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::sym;
14 use crate::utils::usage::mutated_variables;
15 use crate::utils::{in_macro_or_desugar, sext, sugg};
16 use rustc::middle::expr_use_visitor::*;
17 use rustc::middle::mem_categorization::cmt_;
18 use rustc::middle::mem_categorization::Categorization;
19 use rustc::ty::subst::Subst;
20 use rustc::ty::{self, Ty};
21 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
22 use rustc_errors::Applicability;
23 use std::iter::{once, Iterator};
26 use syntax::source_map::Span;
27 use syntax_pos::BytePos;
29 use crate::utils::paths;
31 get_enclosing_block, get_parent_expr, has_iter_method, higher, is_integer_literal, is_refutable, last_path_segment,
32 match_trait_method, match_type, match_var, multispan_sugg, snippet, snippet_opt, snippet_with_applicability,
33 span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then, SpanlessEq,
36 declare_clippy_lint! {
37 /// **What it does:** Checks for for-loops that manually copy items between
38 /// slices that could be optimized by having a memcpy.
40 /// **Why is this bad?** It is not as fast as a memcpy.
42 /// **Known problems:** None.
46 /// for i in 0..src.len() {
47 /// dst[i + 64] = src[i];
52 "manually copying items between slices"
55 declare_clippy_lint! {
56 /// **What it does:** Checks for looping over the range of `0..len` of some
57 /// collection just to get the values by index.
59 /// **Why is this bad?** Just iterating the collection itself makes the intent
60 /// more clear and is probably faster.
62 /// **Known problems:** None.
66 /// for i in 0..vec.len() {
67 /// println!("{}", vec[i]);
70 pub NEEDLESS_RANGE_LOOP,
72 "for-looping over a range of indices where an iterator over items would do"
75 declare_clippy_lint! {
76 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
77 /// suggests the latter.
79 /// **Why is this bad?** Readability.
81 /// **Known problems:** False negatives. We currently only warn on some known
86 /// // with `y` a `Vec` or slice:
87 /// for x in y.iter() {
91 /// can be rewritten to
97 pub EXPLICIT_ITER_LOOP,
99 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
102 declare_clippy_lint! {
103 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
104 /// suggests the latter.
106 /// **Why is this bad?** Readability.
108 /// **Known problems:** None
112 /// // with `y` a `Vec` or slice:
113 /// for x in y.into_iter() {
117 /// can be rewritten to
123 pub EXPLICIT_INTO_ITER_LOOP,
125 "for-looping over `_.into_iter()` when `_` would do"
128 declare_clippy_lint! {
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() {
148 "for-looping over `_.next()` which is probably not intended"
151 declare_clippy_lint! {
152 /// **What it does:** Checks for `for` loops over `Option` values.
154 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
157 /// **Known problems:** None.
161 /// for x in option {
168 /// if let Some(x) = option {
172 pub FOR_LOOP_OVER_OPTION,
174 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
177 declare_clippy_lint! {
178 /// **What it does:** Checks for `for` loops over `Result` values.
180 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
183 /// **Known problems:** None.
187 /// for x in result {
194 /// if let Ok(x) = result {
198 pub FOR_LOOP_OVER_RESULT,
200 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
203 declare_clippy_lint! {
204 /// **What it does:** Detects `loop + match` combinations that are easier
205 /// written as a `while let` loop.
207 /// **Why is this bad?** The `while let` loop is usually shorter and more
210 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
215 /// let x = match y {
219 /// // .. do something with x
221 /// // is easier written as
222 /// while let Some(x) = y {
223 /// // .. do something with x
228 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
231 declare_clippy_lint! {
232 /// **What it does:** Checks for using `collect()` on an iterator without using
235 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
236 /// iterator instead.
238 /// **Known problems:** None.
242 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
246 "`collect()`ing an iterator without using the result; this is usually better written as a for loop"
249 declare_clippy_lint! {
250 /// **What it does:** Checks for functions collecting an iterator when collect
253 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
254 /// when this allocation may not be needed.
256 /// **Known problems:**
261 /// let len = iterator.collect::<Vec<_>>().len();
263 /// let len = iterator.count();
265 pub NEEDLESS_COLLECT,
267 "collecting an iterator when collect is not needed"
270 declare_clippy_lint! {
271 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
272 /// are constant and `x` is greater or equal to `y`, unless the range is
273 /// reversed or has a negative `.step_by(_)`.
275 /// **Why is it bad?** Such loops will either be skipped or loop until
276 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
279 /// **Known problems:** The lint cannot catch loops over dynamically defined
280 /// ranges. Doing this would require simulating all possible inputs and code
281 /// paths through the program, which would be complex and error-prone.
285 /// for x in 5..10 - 5 {
287 /// } // oops, stray `-`
289 pub REVERSE_RANGE_LOOP,
291 "iteration over an empty range, such as `10..0` or `5..5`"
294 declare_clippy_lint! {
295 /// **What it does:** Checks `for` loops over slices with an explicit counter
296 /// and suggests the use of `.enumerate()`.
298 /// **Why is it bad?** Not only is the version using `.enumerate()` more
299 /// readable, the compiler is able to remove bounds checks which can lead to
300 /// faster code in some instances.
302 /// **Known problems:** None.
306 /// for i in 0..v.len() { foo(v[i]);
307 /// for i in 0..v.len() { bar(i, v[i]); }
309 pub EXPLICIT_COUNTER_LOOP,
311 "for-looping with an explicit counter when `_.enumerate()` would do"
314 declare_clippy_lint! {
315 /// **What it does:** Checks for empty `loop` expressions.
317 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
318 /// anything. Think of the environment and either block on something or at least
319 /// make the thread sleep for some microseconds.
321 /// **Known problems:** None.
329 "empty `loop {}`, which should block or sleep"
332 declare_clippy_lint! {
333 /// **What it does:** Checks for `while let` expressions on iterators.
335 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
336 /// the intent better.
338 /// **Known problems:** None.
342 /// while let Some(val) = iter() {
346 pub WHILE_LET_ON_ITERATOR,
348 "using a while-let loop instead of a for loop on an iterator"
351 declare_clippy_lint! {
352 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
353 /// ignoring either the keys or values.
355 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
356 /// can be used to express that don't need the values or keys.
358 /// **Known problems:** None.
362 /// for (k, _) in &map {
367 /// could be replaced by
370 /// for k in map.keys() {
376 "looping on a map using `iter` when `keys` or `values` would do"
379 declare_clippy_lint! {
380 /// **What it does:** Checks for loops that will always `break`, `return` or
381 /// `continue` an outer loop.
383 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
386 /// **Known problems:** None
397 "any loop that will always `break` or `return`"
400 declare_clippy_lint! {
401 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
403 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
405 /// **Known problems:** None
409 /// let mut foo = 42;
410 /// for i in 0..foo {
412 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
417 "for loop over a range where one of the bounds is a mutable variable"
420 declare_clippy_lint! {
421 /// **What it does:** Checks whether variables used within while loop condition
422 /// can be (and are) mutated in the body.
424 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
425 /// will lead to an infinite loop.
427 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
428 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
429 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
435 /// println!("let me loop forever!");
438 pub WHILE_IMMUTABLE_CONDITION,
440 "variables used within while expression are not mutated in the body"
443 declare_lint_pass!(Loops => [
447 EXPLICIT_INTO_ITER_LOOP,
449 FOR_LOOP_OVER_RESULT,
450 FOR_LOOP_OVER_OPTION,
455 EXPLICIT_COUNTER_LOOP,
457 WHILE_LET_ON_ITERATOR,
461 WHILE_IMMUTABLE_CONDITION,
464 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
465 #[allow(clippy::too_many_lines)]
466 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
467 // we don't want to check expanded macros
468 if in_macro_or_desugar(expr.span) {
472 if let Some((pat, arg, body)) = higher::for_loop(expr) {
473 check_for_loop(cx, pat, arg, body, expr);
476 // check for never_loop
478 ExprKind::While(_, ref block, _) | ExprKind::Loop(ref block, _, _) => {
479 match never_loop_block(block, expr.hir_id) {
480 NeverLoopResult::AlwaysBreak => {
481 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops")
483 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
489 // check for `loop { if let {} else break }` that could be `while let`
490 // (also matches an explicit "match" instead of "if let")
491 // (even if the "match" or "if let" is used for declaration)
492 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
493 // also check for empty `loop {}` statements
494 if block.stmts.is_empty() && block.expr.is_none() {
499 "empty `loop {}` detected. You may want to either use `panic!()` or add \
500 `std::thread::sleep(..);` to the loop body.",
504 // extract the expression from the first statement (if any) in a block
505 let inner_stmt_expr = extract_expr_from_first_stmt(block);
506 // or extract the first expression (if any) from the block
507 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
508 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
509 // ensure "if let" compatible match structure
511 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
513 && arms[0].pats.len() == 1
514 && arms[0].guard.is_none()
515 && arms[1].pats.len() == 1
516 && arms[1].guard.is_none()
517 && is_simple_break_expr(&arms[1].body)
519 if in_external_macro(cx.sess(), expr.span) {
523 // NOTE: we used to build a body here instead of using
524 // ellipsis, this was removed because:
525 // 1) it was ugly with big bodies;
526 // 2) it was not indented properly;
527 // 3) it wasn’t very smart (see #675).
528 let mut applicability = Applicability::HasPlaceholders;
533 "this loop could be written as a `while let` loop",
536 "while let {} = {} {{ .. }}",
537 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
538 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
549 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
550 let pat = &arms[0].pats[0].node;
552 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
553 &ExprKind::MethodCall(ref method_path, _, ref method_args),
554 ) = (pat, &match_expr.node)
556 let iter_expr = &method_args[0];
557 let lhs_constructor = last_path_segment(qpath);
558 if method_path.ident.name == *sym::next
559 && match_trait_method(cx, match_expr, &*paths::ITERATOR)
560 && lhs_constructor.ident.name == *sym::Some
561 && (pat_args.is_empty()
562 || !is_refutable(cx, &pat_args[0])
563 && !is_used_inside(cx, iter_expr, &arms[0].body)
564 && !is_iterator_used_after_while_let(cx, iter_expr)
565 && !is_nested(cx, expr, &method_args[0]))
567 let iterator = snippet(cx, method_args[0].span, "_");
568 let loop_var = if pat_args.is_empty() {
571 snippet(cx, pat_args[0].span, "_").into_owned()
575 WHILE_LET_ON_ITERATOR,
577 "this loop could be written as a `for` loop",
579 format!("for {} in {} {{ .. }}", loop_var, iterator),
580 Applicability::HasPlaceholders,
586 // check for while loops which conditions never change
587 if let ExprKind::While(ref cond, _, _) = expr.node {
588 check_infinite_loop(cx, cond, expr);
591 check_needless_collect(expr, cx);
594 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
595 if let StmtKind::Semi(ref expr) = stmt.node {
596 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
598 && method.ident.name == *sym::collect
599 && match_trait_method(cx, expr, &*paths::ITERATOR)
605 "you are collect()ing an iterator and throwing away the result. \
606 Consider using an explicit for loop to exhaust the iterator",
614 enum NeverLoopResult {
615 // A break/return always get triggered but not necessarily for the main loop.
617 // A continue may occur for the main loop.
622 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
624 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
625 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
629 // Combine two results for parts that are called in order.
630 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
632 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
633 NeverLoopResult::Otherwise => second,
637 // Combine two results where both parts are called but not necessarily in order.
638 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
639 match (left, right) {
640 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
641 NeverLoopResult::MayContinueMainLoop
643 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
644 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
648 // Combine two results where only one of the part may have been executed.
649 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
651 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
652 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
653 NeverLoopResult::MayContinueMainLoop
655 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
659 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
660 let stmts = block.stmts.iter().map(stmt_to_expr);
661 let expr = once(block.expr.as_ref().map(|p| &**p));
662 let mut iter = stmts.chain(expr).filter_map(|e| e);
663 never_loop_expr_seq(&mut iter, main_loop_id)
666 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
668 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
669 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
674 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
677 | ExprKind::Unary(_, ref e)
678 | ExprKind::Cast(ref e, _)
679 | ExprKind::Type(ref e, _)
680 | ExprKind::Field(ref e, _)
681 | ExprKind::AddrOf(_, ref e)
682 | ExprKind::Struct(_, _, Some(ref e))
683 | ExprKind::Repeat(ref e, _)
684 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
685 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
686 never_loop_expr_all(&mut es.iter(), main_loop_id)
688 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
689 ExprKind::Binary(_, ref e1, ref e2)
690 | ExprKind::Assign(ref e1, ref e2)
691 | ExprKind::AssignOp(_, ref e1, ref e2)
692 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
693 ExprKind::Loop(ref b, _, _) => {
694 // Break can come from the inner loop so remove them.
695 absorb_break(&never_loop_block(b, main_loop_id))
697 ExprKind::While(ref e, ref b, _) => {
698 let e = never_loop_expr(e, main_loop_id);
699 let result = never_loop_block(b, main_loop_id);
700 // Break can come from the inner loop so remove them.
701 combine_seq(e, absorb_break(&result))
703 ExprKind::Match(ref e, ref arms, _) => {
704 let e = never_loop_expr(e, main_loop_id);
708 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
712 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
713 ExprKind::Continue(d) => {
716 .expect("target ID can only be missing in the presence of compilation errors");
717 if id == main_loop_id {
718 NeverLoopResult::MayContinueMainLoop
720 NeverLoopResult::AlwaysBreak
723 ExprKind::Break(_, _) => NeverLoopResult::AlwaysBreak,
724 ExprKind::Ret(ref e) => {
725 if let Some(ref e) = *e {
726 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
728 NeverLoopResult::AlwaysBreak
731 ExprKind::Struct(_, _, None)
733 | ExprKind::Closure(_, _, _, _, _)
734 | ExprKind::InlineAsm(_, _, _)
737 | ExprKind::Err => NeverLoopResult::Otherwise,
741 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
742 es.map(|e| never_loop_expr(e, main_loop_id))
743 .fold(NeverLoopResult::Otherwise, combine_seq)
746 fn never_loop_expr_all<'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_both)
751 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
752 e.map(|e| never_loop_expr(e, main_loop_id))
753 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
756 fn check_for_loop<'a, 'tcx>(
757 cx: &LateContext<'a, 'tcx>,
763 check_for_loop_range(cx, pat, arg, body, expr);
764 check_for_loop_reverse_range(cx, arg, expr);
765 check_for_loop_arg(cx, pat, arg, expr);
766 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
767 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
768 check_for_mut_range_bound(cx, arg, body);
769 detect_manual_memcpy(cx, pat, arg, body, expr);
772 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
774 if let ExprKind::Path(ref qpath) = expr.node;
775 if let QPath::Resolved(None, ref path) = *qpath;
776 if path.segments.len() == 1;
777 if let Res::Local(local_id) = cx.tables.qpath_res(qpath, expr.hir_id);
794 fn negative(s: String) -> Self {
795 Self { value: s, negate: true }
798 fn positive(s: String) -> Self {
806 struct FixedOffsetVar {
811 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
812 let is_slice = match ty.sty {
813 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
814 ty::Slice(..) | ty::Array(..) => true,
818 is_slice || match_type(cx, ty, &*paths::VEC) || match_type(cx, ty, &*paths::VEC_DEQUE)
821 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
822 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
824 ExprKind::Lit(ref l) => match l.node {
825 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
828 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
833 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
834 let ty = cx.tables.expr_ty(seqexpr);
835 if !is_slice_like(cx, ty) {
839 let offset = match idx.node {
840 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
842 let offset_opt = if same_var(cx, lhs, var) {
843 extract_offset(cx, rhs, var)
844 } else if same_var(cx, rhs, var) {
845 extract_offset(cx, lhs, var)
850 offset_opt.map(Offset::positive)
852 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
855 ExprKind::Path(..) => {
856 if same_var(cx, idx, var) {
857 Some(Offset::positive("0".into()))
865 offset.map(|o| FixedOffsetVar {
866 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
874 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
875 cx: &LateContext<'a, 'tcx>,
878 ) -> Option<FixedOffsetVar> {
880 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
881 if method.ident.name == *sym::clone;
883 if let Some(arg) = args.get(0);
885 return get_fixed_offset_var(cx, arg, var);
889 get_fixed_offset_var(cx, expr, var)
892 fn get_indexed_assignments<'a, 'tcx>(
893 cx: &LateContext<'a, 'tcx>,
896 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
897 fn get_assignment<'a, 'tcx>(
898 cx: &LateContext<'a, 'tcx>,
901 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
902 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
904 get_fixed_offset_var(cx, lhs, var),
905 fetch_cloned_fixed_offset_var(cx, rhs, var),
907 (Some(offset_left), Some(offset_right)) => {
908 // Source and destination must be different
909 if offset_left.var_name == offset_right.var_name {
912 Some((offset_left, offset_right))
922 if let ExprKind::Block(ref b, _) = body.node {
924 ref stmts, ref expr, ..
929 .map(|stmt| match stmt.node {
930 StmtKind::Local(..) | StmtKind::Item(..) => None,
931 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
933 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
935 .collect::<Option<Vec<_>>>()
936 .unwrap_or_else(|| vec![])
938 get_assignment(cx, body, var).into_iter().collect()
942 /// Checks for for loops that sequentially copy items from one slice-like
943 /// object to another.
944 fn detect_manual_memcpy<'a, 'tcx>(
945 cx: &LateContext<'a, 'tcx>,
951 if let Some(higher::Range {
955 }) = higher::range(cx, arg)
957 // the var must be a single name
958 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
959 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
960 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
961 ("0", _, "0", _) => "".into(),
962 ("0", _, x, false) | (x, false, "0", false) => x.into(),
963 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
964 (x, false, y, false) => format!("({} + {})", x, y),
965 (x, false, y, true) => {
969 format!("({} - {})", x, y)
972 (x, true, y, false) => {
976 format!("({} - {})", y, x)
979 (x, true, y, true) => format!("-({} + {})", x, y),
983 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
984 if let Some(end) = *end {
986 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
987 if method.ident.name == *sym::len;
988 if len_args.len() == 1;
989 if let Some(arg) = len_args.get(0);
990 if snippet(cx, arg.span, "??") == var_name;
992 return if offset.negate {
993 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
1000 let end_str = match limits {
1001 ast::RangeLimits::Closed => {
1002 let end = sugg::Sugg::hir(cx, end, "<count>");
1003 format!("{}", end + sugg::ONE)
1005 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1008 print_sum(&Offset::positive(end_str), &offset)
1014 // The only statements in the for loops can be indexed assignments from
1015 // indexed retrievals.
1016 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1018 let big_sugg = manual_copies
1020 .map(|(dst_var, src_var)| {
1021 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1022 let dst_offset = print_sum(&start_str, &dst_var.offset);
1023 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1024 let src_offset = print_sum(&start_str, &src_var.offset);
1025 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1026 let dst = if dst_offset == "" && dst_limit == "" {
1029 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1033 "{}.clone_from_slice(&{}[{}..{}])",
1034 dst, src_var.var_name, src_offset, src_limit
1039 if !big_sugg.is_empty() {
1044 "it looks like you're manually copying between slices",
1045 "try replacing the loop by",
1047 Applicability::Unspecified,
1054 /// Checks for looping over a range and then indexing a sequence with it.
1055 /// The iteratee must be a range literal.
1056 #[allow(clippy::too_many_lines)]
1057 fn check_for_loop_range<'a, 'tcx>(
1058 cx: &LateContext<'a, 'tcx>,
1064 if in_macro_or_desugar(expr.span) {
1068 if let Some(higher::Range {
1072 }) = higher::range(cx, arg)
1074 // the var must be a single name
1075 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1076 let mut visitor = VarVisitor {
1079 indexed_mut: FxHashSet::default(),
1080 indexed_indirectly: FxHashMap::default(),
1081 indexed_directly: FxHashMap::default(),
1082 referenced: FxHashSet::default(),
1084 prefer_mutable: false,
1086 walk_expr(&mut visitor, body);
1088 // linting condition: we only indexed one variable, and indexed it directly
1089 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1090 let (indexed, (indexed_extent, indexed_ty)) = visitor
1094 .expect("already checked that we have exactly 1 element");
1096 // ensure that the indexed variable was declared before the loop, see #601
1097 if let Some(indexed_extent) = indexed_extent {
1098 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1099 let parent_def_id = cx.tcx.hir().local_def_id_from_hir_id(parent_id);
1100 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1101 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1102 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1107 // don't lint if the container that is indexed does not have .iter() method
1108 let has_iter = has_iter_method(cx, indexed_ty);
1109 if has_iter.is_none() {
1113 // don't lint if the container that is indexed into is also used without
1115 if visitor.referenced.contains(&indexed) {
1119 let starts_at_zero = is_integer_literal(start, 0);
1121 let skip = if starts_at_zero {
1124 format!(".skip({})", snippet(cx, start.span, ".."))
1127 let mut end_is_start_plus_val = false;
1129 let take = if let Some(end) = *end {
1130 let mut take_expr = end;
1132 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1133 if let BinOpKind::Add = op.node {
1134 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1135 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1137 if start_equal_left {
1139 } else if start_equal_right {
1143 end_is_start_plus_val = start_equal_left | start_equal_right;
1147 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1151 ast::RangeLimits::Closed => {
1152 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1153 format!(".take({})", take_expr + sugg::ONE)
1155 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1162 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1163 ("mut ", "iter_mut")
1168 let take_is_empty = take.is_empty();
1169 let mut method_1 = take;
1170 let mut method_2 = skip;
1172 if end_is_start_plus_val {
1173 mem::swap(&mut method_1, &mut method_2);
1176 if visitor.nonindex {
1179 NEEDLESS_RANGE_LOOP,
1181 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1185 "consider using an iterator".to_string(),
1187 (pat.span, format!("({}, <item>)", ident.name)),
1190 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1197 let repl = if starts_at_zero && take_is_empty {
1198 format!("&{}{}", ref_mut, indexed)
1200 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1205 NEEDLESS_RANGE_LOOP,
1208 "the loop variable `{}` is only used to index `{}`.",
1214 "consider using an iterator".to_string(),
1215 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1225 fn is_len_call(expr: &Expr, var: Name) -> bool {
1227 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1228 if len_args.len() == 1;
1229 if method.ident.name == *sym::len;
1230 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1231 if path.segments.len() == 1;
1232 if path.segments[0].ident.name == var;
1241 fn is_end_eq_array_len(cx: &LateContext<'_, '_>, end: &Expr, limits: ast::RangeLimits, indexed_ty: Ty<'_>) -> bool {
1243 if let ExprKind::Lit(ref lit) = end.node;
1244 if let ast::LitKind::Int(end_int, _) = lit.node;
1245 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1246 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1248 return match limits {
1249 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1250 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1258 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1259 // if this for loop is iterating over a two-sided range...
1260 if let Some(higher::Range {
1264 }) = higher::range(cx, arg)
1266 // ...and both sides are compile-time constant integers...
1267 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1268 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1269 // ...and the start index is greater than the end index,
1270 // this loop will never run. This is often confusing for developers
1271 // who think that this will iterate from the larger value to the
1273 let ty = cx.tables.expr_ty(start);
1274 let (sup, eq) = match (start_idx, end_idx) {
1275 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1277 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1278 ty::Uint(_) => start_idx > end_idx,
1281 start_idx == end_idx,
1283 _ => (false, false),
1287 let start_snippet = snippet(cx, start.span, "_");
1288 let end_snippet = snippet(cx, end.span, "_");
1289 let dots = if limits == ast::RangeLimits::Closed {
1299 "this range is empty so this for loop will never run",
1303 "consider using the following if you are attempting to iterate over this \
1306 "({end}{dots}{start}).rev()",
1309 start = start_snippet
1311 Applicability::MaybeIncorrect,
1315 } else if eq && limits != ast::RangeLimits::Closed {
1316 // if they are equal, it's also problematic - this loop
1322 "this range is empty so this for loop will never run",
1330 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1331 let mut applicability = Applicability::MachineApplicable;
1332 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1333 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1338 "it is more concise to loop over references to containers instead of using explicit \
1340 "to write this more concisely, try",
1341 format!("&{}{}", muta, object),
1346 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1347 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1348 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1349 // just the receiver, no arguments
1350 if args.len() == 1 {
1351 let method_name = &*method.ident.as_str();
1352 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1353 if method_name == "iter" || method_name == "iter_mut" {
1354 if is_ref_iterable_type(cx, &args[0]) {
1355 lint_iter_method(cx, args, arg, method_name);
1357 } else if method_name == "into_iter" && match_trait_method(cx, arg, &*paths::INTO_ITERATOR) {
1358 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1359 let substs = cx.tables.node_substs(arg.hir_id);
1360 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1362 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1363 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1364 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1365 match cx.tables.expr_ty(&args[0]).sty {
1366 // If the length is greater than 32 no traits are implemented for array and
1367 // therefore we cannot use `&`.
1368 ty::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1369 _ => lint_iter_method(cx, args, arg, method_name),
1372 let mut applicability = Applicability::MachineApplicable;
1373 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1376 EXPLICIT_INTO_ITER_LOOP,
1378 "it is more concise to loop over containers instead of using explicit \
1379 iteration methods`",
1380 "to write this more concisely, try",
1385 } else if method_name == "next" && match_trait_method(cx, arg, &*paths::ITERATOR) {
1390 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1391 probably not what you want",
1393 next_loop_linted = true;
1397 if !next_loop_linted {
1398 check_arg_type(cx, pat, arg);
1402 /// Checks for `for` loops over `Option`s and `Result`s.
1403 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1404 let ty = cx.tables.expr_ty(arg);
1405 if match_type(cx, ty, &*paths::OPTION) {
1408 FOR_LOOP_OVER_OPTION,
1411 "for loop over `{0}`, which is an `Option`. 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 Some({0}) = {1}`",
1417 snippet(cx, pat.span, "_"),
1418 snippet(cx, arg.span, "_")
1421 } else if match_type(cx, ty, &*paths::RESULT) {
1424 FOR_LOOP_OVER_RESULT,
1427 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1428 `if let` statement.",
1429 snippet(cx, arg.span, "_")
1432 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1433 snippet(cx, pat.span, "_"),
1434 snippet(cx, arg.span, "_")
1440 fn check_for_loop_explicit_counter<'a, 'tcx>(
1441 cx: &LateContext<'a, 'tcx>,
1447 // Look for variables that are incremented once per loop iteration.
1448 let mut visitor = IncrementVisitor {
1450 states: FxHashMap::default(),
1454 walk_expr(&mut visitor, body);
1456 // For each candidate, check the parent block to see if
1457 // it's initialized to zero at the start of the loop.
1458 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1459 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1460 let mut visitor2 = InitializeVisitor {
1464 state: VarState::IncrOnce,
1469 walk_block(&mut visitor2, block);
1471 if visitor2.state == VarState::Warn {
1472 if let Some(name) = visitor2.name {
1473 let mut applicability = Applicability::MachineApplicable;
1476 EXPLICIT_COUNTER_LOOP,
1478 &format!("the variable `{}` is used as a loop counter.", name),
1481 "for ({}, {}) in {}.enumerate()",
1483 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1484 if higher::range(cx, arg).is_some() {
1487 snippet_with_applicability(cx, arg.span, "_", &mut applicability)
1492 sugg::Sugg::hir_with_applicability(cx, arg, "_", &mut applicability).maybe_par()
1504 /// Checks for the `FOR_KV_MAP` lint.
1505 fn check_for_loop_over_map_kv<'a, 'tcx>(
1506 cx: &LateContext<'a, 'tcx>,
1512 let pat_span = pat.span;
1514 if let PatKind::Tuple(ref pat, _) = pat.node {
1516 let arg_span = arg.span;
1517 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1518 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1519 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1520 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1525 let mutbl = match mutbl {
1527 MutMutable => "_mut",
1529 let arg = match arg.node {
1530 ExprKind::AddrOf(_, ref expr) => &**expr,
1534 if match_type(cx, ty, &*paths::HASHMAP) || match_type(cx, ty, &*paths::BTREEMAP) {
1539 &format!("you seem to want to iterate on a map's {}s", kind),
1541 let map = sugg::Sugg::hir(cx, arg, "map");
1544 "use the corresponding method".into(),
1546 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1547 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1557 struct MutatePairDelegate {
1558 hir_id_low: Option<HirId>,
1559 hir_id_high: Option<HirId>,
1560 span_low: Option<Span>,
1561 span_high: Option<Span>,
1564 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1565 fn consume(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1567 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1569 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1571 fn borrow(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1572 if let ty::BorrowKind::MutBorrow = bk {
1573 if let Categorization::Local(id) = cmt.cat {
1574 if Some(id) == self.hir_id_low {
1575 self.span_low = Some(sp)
1577 if Some(id) == self.hir_id_high {
1578 self.span_high = Some(sp)
1584 fn mutate(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1585 if let Categorization::Local(id) = cmt.cat {
1586 if Some(id) == self.hir_id_low {
1587 self.span_low = Some(sp)
1589 if Some(id) == self.hir_id_high {
1590 self.span_high = Some(sp)
1595 fn decl_without_init(&mut self, _: HirId, _: Span) {}
1598 impl<'tcx> MutatePairDelegate {
1599 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1600 (self.span_low, self.span_high)
1604 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1605 if let Some(higher::Range {
1609 }) = higher::range(cx, arg)
1611 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1612 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1613 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1614 mut_warn_with_span(cx, span_low);
1615 mut_warn_with_span(cx, span_high);
1620 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1621 if let Some(sp) = span {
1626 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1631 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1633 if let ExprKind::Path(ref qpath) = bound.node;
1634 if let QPath::Resolved(None, _) = *qpath;
1636 let res = cx.tables.qpath_res(qpath, bound.hir_id);
1637 if let Res::Local(node_id) = res {
1638 let node_str = cx.tcx.hir().get_by_hir_id(node_id);
1640 if let Node::Binding(pat) = node_str;
1641 if let PatKind::Binding(bind_ann, ..) = pat.node;
1642 if let BindingAnnotation::Mutable = bind_ann;
1644 return Some(node_id);
1653 fn check_for_mutation(
1654 cx: &LateContext<'_, '_>,
1656 bound_ids: &[Option<HirId>],
1657 ) -> (Option<Span>, Option<Span>) {
1658 let mut delegate = MutatePairDelegate {
1659 hir_id_low: bound_ids[0],
1660 hir_id_high: bound_ids[1],
1664 let def_id = def_id::DefId::local(body.hir_id.owner);
1665 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1666 ExprUseVisitor::new(&mut delegate, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).walk_expr(body);
1667 delegate.mutation_span()
1670 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1671 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1673 PatKind::Wild => true,
1674 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1675 let mut visitor = UsedVisitor {
1679 walk_expr(&mut visitor, body);
1686 struct UsedVisitor {
1687 var: ast::Name, // var to look for
1688 used: bool, // has the var been used otherwise?
1691 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1692 fn visit_expr(&mut self, expr: &'tcx Expr) {
1693 if match_var(expr, self.var) {
1696 walk_expr(self, expr);
1700 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1701 NestedVisitorMap::None
1705 struct LocalUsedVisitor<'a, 'tcx: 'a> {
1706 cx: &'a LateContext<'a, 'tcx>,
1711 impl<'a, 'tcx: 'a> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1712 fn visit_expr(&mut self, expr: &'tcx Expr) {
1713 if same_var(self.cx, expr, self.local) {
1716 walk_expr(self, expr);
1720 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1721 NestedVisitorMap::None
1725 struct VarVisitor<'a, 'tcx: 'a> {
1726 /// context reference
1727 cx: &'a LateContext<'a, 'tcx>,
1728 /// var name to look for as index
1730 /// indexed variables that are used mutably
1731 indexed_mut: FxHashSet<Name>,
1732 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1733 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1734 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1735 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1736 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1737 /// Any names that are used outside an index operation.
1738 /// Used to detect things like `&mut vec` used together with `vec[i]`
1739 referenced: FxHashSet<Name>,
1740 /// has the loop variable been used in expressions other than the index of
1743 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1744 /// takes `&mut self`
1745 prefer_mutable: bool,
1748 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1749 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1751 // the indexed container is referenced by a name
1752 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1753 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1754 if seqvar.segments.len() == 1;
1756 let index_used_directly = same_var(self.cx, idx, self.var);
1757 let indexed_indirectly = {
1758 let mut used_visitor = LocalUsedVisitor {
1763 walk_expr(&mut used_visitor, idx);
1767 if indexed_indirectly || index_used_directly {
1768 if self.prefer_mutable {
1769 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1771 let res = self.cx.tables.qpath_res(seqpath, seqexpr.hir_id);
1773 Res::Local(hir_id) | Res::Upvar(hir_id, ..) => {
1774 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1775 let parent_def_id = self.cx.tcx.hir().local_def_id_from_hir_id(parent_id);
1776 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1777 if indexed_indirectly {
1778 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1780 if index_used_directly {
1781 self.indexed_directly.insert(
1782 seqvar.segments[0].ident.name,
1783 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1786 return false; // no need to walk further *on the variable*
1788 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1789 if indexed_indirectly {
1790 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1792 if index_used_directly {
1793 self.indexed_directly.insert(
1794 seqvar.segments[0].ident.name,
1795 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1798 return false; // no need to walk further *on the variable*
1809 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1810 fn visit_expr(&mut self, expr: &'tcx Expr) {
1813 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1814 if (meth.ident.name == *sym::index && match_trait_method(self.cx, expr, &*paths::INDEX))
1815 || (meth.ident.name == *sym::index_mut && match_trait_method(self.cx, expr, &*paths::INDEX_MUT));
1816 if !self.check(&args[1], &args[0], expr);
1822 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1823 if !self.check(idx, seqexpr, expr);
1828 // directly using a variable
1829 if let ExprKind::Path(ref qpath) = expr.node;
1830 if let QPath::Resolved(None, ref path) = *qpath;
1831 if path.segments.len() == 1;
1833 match self.cx.tables.qpath_res(qpath, expr.hir_id) {
1834 Res::Upvar(local_id, ..) => {
1835 if local_id == self.var {
1836 // we are not indexing anything, record that
1837 self.nonindex = true;
1840 Res::Local(local_id) =>
1843 if local_id == self.var {
1844 self.nonindex = true;
1846 // not the correct variable, but still a variable
1847 self.referenced.insert(path.segments[0].ident.name);
1855 let old = self.prefer_mutable;
1857 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1858 self.prefer_mutable = true;
1859 self.visit_expr(lhs);
1860 self.prefer_mutable = false;
1861 self.visit_expr(rhs);
1863 ExprKind::AddrOf(mutbl, ref expr) => {
1864 if mutbl == MutMutable {
1865 self.prefer_mutable = true;
1867 self.visit_expr(expr);
1869 ExprKind::Call(ref f, ref args) => {
1872 let ty = self.cx.tables.expr_ty_adjusted(expr);
1873 self.prefer_mutable = false;
1874 if let ty::Ref(_, _, mutbl) = ty.sty {
1875 if mutbl == MutMutable {
1876 self.prefer_mutable = true;
1879 self.visit_expr(expr);
1882 ExprKind::MethodCall(_, _, ref args) => {
1883 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1884 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1885 self.prefer_mutable = false;
1886 if let ty::Ref(_, _, mutbl) = ty.sty {
1887 if mutbl == MutMutable {
1888 self.prefer_mutable = true;
1891 self.visit_expr(expr);
1894 ExprKind::Closure(_, _, body_id, ..) => {
1895 let body = self.cx.tcx.hir().body(body_id);
1896 self.visit_expr(&body.value);
1898 _ => walk_expr(self, expr),
1900 self.prefer_mutable = old;
1902 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1903 NestedVisitorMap::None
1907 fn is_used_inside<'a, 'tcx: 'a>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1908 let def_id = match var_def_id(cx, expr) {
1910 None => return false,
1912 if let Some(used_mutably) = mutated_variables(container, cx) {
1913 if used_mutably.contains(&def_id) {
1920 fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1921 let def_id = match var_def_id(cx, iter_expr) {
1923 None => return false,
1925 let mut visitor = VarUsedAfterLoopVisitor {
1928 iter_expr_id: iter_expr.hir_id,
1929 past_while_let: false,
1930 var_used_after_while_let: false,
1932 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1933 walk_block(&mut visitor, enclosing_block);
1935 visitor.var_used_after_while_let
1938 struct VarUsedAfterLoopVisitor<'a, 'tcx: 'a> {
1939 cx: &'a LateContext<'a, 'tcx>,
1941 iter_expr_id: HirId,
1942 past_while_let: bool,
1943 var_used_after_while_let: bool,
1946 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1947 fn visit_expr(&mut self, expr: &'tcx Expr) {
1948 if self.past_while_let {
1949 if Some(self.def_id) == var_def_id(self.cx, expr) {
1950 self.var_used_after_while_let = true;
1952 } else if self.iter_expr_id == expr.hir_id {
1953 self.past_while_let = true;
1955 walk_expr(self, expr);
1957 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1958 NestedVisitorMap::None
1962 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1963 /// for `&T` and `&mut T`, such as `Vec`.
1965 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1966 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1967 // will allow further borrows afterwards
1968 let ty = cx.tables.expr_ty(e);
1969 is_iterable_array(ty, cx) ||
1970 match_type(cx, ty, &*paths::VEC) ||
1971 match_type(cx, ty, &*paths::LINKED_LIST) ||
1972 match_type(cx, ty, &*paths::HASHMAP) ||
1973 match_type(cx, ty, &*paths::HASHSET) ||
1974 match_type(cx, ty, &*paths::VEC_DEQUE) ||
1975 match_type(cx, ty, &*paths::BINARY_HEAP) ||
1976 match_type(cx, ty, &*paths::BTREEMAP) ||
1977 match_type(cx, ty, &*paths::BTREESET)
1980 fn is_iterable_array(ty: Ty<'_>, cx: &LateContext<'_, '_>) -> bool {
1981 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1983 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1988 /// If a block begins with a statement (possibly a `let` binding) and has an
1989 /// expression, return it.
1990 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1991 if block.stmts.is_empty() {
1994 if let StmtKind::Local(ref local) = block.stmts[0].node {
1995 if let Some(ref expr) = local.init {
2005 /// If a block begins with an expression (with or without semicolon), return it.
2006 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2008 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2009 None if !block.stmts.is_empty() => match block.stmts[0].node {
2010 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2011 StmtKind::Local(..) | StmtKind::Item(..) => None,
2017 /// Returns `true` if expr contains a single break expr without destination label
2019 /// passed expression. The expression may be within a block.
2020 fn is_simple_break_expr(expr: &Expr) -> bool {
2022 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2023 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2024 Some(subexpr) => is_simple_break_expr(subexpr),
2031 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2032 // incremented exactly once in the loop body, and initialized to zero
2033 // at the start of the loop.
2034 #[derive(Debug, PartialEq)]
2036 Initial, // Not examined yet
2037 IncrOnce, // Incremented exactly once, may be a loop counter
2038 Declared, // Declared but not (yet) initialized to zero
2043 /// Scan a for loop for variables that are incremented exactly once.
2044 struct IncrementVisitor<'a, 'tcx: 'a> {
2045 cx: &'a LateContext<'a, 'tcx>, // context reference
2046 states: FxHashMap<HirId, VarState>, // incremented variables
2047 depth: u32, // depth of conditional expressions
2051 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2052 fn visit_expr(&mut self, expr: &'tcx Expr) {
2057 // If node is a variable
2058 if let Some(def_id) = var_def_id(self.cx, expr) {
2059 if let Some(parent) = get_parent_expr(self.cx, expr) {
2060 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2063 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2064 if lhs.hir_id == expr.hir_id {
2065 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2066 *state = match *state {
2067 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2068 _ => VarState::DontWarn,
2071 // Assigned some other value
2072 *state = VarState::DontWarn;
2076 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2077 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2081 } else if is_loop(expr) || is_conditional(expr) {
2083 walk_expr(self, expr);
2086 } else if let ExprKind::Continue(_) = expr.node {
2090 walk_expr(self, expr);
2092 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2093 NestedVisitorMap::None
2097 /// Checks whether a variable is initialized to zero at the start of a loop.
2098 struct InitializeVisitor<'a, 'tcx: 'a> {
2099 cx: &'a LateContext<'a, 'tcx>, // context reference
2100 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2104 depth: u32, // depth of conditional expressions
2108 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2109 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2110 // Look for declarations of the variable
2111 if let StmtKind::Local(ref local) = stmt.node {
2112 if local.pat.hir_id == self.var_id {
2113 if let PatKind::Binding(.., ident, _) = local.pat.node {
2114 self.name = Some(ident.name);
2116 self.state = if let Some(ref init) = local.init {
2117 if is_integer_literal(init, 0) {
2128 walk_stmt(self, stmt);
2131 fn visit_expr(&mut self, expr: &'tcx Expr) {
2132 if self.state == VarState::DontWarn {
2135 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2136 self.past_loop = true;
2139 // No need to visit expressions before the variable is
2141 if self.state == VarState::IncrOnce {
2145 // If node is the desired variable, see how it's used
2146 if var_def_id(self.cx, expr) == Some(self.var_id) {
2147 if let Some(parent) = get_parent_expr(self.cx, expr) {
2149 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2150 self.state = VarState::DontWarn;
2152 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2153 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2159 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2165 self.state = VarState::DontWarn;
2168 } else if !self.past_loop && is_loop(expr) {
2169 self.state = VarState::DontWarn;
2171 } else if is_conditional(expr) {
2173 walk_expr(self, expr);
2177 walk_expr(self, expr);
2179 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2180 NestedVisitorMap::None
2184 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2185 if let ExprKind::Path(ref qpath) = expr.node {
2186 let path_res = cx.tables.qpath_res(qpath, expr.hir_id);
2187 if let Res::Local(node_id) = path_res {
2188 return Some(node_id);
2194 fn is_loop(expr: &Expr) -> bool {
2196 ExprKind::Loop(..) | ExprKind::While(..) => true,
2201 fn is_conditional(expr: &Expr) -> bool {
2203 ExprKind::Match(..) => true,
2208 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2210 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2211 let parent_node = cx.tcx.hir().get_parent_node_by_hir_id(loop_block.hir_id);
2212 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find_by_hir_id(parent_node);
2214 return is_loop_nested(cx, loop_expr, iter_expr)
2220 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2221 let mut id = loop_expr.hir_id;
2222 let iter_name = if let Some(name) = path_name(iter_expr) {
2228 let parent = cx.tcx.hir().get_parent_node_by_hir_id(id);
2232 match cx.tcx.hir().find_by_hir_id(parent) {
2233 Some(Node::Expr(expr)) => match expr.node {
2234 ExprKind::Loop(..) | ExprKind::While(..) => {
2239 Some(Node::Block(block)) => {
2240 let mut block_visitor = LoopNestVisitor {
2242 iterator: iter_name,
2245 walk_block(&mut block_visitor, block);
2246 if block_visitor.nesting == RuledOut {
2250 Some(Node::Stmt(_)) => (),
2259 #[derive(PartialEq, Eq)]
2261 Unknown, // no nesting detected yet
2262 RuledOut, // the iterator is initialized or assigned within scope
2263 LookFurther, // no nesting detected, no further walk required
2266 use self::Nesting::{LookFurther, RuledOut, Unknown};
2268 struct LoopNestVisitor {
2274 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2275 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2276 if stmt.hir_id == self.hir_id {
2277 self.nesting = LookFurther;
2278 } else if self.nesting == Unknown {
2279 walk_stmt(self, stmt);
2283 fn visit_expr(&mut self, expr: &'tcx Expr) {
2284 if self.nesting != Unknown {
2287 if expr.hir_id == self.hir_id {
2288 self.nesting = LookFurther;
2292 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2293 if match_var(path, self.iterator) {
2294 self.nesting = RuledOut;
2297 _ => walk_expr(self, expr),
2301 fn visit_pat(&mut self, pat: &'tcx Pat) {
2302 if self.nesting != Unknown {
2305 if let PatKind::Binding(.., span_name, _) = pat.node {
2306 if self.iterator == span_name.name {
2307 self.nesting = RuledOut;
2314 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2315 NestedVisitorMap::None
2319 fn path_name(e: &Expr) -> Option<Name> {
2320 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2321 let segments = &path.segments;
2322 if segments.len() == 1 {
2323 return Some(segments[0].ident.name);
2329 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2330 if constant(cx, cx.tables, cond).is_some() {
2331 // A pure constant condition (e.g., `while false`) is not linted.
2335 let mut var_visitor = VarCollectorVisitor {
2337 ids: FxHashSet::default(),
2338 def_ids: FxHashMap::default(),
2341 var_visitor.visit_expr(cond);
2342 if var_visitor.skip {
2345 let used_in_condition = &var_visitor.ids;
2346 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2347 used_in_condition.is_disjoint(&used_mutably)
2351 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2352 if no_cond_variable_mutated && !mutable_static_in_cond {
2355 WHILE_IMMUTABLE_CONDITION,
2357 "Variable in the condition are not mutated in the loop body. \
2358 This either leads to an infinite or to a never running loop.",
2363 /// Collects the set of variables in an expression
2364 /// Stops analysis if a function call is found
2365 /// Note: In some cases such as `self`, there are no mutable annotation,
2366 /// All variables definition IDs are collected
2367 struct VarCollectorVisitor<'a, 'tcx: 'a> {
2368 cx: &'a LateContext<'a, 'tcx>,
2369 ids: FxHashSet<HirId>,
2370 def_ids: FxHashMap<def_id::DefId, bool>,
2374 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2375 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2377 if let ExprKind::Path(ref qpath) = ex.node;
2378 if let QPath::Resolved(None, _) = *qpath;
2379 let res = self.cx.tables.qpath_res(qpath, ex.hir_id);
2382 Res::Local(node_id) | Res::Upvar(node_id, ..) => {
2383 self.ids.insert(node_id);
2385 Res::Def(DefKind::Static, def_id) => {
2386 let mutable = self.cx.tcx.is_mutable_static(def_id);
2387 self.def_ids.insert(def_id, mutable);
2396 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2397 fn visit_expr(&mut self, ex: &'tcx Expr) {
2399 ExprKind::Path(_) => self.insert_def_id(ex),
2400 // If there is any function/method call… we just stop analysis
2401 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2403 _ => walk_expr(self, ex),
2407 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2408 NestedVisitorMap::None
2412 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2414 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2416 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2417 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2418 if chain_method.ident.name == *sym::collect && match_trait_method(cx, &args[0], &*paths::ITERATOR);
2419 if let Some(ref generic_args) = chain_method.args;
2420 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2422 let ty = cx.tables.node_type(ty.hir_id);
2423 if match_type(cx, ty, &*paths::VEC) ||
2424 match_type(cx, ty, &*paths::VEC_DEQUE) ||
2425 match_type(cx, ty, &*paths::BTREEMAP) ||
2426 match_type(cx, ty, &*paths::HASHMAP) {
2427 if method.ident.name == *sym::len {
2428 let span = shorten_needless_collect_span(expr);
2429 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2433 ".count()".to_string(),
2434 Applicability::MachineApplicable,
2438 if method.ident.name == *sym::is_empty {
2439 let span = shorten_needless_collect_span(expr);
2440 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2444 ".next().is_none()".to_string(),
2445 Applicability::MachineApplicable,
2449 if method.ident.name == *sym::contains {
2450 let contains_arg = snippet(cx, args[1].span, "??");
2451 let span = shorten_needless_collect_span(expr);
2452 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2457 ".any(|&x| x == {})",
2458 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2460 Applicability::MachineApplicable,
2469 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2471 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2472 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2474 return expr.span.with_lo(span.lo() - BytePos(1));