1 use crate::reexport::*;
2 use if_chain::if_chain;
3 use itertools::Itertools;
4 use rustc::hir::def::Def;
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_tool_lint, lint_array};
11 // use rustc::middle::region::CodeExtent;
12 use crate::consts::{constant, Constant};
13 use crate::utils::usage::mutated_variables;
14 use crate::utils::{in_macro, 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 /// for i in 0..src.len() {
46 /// dst[i + 64] = src[i];
51 "manually copying items between slices"
54 declare_clippy_lint! {
55 /// **What it does:** Checks for looping over the range of `0..len` of some
56 /// collection just to get the values by index.
58 /// **Why is this bad?** Just iterating the collection itself makes the intent
59 /// more clear and is probably faster.
61 /// **Known problems:** None.
65 /// for i in 0..vec.len() {
66 /// println!("{}", vec[i]);
69 pub NEEDLESS_RANGE_LOOP,
71 "for-looping over a range of indices where an iterator over items would do"
74 declare_clippy_lint! {
75 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
76 /// suggests the latter.
78 /// **Why is this bad?** Readability.
80 /// **Known problems:** False negatives. We currently only warn on some known
85 /// // with `y` a `Vec` or slice:
86 /// for x in y.iter() {
90 /// can be rewritten to
96 pub EXPLICIT_ITER_LOOP,
98 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
101 declare_clippy_lint! {
102 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
103 /// suggests the latter.
105 /// **Why is this bad?** Readability.
107 /// **Known problems:** None
111 /// // with `y` a `Vec` or slice:
112 /// for x in y.into_iter() {
116 /// can be rewritten to
122 pub EXPLICIT_INTO_ITER_LOOP,
124 "for-looping over `_.into_iter()` when `_` would do"
127 declare_clippy_lint! {
128 /// **What it does:** Checks for loops on `x.next()`.
130 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
131 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
132 /// implements `IntoIterator`, so that possibly one value will be iterated,
133 /// leading to some hard to find bugs. No one will want to write such code
134 /// [except to win an Underhanded Rust
135 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
137 /// **Known problems:** None.
141 /// for x in y.next() {
147 "for-looping over `_.next()` which is probably not intended"
150 declare_clippy_lint! {
151 /// **What it does:** Checks for `for` loops over `Option` values.
153 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
156 /// **Known problems:** None.
160 /// for x in option {
167 /// if let Some(x) = option {
171 pub FOR_LOOP_OVER_OPTION,
173 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
176 declare_clippy_lint! {
177 /// **What it does:** Checks for `for` loops over `Result` values.
179 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
182 /// **Known problems:** None.
186 /// for x in result {
193 /// if let Ok(x) = result {
197 pub FOR_LOOP_OVER_RESULT,
199 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
202 declare_clippy_lint! {
203 /// **What it does:** Detects `loop + match` combinations that are easier
204 /// written as a `while let` loop.
206 /// **Why is this bad?** The `while let` loop is usually shorter and more
209 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
214 /// let x = match y {
218 /// // .. do something with x
220 /// // is easier written as
221 /// while let Some(x) = y {
222 /// // .. do something with x
227 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
230 declare_clippy_lint! {
231 /// **What it does:** Checks for using `collect()` on an iterator without using
234 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
235 /// iterator instead.
237 /// **Known problems:** None.
241 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
245 "`collect()`ing an iterator without using the result; this is usually better written as a for loop"
248 declare_clippy_lint! {
249 /// **What it does:** Checks for functions collecting an iterator when collect
252 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
253 /// when this allocation may not be needed.
255 /// **Known problems:**
260 /// let len = iterator.collect::<Vec<_>>().len();
262 /// let len = iterator.count();
264 pub NEEDLESS_COLLECT,
266 "collecting an iterator when collect is not needed"
269 declare_clippy_lint! {
270 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
271 /// are constant and `x` is greater or equal to `y`, unless the range is
272 /// reversed or has a negative `.step_by(_)`.
274 /// **Why is it bad?** Such loops will either be skipped or loop until
275 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
278 /// **Known problems:** The lint cannot catch loops over dynamically defined
279 /// ranges. Doing this would require simulating all possible inputs and code
280 /// paths through the program, which would be complex and error-prone.
284 /// for x in 5..10 - 5 {
286 /// } // oops, stray `-`
288 pub REVERSE_RANGE_LOOP,
290 "iteration over an empty range, such as `10..0` or `5..5`"
293 declare_clippy_lint! {
294 /// **What it does:** Checks `for` loops over slices with an explicit counter
295 /// and suggests the use of `.enumerate()`.
297 /// **Why is it bad?** Not only is the version using `.enumerate()` more
298 /// readable, the compiler is able to remove bounds checks which can lead to
299 /// faster code in some instances.
301 /// **Known problems:** None.
305 /// for i in 0..v.len() { foo(v[i]);
306 /// for i in 0..v.len() { bar(i, v[i]); }
308 pub EXPLICIT_COUNTER_LOOP,
310 "for-looping with an explicit counter when `_.enumerate()` would do"
313 declare_clippy_lint! {
314 /// **What it does:** Checks for empty `loop` expressions.
316 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
317 /// anything. Think of the environment and either block on something or at least
318 /// make the thread sleep for some microseconds.
320 /// **Known problems:** None.
328 "empty `loop {}`, which should block or sleep"
331 declare_clippy_lint! {
332 /// **What it does:** Checks for `while let` expressions on iterators.
334 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
335 /// the intent better.
337 /// **Known problems:** None.
341 /// while let Some(val) = iter() {
345 pub WHILE_LET_ON_ITERATOR,
347 "using a while-let loop instead of a for loop on an iterator"
350 declare_clippy_lint! {
351 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
352 /// ignoring either the keys or values.
354 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
355 /// can be used to express that don't need the values or keys.
357 /// **Known problems:** None.
361 /// for (k, _) in &map {
366 /// could be replaced by
369 /// for k in map.keys() {
375 "looping on a map using `iter` when `keys` or `values` would do"
378 declare_clippy_lint! {
379 /// **What it does:** Checks for loops that will always `break`, `return` or
380 /// `continue` an outer loop.
382 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
385 /// **Known problems:** None
396 "any loop that will always `break` or `return`"
399 declare_clippy_lint! {
400 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
402 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
404 /// **Known problems:** None
408 /// let mut foo = 42;
409 /// for i in 0..foo {
411 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
416 "for loop over a range where one of the bounds is a mutable variable"
419 declare_clippy_lint! {
420 /// **What it does:** Checks whether variables used within while loop condition
421 /// can be (and are) mutated in the body.
423 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
424 /// will lead to an infinite loop.
426 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
427 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
428 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
434 /// println!("let me loop forever!");
437 pub WHILE_IMMUTABLE_CONDITION,
439 "variables used within while expression are not mutated in the body"
442 #[derive(Copy, Clone)]
445 impl LintPass for Pass {
446 fn get_lints(&self) -> LintArray {
451 EXPLICIT_INTO_ITER_LOOP,
453 FOR_LOOP_OVER_RESULT,
454 FOR_LOOP_OVER_OPTION,
459 EXPLICIT_COUNTER_LOOP,
461 WHILE_LET_ON_ITERATOR,
465 WHILE_IMMUTABLE_CONDITION,
469 fn name(&self) -> &'static str {
474 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
475 #[allow(clippy::too_many_lines)]
476 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
477 // we don't want to check expanded macros
478 if in_macro(expr.span) {
482 if let Some((pat, arg, body)) = higher::for_loop(expr) {
483 check_for_loop(cx, pat, arg, body, expr);
486 // check for never_loop
488 ExprKind::While(_, ref block, _) | ExprKind::Loop(ref block, _, _) => {
489 match never_loop_block(block, expr.hir_id) {
490 NeverLoopResult::AlwaysBreak => {
491 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops")
493 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
499 // check for `loop { if let {} else break }` that could be `while let`
500 // (also matches an explicit "match" instead of "if let")
501 // (even if the "match" or "if let" is used for declaration)
502 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
503 // also check for empty `loop {}` statements
504 if block.stmts.is_empty() && block.expr.is_none() {
509 "empty `loop {}` detected. You may want to either use `panic!()` or add \
510 `std::thread::sleep(..);` to the loop body.",
514 // extract the expression from the first statement (if any) in a block
515 let inner_stmt_expr = extract_expr_from_first_stmt(block);
516 // or extract the first expression (if any) from the block
517 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
518 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
519 // ensure "if let" compatible match structure
521 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
523 && arms[0].pats.len() == 1
524 && arms[0].guard.is_none()
525 && arms[1].pats.len() == 1
526 && arms[1].guard.is_none()
527 && is_simple_break_expr(&arms[1].body)
529 if in_external_macro(cx.sess(), expr.span) {
533 // NOTE: we used to make build a body here instead of using
534 // ellipsis, this was removed because:
535 // 1) it was ugly with big bodies;
536 // 2) it was not indented properly;
537 // 3) it wasn’t very smart (see #675).
538 let mut applicability = Applicability::MachineApplicable;
543 "this loop could be written as a `while let` loop",
546 "while let {} = {} {{ .. }}",
547 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
548 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
559 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
560 let pat = &arms[0].pats[0].node;
562 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
563 &ExprKind::MethodCall(ref method_path, _, ref method_args),
564 ) = (pat, &match_expr.node)
566 let iter_expr = &method_args[0];
567 let lhs_constructor = last_path_segment(qpath);
568 if method_path.ident.name == "next"
569 && match_trait_method(cx, match_expr, &paths::ITERATOR)
570 && lhs_constructor.ident.name == "Some"
571 && (pat_args.is_empty()
572 || !is_refutable(cx, &pat_args[0])
573 && !is_used_inside(cx, iter_expr, &arms[0].body)
574 && !is_iterator_used_after_while_let(cx, iter_expr)
575 && !is_nested(cx, expr, &method_args[0]))
577 let iterator = snippet(cx, method_args[0].span, "_");
578 let loop_var = if pat_args.is_empty() {
581 snippet(cx, pat_args[0].span, "_").into_owned()
585 WHILE_LET_ON_ITERATOR,
587 "this loop could be written as a `for` loop",
589 format!("for {} in {} {{ .. }}", loop_var, iterator),
590 Applicability::HasPlaceholders,
596 // check for while loops which conditions never change
597 if let ExprKind::While(ref cond, _, _) = expr.node {
598 check_infinite_loop(cx, cond, expr);
601 check_needless_collect(expr, cx);
604 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
605 if let StmtKind::Semi(ref expr) = stmt.node {
606 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
607 if args.len() == 1 && method.ident.name == "collect" && match_trait_method(cx, expr, &paths::ITERATOR) {
612 "you are collect()ing an iterator and throwing away the result. \
613 Consider using an explicit for loop to exhaust the iterator",
621 enum NeverLoopResult {
622 // A break/return always get triggered but not necessarily for the main loop.
624 // A continue may occur for the main loop.
629 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
631 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
632 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
636 // Combine two results for parts that are called in order.
637 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
639 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
640 NeverLoopResult::Otherwise => second,
644 // Combine two results where both parts are called but not necessarily in order.
645 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
646 match (left, right) {
647 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
648 NeverLoopResult::MayContinueMainLoop
650 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
651 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
655 // Combine two results where only one of the part may have been executed.
656 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
658 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
659 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
660 NeverLoopResult::MayContinueMainLoop
662 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
666 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
667 let stmts = block.stmts.iter().map(stmt_to_expr);
668 let expr = once(block.expr.as_ref().map(|p| &**p));
669 let mut iter = stmts.chain(expr).filter_map(|e| e);
670 never_loop_expr_seq(&mut iter, main_loop_id)
673 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
675 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
676 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
681 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
684 | ExprKind::Unary(_, ref e)
685 | ExprKind::Cast(ref e, _)
686 | ExprKind::Type(ref e, _)
687 | ExprKind::Field(ref e, _)
688 | ExprKind::AddrOf(_, ref e)
689 | ExprKind::Struct(_, _, Some(ref e))
690 | ExprKind::Repeat(ref e, _) => never_loop_expr(e, main_loop_id),
691 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
692 never_loop_expr_all(&mut es.iter(), main_loop_id)
694 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
695 ExprKind::Binary(_, ref e1, ref e2)
696 | ExprKind::Assign(ref e1, ref e2)
697 | ExprKind::AssignOp(_, ref e1, ref e2)
698 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
699 ExprKind::If(ref e, ref e2, ref e3) => {
700 let e1 = never_loop_expr(e, main_loop_id);
701 let e2 = never_loop_expr(e2, main_loop_id);
704 .map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
705 combine_seq(e1, combine_branches(e2, e3))
707 ExprKind::Loop(ref b, _, _) => {
708 // Break can come from the inner loop so remove them.
709 absorb_break(&never_loop_block(b, main_loop_id))
711 ExprKind::While(ref e, ref b, _) => {
712 let e = never_loop_expr(e, main_loop_id);
713 let result = never_loop_block(b, main_loop_id);
714 // Break can come from the inner loop so remove them.
715 combine_seq(e, absorb_break(&result))
717 ExprKind::Match(ref e, ref arms, _) => {
718 let e = never_loop_expr(e, main_loop_id);
722 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
726 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
727 ExprKind::Continue(d) => {
730 .expect("target ID can only be missing in the presence of compilation errors");
731 if id == main_loop_id {
732 NeverLoopResult::MayContinueMainLoop
734 NeverLoopResult::AlwaysBreak
737 ExprKind::Break(_, _) => NeverLoopResult::AlwaysBreak,
738 ExprKind::Ret(ref e) => {
739 if let Some(ref e) = *e {
740 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
742 NeverLoopResult::AlwaysBreak
745 ExprKind::Struct(_, _, None)
747 | ExprKind::Closure(_, _, _, _, _)
748 | ExprKind::InlineAsm(_, _, _)
751 | ExprKind::Err => NeverLoopResult::Otherwise,
755 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
756 es.map(|e| never_loop_expr(e, main_loop_id))
757 .fold(NeverLoopResult::Otherwise, combine_seq)
760 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
761 es.map(|e| never_loop_expr(e, main_loop_id))
762 .fold(NeverLoopResult::Otherwise, combine_both)
765 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
766 e.map(|e| never_loop_expr(e, main_loop_id))
767 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
770 fn check_for_loop<'a, 'tcx>(
771 cx: &LateContext<'a, 'tcx>,
777 check_for_loop_range(cx, pat, arg, body, expr);
778 check_for_loop_reverse_range(cx, arg, expr);
779 check_for_loop_arg(cx, pat, arg, expr);
780 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
781 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
782 check_for_mut_range_bound(cx, arg, body);
783 detect_manual_memcpy(cx, pat, arg, body, expr);
786 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
788 if let ExprKind::Path(ref qpath) = expr.node;
789 if let QPath::Resolved(None, ref path) = *qpath;
790 if path.segments.len() == 1;
791 if let Def::Local(local_id) = cx.tables.qpath_def(qpath, expr.hir_id);
793 if cx.tcx.hir().node_to_hir_id(local_id) == var;
808 fn negative(s: String) -> Self {
809 Self { value: s, negate: true }
812 fn positive(s: String) -> Self {
820 struct FixedOffsetVar {
825 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
826 let is_slice = match ty.sty {
827 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
828 ty::Slice(..) | ty::Array(..) => true,
832 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
835 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
836 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
838 ExprKind::Lit(ref l) => match l.node {
839 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
842 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
847 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
848 let ty = cx.tables.expr_ty(seqexpr);
849 if !is_slice_like(cx, ty) {
853 let offset = match idx.node {
854 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
856 let offset_opt = if same_var(cx, lhs, var) {
857 extract_offset(cx, rhs, var)
858 } else if same_var(cx, rhs, var) {
859 extract_offset(cx, lhs, var)
864 offset_opt.map(Offset::positive)
866 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
869 ExprKind::Path(..) => {
870 if same_var(cx, idx, var) {
871 Some(Offset::positive("0".into()))
879 offset.map(|o| FixedOffsetVar {
880 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
888 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
889 cx: &LateContext<'a, 'tcx>,
892 ) -> Option<FixedOffsetVar> {
894 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
895 if method.ident.name == "clone";
897 if let Some(arg) = args.get(0);
899 return get_fixed_offset_var(cx, arg, var);
903 get_fixed_offset_var(cx, expr, var)
906 fn get_indexed_assignments<'a, 'tcx>(
907 cx: &LateContext<'a, 'tcx>,
910 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
911 fn get_assignment<'a, 'tcx>(
912 cx: &LateContext<'a, 'tcx>,
915 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
916 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
918 get_fixed_offset_var(cx, lhs, var),
919 fetch_cloned_fixed_offset_var(cx, rhs, var),
921 (Some(offset_left), Some(offset_right)) => {
922 // Source and destination must be different
923 if offset_left.var_name == offset_right.var_name {
926 Some((offset_left, offset_right))
936 if let ExprKind::Block(ref b, _) = body.node {
938 ref stmts, ref expr, ..
943 .map(|stmt| match stmt.node {
944 StmtKind::Local(..) | StmtKind::Item(..) => None,
945 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
947 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
949 .collect::<Option<Vec<_>>>()
950 .unwrap_or_else(|| vec![])
952 get_assignment(cx, body, var).into_iter().collect()
956 /// Checks for for loops that sequentially copy items from one slice-like
957 /// object to another.
958 fn detect_manual_memcpy<'a, 'tcx>(
959 cx: &LateContext<'a, 'tcx>,
965 if let Some(higher::Range {
969 }) = higher::range(cx, arg)
971 // the var must be a single name
972 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
973 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
974 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
975 ("0", _, "0", _) => "".into(),
976 ("0", _, x, false) | (x, false, "0", false) => x.into(),
977 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
978 (x, false, y, false) => format!("({} + {})", x, y),
979 (x, false, y, true) => {
983 format!("({} - {})", x, y)
986 (x, true, y, false) => {
990 format!("({} - {})", y, x)
993 (x, true, y, true) => format!("-({} + {})", x, y),
997 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
998 if let Some(end) = *end {
1000 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
1001 if method.ident.name == "len";
1002 if len_args.len() == 1;
1003 if let Some(arg) = len_args.get(0);
1004 if snippet(cx, arg.span, "??") == var_name;
1006 return if offset.negate {
1007 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
1014 let end_str = match limits {
1015 ast::RangeLimits::Closed => {
1016 let end = sugg::Sugg::hir(cx, end, "<count>");
1017 format!("{}", end + sugg::ONE)
1019 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1022 print_sum(&Offset::positive(end_str), &offset)
1028 // The only statements in the for loops can be indexed assignments from
1029 // indexed retrievals.
1030 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1032 let big_sugg = manual_copies
1034 .map(|(dst_var, src_var)| {
1035 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1036 let dst_offset = print_sum(&start_str, &dst_var.offset);
1037 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1038 let src_offset = print_sum(&start_str, &src_var.offset);
1039 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1040 let dst = if dst_offset == "" && dst_limit == "" {
1043 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1047 "{}.clone_from_slice(&{}[{}..{}])",
1048 dst, src_var.var_name, src_offset, src_limit
1053 if !big_sugg.is_empty() {
1058 "it looks like you're manually copying between slices",
1059 "try replacing the loop by",
1061 Applicability::Unspecified,
1068 /// Checks for looping over a range and then indexing a sequence with it.
1069 /// The iteratee must be a range literal.
1070 #[allow(clippy::too_many_lines)]
1071 fn check_for_loop_range<'a, 'tcx>(
1072 cx: &LateContext<'a, 'tcx>,
1078 if in_macro(expr.span) {
1082 if let Some(higher::Range {
1086 }) = higher::range(cx, arg)
1088 // the var must be a single name
1089 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1090 let mut visitor = VarVisitor {
1093 indexed_mut: FxHashSet::default(),
1094 indexed_indirectly: FxHashMap::default(),
1095 indexed_directly: FxHashMap::default(),
1096 referenced: FxHashSet::default(),
1098 prefer_mutable: false,
1100 walk_expr(&mut visitor, body);
1102 // linting condition: we only indexed one variable, and indexed it directly
1103 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1104 let (indexed, (indexed_extent, indexed_ty)) = visitor
1108 .expect("already checked that we have exactly 1 element");
1110 // ensure that the indexed variable was declared before the loop, see #601
1111 if let Some(indexed_extent) = indexed_extent {
1112 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1113 let parent_def_id = cx.tcx.hir().local_def_id_from_hir_id(parent_id);
1114 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1115 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1116 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1121 // don't lint if the container that is indexed does not have .iter() method
1122 let has_iter = has_iter_method(cx, indexed_ty);
1123 if has_iter.is_none() {
1127 // don't lint if the container that is indexed into is also used without
1129 if visitor.referenced.contains(&indexed) {
1133 let starts_at_zero = is_integer_literal(start, 0);
1135 let skip = if starts_at_zero {
1138 format!(".skip({})", snippet(cx, start.span, ".."))
1141 let mut end_is_start_plus_val = false;
1143 let take = if let Some(end) = *end {
1144 let mut take_expr = end;
1146 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1147 if let BinOpKind::Add = op.node {
1148 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1149 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1151 if start_equal_left {
1153 } else if start_equal_right {
1157 end_is_start_plus_val = start_equal_left | start_equal_right;
1161 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1165 ast::RangeLimits::Closed => {
1166 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1167 format!(".take({})", take_expr + sugg::ONE)
1169 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1176 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1177 ("mut ", "iter_mut")
1182 let take_is_empty = take.is_empty();
1183 let mut method_1 = take;
1184 let mut method_2 = skip;
1186 if end_is_start_plus_val {
1187 mem::swap(&mut method_1, &mut method_2);
1190 if visitor.nonindex {
1193 NEEDLESS_RANGE_LOOP,
1195 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1199 "consider using an iterator".to_string(),
1201 (pat.span, format!("({}, <item>)", ident.name)),
1204 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1211 let repl = if starts_at_zero && take_is_empty {
1212 format!("&{}{}", ref_mut, indexed)
1214 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1219 NEEDLESS_RANGE_LOOP,
1222 "the loop variable `{}` is only used to index `{}`.",
1228 "consider using an iterator".to_string(),
1229 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1239 fn is_len_call(expr: &Expr, var: Name) -> bool {
1241 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1242 if len_args.len() == 1;
1243 if method.ident.name == "len";
1244 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1245 if path.segments.len() == 1;
1246 if path.segments[0].ident.name == var;
1255 fn is_end_eq_array_len(cx: &LateContext<'_, '_>, end: &Expr, limits: ast::RangeLimits, indexed_ty: Ty<'_>) -> bool {
1257 if let ExprKind::Lit(ref lit) = end.node;
1258 if let ast::LitKind::Int(end_int, _) = lit.node;
1259 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1260 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1262 return match limits {
1263 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1264 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1272 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1273 // if this for loop is iterating over a two-sided range...
1274 if let Some(higher::Range {
1278 }) = higher::range(cx, arg)
1280 // ...and both sides are compile-time constant integers...
1281 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1282 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1283 // ...and the start index is greater than the end index,
1284 // this loop will never run. This is often confusing for developers
1285 // who think that this will iterate from the larger value to the
1287 let ty = cx.tables.expr_ty(start);
1288 let (sup, eq) = match (start_idx, end_idx) {
1289 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1291 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1292 ty::Uint(_) => start_idx > end_idx,
1295 start_idx == end_idx,
1297 _ => (false, false),
1301 let start_snippet = snippet(cx, start.span, "_");
1302 let end_snippet = snippet(cx, end.span, "_");
1303 let dots = if limits == ast::RangeLimits::Closed {
1313 "this range is empty so this for loop will never run",
1317 "consider using the following if you are attempting to iterate over this \
1320 "({end}{dots}{start}).rev()",
1323 start = start_snippet
1325 Applicability::MaybeIncorrect,
1329 } else if eq && limits != ast::RangeLimits::Closed {
1330 // if they are equal, it's also problematic - this loop
1336 "this range is empty so this for loop will never run",
1344 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1345 let mut applicability = Applicability::MachineApplicable;
1346 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1347 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1352 "it is more concise to loop over references to containers instead of using explicit \
1354 "to write this more concisely, try",
1355 format!("&{}{}", muta, object),
1360 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1361 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1362 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1363 // just the receiver, no arguments
1364 if args.len() == 1 {
1365 let method_name = &*method.ident.as_str();
1366 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1367 if method_name == "iter" || method_name == "iter_mut" {
1368 if is_ref_iterable_type(cx, &args[0]) {
1369 lint_iter_method(cx, args, arg, method_name);
1371 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1372 let def_id = cx.tables.type_dependent_defs()[arg.hir_id].def_id();
1373 let substs = cx.tables.node_substs(arg.hir_id);
1374 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1376 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1377 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1378 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1379 match cx.tables.expr_ty(&args[0]).sty {
1380 // If the length is greater than 32 no traits are implemented for array and
1381 // therefore we cannot use `&`.
1382 ty::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1383 _ => lint_iter_method(cx, args, arg, method_name),
1386 let mut applicability = Applicability::MachineApplicable;
1387 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1390 EXPLICIT_INTO_ITER_LOOP,
1392 "it is more concise to loop over containers instead of using explicit \
1393 iteration methods`",
1394 "to write this more concisely, try",
1399 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1404 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1405 probably not what you want",
1407 next_loop_linted = true;
1411 if !next_loop_linted {
1412 check_arg_type(cx, pat, arg);
1416 /// Checks for `for` loops over `Option`s and `Result`s.
1417 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1418 let ty = cx.tables.expr_ty(arg);
1419 if match_type(cx, ty, &paths::OPTION) {
1422 FOR_LOOP_OVER_OPTION,
1425 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1426 `if let` statement.",
1427 snippet(cx, arg.span, "_")
1430 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1431 snippet(cx, pat.span, "_"),
1432 snippet(cx, arg.span, "_")
1435 } else if match_type(cx, ty, &paths::RESULT) {
1438 FOR_LOOP_OVER_RESULT,
1441 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1442 `if let` statement.",
1443 snippet(cx, arg.span, "_")
1446 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1447 snippet(cx, pat.span, "_"),
1448 snippet(cx, arg.span, "_")
1454 fn check_for_loop_explicit_counter<'a, 'tcx>(
1455 cx: &LateContext<'a, 'tcx>,
1461 // Look for variables that are incremented once per loop iteration.
1462 let mut visitor = IncrementVisitor {
1464 states: FxHashMap::default(),
1468 walk_expr(&mut visitor, body);
1470 // For each candidate, check the parent block to see if
1471 // it's initialized to zero at the start of the loop.
1472 let map = &cx.tcx.hir();
1473 let expr_node_id = map.hir_to_node_id(expr.hir_id);
1474 let parent_scope = map
1475 .get_enclosing_scope(expr_node_id)
1476 .and_then(|id| map.get_enclosing_scope(id));
1477 if let Some(parent_id) = parent_scope {
1478 if let Node::Block(block) = map.get(parent_id) {
1479 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1480 let mut visitor2 = InitializeVisitor {
1484 state: VarState::IncrOnce,
1489 walk_block(&mut visitor2, block);
1491 if visitor2.state == VarState::Warn {
1492 if let Some(name) = visitor2.name {
1493 let mut applicability = Applicability::MachineApplicable;
1496 EXPLICIT_COUNTER_LOOP,
1498 &format!("the variable `{}` is used as a loop counter.", name),
1501 "for ({}, {}) in {}.enumerate()",
1503 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1504 if higher::range(cx, arg).is_some() {
1507 snippet_with_applicability(cx, arg.span, "_", &mut applicability)
1512 sugg::Sugg::hir_with_applicability(cx, arg, "_", &mut applicability)
1526 /// Checks for the `FOR_KV_MAP` lint.
1527 fn check_for_loop_over_map_kv<'a, 'tcx>(
1528 cx: &LateContext<'a, 'tcx>,
1534 let pat_span = pat.span;
1536 if let PatKind::Tuple(ref pat, _) = pat.node {
1538 let arg_span = arg.span;
1539 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1540 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1541 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1542 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1547 let mutbl = match mutbl {
1549 MutMutable => "_mut",
1551 let arg = match arg.node {
1552 ExprKind::AddrOf(_, ref expr) => &**expr,
1556 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1561 &format!("you seem to want to iterate on a map's {}s", kind),
1563 let map = sugg::Sugg::hir(cx, arg, "map");
1566 "use the corresponding method".into(),
1568 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1569 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1579 struct MutatePairDelegate {
1580 hir_id_low: Option<HirId>,
1581 hir_id_high: Option<HirId>,
1582 span_low: Option<Span>,
1583 span_high: Option<Span>,
1586 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1587 fn consume(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1589 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1591 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1593 fn borrow(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1594 if let ty::BorrowKind::MutBorrow = bk {
1595 if let Categorization::Local(id) = cmt.cat {
1596 if Some(id) == self.hir_id_low {
1597 self.span_low = Some(sp)
1599 if Some(id) == self.hir_id_high {
1600 self.span_high = Some(sp)
1606 fn mutate(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1607 if let Categorization::Local(id) = cmt.cat {
1608 if Some(id) == self.hir_id_low {
1609 self.span_low = Some(sp)
1611 if Some(id) == self.hir_id_high {
1612 self.span_high = Some(sp)
1617 fn decl_without_init(&mut self, _: HirId, _: Span) {}
1620 impl<'tcx> MutatePairDelegate {
1621 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1622 (self.span_low, self.span_high)
1626 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1627 if let Some(higher::Range {
1631 }) = higher::range(cx, arg)
1633 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1634 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1635 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1636 mut_warn_with_span(cx, span_low);
1637 mut_warn_with_span(cx, span_high);
1642 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1643 if let Some(sp) = span {
1648 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1653 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1655 if let ExprKind::Path(ref qpath) = bound.node;
1656 if let QPath::Resolved(None, _) = *qpath;
1658 let def = cx.tables.qpath_def(qpath, bound.hir_id);
1659 if let Def::Local(node_id) = def {
1660 let node_str = cx.tcx.hir().get(node_id);
1662 if let Node::Binding(pat) = node_str;
1663 if let PatKind::Binding(bind_ann, ..) = pat.node;
1664 if let BindingAnnotation::Mutable = bind_ann;
1666 return Some(cx.tcx.hir().node_to_hir_id(node_id));
1675 fn check_for_mutation(
1676 cx: &LateContext<'_, '_>,
1678 bound_ids: &[Option<HirId>],
1679 ) -> (Option<Span>, Option<Span>) {
1680 let mut delegate = MutatePairDelegate {
1681 hir_id_low: bound_ids[0],
1682 hir_id_high: bound_ids[1],
1686 let def_id = def_id::DefId::local(body.hir_id.owner);
1687 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1688 ExprUseVisitor::new(&mut delegate, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).walk_expr(body);
1689 delegate.mutation_span()
1692 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1693 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1695 PatKind::Wild => true,
1696 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1697 let mut visitor = UsedVisitor {
1701 walk_expr(&mut visitor, body);
1708 struct UsedVisitor {
1709 var: ast::Name, // var to look for
1710 used: bool, // has the var been used otherwise?
1713 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1714 fn visit_expr(&mut self, expr: &'tcx Expr) {
1715 if match_var(expr, self.var) {
1718 walk_expr(self, expr);
1722 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1723 NestedVisitorMap::None
1727 struct LocalUsedVisitor<'a, 'tcx: 'a> {
1728 cx: &'a LateContext<'a, 'tcx>,
1733 impl<'a, 'tcx: 'a> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1734 fn visit_expr(&mut self, expr: &'tcx Expr) {
1735 if same_var(self.cx, expr, self.local) {
1738 walk_expr(self, expr);
1742 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1743 NestedVisitorMap::None
1747 struct VarVisitor<'a, 'tcx: 'a> {
1748 /// context reference
1749 cx: &'a LateContext<'a, 'tcx>,
1750 /// var name to look for as index
1752 /// indexed variables that are used mutably
1753 indexed_mut: FxHashSet<Name>,
1754 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1755 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1756 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1757 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1758 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1759 /// Any names that are used outside an index operation.
1760 /// Used to detect things like `&mut vec` used together with `vec[i]`
1761 referenced: FxHashSet<Name>,
1762 /// has the loop variable been used in expressions other than the index of
1765 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1766 /// takes `&mut self`
1767 prefer_mutable: bool,
1770 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1771 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1773 // the indexed container is referenced by a name
1774 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1775 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1776 if seqvar.segments.len() == 1;
1778 let index_used_directly = same_var(self.cx, idx, self.var);
1779 let indexed_indirectly = {
1780 let mut used_visitor = LocalUsedVisitor {
1785 walk_expr(&mut used_visitor, idx);
1789 if indexed_indirectly || index_used_directly {
1790 if self.prefer_mutable {
1791 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1793 let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
1795 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
1796 let hir_id = self.cx.tcx.hir().node_to_hir_id(node_id);
1798 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1799 let parent_def_id = self.cx.tcx.hir().local_def_id_from_hir_id(parent_id);
1800 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1801 if indexed_indirectly {
1802 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1804 if index_used_directly {
1805 self.indexed_directly.insert(
1806 seqvar.segments[0].ident.name,
1807 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1810 return false; // no need to walk further *on the variable*
1812 Def::Static(..) | Def::Const(..) => {
1813 if indexed_indirectly {
1814 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1816 if index_used_directly {
1817 self.indexed_directly.insert(
1818 seqvar.segments[0].ident.name,
1819 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1822 return false; // no need to walk further *on the variable*
1833 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1834 fn visit_expr(&mut self, expr: &'tcx Expr) {
1837 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1838 if (meth.ident.name == "index" && match_trait_method(self.cx, expr, &paths::INDEX))
1839 || (meth.ident.name == "index_mut" && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1840 if !self.check(&args[1], &args[0], expr);
1846 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1847 if !self.check(idx, seqexpr, expr);
1852 // directly using a variable
1853 if let ExprKind::Path(ref qpath) = expr.node;
1854 if let QPath::Resolved(None, ref path) = *qpath;
1855 if path.segments.len() == 1;
1857 match self.cx.tables.qpath_def(qpath, expr.hir_id) {
1858 Def::Upvar(local_id, ..) => {
1859 if self.cx.tcx.hir().node_to_hir_id(local_id) == self.var {
1860 // we are not indexing anything, record that
1861 self.nonindex = true;
1864 Def::Local(local_id) =>
1867 if self.cx.tcx.hir().node_to_hir_id(local_id) == self.var {
1868 self.nonindex = true;
1870 // not the correct variable, but still a variable
1871 self.referenced.insert(path.segments[0].ident.name);
1879 let old = self.prefer_mutable;
1881 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1882 self.prefer_mutable = true;
1883 self.visit_expr(lhs);
1884 self.prefer_mutable = false;
1885 self.visit_expr(rhs);
1887 ExprKind::AddrOf(mutbl, ref expr) => {
1888 if mutbl == MutMutable {
1889 self.prefer_mutable = true;
1891 self.visit_expr(expr);
1893 ExprKind::Call(ref f, ref args) => {
1896 let ty = self.cx.tables.expr_ty_adjusted(expr);
1897 self.prefer_mutable = false;
1898 if let ty::Ref(_, _, mutbl) = ty.sty {
1899 if mutbl == MutMutable {
1900 self.prefer_mutable = true;
1903 self.visit_expr(expr);
1906 ExprKind::MethodCall(_, _, ref args) => {
1907 let def_id = self.cx.tables.type_dependent_defs()[expr.hir_id].def_id();
1908 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1909 self.prefer_mutable = false;
1910 if let ty::Ref(_, _, mutbl) = ty.sty {
1911 if mutbl == MutMutable {
1912 self.prefer_mutable = true;
1915 self.visit_expr(expr);
1918 ExprKind::Closure(_, _, body_id, ..) => {
1919 let body = self.cx.tcx.hir().body(body_id);
1920 self.visit_expr(&body.value);
1922 _ => walk_expr(self, expr),
1924 self.prefer_mutable = old;
1926 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1927 NestedVisitorMap::None
1931 fn is_used_inside<'a, 'tcx: 'a>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1932 let def_id = match var_def_id(cx, expr) {
1934 None => return false,
1936 if let Some(used_mutably) = mutated_variables(container, cx) {
1937 if used_mutably.contains(&def_id) {
1944 fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1945 let def_id = match var_def_id(cx, iter_expr) {
1947 None => return false,
1949 let mut visitor = VarUsedAfterLoopVisitor {
1952 iter_expr_id: iter_expr.hir_id,
1953 past_while_let: false,
1954 var_used_after_while_let: false,
1956 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1957 walk_block(&mut visitor, enclosing_block);
1959 visitor.var_used_after_while_let
1962 struct VarUsedAfterLoopVisitor<'a, 'tcx: 'a> {
1963 cx: &'a LateContext<'a, 'tcx>,
1965 iter_expr_id: HirId,
1966 past_while_let: bool,
1967 var_used_after_while_let: bool,
1970 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1971 fn visit_expr(&mut self, expr: &'tcx Expr) {
1972 if self.past_while_let {
1973 if Some(self.def_id) == var_def_id(self.cx, expr) {
1974 self.var_used_after_while_let = true;
1976 } else if self.iter_expr_id == expr.hir_id {
1977 self.past_while_let = true;
1979 walk_expr(self, expr);
1981 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1982 NestedVisitorMap::None
1986 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1987 /// for `&T` and `&mut T`, such as `Vec`.
1989 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1990 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1991 // will allow further borrows afterwards
1992 let ty = cx.tables.expr_ty(e);
1993 is_iterable_array(ty, cx) ||
1994 match_type(cx, ty, &paths::VEC) ||
1995 match_type(cx, ty, &paths::LINKED_LIST) ||
1996 match_type(cx, ty, &paths::HASHMAP) ||
1997 match_type(cx, ty, &paths::HASHSET) ||
1998 match_type(cx, ty, &paths::VEC_DEQUE) ||
1999 match_type(cx, ty, &paths::BINARY_HEAP) ||
2000 match_type(cx, ty, &paths::BTREEMAP) ||
2001 match_type(cx, ty, &paths::BTREESET)
2004 fn is_iterable_array(ty: Ty<'_>, cx: &LateContext<'_, '_>) -> bool {
2005 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
2007 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
2012 /// If a block begins with a statement (possibly a `let` binding) and has an
2013 /// expression, return it.
2014 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
2015 if block.stmts.is_empty() {
2018 if let StmtKind::Local(ref local) = block.stmts[0].node {
2019 if let Some(ref expr) = local.init {
2029 /// If a block begins with an expression (with or without semicolon), return it.
2030 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2032 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2033 None if !block.stmts.is_empty() => match block.stmts[0].node {
2034 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2035 StmtKind::Local(..) | StmtKind::Item(..) => None,
2041 /// Returns `true` if expr contains a single break expr without destination label
2043 /// passed expression. The expression may be within a block.
2044 fn is_simple_break_expr(expr: &Expr) -> bool {
2046 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2047 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2048 Some(subexpr) => is_simple_break_expr(subexpr),
2055 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2056 // incremented exactly once in the loop body, and initialized to zero
2057 // at the start of the loop.
2058 #[derive(PartialEq)]
2060 Initial, // Not examined yet
2061 IncrOnce, // Incremented exactly once, may be a loop counter
2062 Declared, // Declared but not (yet) initialized to zero
2067 /// Scan a for loop for variables that are incremented exactly once.
2068 struct IncrementVisitor<'a, 'tcx: 'a> {
2069 cx: &'a LateContext<'a, 'tcx>, // context reference
2070 states: FxHashMap<HirId, VarState>, // incremented variables
2071 depth: u32, // depth of conditional expressions
2075 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2076 fn visit_expr(&mut self, expr: &'tcx Expr) {
2081 // If node is a variable
2082 if let Some(def_id) = var_def_id(self.cx, expr) {
2083 if let Some(parent) = get_parent_expr(self.cx, expr) {
2084 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2087 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2088 if lhs.hir_id == expr.hir_id {
2089 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2090 *state = match *state {
2091 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2092 _ => VarState::DontWarn,
2095 // Assigned some other value
2096 *state = VarState::DontWarn;
2100 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2101 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2105 } else if is_loop(expr) || is_conditional(expr) {
2107 walk_expr(self, expr);
2110 } else if let ExprKind::Continue(_) = expr.node {
2114 walk_expr(self, expr);
2116 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2117 NestedVisitorMap::None
2121 /// Checks whether a variable is initialized to zero at the start of a loop.
2122 struct InitializeVisitor<'a, 'tcx: 'a> {
2123 cx: &'a LateContext<'a, 'tcx>, // context reference
2124 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2128 depth: u32, // depth of conditional expressions
2132 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2133 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2134 // Look for declarations of the variable
2135 if let StmtKind::Local(ref local) = stmt.node {
2136 if local.pat.hir_id == self.var_id {
2137 if let PatKind::Binding(.., ident, _) = local.pat.node {
2138 self.name = Some(ident.name);
2140 self.state = if let Some(ref init) = local.init {
2141 if is_integer_literal(init, 0) {
2152 walk_stmt(self, stmt);
2155 fn visit_expr(&mut self, expr: &'tcx Expr) {
2156 if self.state == VarState::DontWarn {
2159 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2160 self.past_loop = true;
2163 // No need to visit expressions before the variable is
2165 if self.state == VarState::IncrOnce {
2169 // If node is the desired variable, see how it's used
2170 if var_def_id(self.cx, expr) == Some(self.var_id) {
2171 if let Some(parent) = get_parent_expr(self.cx, expr) {
2173 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2174 self.state = VarState::DontWarn;
2176 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2177 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2183 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2189 self.state = VarState::DontWarn;
2192 } else if !self.past_loop && is_loop(expr) {
2193 self.state = VarState::DontWarn;
2195 } else if is_conditional(expr) {
2197 walk_expr(self, expr);
2201 walk_expr(self, expr);
2203 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2204 NestedVisitorMap::None
2208 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2209 if let ExprKind::Path(ref qpath) = expr.node {
2210 let path_res = cx.tables.qpath_def(qpath, expr.hir_id);
2211 if let Def::Local(node_id) = path_res {
2212 return Some(cx.tcx.hir().node_to_hir_id(node_id));
2218 fn is_loop(expr: &Expr) -> bool {
2220 ExprKind::Loop(..) | ExprKind::While(..) => true,
2225 fn is_conditional(expr: &Expr) -> bool {
2227 ExprKind::If(..) | ExprKind::Match(..) => true,
2232 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2234 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2235 let parent_node = cx.tcx.hir().get_parent_node_by_hir_id(loop_block.hir_id);
2236 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find_by_hir_id(parent_node);
2238 return is_loop_nested(cx, loop_expr, iter_expr)
2244 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2245 let mut id = loop_expr.hir_id;
2246 let iter_name = if let Some(name) = path_name(iter_expr) {
2252 let parent = cx.tcx.hir().get_parent_node_by_hir_id(id);
2256 match cx.tcx.hir().find_by_hir_id(parent) {
2257 Some(Node::Expr(expr)) => match expr.node {
2258 ExprKind::Loop(..) | ExprKind::While(..) => {
2263 Some(Node::Block(block)) => {
2264 let mut block_visitor = LoopNestVisitor {
2266 iterator: iter_name,
2269 walk_block(&mut block_visitor, block);
2270 if block_visitor.nesting == RuledOut {
2274 Some(Node::Stmt(_)) => (),
2283 #[derive(PartialEq, Eq)]
2285 Unknown, // no nesting detected yet
2286 RuledOut, // the iterator is initialized or assigned within scope
2287 LookFurther, // no nesting detected, no further walk required
2290 use self::Nesting::{LookFurther, RuledOut, Unknown};
2292 struct LoopNestVisitor {
2298 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2299 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2300 if stmt.hir_id == self.hir_id {
2301 self.nesting = LookFurther;
2302 } else if self.nesting == Unknown {
2303 walk_stmt(self, stmt);
2307 fn visit_expr(&mut self, expr: &'tcx Expr) {
2308 if self.nesting != Unknown {
2311 if expr.hir_id == self.hir_id {
2312 self.nesting = LookFurther;
2316 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2317 if match_var(path, self.iterator) {
2318 self.nesting = RuledOut;
2321 _ => walk_expr(self, expr),
2325 fn visit_pat(&mut self, pat: &'tcx Pat) {
2326 if self.nesting != Unknown {
2329 if let PatKind::Binding(.., span_name, _) = pat.node {
2330 if self.iterator == span_name.name {
2331 self.nesting = RuledOut;
2338 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2339 NestedVisitorMap::None
2343 fn path_name(e: &Expr) -> Option<Name> {
2344 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2345 let segments = &path.segments;
2346 if segments.len() == 1 {
2347 return Some(segments[0].ident.name);
2353 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2354 if constant(cx, cx.tables, cond).is_some() {
2355 // A pure constant condition (e.g., `while false`) is not linted.
2359 let mut var_visitor = VarCollectorVisitor {
2361 ids: FxHashSet::default(),
2362 def_ids: FxHashMap::default(),
2365 var_visitor.visit_expr(cond);
2366 if var_visitor.skip {
2369 let used_in_condition = &var_visitor.ids;
2370 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2371 used_in_condition.is_disjoint(&used_mutably)
2375 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2376 if no_cond_variable_mutated && !mutable_static_in_cond {
2379 WHILE_IMMUTABLE_CONDITION,
2381 "Variable in the condition are not mutated in the loop body. \
2382 This either leads to an infinite or to a never running loop.",
2387 /// Collects the set of variables in an expression
2388 /// Stops analysis if a function call is found
2389 /// Note: In some cases such as `self`, there are no mutable annotation,
2390 /// All variables definition IDs are collected
2391 struct VarCollectorVisitor<'a, 'tcx: 'a> {
2392 cx: &'a LateContext<'a, 'tcx>,
2393 ids: FxHashSet<HirId>,
2394 def_ids: FxHashMap<def_id::DefId, bool>,
2398 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2399 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2401 if let ExprKind::Path(ref qpath) = ex.node;
2402 if let QPath::Resolved(None, _) = *qpath;
2403 let def = self.cx.tables.qpath_def(qpath, ex.hir_id);
2406 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
2407 self.ids.insert(self.cx.tcx.hir().node_to_hir_id(node_id));
2409 Def::Static(def_id, mutable) => {
2410 self.def_ids.insert(def_id, mutable);
2419 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2420 fn visit_expr(&mut self, ex: &'tcx Expr) {
2422 ExprKind::Path(_) => self.insert_def_id(ex),
2423 // If there is any function/method call… we just stop analysis
2424 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2426 _ => walk_expr(self, ex),
2430 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2431 NestedVisitorMap::None
2435 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2437 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2439 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2440 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2441 if chain_method.ident.name == "collect" && match_trait_method(cx, &args[0], &paths::ITERATOR);
2442 if let Some(ref generic_args) = chain_method.args;
2443 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2445 let ty = cx.tables.node_type(ty.hir_id);
2446 if match_type(cx, ty, &paths::VEC) ||
2447 match_type(cx, ty, &paths::VEC_DEQUE) ||
2448 match_type(cx, ty, &paths::BTREEMAP) ||
2449 match_type(cx, ty, &paths::HASHMAP) {
2450 if method.ident.name == "len" {
2451 let span = shorten_needless_collect_span(expr);
2452 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2456 ".count()".to_string(),
2457 Applicability::MachineApplicable,
2461 if method.ident.name == "is_empty" {
2462 let span = shorten_needless_collect_span(expr);
2463 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2467 ".next().is_none()".to_string(),
2468 Applicability::MachineApplicable,
2472 if method.ident.name == "contains" {
2473 let contains_arg = snippet(cx, args[1].span, "??");
2474 let span = shorten_needless_collect_span(expr);
2475 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2480 ".any(|&x| x == {})",
2481 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2483 Applicability::MachineApplicable,
2492 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2494 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2495 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2497 return expr.span.with_lo(span.lo() - BytePos(1));