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,
469 fn name(&self) -> &'static str {
474 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
475 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
476 // we don't want to check expanded macros
477 if in_macro(expr.span) {
481 if let Some((pat, arg, body)) = higher::for_loop(expr) {
482 check_for_loop(cx, pat, arg, body, expr);
485 // check for never_loop
487 ExprKind::While(_, ref block, _) | ExprKind::Loop(ref block, _, _) => {
488 match never_loop_block(block, expr.id) {
489 NeverLoopResult::AlwaysBreak => {
490 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops")
492 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
498 // check for `loop { if let {} else break }` that could be `while let`
499 // (also matches an explicit "match" instead of "if let")
500 // (even if the "match" or "if let" is used for declaration)
501 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
502 // also check for empty `loop {}` statements
503 if block.stmts.is_empty() && block.expr.is_none() {
508 "empty `loop {}` detected. You may want to either use `panic!()` or add \
509 `std::thread::sleep(..);` to the loop body.",
513 // extract the expression from the first statement (if any) in a block
514 let inner_stmt_expr = extract_expr_from_first_stmt(block);
515 // or extract the first expression (if any) from the block
516 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
517 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
518 // ensure "if let" compatible match structure
520 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
522 && arms[0].pats.len() == 1
523 && arms[0].guard.is_none()
524 && arms[1].pats.len() == 1
525 && arms[1].guard.is_none()
526 && is_simple_break_expr(&arms[1].body)
528 if in_external_macro(cx.sess(), expr.span) {
532 // NOTE: we used to make build a body here instead of using
533 // ellipsis, this was removed because:
534 // 1) it was ugly with big bodies;
535 // 2) it was not indented properly;
536 // 3) it wasn’t very smart (see #675).
537 let mut applicability = Applicability::MachineApplicable;
542 "this loop could be written as a `while let` loop",
545 "while let {} = {} {{ .. }}",
546 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
547 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
558 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
559 let pat = &arms[0].pats[0].node;
561 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
562 &ExprKind::MethodCall(ref method_path, _, ref method_args),
563 ) = (pat, &match_expr.node)
565 let iter_expr = &method_args[0];
566 let lhs_constructor = last_path_segment(qpath);
567 if method_path.ident.name == "next"
568 && match_trait_method(cx, match_expr, &paths::ITERATOR)
569 && lhs_constructor.ident.name == "Some"
570 && (pat_args.is_empty()
571 || !is_refutable(cx, &pat_args[0])
572 && !is_used_inside(cx, iter_expr, &arms[0].body)
573 && !is_iterator_used_after_while_let(cx, iter_expr)
574 && !is_nested(cx, expr, &method_args[0]))
576 let iterator = snippet(cx, method_args[0].span, "_");
577 let loop_var = if pat_args.is_empty() {
580 snippet(cx, pat_args[0].span, "_").into_owned()
584 WHILE_LET_ON_ITERATOR,
586 "this loop could be written as a `for` loop",
588 format!("for {} in {} {{ .. }}", loop_var, iterator),
589 Applicability::HasPlaceholders,
595 // check for while loops which conditions never change
596 if let ExprKind::While(ref cond, _, _) = expr.node {
597 check_infinite_loop(cx, cond, expr);
600 check_needless_collect(expr, cx);
603 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
604 if let StmtKind::Semi(ref expr) = stmt.node {
605 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
606 if args.len() == 1 && method.ident.name == "collect" && match_trait_method(cx, expr, &paths::ITERATOR) {
611 "you are collect()ing an iterator and throwing away the result. \
612 Consider using an explicit for loop to exhaust the iterator",
620 enum NeverLoopResult {
621 // A break/return always get triggered but not necessarily for the main loop.
623 // A continue may occur for the main loop.
628 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
630 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
631 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
635 // Combine two results for parts that are called in order.
636 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
638 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
639 NeverLoopResult::Otherwise => second,
643 // Combine two results where both parts are called but not necessarily in order.
644 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
645 match (left, right) {
646 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
647 NeverLoopResult::MayContinueMainLoop
649 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
650 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
654 // Combine two results where only one of the part may have been executed.
655 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
657 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
658 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
659 NeverLoopResult::MayContinueMainLoop
661 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
665 fn never_loop_block(block: &Block, main_loop_id: NodeId) -> NeverLoopResult {
666 let stmts = block.stmts.iter().map(stmt_to_expr);
667 let expr = once(block.expr.as_ref().map(|p| &**p));
668 let mut iter = stmts.chain(expr).filter_map(|e| e);
669 never_loop_expr_seq(&mut iter, main_loop_id)
672 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
674 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
675 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
680 fn never_loop_expr(expr: &Expr, main_loop_id: NodeId) -> NeverLoopResult {
683 | ExprKind::Unary(_, ref e)
684 | ExprKind::Cast(ref e, _)
685 | ExprKind::Type(ref e, _)
686 | ExprKind::Field(ref e, _)
687 | ExprKind::AddrOf(_, ref e)
688 | ExprKind::Struct(_, _, Some(ref e))
689 | ExprKind::Repeat(ref e, _) => never_loop_expr(e, main_loop_id),
690 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
691 never_loop_expr_all(&mut es.iter(), main_loop_id)
693 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
694 ExprKind::Binary(_, ref e1, ref e2)
695 | ExprKind::Assign(ref e1, ref e2)
696 | ExprKind::AssignOp(_, ref e1, ref e2)
697 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
698 ExprKind::If(ref e, ref e2, ref e3) => {
699 let e1 = never_loop_expr(e, main_loop_id);
700 let e2 = never_loop_expr(e2, main_loop_id);
703 .map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
704 combine_seq(e1, combine_branches(e2, e3))
706 ExprKind::Loop(ref b, _, _) => {
707 // Break can come from the inner loop so remove them.
708 absorb_break(&never_loop_block(b, main_loop_id))
710 ExprKind::While(ref e, ref b, _) => {
711 let e = never_loop_expr(e, main_loop_id);
712 let result = never_loop_block(b, main_loop_id);
713 // Break can come from the inner loop so remove them.
714 combine_seq(e, absorb_break(&result))
716 ExprKind::Match(ref e, ref arms, _) => {
717 let e = never_loop_expr(e, main_loop_id);
721 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
725 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
726 ExprKind::Continue(d) => {
729 .expect("target id can only be missing in the presence of compilation errors");
730 if id == main_loop_id {
731 NeverLoopResult::MayContinueMainLoop
733 NeverLoopResult::AlwaysBreak
736 ExprKind::Break(_, _) => NeverLoopResult::AlwaysBreak,
737 ExprKind::Ret(ref e) => {
738 if let Some(ref e) = *e {
739 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
741 NeverLoopResult::AlwaysBreak
744 ExprKind::Struct(_, _, None)
746 | ExprKind::Closure(_, _, _, _, _)
747 | ExprKind::InlineAsm(_, _, _)
750 | ExprKind::Err => NeverLoopResult::Otherwise,
754 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
755 es.map(|e| never_loop_expr(e, main_loop_id))
756 .fold(NeverLoopResult::Otherwise, combine_seq)
759 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
760 es.map(|e| never_loop_expr(e, main_loop_id))
761 .fold(NeverLoopResult::Otherwise, combine_both)
764 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: NodeId) -> NeverLoopResult {
765 e.map(|e| never_loop_expr(e, main_loop_id))
766 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
769 fn check_for_loop<'a, 'tcx>(
770 cx: &LateContext<'a, 'tcx>,
776 check_for_loop_range(cx, pat, arg, body, expr);
777 check_for_loop_reverse_range(cx, arg, expr);
778 check_for_loop_arg(cx, pat, arg, expr);
779 check_for_loop_explicit_counter(cx, arg, body, expr);
780 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
781 check_for_mut_range_bound(cx, arg, body);
782 detect_manual_memcpy(cx, pat, arg, body, expr);
785 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> bool {
787 if let ExprKind::Path(ref qpath) = expr.node;
788 if let QPath::Resolved(None, ref path) = *qpath;
789 if path.segments.len() == 1;
790 if let Def::Local(local_id) = cx.tables.qpath_def(qpath, expr.hir_id);
807 fn negative(s: String) -> Self {
808 Self { value: s, negate: true }
811 fn positive(s: String) -> Self {
819 struct FixedOffsetVar {
824 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
825 let is_slice = match ty.sty {
826 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
827 ty::Slice(..) | ty::Array(..) => true,
831 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
834 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: ast::NodeId) -> Option<FixedOffsetVar> {
835 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: ast::NodeId) -> Option<String> {
837 ExprKind::Lit(ref l) => match l.node {
838 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
841 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
846 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
847 let ty = cx.tables.expr_ty(seqexpr);
848 if !is_slice_like(cx, ty) {
852 let offset = match idx.node {
853 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
855 let offset_opt = if same_var(cx, lhs, var) {
856 extract_offset(cx, rhs, var)
857 } else if same_var(cx, rhs, var) {
858 extract_offset(cx, lhs, var)
863 offset_opt.map(Offset::positive)
865 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
868 ExprKind::Path(..) => {
869 if same_var(cx, idx, var) {
870 Some(Offset::positive("0".into()))
878 offset.map(|o| FixedOffsetVar {
879 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
887 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
888 cx: &LateContext<'a, 'tcx>,
891 ) -> Option<FixedOffsetVar> {
893 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
894 if method.ident.name == "clone";
896 if let Some(arg) = args.get(0);
898 return get_fixed_offset_var(cx, arg, var);
902 get_fixed_offset_var(cx, expr, var)
905 fn get_indexed_assignments<'a, 'tcx>(
906 cx: &LateContext<'a, 'tcx>,
909 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
910 fn get_assignment<'a, 'tcx>(
911 cx: &LateContext<'a, 'tcx>,
914 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
915 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
917 get_fixed_offset_var(cx, lhs, var),
918 fetch_cloned_fixed_offset_var(cx, rhs, var),
920 (Some(offset_left), Some(offset_right)) => {
921 // Source and destination must be different
922 if offset_left.var_name == offset_right.var_name {
925 Some((offset_left, offset_right))
935 if let ExprKind::Block(ref b, _) = body.node {
937 ref stmts, ref expr, ..
942 .map(|stmt| match stmt.node {
943 StmtKind::Local(..) | StmtKind::Item(..) => None,
944 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
946 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
948 .collect::<Option<Vec<_>>>()
949 .unwrap_or_else(|| vec![])
951 get_assignment(cx, body, var).into_iter().collect()
955 /// Check for for loops that sequentially copy items from one slice-like
956 /// object to another.
957 fn detect_manual_memcpy<'a, 'tcx>(
958 cx: &LateContext<'a, 'tcx>,
964 if let Some(higher::Range {
968 }) = higher::range(cx, arg)
970 // the var must be a single name
971 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
972 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
973 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
974 ("0", _, "0", _) => "".into(),
975 ("0", _, x, false) | (x, false, "0", false) => x.into(),
976 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
977 (x, false, y, false) => format!("({} + {})", x, y),
978 (x, false, y, true) => {
982 format!("({} - {})", x, y)
985 (x, true, y, false) => {
989 format!("({} - {})", y, x)
992 (x, true, y, true) => format!("-({} + {})", x, y),
996 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
997 if let Some(end) = *end {
999 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
1000 if method.ident.name == "len";
1001 if len_args.len() == 1;
1002 if let Some(arg) = len_args.get(0);
1003 if snippet(cx, arg.span, "??") == var_name;
1005 return if offset.negate {
1006 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
1013 let end_str = match limits {
1014 ast::RangeLimits::Closed => {
1015 let end = sugg::Sugg::hir(cx, end, "<count>");
1016 format!("{}", end + sugg::ONE)
1018 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1021 print_sum(&Offset::positive(end_str), &offset)
1027 // The only statements in the for loops can be indexed assignments from
1028 // indexed retrievals.
1029 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1031 let big_sugg = manual_copies
1033 .map(|(dst_var, src_var)| {
1034 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1035 let dst_offset = print_sum(&start_str, &dst_var.offset);
1036 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1037 let src_offset = print_sum(&start_str, &src_var.offset);
1038 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1039 let dst = if dst_offset == "" && dst_limit == "" {
1042 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1046 "{}.clone_from_slice(&{}[{}..{}])",
1047 dst, src_var.var_name, src_offset, src_limit
1052 if !big_sugg.is_empty() {
1057 "it looks like you're manually copying between slices",
1058 "try replacing the loop by",
1060 Applicability::Unspecified,
1067 /// Check for looping over a range and then indexing a sequence with it.
1068 /// The iteratee must be a range literal.
1069 fn check_for_loop_range<'a, 'tcx>(
1070 cx: &LateContext<'a, 'tcx>,
1076 if in_macro(expr.span) {
1080 if let Some(higher::Range {
1084 }) = higher::range(cx, arg)
1086 // the var must be a single name
1087 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1088 let mut visitor = VarVisitor {
1091 indexed_mut: FxHashSet::default(),
1092 indexed_indirectly: FxHashMap::default(),
1093 indexed_directly: FxHashMap::default(),
1094 referenced: FxHashSet::default(),
1096 prefer_mutable: false,
1098 walk_expr(&mut visitor, body);
1100 // linting condition: we only indexed one variable, and indexed it directly
1101 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1102 let (indexed, (indexed_extent, indexed_ty)) = visitor
1106 .expect("already checked that we have exactly 1 element");
1108 // ensure that the indexed variable was declared before the loop, see #601
1109 if let Some(indexed_extent) = indexed_extent {
1110 let parent_id = cx.tcx.hir().get_parent(expr.id);
1111 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1112 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1113 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1114 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1119 // don't lint if the container that is indexed into is also used without
1121 if visitor.referenced.contains(&indexed) {
1125 let starts_at_zero = is_integer_literal(start, 0);
1127 let skip = if starts_at_zero {
1130 format!(".skip({})", snippet(cx, start.span, ".."))
1133 let mut end_is_start_plus_val = false;
1135 let take = if let Some(end) = *end {
1136 let mut take_expr = end;
1138 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1139 if let BinOpKind::Add = op.node {
1140 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1141 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1143 if start_equal_left {
1145 } else if start_equal_right {
1149 end_is_start_plus_val = start_equal_left | start_equal_right;
1153 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1157 ast::RangeLimits::Closed => {
1158 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1159 format!(".take({})", take_expr + sugg::ONE)
1161 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1168 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1169 ("mut ", "iter_mut")
1174 let take_is_empty = take.is_empty();
1175 let mut method_1 = take;
1176 let mut method_2 = skip;
1178 if end_is_start_plus_val {
1179 mem::swap(&mut method_1, &mut method_2);
1182 if visitor.nonindex {
1185 NEEDLESS_RANGE_LOOP,
1187 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1191 "consider using an iterator".to_string(),
1193 (pat.span, format!("({}, <item>)", ident.name)),
1196 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1203 let repl = if starts_at_zero && take_is_empty {
1204 format!("&{}{}", ref_mut, indexed)
1206 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1211 NEEDLESS_RANGE_LOOP,
1214 "the loop variable `{}` is only used to index `{}`.",
1220 "consider using an iterator".to_string(),
1221 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1231 fn is_len_call(expr: &Expr, var: Name) -> bool {
1233 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1234 if len_args.len() == 1;
1235 if method.ident.name == "len";
1236 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1237 if path.segments.len() == 1;
1238 if path.segments[0].ident.name == var;
1247 fn is_end_eq_array_len(cx: &LateContext<'_, '_>, end: &Expr, limits: ast::RangeLimits, indexed_ty: Ty<'_>) -> bool {
1249 if let ExprKind::Lit(ref lit) = end.node;
1250 if let ast::LitKind::Int(end_int, _) = lit.node;
1251 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1252 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1254 return match limits {
1255 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1256 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1264 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1265 // if this for loop is iterating over a two-sided range...
1266 if let Some(higher::Range {
1270 }) = higher::range(cx, arg)
1272 // ...and both sides are compile-time constant integers...
1273 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1274 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1275 // ...and the start index is greater than the end index,
1276 // this loop will never run. This is often confusing for developers
1277 // who think that this will iterate from the larger value to the
1279 let ty = cx.tables.expr_ty(start);
1280 let (sup, eq) = match (start_idx, end_idx) {
1281 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1283 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1284 ty::Uint(_) => start_idx > end_idx,
1287 start_idx == end_idx,
1289 _ => (false, false),
1293 let start_snippet = snippet(cx, start.span, "_");
1294 let end_snippet = snippet(cx, end.span, "_");
1295 let dots = if limits == ast::RangeLimits::Closed {
1305 "this range is empty so this for loop will never run",
1307 db.span_suggestion_with_applicability(
1309 "consider using the following if you are attempting to iterate over this \
1312 "({end}{dots}{start}).rev()",
1315 start = start_snippet
1317 Applicability::MaybeIncorrect,
1321 } else if eq && limits != ast::RangeLimits::Closed {
1322 // if they are equal, it's also problematic - this loop
1328 "this range is empty so this for loop will never run",
1336 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1337 let mut applicability = Applicability::MachineApplicable;
1338 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1339 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1344 "it is more concise to loop over references to containers instead of using explicit \
1346 "to write this more concisely, try",
1347 format!("&{}{}", muta, object),
1352 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1353 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1354 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1355 // just the receiver, no arguments
1356 if args.len() == 1 {
1357 let method_name = &*method.ident.as_str();
1358 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1359 if method_name == "iter" || method_name == "iter_mut" {
1360 if is_ref_iterable_type(cx, &args[0]) {
1361 lint_iter_method(cx, args, arg, method_name);
1363 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1364 let def_id = cx.tables.type_dependent_defs()[arg.hir_id].def_id();
1365 let substs = cx.tables.node_substs(arg.hir_id);
1366 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1368 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1369 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1370 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1371 match cx.tables.expr_ty(&args[0]).sty {
1372 // If the length is greater than 32 no traits are implemented for array and
1373 // therefore we cannot use `&`.
1374 ty::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1375 _ => lint_iter_method(cx, args, arg, method_name),
1378 let mut applicability = Applicability::MachineApplicable;
1379 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1382 EXPLICIT_INTO_ITER_LOOP,
1384 "it is more concise to loop over containers instead of using explicit \
1385 iteration methods`",
1386 "to write this more concisely, try",
1391 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1396 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1397 probably not what you want",
1399 next_loop_linted = true;
1403 if !next_loop_linted {
1404 check_arg_type(cx, pat, arg);
1408 /// Check for `for` loops over `Option`s and `Results`
1409 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1410 let ty = cx.tables.expr_ty(arg);
1411 if match_type(cx, ty, &paths::OPTION) {
1414 FOR_LOOP_OVER_OPTION,
1417 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1418 `if let` statement.",
1419 snippet(cx, arg.span, "_")
1422 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1423 snippet(cx, pat.span, "_"),
1424 snippet(cx, arg.span, "_")
1427 } else if match_type(cx, ty, &paths::RESULT) {
1430 FOR_LOOP_OVER_RESULT,
1433 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1434 `if let` statement.",
1435 snippet(cx, arg.span, "_")
1438 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1439 snippet(cx, pat.span, "_"),
1440 snippet(cx, arg.span, "_")
1446 fn check_for_loop_explicit_counter<'a, 'tcx>(
1447 cx: &LateContext<'a, 'tcx>,
1452 // Look for variables that are incremented once per loop iteration.
1453 let mut visitor = IncrementVisitor {
1455 states: FxHashMap::default(),
1459 walk_expr(&mut visitor, body);
1461 // For each candidate, check the parent block to see if
1462 // it's initialized to zero at the start of the loop.
1463 let map = &cx.tcx.hir();
1464 let parent_scope = map
1465 .get_enclosing_scope(expr.id)
1466 .and_then(|id| map.get_enclosing_scope(id));
1467 if let Some(parent_id) = parent_scope {
1468 if let Node::Block(block) = map.get(parent_id) {
1469 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1470 let mut visitor2 = InitializeVisitor {
1474 state: VarState::IncrOnce,
1479 walk_block(&mut visitor2, block);
1481 if visitor2.state == VarState::Warn {
1482 if let Some(name) = visitor2.name {
1485 EXPLICIT_COUNTER_LOOP,
1488 "the variable `{0}` is used as a loop counter. Consider using `for ({0}, \
1489 item) in {1}.enumerate()` or similar iterators",
1491 snippet(cx, arg.span, "_")
1501 /// Check for the `FOR_KV_MAP` lint.
1502 fn check_for_loop_over_map_kv<'a, 'tcx>(
1503 cx: &LateContext<'a, 'tcx>,
1509 let pat_span = pat.span;
1511 if let PatKind::Tuple(ref pat, _) = pat.node {
1513 let arg_span = arg.span;
1514 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1515 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1516 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1517 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1522 let mutbl = match mutbl {
1524 MutMutable => "_mut",
1526 let arg = match arg.node {
1527 ExprKind::AddrOf(_, ref expr) => &**expr,
1531 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1536 &format!("you seem to want to iterate on a map's {}s", kind),
1538 let map = sugg::Sugg::hir(cx, arg, "map");
1541 "use the corresponding method".into(),
1543 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1544 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1554 struct MutatePairDelegate {
1555 node_id_low: Option<NodeId>,
1556 node_id_high: Option<NodeId>,
1557 span_low: Option<Span>,
1558 span_high: Option<Span>,
1561 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1562 fn consume(&mut self, _: NodeId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1564 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1566 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1568 fn borrow(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1569 if let ty::BorrowKind::MutBorrow = bk {
1570 if let Categorization::Local(id) = cmt.cat {
1571 if Some(id) == self.node_id_low {
1572 self.span_low = Some(sp)
1574 if Some(id) == self.node_id_high {
1575 self.span_high = Some(sp)
1581 fn mutate(&mut self, _: NodeId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1582 if let Categorization::Local(id) = cmt.cat {
1583 if Some(id) == self.node_id_low {
1584 self.span_low = Some(sp)
1586 if Some(id) == self.node_id_high {
1587 self.span_high = Some(sp)
1592 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1595 impl<'tcx> MutatePairDelegate {
1596 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1597 (self.span_low, self.span_high)
1601 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1602 if let Some(higher::Range {
1606 }) = higher::range(cx, arg)
1608 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1609 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1610 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1611 mut_warn_with_span(cx, span_low);
1612 mut_warn_with_span(cx, span_high);
1617 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1618 if let Some(sp) = span {
1623 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1628 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<NodeId> {
1630 if let ExprKind::Path(ref qpath) = bound.node;
1631 if let QPath::Resolved(None, _) = *qpath;
1633 let def = cx.tables.qpath_def(qpath, bound.hir_id);
1634 if let Def::Local(node_id) = def {
1635 let node_str = cx.tcx.hir().get(node_id);
1637 if let Node::Binding(pat) = node_str;
1638 if let PatKind::Binding(bind_ann, _, _, _) = pat.node;
1639 if let BindingAnnotation::Mutable = bind_ann;
1641 return Some(node_id);
1650 fn check_for_mutation(
1651 cx: &LateContext<'_, '_>,
1653 bound_ids: &[Option<NodeId>],
1654 ) -> (Option<Span>, Option<Span>) {
1655 let mut delegate = MutatePairDelegate {
1656 node_id_low: bound_ids[0],
1657 node_id_high: bound_ids[1],
1661 let def_id = def_id::DefId::local(body.hir_id.owner);
1662 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1663 ExprUseVisitor::new(&mut delegate, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None).walk_expr(body);
1664 delegate.mutation_span()
1667 /// Return true if the pattern is a `PatWild` or an ident prefixed with `'_'`.
1668 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1670 PatKind::Wild => true,
1671 PatKind::Binding(_, _, ident, None) if ident.as_str().starts_with('_') => {
1672 let mut visitor = UsedVisitor {
1676 walk_expr(&mut visitor, body);
1683 struct UsedVisitor {
1684 var: ast::Name, // var to look for
1685 used: bool, // has the var been used otherwise?
1688 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1689 fn visit_expr(&mut self, expr: &'tcx Expr) {
1690 if match_var(expr, self.var) {
1693 walk_expr(self, expr);
1697 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1698 NestedVisitorMap::None
1702 struct LocalUsedVisitor<'a, 'tcx: 'a> {
1703 cx: &'a LateContext<'a, 'tcx>,
1708 impl<'a, 'tcx: 'a> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1709 fn visit_expr(&mut self, expr: &'tcx Expr) {
1710 if same_var(self.cx, expr, self.local) {
1713 walk_expr(self, expr);
1717 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1718 NestedVisitorMap::None
1722 struct VarVisitor<'a, 'tcx: 'a> {
1723 /// context reference
1724 cx: &'a LateContext<'a, 'tcx>,
1725 /// var name to look for as index
1727 /// indexed variables that are used mutably
1728 indexed_mut: FxHashSet<Name>,
1729 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1730 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1731 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1732 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1733 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1734 /// Any names that are used outside an index operation.
1735 /// Used to detect things like `&mut vec` used together with `vec[i]`
1736 referenced: FxHashSet<Name>,
1737 /// has the loop variable been used in expressions other than the index of
1740 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1741 /// takes `&mut self`
1742 prefer_mutable: bool,
1745 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1746 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1748 // the indexed container is referenced by a name
1749 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1750 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1751 if seqvar.segments.len() == 1;
1753 let index_used_directly = same_var(self.cx, idx, self.var);
1754 let indexed_indirectly = {
1755 let mut used_visitor = LocalUsedVisitor {
1760 walk_expr(&mut used_visitor, idx);
1764 if indexed_indirectly || index_used_directly {
1765 if self.prefer_mutable {
1766 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1768 let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
1770 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
1771 let hir_id = self.cx.tcx.hir().node_to_hir_id(node_id);
1773 let parent_id = self.cx.tcx.hir().get_parent(expr.id);
1774 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1775 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1776 if indexed_indirectly {
1777 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1779 if index_used_directly {
1780 self.indexed_directly.insert(
1781 seqvar.segments[0].ident.name,
1782 (Some(extent), self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1785 return false; // no need to walk further *on the variable*
1787 Def::Static(..) | Def::Const(..) => {
1788 if indexed_indirectly {
1789 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1791 if index_used_directly {
1792 self.indexed_directly.insert(
1793 seqvar.segments[0].ident.name,
1794 (None, self.cx.tables.node_id_to_type(seqexpr.hir_id)),
1797 return false; // no need to walk further *on the variable*
1808 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1809 fn visit_expr(&mut self, expr: &'tcx Expr) {
1812 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1813 if (meth.ident.name == "index" && match_trait_method(self.cx, expr, &paths::INDEX))
1814 || (meth.ident.name == "index_mut" && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1815 if !self.check(&args[1], &args[0], expr);
1821 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1822 if !self.check(idx, seqexpr, expr);
1827 // directly using a variable
1828 if let ExprKind::Path(ref qpath) = expr.node;
1829 if let QPath::Resolved(None, ref path) = *qpath;
1830 if path.segments.len() == 1;
1831 if let Def::Local(local_id) = self.cx.tables.qpath_def(qpath, expr.hir_id);
1833 if local_id == self.var {
1834 // we are not indexing anything, record that
1835 self.nonindex = true;
1837 // not the correct variable, but still a variable
1838 self.referenced.insert(path.segments[0].ident.name);
1842 let old = self.prefer_mutable;
1844 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1845 self.prefer_mutable = true;
1846 self.visit_expr(lhs);
1847 self.prefer_mutable = false;
1848 self.visit_expr(rhs);
1850 ExprKind::AddrOf(mutbl, ref expr) => {
1851 if mutbl == MutMutable {
1852 self.prefer_mutable = true;
1854 self.visit_expr(expr);
1856 ExprKind::Call(ref f, ref args) => {
1859 let ty = self.cx.tables.expr_ty_adjusted(expr);
1860 self.prefer_mutable = false;
1861 if let ty::Ref(_, _, mutbl) = ty.sty {
1862 if mutbl == MutMutable {
1863 self.prefer_mutable = true;
1866 self.visit_expr(expr);
1869 ExprKind::MethodCall(_, _, ref args) => {
1870 let def_id = self.cx.tables.type_dependent_defs()[expr.hir_id].def_id();
1871 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1872 self.prefer_mutable = false;
1873 if let ty::Ref(_, _, mutbl) = ty.sty {
1874 if mutbl == MutMutable {
1875 self.prefer_mutable = true;
1878 self.visit_expr(expr);
1881 _ => walk_expr(self, expr),
1883 self.prefer_mutable = old;
1885 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1886 NestedVisitorMap::None
1890 fn is_used_inside<'a, 'tcx: 'a>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1891 let def_id = match var_def_id(cx, expr) {
1893 None => return false,
1895 if let Some(used_mutably) = mutated_variables(container, cx) {
1896 if used_mutably.contains(&def_id) {
1903 fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1904 let def_id = match var_def_id(cx, iter_expr) {
1906 None => return false,
1908 let mut visitor = VarUsedAfterLoopVisitor {
1911 iter_expr_id: iter_expr.id,
1912 past_while_let: false,
1913 var_used_after_while_let: false,
1915 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1916 walk_block(&mut visitor, enclosing_block);
1918 visitor.var_used_after_while_let
1921 struct VarUsedAfterLoopVisitor<'a, 'tcx: 'a> {
1922 cx: &'a LateContext<'a, 'tcx>,
1924 iter_expr_id: NodeId,
1925 past_while_let: bool,
1926 var_used_after_while_let: bool,
1929 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1930 fn visit_expr(&mut self, expr: &'tcx Expr) {
1931 if self.past_while_let {
1932 if Some(self.def_id) == var_def_id(self.cx, expr) {
1933 self.var_used_after_while_let = true;
1935 } else if self.iter_expr_id == expr.id {
1936 self.past_while_let = true;
1938 walk_expr(self, expr);
1940 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1941 NestedVisitorMap::None
1945 /// Return true if the type of expr is one that provides `IntoIterator` impls
1946 /// for `&T` and `&mut T`, such as `Vec`.
1948 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1949 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1950 // will allow further borrows afterwards
1951 let ty = cx.tables.expr_ty(e);
1952 is_iterable_array(ty, cx) ||
1953 match_type(cx, ty, &paths::VEC) ||
1954 match_type(cx, ty, &paths::LINKED_LIST) ||
1955 match_type(cx, ty, &paths::HASHMAP) ||
1956 match_type(cx, ty, &paths::HASHSET) ||
1957 match_type(cx, ty, &paths::VEC_DEQUE) ||
1958 match_type(cx, ty, &paths::BINARY_HEAP) ||
1959 match_type(cx, ty, &paths::BTREEMAP) ||
1960 match_type(cx, ty, &paths::BTREESET)
1963 fn is_iterable_array(ty: Ty<'_>, cx: &LateContext<'_, '_>) -> bool {
1964 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1966 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1971 /// If a block begins with a statement (possibly a `let` binding) and has an
1972 /// expression, return it.
1973 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1974 if block.stmts.is_empty() {
1977 if let StmtKind::Local(ref local) = block.stmts[0].node {
1978 if let Some(ref expr) = local.init {
1988 /// If a block begins with an expression (with or without semicolon), return it.
1989 fn extract_first_expr(block: &Block) -> Option<&Expr> {
1991 Some(ref expr) if block.stmts.is_empty() => Some(expr),
1992 None if !block.stmts.is_empty() => match block.stmts[0].node {
1993 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
1994 StmtKind::Local(..) | StmtKind::Item(..) => None,
2000 /// Return true if expr contains a single break expr without destination label
2002 /// passed expression. The expression may be within a block.
2003 fn is_simple_break_expr(expr: &Expr) -> bool {
2005 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2006 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2007 Some(subexpr) => is_simple_break_expr(subexpr),
2014 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2015 // incremented exactly once in the loop body, and initialized to zero
2016 // at the start of the loop.
2017 #[derive(PartialEq)]
2019 Initial, // Not examined yet
2020 IncrOnce, // Incremented exactly once, may be a loop counter
2021 Declared, // Declared but not (yet) initialized to zero
2026 /// Scan a for loop for variables that are incremented exactly once.
2027 struct IncrementVisitor<'a, 'tcx: 'a> {
2028 cx: &'a LateContext<'a, 'tcx>, // context reference
2029 states: FxHashMap<NodeId, VarState>, // incremented variables
2030 depth: u32, // depth of conditional expressions
2034 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2035 fn visit_expr(&mut self, expr: &'tcx Expr) {
2040 // If node is a variable
2041 if let Some(def_id) = var_def_id(self.cx, expr) {
2042 if let Some(parent) = get_parent_expr(self.cx, expr) {
2043 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2046 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2047 if lhs.id == expr.id {
2048 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2049 *state = match *state {
2050 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2051 _ => VarState::DontWarn,
2054 // Assigned some other value
2055 *state = VarState::DontWarn;
2059 ExprKind::Assign(ref lhs, _) if lhs.id == expr.id => *state = VarState::DontWarn,
2060 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2064 } else if is_loop(expr) || is_conditional(expr) {
2066 walk_expr(self, expr);
2069 } else if let ExprKind::Continue(_) = expr.node {
2073 walk_expr(self, expr);
2075 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2076 NestedVisitorMap::None
2080 /// Check whether a variable is initialized to zero at the start of a loop.
2081 struct InitializeVisitor<'a, 'tcx: 'a> {
2082 cx: &'a LateContext<'a, 'tcx>, // context reference
2083 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2087 depth: u32, // depth of conditional expressions
2091 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2092 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2093 // Look for declarations of the variable
2094 if let StmtKind::Local(ref local) = stmt.node {
2095 if local.pat.id == self.var_id {
2096 if let PatKind::Binding(_, _, ident, _) = local.pat.node {
2097 self.name = Some(ident.name);
2099 self.state = if let Some(ref init) = local.init {
2100 if is_integer_literal(init, 0) {
2111 walk_stmt(self, stmt);
2114 fn visit_expr(&mut self, expr: &'tcx Expr) {
2115 if self.state == VarState::DontWarn {
2118 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2119 self.past_loop = true;
2122 // No need to visit expressions before the variable is
2124 if self.state == VarState::IncrOnce {
2128 // If node is the desired variable, see how it's used
2129 if var_def_id(self.cx, expr) == Some(self.var_id) {
2130 if let Some(parent) = get_parent_expr(self.cx, expr) {
2132 ExprKind::AssignOp(_, ref lhs, _) if lhs.id == expr.id => {
2133 self.state = VarState::DontWarn;
2135 ExprKind::Assign(ref lhs, ref rhs) if lhs.id == expr.id => {
2136 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2142 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2148 self.state = VarState::DontWarn;
2151 } else if !self.past_loop && is_loop(expr) {
2152 self.state = VarState::DontWarn;
2154 } else if is_conditional(expr) {
2156 walk_expr(self, expr);
2160 walk_expr(self, expr);
2162 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2163 NestedVisitorMap::None
2167 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<NodeId> {
2168 if let ExprKind::Path(ref qpath) = expr.node {
2169 let path_res = cx.tables.qpath_def(qpath, expr.hir_id);
2170 if let Def::Local(node_id) = path_res {
2171 return Some(node_id);
2177 fn is_loop(expr: &Expr) -> bool {
2179 ExprKind::Loop(..) | ExprKind::While(..) => true,
2184 fn is_conditional(expr: &Expr) -> bool {
2186 ExprKind::If(..) | ExprKind::Match(..) => true,
2191 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2193 if let Some(loop_block) = get_enclosing_block(cx, match_expr.id);
2194 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(loop_block.id));
2196 return is_loop_nested(cx, loop_expr, iter_expr)
2202 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2203 let mut id = loop_expr.id;
2204 let iter_name = if let Some(name) = path_name(iter_expr) {
2210 let parent = cx.tcx.hir().get_parent_node(id);
2214 match cx.tcx.hir().find(parent) {
2215 Some(Node::Expr(expr)) => match expr.node {
2216 ExprKind::Loop(..) | ExprKind::While(..) => {
2221 Some(Node::Block(block)) => {
2222 let mut block_visitor = LoopNestVisitor {
2224 iterator: iter_name,
2227 walk_block(&mut block_visitor, block);
2228 if block_visitor.nesting == RuledOut {
2232 Some(Node::Stmt(_)) => (),
2241 #[derive(PartialEq, Eq)]
2243 Unknown, // no nesting detected yet
2244 RuledOut, // the iterator is initialized or assigned within scope
2245 LookFurther, // no nesting detected, no further walk required
2248 use self::Nesting::{LookFurther, RuledOut, Unknown};
2250 struct LoopNestVisitor {
2256 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2257 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2258 if stmt.id == self.id {
2259 self.nesting = LookFurther;
2260 } else if self.nesting == Unknown {
2261 walk_stmt(self, stmt);
2265 fn visit_expr(&mut self, expr: &'tcx Expr) {
2266 if self.nesting != Unknown {
2269 if expr.id == self.id {
2270 self.nesting = LookFurther;
2274 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2275 if match_var(path, self.iterator) {
2276 self.nesting = RuledOut;
2279 _ => walk_expr(self, expr),
2283 fn visit_pat(&mut self, pat: &'tcx Pat) {
2284 if self.nesting != Unknown {
2287 if let PatKind::Binding(_, _, span_name, _) = pat.node {
2288 if self.iterator == span_name.name {
2289 self.nesting = RuledOut;
2296 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2297 NestedVisitorMap::None
2301 fn path_name(e: &Expr) -> Option<Name> {
2302 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2303 let segments = &path.segments;
2304 if segments.len() == 1 {
2305 return Some(segments[0].ident.name);
2311 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2312 if constant(cx, cx.tables, cond).is_some() {
2313 // A pure constant condition (e.g. while false) is not linted.
2317 let mut var_visitor = VarCollectorVisitor {
2319 ids: FxHashSet::default(),
2320 def_ids: FxHashMap::default(),
2323 var_visitor.visit_expr(cond);
2324 if var_visitor.skip {
2327 let used_in_condition = &var_visitor.ids;
2328 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2329 used_in_condition.is_disjoint(&used_mutably)
2333 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2334 if no_cond_variable_mutated && !mutable_static_in_cond {
2337 WHILE_IMMUTABLE_CONDITION,
2339 "Variable in the condition are not mutated in the loop body. \
2340 This either leads to an infinite or to a never running loop.",
2345 /// Collects the set of variables in an expression
2346 /// Stops analysis if a function call is found
2347 /// Note: In some cases such as `self`, there are no mutable annotation,
2348 /// All variables definition IDs are collected
2349 struct VarCollectorVisitor<'a, 'tcx: 'a> {
2350 cx: &'a LateContext<'a, 'tcx>,
2351 ids: FxHashSet<NodeId>,
2352 def_ids: FxHashMap<def_id::DefId, bool>,
2356 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2357 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2359 if let ExprKind::Path(ref qpath) = ex.node;
2360 if let QPath::Resolved(None, _) = *qpath;
2361 let def = self.cx.tables.qpath_def(qpath, ex.hir_id);
2364 Def::Local(node_id) | Def::Upvar(node_id, ..) => {
2365 self.ids.insert(node_id);
2367 Def::Static(def_id, mutable) => {
2368 self.def_ids.insert(def_id, mutable);
2377 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2378 fn visit_expr(&mut self, ex: &'tcx Expr) {
2380 ExprKind::Path(_) => self.insert_def_id(ex),
2381 // If there is any function/method call… we just stop analysis
2382 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2384 _ => walk_expr(self, ex),
2388 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2389 NestedVisitorMap::None
2393 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2395 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2397 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2398 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2399 if chain_method.ident.name == "collect" && match_trait_method(cx, &args[0], &paths::ITERATOR);
2400 if let Some(ref generic_args) = chain_method.args;
2401 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2403 let ty = cx.tables.node_id_to_type(ty.hir_id);
2404 if match_type(cx, ty, &paths::VEC) ||
2405 match_type(cx, ty, &paths::VEC_DEQUE) ||
2406 match_type(cx, ty, &paths::BTREEMAP) ||
2407 match_type(cx, ty, &paths::HASHMAP) {
2408 if method.ident.name == "len" {
2409 let span = shorten_needless_collect_span(expr);
2410 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2411 db.span_suggestion_with_applicability(
2414 ".count()".to_string(),
2415 Applicability::MachineApplicable,
2419 if method.ident.name == "is_empty" {
2420 let span = shorten_needless_collect_span(expr);
2421 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2422 db.span_suggestion_with_applicability(
2425 ".next().is_none()".to_string(),
2426 Applicability::MachineApplicable,
2430 if method.ident.name == "contains" {
2431 let contains_arg = snippet(cx, args[1].span, "??");
2432 let span = shorten_needless_collect_span(expr);
2433 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2434 db.span_suggestion_with_applicability(
2438 ".any(|&x| x == {})",
2439 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2441 Applicability::MachineApplicable,
2450 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2452 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2453 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2455 return expr.span.with_lo(span.lo() - BytePos(1));