependent_defs()[arg.hir_id].def_id();
1343 let substs = cx.tables.node_substs(arg.hir_id);
1344 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1346 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1347 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1348 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1349 match cx.tables.expr_ty(&args[0]).sty {
1350 // If the length is greater than 32 no traits are implemented for array and
1351 // therefore we cannot use `&`.
1352 ty::TyKind::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1353 _ => lint_iter_method(cx, args, arg, method_name),
1356 let mut applicability = Applicability::MachineApplicable;
1357 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1360 EXPLICIT_INTO_ITER_LOOP,
1362 "it is more concise to loop over containers instead of using explicit \
1363 iteration methods`",
1364 "to write this more concisely, try",
1369 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1374 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1375 probably not what you want",
1377 next_loop_linted = true;
1381 if !next_loop_linted {
1382 check_arg_type(cx, pat, arg);
1386 /// Check for `for` loops over `Option`s and `Results`
1387 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1388 let ty = cx.tables.expr_ty(arg);
1389 if match_type(cx, ty, &paths::OPTION) {
1392 FOR_LOOP_OVER_OPTION,
1395 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1396 `if let` statement.",
1397 snippet(cx, arg.span, "_")
1400 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1401 snippet(cx, pat.span, "_"),
1402 snippet(cx, arg.span, "_")
1405 } else if match_type(cx, ty, &paths::RESULT) {
1408 FOR_LOOP_OVER_RESULT,
1411 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1412 `if let` statement.",
1413 snippet(cx, arg.span, "_")
1416 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1417 snippet(cx, pat.span, "_"),
1418 snippet(cx, arg.span, "_")
1424 fn check_for_loop_explicit_counter<'a, 'tcx>(
1425 cx: &LateContext<'a, 'tcx>,
1430 // Look for variables that are incremented once per loop iteration.
1431 let mut visitor = IncrementVisitor {
1433 states: FxHashMap::default(),
1437 walk_expr(&mut visitor, body);
1439 // For each candidate, check the parent block to see if
1440 // it's initialized to zero at the start of the loop.
1441 let map = &cx.tcx.hir;
1442 let parent_scope = map.get_enclosing_scope(expr.id)
1443 .and_then(|id| map.get_enclosing_scope(id));
1444 if let Some(parent_id) = parent_scope {
1445 if let Node::Block(block) = map.get(parent_id) {
1446 for (id, _) in visitor
1449 .filter(|&(_, v)| *v == VarState::IncrOnce)
1451 let mut visitor2 = InitializeVisitor {
1455 state: VarState::IncrOnce,
1460 walk_block(&mut visitor2, block);
1462 if visitor2.state == VarState::Warn {
1463 if let Some(name) = visitor2.name {
1466 EXPLICIT_COUNTER_LOOP,
1469 "the variable `{0}` is used as a loop counter. Consider using `for ({0}, \
1470 item) in {1}.enumerate()` or similar iterators",
1472 snippet(cx, arg.span, "_")
1482 /// Check for the `FOR_KV_MAP` lint.
1483 fn check_for_loop_over_map_kv<'a, 'tcx>(
1484 cx: &LateContext<'a, 'tcx>,
1490 let pat_span = pat.span;
1492 if let PatKind::Tuple(ref pat, _) = pat.node {
1494 let arg_span = arg.span;
1495 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1496 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1497 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1498 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1503 let mutbl = match mutbl {
1505 MutMutable => "_mut",
1507 let arg = match arg.node {
1508 ExprKind::AddrOf(_, ref expr) => &**expr,
1512 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1517 &format!("you seem to want to iterate on a map's {}s", kind),
1519 let map = sugg::Sugg::hir(cx, arg, "map");
1522 "use the corresponding method".into(),
1524 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1525 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1535 struct MutatePairDelegate {
1536 node_id_low: Option<NodeId>,
1537 node_id_high: Option<NodeId>,
1538 span_low: Option<Span>,
1539 span_high: Option<Span>,
1542 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1543 fn consume(&mut self, _: NodeId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1545 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1547 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1549 fn borrow(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1550 if let ty::BorrowKind::MutBorrow = bk {
1551 if let Categorization::Local(id) = cmt.cat {
1552 if Some(id) == self.node_id_low {
1553 self.span_low = Some(sp)
1555 if Some(id) == self.node_id_high {
1556 self.span_high = Some(sp)
1562 fn mutate(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1563 if let Categorization::Local(id) = cmt.cat {
1564 if Some(id) == self.node_id_low {
1565 self.span_low = Some(sp)
1567 if Some(id) == self.node_id_high {
1568 self.span_high = Some(sp)
1573 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1576 impl<'tcx> MutatePairDelegate {
1577 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1578 (self.span_low, self.span_high)
1582 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1583 if let Some(higher::Range {
1587 }) = higher::range(cx, arg)
1590 check_for_mutability(cx, start),
1591 check_for_mutability(cx, end),
1593 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1594 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1595 mut_warn_with_span(cx, span_low);
1596 mut_warn_with_span(cx, span_high);
1601 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1602 if let Some(sp) = span {
1607 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1612 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<NodeId> {
1614 if let ExprKind::Path(ref qpath) = bound.node;
1615 if let QPath::Resolved(None, _) = *qpath;
1617 let def = cx.tables.qpath_def(qpath, bound.hir_id);
1618 if let Def::Local(node_id) = def {
1619 let node_str = cx.tcx.hir.get(node_id);
1621 if let Node::Binding(pat) = node_str;
1622 if let PatKind::Binding(bind_ann, _, _, _) = pat.node;
1623 if let BindingAnnotation::Mutable = bind_ann;
1625 return Some(node_id);
1634 fn check_for_mutation(cx: &LateContext<'_, '_>, body: &Expr, bound_ids: &[Option<NodeId>]) -> (Option<Span>, Option<Span>) {
1635 let mut delegate = MutatePairDelegate {
1636 node_id_low: bound_ids[0],
1637 node_id_high: bound_ids[1],
1641 let def_id = def_id::DefId::local(body.hir_id.owner);
1642 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1643 ExprUseVisitor::new(&mut delegate, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).walk_expr(body);
1644 delegate.mutation_span()
1647 /// Return true if the pattern is a `PatWild` or an ident prefixed with `'_'`.
1648 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1650 PatKind::Wild => true,
1651 PatKind::Binding(_, _, ident, None) if ident.as_str().starts_with('_') => {
1652 let mut visitor = UsedVisitor {
1656 walk_expr(&mut visitor, body);
1663 struct UsedVisitor {
1664 var: ast::Name, // var to look for
1665 used: bool, // has the var been used otherwise?
1668 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1669 fn visit_expr(&mut self, expr: &'tcx Expr) {
1670 if match_var(expr, self.var) {
1673 walk_expr(self, expr);
1677 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1678 NestedVisitorMap::None
1682 struct LocalUsedVisitor<'a, 'tcx: 'a> {
1683 cx: &'a LateContext<'a, 'tcx>,
1688 impl<'a, 'tcx: 'a> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1689 fn visit_expr(&mut self, expr: &'tcx Expr) {
1690 if same_var(self.cx, expr, self.local) {
1693 walk_expr(self, expr);
1697 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1698 NestedVisitorMap::None
1702 struct VarVisitor<'a, 'tcx: 'a> {
1703 /// context reference
1704 cx: &'a LateContext<'a, 'tcx>,
1705 /// var name to look for as index
1707 /// indexed variables that are used mutably
1708 indexed_mut: FxHashSet<Name>,
1709 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1710 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1711 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1712 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1713 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1714 /// Any names that are used outside an index operation.
1715 /// Used to detect things like `&mut vec` used together with `vec[i]`
1716 referenced: FxHashSet<Name>,
1717 /// has the loop variable been used in expressions other than the index of
1720 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1721 /// takes `&mut self`
1722 prefer_mutable: bool,
1725 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1726 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1728 // the indexed container is referenced by a name
1729 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1730 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1731 if seqvar.segments.len() == 1;
1733 let index_used_directly = same_var(self.cx, idx, self.var);
1734 let indexed_indirectly = {
1735 let mut used_visitor = LocalUsedVisitor {
1740 walk_expr(&mut used_visitor, idx);
1744 if indexed_indirectly || index_used_directly {
1745 if self.prefer_mutable {
1746 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1748 let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
1750 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
1751 let hir_id = self.cx.tcx.hir.node_to_hir_id(node_id);
1753 let parent_id = self.cx.tcx.hir.get_parent(expr.id);
1754 let parent_def_id = self.cx.tcx.hir.local_def_id(parent_id);
1755 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1756 if indexed_indirectly {
1757 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1759 if index_used_directly {
1760 self.indexed_directly.insert(
1761 seqvar.segments[0].ident.name,
1762 (Some(extent), self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1765 return false; // no need to walk further *on the variable*
1767 Def::Static(..) | Def::Const(..) => {
1768 if indexed_indirectly {
1769 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1771 if index_used_directly {
1772 self.indexed_directly.insert(
1773 seqvar.segments[0].ident.name,
1774 (None, self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1777 return false; // no need to walk further *on the variable*
1788 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1789 fn visit_expr(&mut self, expr: &'tcx Expr) {
1792 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1793 if (meth.ident.name == "index" && match_trait_method(self.cx, expr, &paths::INDEX))
1794 || (meth.ident.name == "index_mut" && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1795 if !self.check(&args[1], &args[0], expr);
1801 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1802 if !self.check(idx, seqexpr, expr);
1807 // directly using a variable
1808 if let ExprKind::Path(ref qpath) = expr.node;
1809 if let QPath::Resolved(None, ref path) = *qpath;
1810 if path.segments.len() == 1;
1811 if let Def::Local(local_id) = self.cx.tables.qpath_def(qpath, expr.hir_id);
1813 if local_id == self.var {
1814 // we are not indexing anything, record that
1815 self.nonindex = true;
1817 // not the correct variable, but still a variable
1818 self.referenced.insert(path.segments[0].ident.name);
1822 let old = self.prefer_mutable;
1824 ExprKind::AssignOp(_, ref lhs, ref rhs) |
1825 ExprKind::Assign(ref lhs, ref rhs) => {
1826 self.prefer_mutable = true;
1827 self.visit_expr(lhs);
1828 self.prefer_mutable = false;
1829 self.visit_expr(rhs);
1831 ExprKind::AddrOf(mutbl, ref expr) => {
1832 if mutbl == MutMutable {
1833 self.prefer_mutable = true;
1835 self.visit_expr(expr);
1837 ExprKind::Call(ref f, ref args) => {
1840 let ty = self.cx.tables.expr_ty_adjusted(expr);
1841 self.prefer_mutable = false;
1842 if let ty::Ref(_, _, mutbl) = ty.sty {
1843 if mutbl == MutMutable {
1844 self.prefer_mutable = true;
1847 self.visit_expr(expr);
1850 ExprKind::MethodCall(_, _, ref args) => {
1851 let def_id = self.cx.tables.type_dependent_defs()[expr.hir_id].def_id();
1852 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1853 self.prefer_mutable = false;
1854 if let ty::Ref(_, _, mutbl) = ty.sty {
1855 if mutbl == MutMutable {
1856 self.prefer_mutable = true;
1859 self.visit_expr(expr);
1862 _ => walk_expr(self, expr),
1864 self.prefer_mutable = old;
1866 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1867 NestedVisitorMap::None
1871 fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1872 let def_id = match var_def_id(cx, iter_expr) {
1874 None => return false,
1876 let mut visitor = VarUsedAfterLoopVisitor {
1879 iter_expr_id: iter_expr.id,
1880 past_while_let: false,
1881 var_used_after_while_let: false,
1883 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1884 walk_block(&mut visitor, enclosing_block);
1886 visitor.var_used_after_while_let
1889 struct VarUsedAfterLoopVisitor<'a, 'tcx: 'a> {
1890 cx: &'a LateContext<'a, 'tcx>,
1892 iter_expr_id: NodeId,
1893 past_while_let: bool,
1894 var_used_after_while_let: bool,
1897 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1898 fn visit_expr(&mut self, expr: &'tcx Expr) {
1899 if self.past_while_let {
1900 if Some(self.def_id) == var_def_id(self.cx, expr) {
1901 self.var_used_after_while_let = true;
1903 } else if self.iter_expr_id == expr.id {
1904 self.past_while_let = true;
1906 walk_expr(self, expr);
1908 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1909 NestedVisitorMap::None
1914 /// Return true if the type of expr is one that provides `IntoIterator` impls
1915 /// for `&T` and `&mut T`, such as `Vec`.
1917 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1918 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1919 // will allow further borrows afterwards
1920 let ty = cx.tables.expr_ty(e);
1921 is_iterable_array(ty, cx) ||
1922 match_type(cx, ty, &paths::VEC) ||
1923 match_type(cx, ty, &paths::LINKED_LIST) ||
1924 match_type(cx, ty, &paths::HASHMAP) ||
1925 match_type(cx, ty, &paths::HASHSET) ||
1926 match_type(cx, ty, &paths::VEC_DEQUE) ||
1927 match_type(cx, ty, &paths::BINARY_HEAP) ||
1928 match_type(cx, ty, &paths::BTREEMAP) ||
1929 match_type(cx, ty, &paths::BTREESET)
1932 fn is_iterable_array(ty: Ty<'_>, cx: &LateContext<'_, '_>) -> bool {
1933 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1935 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1940 /// If a block begins with a statement (possibly a `let` binding) and has an
1941 /// expression, return it.
1942 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1943 if block.stmts.is_empty() {
1946 if let StmtKind::Decl(ref decl, _) = block.stmts[0].node {
1947 if let DeclKind::Local(ref local) = decl.node {
1948 if let Some(ref expr) = local.init {
1961 /// If a block begins with an expression (with or without semicolon), return it.
1962 fn extract_first_expr(block: &Block) -> Option<&Expr> {
1964 Some(ref expr) if block.stmts.is_empty() => Some(expr),
1965 None if !block.stmts.is_empty() => match block.stmts[0].node {
1966 StmtKind::Expr(ref expr, _) | StmtKind::Semi(ref expr, _) => Some(expr),
1967 StmtKind::Decl(..) => None,
1973 /// Return true if expr contains a single break expr without destination label
1975 /// passed expression. The expression may be within a block.
1976 fn is_simple_break_expr(expr: &Expr) -> bool {
1978 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
1979 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
1980 Some(subexpr) => is_simple_break_expr(subexpr),
1987 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
1988 // incremented exactly once in the loop body, and initialized to zero
1989 // at the start of the loop.
1990 #[derive(PartialEq)]
1992 Initial, // Not examined yet
1993 IncrOnce, // Incremented exactly once, may be a loop counter
1994 Declared, // Declared but not (yet) initialized to zero
1999 /// Scan a for loop for variables that are incremented exactly once.
2000 struct IncrementVisitor<'a, 'tcx: 'a> {
2001 cx: &'a LateContext<'a, 'tcx>, // context reference
2002 states: FxHashMap<NodeId, VarState>, // incremented variables
2003 depth: u32, // depth of conditional expressions
2007 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2008 fn visit_expr(&mut self, expr: &'tcx Expr) {
2013 // If node is a variable
2014 if let Some(def_id) = var_def_id(self.cx, expr) {
2015 if let Some(parent) = get_parent_expr(self.cx, expr) {
2016 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2019 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2020 if lhs.id == expr.id {
2021 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2022 *state = match *state {
2023 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2024 _ => VarState::DontWarn,
2027 // Assigned some other value
2028 *state = VarState::DontWarn;
2032 ExprKind::Assign(ref lhs, _) if lhs.id == expr.id => *state = VarState::DontWarn,
2033 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2037 } else if is_loop(expr) || is_conditional(expr) {
2039 walk_expr(self, expr);
2042 } else if let ExprKind::Continue(_) = expr.node {
2046 walk_expr(self, expr);
2048 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2049 NestedVisitorMap::None
2053 /// Check whether a variable is initialized to zero at the start of a loop.
2054 struct InitializeVisitor<'a, 'tcx: 'a> {
2055 cx: &'a LateContext<'a, 'tcx>, // context reference
2056 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2060 depth: u32, // depth of conditional expressions
2064 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2065 fn visit_decl(&mut self, decl: &'tcx Decl) {
2066 // Look for declarations of the variable
2067 if let DeclKind::Local(ref local) = decl.node {
2068 if local.pat.id == self.var_id {
2069 if let PatKind::Binding(_, _, ident, _) = local.pat.node {
2070 self.name = Some(ident.name);
2072 self.state = if let Some(ref init) = local.init {
2073 if is_integer_literal(init, 0) {
2084 walk_decl(self, decl);
2087 fn visit_expr(&mut self, expr: &'tcx Expr) {
2088 if self.state == VarState::DontWarn {
2091 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2092 self.past_loop = true;
2095 // No need to visit expressions before the variable is
2097 if self.state == VarState::IncrOnce {
2101 // If node is the desired variable, see how it's used
2102 if var_def_id(self.cx, expr) == Some(self.var_id) {
2103 if let Some(parent) = get_parent_expr(self.cx, expr) {
2105 ExprKind::AssignOp(_, ref lhs, _) if lhs.id == expr.id => {
2106 self.state = VarState::DontWarn;
2108 ExprKind::Assign(ref lhs, ref rhs) if lhs.id == expr.id => {
2109 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2115 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2121 self.state = VarState::DontWarn;
2124 } else if !self.past_loop && is_loop(expr) {
2125 self.state = VarState::DontWarn;
2127 } else if is_conditional(expr) {
2129 walk_expr(self, expr);
2133 walk_expr(self, expr);
2135 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2136 NestedVisitorMap::None
2140 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<NodeId> {
2141 if let ExprKind::Path(ref qpath) = expr.node {
2142 let path_res = cx.tables.qpath_def(qpath, expr.hir_id);
2143 if let Def::Local(node_id) = path_res {
2144 return Some(node_id);
2150 fn is_loop(expr: &Expr) -> bool {
2152 ExprKind::Loop(..) | ExprKind::While(..) => true,
2157 fn is_conditional(expr: &Expr) -> bool {
2159 ExprKind::If(..) | ExprKind::Match(..) => true,
2164 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2166 if let Some(loop_block) = get_enclosing_block(cx, match_expr.id);
2167 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(loop_block.id));
2169 return is_loop_nested(cx, loop_expr, iter_expr)
2175 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2176 let mut id = loop_expr.id;
2177 let iter_name = if let Some(name) = path_name(iter_expr) {
2183 let parent = cx.tcx.hir.get_parent_node(id);
2187 match cx.tcx.hir.find(parent) {
2188 Some(Node::Expr(expr)) => match expr.node {
2189 ExprKind::Loop(..) | ExprKind::While(..) => {
2194 Some(Node::Block(block)) => {
2195 let mut block_visitor = LoopNestVisitor {
2197 iterator: iter_name,
2200 walk_block(&mut block_visitor, block);
2201 if block_visitor.nesting == RuledOut {
2205 Some(Node::Stmt(_)) => (),
2214 #[derive(PartialEq, Eq)]
2216 Unknown, // no nesting detected yet
2217 RuledOut, // the iterator is initialized or assigned within scope
2218 LookFurther, // no nesting detected, no further walk required
2221 use self::Nesting::{LookFurther, RuledOut, Unknown};
2223 struct LoopNestVisitor {
2229 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2230 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2231 if stmt.node.id() == self.id {
2232 self.nesting = LookFurther;
2233 } else if self.nesting == Unknown {
2234 walk_stmt(self, stmt);
2238 fn visit_expr(&mut self, expr: &'tcx Expr) {
2239 if self.nesting != Unknown {
2242 if expr.id == self.id {
2243 self.nesting = LookFurther;
2247 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => if match_var(path, self.iterator) {
2248 self.nesting = RuledOut;
2250 _ => walk_expr(self, expr),
2254 fn visit_pat(&mut self, pat: &'tcx Pat) {
2255 if self.nesting != Unknown {
2258 if let PatKind::Binding(_, _, span_name, _) = pat.node {
2259 if self.iterator == span_name.name {
2260 self.nesting = RuledOut;
2267 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2268 NestedVisitorMap::None
2272 fn path_name(e: &Expr) -> Option<Name> {
2273 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2274 let segments = &path.segments;
2275 if segments.len() == 1 {
2276 return Some(segments[0].ident.name);
2282 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2283 if constant(cx, cx.tables, cond).is_some() {
2284 // A pure constant condition (e.g. while false) is not linted.
2288 let mut var_visitor = VarCollectorVisitor {
2290 ids: FxHashSet::default(),
2291 def_ids: FxHashMap::default(),
2294 var_visitor.visit_expr(cond);
2295 if var_visitor.skip {
2298 let used_in_condition = &var_visitor.ids;
2299 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2300 used_in_condition.is_disjoint(&used_mutably)
2304 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2305 if no_cond_variable_mutated && !mutable_static_in_cond {
2308 WHILE_IMMUTABLE_CONDITION,
2310 "Variable in the condition are not mutated in the loop body. This either leads to an infinite or to a never running loop.",
2315 /// Collects the set of variables in an expression
2316 /// Stops analysis if a function call is found
2317 /// Note: In some cases such as `self`, there are no mutable annotation,
2318 /// All variables definition IDs are collected
2319 struct VarCollectorVisitor<'a, 'tcx: 'a> {
2320 cx: &'a LateContext<'a, 'tcx>,
2321 ids: FxHashSet<NodeId>,
2322 def_ids: FxHashMap<def_id::DefId, bool>,
2326 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2327 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2329 if let ExprKind::Path(ref qpath) = ex.node;
2330 if let QPath::Resolved(None, _) = *qpath;
2331 let def = self.cx.tables.qpath_def(qpath, ex.hir_id);
2334 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
2335 self.ids.insert(node_id);
2337 Def::Static(def_id, mutable) => {
2338 self.def_ids.insert(def_id, mutable);
2347 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2348 fn visit_expr(&mut self, ex: &'tcx Expr) {
2350 ExprKind::Path(_) => self.insert_def_id(ex),
2351 // If there is any function/method call… we just stop analysis
2352 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2354 _ => walk_expr(self, ex),
2358 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2359 NestedVisitorMap::None
2363 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2365 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2367 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2368 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2369 if chain_method.ident.name == "collect" && match_trait_method(cx, &args[0], &paths::ITERATOR);
2370 if let Some(ref generic_args) = chain_method.args;
2371 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2373 let ty = cx.tables.node_id_to_type(ty.hir_id);
2374 if match_type(cx, ty, &paths::VEC) ||
2375 match_type(cx, ty, &paths::VEC_DEQUE) ||
2376 match_type(cx, ty, &paths::BTREEMAP) ||
2377 match_type(cx, ty, &paths::HASHMAP) {
2378 if method.ident.name == "len" {
2379 let span = shorten_needless_collect_span(expr);
2380 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2381 db.span_suggestion_with_applicability(
2384 ".count()".to_string(),
2385 Applicability::MachineApplicable,
2389 if method.ident.name == "is_empty" {
2390 let span = shorten_needless_collect_span(expr);
2391 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2392 db.span_suggestion_with_applicability(
2395 ".next().is_none()".to_string(),
2396 Applicability::MachineApplicable,
2400 if method.ident.name == "contains" {
2401 let contains_arg = snippet(cx, args[1].span, "??");
2402 let span = shorten_needless_collect_span(expr);
2403 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2404 db.span_suggestion_with_applicability(
2408 ".any(|&x| x == {})",
2409 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2411 Applicability::MachineApplicable,
2420 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2422 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2423 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2425 return expr.span.with_lo(span.lo() - BytePos(1));