1 use crate::reexport::*;
2 use if_chain::if_chain;
3 use itertools::Itertools;
4 use rustc::hir::def::{DefKind, Res};
5 use rustc::hir::def_id;
6 use rustc::hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
8 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
9 use rustc::middle::region;
10 use rustc::{declare_lint_pass, declare_tool_lint};
11 // use rustc::middle::region::CodeExtent;
12 use crate::consts::{constant, Constant};
13 use crate::utils::usage::mutated_variables;
14 use crate::utils::{in_macro_or_desugar, sext, sugg};
15 use rustc::middle::expr_use_visitor::*;
16 use rustc::middle::mem_categorization::cmt_;
17 use rustc::middle::mem_categorization::Categorization;
18 use rustc::ty::subst::Subst;
19 use rustc::ty::{self, Ty};
20 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
21 use rustc_errors::Applicability;
22 use std::iter::{once, Iterator};
25 use syntax::source_map::Span;
26 use syntax_pos::BytePos;
28 use crate::utils::paths;
30 get_enclosing_block, get_parent_expr, has_iter_method, higher, is_integer_literal, is_refutable, last_path_segment,
31 match_trait_method, match_type, match_var, multispan_sugg, snippet, snippet_opt, snippet_with_applicability,
32 span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then, SpanlessEq,
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// # let src = vec![1];
46 /// # let mut dst = vec![0; 65];
47 /// for i in 0..src.len() {
48 /// dst[i + 64] = src[i];
53 "manually copying items between slices"
56 declare_clippy_lint! {
57 /// **What it does:** Checks for looping over the range of `0..len` of some
58 /// collection just to get the values by index.
60 /// **Why is this bad?** Just iterating the collection itself makes the intent
61 /// more clear and is probably faster.
63 /// **Known problems:** None.
67 /// let vec = vec!['a', 'b', 'c'];
68 /// for i in 0..vec.len() {
69 /// println!("{}", vec[i]);
72 /// Could be written as:
74 /// let vec = vec!['a', 'b', 'c'];
76 /// println!("{}", i);
79 pub NEEDLESS_RANGE_LOOP,
81 "for-looping over a range of indices where an iterator over items would do"
84 declare_clippy_lint! {
85 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
86 /// suggests the latter.
88 /// **Why is this bad?** Readability.
90 /// **Known problems:** False negatives. We currently only warn on some known
95 /// // with `y` a `Vec` or slice:
96 /// # let y = vec![1];
97 /// for x in y.iter() {
101 /// can be rewritten to
103 /// # let y = vec![1];
108 pub EXPLICIT_ITER_LOOP,
110 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
113 declare_clippy_lint! {
114 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
115 /// suggests the latter.
117 /// **Why is this bad?** Readability.
119 /// **Known problems:** None
123 /// # let y = vec![1];
124 /// // with `y` a `Vec` or slice:
125 /// for x in y.into_iter() {
129 /// can be rewritten to
131 /// # let y = vec![1];
136 pub EXPLICIT_INTO_ITER_LOOP,
138 "for-looping over `_.into_iter()` when `_` would do"
141 declare_clippy_lint! {
142 /// **What it does:** Checks for loops on `x.next()`.
144 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
145 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
146 /// implements `IntoIterator`, so that possibly one value will be iterated,
147 /// leading to some hard to find bugs. No one will want to write such code
148 /// [except to win an Underhanded Rust
149 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
151 /// **Known problems:** None.
155 /// for x in y.next() {
161 "for-looping over `_.next()` which is probably not intended"
164 declare_clippy_lint! {
165 /// **What it does:** Checks for `for` loops over `Option` values.
167 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
170 /// **Known problems:** None.
174 /// for x in option {
181 /// if let Some(x) = option {
185 pub FOR_LOOP_OVER_OPTION,
187 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
190 declare_clippy_lint! {
191 /// **What it does:** Checks for `for` loops over `Result` values.
193 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
196 /// **Known problems:** None.
200 /// for x in result {
207 /// if let Ok(x) = result {
211 pub FOR_LOOP_OVER_RESULT,
213 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
216 declare_clippy_lint! {
217 /// **What it does:** Detects `loop + match` combinations that are easier
218 /// written as a `while let` loop.
220 /// **Why is this bad?** The `while let` loop is usually shorter and more
223 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
227 /// # let y = Some(1);
229 /// let x = match y {
233 /// // .. do something with x
235 /// // is easier written as
236 /// while let Some(x) = y {
237 /// // .. do something with x
242 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
245 declare_clippy_lint! {
246 /// **What it does:** Checks for functions collecting an iterator when collect
249 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
250 /// when this allocation may not be needed.
252 /// **Known problems:**
257 /// # let iterator = vec![1].into_iter();
258 /// let len = iterator.clone().collect::<Vec<_>>().len();
260 /// let len = iterator.count();
262 pub NEEDLESS_COLLECT,
264 "collecting an iterator when collect is not needed"
267 declare_clippy_lint! {
268 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
269 /// are constant and `x` is greater or equal to `y`, unless the range is
270 /// reversed or has a negative `.step_by(_)`.
272 /// **Why is it bad?** Such loops will either be skipped or loop until
273 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
276 /// **Known problems:** The lint cannot catch loops over dynamically defined
277 /// ranges. Doing this would require simulating all possible inputs and code
278 /// paths through the program, which would be complex and error-prone.
282 /// for x in 5..10 - 5 {
284 /// } // oops, stray `-`
286 pub REVERSE_RANGE_LOOP,
288 "iteration over an empty range, such as `10..0` or `5..5`"
291 declare_clippy_lint! {
292 /// **What it does:** Checks `for` loops over slices with an explicit counter
293 /// and suggests the use of `.enumerate()`.
295 /// **Why is it bad?** Not only is the version using `.enumerate()` more
296 /// readable, the compiler is able to remove bounds checks which can lead to
297 /// faster code in some instances.
299 /// **Known problems:** None.
303 /// # let v = vec![1];
304 /// # fn foo(bar: usize) {}
305 /// # fn bar(bar: usize, baz: usize) {}
306 /// for i in 0..v.len() { foo(v[i]); }
307 /// for i in 0..v.len() { bar(i, v[i]); }
309 pub EXPLICIT_COUNTER_LOOP,
311 "for-looping with an explicit counter when `_.enumerate()` would do"
314 declare_clippy_lint! {
315 /// **What it does:** Checks for empty `loop` expressions.
317 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
318 /// anything. Think of the environment and either block on something or at least
319 /// make the thread sleep for some microseconds.
321 /// **Known problems:** None.
329 "empty `loop {}`, which should block or sleep"
332 declare_clippy_lint! {
333 /// **What it does:** Checks for `while let` expressions on iterators.
335 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
336 /// the intent better.
338 /// **Known problems:** None.
342 /// while let Some(val) = iter() {
346 pub WHILE_LET_ON_ITERATOR,
348 "using a while-let loop instead of a for loop on an iterator"
351 declare_clippy_lint! {
352 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
353 /// ignoring either the keys or values.
355 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
356 /// can be used to express that don't need the values or keys.
358 /// **Known problems:** None.
362 /// for (k, _) in &map {
367 /// could be replaced by
370 /// for k in map.keys() {
376 "looping on a map using `iter` when `keys` or `values` would do"
379 declare_clippy_lint! {
380 /// **What it does:** Checks for loops that will always `break`, `return` or
381 /// `continue` an outer loop.
383 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
386 /// **Known problems:** None
397 "any loop that will always `break` or `return`"
400 declare_clippy_lint! {
401 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
403 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
405 /// **Known problems:** None
409 /// let mut foo = 42;
410 /// for i in 0..foo {
412 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
417 "for loop over a range where one of the bounds is a mutable variable"
420 declare_clippy_lint! {
421 /// **What it does:** Checks whether variables used within while loop condition
422 /// can be (and are) mutated in the body.
424 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
425 /// will lead to an infinite loop.
427 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
428 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
429 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
435 /// println!("let me loop forever!");
438 pub WHILE_IMMUTABLE_CONDITION,
440 "variables used within while expression are not mutated in the body"
443 declare_lint_pass!(Loops => [
447 EXPLICIT_INTO_ITER_LOOP,
449 FOR_LOOP_OVER_RESULT,
450 FOR_LOOP_OVER_OPTION,
454 EXPLICIT_COUNTER_LOOP,
456 WHILE_LET_ON_ITERATOR,
460 WHILE_IMMUTABLE_CONDITION,
463 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
464 #[allow(clippy::too_many_lines)]
465 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
466 // we don't want to check expanded macros
467 if in_macro_or_desugar(expr.span) {
471 if let Some((pat, arg, body)) = higher::for_loop(expr) {
472 check_for_loop(cx, pat, arg, body, expr);
475 // check for never_loop
476 if let ExprKind::Loop(ref block, _, _) = expr.node {
477 match never_loop_block(block, expr.hir_id) {
478 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
479 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
483 // check for `loop { if let {} else break }` that could be `while let`
484 // (also matches an explicit "match" instead of "if let")
485 // (even if the "match" or "if let" is used for declaration)
486 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
487 // also check for empty `loop {}` statements
488 if block.stmts.is_empty() && block.expr.is_none() {
493 "empty `loop {}` detected. You may want to either use `panic!()` or add \
494 `std::thread::sleep(..);` to the loop body.",
498 // extract the expression from the first statement (if any) in a block
499 let inner_stmt_expr = extract_expr_from_first_stmt(block);
500 // or extract the first expression (if any) from the block
501 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
502 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
503 // ensure "if let" compatible match structure
505 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
507 && arms[0].pats.len() == 1
508 && arms[0].guard.is_none()
509 && arms[1].pats.len() == 1
510 && arms[1].guard.is_none()
511 && is_simple_break_expr(&arms[1].body)
513 if in_external_macro(cx.sess(), expr.span) {
517 // NOTE: we used to build a body here instead of using
518 // ellipsis, this was removed because:
519 // 1) it was ugly with big bodies;
520 // 2) it was not indented properly;
521 // 3) it wasn’t very smart (see #675).
522 let mut applicability = Applicability::HasPlaceholders;
527 "this loop could be written as a `while let` loop",
530 "while let {} = {} {{ .. }}",
531 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
532 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
543 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
544 let pat = &arms[0].pats[0].node;
546 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
547 &ExprKind::MethodCall(ref method_path, _, ref method_args),
548 ) = (pat, &match_expr.node)
550 let iter_expr = &method_args[0];
551 let lhs_constructor = last_path_segment(qpath);
552 if method_path.ident.name == sym!(next)
553 && match_trait_method(cx, match_expr, &paths::ITERATOR)
554 && lhs_constructor.ident.name == sym!(Some)
555 && (pat_args.is_empty()
556 || !is_refutable(cx, &pat_args[0])
557 && !is_used_inside(cx, iter_expr, &arms[0].body)
558 && !is_iterator_used_after_while_let(cx, iter_expr)
559 && !is_nested(cx, expr, &method_args[0]))
561 let iterator = snippet(cx, method_args[0].span, "_");
562 let loop_var = if pat_args.is_empty() {
565 snippet(cx, pat_args[0].span, "_").into_owned()
569 WHILE_LET_ON_ITERATOR,
571 "this loop could be written as a `for` loop",
573 format!("for {} in {} {{ .. }}", loop_var, iterator),
574 Applicability::HasPlaceholders,
580 if let Some((cond, body)) = higher::while_loop(&expr) {
581 check_infinite_loop(cx, cond, body);
584 check_needless_collect(expr, cx);
588 enum NeverLoopResult {
589 // A break/return always get triggered but not necessarily for the main loop.
591 // A continue may occur for the main loop.
596 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
598 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
599 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
603 // Combine two results for parts that are called in order.
604 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
606 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
607 NeverLoopResult::Otherwise => second,
611 // Combine two results where both parts are called but not necessarily in order.
612 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
613 match (left, right) {
614 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
615 NeverLoopResult::MayContinueMainLoop
617 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
618 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
622 // Combine two results where only one of the part may have been executed.
623 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
625 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
626 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
627 NeverLoopResult::MayContinueMainLoop
629 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
633 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
634 let stmts = block.stmts.iter().map(stmt_to_expr);
635 let expr = once(block.expr.as_ref().map(|p| &**p));
636 let mut iter = stmts.chain(expr).filter_map(|e| e);
637 never_loop_expr_seq(&mut iter, main_loop_id)
640 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
642 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
643 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
648 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
651 | ExprKind::Unary(_, ref e)
652 | ExprKind::Cast(ref e, _)
653 | ExprKind::Type(ref e, _)
654 | ExprKind::Field(ref e, _)
655 | ExprKind::AddrOf(_, ref e)
656 | ExprKind::Struct(_, _, Some(ref e))
657 | ExprKind::Repeat(ref e, _)
658 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
659 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
660 never_loop_expr_all(&mut es.iter(), main_loop_id)
662 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
663 ExprKind::Binary(_, ref e1, ref e2)
664 | ExprKind::Assign(ref e1, ref e2)
665 | ExprKind::AssignOp(_, ref e1, ref e2)
666 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
667 ExprKind::Loop(ref b, _, _) => {
668 // Break can come from the inner loop so remove them.
669 absorb_break(&never_loop_block(b, main_loop_id))
671 ExprKind::Match(ref e, ref arms, _) => {
672 let e = never_loop_expr(e, main_loop_id);
676 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
680 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
681 ExprKind::Continue(d) => {
684 .expect("target ID can only be missing in the presence of compilation errors");
685 if id == main_loop_id {
686 NeverLoopResult::MayContinueMainLoop
688 NeverLoopResult::AlwaysBreak
691 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
692 if let Some(ref e) = *e {
693 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
695 NeverLoopResult::AlwaysBreak
698 ExprKind::Struct(_, _, None)
699 | ExprKind::Yield(_, _)
700 | ExprKind::Closure(_, _, _, _, _)
701 | ExprKind::InlineAsm(_, _, _)
704 | ExprKind::Err => NeverLoopResult::Otherwise,
708 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
709 es.map(|e| never_loop_expr(e, main_loop_id))
710 .fold(NeverLoopResult::Otherwise, combine_seq)
713 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
714 es.map(|e| never_loop_expr(e, main_loop_id))
715 .fold(NeverLoopResult::Otherwise, combine_both)
718 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
719 e.map(|e| never_loop_expr(e, main_loop_id))
720 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
723 fn check_for_loop<'a, 'tcx>(
724 cx: &LateContext<'a, 'tcx>,
730 check_for_loop_range(cx, pat, arg, body, expr);
731 check_for_loop_reverse_range(cx, arg, expr);
732 check_for_loop_arg(cx, pat, arg, expr);
733 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
734 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
735 check_for_mut_range_bound(cx, arg, body);
736 detect_manual_memcpy(cx, pat, arg, body, expr);
739 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
741 if let ExprKind::Path(ref qpath) = expr.node;
742 if let QPath::Resolved(None, ref path) = *qpath;
743 if path.segments.len() == 1;
744 if let Res::Local(local_id) = cx.tables.qpath_res(qpath, expr.hir_id);
761 fn negative(s: String) -> Self {
762 Self { value: s, negate: true }
765 fn positive(s: String) -> Self {
773 struct FixedOffsetVar {
778 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
779 let is_slice = match ty.sty {
780 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
781 ty::Slice(..) | ty::Array(..) => true,
785 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
788 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
789 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
791 ExprKind::Lit(ref l) => match l.node {
792 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
795 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
800 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
801 let ty = cx.tables.expr_ty(seqexpr);
802 if !is_slice_like(cx, ty) {
806 let offset = match idx.node {
807 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
809 let offset_opt = if same_var(cx, lhs, var) {
810 extract_offset(cx, rhs, var)
811 } else if same_var(cx, rhs, var) {
812 extract_offset(cx, lhs, var)
817 offset_opt.map(Offset::positive)
819 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
822 ExprKind::Path(..) => {
823 if same_var(cx, idx, var) {
824 Some(Offset::positive("0".into()))
832 offset.map(|o| FixedOffsetVar {
833 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
841 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
842 cx: &LateContext<'a, 'tcx>,
845 ) -> Option<FixedOffsetVar> {
847 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
848 if method.ident.name == sym!(clone);
850 if let Some(arg) = args.get(0);
852 return get_fixed_offset_var(cx, arg, var);
856 get_fixed_offset_var(cx, expr, var)
859 fn get_indexed_assignments<'a, 'tcx>(
860 cx: &LateContext<'a, 'tcx>,
863 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
864 fn get_assignment<'a, 'tcx>(
865 cx: &LateContext<'a, 'tcx>,
868 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
869 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
871 get_fixed_offset_var(cx, lhs, var),
872 fetch_cloned_fixed_offset_var(cx, rhs, var),
874 (Some(offset_left), Some(offset_right)) => {
875 // Source and destination must be different
876 if offset_left.var_name == offset_right.var_name {
879 Some((offset_left, offset_right))
889 if let ExprKind::Block(ref b, _) = body.node {
891 ref stmts, ref expr, ..
896 .map(|stmt| match stmt.node {
897 StmtKind::Local(..) | StmtKind::Item(..) => None,
898 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
900 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
902 .collect::<Option<Vec<_>>>()
903 .unwrap_or_else(|| vec![])
905 get_assignment(cx, body, var).into_iter().collect()
909 /// Checks for for loops that sequentially copy items from one slice-like
910 /// object to another.
911 fn detect_manual_memcpy<'a, 'tcx>(
912 cx: &LateContext<'a, 'tcx>,
918 if let Some(higher::Range {
922 }) = higher::range(cx, arg)
924 // the var must be a single name
925 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
926 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
927 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
928 ("0", _, "0", _) => "".into(),
929 ("0", _, x, false) | (x, false, "0", false) => x.into(),
930 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
931 (x, false, y, false) => format!("({} + {})", x, y),
932 (x, false, y, true) => {
936 format!("({} - {})", x, y)
939 (x, true, y, false) => {
943 format!("({} - {})", y, x)
946 (x, true, y, true) => format!("-({} + {})", x, y),
950 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
951 if let Some(end) = *end {
953 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
954 if method.ident.name == sym!(len);
955 if len_args.len() == 1;
956 if let Some(arg) = len_args.get(0);
957 if snippet(cx, arg.span, "??") == var_name;
959 return if offset.negate {
960 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
967 let end_str = match limits {
968 ast::RangeLimits::Closed => {
969 let end = sugg::Sugg::hir(cx, end, "<count>");
970 format!("{}", end + sugg::ONE)
972 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
975 print_sum(&Offset::positive(end_str), &offset)
981 // The only statements in the for loops can be indexed assignments from
982 // indexed retrievals.
983 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
985 let big_sugg = manual_copies
987 .map(|(dst_var, src_var)| {
988 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
989 let dst_offset = print_sum(&start_str, &dst_var.offset);
990 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
991 let src_offset = print_sum(&start_str, &src_var.offset);
992 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
993 let dst = if dst_offset == "" && dst_limit == "" {
996 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1000 "{}.clone_from_slice(&{}[{}..{}])",
1001 dst, src_var.var_name, src_offset, src_limit
1006 if !big_sugg.is_empty() {
1011 "it looks like you're manually copying between slices",
1012 "try replacing the loop by",
1014 Applicability::Unspecified,
1021 /// Checks for looping over a range and then indexing a sequence with it.
1022 /// The iteratee must be a range literal.
1023 #[allow(clippy::too_many_lines)]
1024 fn check_for_loop_range<'a, 'tcx>(
1025 cx: &LateContext<'a, 'tcx>,
1031 if in_macro_or_desugar(expr.span) {
1035 if let Some(higher::Range {
1039 }) = higher::range(cx, arg)
1041 // the var must be a single name
1042 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1043 let mut visitor = VarVisitor {
1046 indexed_mut: FxHashSet::default(),
1047 indexed_indirectly: FxHashMap::default(),
1048 indexed_directly: FxHashMap::default(),
1049 referenced: FxHashSet::default(),
1051 prefer_mutable: false,
1053 walk_expr(&mut visitor, body);
1055 // linting condition: we only indexed one variable, and indexed it directly
1056 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1057 let (indexed, (indexed_extent, indexed_ty)) = visitor
1061 .expect("already checked that we have exactly 1 element");
1063 // ensure that the indexed variable was declared before the loop, see #601
1064 if let Some(indexed_extent) = indexed_extent {
1065 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1066 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1067 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1068 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1069 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1074 // don't lint if the container that is indexed does not have .iter() method
1075 let has_iter = has_iter_method(cx, indexed_ty);
1076 if has_iter.is_none() {
1080 // don't lint if the container that is indexed into is also used without
1082 if visitor.referenced.contains(&indexed) {
1086 let starts_at_zero = is_integer_literal(start, 0);
1088 let skip = if starts_at_zero {
1091 format!(".skip({})", snippet(cx, start.span, ".."))
1094 let mut end_is_start_plus_val = false;
1096 let take = if let Some(end) = *end {
1097 let mut take_expr = end;
1099 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1100 if let BinOpKind::Add = op.node {
1101 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1102 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1104 if start_equal_left {
1106 } else if start_equal_right {
1110 end_is_start_plus_val = start_equal_left | start_equal_right;
1114 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1118 ast::RangeLimits::Closed => {
1119 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1120 format!(".take({})", take_expr + sugg::ONE)
1122 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1129 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1130 ("mut ", "iter_mut")
1135 let take_is_empty = take.is_empty();
1136 let mut method_1 = take;
1137 let mut method_2 = skip;
1139 if end_is_start_plus_val {
1140 mem::swap(&mut method_1, &mut method_2);
1143 if visitor.nonindex {
1146 NEEDLESS_RANGE_LOOP,
1148 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1152 "consider using an iterator".to_string(),
1154 (pat.span, format!("({}, <item>)", ident.name)),
1157 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1164 let repl = if starts_at_zero && take_is_empty {
1165 format!("&{}{}", ref_mut, indexed)
1167 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1172 NEEDLESS_RANGE_LOOP,
1175 "the loop variable `{}` is only used to index `{}`.",
1181 "consider using an iterator".to_string(),
1182 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1192 fn is_len_call(expr: &Expr, var: Name) -> bool {
1194 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1195 if len_args.len() == 1;
1196 if method.ident.name == sym!(len);
1197 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1198 if path.segments.len() == 1;
1199 if path.segments[0].ident.name == var;
1208 fn is_end_eq_array_len<'tcx>(
1209 cx: &LateContext<'_, 'tcx>,
1211 limits: ast::RangeLimits,
1212 indexed_ty: Ty<'tcx>,
1215 if let ExprKind::Lit(ref lit) = end.node;
1216 if let ast::LitKind::Int(end_int, _) = lit.node;
1217 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1218 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1220 return match limits {
1221 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1222 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1230 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1231 // if this for loop is iterating over a two-sided range...
1232 if let Some(higher::Range {
1236 }) = higher::range(cx, arg)
1238 // ...and both sides are compile-time constant integers...
1239 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1240 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1241 // ...and the start index is greater than the end index,
1242 // this loop will never run. This is often confusing for developers
1243 // who think that this will iterate from the larger value to the
1245 let ty = cx.tables.expr_ty(start);
1246 let (sup, eq) = match (start_idx, end_idx) {
1247 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1249 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1250 ty::Uint(_) => start_idx > end_idx,
1253 start_idx == end_idx,
1255 _ => (false, false),
1259 let start_snippet = snippet(cx, start.span, "_");
1260 let end_snippet = snippet(cx, end.span, "_");
1261 let dots = if limits == ast::RangeLimits::Closed {
1271 "this range is empty so this for loop will never run",
1275 "consider using the following if you are attempting to iterate over this \
1278 "({end}{dots}{start}).rev()",
1281 start = start_snippet
1283 Applicability::MaybeIncorrect,
1287 } else if eq && limits != ast::RangeLimits::Closed {
1288 // if they are equal, it's also problematic - this loop
1294 "this range is empty so this for loop will never run",
1302 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1303 let mut applicability = Applicability::MachineApplicable;
1304 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1305 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1310 "it is more concise to loop over references to containers instead of using explicit \
1312 "to write this more concisely, try",
1313 format!("&{}{}", muta, object),
1318 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1319 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1320 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1321 // just the receiver, no arguments
1322 if args.len() == 1 {
1323 let method_name = &*method.ident.as_str();
1324 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1325 if method_name == "iter" || method_name == "iter_mut" {
1326 if is_ref_iterable_type(cx, &args[0]) {
1327 lint_iter_method(cx, args, arg, method_name);
1329 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1330 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1331 let substs = cx.tables.node_substs(arg.hir_id);
1332 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1334 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1335 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1336 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1337 match cx.tables.expr_ty(&args[0]).sty {
1338 // If the length is greater than 32 no traits are implemented for array and
1339 // therefore we cannot use `&`.
1340 ty::Array(_, size) if size.eval_usize(cx.tcx, cx.param_env) > 32 => {},
1341 _ => lint_iter_method(cx, args, arg, method_name),
1344 let mut applicability = Applicability::MachineApplicable;
1345 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1348 EXPLICIT_INTO_ITER_LOOP,
1350 "it is more concise to loop over containers instead of using explicit \
1351 iteration methods`",
1352 "to write this more concisely, try",
1357 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1362 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1363 probably not what you want",
1365 next_loop_linted = true;
1369 if !next_loop_linted {
1370 check_arg_type(cx, pat, arg);
1374 /// Checks for `for` loops over `Option`s and `Result`s.
1375 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1376 let ty = cx.tables.expr_ty(arg);
1377 if match_type(cx, ty, &paths::OPTION) {
1380 FOR_LOOP_OVER_OPTION,
1383 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1384 `if let` statement.",
1385 snippet(cx, arg.span, "_")
1388 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1389 snippet(cx, pat.span, "_"),
1390 snippet(cx, arg.span, "_")
1393 } else if match_type(cx, ty, &paths::RESULT) {
1396 FOR_LOOP_OVER_RESULT,
1399 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1400 `if let` statement.",
1401 snippet(cx, arg.span, "_")
1404 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1405 snippet(cx, pat.span, "_"),
1406 snippet(cx, arg.span, "_")
1412 fn check_for_loop_explicit_counter<'a, 'tcx>(
1413 cx: &LateContext<'a, 'tcx>,
1419 // Look for variables that are incremented once per loop iteration.
1420 let mut visitor = IncrementVisitor {
1422 states: FxHashMap::default(),
1426 walk_expr(&mut visitor, body);
1428 // For each candidate, check the parent block to see if
1429 // it's initialized to zero at the start of the loop.
1430 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1431 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1432 let mut visitor2 = InitializeVisitor {
1436 state: VarState::IncrOnce,
1441 walk_block(&mut visitor2, block);
1443 if visitor2.state == VarState::Warn {
1444 if let Some(name) = visitor2.name {
1445 let mut applicability = Applicability::MachineApplicable;
1448 EXPLICIT_COUNTER_LOOP,
1450 &format!("the variable `{}` is used as a loop counter.", name),
1453 "for ({}, {}) in {}.enumerate()",
1455 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1456 if higher::range(cx, arg).is_some() {
1459 snippet_with_applicability(cx, arg.span, "_", &mut applicability)
1464 sugg::Sugg::hir_with_applicability(cx, arg, "_", &mut applicability).maybe_par()
1476 /// Checks for the `FOR_KV_MAP` lint.
1477 fn check_for_loop_over_map_kv<'a, 'tcx>(
1478 cx: &LateContext<'a, 'tcx>,
1484 let pat_span = pat.span;
1486 if let PatKind::Tuple(ref pat, _) = pat.node {
1488 let arg_span = arg.span;
1489 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1490 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1491 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1492 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1497 let mutbl = match mutbl {
1499 MutMutable => "_mut",
1501 let arg = match arg.node {
1502 ExprKind::AddrOf(_, ref expr) => &**expr,
1506 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1511 &format!("you seem to want to iterate on a map's {}s", kind),
1513 let map = sugg::Sugg::hir(cx, arg, "map");
1516 "use the corresponding method".into(),
1518 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1519 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1529 struct MutatePairDelegate {
1530 hir_id_low: Option<HirId>,
1531 hir_id_high: Option<HirId>,
1532 span_low: Option<Span>,
1533 span_high: Option<Span>,
1536 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1537 fn consume(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1539 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1541 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1543 fn borrow(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1544 if let ty::BorrowKind::MutBorrow = bk {
1545 if let Categorization::Local(id) = cmt.cat {
1546 if Some(id) == self.hir_id_low {
1547 self.span_low = Some(sp)
1549 if Some(id) == self.hir_id_high {
1550 self.span_high = Some(sp)
1556 fn mutate(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1557 if let Categorization::Local(id) = cmt.cat {
1558 if Some(id) == self.hir_id_low {
1559 self.span_low = Some(sp)
1561 if Some(id) == self.hir_id_high {
1562 self.span_high = Some(sp)
1567 fn decl_without_init(&mut self, _: HirId, _: Span) {}
1570 impl<'tcx> MutatePairDelegate {
1571 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1572 (self.span_low, self.span_high)
1576 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1577 if let Some(higher::Range {
1581 }) = higher::range(cx, arg)
1583 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1584 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1585 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1586 mut_warn_with_span(cx, span_low);
1587 mut_warn_with_span(cx, span_high);
1592 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1593 if let Some(sp) = span {
1598 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1603 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1605 if let ExprKind::Path(ref qpath) = bound.node;
1606 if let QPath::Resolved(None, _) = *qpath;
1608 let res = cx.tables.qpath_res(qpath, bound.hir_id);
1609 if let Res::Local(node_id) = res {
1610 let node_str = cx.tcx.hir().get(node_id);
1612 if let Node::Binding(pat) = node_str;
1613 if let PatKind::Binding(bind_ann, ..) = pat.node;
1614 if let BindingAnnotation::Mutable = bind_ann;
1616 return Some(node_id);
1625 fn check_for_mutation(
1626 cx: &LateContext<'_, '_>,
1628 bound_ids: &[Option<HirId>],
1629 ) -> (Option<Span>, Option<Span>) {
1630 let mut delegate = MutatePairDelegate {
1631 hir_id_low: bound_ids[0],
1632 hir_id_high: bound_ids[1],
1636 let def_id = def_id::DefId::local(body.hir_id.owner);
1637 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1638 ExprUseVisitor::new(
1648 delegate.mutation_span()
1651 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1652 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1654 PatKind::Wild => true,
1655 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1656 let mut visitor = UsedVisitor {
1660 walk_expr(&mut visitor, body);
1667 struct UsedVisitor {
1668 var: ast::Name, // var to look for
1669 used: bool, // has the var been used otherwise?
1672 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1673 fn visit_expr(&mut self, expr: &'tcx Expr) {
1674 if match_var(expr, self.var) {
1677 walk_expr(self, expr);
1681 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1682 NestedVisitorMap::None
1686 struct LocalUsedVisitor<'a, 'tcx> {
1687 cx: &'a LateContext<'a, 'tcx>,
1692 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1693 fn visit_expr(&mut self, expr: &'tcx Expr) {
1694 if same_var(self.cx, expr, self.local) {
1697 walk_expr(self, expr);
1701 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1702 NestedVisitorMap::None
1706 struct VarVisitor<'a, 'tcx> {
1707 /// context reference
1708 cx: &'a LateContext<'a, 'tcx>,
1709 /// var name to look for as index
1711 /// indexed variables that are used mutably
1712 indexed_mut: FxHashSet<Name>,
1713 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1714 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1715 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1716 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1717 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1718 /// Any names that are used outside an index operation.
1719 /// Used to detect things like `&mut vec` used together with `vec[i]`
1720 referenced: FxHashSet<Name>,
1721 /// has the loop variable been used in expressions other than the index of
1724 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1725 /// takes `&mut self`
1726 prefer_mutable: bool,
1729 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1730 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1732 // the indexed container is referenced by a name
1733 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1734 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1735 if seqvar.segments.len() == 1;
1737 let index_used_directly = same_var(self.cx, idx, self.var);
1738 let indexed_indirectly = {
1739 let mut used_visitor = LocalUsedVisitor {
1744 walk_expr(&mut used_visitor, idx);
1748 if indexed_indirectly || index_used_directly {
1749 if self.prefer_mutable {
1750 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1752 let res = self.cx.tables.qpath_res(seqpath, seqexpr.hir_id);
1754 Res::Local(hir_id) => {
1755 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1756 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1757 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1758 if indexed_indirectly {
1759 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1761 if index_used_directly {
1762 self.indexed_directly.insert(
1763 seqvar.segments[0].ident.name,
1764 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1767 return false; // no need to walk further *on the variable*
1769 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1770 if indexed_indirectly {
1771 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1773 if index_used_directly {
1774 self.indexed_directly.insert(
1775 seqvar.segments[0].ident.name,
1776 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1779 return false; // no need to walk further *on the variable*
1790 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1791 fn visit_expr(&mut self, expr: &'tcx Expr) {
1794 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1795 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1796 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1797 if !self.check(&args[1], &args[0], expr);
1803 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1804 if !self.check(idx, seqexpr, expr);
1809 // directly using a variable
1810 if let ExprKind::Path(ref qpath) = expr.node;
1811 if let QPath::Resolved(None, ref path) = *qpath;
1812 if path.segments.len() == 1;
1814 if let Res::Local(local_id) = self.cx.tables.qpath_res(qpath, expr.hir_id) {
1815 if local_id == self.var {
1816 self.nonindex = true;
1818 // not the correct variable, but still a variable
1819 self.referenced.insert(path.segments[0].ident.name);
1825 let old = self.prefer_mutable;
1827 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1828 self.prefer_mutable = true;
1829 self.visit_expr(lhs);
1830 self.prefer_mutable = false;
1831 self.visit_expr(rhs);
1833 ExprKind::AddrOf(mutbl, ref expr) => {
1834 if mutbl == MutMutable {
1835 self.prefer_mutable = true;
1837 self.visit_expr(expr);
1839 ExprKind::Call(ref f, ref args) => {
1842 let ty = self.cx.tables.expr_ty_adjusted(expr);
1843 self.prefer_mutable = false;
1844 if let ty::Ref(_, _, mutbl) = ty.sty {
1845 if mutbl == MutMutable {
1846 self.prefer_mutable = true;
1849 self.visit_expr(expr);
1852 ExprKind::MethodCall(_, _, ref args) => {
1853 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1854 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1855 self.prefer_mutable = false;
1856 if let ty::Ref(_, _, mutbl) = ty.sty {
1857 if mutbl == MutMutable {
1858 self.prefer_mutable = true;
1861 self.visit_expr(expr);
1864 ExprKind::Closure(_, _, body_id, ..) => {
1865 let body = self.cx.tcx.hir().body(body_id);
1866 self.visit_expr(&body.value);
1868 _ => walk_expr(self, expr),
1870 self.prefer_mutable = old;
1872 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1873 NestedVisitorMap::None
1877 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1878 let def_id = match var_def_id(cx, expr) {
1880 None => return false,
1882 if let Some(used_mutably) = mutated_variables(container, cx) {
1883 if used_mutably.contains(&def_id) {
1890 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1891 let def_id = match var_def_id(cx, iter_expr) {
1893 None => return false,
1895 let mut visitor = VarUsedAfterLoopVisitor {
1898 iter_expr_id: iter_expr.hir_id,
1899 past_while_let: false,
1900 var_used_after_while_let: false,
1902 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1903 walk_block(&mut visitor, enclosing_block);
1905 visitor.var_used_after_while_let
1908 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1909 cx: &'a LateContext<'a, 'tcx>,
1911 iter_expr_id: HirId,
1912 past_while_let: bool,
1913 var_used_after_while_let: bool,
1916 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1917 fn visit_expr(&mut self, expr: &'tcx Expr) {
1918 if self.past_while_let {
1919 if Some(self.def_id) == var_def_id(self.cx, expr) {
1920 self.var_used_after_while_let = true;
1922 } else if self.iter_expr_id == expr.hir_id {
1923 self.past_while_let = true;
1925 walk_expr(self, expr);
1927 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1928 NestedVisitorMap::None
1932 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1933 /// for `&T` and `&mut T`, such as `Vec`.
1935 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1936 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1937 // will allow further borrows afterwards
1938 let ty = cx.tables.expr_ty(e);
1939 is_iterable_array(ty, cx) ||
1940 match_type(cx, ty, &paths::VEC) ||
1941 match_type(cx, ty, &paths::LINKED_LIST) ||
1942 match_type(cx, ty, &paths::HASHMAP) ||
1943 match_type(cx, ty, &paths::HASHSET) ||
1944 match_type(cx, ty, &paths::VEC_DEQUE) ||
1945 match_type(cx, ty, &paths::BINARY_HEAP) ||
1946 match_type(cx, ty, &paths::BTREEMAP) ||
1947 match_type(cx, ty, &paths::BTREESET)
1950 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1951 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1953 ty::Array(_, n) => (0..=32).contains(&n.eval_usize(cx.tcx, cx.param_env)),
1958 /// If a block begins with a statement (possibly a `let` binding) and has an
1959 /// expression, return it.
1960 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1961 if block.stmts.is_empty() {
1964 if let StmtKind::Local(ref local) = block.stmts[0].node {
1965 if let Some(ref expr) = local.init {
1975 /// If a block begins with an expression (with or without semicolon), return it.
1976 fn extract_first_expr(block: &Block) -> Option<&Expr> {
1978 Some(ref expr) if block.stmts.is_empty() => Some(expr),
1979 None if !block.stmts.is_empty() => match block.stmts[0].node {
1980 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
1981 StmtKind::Local(..) | StmtKind::Item(..) => None,
1987 /// Returns `true` if expr contains a single break expr without destination label
1989 /// passed expression. The expression may be within a block.
1990 fn is_simple_break_expr(expr: &Expr) -> bool {
1992 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
1993 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
1994 Some(subexpr) => is_simple_break_expr(subexpr),
2001 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2002 // incremented exactly once in the loop body, and initialized to zero
2003 // at the start of the loop.
2004 #[derive(Debug, PartialEq)]
2006 Initial, // Not examined yet
2007 IncrOnce, // Incremented exactly once, may be a loop counter
2008 Declared, // Declared but not (yet) initialized to zero
2013 /// Scan a for loop for variables that are incremented exactly once.
2014 struct IncrementVisitor<'a, 'tcx> {
2015 cx: &'a LateContext<'a, 'tcx>, // context reference
2016 states: FxHashMap<HirId, VarState>, // incremented variables
2017 depth: u32, // depth of conditional expressions
2021 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2022 fn visit_expr(&mut self, expr: &'tcx Expr) {
2027 // If node is a variable
2028 if let Some(def_id) = var_def_id(self.cx, expr) {
2029 if let Some(parent) = get_parent_expr(self.cx, expr) {
2030 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2033 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2034 if lhs.hir_id == expr.hir_id {
2035 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2036 *state = match *state {
2037 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2038 _ => VarState::DontWarn,
2041 // Assigned some other value
2042 *state = VarState::DontWarn;
2046 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2047 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2051 } else if is_loop(expr) || is_conditional(expr) {
2053 walk_expr(self, expr);
2056 } else if let ExprKind::Continue(_) = expr.node {
2060 walk_expr(self, expr);
2062 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2063 NestedVisitorMap::None
2067 /// Checks whether a variable is initialized to zero at the start of a loop.
2068 struct InitializeVisitor<'a, 'tcx> {
2069 cx: &'a LateContext<'a, 'tcx>, // context reference
2070 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2074 depth: u32, // depth of conditional expressions
2078 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2079 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2080 // Look for declarations of the variable
2081 if let StmtKind::Local(ref local) = stmt.node {
2082 if local.pat.hir_id == self.var_id {
2083 if let PatKind::Binding(.., ident, _) = local.pat.node {
2084 self.name = Some(ident.name);
2086 self.state = if let Some(ref init) = local.init {
2087 if is_integer_literal(init, 0) {
2098 walk_stmt(self, stmt);
2101 fn visit_expr(&mut self, expr: &'tcx Expr) {
2102 if self.state == VarState::DontWarn {
2105 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2106 self.past_loop = true;
2109 // No need to visit expressions before the variable is
2111 if self.state == VarState::IncrOnce {
2115 // If node is the desired variable, see how it's used
2116 if var_def_id(self.cx, expr) == Some(self.var_id) {
2117 if let Some(parent) = get_parent_expr(self.cx, expr) {
2119 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2120 self.state = VarState::DontWarn;
2122 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2123 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2129 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2135 self.state = VarState::DontWarn;
2138 } else if !self.past_loop && is_loop(expr) {
2139 self.state = VarState::DontWarn;
2141 } else if is_conditional(expr) {
2143 walk_expr(self, expr);
2147 walk_expr(self, expr);
2149 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2150 NestedVisitorMap::None
2154 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2155 if let ExprKind::Path(ref qpath) = expr.node {
2156 let path_res = cx.tables.qpath_res(qpath, expr.hir_id);
2157 if let Res::Local(node_id) = path_res {
2158 return Some(node_id);
2164 fn is_loop(expr: &Expr) -> bool {
2166 ExprKind::Loop(..) => true,
2171 fn is_conditional(expr: &Expr) -> bool {
2173 ExprKind::Match(..) => true,
2178 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2180 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2181 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2182 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2184 return is_loop_nested(cx, loop_expr, iter_expr)
2190 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2191 let mut id = loop_expr.hir_id;
2192 let iter_name = if let Some(name) = path_name(iter_expr) {
2198 let parent = cx.tcx.hir().get_parent_node(id);
2202 match cx.tcx.hir().find(parent) {
2203 Some(Node::Expr(expr)) => {
2204 if let ExprKind::Loop(..) = expr.node {
2208 Some(Node::Block(block)) => {
2209 let mut block_visitor = LoopNestVisitor {
2211 iterator: iter_name,
2214 walk_block(&mut block_visitor, block);
2215 if block_visitor.nesting == RuledOut {
2219 Some(Node::Stmt(_)) => (),
2228 #[derive(PartialEq, Eq)]
2230 Unknown, // no nesting detected yet
2231 RuledOut, // the iterator is initialized or assigned within scope
2232 LookFurther, // no nesting detected, no further walk required
2235 use self::Nesting::{LookFurther, RuledOut, Unknown};
2237 struct LoopNestVisitor {
2243 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2244 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2245 if stmt.hir_id == self.hir_id {
2246 self.nesting = LookFurther;
2247 } else if self.nesting == Unknown {
2248 walk_stmt(self, stmt);
2252 fn visit_expr(&mut self, expr: &'tcx Expr) {
2253 if self.nesting != Unknown {
2256 if expr.hir_id == self.hir_id {
2257 self.nesting = LookFurther;
2261 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2262 if match_var(path, self.iterator) {
2263 self.nesting = RuledOut;
2266 _ => walk_expr(self, expr),
2270 fn visit_pat(&mut self, pat: &'tcx Pat) {
2271 if self.nesting != Unknown {
2274 if let PatKind::Binding(.., span_name, _) = pat.node {
2275 if self.iterator == span_name.name {
2276 self.nesting = RuledOut;
2283 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2284 NestedVisitorMap::None
2288 fn path_name(e: &Expr) -> Option<Name> {
2289 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2290 let segments = &path.segments;
2291 if segments.len() == 1 {
2292 return Some(segments[0].ident.name);
2298 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2299 if constant(cx, cx.tables, cond).is_some() {
2300 // A pure constant condition (e.g., `while false`) is not linted.
2304 let mut var_visitor = VarCollectorVisitor {
2306 ids: FxHashSet::default(),
2307 def_ids: FxHashMap::default(),
2310 var_visitor.visit_expr(cond);
2311 if var_visitor.skip {
2314 let used_in_condition = &var_visitor.ids;
2315 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2316 used_in_condition.is_disjoint(&used_mutably)
2320 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2321 if no_cond_variable_mutated && !mutable_static_in_cond {
2324 WHILE_IMMUTABLE_CONDITION,
2326 "Variable in the condition are not mutated in the loop body. \
2327 This either leads to an infinite or to a never running loop.",
2332 /// Collects the set of variables in an expression
2333 /// Stops analysis if a function call is found
2334 /// Note: In some cases such as `self`, there are no mutable annotation,
2335 /// All variables definition IDs are collected
2336 struct VarCollectorVisitor<'a, 'tcx> {
2337 cx: &'a LateContext<'a, 'tcx>,
2338 ids: FxHashSet<HirId>,
2339 def_ids: FxHashMap<def_id::DefId, bool>,
2343 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2344 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2346 if let ExprKind::Path(ref qpath) = ex.node;
2347 if let QPath::Resolved(None, _) = *qpath;
2348 let res = self.cx.tables.qpath_res(qpath, ex.hir_id);
2351 Res::Local(node_id) => {
2352 self.ids.insert(node_id);
2354 Res::Def(DefKind::Static, def_id) => {
2355 let mutable = self.cx.tcx.is_mutable_static(def_id);
2356 self.def_ids.insert(def_id, mutable);
2365 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2366 fn visit_expr(&mut self, ex: &'tcx Expr) {
2368 ExprKind::Path(_) => self.insert_def_id(ex),
2369 // If there is any function/method call… we just stop analysis
2370 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2372 _ => walk_expr(self, ex),
2376 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2377 NestedVisitorMap::None
2381 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2383 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2385 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2386 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2387 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2388 if let Some(ref generic_args) = chain_method.args;
2389 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2391 let ty = cx.tables.node_type(ty.hir_id);
2392 if match_type(cx, ty, &paths::VEC) ||
2393 match_type(cx, ty, &paths::VEC_DEQUE) ||
2394 match_type(cx, ty, &paths::BTREEMAP) ||
2395 match_type(cx, ty, &paths::HASHMAP) {
2396 if method.ident.name == sym!(len) {
2397 let span = shorten_needless_collect_span(expr);
2398 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2402 ".count()".to_string(),
2403 Applicability::MachineApplicable,
2407 if method.ident.name == sym!(is_empty) {
2408 let span = shorten_needless_collect_span(expr);
2409 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2413 ".next().is_none()".to_string(),
2414 Applicability::MachineApplicable,
2418 if method.ident.name == sym!(contains) {
2419 let contains_arg = snippet(cx, args[1].span, "??");
2420 let span = shorten_needless_collect_span(expr);
2421 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2426 ".any(|&x| x == {})",
2427 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2429 Applicability::MachineApplicable,
2438 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2440 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2441 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2443 return expr.span.with_lo(span.lo() - BytePos(1));