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::{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];
51 /// Could be written as:
53 /// # let src = vec![1];
54 /// # let mut dst = vec![0; 65];
55 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
59 "manually copying items between slices"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for looping over the range of `0..len` of some
64 /// collection just to get the values by index.
66 /// **Why is this bad?** Just iterating the collection itself makes the intent
67 /// more clear and is probably faster.
69 /// **Known problems:** None.
73 /// let vec = vec!['a', 'b', 'c'];
74 /// for i in 0..vec.len() {
75 /// println!("{}", vec[i]);
78 /// Could be written as:
80 /// let vec = vec!['a', 'b', 'c'];
82 /// println!("{}", i);
85 pub NEEDLESS_RANGE_LOOP,
87 "for-looping over a range of indices where an iterator over items would do"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
92 /// suggests the latter.
94 /// **Why is this bad?** Readability.
96 /// **Known problems:** False negatives. We currently only warn on some known
101 /// // with `y` a `Vec` or slice:
102 /// # let y = vec![1];
103 /// for x in y.iter() {
107 /// can be rewritten to
109 /// # let y = vec![1];
114 pub EXPLICIT_ITER_LOOP,
116 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
121 /// suggests the latter.
123 /// **Why is this bad?** Readability.
125 /// **Known problems:** None
129 /// # let y = vec![1];
130 /// // with `y` a `Vec` or slice:
131 /// for x in y.into_iter() {
135 /// can be rewritten to
137 /// # let y = vec![1];
142 pub EXPLICIT_INTO_ITER_LOOP,
144 "for-looping over `_.into_iter()` when `_` would do"
147 declare_clippy_lint! {
148 /// **What it does:** Checks for loops on `x.next()`.
150 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
151 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
152 /// implements `IntoIterator`, so that possibly one value will be iterated,
153 /// leading to some hard to find bugs. No one will want to write such code
154 /// [except to win an Underhanded Rust
155 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
157 /// **Known problems:** None.
161 /// for x in y.next() {
167 "for-looping over `_.next()` which is probably not intended"
170 declare_clippy_lint! {
171 /// **What it does:** Checks for `for` loops over `Option` values.
173 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
176 /// **Known problems:** None.
180 /// for x in option {
187 /// if let Some(x) = option {
191 pub FOR_LOOP_OVER_OPTION,
193 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
196 declare_clippy_lint! {
197 /// **What it does:** Checks for `for` loops over `Result` values.
199 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
202 /// **Known problems:** None.
206 /// for x in result {
213 /// if let Ok(x) = result {
217 pub FOR_LOOP_OVER_RESULT,
219 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
222 declare_clippy_lint! {
223 /// **What it does:** Detects `loop + match` combinations that are easier
224 /// written as a `while let` loop.
226 /// **Why is this bad?** The `while let` loop is usually shorter and more
229 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
233 /// # let y = Some(1);
235 /// let x = match y {
239 /// // .. do something with x
241 /// // is easier written as
242 /// while let Some(x) = y {
243 /// // .. do something with x
248 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
251 declare_clippy_lint! {
252 /// **What it does:** Checks for functions collecting an iterator when collect
255 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
256 /// when this allocation may not be needed.
258 /// **Known problems:**
263 /// # let iterator = vec![1].into_iter();
264 /// let len = iterator.clone().collect::<Vec<_>>().len();
266 /// let len = iterator.count();
268 pub NEEDLESS_COLLECT,
270 "collecting an iterator when collect is not needed"
273 declare_clippy_lint! {
274 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
275 /// are constant and `x` is greater or equal to `y`, unless the range is
276 /// reversed or has a negative `.step_by(_)`.
278 /// **Why is it bad?** Such loops will either be skipped or loop until
279 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
282 /// **Known problems:** The lint cannot catch loops over dynamically defined
283 /// ranges. Doing this would require simulating all possible inputs and code
284 /// paths through the program, which would be complex and error-prone.
288 /// for x in 5..10 - 5 {
290 /// } // oops, stray `-`
292 pub REVERSE_RANGE_LOOP,
294 "iteration over an empty range, such as `10..0` or `5..5`"
297 declare_clippy_lint! {
298 /// **What it does:** Checks `for` loops over slices with an explicit counter
299 /// and suggests the use of `.enumerate()`.
301 /// **Why is it bad?** Not only is the version using `.enumerate()` more
302 /// readable, the compiler is able to remove bounds checks which can lead to
303 /// faster code in some instances.
305 /// **Known problems:** None.
309 /// # let v = vec![1];
310 /// # fn foo(bar: usize) {}
311 /// # fn bar(bar: usize, baz: usize) {}
312 /// for i in 0..v.len() { foo(v[i]); }
313 /// for i in 0..v.len() { bar(i, v[i]); }
315 /// Could be written as
317 /// # let v = vec![1];
318 /// # fn foo(bar: usize) {}
319 /// # fn bar(bar: usize, baz: usize) {}
320 /// for item in &v { foo(*item); }
321 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
323 pub EXPLICIT_COUNTER_LOOP,
325 "for-looping with an explicit counter when `_.enumerate()` would do"
328 declare_clippy_lint! {
329 /// **What it does:** Checks for empty `loop` expressions.
331 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
332 /// anything. Think of the environment and either block on something or at least
333 /// make the thread sleep for some microseconds.
335 /// **Known problems:** None.
343 "empty `loop {}`, which should block or sleep"
346 declare_clippy_lint! {
347 /// **What it does:** Checks for `while let` expressions on iterators.
349 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
350 /// the intent better.
352 /// **Known problems:** None.
356 /// while let Some(val) = iter() {
360 pub WHILE_LET_ON_ITERATOR,
362 "using a while-let loop instead of a for loop on an iterator"
365 declare_clippy_lint! {
366 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
367 /// ignoring either the keys or values.
369 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
370 /// can be used to express that don't need the values or keys.
372 /// **Known problems:** None.
376 /// for (k, _) in &map {
381 /// could be replaced by
384 /// for k in map.keys() {
390 "looping on a map using `iter` when `keys` or `values` would do"
393 declare_clippy_lint! {
394 /// **What it does:** Checks for loops that will always `break`, `return` or
395 /// `continue` an outer loop.
397 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
400 /// **Known problems:** None
411 "any loop that will always `break` or `return`"
414 declare_clippy_lint! {
415 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
417 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
419 /// **Known problems:** None
423 /// let mut foo = 42;
424 /// for i in 0..foo {
426 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
431 "for loop over a range where one of the bounds is a mutable variable"
434 declare_clippy_lint! {
435 /// **What it does:** Checks whether variables used within while loop condition
436 /// can be (and are) mutated in the body.
438 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
439 /// will lead to an infinite loop.
441 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
442 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
443 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
449 /// println!("let me loop forever!");
452 pub WHILE_IMMUTABLE_CONDITION,
454 "variables used within while expression are not mutated in the body"
457 declare_lint_pass!(Loops => [
461 EXPLICIT_INTO_ITER_LOOP,
463 FOR_LOOP_OVER_RESULT,
464 FOR_LOOP_OVER_OPTION,
468 EXPLICIT_COUNTER_LOOP,
470 WHILE_LET_ON_ITERATOR,
474 WHILE_IMMUTABLE_CONDITION,
477 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
478 #[allow(clippy::too_many_lines)]
479 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
480 // we don't want to check expanded macros
481 if expr.span.from_expansion() {
485 if let Some((pat, arg, body)) = higher::for_loop(expr) {
486 check_for_loop(cx, pat, arg, body, expr);
489 // check for never_loop
490 if let ExprKind::Loop(ref block, _, _) = expr.node {
491 match never_loop_block(block, expr.hir_id) {
492 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
493 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
497 // check for `loop { if let {} else break }` that could be `while let`
498 // (also matches an explicit "match" instead of "if let")
499 // (even if the "match" or "if let" is used for declaration)
500 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
501 // also check for empty `loop {}` statements
502 if block.stmts.is_empty() && block.expr.is_none() {
507 "empty `loop {}` detected. You may want to either use `panic!()` or add \
508 `std::thread::sleep(..);` to the loop body.",
512 // extract the expression from the first statement (if any) in a block
513 let inner_stmt_expr = extract_expr_from_first_stmt(block);
514 // or extract the first expression (if any) from the block
515 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
516 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
517 // ensure "if let" compatible match structure
519 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
521 && arms[0].pats.len() == 1
522 && arms[0].guard.is_none()
523 && arms[1].pats.len() == 1
524 && arms[1].guard.is_none()
525 && is_simple_break_expr(&arms[1].body)
527 if in_external_macro(cx.sess(), expr.span) {
531 // NOTE: we used to build a body here instead of using
532 // ellipsis, this was removed because:
533 // 1) it was ugly with big bodies;
534 // 2) it was not indented properly;
535 // 3) it wasn’t very smart (see #675).
536 let mut applicability = Applicability::HasPlaceholders;
541 "this loop could be written as a `while let` loop",
544 "while let {} = {} {{ .. }}",
545 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
546 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
557 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
558 let pat = &arms[0].pats[0].node;
560 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
561 &ExprKind::MethodCall(ref method_path, _, ref method_args),
562 ) = (pat, &match_expr.node)
564 let iter_expr = &method_args[0];
565 let lhs_constructor = last_path_segment(qpath);
566 if method_path.ident.name == sym!(next)
567 && match_trait_method(cx, match_expr, &paths::ITERATOR)
568 && lhs_constructor.ident.name == sym!(Some)
569 && (pat_args.is_empty()
570 || !is_refutable(cx, &pat_args[0])
571 && !is_used_inside(cx, iter_expr, &arms[0].body)
572 && !is_iterator_used_after_while_let(cx, iter_expr)
573 && !is_nested(cx, expr, &method_args[0]))
575 let iterator = snippet(cx, method_args[0].span, "_");
576 let loop_var = if pat_args.is_empty() {
579 snippet(cx, pat_args[0].span, "_").into_owned()
583 WHILE_LET_ON_ITERATOR,
585 "this loop could be written as a `for` loop",
587 format!("for {} in {} {{ .. }}", loop_var, iterator),
588 Applicability::HasPlaceholders,
594 if let Some((cond, body)) = higher::while_loop(&expr) {
595 check_infinite_loop(cx, cond, body);
598 check_needless_collect(expr, cx);
602 enum NeverLoopResult {
603 // A break/return always get triggered but not necessarily for the main loop.
605 // A continue may occur for the main loop.
610 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
612 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
613 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
617 // Combine two results for parts that are called in order.
618 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
620 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
621 NeverLoopResult::Otherwise => second,
625 // Combine two results where both parts are called but not necessarily in order.
626 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
627 match (left, right) {
628 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
629 NeverLoopResult::MayContinueMainLoop
631 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
632 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
636 // Combine two results where only one of the part may have been executed.
637 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
639 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
640 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
641 NeverLoopResult::MayContinueMainLoop
643 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
647 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
648 let stmts = block.stmts.iter().map(stmt_to_expr);
649 let expr = once(block.expr.as_ref().map(|p| &**p));
650 let mut iter = stmts.chain(expr).filter_map(|e| e);
651 never_loop_expr_seq(&mut iter, main_loop_id)
654 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
656 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
657 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
662 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
665 | ExprKind::Unary(_, ref e)
666 | ExprKind::Cast(ref e, _)
667 | ExprKind::Type(ref e, _)
668 | ExprKind::Field(ref e, _)
669 | ExprKind::AddrOf(_, ref e)
670 | ExprKind::Struct(_, _, Some(ref e))
671 | ExprKind::Repeat(ref e, _)
672 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
673 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
674 never_loop_expr_all(&mut es.iter(), main_loop_id)
676 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
677 ExprKind::Binary(_, ref e1, ref e2)
678 | ExprKind::Assign(ref e1, ref e2)
679 | ExprKind::AssignOp(_, ref e1, ref e2)
680 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
681 ExprKind::Loop(ref b, _, _) => {
682 // Break can come from the inner loop so remove them.
683 absorb_break(&never_loop_block(b, main_loop_id))
685 ExprKind::Match(ref e, ref arms, _) => {
686 let e = never_loop_expr(e, main_loop_id);
690 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
694 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
695 ExprKind::Continue(d) => {
698 .expect("target ID can only be missing in the presence of compilation errors");
699 if id == main_loop_id {
700 NeverLoopResult::MayContinueMainLoop
702 NeverLoopResult::AlwaysBreak
705 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
706 if let Some(ref e) = *e {
707 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
709 NeverLoopResult::AlwaysBreak
712 ExprKind::Struct(_, _, None)
713 | ExprKind::Yield(_, _)
714 | ExprKind::Closure(_, _, _, _, _)
715 | ExprKind::InlineAsm(_, _, _)
718 | ExprKind::Err => NeverLoopResult::Otherwise,
722 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
723 es.map(|e| never_loop_expr(e, main_loop_id))
724 .fold(NeverLoopResult::Otherwise, combine_seq)
727 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
728 es.map(|e| never_loop_expr(e, main_loop_id))
729 .fold(NeverLoopResult::Otherwise, combine_both)
732 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
733 e.map(|e| never_loop_expr(e, main_loop_id))
734 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
737 fn check_for_loop<'a, 'tcx>(
738 cx: &LateContext<'a, 'tcx>,
744 check_for_loop_range(cx, pat, arg, body, expr);
745 check_for_loop_reverse_range(cx, arg, expr);
746 check_for_loop_arg(cx, pat, arg, expr);
747 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
748 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
749 check_for_mut_range_bound(cx, arg, body);
750 detect_manual_memcpy(cx, pat, arg, body, expr);
753 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
755 if let ExprKind::Path(ref qpath) = expr.node;
756 if let QPath::Resolved(None, ref path) = *qpath;
757 if path.segments.len() == 1;
758 if let Res::Local(local_id) = cx.tables.qpath_res(qpath, expr.hir_id);
775 fn negative(s: String) -> Self {
776 Self { value: s, negate: true }
779 fn positive(s: String) -> Self {
787 struct FixedOffsetVar {
792 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
793 let is_slice = match ty.sty {
794 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
795 ty::Slice(..) | ty::Array(..) => true,
799 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
802 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
803 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
805 ExprKind::Lit(ref l) => match l.node {
806 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
809 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
814 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
815 let ty = cx.tables.expr_ty(seqexpr);
816 if !is_slice_like(cx, ty) {
820 let offset = match idx.node {
821 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
823 let offset_opt = if same_var(cx, lhs, var) {
824 extract_offset(cx, rhs, var)
825 } else if same_var(cx, rhs, var) {
826 extract_offset(cx, lhs, var)
831 offset_opt.map(Offset::positive)
833 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
836 ExprKind::Path(..) => {
837 if same_var(cx, idx, var) {
838 Some(Offset::positive("0".into()))
846 offset.map(|o| FixedOffsetVar {
847 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
855 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
856 cx: &LateContext<'a, 'tcx>,
859 ) -> Option<FixedOffsetVar> {
861 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
862 if method.ident.name == sym!(clone);
864 if let Some(arg) = args.get(0);
866 return get_fixed_offset_var(cx, arg, var);
870 get_fixed_offset_var(cx, expr, var)
873 fn get_indexed_assignments<'a, 'tcx>(
874 cx: &LateContext<'a, 'tcx>,
877 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
878 fn get_assignment<'a, 'tcx>(
879 cx: &LateContext<'a, 'tcx>,
882 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
883 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
885 get_fixed_offset_var(cx, lhs, var),
886 fetch_cloned_fixed_offset_var(cx, rhs, var),
888 (Some(offset_left), Some(offset_right)) => {
889 // Source and destination must be different
890 if offset_left.var_name == offset_right.var_name {
893 Some((offset_left, offset_right))
903 if let ExprKind::Block(ref b, _) = body.node {
905 ref stmts, ref expr, ..
910 .map(|stmt| match stmt.node {
911 StmtKind::Local(..) | StmtKind::Item(..) => None,
912 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
914 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
916 .collect::<Option<Vec<_>>>()
917 .unwrap_or_else(|| vec![])
919 get_assignment(cx, body, var).into_iter().collect()
923 /// Checks for for loops that sequentially copy items from one slice-like
924 /// object to another.
925 fn detect_manual_memcpy<'a, 'tcx>(
926 cx: &LateContext<'a, 'tcx>,
932 if let Some(higher::Range {
936 }) = higher::range(cx, arg)
938 // the var must be a single name
939 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
940 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
941 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
942 ("0", _, "0", _) => "".into(),
943 ("0", _, x, false) | (x, false, "0", false) => x.into(),
944 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
945 (x, false, y, false) => format!("({} + {})", x, y),
946 (x, false, y, true) => {
950 format!("({} - {})", x, y)
953 (x, true, y, false) => {
957 format!("({} - {})", y, x)
960 (x, true, y, true) => format!("-({} + {})", x, y),
964 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
965 if let Some(end) = *end {
967 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
968 if method.ident.name == sym!(len);
969 if len_args.len() == 1;
970 if let Some(arg) = len_args.get(0);
971 if snippet(cx, arg.span, "??") == var_name;
973 return if offset.negate {
974 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
981 let end_str = match limits {
982 ast::RangeLimits::Closed => {
983 let end = sugg::Sugg::hir(cx, end, "<count>");
984 format!("{}", end + sugg::ONE)
986 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
989 print_sum(&Offset::positive(end_str), &offset)
995 // The only statements in the for loops can be indexed assignments from
996 // indexed retrievals.
997 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
999 let big_sugg = manual_copies
1001 .map(|(dst_var, src_var)| {
1002 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1003 let dst_offset = print_sum(&start_str, &dst_var.offset);
1004 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1005 let src_offset = print_sum(&start_str, &src_var.offset);
1006 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1007 let dst = if dst_offset == "" && dst_limit == "" {
1010 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1014 "{}.clone_from_slice(&{}[{}..{}])",
1015 dst, src_var.var_name, src_offset, src_limit
1020 if !big_sugg.is_empty() {
1025 "it looks like you're manually copying between slices",
1026 "try replacing the loop by",
1028 Applicability::Unspecified,
1035 /// Checks for looping over a range and then indexing a sequence with it.
1036 /// The iteratee must be a range literal.
1037 #[allow(clippy::too_many_lines)]
1038 fn check_for_loop_range<'a, 'tcx>(
1039 cx: &LateContext<'a, 'tcx>,
1045 if expr.span.from_expansion() {
1049 if let Some(higher::Range {
1053 }) = higher::range(cx, arg)
1055 // the var must be a single name
1056 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1057 let mut visitor = VarVisitor {
1060 indexed_mut: FxHashSet::default(),
1061 indexed_indirectly: FxHashMap::default(),
1062 indexed_directly: FxHashMap::default(),
1063 referenced: FxHashSet::default(),
1065 prefer_mutable: false,
1067 walk_expr(&mut visitor, body);
1069 // linting condition: we only indexed one variable, and indexed it directly
1070 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1071 let (indexed, (indexed_extent, indexed_ty)) = visitor
1075 .expect("already checked that we have exactly 1 element");
1077 // ensure that the indexed variable was declared before the loop, see #601
1078 if let Some(indexed_extent) = indexed_extent {
1079 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1080 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1081 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1082 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1083 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1088 // don't lint if the container that is indexed does not have .iter() method
1089 let has_iter = has_iter_method(cx, indexed_ty);
1090 if has_iter.is_none() {
1094 // don't lint if the container that is indexed into is also used without
1096 if visitor.referenced.contains(&indexed) {
1100 let starts_at_zero = is_integer_literal(start, 0);
1102 let skip = if starts_at_zero {
1105 format!(".skip({})", snippet(cx, start.span, ".."))
1108 let mut end_is_start_plus_val = false;
1110 let take = if let Some(end) = *end {
1111 let mut take_expr = end;
1113 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1114 if let BinOpKind::Add = op.node {
1115 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1116 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1118 if start_equal_left {
1120 } else if start_equal_right {
1124 end_is_start_plus_val = start_equal_left | start_equal_right;
1128 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1132 ast::RangeLimits::Closed => {
1133 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1134 format!(".take({})", take_expr + sugg::ONE)
1136 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1143 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1144 ("mut ", "iter_mut")
1149 let take_is_empty = take.is_empty();
1150 let mut method_1 = take;
1151 let mut method_2 = skip;
1153 if end_is_start_plus_val {
1154 mem::swap(&mut method_1, &mut method_2);
1157 if visitor.nonindex {
1160 NEEDLESS_RANGE_LOOP,
1162 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1166 "consider using an iterator".to_string(),
1168 (pat.span, format!("({}, <item>)", ident.name)),
1171 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1178 let repl = if starts_at_zero && take_is_empty {
1179 format!("&{}{}", ref_mut, indexed)
1181 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1186 NEEDLESS_RANGE_LOOP,
1189 "the loop variable `{}` is only used to index `{}`.",
1195 "consider using an iterator".to_string(),
1196 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1206 fn is_len_call(expr: &Expr, var: Name) -> bool {
1208 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1209 if len_args.len() == 1;
1210 if method.ident.name == sym!(len);
1211 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1212 if path.segments.len() == 1;
1213 if path.segments[0].ident.name == var;
1222 fn is_end_eq_array_len<'tcx>(
1223 cx: &LateContext<'_, 'tcx>,
1225 limits: ast::RangeLimits,
1226 indexed_ty: Ty<'tcx>,
1229 if let ExprKind::Lit(ref lit) = end.node;
1230 if let ast::LitKind::Int(end_int, _) = lit.node;
1231 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1232 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1234 return match limits {
1235 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1236 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1244 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1245 // if this for loop is iterating over a two-sided range...
1246 if let Some(higher::Range {
1250 }) = higher::range(cx, arg)
1252 // ...and both sides are compile-time constant integers...
1253 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1254 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1255 // ...and the start index is greater than the end index,
1256 // this loop will never run. This is often confusing for developers
1257 // who think that this will iterate from the larger value to the
1259 let ty = cx.tables.expr_ty(start);
1260 let (sup, eq) = match (start_idx, end_idx) {
1261 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1263 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1264 ty::Uint(_) => start_idx > end_idx,
1267 start_idx == end_idx,
1269 _ => (false, false),
1273 let start_snippet = snippet(cx, start.span, "_");
1274 let end_snippet = snippet(cx, end.span, "_");
1275 let dots = if limits == ast::RangeLimits::Closed {
1285 "this range is empty so this for loop will never run",
1289 "consider using the following if you are attempting to iterate over this \
1292 "({end}{dots}{start}).rev()",
1295 start = start_snippet
1297 Applicability::MaybeIncorrect,
1301 } else if eq && limits != ast::RangeLimits::Closed {
1302 // if they are equal, it's also problematic - this loop
1308 "this range is empty so this for loop will never run",
1316 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1317 let mut applicability = Applicability::MachineApplicable;
1318 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1319 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1324 "it is more concise to loop over references to containers instead of using explicit \
1326 "to write this more concisely, try",
1327 format!("&{}{}", muta, object),
1332 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1333 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1334 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1335 // just the receiver, no arguments
1336 if args.len() == 1 {
1337 let method_name = &*method.ident.as_str();
1338 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1339 if method_name == "iter" || method_name == "iter_mut" {
1340 if is_ref_iterable_type(cx, &args[0]) {
1341 lint_iter_method(cx, args, arg, method_name);
1343 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1344 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1345 let substs = cx.tables.node_substs(arg.hir_id);
1346 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1348 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1349 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1350 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1351 match cx.tables.expr_ty(&args[0]).sty {
1352 // If the length is greater than 32 no traits are implemented for array and
1353 // therefore we cannot use `&`.
1354 ty::Array(_, size) if size.eval_usize(cx.tcx, cx.param_env) > 32 => {},
1355 _ => lint_iter_method(cx, args, arg, method_name),
1358 let mut applicability = Applicability::MachineApplicable;
1359 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1362 EXPLICIT_INTO_ITER_LOOP,
1364 "it is more concise to loop over containers instead of using explicit \
1365 iteration methods`",
1366 "to write this more concisely, try",
1371 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1376 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1377 probably not what you want",
1379 next_loop_linted = true;
1383 if !next_loop_linted {
1384 check_arg_type(cx, pat, arg);
1388 /// Checks for `for` loops over `Option`s and `Result`s.
1389 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1390 let ty = cx.tables.expr_ty(arg);
1391 if match_type(cx, ty, &paths::OPTION) {
1394 FOR_LOOP_OVER_OPTION,
1397 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1398 `if let` statement.",
1399 snippet(cx, arg.span, "_")
1402 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1403 snippet(cx, pat.span, "_"),
1404 snippet(cx, arg.span, "_")
1407 } else if match_type(cx, ty, &paths::RESULT) {
1410 FOR_LOOP_OVER_RESULT,
1413 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1414 `if let` statement.",
1415 snippet(cx, arg.span, "_")
1418 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1419 snippet(cx, pat.span, "_"),
1420 snippet(cx, arg.span, "_")
1426 fn check_for_loop_explicit_counter<'a, 'tcx>(
1427 cx: &LateContext<'a, 'tcx>,
1433 // Look for variables that are incremented once per loop iteration.
1434 let mut visitor = IncrementVisitor {
1436 states: FxHashMap::default(),
1440 walk_expr(&mut visitor, body);
1442 // For each candidate, check the parent block to see if
1443 // it's initialized to zero at the start of the loop.
1444 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1445 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1446 let mut visitor2 = InitializeVisitor {
1450 state: VarState::IncrOnce,
1455 walk_block(&mut visitor2, block);
1457 if visitor2.state == VarState::Warn {
1458 if let Some(name) = visitor2.name {
1459 let mut applicability = Applicability::MachineApplicable;
1462 EXPLICIT_COUNTER_LOOP,
1464 &format!("the variable `{}` is used as a loop counter.", name),
1467 "for ({}, {}) in {}.enumerate()",
1469 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1470 if higher::range(cx, arg).is_some() {
1473 snippet_with_applicability(cx, arg.span, "_", &mut applicability)
1478 sugg::Sugg::hir_with_applicability(cx, arg, "_", &mut applicability).maybe_par()
1490 /// Checks for the `FOR_KV_MAP` lint.
1491 fn check_for_loop_over_map_kv<'a, 'tcx>(
1492 cx: &LateContext<'a, 'tcx>,
1498 let pat_span = pat.span;
1500 if let PatKind::Tuple(ref pat, _) = pat.node {
1502 let arg_span = arg.span;
1503 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1504 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1505 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1506 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1511 let mutbl = match mutbl {
1513 MutMutable => "_mut",
1515 let arg = match arg.node {
1516 ExprKind::AddrOf(_, ref expr) => &**expr,
1520 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1525 &format!("you seem to want to iterate on a map's {}s", kind),
1527 let map = sugg::Sugg::hir(cx, arg, "map");
1530 "use the corresponding method".into(),
1532 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1533 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1543 struct MutatePairDelegate {
1544 hir_id_low: Option<HirId>,
1545 hir_id_high: Option<HirId>,
1546 span_low: Option<Span>,
1547 span_high: Option<Span>,
1550 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1551 fn consume(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1553 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1555 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1557 fn borrow(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1558 if let ty::BorrowKind::MutBorrow = bk {
1559 if let Categorization::Local(id) = cmt.cat {
1560 if Some(id) == self.hir_id_low {
1561 self.span_low = Some(sp)
1563 if Some(id) == self.hir_id_high {
1564 self.span_high = Some(sp)
1570 fn mutate(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1571 if let Categorization::Local(id) = cmt.cat {
1572 if Some(id) == self.hir_id_low {
1573 self.span_low = Some(sp)
1575 if Some(id) == self.hir_id_high {
1576 self.span_high = Some(sp)
1581 fn decl_without_init(&mut self, _: HirId, _: Span) {}
1584 impl<'tcx> MutatePairDelegate {
1585 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1586 (self.span_low, self.span_high)
1590 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1591 if let Some(higher::Range {
1595 }) = higher::range(cx, arg)
1597 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1598 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1599 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1600 mut_warn_with_span(cx, span_low);
1601 mut_warn_with_span(cx, span_high);
1606 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1607 if let Some(sp) = span {
1612 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1617 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1619 if let ExprKind::Path(ref qpath) = bound.node;
1620 if let QPath::Resolved(None, _) = *qpath;
1622 let res = cx.tables.qpath_res(qpath, bound.hir_id);
1623 if let Res::Local(node_id) = res {
1624 let node_str = cx.tcx.hir().get(node_id);
1626 if let Node::Binding(pat) = node_str;
1627 if let PatKind::Binding(bind_ann, ..) = pat.node;
1628 if let BindingAnnotation::Mutable = bind_ann;
1630 return Some(node_id);
1639 fn check_for_mutation(
1640 cx: &LateContext<'_, '_>,
1642 bound_ids: &[Option<HirId>],
1643 ) -> (Option<Span>, Option<Span>) {
1644 let mut delegate = MutatePairDelegate {
1645 hir_id_low: bound_ids[0],
1646 hir_id_high: bound_ids[1],
1650 let def_id = def_id::DefId::local(body.hir_id.owner);
1651 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1652 ExprUseVisitor::new(
1662 delegate.mutation_span()
1665 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1666 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1668 PatKind::Wild => true,
1669 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1670 let mut visitor = UsedVisitor {
1674 walk_expr(&mut visitor, body);
1681 struct UsedVisitor {
1682 var: ast::Name, // var to look for
1683 used: bool, // has the var been used otherwise?
1686 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1687 fn visit_expr(&mut self, expr: &'tcx Expr) {
1688 if match_var(expr, self.var) {
1691 walk_expr(self, expr);
1695 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1696 NestedVisitorMap::None
1700 struct LocalUsedVisitor<'a, 'tcx> {
1701 cx: &'a LateContext<'a, 'tcx>,
1706 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1707 fn visit_expr(&mut self, expr: &'tcx Expr) {
1708 if same_var(self.cx, expr, self.local) {
1711 walk_expr(self, expr);
1715 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1716 NestedVisitorMap::None
1720 struct VarVisitor<'a, 'tcx> {
1721 /// context reference
1722 cx: &'a LateContext<'a, 'tcx>,
1723 /// var name to look for as index
1725 /// indexed variables that are used mutably
1726 indexed_mut: FxHashSet<Name>,
1727 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1728 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1729 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1730 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1731 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1732 /// Any names that are used outside an index operation.
1733 /// Used to detect things like `&mut vec` used together with `vec[i]`
1734 referenced: FxHashSet<Name>,
1735 /// has the loop variable been used in expressions other than the index of
1738 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1739 /// takes `&mut self`
1740 prefer_mutable: bool,
1743 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1744 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1746 // the indexed container is referenced by a name
1747 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1748 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1749 if seqvar.segments.len() == 1;
1751 let index_used_directly = same_var(self.cx, idx, self.var);
1752 let indexed_indirectly = {
1753 let mut used_visitor = LocalUsedVisitor {
1758 walk_expr(&mut used_visitor, idx);
1762 if indexed_indirectly || index_used_directly {
1763 if self.prefer_mutable {
1764 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1766 let res = self.cx.tables.qpath_res(seqpath, seqexpr.hir_id);
1768 Res::Local(hir_id) => {
1769 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1770 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1771 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1772 if indexed_indirectly {
1773 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1775 if index_used_directly {
1776 self.indexed_directly.insert(
1777 seqvar.segments[0].ident.name,
1778 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1781 return false; // no need to walk further *on the variable*
1783 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1784 if indexed_indirectly {
1785 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1787 if index_used_directly {
1788 self.indexed_directly.insert(
1789 seqvar.segments[0].ident.name,
1790 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1793 return false; // no need to walk further *on the variable*
1804 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1805 fn visit_expr(&mut self, expr: &'tcx Expr) {
1808 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1809 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1810 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1811 if !self.check(&args[1], &args[0], expr);
1817 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1818 if !self.check(idx, seqexpr, expr);
1823 // directly using a variable
1824 if let ExprKind::Path(ref qpath) = expr.node;
1825 if let QPath::Resolved(None, ref path) = *qpath;
1826 if path.segments.len() == 1;
1828 if let Res::Local(local_id) = self.cx.tables.qpath_res(qpath, expr.hir_id) {
1829 if local_id == self.var {
1830 self.nonindex = true;
1832 // not the correct variable, but still a variable
1833 self.referenced.insert(path.segments[0].ident.name);
1839 let old = self.prefer_mutable;
1841 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1842 self.prefer_mutable = true;
1843 self.visit_expr(lhs);
1844 self.prefer_mutable = false;
1845 self.visit_expr(rhs);
1847 ExprKind::AddrOf(mutbl, ref expr) => {
1848 if mutbl == MutMutable {
1849 self.prefer_mutable = true;
1851 self.visit_expr(expr);
1853 ExprKind::Call(ref f, ref args) => {
1856 let ty = self.cx.tables.expr_ty_adjusted(expr);
1857 self.prefer_mutable = false;
1858 if let ty::Ref(_, _, mutbl) = ty.sty {
1859 if mutbl == MutMutable {
1860 self.prefer_mutable = true;
1863 self.visit_expr(expr);
1866 ExprKind::MethodCall(_, _, ref args) => {
1867 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1868 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1869 self.prefer_mutable = false;
1870 if let ty::Ref(_, _, mutbl) = ty.sty {
1871 if mutbl == MutMutable {
1872 self.prefer_mutable = true;
1875 self.visit_expr(expr);
1878 ExprKind::Closure(_, _, body_id, ..) => {
1879 let body = self.cx.tcx.hir().body(body_id);
1880 self.visit_expr(&body.value);
1882 _ => walk_expr(self, expr),
1884 self.prefer_mutable = old;
1886 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1887 NestedVisitorMap::None
1891 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1892 let def_id = match var_def_id(cx, expr) {
1894 None => return false,
1896 if let Some(used_mutably) = mutated_variables(container, cx) {
1897 if used_mutably.contains(&def_id) {
1904 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1905 let def_id = match var_def_id(cx, iter_expr) {
1907 None => return false,
1909 let mut visitor = VarUsedAfterLoopVisitor {
1912 iter_expr_id: iter_expr.hir_id,
1913 past_while_let: false,
1914 var_used_after_while_let: false,
1916 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1917 walk_block(&mut visitor, enclosing_block);
1919 visitor.var_used_after_while_let
1922 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1923 cx: &'a LateContext<'a, 'tcx>,
1925 iter_expr_id: HirId,
1926 past_while_let: bool,
1927 var_used_after_while_let: bool,
1930 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1931 fn visit_expr(&mut self, expr: &'tcx Expr) {
1932 if self.past_while_let {
1933 if Some(self.def_id) == var_def_id(self.cx, expr) {
1934 self.var_used_after_while_let = true;
1936 } else if self.iter_expr_id == expr.hir_id {
1937 self.past_while_let = true;
1939 walk_expr(self, expr);
1941 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1942 NestedVisitorMap::None
1946 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1947 /// for `&T` and `&mut T`, such as `Vec`.
1949 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1950 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1951 // will allow further borrows afterwards
1952 let ty = cx.tables.expr_ty(e);
1953 is_iterable_array(ty, cx) ||
1954 match_type(cx, ty, &paths::VEC) ||
1955 match_type(cx, ty, &paths::LINKED_LIST) ||
1956 match_type(cx, ty, &paths::HASHMAP) ||
1957 match_type(cx, ty, &paths::HASHSET) ||
1958 match_type(cx, ty, &paths::VEC_DEQUE) ||
1959 match_type(cx, ty, &paths::BINARY_HEAP) ||
1960 match_type(cx, ty, &paths::BTREEMAP) ||
1961 match_type(cx, ty, &paths::BTREESET)
1964 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1965 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1967 ty::Array(_, n) => (0..=32).contains(&n.eval_usize(cx.tcx, cx.param_env)),
1972 /// If a block begins with a statement (possibly a `let` binding) and has an
1973 /// expression, return it.
1974 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1975 if block.stmts.is_empty() {
1978 if let StmtKind::Local(ref local) = block.stmts[0].node {
1979 if let Some(ref expr) = local.init {
1989 /// If a block begins with an expression (with or without semicolon), return it.
1990 fn extract_first_expr(block: &Block) -> Option<&Expr> {
1992 Some(ref expr) if block.stmts.is_empty() => Some(expr),
1993 None if !block.stmts.is_empty() => match block.stmts[0].node {
1994 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
1995 StmtKind::Local(..) | StmtKind::Item(..) => None,
2001 /// Returns `true` if expr contains a single break expr without destination label
2003 /// passed expression. The expression may be within a block.
2004 fn is_simple_break_expr(expr: &Expr) -> bool {
2006 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2007 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2008 Some(subexpr) => is_simple_break_expr(subexpr),
2015 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2016 // incremented exactly once in the loop body, and initialized to zero
2017 // at the start of the loop.
2018 #[derive(Debug, PartialEq)]
2020 Initial, // Not examined yet
2021 IncrOnce, // Incremented exactly once, may be a loop counter
2022 Declared, // Declared but not (yet) initialized to zero
2027 /// Scan a for loop for variables that are incremented exactly once.
2028 struct IncrementVisitor<'a, 'tcx> {
2029 cx: &'a LateContext<'a, 'tcx>, // context reference
2030 states: FxHashMap<HirId, VarState>, // incremented variables
2031 depth: u32, // depth of conditional expressions
2035 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2036 fn visit_expr(&mut self, expr: &'tcx Expr) {
2041 // If node is a variable
2042 if let Some(def_id) = var_def_id(self.cx, expr) {
2043 if let Some(parent) = get_parent_expr(self.cx, expr) {
2044 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2047 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2048 if lhs.hir_id == expr.hir_id {
2049 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2050 *state = match *state {
2051 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2052 _ => VarState::DontWarn,
2055 // Assigned some other value
2056 *state = VarState::DontWarn;
2060 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2061 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2065 } else if is_loop(expr) || is_conditional(expr) {
2067 walk_expr(self, expr);
2070 } else if let ExprKind::Continue(_) = expr.node {
2074 walk_expr(self, expr);
2076 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2077 NestedVisitorMap::None
2081 /// Checks whether a variable is initialized to zero at the start of a loop.
2082 struct InitializeVisitor<'a, 'tcx> {
2083 cx: &'a LateContext<'a, 'tcx>, // context reference
2084 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2088 depth: u32, // depth of conditional expressions
2092 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2093 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2094 // Look for declarations of the variable
2095 if let StmtKind::Local(ref local) = stmt.node {
2096 if local.pat.hir_id == self.var_id {
2097 if let PatKind::Binding(.., ident, _) = local.pat.node {
2098 self.name = Some(ident.name);
2100 self.state = if let Some(ref init) = local.init {
2101 if is_integer_literal(init, 0) {
2112 walk_stmt(self, stmt);
2115 fn visit_expr(&mut self, expr: &'tcx Expr) {
2116 if self.state == VarState::DontWarn {
2119 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2120 self.past_loop = true;
2123 // No need to visit expressions before the variable is
2125 if self.state == VarState::IncrOnce {
2129 // If node is the desired variable, see how it's used
2130 if var_def_id(self.cx, expr) == Some(self.var_id) {
2131 if let Some(parent) = get_parent_expr(self.cx, expr) {
2133 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2134 self.state = VarState::DontWarn;
2136 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2137 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2143 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2149 self.state = VarState::DontWarn;
2152 } else if !self.past_loop && is_loop(expr) {
2153 self.state = VarState::DontWarn;
2155 } else if is_conditional(expr) {
2157 walk_expr(self, expr);
2161 walk_expr(self, expr);
2163 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2164 NestedVisitorMap::None
2168 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2169 if let ExprKind::Path(ref qpath) = expr.node {
2170 let path_res = cx.tables.qpath_res(qpath, expr.hir_id);
2171 if let Res::Local(node_id) = path_res {
2172 return Some(node_id);
2178 fn is_loop(expr: &Expr) -> bool {
2180 ExprKind::Loop(..) => true,
2185 fn is_conditional(expr: &Expr) -> bool {
2187 ExprKind::Match(..) => true,
2192 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2194 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2195 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2196 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2198 return is_loop_nested(cx, loop_expr, iter_expr)
2204 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2205 let mut id = loop_expr.hir_id;
2206 let iter_name = if let Some(name) = path_name(iter_expr) {
2212 let parent = cx.tcx.hir().get_parent_node(id);
2216 match cx.tcx.hir().find(parent) {
2217 Some(Node::Expr(expr)) => {
2218 if let ExprKind::Loop(..) = expr.node {
2222 Some(Node::Block(block)) => {
2223 let mut block_visitor = LoopNestVisitor {
2225 iterator: iter_name,
2228 walk_block(&mut block_visitor, block);
2229 if block_visitor.nesting == RuledOut {
2233 Some(Node::Stmt(_)) => (),
2242 #[derive(PartialEq, Eq)]
2244 Unknown, // no nesting detected yet
2245 RuledOut, // the iterator is initialized or assigned within scope
2246 LookFurther, // no nesting detected, no further walk required
2249 use self::Nesting::{LookFurther, RuledOut, Unknown};
2251 struct LoopNestVisitor {
2257 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2258 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2259 if stmt.hir_id == self.hir_id {
2260 self.nesting = LookFurther;
2261 } else if self.nesting == Unknown {
2262 walk_stmt(self, stmt);
2266 fn visit_expr(&mut self, expr: &'tcx Expr) {
2267 if self.nesting != Unknown {
2270 if expr.hir_id == self.hir_id {
2271 self.nesting = LookFurther;
2275 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2276 if match_var(path, self.iterator) {
2277 self.nesting = RuledOut;
2280 _ => walk_expr(self, expr),
2284 fn visit_pat(&mut self, pat: &'tcx Pat) {
2285 if self.nesting != Unknown {
2288 if let PatKind::Binding(.., span_name, _) = pat.node {
2289 if self.iterator == span_name.name {
2290 self.nesting = RuledOut;
2297 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2298 NestedVisitorMap::None
2302 fn path_name(e: &Expr) -> Option<Name> {
2303 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2304 let segments = &path.segments;
2305 if segments.len() == 1 {
2306 return Some(segments[0].ident.name);
2312 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2313 if constant(cx, cx.tables, cond).is_some() {
2314 // A pure constant condition (e.g., `while false`) is not linted.
2318 let mut var_visitor = VarCollectorVisitor {
2320 ids: FxHashSet::default(),
2321 def_ids: FxHashMap::default(),
2324 var_visitor.visit_expr(cond);
2325 if var_visitor.skip {
2328 let used_in_condition = &var_visitor.ids;
2329 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2330 used_in_condition.is_disjoint(&used_mutably)
2334 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2335 if no_cond_variable_mutated && !mutable_static_in_cond {
2338 WHILE_IMMUTABLE_CONDITION,
2340 "Variable in the condition are not mutated in the loop body. \
2341 This either leads to an infinite or to a never running loop.",
2346 /// Collects the set of variables in an expression
2347 /// Stops analysis if a function call is found
2348 /// Note: In some cases such as `self`, there are no mutable annotation,
2349 /// All variables definition IDs are collected
2350 struct VarCollectorVisitor<'a, 'tcx> {
2351 cx: &'a LateContext<'a, 'tcx>,
2352 ids: FxHashSet<HirId>,
2353 def_ids: FxHashMap<def_id::DefId, bool>,
2357 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2358 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2360 if let ExprKind::Path(ref qpath) = ex.node;
2361 if let QPath::Resolved(None, _) = *qpath;
2362 let res = self.cx.tables.qpath_res(qpath, ex.hir_id);
2365 Res::Local(node_id) => {
2366 self.ids.insert(node_id);
2368 Res::Def(DefKind::Static, def_id) => {
2369 let mutable = self.cx.tcx.is_mutable_static(def_id);
2370 self.def_ids.insert(def_id, mutable);
2379 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2380 fn visit_expr(&mut self, ex: &'tcx Expr) {
2382 ExprKind::Path(_) => self.insert_def_id(ex),
2383 // If there is any function/method call… we just stop analysis
2384 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2386 _ => walk_expr(self, ex),
2390 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2391 NestedVisitorMap::None
2395 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2397 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2399 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2400 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2401 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2402 if let Some(ref generic_args) = chain_method.args;
2403 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2405 let ty = cx.tables.node_type(ty.hir_id);
2406 if match_type(cx, ty, &paths::VEC) ||
2407 match_type(cx, ty, &paths::VEC_DEQUE) ||
2408 match_type(cx, ty, &paths::BTREEMAP) ||
2409 match_type(cx, ty, &paths::HASHMAP) {
2410 if method.ident.name == sym!(len) {
2411 let span = shorten_needless_collect_span(expr);
2412 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2416 ".count()".to_string(),
2417 Applicability::MachineApplicable,
2421 if method.ident.name == sym!(is_empty) {
2422 let span = shorten_needless_collect_span(expr);
2423 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2427 ".next().is_none()".to_string(),
2428 Applicability::MachineApplicable,
2432 if method.ident.name == sym!(contains) {
2433 let contains_arg = snippet(cx, args[1].span, "??");
2434 let span = shorten_needless_collect_span(expr);
2435 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2440 ".any(|&x| x == {})",
2441 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2443 Applicability::MachineApplicable,
2452 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2454 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2455 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2457 return expr.span.with_lo(span.lo() - BytePos(1));