1 use crate::reexport::*;
2 use if_chain::if_chain;
3 use itertools::Itertools;
4 use rustc::hir::def::{DefKind, Res};
5 use rustc::hir::def_id;
6 use rustc::hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
8 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
9 use rustc::middle::region;
10 use rustc::{declare_lint_pass, declare_tool_lint};
11 // use rustc::middle::region::CodeExtent;
12 use crate::consts::{constant, Constant};
13 use crate::utils::usage::mutated_variables;
14 use crate::utils::{in_macro_or_desugar, sext, sugg};
15 use rustc::middle::expr_use_visitor::*;
16 use rustc::middle::mem_categorization::cmt_;
17 use rustc::middle::mem_categorization::Categorization;
18 use rustc::ty::subst::Subst;
19 use rustc::ty::{self, Ty};
20 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
21 use rustc_errors::Applicability;
22 use std::iter::{once, Iterator};
25 use syntax::source_map::Span;
26 use syntax_pos::BytePos;
28 use crate::utils::paths;
30 get_enclosing_block, get_parent_expr, has_iter_method, higher, is_integer_literal, is_refutable, last_path_segment,
31 match_trait_method, match_type, match_var, multispan_sugg, snippet, snippet_opt, snippet_with_applicability,
32 span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then, SpanlessEq,
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// # let src = vec![1];
46 /// # let mut dst = vec![0; 65];
47 /// for i in 0..src.len() {
48 /// dst[i + 64] = src[i];
53 "manually copying items between slices"
56 declare_clippy_lint! {
57 /// **What it does:** Checks for looping over the range of `0..len` of some
58 /// collection just to get the values by index.
60 /// **Why is this bad?** Just iterating the collection itself makes the intent
61 /// more clear and is probably faster.
63 /// **Known problems:** None.
67 /// let vec = vec!['a', 'b', 'c'];
68 /// for i in 0..vec.len() {
69 /// println!("{}", vec[i]);
72 /// Could be written as:
74 /// let vec = vec!['a', 'b', 'c'];
76 /// println!("{}", i);
79 pub NEEDLESS_RANGE_LOOP,
81 "for-looping over a range of indices where an iterator over items would do"
84 declare_clippy_lint! {
85 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
86 /// suggests the latter.
88 /// **Why is this bad?** Readability.
90 /// **Known problems:** False negatives. We currently only warn on some known
95 /// // with `y` a `Vec` or slice:
96 /// # let y = vec![1];
97 /// for x in y.iter() {
101 /// can be rewritten to
103 /// # let y = vec![1];
108 pub EXPLICIT_ITER_LOOP,
110 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
113 declare_clippy_lint! {
114 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
115 /// suggests the latter.
117 /// **Why is this bad?** Readability.
119 /// **Known problems:** None
123 /// # let y = vec![1];
124 /// // with `y` a `Vec` or slice:
125 /// for x in y.into_iter() {
129 /// can be rewritten to
131 /// # let y = vec![1];
136 pub EXPLICIT_INTO_ITER_LOOP,
138 "for-looping over `_.into_iter()` when `_` would do"
141 declare_clippy_lint! {
142 /// **What it does:** Checks for loops on `x.next()`.
144 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
145 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
146 /// implements `IntoIterator`, so that possibly one value will be iterated,
147 /// leading to some hard to find bugs. No one will want to write such code
148 /// [except to win an Underhanded Rust
149 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
151 /// **Known problems:** None.
155 /// for x in y.next() {
161 "for-looping over `_.next()` which is probably not intended"
164 declare_clippy_lint! {
165 /// **What it does:** Checks for `for` loops over `Option` values.
167 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
170 /// **Known problems:** None.
174 /// for x in option {
181 /// if let Some(x) = option {
185 pub FOR_LOOP_OVER_OPTION,
187 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
190 declare_clippy_lint! {
191 /// **What it does:** Checks for `for` loops over `Result` values.
193 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
196 /// **Known problems:** None.
200 /// for x in result {
207 /// if let Ok(x) = result {
211 pub FOR_LOOP_OVER_RESULT,
213 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
216 declare_clippy_lint! {
217 /// **What it does:** Detects `loop + match` combinations that are easier
218 /// written as a `while let` loop.
220 /// **Why is this bad?** The `while let` loop is usually shorter and more
223 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
227 /// # let y = Some(1);
229 /// let x = match y {
233 /// // .. do something with x
235 /// // is easier written as
236 /// while let Some(x) = y {
237 /// // .. do something with x
242 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
245 declare_clippy_lint! {
246 /// **What it does:** Checks for using `collect()` on an iterator without using
249 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
250 /// iterator instead.
252 /// **Known problems:** None.
256 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
260 "`collect()`ing an iterator without using the result; this is usually better written as a for loop"
263 declare_clippy_lint! {
264 /// **What it does:** Checks for functions collecting an iterator when collect
267 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
268 /// when this allocation may not be needed.
270 /// **Known problems:**
275 /// # let iterator = vec![1].into_iter();
276 /// let len = iterator.clone().collect::<Vec<_>>().len();
278 /// let len = iterator.count();
280 pub NEEDLESS_COLLECT,
282 "collecting an iterator when collect is not needed"
285 declare_clippy_lint! {
286 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
287 /// are constant and `x` is greater or equal to `y`, unless the range is
288 /// reversed or has a negative `.step_by(_)`.
290 /// **Why is it bad?** Such loops will either be skipped or loop until
291 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
294 /// **Known problems:** The lint cannot catch loops over dynamically defined
295 /// ranges. Doing this would require simulating all possible inputs and code
296 /// paths through the program, which would be complex and error-prone.
300 /// for x in 5..10 - 5 {
302 /// } // oops, stray `-`
304 pub REVERSE_RANGE_LOOP,
306 "iteration over an empty range, such as `10..0` or `5..5`"
309 declare_clippy_lint! {
310 /// **What it does:** Checks `for` loops over slices with an explicit counter
311 /// and suggests the use of `.enumerate()`.
313 /// **Why is it bad?** Not only is the version using `.enumerate()` more
314 /// readable, the compiler is able to remove bounds checks which can lead to
315 /// faster code in some instances.
317 /// **Known problems:** None.
321 /// # let v = vec![1];
322 /// # fn foo(bar: usize) {}
323 /// # fn bar(bar: usize, baz: usize) {}
324 /// for i in 0..v.len() { foo(v[i]); }
325 /// for i in 0..v.len() { bar(i, v[i]); }
327 pub EXPLICIT_COUNTER_LOOP,
329 "for-looping with an explicit counter when `_.enumerate()` would do"
332 declare_clippy_lint! {
333 /// **What it does:** Checks for empty `loop` expressions.
335 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
336 /// anything. Think of the environment and either block on something or at least
337 /// make the thread sleep for some microseconds.
339 /// **Known problems:** None.
347 "empty `loop {}`, which should block or sleep"
350 declare_clippy_lint! {
351 /// **What it does:** Checks for `while let` expressions on iterators.
353 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
354 /// the intent better.
356 /// **Known problems:** None.
360 /// while let Some(val) = iter() {
364 pub WHILE_LET_ON_ITERATOR,
366 "using a while-let loop instead of a for loop on an iterator"
369 declare_clippy_lint! {
370 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
371 /// ignoring either the keys or values.
373 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
374 /// can be used to express that don't need the values or keys.
376 /// **Known problems:** None.
380 /// for (k, _) in &map {
385 /// could be replaced by
388 /// for k in map.keys() {
394 "looping on a map using `iter` when `keys` or `values` would do"
397 declare_clippy_lint! {
398 /// **What it does:** Checks for loops that will always `break`, `return` or
399 /// `continue` an outer loop.
401 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
404 /// **Known problems:** None
415 "any loop that will always `break` or `return`"
418 declare_clippy_lint! {
419 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
421 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
423 /// **Known problems:** None
427 /// let mut foo = 42;
428 /// for i in 0..foo {
430 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
435 "for loop over a range where one of the bounds is a mutable variable"
438 declare_clippy_lint! {
439 /// **What it does:** Checks whether variables used within while loop condition
440 /// can be (and are) mutated in the body.
442 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
443 /// will lead to an infinite loop.
445 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
446 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
447 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
453 /// println!("let me loop forever!");
456 pub WHILE_IMMUTABLE_CONDITION,
458 "variables used within while expression are not mutated in the body"
461 declare_lint_pass!(Loops => [
465 EXPLICIT_INTO_ITER_LOOP,
467 FOR_LOOP_OVER_RESULT,
468 FOR_LOOP_OVER_OPTION,
473 EXPLICIT_COUNTER_LOOP,
475 WHILE_LET_ON_ITERATOR,
479 WHILE_IMMUTABLE_CONDITION,
482 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
483 #[allow(clippy::too_many_lines)]
484 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
485 // we don't want to check expanded macros
486 if in_macro_or_desugar(expr.span) {
490 if let Some((pat, arg, body)) = higher::for_loop(expr) {
491 check_for_loop(cx, pat, arg, body, expr);
494 // check for never_loop
495 if let ExprKind::Loop(ref block, _, _) = expr.node {
496 match never_loop_block(block, expr.hir_id) {
497 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
498 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
502 // check for `loop { if let {} else break }` that could be `while let`
503 // (also matches an explicit "match" instead of "if let")
504 // (even if the "match" or "if let" is used for declaration)
505 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
506 // also check for empty `loop {}` statements
507 if block.stmts.is_empty() && block.expr.is_none() {
512 "empty `loop {}` detected. You may want to either use `panic!()` or add \
513 `std::thread::sleep(..);` to the loop body.",
517 // extract the expression from the first statement (if any) in a block
518 let inner_stmt_expr = extract_expr_from_first_stmt(block);
519 // or extract the first expression (if any) from the block
520 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
521 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
522 // ensure "if let" compatible match structure
524 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
526 && arms[0].pats.len() == 1
527 && arms[0].guard.is_none()
528 && arms[1].pats.len() == 1
529 && arms[1].guard.is_none()
530 && is_simple_break_expr(&arms[1].body)
532 if in_external_macro(cx.sess(), expr.span) {
536 // NOTE: we used to build a body here instead of using
537 // ellipsis, this was removed because:
538 // 1) it was ugly with big bodies;
539 // 2) it was not indented properly;
540 // 3) it wasn’t very smart (see #675).
541 let mut applicability = Applicability::HasPlaceholders;
546 "this loop could be written as a `while let` loop",
549 "while let {} = {} {{ .. }}",
550 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
551 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
562 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
563 let pat = &arms[0].pats[0].node;
565 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
566 &ExprKind::MethodCall(ref method_path, _, ref method_args),
567 ) = (pat, &match_expr.node)
569 let iter_expr = &method_args[0];
570 let lhs_constructor = last_path_segment(qpath);
571 if method_path.ident.name == sym!(next)
572 && match_trait_method(cx, match_expr, &paths::ITERATOR)
573 && lhs_constructor.ident.name == sym!(Some)
574 && (pat_args.is_empty()
575 || !is_refutable(cx, &pat_args[0])
576 && !is_used_inside(cx, iter_expr, &arms[0].body)
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 if let Some((cond, body)) = higher::while_loop(&expr) {
600 check_infinite_loop(cx, cond, body);
603 check_needless_collect(expr, cx);
606 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
607 if let StmtKind::Semi(ref expr) = stmt.node {
608 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
610 && method.ident.name == sym!(collect)
611 && match_trait_method(cx, expr, &paths::ITERATOR)
617 "you are collect()ing an iterator and throwing away the result. \
618 Consider using an explicit for loop to exhaust the iterator",
626 enum NeverLoopResult {
627 // A break/return always get triggered but not necessarily for the main loop.
629 // A continue may occur for the main loop.
634 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
636 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
637 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
641 // Combine two results for parts that are called in order.
642 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
644 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
645 NeverLoopResult::Otherwise => second,
649 // Combine two results where both parts are called but not necessarily in order.
650 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
651 match (left, right) {
652 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
653 NeverLoopResult::MayContinueMainLoop
655 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
656 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
660 // Combine two results where only one of the part may have been executed.
661 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
663 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
664 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
665 NeverLoopResult::MayContinueMainLoop
667 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
671 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
672 let stmts = block.stmts.iter().map(stmt_to_expr);
673 let expr = once(block.expr.as_ref().map(|p| &**p));
674 let mut iter = stmts.chain(expr).filter_map(|e| e);
675 never_loop_expr_seq(&mut iter, main_loop_id)
678 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
680 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
681 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
686 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
689 | ExprKind::Unary(_, ref e)
690 | ExprKind::Cast(ref e, _)
691 | ExprKind::Type(ref e, _)
692 | ExprKind::Field(ref e, _)
693 | ExprKind::AddrOf(_, ref e)
694 | ExprKind::Struct(_, _, Some(ref e))
695 | ExprKind::Repeat(ref e, _)
696 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
697 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
698 never_loop_expr_all(&mut es.iter(), main_loop_id)
700 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
701 ExprKind::Binary(_, ref e1, ref e2)
702 | ExprKind::Assign(ref e1, ref e2)
703 | ExprKind::AssignOp(_, ref e1, ref e2)
704 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
705 ExprKind::Loop(ref b, _, _) => {
706 // Break can come from the inner loop so remove them.
707 absorb_break(&never_loop_block(b, main_loop_id))
709 ExprKind::Match(ref e, ref arms, _) => {
710 let e = never_loop_expr(e, main_loop_id);
714 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
718 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
719 ExprKind::Continue(d) => {
722 .expect("target ID can only be missing in the presence of compilation errors");
723 if id == main_loop_id {
724 NeverLoopResult::MayContinueMainLoop
726 NeverLoopResult::AlwaysBreak
729 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
730 if let Some(ref e) = *e {
731 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
733 NeverLoopResult::AlwaysBreak
736 ExprKind::Struct(_, _, None)
737 | ExprKind::Yield(_, _)
738 | ExprKind::Closure(_, _, _, _, _)
739 | ExprKind::InlineAsm(_, _, _)
742 | ExprKind::Err => NeverLoopResult::Otherwise,
746 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
747 es.map(|e| never_loop_expr(e, main_loop_id))
748 .fold(NeverLoopResult::Otherwise, combine_seq)
751 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
752 es.map(|e| never_loop_expr(e, main_loop_id))
753 .fold(NeverLoopResult::Otherwise, combine_both)
756 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
757 e.map(|e| never_loop_expr(e, main_loop_id))
758 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
761 fn check_for_loop<'a, 'tcx>(
762 cx: &LateContext<'a, 'tcx>,
768 check_for_loop_range(cx, pat, arg, body, expr);
769 check_for_loop_reverse_range(cx, arg, expr);
770 check_for_loop_arg(cx, pat, arg, expr);
771 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
772 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
773 check_for_mut_range_bound(cx, arg, body);
774 detect_manual_memcpy(cx, pat, arg, body, expr);
777 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
779 if let ExprKind::Path(ref qpath) = expr.node;
780 if let QPath::Resolved(None, ref path) = *qpath;
781 if path.segments.len() == 1;
782 if let Res::Local(local_id) = cx.tables.qpath_res(qpath, expr.hir_id);
799 fn negative(s: String) -> Self {
800 Self { value: s, negate: true }
803 fn positive(s: String) -> Self {
811 struct FixedOffsetVar {
816 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
817 let is_slice = match ty.sty {
818 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
819 ty::Slice(..) | ty::Array(..) => true,
823 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
826 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
827 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
829 ExprKind::Lit(ref l) => match l.node {
830 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
833 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
838 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
839 let ty = cx.tables.expr_ty(seqexpr);
840 if !is_slice_like(cx, ty) {
844 let offset = match idx.node {
845 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
847 let offset_opt = if same_var(cx, lhs, var) {
848 extract_offset(cx, rhs, var)
849 } else if same_var(cx, rhs, var) {
850 extract_offset(cx, lhs, var)
855 offset_opt.map(Offset::positive)
857 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
860 ExprKind::Path(..) => {
861 if same_var(cx, idx, var) {
862 Some(Offset::positive("0".into()))
870 offset.map(|o| FixedOffsetVar {
871 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
879 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
880 cx: &LateContext<'a, 'tcx>,
883 ) -> Option<FixedOffsetVar> {
885 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
886 if method.ident.name == sym!(clone);
888 if let Some(arg) = args.get(0);
890 return get_fixed_offset_var(cx, arg, var);
894 get_fixed_offset_var(cx, expr, var)
897 fn get_indexed_assignments<'a, 'tcx>(
898 cx: &LateContext<'a, 'tcx>,
901 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
902 fn get_assignment<'a, 'tcx>(
903 cx: &LateContext<'a, 'tcx>,
906 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
907 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
909 get_fixed_offset_var(cx, lhs, var),
910 fetch_cloned_fixed_offset_var(cx, rhs, var),
912 (Some(offset_left), Some(offset_right)) => {
913 // Source and destination must be different
914 if offset_left.var_name == offset_right.var_name {
917 Some((offset_left, offset_right))
927 if let ExprKind::Block(ref b, _) = body.node {
929 ref stmts, ref expr, ..
934 .map(|stmt| match stmt.node {
935 StmtKind::Local(..) | StmtKind::Item(..) => None,
936 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
938 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
940 .collect::<Option<Vec<_>>>()
941 .unwrap_or_else(|| vec![])
943 get_assignment(cx, body, var).into_iter().collect()
947 /// Checks for for loops that sequentially copy items from one slice-like
948 /// object to another.
949 fn detect_manual_memcpy<'a, 'tcx>(
950 cx: &LateContext<'a, 'tcx>,
956 if let Some(higher::Range {
960 }) = higher::range(cx, arg)
962 // the var must be a single name
963 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
964 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
965 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
966 ("0", _, "0", _) => "".into(),
967 ("0", _, x, false) | (x, false, "0", false) => x.into(),
968 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
969 (x, false, y, false) => format!("({} + {})", x, y),
970 (x, false, y, true) => {
974 format!("({} - {})", x, y)
977 (x, true, y, false) => {
981 format!("({} - {})", y, x)
984 (x, true, y, true) => format!("-({} + {})", x, y),
988 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
989 if let Some(end) = *end {
991 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
992 if method.ident.name == sym!(len);
993 if len_args.len() == 1;
994 if let Some(arg) = len_args.get(0);
995 if snippet(cx, arg.span, "??") == var_name;
997 return if offset.negate {
998 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
1005 let end_str = match limits {
1006 ast::RangeLimits::Closed => {
1007 let end = sugg::Sugg::hir(cx, end, "<count>");
1008 format!("{}", end + sugg::ONE)
1010 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1013 print_sum(&Offset::positive(end_str), &offset)
1019 // The only statements in the for loops can be indexed assignments from
1020 // indexed retrievals.
1021 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1023 let big_sugg = manual_copies
1025 .map(|(dst_var, src_var)| {
1026 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1027 let dst_offset = print_sum(&start_str, &dst_var.offset);
1028 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1029 let src_offset = print_sum(&start_str, &src_var.offset);
1030 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1031 let dst = if dst_offset == "" && dst_limit == "" {
1034 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1038 "{}.clone_from_slice(&{}[{}..{}])",
1039 dst, src_var.var_name, src_offset, src_limit
1044 if !big_sugg.is_empty() {
1049 "it looks like you're manually copying between slices",
1050 "try replacing the loop by",
1052 Applicability::Unspecified,
1059 /// Checks for looping over a range and then indexing a sequence with it.
1060 /// The iteratee must be a range literal.
1061 #[allow(clippy::too_many_lines)]
1062 fn check_for_loop_range<'a, 'tcx>(
1063 cx: &LateContext<'a, 'tcx>,
1069 if in_macro_or_desugar(expr.span) {
1073 if let Some(higher::Range {
1077 }) = higher::range(cx, arg)
1079 // the var must be a single name
1080 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1081 let mut visitor = VarVisitor {
1084 indexed_mut: FxHashSet::default(),
1085 indexed_indirectly: FxHashMap::default(),
1086 indexed_directly: FxHashMap::default(),
1087 referenced: FxHashSet::default(),
1089 prefer_mutable: false,
1091 walk_expr(&mut visitor, body);
1093 // linting condition: we only indexed one variable, and indexed it directly
1094 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1095 let (indexed, (indexed_extent, indexed_ty)) = visitor
1099 .expect("already checked that we have exactly 1 element");
1101 // ensure that the indexed variable was declared before the loop, see #601
1102 if let Some(indexed_extent) = indexed_extent {
1103 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1104 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1105 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1106 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1107 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1112 // don't lint if the container that is indexed does not have .iter() method
1113 let has_iter = has_iter_method(cx, indexed_ty);
1114 if has_iter.is_none() {
1118 // don't lint if the container that is indexed into is also used without
1120 if visitor.referenced.contains(&indexed) {
1124 let starts_at_zero = is_integer_literal(start, 0);
1126 let skip = if starts_at_zero {
1129 format!(".skip({})", snippet(cx, start.span, ".."))
1132 let mut end_is_start_plus_val = false;
1134 let take = if let Some(end) = *end {
1135 let mut take_expr = end;
1137 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1138 if let BinOpKind::Add = op.node {
1139 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1140 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1142 if start_equal_left {
1144 } else if start_equal_right {
1148 end_is_start_plus_val = start_equal_left | start_equal_right;
1152 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1156 ast::RangeLimits::Closed => {
1157 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1158 format!(".take({})", take_expr + sugg::ONE)
1160 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1167 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1168 ("mut ", "iter_mut")
1173 let take_is_empty = take.is_empty();
1174 let mut method_1 = take;
1175 let mut method_2 = skip;
1177 if end_is_start_plus_val {
1178 mem::swap(&mut method_1, &mut method_2);
1181 if visitor.nonindex {
1184 NEEDLESS_RANGE_LOOP,
1186 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1190 "consider using an iterator".to_string(),
1192 (pat.span, format!("({}, <item>)", ident.name)),
1195 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1202 let repl = if starts_at_zero && take_is_empty {
1203 format!("&{}{}", ref_mut, indexed)
1205 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1210 NEEDLESS_RANGE_LOOP,
1213 "the loop variable `{}` is only used to index `{}`.",
1219 "consider using an iterator".to_string(),
1220 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1230 fn is_len_call(expr: &Expr, var: Name) -> bool {
1232 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1233 if len_args.len() == 1;
1234 if method.ident.name == sym!(len);
1235 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1236 if path.segments.len() == 1;
1237 if path.segments[0].ident.name == var;
1246 fn is_end_eq_array_len<'tcx>(
1247 cx: &LateContext<'_, 'tcx>,
1249 limits: ast::RangeLimits,
1250 indexed_ty: Ty<'tcx>,
1253 if let ExprKind::Lit(ref lit) = end.node;
1254 if let ast::LitKind::Int(end_int, _) = lit.node;
1255 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1256 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1258 return match limits {
1259 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1260 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1268 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1269 // if this for loop is iterating over a two-sided range...
1270 if let Some(higher::Range {
1274 }) = higher::range(cx, arg)
1276 // ...and both sides are compile-time constant integers...
1277 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1278 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1279 // ...and the start index is greater than the end index,
1280 // this loop will never run. This is often confusing for developers
1281 // who think that this will iterate from the larger value to the
1283 let ty = cx.tables.expr_ty(start);
1284 let (sup, eq) = match (start_idx, end_idx) {
1285 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1287 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1288 ty::Uint(_) => start_idx > end_idx,
1291 start_idx == end_idx,
1293 _ => (false, false),
1297 let start_snippet = snippet(cx, start.span, "_");
1298 let end_snippet = snippet(cx, end.span, "_");
1299 let dots = if limits == ast::RangeLimits::Closed {
1309 "this range is empty so this for loop will never run",
1313 "consider using the following if you are attempting to iterate over this \
1316 "({end}{dots}{start}).rev()",
1319 start = start_snippet
1321 Applicability::MaybeIncorrect,
1325 } else if eq && limits != ast::RangeLimits::Closed {
1326 // if they are equal, it's also problematic - this loop
1332 "this range is empty so this for loop will never run",
1340 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1341 let mut applicability = Applicability::MachineApplicable;
1342 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1343 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1348 "it is more concise to loop over references to containers instead of using explicit \
1350 "to write this more concisely, try",
1351 format!("&{}{}", muta, object),
1356 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1357 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1358 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1359 // just the receiver, no arguments
1360 if args.len() == 1 {
1361 let method_name = &*method.ident.as_str();
1362 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1363 if method_name == "iter" || method_name == "iter_mut" {
1364 if is_ref_iterable_type(cx, &args[0]) {
1365 lint_iter_method(cx, args, arg, method_name);
1367 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1368 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1369 let substs = cx.tables.node_substs(arg.hir_id);
1370 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1372 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1373 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1374 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1375 match cx.tables.expr_ty(&args[0]).sty {
1376 // If the length is greater than 32 no traits are implemented for array and
1377 // therefore we cannot use `&`.
1378 ty::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1379 _ => lint_iter_method(cx, args, arg, method_name),
1382 let mut applicability = Applicability::MachineApplicable;
1383 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1386 EXPLICIT_INTO_ITER_LOOP,
1388 "it is more concise to loop over containers instead of using explicit \
1389 iteration methods`",
1390 "to write this more concisely, try",
1395 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1400 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1401 probably not what you want",
1403 next_loop_linted = true;
1407 if !next_loop_linted {
1408 check_arg_type(cx, pat, arg);
1412 /// Checks for `for` loops over `Option`s and `Result`s.
1413 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1414 let ty = cx.tables.expr_ty(arg);
1415 if match_type(cx, ty, &paths::OPTION) {
1418 FOR_LOOP_OVER_OPTION,
1421 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1422 `if let` statement.",
1423 snippet(cx, arg.span, "_")
1426 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1427 snippet(cx, pat.span, "_"),
1428 snippet(cx, arg.span, "_")
1431 } else if match_type(cx, ty, &paths::RESULT) {
1434 FOR_LOOP_OVER_RESULT,
1437 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1438 `if let` statement.",
1439 snippet(cx, arg.span, "_")
1442 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1443 snippet(cx, pat.span, "_"),
1444 snippet(cx, arg.span, "_")
1450 fn check_for_loop_explicit_counter<'a, 'tcx>(
1451 cx: &LateContext<'a, 'tcx>,
1457 // Look for variables that are incremented once per loop iteration.
1458 let mut visitor = IncrementVisitor {
1460 states: FxHashMap::default(),
1464 walk_expr(&mut visitor, body);
1466 // For each candidate, check the parent block to see if
1467 // it's initialized to zero at the start of the loop.
1468 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1469 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1470 let mut visitor2 = InitializeVisitor {
1474 state: VarState::IncrOnce,
1479 walk_block(&mut visitor2, block);
1481 if visitor2.state == VarState::Warn {
1482 if let Some(name) = visitor2.name {
1483 let mut applicability = Applicability::MachineApplicable;
1486 EXPLICIT_COUNTER_LOOP,
1488 &format!("the variable `{}` is used as a loop counter.", name),
1491 "for ({}, {}) in {}.enumerate()",
1493 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1494 if higher::range(cx, arg).is_some() {
1497 snippet_with_applicability(cx, arg.span, "_", &mut applicability)
1502 sugg::Sugg::hir_with_applicability(cx, arg, "_", &mut applicability).maybe_par()
1514 /// Checks for the `FOR_KV_MAP` lint.
1515 fn check_for_loop_over_map_kv<'a, 'tcx>(
1516 cx: &LateContext<'a, 'tcx>,
1522 let pat_span = pat.span;
1524 if let PatKind::Tuple(ref pat, _) = pat.node {
1526 let arg_span = arg.span;
1527 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1528 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1529 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1530 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1535 let mutbl = match mutbl {
1537 MutMutable => "_mut",
1539 let arg = match arg.node {
1540 ExprKind::AddrOf(_, ref expr) => &**expr,
1544 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1549 &format!("you seem to want to iterate on a map's {}s", kind),
1551 let map = sugg::Sugg::hir(cx, arg, "map");
1554 "use the corresponding method".into(),
1556 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1557 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1567 struct MutatePairDelegate {
1568 hir_id_low: Option<HirId>,
1569 hir_id_high: Option<HirId>,
1570 span_low: Option<Span>,
1571 span_high: Option<Span>,
1574 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1575 fn consume(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1577 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1579 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1581 fn borrow(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1582 if let ty::BorrowKind::MutBorrow = bk {
1583 if let Categorization::Local(id) = cmt.cat {
1584 if Some(id) == self.hir_id_low {
1585 self.span_low = Some(sp)
1587 if Some(id) == self.hir_id_high {
1588 self.span_high = Some(sp)
1594 fn mutate(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1595 if let Categorization::Local(id) = cmt.cat {
1596 if Some(id) == self.hir_id_low {
1597 self.span_low = Some(sp)
1599 if Some(id) == self.hir_id_high {
1600 self.span_high = Some(sp)
1605 fn decl_without_init(&mut self, _: HirId, _: Span) {}
1608 impl<'tcx> MutatePairDelegate {
1609 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1610 (self.span_low, self.span_high)
1614 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1615 if let Some(higher::Range {
1619 }) = higher::range(cx, arg)
1621 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1622 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1623 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1624 mut_warn_with_span(cx, span_low);
1625 mut_warn_with_span(cx, span_high);
1630 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1631 if let Some(sp) = span {
1636 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1641 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1643 if let ExprKind::Path(ref qpath) = bound.node;
1644 if let QPath::Resolved(None, _) = *qpath;
1646 let res = cx.tables.qpath_res(qpath, bound.hir_id);
1647 if let Res::Local(node_id) = res {
1648 let node_str = cx.tcx.hir().get(node_id);
1650 if let Node::Binding(pat) = node_str;
1651 if let PatKind::Binding(bind_ann, ..) = pat.node;
1652 if let BindingAnnotation::Mutable = bind_ann;
1654 return Some(node_id);
1663 fn check_for_mutation(
1664 cx: &LateContext<'_, '_>,
1666 bound_ids: &[Option<HirId>],
1667 ) -> (Option<Span>, Option<Span>) {
1668 let mut delegate = MutatePairDelegate {
1669 hir_id_low: bound_ids[0],
1670 hir_id_high: bound_ids[1],
1674 let def_id = def_id::DefId::local(body.hir_id.owner);
1675 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1676 ExprUseVisitor::new(
1686 delegate.mutation_span()
1689 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1690 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1692 PatKind::Wild => true,
1693 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1694 let mut visitor = UsedVisitor {
1698 walk_expr(&mut visitor, body);
1705 struct UsedVisitor {
1706 var: ast::Name, // var to look for
1707 used: bool, // has the var been used otherwise?
1710 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1711 fn visit_expr(&mut self, expr: &'tcx Expr) {
1712 if match_var(expr, self.var) {
1715 walk_expr(self, expr);
1719 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1720 NestedVisitorMap::None
1724 struct LocalUsedVisitor<'a, 'tcx> {
1725 cx: &'a LateContext<'a, 'tcx>,
1730 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1731 fn visit_expr(&mut self, expr: &'tcx Expr) {
1732 if same_var(self.cx, expr, self.local) {
1735 walk_expr(self, expr);
1739 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1740 NestedVisitorMap::None
1744 struct VarVisitor<'a, 'tcx> {
1745 /// context reference
1746 cx: &'a LateContext<'a, 'tcx>,
1747 /// var name to look for as index
1749 /// indexed variables that are used mutably
1750 indexed_mut: FxHashSet<Name>,
1751 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1752 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1753 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1754 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1755 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1756 /// Any names that are used outside an index operation.
1757 /// Used to detect things like `&mut vec` used together with `vec[i]`
1758 referenced: FxHashSet<Name>,
1759 /// has the loop variable been used in expressions other than the index of
1762 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1763 /// takes `&mut self`
1764 prefer_mutable: bool,
1767 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1768 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1770 // the indexed container is referenced by a name
1771 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1772 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1773 if seqvar.segments.len() == 1;
1775 let index_used_directly = same_var(self.cx, idx, self.var);
1776 let indexed_indirectly = {
1777 let mut used_visitor = LocalUsedVisitor {
1782 walk_expr(&mut used_visitor, idx);
1786 if indexed_indirectly || index_used_directly {
1787 if self.prefer_mutable {
1788 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1790 let res = self.cx.tables.qpath_res(seqpath, seqexpr.hir_id);
1792 Res::Local(hir_id) => {
1793 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1794 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1795 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1796 if indexed_indirectly {
1797 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1799 if index_used_directly {
1800 self.indexed_directly.insert(
1801 seqvar.segments[0].ident.name,
1802 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1805 return false; // no need to walk further *on the variable*
1807 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1808 if indexed_indirectly {
1809 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1811 if index_used_directly {
1812 self.indexed_directly.insert(
1813 seqvar.segments[0].ident.name,
1814 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1817 return false; // no need to walk further *on the variable*
1828 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1829 fn visit_expr(&mut self, expr: &'tcx Expr) {
1832 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1833 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1834 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1835 if !self.check(&args[1], &args[0], expr);
1841 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1842 if !self.check(idx, seqexpr, expr);
1847 // directly using a variable
1848 if let ExprKind::Path(ref qpath) = expr.node;
1849 if let QPath::Resolved(None, ref path) = *qpath;
1850 if path.segments.len() == 1;
1852 if let Res::Local(local_id) = self.cx.tables.qpath_res(qpath, expr.hir_id) {
1853 if local_id == self.var {
1854 self.nonindex = true;
1856 // not the correct variable, but still a variable
1857 self.referenced.insert(path.segments[0].ident.name);
1863 let old = self.prefer_mutable;
1865 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1866 self.prefer_mutable = true;
1867 self.visit_expr(lhs);
1868 self.prefer_mutable = false;
1869 self.visit_expr(rhs);
1871 ExprKind::AddrOf(mutbl, ref expr) => {
1872 if mutbl == MutMutable {
1873 self.prefer_mutable = true;
1875 self.visit_expr(expr);
1877 ExprKind::Call(ref f, ref args) => {
1880 let ty = self.cx.tables.expr_ty_adjusted(expr);
1881 self.prefer_mutable = false;
1882 if let ty::Ref(_, _, mutbl) = ty.sty {
1883 if mutbl == MutMutable {
1884 self.prefer_mutable = true;
1887 self.visit_expr(expr);
1890 ExprKind::MethodCall(_, _, ref args) => {
1891 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1892 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1893 self.prefer_mutable = false;
1894 if let ty::Ref(_, _, mutbl) = ty.sty {
1895 if mutbl == MutMutable {
1896 self.prefer_mutable = true;
1899 self.visit_expr(expr);
1902 ExprKind::Closure(_, _, body_id, ..) => {
1903 let body = self.cx.tcx.hir().body(body_id);
1904 self.visit_expr(&body.value);
1906 _ => walk_expr(self, expr),
1908 self.prefer_mutable = old;
1910 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1911 NestedVisitorMap::None
1915 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1916 let def_id = match var_def_id(cx, expr) {
1918 None => return false,
1920 if let Some(used_mutably) = mutated_variables(container, cx) {
1921 if used_mutably.contains(&def_id) {
1928 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1929 let def_id = match var_def_id(cx, iter_expr) {
1931 None => return false,
1933 let mut visitor = VarUsedAfterLoopVisitor {
1936 iter_expr_id: iter_expr.hir_id,
1937 past_while_let: false,
1938 var_used_after_while_let: false,
1940 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1941 walk_block(&mut visitor, enclosing_block);
1943 visitor.var_used_after_while_let
1946 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1947 cx: &'a LateContext<'a, 'tcx>,
1949 iter_expr_id: HirId,
1950 past_while_let: bool,
1951 var_used_after_while_let: bool,
1954 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1955 fn visit_expr(&mut self, expr: &'tcx Expr) {
1956 if self.past_while_let {
1957 if Some(self.def_id) == var_def_id(self.cx, expr) {
1958 self.var_used_after_while_let = true;
1960 } else if self.iter_expr_id == expr.hir_id {
1961 self.past_while_let = true;
1963 walk_expr(self, expr);
1965 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1966 NestedVisitorMap::None
1970 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1971 /// for `&T` and `&mut T`, such as `Vec`.
1973 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1974 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1975 // will allow further borrows afterwards
1976 let ty = cx.tables.expr_ty(e);
1977 is_iterable_array(ty, cx) ||
1978 match_type(cx, ty, &paths::VEC) ||
1979 match_type(cx, ty, &paths::LINKED_LIST) ||
1980 match_type(cx, ty, &paths::HASHMAP) ||
1981 match_type(cx, ty, &paths::HASHSET) ||
1982 match_type(cx, ty, &paths::VEC_DEQUE) ||
1983 match_type(cx, ty, &paths::BINARY_HEAP) ||
1984 match_type(cx, ty, &paths::BTREEMAP) ||
1985 match_type(cx, ty, &paths::BTREESET)
1988 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1989 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1991 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1996 /// If a block begins with a statement (possibly a `let` binding) and has an
1997 /// expression, return it.
1998 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1999 if block.stmts.is_empty() {
2002 if let StmtKind::Local(ref local) = block.stmts[0].node {
2003 if let Some(ref expr) = local.init {
2013 /// If a block begins with an expression (with or without semicolon), return it.
2014 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2016 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2017 None if !block.stmts.is_empty() => match block.stmts[0].node {
2018 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2019 StmtKind::Local(..) | StmtKind::Item(..) => None,
2025 /// Returns `true` if expr contains a single break expr without destination label
2027 /// passed expression. The expression may be within a block.
2028 fn is_simple_break_expr(expr: &Expr) -> bool {
2030 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2031 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2032 Some(subexpr) => is_simple_break_expr(subexpr),
2039 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2040 // incremented exactly once in the loop body, and initialized to zero
2041 // at the start of the loop.
2042 #[derive(Debug, PartialEq)]
2044 Initial, // Not examined yet
2045 IncrOnce, // Incremented exactly once, may be a loop counter
2046 Declared, // Declared but not (yet) initialized to zero
2051 /// Scan a for loop for variables that are incremented exactly once.
2052 struct IncrementVisitor<'a, 'tcx> {
2053 cx: &'a LateContext<'a, 'tcx>, // context reference
2054 states: FxHashMap<HirId, VarState>, // incremented variables
2055 depth: u32, // depth of conditional expressions
2059 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2060 fn visit_expr(&mut self, expr: &'tcx Expr) {
2065 // If node is a variable
2066 if let Some(def_id) = var_def_id(self.cx, expr) {
2067 if let Some(parent) = get_parent_expr(self.cx, expr) {
2068 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2071 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2072 if lhs.hir_id == expr.hir_id {
2073 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2074 *state = match *state {
2075 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2076 _ => VarState::DontWarn,
2079 // Assigned some other value
2080 *state = VarState::DontWarn;
2084 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2085 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2089 } else if is_loop(expr) || is_conditional(expr) {
2091 walk_expr(self, expr);
2094 } else if let ExprKind::Continue(_) = expr.node {
2098 walk_expr(self, expr);
2100 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2101 NestedVisitorMap::None
2105 /// Checks whether a variable is initialized to zero at the start of a loop.
2106 struct InitializeVisitor<'a, 'tcx> {
2107 cx: &'a LateContext<'a, 'tcx>, // context reference
2108 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2112 depth: u32, // depth of conditional expressions
2116 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2117 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2118 // Look for declarations of the variable
2119 if let StmtKind::Local(ref local) = stmt.node {
2120 if local.pat.hir_id == self.var_id {
2121 if let PatKind::Binding(.., ident, _) = local.pat.node {
2122 self.name = Some(ident.name);
2124 self.state = if let Some(ref init) = local.init {
2125 if is_integer_literal(init, 0) {
2136 walk_stmt(self, stmt);
2139 fn visit_expr(&mut self, expr: &'tcx Expr) {
2140 if self.state == VarState::DontWarn {
2143 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2144 self.past_loop = true;
2147 // No need to visit expressions before the variable is
2149 if self.state == VarState::IncrOnce {
2153 // If node is the desired variable, see how it's used
2154 if var_def_id(self.cx, expr) == Some(self.var_id) {
2155 if let Some(parent) = get_parent_expr(self.cx, expr) {
2157 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2158 self.state = VarState::DontWarn;
2160 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2161 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2167 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2173 self.state = VarState::DontWarn;
2176 } else if !self.past_loop && is_loop(expr) {
2177 self.state = VarState::DontWarn;
2179 } else if is_conditional(expr) {
2181 walk_expr(self, expr);
2185 walk_expr(self, expr);
2187 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2188 NestedVisitorMap::None
2192 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2193 if let ExprKind::Path(ref qpath) = expr.node {
2194 let path_res = cx.tables.qpath_res(qpath, expr.hir_id);
2195 if let Res::Local(node_id) = path_res {
2196 return Some(node_id);
2202 fn is_loop(expr: &Expr) -> bool {
2204 ExprKind::Loop(..) => true,
2209 fn is_conditional(expr: &Expr) -> bool {
2211 ExprKind::Match(..) => true,
2216 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2218 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2219 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2220 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2222 return is_loop_nested(cx, loop_expr, iter_expr)
2228 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2229 let mut id = loop_expr.hir_id;
2230 let iter_name = if let Some(name) = path_name(iter_expr) {
2236 let parent = cx.tcx.hir().get_parent_node(id);
2240 match cx.tcx.hir().find(parent) {
2241 Some(Node::Expr(expr)) => {
2242 if let ExprKind::Loop(..) = expr.node {
2246 Some(Node::Block(block)) => {
2247 let mut block_visitor = LoopNestVisitor {
2249 iterator: iter_name,
2252 walk_block(&mut block_visitor, block);
2253 if block_visitor.nesting == RuledOut {
2257 Some(Node::Stmt(_)) => (),
2266 #[derive(PartialEq, Eq)]
2268 Unknown, // no nesting detected yet
2269 RuledOut, // the iterator is initialized or assigned within scope
2270 LookFurther, // no nesting detected, no further walk required
2273 use self::Nesting::{LookFurther, RuledOut, Unknown};
2275 struct LoopNestVisitor {
2281 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2282 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2283 if stmt.hir_id == self.hir_id {
2284 self.nesting = LookFurther;
2285 } else if self.nesting == Unknown {
2286 walk_stmt(self, stmt);
2290 fn visit_expr(&mut self, expr: &'tcx Expr) {
2291 if self.nesting != Unknown {
2294 if expr.hir_id == self.hir_id {
2295 self.nesting = LookFurther;
2299 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2300 if match_var(path, self.iterator) {
2301 self.nesting = RuledOut;
2304 _ => walk_expr(self, expr),
2308 fn visit_pat(&mut self, pat: &'tcx Pat) {
2309 if self.nesting != Unknown {
2312 if let PatKind::Binding(.., span_name, _) = pat.node {
2313 if self.iterator == span_name.name {
2314 self.nesting = RuledOut;
2321 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2322 NestedVisitorMap::None
2326 fn path_name(e: &Expr) -> Option<Name> {
2327 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2328 let segments = &path.segments;
2329 if segments.len() == 1 {
2330 return Some(segments[0].ident.name);
2336 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2337 if constant(cx, cx.tables, cond).is_some() {
2338 // A pure constant condition (e.g., `while false`) is not linted.
2342 let mut var_visitor = VarCollectorVisitor {
2344 ids: FxHashSet::default(),
2345 def_ids: FxHashMap::default(),
2348 var_visitor.visit_expr(cond);
2349 if var_visitor.skip {
2352 let used_in_condition = &var_visitor.ids;
2353 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2354 used_in_condition.is_disjoint(&used_mutably)
2358 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2359 if no_cond_variable_mutated && !mutable_static_in_cond {
2362 WHILE_IMMUTABLE_CONDITION,
2364 "Variable in the condition are not mutated in the loop body. \
2365 This either leads to an infinite or to a never running loop.",
2370 /// Collects the set of variables in an expression
2371 /// Stops analysis if a function call is found
2372 /// Note: In some cases such as `self`, there are no mutable annotation,
2373 /// All variables definition IDs are collected
2374 struct VarCollectorVisitor<'a, 'tcx> {
2375 cx: &'a LateContext<'a, 'tcx>,
2376 ids: FxHashSet<HirId>,
2377 def_ids: FxHashMap<def_id::DefId, bool>,
2381 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2382 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2384 if let ExprKind::Path(ref qpath) = ex.node;
2385 if let QPath::Resolved(None, _) = *qpath;
2386 let res = self.cx.tables.qpath_res(qpath, ex.hir_id);
2389 Res::Local(node_id) => {
2390 self.ids.insert(node_id);
2392 Res::Def(DefKind::Static, def_id) => {
2393 let mutable = self.cx.tcx.is_mutable_static(def_id);
2394 self.def_ids.insert(def_id, mutable);
2403 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2404 fn visit_expr(&mut self, ex: &'tcx Expr) {
2406 ExprKind::Path(_) => self.insert_def_id(ex),
2407 // If there is any function/method call… we just stop analysis
2408 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2410 _ => walk_expr(self, ex),
2414 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2415 NestedVisitorMap::None
2419 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2421 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2423 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2424 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2425 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2426 if let Some(ref generic_args) = chain_method.args;
2427 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2429 let ty = cx.tables.node_type(ty.hir_id);
2430 if match_type(cx, ty, &paths::VEC) ||
2431 match_type(cx, ty, &paths::VEC_DEQUE) ||
2432 match_type(cx, ty, &paths::BTREEMAP) ||
2433 match_type(cx, ty, &paths::HASHMAP) {
2434 if method.ident.name == sym!(len) {
2435 let span = shorten_needless_collect_span(expr);
2436 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2440 ".count()".to_string(),
2441 Applicability::MachineApplicable,
2445 if method.ident.name == sym!(is_empty) {
2446 let span = shorten_needless_collect_span(expr);
2447 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2451 ".next().is_none()".to_string(),
2452 Applicability::MachineApplicable,
2456 if method.ident.name == sym!(contains) {
2457 let contains_arg = snippet(cx, args[1].span, "??");
2458 let span = shorten_needless_collect_span(expr);
2459 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2464 ".any(|&x| x == {})",
2465 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2467 Applicability::MachineApplicable,
2476 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2478 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2479 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2481 return expr.span.with_lo(span.lo() - BytePos(1));