1 use crate::reexport::*;
2 use if_chain::if_chain;
3 use itertools::Itertools;
4 use rustc::hir::def::Def;
5 use rustc::hir::def_id;
6 use rustc::hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
8 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
9 use rustc::middle::region;
10 use rustc::{declare_tool_lint, lint_array};
11 // use rustc::middle::region::CodeExtent;
12 use crate::consts::{constant, Constant};
13 use crate::utils::usage::mutated_variables;
14 use crate::utils::{in_macro, sext, sugg};
15 use rustc::middle::expr_use_visitor::*;
16 use rustc::middle::mem_categorization::cmt_;
17 use rustc::middle::mem_categorization::Categorization;
18 use rustc::ty::subst::Subst;
19 use rustc::ty::{self, Ty};
20 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
21 use rustc_errors::Applicability;
22 use std::iter::{once, Iterator};
25 use syntax::source_map::Span;
26 use syntax_pos::BytePos;
28 use crate::utils::paths;
30 get_enclosing_block, get_parent_expr, 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 /// **What it does:** Checks for for-loops that manually copy items between
36 /// slices that could be optimized by having a memcpy.
38 /// **Why is this bad?** It is not as fast as a memcpy.
40 /// **Known problems:** None.
44 /// for i in 0..src.len() {
45 /// dst[i + 64] = src[i];
48 declare_clippy_lint! {
51 "manually copying items between slices"
54 /// **What it does:** Checks for looping over the range of `0..len` of some
55 /// collection just to get the values by index.
57 /// **Why is this bad?** Just iterating the collection itself makes the intent
58 /// more clear and is probably faster.
60 /// **Known problems:** None.
64 /// for i in 0..vec.len() {
65 /// println!("{}", vec[i]);
68 declare_clippy_lint! {
69 pub NEEDLESS_RANGE_LOOP,
71 "for-looping over a range of indices where an iterator over items would do"
74 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
75 /// suggests the latter.
77 /// **Why is this bad?** Readability.
79 /// **Known problems:** False negatives. We currently only warn on some known
84 /// // with `y` a `Vec` or slice:
85 /// for x in y.iter() {
89 /// can be rewritten to
95 declare_clippy_lint! {
96 pub EXPLICIT_ITER_LOOP,
98 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
101 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
102 /// suggests the latter.
104 /// **Why is this bad?** Readability.
106 /// **Known problems:** None
110 /// // with `y` a `Vec` or slice:
111 /// for x in y.into_iter() {
115 /// can be rewritten to
121 declare_clippy_lint! {
122 pub EXPLICIT_INTO_ITER_LOOP,
124 "for-looping over `_.into_iter()` when `_` would do"
127 /// **What it does:** Checks for loops on `x.next()`.
129 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
130 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
131 /// implements `IntoIterator`, so that possibly one value will be iterated,
132 /// leading to some hard to find bugs. No one will want to write such code
133 /// [except to win an Underhanded Rust
134 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
136 /// **Known problems:** None.
140 /// for x in y.next() {
144 declare_clippy_lint! {
147 "for-looping over `_.next()` which is probably not intended"
150 /// **What it does:** Checks for `for` loops over `Option` values.
152 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
155 /// **Known problems:** None.
159 /// for x in option {
166 /// if let Some(x) = option {
170 declare_clippy_lint! {
171 pub FOR_LOOP_OVER_OPTION,
173 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
176 /// **What it does:** Checks for `for` loops over `Result` values.
178 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
181 /// **Known problems:** None.
185 /// for x in result {
192 /// if let Ok(x) = result {
196 declare_clippy_lint! {
197 pub FOR_LOOP_OVER_RESULT,
199 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
202 /// **What it does:** Detects `loop + match` combinations that are easier
203 /// written as a `while let` loop.
205 /// **Why is this bad?** The `while let` loop is usually shorter and more
208 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
213 /// let x = match y {
217 /// // .. do something with x
219 /// // is easier written as
220 /// while let Some(x) = y {
221 /// // .. do something with x
224 declare_clippy_lint! {
227 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
230 /// **What it does:** Checks for using `collect()` on an iterator without using
233 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
234 /// iterator instead.
236 /// **Known problems:** None.
240 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
242 declare_clippy_lint! {
245 "`collect()`ing an iterator without using the result; this is usually better written as a for loop"
248 /// **What it does:** Checks for functions collecting an iterator when collect
251 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
252 /// when this allocation may not be needed.
254 /// **Known problems:**
259 /// let len = iterator.collect::<Vec<_>>().len();
261 /// let len = iterator.count();
263 declare_clippy_lint! {
264 pub NEEDLESS_COLLECT,
266 "collecting an iterator when collect is not needed"
269 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
270 /// are constant and `x` is greater or equal to `y`, unless the range is
271 /// reversed or has a negative `.step_by(_)`.
273 /// **Why is it bad?** Such loops will either be skipped or loop until
274 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
277 /// **Known problems:** The lint cannot catch loops over dynamically defined
278 /// ranges. Doing this would require simulating all possible inputs and code
279 /// paths through the program, which would be complex and error-prone.
283 /// for x in 5..10 - 5 {
285 /// } // oops, stray `-`
287 declare_clippy_lint! {
288 pub REVERSE_RANGE_LOOP,
290 "iteration over an empty range, such as `10..0` or `5..5`"
293 /// **What it does:** Checks `for` loops over slices with an explicit counter
294 /// and suggests the use of `.enumerate()`.
296 /// **Why is it bad?** Not only is the version using `.enumerate()` more
297 /// readable, the compiler is able to remove bounds checks which can lead to
298 /// faster code in some instances.
300 /// **Known problems:** None.
304 /// for i in 0..v.len() { foo(v[i]);
305 /// for i in 0..v.len() { bar(i, v[i]); }
307 declare_clippy_lint! {
308 pub EXPLICIT_COUNTER_LOOP,
310 "for-looping with an explicit counter when `_.enumerate()` would do"
313 /// **What it does:** Checks for empty `loop` expressions.
315 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
316 /// anything. Think of the environment and either block on something or at least
317 /// make the thread sleep for some microseconds.
319 /// **Known problems:** None.
325 declare_clippy_lint! {
328 "empty `loop {}`, which should block or sleep"
331 /// **What it does:** Checks for `while let` expressions on iterators.
333 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
334 /// the intent better.
336 /// **Known problems:** None.
340 /// while let Some(val) = iter() {
344 declare_clippy_lint! {
345 pub WHILE_LET_ON_ITERATOR,
347 "using a while-let loop instead of a for loop on an iterator"
350 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
351 /// ignoring either the keys or values.
353 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
354 /// can be used to express that don't need the values or keys.
356 /// **Known problems:** None.
360 /// for (k, _) in &map {
365 /// could be replaced by
368 /// for k in map.keys() {
372 declare_clippy_lint! {
375 "looping on a map using `iter` when `keys` or `values` would do"
378 /// **What it does:** Checks for loops that will always `break`, `return` or
379 /// `continue` an outer loop.
381 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
384 /// **Known problems:** None
393 declare_clippy_lint! {
396 "any loop that will always `break` or `return`"
399 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
401 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
403 /// **Known problems:** None
407 /// let mut foo = 42;
408 /// for i in 0..foo {
410 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
413 declare_clippy_lint! {
416 "for loop over a range where one of the bounds is a mutable variable"
419 /// **What it does:** Checks whether variables used within while loop condition
420 /// can be (and are) mutated in the body.
422 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
423 /// will lead to an infinite loop.
425 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
426 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
427 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
433 /// println!("let me loop forever!");
436 declare_clippy_lint! {
437 pub WHILE_IMMUTABLE_CONDITION,
439 "variables used within while expression are not mutated in the body"
442 #[derive(Copy, Clone)]
445 impl LintPass for Pass {
446 fn get_lints(&self) -> LintArray {
451 EXPLICIT_INTO_ITER_LOOP,
453 FOR_LOOP_OVER_RESULT,
454 FOR_LOOP_OVER_OPTION,
459 EXPLICIT_COUNTER_LOOP,
461 WHILE_LET_ON_ITERATOR,
465 WHILE_IMMUTABLE_CONDITION,
470 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
471 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
472 // we don't want to check expanded macros
473 if in_macro(expr.span) {
477 if let Some((pat, arg, body)) = higher::for_loop(expr) {
478 check_for_loop(cx, pat, arg, body, expr);
481 // check for never_loop
483 ExprKind::While(_, ref block, _) | ExprKind::Loop(ref block, _, _) => {
484 match never_loop_block(block, expr.id) {
485 NeverLoopResult::AlwaysBreak => {
486 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops")
488 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 make 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::MachineApplicable;
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 == "next"
564 && match_trait_method(cx, match_expr, &paths::ITERATOR)
565 && lhs_constructor.ident.name == "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 // check for while loops which conditions never change
592 if let ExprKind::While(ref cond, _, _) = expr.node {
593 check_infinite_loop(cx, cond, expr);
596 check_needless_collect(expr, cx);
599 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
600 if let StmtKind::Semi(ref expr) = stmt.node {
601 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
602 if args.len() == 1 && method.ident.name == "collect" && match_trait_method(cx, expr, &paths::ITERATOR) {
607 "you are collect()ing an iterator and throwing away the result. \
608 Consider using an explicit for loop to exhaust the iterator",
616 enum NeverLoopResult {
617 // A break/return always get triggered but not necessarily for the main loop.
619 // A continue may occur for the main loop.
624 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
626 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
627 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
631 // Combine two results for parts that are called in order.
632 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
634 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
635 NeverLoopResult::Otherwise => second,
639 // Combine two results where both parts are called but not necessarily in order.
640 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
641 match (left, right) {
642 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
643 NeverLoopResult::MayContinueMainLoop
645 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
646 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
650 // Combine two results where only one of the part may have been executed.
651 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
653 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
654 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
655 NeverLoopResult::MayContinueMainLoop
657 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
661 fn never_loop_block(block: &Block, main_loop_id: NodeId) -> NeverLoopResult {
662 let stmts = block.stmts.iter().map(stmt_to_expr);
663 let expr = once(block.expr.as_ref().map(|p| &**p));
664 let mut iter = stmts.chain(expr).filter_map(|e| e);
665 never_loop_expr_seq(&mut iter, main_loop_id)
668 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
670 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
671 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
676 fn never_loop_expr(expr: &Expr, main_loop_id: NodeId) -> NeverLoopResult {
679 | ExprKind::Unary(_, ref e)
680 | ExprKind::Cast(ref e, _)
681 | ExprKind::Type(ref e, _)
682 | ExprKind::Field(ref e, _)
683 | ExprKind::AddrOf(_, ref e)
684 | ExprKind::Struct(_, _, Some(ref e))
685 | ExprKind::Repeat(ref e, _) => never_loop_expr(e, main_loop_id),
686 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
687 never_loop_expr_all(&mut es.iter(), main_loop_id)
689 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
690 ExprKind::Binary(_, ref e1, ref e2)
691 | ExprKind::Assign(ref e1, ref e2)
692 | ExprKind::AssignOp(_, ref e1, ref e2)
693 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
694 ExprKind::If(ref e, ref e2, ref e3) => {
695 let e1 = never_loop_expr(e, main_loop_id);
696 let e2 = never_loop_expr(e2, main_loop_id);
699 .map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
700 combine_seq(e1, combine_branches(e2, e3))
702 ExprKind::Loop(ref b, _, _) => {
703 // Break can come from the inner loop so remove them.
704 absorb_break(&never_loop_block(b, main_loop_id))
706 ExprKind::While(ref e, ref b, _) => {
707 let e = never_loop_expr(e, main_loop_id);
708 let result = never_loop_block(b, main_loop_id);
709 // Break can come from the inner loop so remove them.
710 combine_seq(e, absorb_break(&result))
712 ExprKind::Match(ref e, ref arms, _) => {
713 let e = never_loop_expr(e, main_loop_id);
717 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
721 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
722 ExprKind::Continue(d) => {
725 .expect("target id can only be missing in the presence of compilation errors");
726 if id == main_loop_id {
727 NeverLoopResult::MayContinueMainLoop
729 NeverLoopResult::AlwaysBreak
732 ExprKind::Break(_, _) => NeverLoopResult::AlwaysBreak,
733 ExprKind::Ret(ref e) => {
734 if let Some(ref e) = *e {
735 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
737 NeverLoopResult::AlwaysBreak
740 ExprKind::Struct(_, _, None)
742 | ExprKind::Closure(_, _, _, _, _)
743 | ExprKind::InlineAsm(_, _, _)
746 | ExprKind::Err => NeverLoopResult::Otherwise,
750 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
751 es.map(|e| never_loop_expr(e, main_loop_id))
752 .fold(NeverLoopResult::Otherwise, combine_seq)
755 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
756 es.map(|e| never_loop_expr(e, main_loop_id))
757 .fold(NeverLoopResult::Otherwise, combine_both)
760 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
761 e.map(|e| never_loop_expr(e, main_loop_id))
762 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
765 fn check_for_loop<'a, 'tcx>(
766 cx: &LateContext<'a, 'tcx>,
772 check_for_loop_range(cx, pat, arg, body, expr);
773 check_for_loop_reverse_range(cx, arg, expr);
774 check_for_loop_arg(cx, pat, arg, expr);
775 check_for_loop_explicit_counter(cx, arg, body, expr);
776 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
777 check_for_mut_range_bound(cx, arg, body);
778 detect_manual_memcpy(cx, pat, arg, body, expr);
781 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> bool {
783 if let ExprKind::Path(ref qpath) = expr.node;
784 if let QPath::Resolved(None, ref path) = *qpath;
785 if path.segments.len() == 1;
786 if let Def::Local(local_id) = cx.tables.qpath_def(qpath, expr.hir_id);
803 fn negative(s: String) -> Self {
804 Self { value: s, negate: true }
807 fn positive(s: String) -> Self {
815 struct FixedOffsetVar {
820 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
821 let is_slice = match ty.sty {
822 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
823 ty::Slice(..) | ty::Array(..) => true,
827 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
830 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> Option<FixedOffsetVar> {
831 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: ast::NodeId) -> Option<String> {
833 ExprKind::Lit(ref l) => match l.node {
834 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
837 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
842 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
843 let ty = cx.tables.expr_ty(seqexpr);
844 if !is_slice_like(cx, ty) {
848 let offset = match idx.node {
849 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
851 let offset_opt = if same_var(cx, lhs, var) {
852 extract_offset(cx, rhs, var)
853 } else if same_var(cx, rhs, var) {
854 extract_offset(cx, lhs, var)
859 offset_opt.map(Offset::positive)
861 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
864 ExprKind::Path(..) => {
865 if same_var(cx, idx, var) {
866 Some(Offset::positive("0".into()))
874 offset.map(|o| FixedOffsetVar {
875 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
883 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
884 cx: &LateContext<'a, 'tcx>,
887 ) -> Option<FixedOffsetVar> {
889 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
890 if method.ident.name == "clone";
892 if let Some(arg) = args.get(0);
894 return get_fixed_offset_var(cx, arg, var);
898 get_fixed_offset_var(cx, expr, var)
901 fn get_indexed_assignments<'a, 'tcx>(
902 cx: &LateContext<'a, 'tcx>,
905 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
906 fn get_assignment<'a, 'tcx>(
907 cx: &LateContext<'a, 'tcx>,
910 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
911 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
913 get_fixed_offset_var(cx, lhs, var),
914 fetch_cloned_fixed_offset_var(cx, rhs, var),
916 (Some(offset_left), Some(offset_right)) => {
917 // Source and destination must be different
918 if offset_left.var_name == offset_right.var_name {
921 Some((offset_left, offset_right))
931 if let ExprKind::Block(ref b, _) = body.node {
933 ref stmts, ref expr, ..
938 .map(|stmt| match stmt.node {
939 StmtKind::Local(..) | StmtKind::Item(..) => None,
940 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
942 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
944 .collect::<Option<Vec<_>>>()
945 .unwrap_or_else(|| vec![])
947 get_assignment(cx, body, var).into_iter().collect()
951 /// Check for for loops that sequentially copy items from one slice-like
952 /// object to another.
953 fn detect_manual_memcpy<'a, 'tcx>(
954 cx: &LateContext<'a, 'tcx>,
960 if let Some(higher::Range {
964 }) = higher::range(cx, arg)
966 // the var must be a single name
967 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
968 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
969 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
970 ("0", _, "0", _) => "".into(),
971 ("0", _, x, false) | (x, false, "0", false) => x.into(),
972 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
973 (x, false, y, false) => format!("({} + {})", x, y),
974 (x, false, y, true) => {
978 format!("({} - {})", x, y)
981 (x, true, y, false) => {
985 format!("({} - {})", y, x)
988 (x, true, y, true) => format!("-({} + {})", x, y),
992 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
993 if let Some(end) = *end {
995 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
996 if method.ident.name == "len";
997 if len_args.len() == 1;
998 if let Some(arg) = len_args.get(0);
999 if snippet(cx, arg.span, "??") == var_name;
1001 return if offset.negate {
1002 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
1009 let end_str = match limits {
1010 ast::RangeLimits::Closed => {
1011 let end = sugg::Sugg::hir(cx, end, "<count>");
1012 format!("{}", end + sugg::ONE)
1014 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1017 print_sum(&Offset::positive(end_str), &offset)
1023 // The only statements in the for loops can be indexed assignments from
1024 // indexed retrievals.
1025 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1027 let big_sugg = manual_copies
1029 .map(|(dst_var, src_var)| {
1030 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1031 let dst_offset = print_sum(&start_str, &dst_var.offset);
1032 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1033 let src_offset = print_sum(&start_str, &src_var.offset);
1034 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1035 let dst = if dst_offset == "" && dst_limit == "" {
1038 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1042 "{}.clone_from_slice(&{}[{}..{}])",
1043 dst, src_var.var_name, src_offset, src_limit
1048 if !big_sugg.is_empty() {
1053 "it looks like you're manually copying between slices",
1054 "try replacing the loop by",
1056 Applicability::Unspecified,
1063 /// Check for looping over a range and then indexing a sequence with it.
1064 /// The iteratee must be a range literal.
1065 fn check_for_loop_range<'a, 'tcx>(
1066 cx: &LateContext<'a, 'tcx>,
1072 if in_macro(expr.span) {
1076 if let Some(higher::Range {
1080 }) = higher::range(cx, arg)
1082 // the var must be a single name
1083 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1084 let mut visitor = VarVisitor {
1087 indexed_mut: FxHashSet::default(),
1088 indexed_indirectly: FxHashMap::default(),
1089 indexed_directly: FxHashMap::default(),
1090 referenced: FxHashSet::default(),
1092 prefer_mutable: false,
1094 walk_expr(&mut visitor, body);
1096 // linting condition: we only indexed one variable, and indexed it directly
1097 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1098 let (indexed, (indexed_extent, indexed_ty)) = visitor
1102 .expect("already checked that we have exactly 1 element");
1104 // ensure that the indexed variable was declared before the loop, see #601
1105 if let Some(indexed_extent) = indexed_extent {
1106 let parent_id = cx.tcx.hir().get_parent(expr.id);
1107 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1108 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1109 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1110 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1115 // don't lint if the container that is indexed into is also used without
1117 if visitor.referenced.contains(&indexed) {
1121 let starts_at_zero = is_integer_literal(start, 0);
1123 let skip = if starts_at_zero {
1126 format!(".skip({})", snippet(cx, start.span, ".."))
1129 let mut end_is_start_plus_val = false;
1131 let take = if let Some(end) = *end {
1132 let mut take_expr = end;
1134 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1135 if let BinOpKind::Add = op.node {
1136 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1137 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1139 if start_equal_left {
1141 } else if start_equal_right {
1145 end_is_start_plus_val = start_equal_left | start_equal_right;
1149 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1153 ast::RangeLimits::Closed => {
1154 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1155 format!(".take({})", take_expr + sugg::ONE)
1157 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1164 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1165 ("mut ", "iter_mut")
1170 let take_is_empty = take.is_empty();
1171 let mut method_1 = take;
1172 let mut method_2 = skip;
1174 if end_is_start_plus_val {
1175 mem::swap(&mut method_1, &mut method_2);
1178 if visitor.nonindex {
1181 NEEDLESS_RANGE_LOOP,
1183 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1187 "consider using an iterator".to_string(),
1189 (pat.span, format!("({}, <item>)", ident.name)),
1192 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1199 let repl = if starts_at_zero && take_is_empty {
1200 format!("&{}{}", ref_mut, indexed)
1202 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1207 NEEDLESS_RANGE_LOOP,
1210 "the loop variable `{}` is only used to index `{}`.",
1216 "consider using an iterator".to_string(),
1217 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1227 fn is_len_call(expr: &Expr, var: Name) -> bool {
1229 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1230 if len_args.len() == 1;
1231 if method.ident.name == "len";
1232 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1233 if path.segments.len() == 1;
1234 if path.segments[0].ident.name == var;
1243 fn is_end_eq_array_len(cx: &LateContext<'_, '_>, end: &Expr, limits: ast::RangeLimits, indexed_ty: Ty<'_>) -> bool {
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",
1303 db.span_suggestion_with_applicability(
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_defs()[arg.hir_id].def_id();
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 /// Check for `for` loops over `Option`s and `Results`
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>,
1448 // Look for variables that are incremented once per loop iteration.
1449 let mut visitor = IncrementVisitor {
1451 states: FxHashMap::default(),
1455 walk_expr(&mut visitor, body);
1457 // For each candidate, check the parent block to see if
1458 // it's initialized to zero at the start of the loop.
1459 let map = &cx.tcx.hir();
1460 let parent_scope = map
1461 .get_enclosing_scope(expr.id)
1462 .and_then(|id| map.get_enclosing_scope(id));
1463 if let Some(parent_id) = parent_scope {
1464 if let Node::Block(block) = map.get(parent_id) {
1465 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1466 let mut visitor2 = InitializeVisitor {
1470 state: VarState::IncrOnce,
1475 walk_block(&mut visitor2, block);
1477 if visitor2.state == VarState::Warn {
1478 if let Some(name) = visitor2.name {
1481 EXPLICIT_COUNTER_LOOP,
1484 "the variable `{0}` is used as a loop counter. Consider using `for ({0}, \
1485 item) in {1}.enumerate()` or similar iterators",
1487 snippet(cx, arg.span, "_")
1497 /// Check for the `FOR_KV_MAP` lint.
1498 fn check_for_loop_over_map_kv<'a, 'tcx>(
1499 cx: &LateContext<'a, 'tcx>,
1505 let pat_span = pat.span;
1507 if let PatKind::Tuple(ref pat, _) = pat.node {
1509 let arg_span = arg.span;
1510 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1511 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1512 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1513 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1518 let mutbl = match mutbl {
1520 MutMutable => "_mut",
1522 let arg = match arg.node {
1523 ExprKind::AddrOf(_, ref expr) => &**expr,
1527 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1532 &format!("you seem to want to iterate on a map's {}s", kind),
1534 let map = sugg::Sugg::hir(cx, arg, "map");
1537 "use the corresponding method".into(),
1539 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1540 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1550 struct MutatePairDelegate {
1551 node_id_low: Option<NodeId>,
1552 node_id_high: Option<NodeId>,
1553 span_low: Option<Span>,
1554 span_high: Option<Span>,
1557 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1558 fn consume(&mut self, _: NodeId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1560 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1562 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1564 fn borrow(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1565 if let ty::BorrowKind::MutBorrow = bk {
1566 if let Categorization::Local(id) = cmt.cat {
1567 if Some(id) == self.node_id_low {
1568 self.span_low = Some(sp)
1570 if Some(id) == self.node_id_high {
1571 self.span_high = Some(sp)
1577 fn mutate(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1578 if let Categorization::Local(id) = cmt.cat {
1579 if Some(id) == self.node_id_low {
1580 self.span_low = Some(sp)
1582 if Some(id) == self.node_id_high {
1583 self.span_high = Some(sp)
1588 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1591 impl<'tcx> MutatePairDelegate {
1592 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1593 (self.span_low, self.span_high)
1597 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1598 if let Some(higher::Range {
1602 }) = higher::range(cx, arg)
1604 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1605 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1606 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1607 mut_warn_with_span(cx, span_low);
1608 mut_warn_with_span(cx, span_high);
1613 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1614 if let Some(sp) = span {
1619 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1624 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<NodeId> {
1626 if let ExprKind::Path(ref qpath) = bound.node;
1627 if let QPath::Resolved(None, _) = *qpath;
1629 let def = cx.tables.qpath_def(qpath, bound.hir_id);
1630 if let Def::Local(node_id) = def {
1631 let node_str = cx.tcx.hir().get(node_id);
1633 if let Node::Binding(pat) = node_str;
1634 if let PatKind::Binding(bind_ann, _, _, _) = pat.node;
1635 if let BindingAnnotation::Mutable = bind_ann;
1637 return Some(node_id);
1646 fn check_for_mutation(
1647 cx: &LateContext<'_, '_>,
1649 bound_ids: &[Option<NodeId>],
1650 ) -> (Option<Span>, Option<Span>) {
1651 let mut delegate = MutatePairDelegate {
1652 node_id_low: bound_ids[0],
1653 node_id_high: bound_ids[1],
1657 let def_id = def_id::DefId::local(body.hir_id.owner);
1658 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1659 ExprUseVisitor::new(&mut delegate, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).walk_expr(body);
1660 delegate.mutation_span()
1663 /// Return true if the pattern is a `PatWild` or an ident prefixed with `'_'`.
1664 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1666 PatKind::Wild => true,
1667 PatKind::Binding(_, _, ident, None) if ident.as_str().starts_with('_') => {
1668 let mut visitor = UsedVisitor {
1672 walk_expr(&mut visitor, body);
1679 struct UsedVisitor {
1680 var: ast::Name, // var to look for
1681 used: bool, // has the var been used otherwise?
1684 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1685 fn visit_expr(&mut self, expr: &'tcx Expr) {
1686 if match_var(expr, self.var) {
1689 walk_expr(self, expr);
1693 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1694 NestedVisitorMap::None
1698 struct LocalUsedVisitor<'a, 'tcx: 'a> {
1699 cx: &'a LateContext<'a, 'tcx>,
1704 impl<'a, 'tcx: 'a> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1705 fn visit_expr(&mut self, expr: &'tcx Expr) {
1706 if same_var(self.cx, expr, self.local) {
1709 walk_expr(self, expr);
1713 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1714 NestedVisitorMap::None
1718 struct VarVisitor<'a, 'tcx: 'a> {
1719 /// context reference
1720 cx: &'a LateContext<'a, 'tcx>,
1721 /// var name to look for as index
1723 /// indexed variables that are used mutably
1724 indexed_mut: FxHashSet<Name>,
1725 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1726 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1727 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1728 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1729 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1730 /// Any names that are used outside an index operation.
1731 /// Used to detect things like `&mut vec` used together with `vec[i]`
1732 referenced: FxHashSet<Name>,
1733 /// has the loop variable been used in expressions other than the index of
1736 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1737 /// takes `&mut self`
1738 prefer_mutable: bool,
1741 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1742 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1744 // the indexed container is referenced by a name
1745 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1746 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1747 if seqvar.segments.len() == 1;
1749 let index_used_directly = same_var(self.cx, idx, self.var);
1750 let indexed_indirectly = {
1751 let mut used_visitor = LocalUsedVisitor {
1756 walk_expr(&mut used_visitor, idx);
1760 if indexed_indirectly || index_used_directly {
1761 if self.prefer_mutable {
1762 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1764 let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
1766 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
1767 let hir_id = self.cx.tcx.hir().node_to_hir_id(node_id);
1769 let parent_id = self.cx.tcx.hir().get_parent(expr.id);
1770 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1771 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1772 if indexed_indirectly {
1773 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1775 if index_used_directly {
1776 self.indexed_directly.insert(
1777 seqvar.segments[0].ident.name,
1778 (Some(extent), self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1781 return false; // no need to walk further *on the variable*
1783 Def::Static(..) | Def::Const(..) => {
1784 if indexed_indirectly {
1785 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1787 if index_used_directly {
1788 self.indexed_directly.insert(
1789 seqvar.segments[0].ident.name,
1790 (None, self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1793 return false; // no need to walk further *on the variable*
1804 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1805 fn visit_expr(&mut self, expr: &'tcx Expr) {
1808 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1809 if (meth.ident.name == "index" && match_trait_method(self.cx, expr, &paths::INDEX))
1810 || (meth.ident.name == "index_mut" && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1811 if !self.check(&args[1], &args[0], expr);
1817 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1818 if !self.check(idx, seqexpr, expr);
1823 // directly using a variable
1824 if let ExprKind::Path(ref qpath) = expr.node;
1825 if let QPath::Resolved(None, ref path) = *qpath;
1826 if path.segments.len() == 1;
1827 if let Def::Local(local_id) = self.cx.tables.qpath_def(qpath, expr.hir_id);
1829 if local_id == self.var {
1830 // we are not indexing anything, record that
1831 self.nonindex = true;
1833 // not the correct variable, but still a variable
1834 self.referenced.insert(path.segments[0].ident.name);
1838 let old = self.prefer_mutable;
1840 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1841 self.prefer_mutable = true;
1842 self.visit_expr(lhs);
1843 self.prefer_mutable = false;
1844 self.visit_expr(rhs);
1846 ExprKind::AddrOf(mutbl, ref expr) => {
1847 if mutbl == MutMutable {
1848 self.prefer_mutable = true;
1850 self.visit_expr(expr);
1852 ExprKind::Call(ref f, ref args) => {
1855 let ty = self.cx.tables.expr_ty_adjusted(expr);
1856 self.prefer_mutable = false;
1857 if let ty::Ref(_, _, mutbl) = ty.sty {
1858 if mutbl == MutMutable {
1859 self.prefer_mutable = true;
1862 self.visit_expr(expr);
1865 ExprKind::MethodCall(_, _, ref args) => {
1866 let def_id = self.cx.tables.type_dependent_defs()[expr.hir_id].def_id();
1867 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1868 self.prefer_mutable = false;
1869 if let ty::Ref(_, _, mutbl) = ty.sty {
1870 if mutbl == MutMutable {
1871 self.prefer_mutable = true;
1874 self.visit_expr(expr);
1877 _ => walk_expr(self, expr),
1879 self.prefer_mutable = old;
1881 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1882 NestedVisitorMap::None
1886 fn is_used_inside<'a, 'tcx: 'a>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1887 let def_id = match var_def_id(cx, expr) {
1889 None => return false,
1891 if let Some(used_mutably) = mutated_variables(container, cx) {
1892 if used_mutably.contains(&def_id) {
1899 fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1900 let def_id = match var_def_id(cx, iter_expr) {
1902 None => return false,
1904 let mut visitor = VarUsedAfterLoopVisitor {
1907 iter_expr_id: iter_expr.id,
1908 past_while_let: false,
1909 var_used_after_while_let: false,
1911 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1912 walk_block(&mut visitor, enclosing_block);
1914 visitor.var_used_after_while_let
1917 struct VarUsedAfterLoopVisitor<'a, 'tcx: 'a> {
1918 cx: &'a LateContext<'a, 'tcx>,
1920 iter_expr_id: NodeId,
1921 past_while_let: bool,
1922 var_used_after_while_let: bool,
1925 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1926 fn visit_expr(&mut self, expr: &'tcx Expr) {
1927 if self.past_while_let {
1928 if Some(self.def_id) == var_def_id(self.cx, expr) {
1929 self.var_used_after_while_let = true;
1931 } else if self.iter_expr_id == expr.id {
1932 self.past_while_let = true;
1934 walk_expr(self, expr);
1936 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1937 NestedVisitorMap::None
1941 /// Return true if the type of expr is one that provides `IntoIterator` impls
1942 /// for `&T` and `&mut T`, such as `Vec`.
1944 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1945 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1946 // will allow further borrows afterwards
1947 let ty = cx.tables.expr_ty(e);
1948 is_iterable_array(ty, cx) ||
1949 match_type(cx, ty, &paths::VEC) ||
1950 match_type(cx, ty, &paths::LINKED_LIST) ||
1951 match_type(cx, ty, &paths::HASHMAP) ||
1952 match_type(cx, ty, &paths::HASHSET) ||
1953 match_type(cx, ty, &paths::VEC_DEQUE) ||
1954 match_type(cx, ty, &paths::BINARY_HEAP) ||
1955 match_type(cx, ty, &paths::BTREEMAP) ||
1956 match_type(cx, ty, &paths::BTREESET)
1959 fn is_iterable_array(ty: Ty<'_>, cx: &LateContext<'_, '_>) -> bool {
1960 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1962 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1967 /// If a block begins with a statement (possibly a `let` binding) and has an
1968 /// expression, return it.
1969 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1970 if block.stmts.is_empty() {
1973 if let StmtKind::Local(ref local) = block.stmts[0].node {
1974 if let Some(ref expr) = local.init {
1984 /// If a block begins with an expression (with or without semicolon), return it.
1985 fn extract_first_expr(block: &Block) -> Option<&Expr> {
1987 Some(ref expr) if block.stmts.is_empty() => Some(expr),
1988 None if !block.stmts.is_empty() => match block.stmts[0].node {
1989 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
1990 StmtKind::Local(..) | StmtKind::Item(..) => None,
1996 /// Return true if expr contains a single break expr without destination label
1998 /// passed expression. The expression may be within a block.
1999 fn is_simple_break_expr(expr: &Expr) -> bool {
2001 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2002 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2003 Some(subexpr) => is_simple_break_expr(subexpr),
2010 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2011 // incremented exactly once in the loop body, and initialized to zero
2012 // at the start of the loop.
2013 #[derive(PartialEq)]
2015 Initial, // Not examined yet
2016 IncrOnce, // Incremented exactly once, may be a loop counter
2017 Declared, // Declared but not (yet) initialized to zero
2022 /// Scan a for loop for variables that are incremented exactly once.
2023 struct IncrementVisitor<'a, 'tcx: 'a> {
2024 cx: &'a LateContext<'a, 'tcx>, // context reference
2025 states: FxHashMap<NodeId, VarState>, // incremented variables
2026 depth: u32, // depth of conditional expressions
2030 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2031 fn visit_expr(&mut self, expr: &'tcx Expr) {
2036 // If node is a variable
2037 if let Some(def_id) = var_def_id(self.cx, expr) {
2038 if let Some(parent) = get_parent_expr(self.cx, expr) {
2039 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2042 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2043 if lhs.id == expr.id {
2044 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2045 *state = match *state {
2046 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2047 _ => VarState::DontWarn,
2050 // Assigned some other value
2051 *state = VarState::DontWarn;
2055 ExprKind::Assign(ref lhs, _) if lhs.id == expr.id => *state = VarState::DontWarn,
2056 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2060 } else if is_loop(expr) || is_conditional(expr) {
2062 walk_expr(self, expr);
2065 } else if let ExprKind::Continue(_) = expr.node {
2069 walk_expr(self, expr);
2071 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2072 NestedVisitorMap::None
2076 /// Check whether a variable is initialized to zero at the start of a loop.
2077 struct InitializeVisitor<'a, 'tcx: 'a> {
2078 cx: &'a LateContext<'a, 'tcx>, // context reference
2079 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2083 depth: u32, // depth of conditional expressions
2087 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2088 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2089 // Look for declarations of the variable
2090 if let StmtKind::Local(ref local) = stmt.node {
2091 if local.pat.id == self.var_id {
2092 if let PatKind::Binding(_, _, ident, _) = local.pat.node {
2093 self.name = Some(ident.name);
2095 self.state = if let Some(ref init) = local.init {
2096 if is_integer_literal(init, 0) {
2107 walk_stmt(self, stmt);
2110 fn visit_expr(&mut self, expr: &'tcx Expr) {
2111 if self.state == VarState::DontWarn {
2114 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2115 self.past_loop = true;
2118 // No need to visit expressions before the variable is
2120 if self.state == VarState::IncrOnce {
2124 // If node is the desired variable, see how it's used
2125 if var_def_id(self.cx, expr) == Some(self.var_id) {
2126 if let Some(parent) = get_parent_expr(self.cx, expr) {
2128 ExprKind::AssignOp(_, ref lhs, _) if lhs.id == expr.id => {
2129 self.state = VarState::DontWarn;
2131 ExprKind::Assign(ref lhs, ref rhs) if lhs.id == expr.id => {
2132 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2138 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2144 self.state = VarState::DontWarn;
2147 } else if !self.past_loop && is_loop(expr) {
2148 self.state = VarState::DontWarn;
2150 } else if is_conditional(expr) {
2152 walk_expr(self, expr);
2156 walk_expr(self, expr);
2158 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2159 NestedVisitorMap::None
2163 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<NodeId> {
2164 if let ExprKind::Path(ref qpath) = expr.node {
2165 let path_res = cx.tables.qpath_def(qpath, expr.hir_id);
2166 if let Def::Local(node_id) = path_res {
2167 return Some(node_id);
2173 fn is_loop(expr: &Expr) -> bool {
2175 ExprKind::Loop(..) | ExprKind::While(..) => true,
2180 fn is_conditional(expr: &Expr) -> bool {
2182 ExprKind::If(..) | ExprKind::Match(..) => true,
2187 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2189 if let Some(loop_block) = get_enclosing_block(cx, match_expr.id);
2190 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(loop_block.id));
2192 return is_loop_nested(cx, loop_expr, iter_expr)
2198 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2199 let mut id = loop_expr.id;
2200 let iter_name = if let Some(name) = path_name(iter_expr) {
2206 let parent = cx.tcx.hir().get_parent_node(id);
2210 match cx.tcx.hir().find(parent) {
2211 Some(Node::Expr(expr)) => match expr.node {
2212 ExprKind::Loop(..) | ExprKind::While(..) => {
2217 Some(Node::Block(block)) => {
2218 let mut block_visitor = LoopNestVisitor {
2220 iterator: iter_name,
2223 walk_block(&mut block_visitor, block);
2224 if block_visitor.nesting == RuledOut {
2228 Some(Node::Stmt(_)) => (),
2237 #[derive(PartialEq, Eq)]
2239 Unknown, // no nesting detected yet
2240 RuledOut, // the iterator is initialized or assigned within scope
2241 LookFurther, // no nesting detected, no further walk required
2244 use self::Nesting::{LookFurther, RuledOut, Unknown};
2246 struct LoopNestVisitor {
2252 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2253 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2254 if stmt.id == self.id {
2255 self.nesting = LookFurther;
2256 } else if self.nesting == Unknown {
2257 walk_stmt(self, stmt);
2261 fn visit_expr(&mut self, expr: &'tcx Expr) {
2262 if self.nesting != Unknown {
2265 if expr.id == self.id {
2266 self.nesting = LookFurther;
2270 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2271 if match_var(path, self.iterator) {
2272 self.nesting = RuledOut;
2275 _ => walk_expr(self, expr),
2279 fn visit_pat(&mut self, pat: &'tcx Pat) {
2280 if self.nesting != Unknown {
2283 if let PatKind::Binding(_, _, span_name, _) = pat.node {
2284 if self.iterator == span_name.name {
2285 self.nesting = RuledOut;
2292 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2293 NestedVisitorMap::None
2297 fn path_name(e: &Expr) -> Option<Name> {
2298 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2299 let segments = &path.segments;
2300 if segments.len() == 1 {
2301 return Some(segments[0].ident.name);
2307 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2308 if constant(cx, cx.tables, cond).is_some() {
2309 // A pure constant condition (e.g. while false) is not linted.
2313 let mut var_visitor = VarCollectorVisitor {
2315 ids: FxHashSet::default(),
2316 def_ids: FxHashMap::default(),
2319 var_visitor.visit_expr(cond);
2320 if var_visitor.skip {
2323 let used_in_condition = &var_visitor.ids;
2324 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2325 used_in_condition.is_disjoint(&used_mutably)
2329 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2330 if no_cond_variable_mutated && !mutable_static_in_cond {
2333 WHILE_IMMUTABLE_CONDITION,
2335 "Variable in the condition are not mutated in the loop body. \
2336 This either leads to an infinite or to a never running loop.",
2341 /// Collects the set of variables in an expression
2342 /// Stops analysis if a function call is found
2343 /// Note: In some cases such as `self`, there are no mutable annotation,
2344 /// All variables definition IDs are collected
2345 struct VarCollectorVisitor<'a, 'tcx: 'a> {
2346 cx: &'a LateContext<'a, 'tcx>,
2347 ids: FxHashSet<NodeId>,
2348 def_ids: FxHashMap<def_id::DefId, bool>,
2352 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2353 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2355 if let ExprKind::Path(ref qpath) = ex.node;
2356 if let QPath::Resolved(None, _) = *qpath;
2357 let def = self.cx.tables.qpath_def(qpath, ex.hir_id);
2360 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
2361 self.ids.insert(node_id);
2363 Def::Static(def_id, mutable) => {
2364 self.def_ids.insert(def_id, mutable);
2373 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2374 fn visit_expr(&mut self, ex: &'tcx Expr) {
2376 ExprKind::Path(_) => self.insert_def_id(ex),
2377 // If there is any function/method call… we just stop analysis
2378 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2380 _ => walk_expr(self, ex),
2384 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2385 NestedVisitorMap::None
2389 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2391 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2393 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2394 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2395 if chain_method.ident.name == "collect" && match_trait_method(cx, &args[0], &paths::ITERATOR);
2396 if let Some(ref generic_args) = chain_method.args;
2397 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2399 let ty = cx.tables.node_id_to_type(ty.hir_id);
2400 if match_type(cx, ty, &paths::VEC) ||
2401 match_type(cx, ty, &paths::VEC_DEQUE) ||
2402 match_type(cx, ty, &paths::BTREEMAP) ||
2403 match_type(cx, ty, &paths::HASHMAP) {
2404 if method.ident.name == "len" {
2405 let span = shorten_needless_collect_span(expr);
2406 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2407 db.span_suggestion_with_applicability(
2410 ".count()".to_string(),
2411 Applicability::MachineApplicable,
2415 if method.ident.name == "is_empty" {
2416 let span = shorten_needless_collect_span(expr);
2417 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2418 db.span_suggestion_with_applicability(
2421 ".next().is_none()".to_string(),
2422 Applicability::MachineApplicable,
2426 if method.ident.name == "contains" {
2427 let contains_arg = snippet(cx, args[1].span, "??");
2428 let span = shorten_needless_collect_span(expr);
2429 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2430 db.span_suggestion_with_applicability(
2434 ".any(|&x| x == {})",
2435 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2437 Applicability::MachineApplicable,
2446 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2448 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2449 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2451 return expr.span.with_lo(span.lo() - BytePos(1));