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 /// for x in y.iter() {
100 /// can be rewritten to
106 pub EXPLICIT_ITER_LOOP,
108 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
111 declare_clippy_lint! {
112 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
113 /// suggests the latter.
115 /// **Why is this bad?** Readability.
117 /// **Known problems:** None
121 /// // with `y` a `Vec` or slice:
122 /// for x in y.into_iter() {
126 /// can be rewritten to
132 pub EXPLICIT_INTO_ITER_LOOP,
134 "for-looping over `_.into_iter()` when `_` would do"
137 declare_clippy_lint! {
138 /// **What it does:** Checks for loops on `x.next()`.
140 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
141 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
142 /// implements `IntoIterator`, so that possibly one value will be iterated,
143 /// leading to some hard to find bugs. No one will want to write such code
144 /// [except to win an Underhanded Rust
145 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
147 /// **Known problems:** None.
151 /// for x in y.next() {
157 "for-looping over `_.next()` which is probably not intended"
160 declare_clippy_lint! {
161 /// **What it does:** Checks for `for` loops over `Option` values.
163 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
166 /// **Known problems:** None.
170 /// for x in option {
177 /// if let Some(x) = option {
181 pub FOR_LOOP_OVER_OPTION,
183 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
186 declare_clippy_lint! {
187 /// **What it does:** Checks for `for` loops over `Result` values.
189 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
192 /// **Known problems:** None.
196 /// for x in result {
203 /// if let Ok(x) = result {
207 pub FOR_LOOP_OVER_RESULT,
209 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
212 declare_clippy_lint! {
213 /// **What it does:** Detects `loop + match` combinations that are easier
214 /// written as a `while let` loop.
216 /// **Why is this bad?** The `while let` loop is usually shorter and more
219 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
224 /// let x = match y {
228 /// // .. do something with x
230 /// // is easier written as
231 /// while let Some(x) = y {
232 /// // .. do something with x
237 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
240 declare_clippy_lint! {
241 /// **What it does:** Checks for using `collect()` on an iterator without using
244 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
245 /// iterator instead.
247 /// **Known problems:** None.
251 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
255 "`collect()`ing an iterator without using the result; this is usually better written as a for loop"
258 declare_clippy_lint! {
259 /// **What it does:** Checks for functions collecting an iterator when collect
262 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
263 /// when this allocation may not be needed.
265 /// **Known problems:**
270 /// # let iterator = vec![1].into_iter();
271 /// let len = iterator.clone().collect::<Vec<_>>().len();
273 /// let len = iterator.count();
275 pub NEEDLESS_COLLECT,
277 "collecting an iterator when collect is not needed"
280 declare_clippy_lint! {
281 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
282 /// are constant and `x` is greater or equal to `y`, unless the range is
283 /// reversed or has a negative `.step_by(_)`.
285 /// **Why is it bad?** Such loops will either be skipped or loop until
286 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
289 /// **Known problems:** The lint cannot catch loops over dynamically defined
290 /// ranges. Doing this would require simulating all possible inputs and code
291 /// paths through the program, which would be complex and error-prone.
295 /// for x in 5..10 - 5 {
297 /// } // oops, stray `-`
299 pub REVERSE_RANGE_LOOP,
301 "iteration over an empty range, such as `10..0` or `5..5`"
304 declare_clippy_lint! {
305 /// **What it does:** Checks `for` loops over slices with an explicit counter
306 /// and suggests the use of `.enumerate()`.
308 /// **Why is it bad?** Not only is the version using `.enumerate()` more
309 /// readable, the compiler is able to remove bounds checks which can lead to
310 /// faster code in some instances.
312 /// **Known problems:** None.
316 /// for i in 0..v.len() { foo(v[i]);
317 /// for i in 0..v.len() { bar(i, v[i]); }
319 pub EXPLICIT_COUNTER_LOOP,
321 "for-looping with an explicit counter when `_.enumerate()` would do"
324 declare_clippy_lint! {
325 /// **What it does:** Checks for empty `loop` expressions.
327 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
328 /// anything. Think of the environment and either block on something or at least
329 /// make the thread sleep for some microseconds.
331 /// **Known problems:** None.
339 "empty `loop {}`, which should block or sleep"
342 declare_clippy_lint! {
343 /// **What it does:** Checks for `while let` expressions on iterators.
345 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
346 /// the intent better.
348 /// **Known problems:** None.
352 /// while let Some(val) = iter() {
356 pub WHILE_LET_ON_ITERATOR,
358 "using a while-let loop instead of a for loop on an iterator"
361 declare_clippy_lint! {
362 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
363 /// ignoring either the keys or values.
365 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
366 /// can be used to express that don't need the values or keys.
368 /// **Known problems:** None.
372 /// for (k, _) in &map {
377 /// could be replaced by
380 /// for k in map.keys() {
386 "looping on a map using `iter` when `keys` or `values` would do"
389 declare_clippy_lint! {
390 /// **What it does:** Checks for loops that will always `break`, `return` or
391 /// `continue` an outer loop.
393 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
396 /// **Known problems:** None
407 "any loop that will always `break` or `return`"
410 declare_clippy_lint! {
411 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
413 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
415 /// **Known problems:** None
419 /// let mut foo = 42;
420 /// for i in 0..foo {
422 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
427 "for loop over a range where one of the bounds is a mutable variable"
430 declare_clippy_lint! {
431 /// **What it does:** Checks whether variables used within while loop condition
432 /// can be (and are) mutated in the body.
434 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
435 /// will lead to an infinite loop.
437 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
438 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
439 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
445 /// println!("let me loop forever!");
448 pub WHILE_IMMUTABLE_CONDITION,
450 "variables used within while expression are not mutated in the body"
453 declare_lint_pass!(Loops => [
457 EXPLICIT_INTO_ITER_LOOP,
459 FOR_LOOP_OVER_RESULT,
460 FOR_LOOP_OVER_OPTION,
465 EXPLICIT_COUNTER_LOOP,
467 WHILE_LET_ON_ITERATOR,
471 WHILE_IMMUTABLE_CONDITION,
474 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
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_or_desugar(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
487 if let ExprKind::Loop(ref block, _, _) = expr.node {
488 match never_loop_block(block, expr.hir_id) {
489 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
490 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
494 // check for `loop { if let {} else break }` that could be `while let`
495 // (also matches an explicit "match" instead of "if let")
496 // (even if the "match" or "if let" is used for declaration)
497 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
498 // also check for empty `loop {}` statements
499 if block.stmts.is_empty() && block.expr.is_none() {
504 "empty `loop {}` detected. You may want to either use `panic!()` or add \
505 `std::thread::sleep(..);` to the loop body.",
509 // extract the expression from the first statement (if any) in a block
510 let inner_stmt_expr = extract_expr_from_first_stmt(block);
511 // or extract the first expression (if any) from the block
512 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
513 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
514 // ensure "if let" compatible match structure
516 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
518 && arms[0].pats.len() == 1
519 && arms[0].guard.is_none()
520 && arms[1].pats.len() == 1
521 && arms[1].guard.is_none()
522 && is_simple_break_expr(&arms[1].body)
524 if in_external_macro(cx.sess(), expr.span) {
528 // NOTE: we used to build a body here instead of using
529 // ellipsis, this was removed because:
530 // 1) it was ugly with big bodies;
531 // 2) it was not indented properly;
532 // 3) it wasn’t very smart (see #675).
533 let mut applicability = Applicability::HasPlaceholders;
538 "this loop could be written as a `while let` loop",
541 "while let {} = {} {{ .. }}",
542 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
543 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
554 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
555 let pat = &arms[0].pats[0].node;
557 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
558 &ExprKind::MethodCall(ref method_path, _, ref method_args),
559 ) = (pat, &match_expr.node)
561 let iter_expr = &method_args[0];
562 let lhs_constructor = last_path_segment(qpath);
563 if method_path.ident.name == sym!(next)
564 && match_trait_method(cx, match_expr, &paths::ITERATOR)
565 && lhs_constructor.ident.name == sym!(Some)
566 && (pat_args.is_empty()
567 || !is_refutable(cx, &pat_args[0])
568 && !is_used_inside(cx, iter_expr, &arms[0].body)
569 && !is_iterator_used_after_while_let(cx, iter_expr)
570 && !is_nested(cx, expr, &method_args[0]))
572 let iterator = snippet(cx, method_args[0].span, "_");
573 let loop_var = if pat_args.is_empty() {
576 snippet(cx, pat_args[0].span, "_").into_owned()
580 WHILE_LET_ON_ITERATOR,
582 "this loop could be written as a `for` loop",
584 format!("for {} in {} {{ .. }}", loop_var, iterator),
585 Applicability::HasPlaceholders,
591 if let Some((cond, body)) = higher::while_loop(&expr) {
592 check_infinite_loop(cx, cond, body);
595 check_needless_collect(expr, cx);
598 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
599 if let StmtKind::Semi(ref expr) = stmt.node {
600 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
602 && method.ident.name == sym!(collect)
603 && match_trait_method(cx, expr, &paths::ITERATOR)
609 "you are collect()ing an iterator and throwing away the result. \
610 Consider using an explicit for loop to exhaust the iterator",
618 enum NeverLoopResult {
619 // A break/return always get triggered but not necessarily for the main loop.
621 // A continue may occur for the main loop.
626 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
628 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
629 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
633 // Combine two results for parts that are called in order.
634 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
636 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
637 NeverLoopResult::Otherwise => second,
641 // Combine two results where both parts are called but not necessarily in order.
642 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
643 match (left, right) {
644 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
645 NeverLoopResult::MayContinueMainLoop
647 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
648 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
652 // Combine two results where only one of the part may have been executed.
653 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
655 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
656 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
657 NeverLoopResult::MayContinueMainLoop
659 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
663 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
664 let stmts = block.stmts.iter().map(stmt_to_expr);
665 let expr = once(block.expr.as_ref().map(|p| &**p));
666 let mut iter = stmts.chain(expr).filter_map(|e| e);
667 never_loop_expr_seq(&mut iter, main_loop_id)
670 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
672 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
673 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
678 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
681 | ExprKind::Unary(_, ref e)
682 | ExprKind::Cast(ref e, _)
683 | ExprKind::Type(ref e, _)
684 | ExprKind::Field(ref e, _)
685 | ExprKind::AddrOf(_, ref e)
686 | ExprKind::Struct(_, _, Some(ref e))
687 | ExprKind::Repeat(ref e, _)
688 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
689 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
690 never_loop_expr_all(&mut es.iter(), main_loop_id)
692 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
693 ExprKind::Binary(_, ref e1, ref e2)
694 | ExprKind::Assign(ref e1, ref e2)
695 | ExprKind::AssignOp(_, ref e1, ref e2)
696 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
697 ExprKind::Loop(ref b, _, _) => {
698 // Break can come from the inner loop so remove them.
699 absorb_break(&never_loop_block(b, main_loop_id))
701 ExprKind::Match(ref e, ref arms, _) => {
702 let e = never_loop_expr(e, main_loop_id);
706 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
710 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
711 ExprKind::Continue(d) => {
714 .expect("target ID can only be missing in the presence of compilation errors");
715 if id == main_loop_id {
716 NeverLoopResult::MayContinueMainLoop
718 NeverLoopResult::AlwaysBreak
721 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
722 if let Some(ref e) = *e {
723 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
725 NeverLoopResult::AlwaysBreak
728 ExprKind::Struct(_, _, None)
729 | ExprKind::Yield(_, _)
730 | ExprKind::Closure(_, _, _, _, _)
731 | ExprKind::InlineAsm(_, _, _)
734 | ExprKind::Err => NeverLoopResult::Otherwise,
738 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
739 es.map(|e| never_loop_expr(e, main_loop_id))
740 .fold(NeverLoopResult::Otherwise, combine_seq)
743 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
744 es.map(|e| never_loop_expr(e, main_loop_id))
745 .fold(NeverLoopResult::Otherwise, combine_both)
748 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
749 e.map(|e| never_loop_expr(e, main_loop_id))
750 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
753 fn check_for_loop<'a, 'tcx>(
754 cx: &LateContext<'a, 'tcx>,
760 check_for_loop_range(cx, pat, arg, body, expr);
761 check_for_loop_reverse_range(cx, arg, expr);
762 check_for_loop_arg(cx, pat, arg, expr);
763 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
764 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
765 check_for_mut_range_bound(cx, arg, body);
766 detect_manual_memcpy(cx, pat, arg, body, expr);
769 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
771 if let ExprKind::Path(ref qpath) = expr.node;
772 if let QPath::Resolved(None, ref path) = *qpath;
773 if path.segments.len() == 1;
774 if let Res::Local(local_id) = cx.tables.qpath_res(qpath, expr.hir_id);
791 fn negative(s: String) -> Self {
792 Self { value: s, negate: true }
795 fn positive(s: String) -> Self {
803 struct FixedOffsetVar {
808 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
809 let is_slice = match ty.sty {
810 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
811 ty::Slice(..) | ty::Array(..) => true,
815 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
818 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
819 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
821 ExprKind::Lit(ref l) => match l.node {
822 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
825 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
830 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
831 let ty = cx.tables.expr_ty(seqexpr);
832 if !is_slice_like(cx, ty) {
836 let offset = match idx.node {
837 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
839 let offset_opt = if same_var(cx, lhs, var) {
840 extract_offset(cx, rhs, var)
841 } else if same_var(cx, rhs, var) {
842 extract_offset(cx, lhs, var)
847 offset_opt.map(Offset::positive)
849 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
852 ExprKind::Path(..) => {
853 if same_var(cx, idx, var) {
854 Some(Offset::positive("0".into()))
862 offset.map(|o| FixedOffsetVar {
863 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
871 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
872 cx: &LateContext<'a, 'tcx>,
875 ) -> Option<FixedOffsetVar> {
877 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
878 if method.ident.name == sym!(clone);
880 if let Some(arg) = args.get(0);
882 return get_fixed_offset_var(cx, arg, var);
886 get_fixed_offset_var(cx, expr, var)
889 fn get_indexed_assignments<'a, 'tcx>(
890 cx: &LateContext<'a, 'tcx>,
893 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
894 fn get_assignment<'a, 'tcx>(
895 cx: &LateContext<'a, 'tcx>,
898 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
899 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
901 get_fixed_offset_var(cx, lhs, var),
902 fetch_cloned_fixed_offset_var(cx, rhs, var),
904 (Some(offset_left), Some(offset_right)) => {
905 // Source and destination must be different
906 if offset_left.var_name == offset_right.var_name {
909 Some((offset_left, offset_right))
919 if let ExprKind::Block(ref b, _) = body.node {
921 ref stmts, ref expr, ..
926 .map(|stmt| match stmt.node {
927 StmtKind::Local(..) | StmtKind::Item(..) => None,
928 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
930 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
932 .collect::<Option<Vec<_>>>()
933 .unwrap_or_else(|| vec![])
935 get_assignment(cx, body, var).into_iter().collect()
939 /// Checks for for loops that sequentially copy items from one slice-like
940 /// object to another.
941 fn detect_manual_memcpy<'a, 'tcx>(
942 cx: &LateContext<'a, 'tcx>,
948 if let Some(higher::Range {
952 }) = higher::range(cx, arg)
954 // the var must be a single name
955 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
956 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
957 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
958 ("0", _, "0", _) => "".into(),
959 ("0", _, x, false) | (x, false, "0", false) => x.into(),
960 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
961 (x, false, y, false) => format!("({} + {})", x, y),
962 (x, false, y, true) => {
966 format!("({} - {})", x, y)
969 (x, true, y, false) => {
973 format!("({} - {})", y, x)
976 (x, true, y, true) => format!("-({} + {})", x, y),
980 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
981 if let Some(end) = *end {
983 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
984 if method.ident.name == sym!(len);
985 if len_args.len() == 1;
986 if let Some(arg) = len_args.get(0);
987 if snippet(cx, arg.span, "??") == var_name;
989 return if offset.negate {
990 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
997 let end_str = match limits {
998 ast::RangeLimits::Closed => {
999 let end = sugg::Sugg::hir(cx, end, "<count>");
1000 format!("{}", end + sugg::ONE)
1002 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1005 print_sum(&Offset::positive(end_str), &offset)
1011 // The only statements in the for loops can be indexed assignments from
1012 // indexed retrievals.
1013 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1015 let big_sugg = manual_copies
1017 .map(|(dst_var, src_var)| {
1018 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1019 let dst_offset = print_sum(&start_str, &dst_var.offset);
1020 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1021 let src_offset = print_sum(&start_str, &src_var.offset);
1022 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1023 let dst = if dst_offset == "" && dst_limit == "" {
1026 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1030 "{}.clone_from_slice(&{}[{}..{}])",
1031 dst, src_var.var_name, src_offset, src_limit
1036 if !big_sugg.is_empty() {
1041 "it looks like you're manually copying between slices",
1042 "try replacing the loop by",
1044 Applicability::Unspecified,
1051 /// Checks for looping over a range and then indexing a sequence with it.
1052 /// The iteratee must be a range literal.
1053 #[allow(clippy::too_many_lines)]
1054 fn check_for_loop_range<'a, 'tcx>(
1055 cx: &LateContext<'a, 'tcx>,
1061 if in_macro_or_desugar(expr.span) {
1065 if let Some(higher::Range {
1069 }) = higher::range(cx, arg)
1071 // the var must be a single name
1072 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1073 let mut visitor = VarVisitor {
1076 indexed_mut: FxHashSet::default(),
1077 indexed_indirectly: FxHashMap::default(),
1078 indexed_directly: FxHashMap::default(),
1079 referenced: FxHashSet::default(),
1081 prefer_mutable: false,
1083 walk_expr(&mut visitor, body);
1085 // linting condition: we only indexed one variable, and indexed it directly
1086 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1087 let (indexed, (indexed_extent, indexed_ty)) = visitor
1091 .expect("already checked that we have exactly 1 element");
1093 // ensure that the indexed variable was declared before the loop, see #601
1094 if let Some(indexed_extent) = indexed_extent {
1095 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1096 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1097 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1098 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1099 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1104 // don't lint if the container that is indexed does not have .iter() method
1105 let has_iter = has_iter_method(cx, indexed_ty);
1106 if has_iter.is_none() {
1110 // don't lint if the container that is indexed into is also used without
1112 if visitor.referenced.contains(&indexed) {
1116 let starts_at_zero = is_integer_literal(start, 0);
1118 let skip = if starts_at_zero {
1121 format!(".skip({})", snippet(cx, start.span, ".."))
1124 let mut end_is_start_plus_val = false;
1126 let take = if let Some(end) = *end {
1127 let mut take_expr = end;
1129 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1130 if let BinOpKind::Add = op.node {
1131 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1132 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1134 if start_equal_left {
1136 } else if start_equal_right {
1140 end_is_start_plus_val = start_equal_left | start_equal_right;
1144 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1148 ast::RangeLimits::Closed => {
1149 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1150 format!(".take({})", take_expr + sugg::ONE)
1152 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1159 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1160 ("mut ", "iter_mut")
1165 let take_is_empty = take.is_empty();
1166 let mut method_1 = take;
1167 let mut method_2 = skip;
1169 if end_is_start_plus_val {
1170 mem::swap(&mut method_1, &mut method_2);
1173 if visitor.nonindex {
1176 NEEDLESS_RANGE_LOOP,
1178 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1182 "consider using an iterator".to_string(),
1184 (pat.span, format!("({}, <item>)", ident.name)),
1187 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1194 let repl = if starts_at_zero && take_is_empty {
1195 format!("&{}{}", ref_mut, indexed)
1197 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1202 NEEDLESS_RANGE_LOOP,
1205 "the loop variable `{}` is only used to index `{}`.",
1211 "consider using an iterator".to_string(),
1212 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1222 fn is_len_call(expr: &Expr, var: Name) -> bool {
1224 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1225 if len_args.len() == 1;
1226 if method.ident.name == sym!(len);
1227 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1228 if path.segments.len() == 1;
1229 if path.segments[0].ident.name == var;
1238 fn is_end_eq_array_len<'tcx>(
1239 cx: &LateContext<'_, 'tcx>,
1241 limits: ast::RangeLimits,
1242 indexed_ty: Ty<'tcx>,
1245 if let ExprKind::Lit(ref lit) = end.node;
1246 if let ast::LitKind::Int(end_int, _) = lit.node;
1247 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1248 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1250 return match limits {
1251 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1252 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1260 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1261 // if this for loop is iterating over a two-sided range...
1262 if let Some(higher::Range {
1266 }) = higher::range(cx, arg)
1268 // ...and both sides are compile-time constant integers...
1269 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1270 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1271 // ...and the start index is greater than the end index,
1272 // this loop will never run. This is often confusing for developers
1273 // who think that this will iterate from the larger value to the
1275 let ty = cx.tables.expr_ty(start);
1276 let (sup, eq) = match (start_idx, end_idx) {
1277 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1279 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1280 ty::Uint(_) => start_idx > end_idx,
1283 start_idx == end_idx,
1285 _ => (false, false),
1289 let start_snippet = snippet(cx, start.span, "_");
1290 let end_snippet = snippet(cx, end.span, "_");
1291 let dots = if limits == ast::RangeLimits::Closed {
1301 "this range is empty so this for loop will never run",
1305 "consider using the following if you are attempting to iterate over this \
1308 "({end}{dots}{start}).rev()",
1311 start = start_snippet
1313 Applicability::MaybeIncorrect,
1317 } else if eq && limits != ast::RangeLimits::Closed {
1318 // if they are equal, it's also problematic - this loop
1324 "this range is empty so this for loop will never run",
1332 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1333 let mut applicability = Applicability::MachineApplicable;
1334 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1335 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1340 "it is more concise to loop over references to containers instead of using explicit \
1342 "to write this more concisely, try",
1343 format!("&{}{}", muta, object),
1348 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1349 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1350 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1351 // just the receiver, no arguments
1352 if args.len() == 1 {
1353 let method_name = &*method.ident.as_str();
1354 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1355 if method_name == "iter" || method_name == "iter_mut" {
1356 if is_ref_iterable_type(cx, &args[0]) {
1357 lint_iter_method(cx, args, arg, method_name);
1359 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1360 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1361 let substs = cx.tables.node_substs(arg.hir_id);
1362 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1364 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1365 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1366 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1367 match cx.tables.expr_ty(&args[0]).sty {
1368 // If the length is greater than 32 no traits are implemented for array and
1369 // therefore we cannot use `&`.
1370 ty::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1371 _ => lint_iter_method(cx, args, arg, method_name),
1374 let mut applicability = Applicability::MachineApplicable;
1375 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1378 EXPLICIT_INTO_ITER_LOOP,
1380 "it is more concise to loop over containers instead of using explicit \
1381 iteration methods`",
1382 "to write this more concisely, try",
1387 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1392 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1393 probably not what you want",
1395 next_loop_linted = true;
1399 if !next_loop_linted {
1400 check_arg_type(cx, pat, arg);
1404 /// Checks for `for` loops over `Option`s and `Result`s.
1405 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1406 let ty = cx.tables.expr_ty(arg);
1407 if match_type(cx, ty, &paths::OPTION) {
1410 FOR_LOOP_OVER_OPTION,
1413 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1414 `if let` statement.",
1415 snippet(cx, arg.span, "_")
1418 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1419 snippet(cx, pat.span, "_"),
1420 snippet(cx, arg.span, "_")
1423 } else if match_type(cx, ty, &paths::RESULT) {
1426 FOR_LOOP_OVER_RESULT,
1429 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1430 `if let` statement.",
1431 snippet(cx, arg.span, "_")
1434 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1435 snippet(cx, pat.span, "_"),
1436 snippet(cx, arg.span, "_")
1442 fn check_for_loop_explicit_counter<'a, 'tcx>(
1443 cx: &LateContext<'a, 'tcx>,
1449 // Look for variables that are incremented once per loop iteration.
1450 let mut visitor = IncrementVisitor {
1452 states: FxHashMap::default(),
1456 walk_expr(&mut visitor, body);
1458 // For each candidate, check the parent block to see if
1459 // it's initialized to zero at the start of the loop.
1460 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1461 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1462 let mut visitor2 = InitializeVisitor {
1466 state: VarState::IncrOnce,
1471 walk_block(&mut visitor2, block);
1473 if visitor2.state == VarState::Warn {
1474 if let Some(name) = visitor2.name {
1475 let mut applicability = Applicability::MachineApplicable;
1478 EXPLICIT_COUNTER_LOOP,
1480 &format!("the variable `{}` is used as a loop counter.", name),
1483 "for ({}, {}) in {}.enumerate()",
1485 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1486 if higher::range(cx, arg).is_some() {
1489 snippet_with_applicability(cx, arg.span, "_", &mut applicability)
1494 sugg::Sugg::hir_with_applicability(cx, arg, "_", &mut applicability).maybe_par()
1506 /// Checks for the `FOR_KV_MAP` lint.
1507 fn check_for_loop_over_map_kv<'a, 'tcx>(
1508 cx: &LateContext<'a, 'tcx>,
1514 let pat_span = pat.span;
1516 if let PatKind::Tuple(ref pat, _) = pat.node {
1518 let arg_span = arg.span;
1519 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1520 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1521 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1522 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1527 let mutbl = match mutbl {
1529 MutMutable => "_mut",
1531 let arg = match arg.node {
1532 ExprKind::AddrOf(_, ref expr) => &**expr,
1536 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1541 &format!("you seem to want to iterate on a map's {}s", kind),
1543 let map = sugg::Sugg::hir(cx, arg, "map");
1546 "use the corresponding method".into(),
1548 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1549 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1559 struct MutatePairDelegate {
1560 hir_id_low: Option<HirId>,
1561 hir_id_high: Option<HirId>,
1562 span_low: Option<Span>,
1563 span_high: Option<Span>,
1566 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1567 fn consume(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1569 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1571 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1573 fn borrow(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1574 if let ty::BorrowKind::MutBorrow = bk {
1575 if let Categorization::Local(id) = cmt.cat {
1576 if Some(id) == self.hir_id_low {
1577 self.span_low = Some(sp)
1579 if Some(id) == self.hir_id_high {
1580 self.span_high = Some(sp)
1586 fn mutate(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1587 if let Categorization::Local(id) = cmt.cat {
1588 if Some(id) == self.hir_id_low {
1589 self.span_low = Some(sp)
1591 if Some(id) == self.hir_id_high {
1592 self.span_high = Some(sp)
1597 fn decl_without_init(&mut self, _: HirId, _: Span) {}
1600 impl<'tcx> MutatePairDelegate {
1601 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1602 (self.span_low, self.span_high)
1606 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1607 if let Some(higher::Range {
1611 }) = higher::range(cx, arg)
1613 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1614 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1615 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1616 mut_warn_with_span(cx, span_low);
1617 mut_warn_with_span(cx, span_high);
1622 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1623 if let Some(sp) = span {
1628 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1633 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1635 if let ExprKind::Path(ref qpath) = bound.node;
1636 if let QPath::Resolved(None, _) = *qpath;
1638 let res = cx.tables.qpath_res(qpath, bound.hir_id);
1639 if let Res::Local(node_id) = res {
1640 let node_str = cx.tcx.hir().get(node_id);
1642 if let Node::Binding(pat) = node_str;
1643 if let PatKind::Binding(bind_ann, ..) = pat.node;
1644 if let BindingAnnotation::Mutable = bind_ann;
1646 return Some(node_id);
1655 fn check_for_mutation(
1656 cx: &LateContext<'_, '_>,
1658 bound_ids: &[Option<HirId>],
1659 ) -> (Option<Span>, Option<Span>) {
1660 let mut delegate = MutatePairDelegate {
1661 hir_id_low: bound_ids[0],
1662 hir_id_high: bound_ids[1],
1666 let def_id = def_id::DefId::local(body.hir_id.owner);
1667 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1668 ExprUseVisitor::new(
1678 delegate.mutation_span()
1681 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1682 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1684 PatKind::Wild => true,
1685 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1686 let mut visitor = UsedVisitor {
1690 walk_expr(&mut visitor, body);
1697 struct UsedVisitor {
1698 var: ast::Name, // var to look for
1699 used: bool, // has the var been used otherwise?
1702 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1703 fn visit_expr(&mut self, expr: &'tcx Expr) {
1704 if match_var(expr, self.var) {
1707 walk_expr(self, expr);
1711 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1712 NestedVisitorMap::None
1716 struct LocalUsedVisitor<'a, 'tcx> {
1717 cx: &'a LateContext<'a, 'tcx>,
1722 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1723 fn visit_expr(&mut self, expr: &'tcx Expr) {
1724 if same_var(self.cx, expr, self.local) {
1727 walk_expr(self, expr);
1731 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1732 NestedVisitorMap::None
1736 struct VarVisitor<'a, 'tcx> {
1737 /// context reference
1738 cx: &'a LateContext<'a, 'tcx>,
1739 /// var name to look for as index
1741 /// indexed variables that are used mutably
1742 indexed_mut: FxHashSet<Name>,
1743 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1744 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1745 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1746 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1747 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1748 /// Any names that are used outside an index operation.
1749 /// Used to detect things like `&mut vec` used together with `vec[i]`
1750 referenced: FxHashSet<Name>,
1751 /// has the loop variable been used in expressions other than the index of
1754 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1755 /// takes `&mut self`
1756 prefer_mutable: bool,
1759 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1760 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1762 // the indexed container is referenced by a name
1763 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1764 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1765 if seqvar.segments.len() == 1;
1767 let index_used_directly = same_var(self.cx, idx, self.var);
1768 let indexed_indirectly = {
1769 let mut used_visitor = LocalUsedVisitor {
1774 walk_expr(&mut used_visitor, idx);
1778 if indexed_indirectly || index_used_directly {
1779 if self.prefer_mutable {
1780 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1782 let res = self.cx.tables.qpath_res(seqpath, seqexpr.hir_id);
1784 Res::Local(hir_id) => {
1785 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1786 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1787 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1788 if indexed_indirectly {
1789 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1791 if index_used_directly {
1792 self.indexed_directly.insert(
1793 seqvar.segments[0].ident.name,
1794 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1797 return false; // no need to walk further *on the variable*
1799 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1800 if indexed_indirectly {
1801 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1803 if index_used_directly {
1804 self.indexed_directly.insert(
1805 seqvar.segments[0].ident.name,
1806 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1809 return false; // no need to walk further *on the variable*
1820 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1821 fn visit_expr(&mut self, expr: &'tcx Expr) {
1824 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1825 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1826 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1827 if !self.check(&args[1], &args[0], expr);
1833 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1834 if !self.check(idx, seqexpr, expr);
1839 // directly using a variable
1840 if let ExprKind::Path(ref qpath) = expr.node;
1841 if let QPath::Resolved(None, ref path) = *qpath;
1842 if path.segments.len() == 1;
1844 if let Res::Local(local_id) = self.cx.tables.qpath_res(qpath, expr.hir_id) {
1845 if local_id == self.var {
1846 self.nonindex = true;
1848 // not the correct variable, but still a variable
1849 self.referenced.insert(path.segments[0].ident.name);
1855 let old = self.prefer_mutable;
1857 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1858 self.prefer_mutable = true;
1859 self.visit_expr(lhs);
1860 self.prefer_mutable = false;
1861 self.visit_expr(rhs);
1863 ExprKind::AddrOf(mutbl, ref expr) => {
1864 if mutbl == MutMutable {
1865 self.prefer_mutable = true;
1867 self.visit_expr(expr);
1869 ExprKind::Call(ref f, ref args) => {
1872 let ty = self.cx.tables.expr_ty_adjusted(expr);
1873 self.prefer_mutable = false;
1874 if let ty::Ref(_, _, mutbl) = ty.sty {
1875 if mutbl == MutMutable {
1876 self.prefer_mutable = true;
1879 self.visit_expr(expr);
1882 ExprKind::MethodCall(_, _, ref args) => {
1883 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1884 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1885 self.prefer_mutable = false;
1886 if let ty::Ref(_, _, mutbl) = ty.sty {
1887 if mutbl == MutMutable {
1888 self.prefer_mutable = true;
1891 self.visit_expr(expr);
1894 ExprKind::Closure(_, _, body_id, ..) => {
1895 let body = self.cx.tcx.hir().body(body_id);
1896 self.visit_expr(&body.value);
1898 _ => walk_expr(self, expr),
1900 self.prefer_mutable = old;
1902 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1903 NestedVisitorMap::None
1907 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1908 let def_id = match var_def_id(cx, expr) {
1910 None => return false,
1912 if let Some(used_mutably) = mutated_variables(container, cx) {
1913 if used_mutably.contains(&def_id) {
1920 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1921 let def_id = match var_def_id(cx, iter_expr) {
1923 None => return false,
1925 let mut visitor = VarUsedAfterLoopVisitor {
1928 iter_expr_id: iter_expr.hir_id,
1929 past_while_let: false,
1930 var_used_after_while_let: false,
1932 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1933 walk_block(&mut visitor, enclosing_block);
1935 visitor.var_used_after_while_let
1938 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1939 cx: &'a LateContext<'a, 'tcx>,
1941 iter_expr_id: HirId,
1942 past_while_let: bool,
1943 var_used_after_while_let: bool,
1946 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1947 fn visit_expr(&mut self, expr: &'tcx Expr) {
1948 if self.past_while_let {
1949 if Some(self.def_id) == var_def_id(self.cx, expr) {
1950 self.var_used_after_while_let = true;
1952 } else if self.iter_expr_id == expr.hir_id {
1953 self.past_while_let = true;
1955 walk_expr(self, expr);
1957 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1958 NestedVisitorMap::None
1962 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1963 /// for `&T` and `&mut T`, such as `Vec`.
1965 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1966 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1967 // will allow further borrows afterwards
1968 let ty = cx.tables.expr_ty(e);
1969 is_iterable_array(ty, cx) ||
1970 match_type(cx, ty, &paths::VEC) ||
1971 match_type(cx, ty, &paths::LINKED_LIST) ||
1972 match_type(cx, ty, &paths::HASHMAP) ||
1973 match_type(cx, ty, &paths::HASHSET) ||
1974 match_type(cx, ty, &paths::VEC_DEQUE) ||
1975 match_type(cx, ty, &paths::BINARY_HEAP) ||
1976 match_type(cx, ty, &paths::BTREEMAP) ||
1977 match_type(cx, ty, &paths::BTREESET)
1980 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1981 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1983 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1988 /// If a block begins with a statement (possibly a `let` binding) and has an
1989 /// expression, return it.
1990 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1991 if block.stmts.is_empty() {
1994 if let StmtKind::Local(ref local) = block.stmts[0].node {
1995 if let Some(ref expr) = local.init {
2005 /// If a block begins with an expression (with or without semicolon), return it.
2006 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2008 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2009 None if !block.stmts.is_empty() => match block.stmts[0].node {
2010 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2011 StmtKind::Local(..) | StmtKind::Item(..) => None,
2017 /// Returns `true` if expr contains a single break expr without destination label
2019 /// passed expression. The expression may be within a block.
2020 fn is_simple_break_expr(expr: &Expr) -> bool {
2022 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2023 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2024 Some(subexpr) => is_simple_break_expr(subexpr),
2031 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2032 // incremented exactly once in the loop body, and initialized to zero
2033 // at the start of the loop.
2034 #[derive(Debug, PartialEq)]
2036 Initial, // Not examined yet
2037 IncrOnce, // Incremented exactly once, may be a loop counter
2038 Declared, // Declared but not (yet) initialized to zero
2043 /// Scan a for loop for variables that are incremented exactly once.
2044 struct IncrementVisitor<'a, 'tcx> {
2045 cx: &'a LateContext<'a, 'tcx>, // context reference
2046 states: FxHashMap<HirId, VarState>, // incremented variables
2047 depth: u32, // depth of conditional expressions
2051 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2052 fn visit_expr(&mut self, expr: &'tcx Expr) {
2057 // If node is a variable
2058 if let Some(def_id) = var_def_id(self.cx, expr) {
2059 if let Some(parent) = get_parent_expr(self.cx, expr) {
2060 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2063 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2064 if lhs.hir_id == expr.hir_id {
2065 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2066 *state = match *state {
2067 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2068 _ => VarState::DontWarn,
2071 // Assigned some other value
2072 *state = VarState::DontWarn;
2076 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2077 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2081 } else if is_loop(expr) || is_conditional(expr) {
2083 walk_expr(self, expr);
2086 } else if let ExprKind::Continue(_) = expr.node {
2090 walk_expr(self, expr);
2092 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2093 NestedVisitorMap::None
2097 /// Checks whether a variable is initialized to zero at the start of a loop.
2098 struct InitializeVisitor<'a, 'tcx> {
2099 cx: &'a LateContext<'a, 'tcx>, // context reference
2100 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2104 depth: u32, // depth of conditional expressions
2108 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2109 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2110 // Look for declarations of the variable
2111 if let StmtKind::Local(ref local) = stmt.node {
2112 if local.pat.hir_id == self.var_id {
2113 if let PatKind::Binding(.., ident, _) = local.pat.node {
2114 self.name = Some(ident.name);
2116 self.state = if let Some(ref init) = local.init {
2117 if is_integer_literal(init, 0) {
2128 walk_stmt(self, stmt);
2131 fn visit_expr(&mut self, expr: &'tcx Expr) {
2132 if self.state == VarState::DontWarn {
2135 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2136 self.past_loop = true;
2139 // No need to visit expressions before the variable is
2141 if self.state == VarState::IncrOnce {
2145 // If node is the desired variable, see how it's used
2146 if var_def_id(self.cx, expr) == Some(self.var_id) {
2147 if let Some(parent) = get_parent_expr(self.cx, expr) {
2149 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2150 self.state = VarState::DontWarn;
2152 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2153 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2159 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2165 self.state = VarState::DontWarn;
2168 } else if !self.past_loop && is_loop(expr) {
2169 self.state = VarState::DontWarn;
2171 } else if is_conditional(expr) {
2173 walk_expr(self, expr);
2177 walk_expr(self, expr);
2179 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2180 NestedVisitorMap::None
2184 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2185 if let ExprKind::Path(ref qpath) = expr.node {
2186 let path_res = cx.tables.qpath_res(qpath, expr.hir_id);
2187 if let Res::Local(node_id) = path_res {
2188 return Some(node_id);
2194 fn is_loop(expr: &Expr) -> bool {
2196 ExprKind::Loop(..) => true,
2201 fn is_conditional(expr: &Expr) -> bool {
2203 ExprKind::Match(..) => true,
2208 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2210 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2211 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2212 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2214 return is_loop_nested(cx, loop_expr, iter_expr)
2220 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2221 let mut id = loop_expr.hir_id;
2222 let iter_name = if let Some(name) = path_name(iter_expr) {
2228 let parent = cx.tcx.hir().get_parent_node(id);
2232 match cx.tcx.hir().find(parent) {
2233 Some(Node::Expr(expr)) => {
2234 if let ExprKind::Loop(..) = expr.node {
2238 Some(Node::Block(block)) => {
2239 let mut block_visitor = LoopNestVisitor {
2241 iterator: iter_name,
2244 walk_block(&mut block_visitor, block);
2245 if block_visitor.nesting == RuledOut {
2249 Some(Node::Stmt(_)) => (),
2258 #[derive(PartialEq, Eq)]
2260 Unknown, // no nesting detected yet
2261 RuledOut, // the iterator is initialized or assigned within scope
2262 LookFurther, // no nesting detected, no further walk required
2265 use self::Nesting::{LookFurther, RuledOut, Unknown};
2267 struct LoopNestVisitor {
2273 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2274 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2275 if stmt.hir_id == self.hir_id {
2276 self.nesting = LookFurther;
2277 } else if self.nesting == Unknown {
2278 walk_stmt(self, stmt);
2282 fn visit_expr(&mut self, expr: &'tcx Expr) {
2283 if self.nesting != Unknown {
2286 if expr.hir_id == self.hir_id {
2287 self.nesting = LookFurther;
2291 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2292 if match_var(path, self.iterator) {
2293 self.nesting = RuledOut;
2296 _ => walk_expr(self, expr),
2300 fn visit_pat(&mut self, pat: &'tcx Pat) {
2301 if self.nesting != Unknown {
2304 if let PatKind::Binding(.., span_name, _) = pat.node {
2305 if self.iterator == span_name.name {
2306 self.nesting = RuledOut;
2313 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2314 NestedVisitorMap::None
2318 fn path_name(e: &Expr) -> Option<Name> {
2319 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2320 let segments = &path.segments;
2321 if segments.len() == 1 {
2322 return Some(segments[0].ident.name);
2328 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2329 if constant(cx, cx.tables, cond).is_some() {
2330 // A pure constant condition (e.g., `while false`) is not linted.
2334 let mut var_visitor = VarCollectorVisitor {
2336 ids: FxHashSet::default(),
2337 def_ids: FxHashMap::default(),
2340 var_visitor.visit_expr(cond);
2341 if var_visitor.skip {
2344 let used_in_condition = &var_visitor.ids;
2345 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2346 used_in_condition.is_disjoint(&used_mutably)
2350 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2351 if no_cond_variable_mutated && !mutable_static_in_cond {
2354 WHILE_IMMUTABLE_CONDITION,
2356 "Variable in the condition are not mutated in the loop body. \
2357 This either leads to an infinite or to a never running loop.",
2362 /// Collects the set of variables in an expression
2363 /// Stops analysis if a function call is found
2364 /// Note: In some cases such as `self`, there are no mutable annotation,
2365 /// All variables definition IDs are collected
2366 struct VarCollectorVisitor<'a, 'tcx> {
2367 cx: &'a LateContext<'a, 'tcx>,
2368 ids: FxHashSet<HirId>,
2369 def_ids: FxHashMap<def_id::DefId, bool>,
2373 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2374 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2376 if let ExprKind::Path(ref qpath) = ex.node;
2377 if let QPath::Resolved(None, _) = *qpath;
2378 let res = self.cx.tables.qpath_res(qpath, ex.hir_id);
2381 Res::Local(node_id) => {
2382 self.ids.insert(node_id);
2384 Res::Def(DefKind::Static, def_id) => {
2385 let mutable = self.cx.tcx.is_mutable_static(def_id);
2386 self.def_ids.insert(def_id, mutable);
2395 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2396 fn visit_expr(&mut self, ex: &'tcx Expr) {
2398 ExprKind::Path(_) => self.insert_def_id(ex),
2399 // If there is any function/method call… we just stop analysis
2400 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2402 _ => walk_expr(self, ex),
2406 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2407 NestedVisitorMap::None
2411 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2413 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2415 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2416 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2417 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2418 if let Some(ref generic_args) = chain_method.args;
2419 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2421 let ty = cx.tables.node_type(ty.hir_id);
2422 if match_type(cx, ty, &paths::VEC) ||
2423 match_type(cx, ty, &paths::VEC_DEQUE) ||
2424 match_type(cx, ty, &paths::BTREEMAP) ||
2425 match_type(cx, ty, &paths::HASHMAP) {
2426 if method.ident.name == sym!(len) {
2427 let span = shorten_needless_collect_span(expr);
2428 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2432 ".count()".to_string(),
2433 Applicability::MachineApplicable,
2437 if method.ident.name == sym!(is_empty) {
2438 let span = shorten_needless_collect_span(expr);
2439 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2443 ".next().is_none()".to_string(),
2444 Applicability::MachineApplicable,
2448 if method.ident.name == sym!(contains) {
2449 let contains_arg = snippet(cx, args[1].span, "??");
2450 let span = shorten_needless_collect_span(expr);
2451 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2456 ".any(|&x| x == {})",
2457 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2459 Applicability::MachineApplicable,
2468 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2470 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2471 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2473 return expr.span.with_lo(span.lo() - BytePos(1));