1 use crate::reexport::*;
2 use if_chain::if_chain;
3 use itertools::Itertools;
4 use rustc::hir::def::{DefKind, Res};
5 use rustc::hir::def_id;
6 use rustc::hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
8 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
9 use rustc::middle::region;
10 use rustc::{declare_lint_pass, declare_tool_lint};
11 // use rustc::middle::region::CodeExtent;
12 use crate::consts::{constant, Constant};
13 use crate::utils::usage::mutated_variables;
14 use crate::utils::{is_type_diagnostic_item, qpath_res, 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, Symbol};
28 use crate::utils::paths;
30 get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
31 is_integer_const, is_refutable, last_path_segment, match_trait_method, match_type, match_var, multispan_sugg,
32 snippet, snippet_opt, snippet_with_applicability, span_help_and_lint, span_lint, span_lint_and_sugg,
33 span_lint_and_then, SpanlessEq,
36 declare_clippy_lint! {
37 /// **What it does:** Checks for for-loops that manually copy items between
38 /// slices that could be optimized by having a memcpy.
40 /// **Why is this bad?** It is not as fast as a memcpy.
42 /// **Known problems:** None.
46 /// # let src = vec![1];
47 /// # let mut dst = vec![0; 65];
48 /// for i in 0..src.len() {
49 /// dst[i + 64] = src[i];
52 /// Could be written as:
54 /// # let src = vec![1];
55 /// # let mut dst = vec![0; 65];
56 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
60 "manually copying items between slices"
63 declare_clippy_lint! {
64 /// **What it does:** Checks for looping over the range of `0..len` of some
65 /// collection just to get the values by index.
67 /// **Why is this bad?** Just iterating the collection itself makes the intent
68 /// more clear and is probably faster.
70 /// **Known problems:** None.
74 /// let vec = vec!['a', 'b', 'c'];
75 /// for i in 0..vec.len() {
76 /// println!("{}", vec[i]);
79 /// Could be written as:
81 /// let vec = vec!['a', 'b', 'c'];
83 /// println!("{}", i);
86 pub NEEDLESS_RANGE_LOOP,
88 "for-looping over a range of indices where an iterator over items would do"
91 declare_clippy_lint! {
92 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
93 /// suggests the latter.
95 /// **Why is this bad?** Readability.
97 /// **Known problems:** False negatives. We currently only warn on some known
102 /// // with `y` a `Vec` or slice:
103 /// # let y = vec![1];
104 /// for x in y.iter() {
108 /// can be rewritten to
110 /// # let y = vec![1];
115 pub EXPLICIT_ITER_LOOP,
117 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
120 declare_clippy_lint! {
121 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
122 /// suggests the latter.
124 /// **Why is this bad?** Readability.
126 /// **Known problems:** None
130 /// # let y = vec![1];
131 /// // with `y` a `Vec` or slice:
132 /// for x in y.into_iter() {
136 /// can be rewritten to
138 /// # let y = vec![1];
143 pub EXPLICIT_INTO_ITER_LOOP,
145 "for-looping over `_.into_iter()` when `_` would do"
148 declare_clippy_lint! {
149 /// **What it does:** Checks for loops on `x.next()`.
151 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
152 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
153 /// implements `IntoIterator`, so that possibly one value will be iterated,
154 /// leading to some hard to find bugs. No one will want to write such code
155 /// [except to win an Underhanded Rust
156 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
158 /// **Known problems:** None.
162 /// for x in y.next() {
168 "for-looping over `_.next()` which is probably not intended"
171 declare_clippy_lint! {
172 /// **What it does:** Checks for `for` loops over `Option` values.
174 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
177 /// **Known problems:** None.
181 /// for x in option {
188 /// if let Some(x) = option {
192 pub FOR_LOOP_OVER_OPTION,
194 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
197 declare_clippy_lint! {
198 /// **What it does:** Checks for `for` loops over `Result` values.
200 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
203 /// **Known problems:** None.
207 /// for x in result {
214 /// if let Ok(x) = result {
218 pub FOR_LOOP_OVER_RESULT,
220 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
223 declare_clippy_lint! {
224 /// **What it does:** Detects `loop + match` combinations that are easier
225 /// written as a `while let` loop.
227 /// **Why is this bad?** The `while let` loop is usually shorter and more
230 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
234 /// # let y = Some(1);
236 /// let x = match y {
240 /// // .. do something with x
242 /// // is easier written as
243 /// while let Some(x) = y {
244 /// // .. do something with x
249 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
252 declare_clippy_lint! {
253 /// **What it does:** Checks for functions collecting an iterator when collect
256 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
257 /// when this allocation may not be needed.
259 /// **Known problems:**
264 /// # let iterator = vec![1].into_iter();
265 /// let len = iterator.clone().collect::<Vec<_>>().len();
267 /// let len = iterator.count();
269 pub NEEDLESS_COLLECT,
271 "collecting an iterator when collect is not needed"
274 declare_clippy_lint! {
275 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
276 /// are constant and `x` is greater or equal to `y`, unless the range is
277 /// reversed or has a negative `.step_by(_)`.
279 /// **Why is it bad?** Such loops will either be skipped or loop until
280 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
283 /// **Known problems:** The lint cannot catch loops over dynamically defined
284 /// ranges. Doing this would require simulating all possible inputs and code
285 /// paths through the program, which would be complex and error-prone.
289 /// for x in 5..10 - 5 {
291 /// } // oops, stray `-`
293 pub REVERSE_RANGE_LOOP,
295 "iteration over an empty range, such as `10..0` or `5..5`"
298 declare_clippy_lint! {
299 /// **What it does:** Checks `for` loops over slices with an explicit counter
300 /// and suggests the use of `.enumerate()`.
302 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
303 /// declutters the code and may be faster in some instances.
305 /// **Known problems:** None.
309 /// # let v = vec![1];
310 /// # fn bar(bar: usize, baz: usize) {}
317 /// Could be written as
319 /// # let v = vec![1];
320 /// # fn bar(bar: usize, baz: usize) {}
321 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
323 pub EXPLICIT_COUNTER_LOOP,
325 "for-looping with an explicit counter when `_.enumerate()` would do"
328 declare_clippy_lint! {
329 /// **What it does:** Checks for empty `loop` expressions.
331 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
332 /// anything. Think of the environment and either block on something or at least
333 /// make the thread sleep for some microseconds.
335 /// **Known problems:** None.
343 "empty `loop {}`, which should block or sleep"
346 declare_clippy_lint! {
347 /// **What it does:** Checks for `while let` expressions on iterators.
349 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
350 /// the intent better.
352 /// **Known problems:** None.
356 /// while let Some(val) = iter() {
360 pub WHILE_LET_ON_ITERATOR,
362 "using a while-let loop instead of a for loop on an iterator"
365 declare_clippy_lint! {
366 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
367 /// ignoring either the keys or values.
369 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
370 /// can be used to express that don't need the values or keys.
372 /// **Known problems:** None.
376 /// for (k, _) in &map {
381 /// could be replaced by
384 /// for k in map.keys() {
390 "looping on a map using `iter` when `keys` or `values` would do"
393 declare_clippy_lint! {
394 /// **What it does:** Checks for loops that will always `break`, `return` or
395 /// `continue` an outer loop.
397 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
400 /// **Known problems:** None
411 "any loop that will always `break` or `return`"
414 declare_clippy_lint! {
415 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
417 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
419 /// **Known problems:** None
423 /// let mut foo = 42;
424 /// for i in 0..foo {
426 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
431 "for loop over a range where one of the bounds is a mutable variable"
434 declare_clippy_lint! {
435 /// **What it does:** Checks whether variables used within while loop condition
436 /// can be (and are) mutated in the body.
438 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
439 /// will lead to an infinite loop.
441 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
442 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
443 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
449 /// println!("let me loop forever!");
452 pub WHILE_IMMUTABLE_CONDITION,
454 "variables used within while expression are not mutated in the body"
457 declare_lint_pass!(Loops => [
461 EXPLICIT_INTO_ITER_LOOP,
463 FOR_LOOP_OVER_RESULT,
464 FOR_LOOP_OVER_OPTION,
468 EXPLICIT_COUNTER_LOOP,
470 WHILE_LET_ON_ITERATOR,
474 WHILE_IMMUTABLE_CONDITION,
477 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
478 #[allow(clippy::too_many_lines)]
479 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
480 if let Some((pat, arg, body)) = higher::for_loop(expr) {
481 // we don't want to check expanded macros
482 // this check is not at the top of the function
483 // since higher::for_loop expressions are marked as expansions
484 if body.span.from_expansion() {
487 check_for_loop(cx, pat, arg, body, expr);
490 // we don't want to check expanded macros
491 if expr.span.from_expansion() {
495 // check for never_loop
496 if let ExprKind::Loop(ref block, _, _) = expr.kind {
497 match never_loop_block(block, expr.hir_id) {
498 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
499 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
503 // check for `loop { if let {} else break }` that could be `while let`
504 // (also matches an explicit "match" instead of "if let")
505 // (even if the "match" or "if let" is used for declaration)
506 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
507 // also check for empty `loop {}` statements
508 if block.stmts.is_empty() && block.expr.is_none() {
513 "empty `loop {}` detected. You may want to either use `panic!()` or add \
514 `std::thread::sleep(..);` to the loop body.",
518 // extract the expression from the first statement (if any) in a block
519 let inner_stmt_expr = extract_expr_from_first_stmt(block);
520 // or extract the first expression (if any) from the block
521 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
522 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
523 // ensure "if let" compatible match structure
525 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
527 && arms[0].guard.is_none()
528 && arms[1].guard.is_none()
529 && is_simple_break_expr(&arms[1].body)
531 if in_external_macro(cx.sess(), expr.span) {
535 // NOTE: we used to build a body here instead of using
536 // ellipsis, this was removed because:
537 // 1) it was ugly with big bodies;
538 // 2) it was not indented properly;
539 // 3) it wasn’t very smart (see #675).
540 let mut applicability = Applicability::HasPlaceholders;
545 "this loop could be written as a `while let` loop",
548 "while let {} = {} {{ .. }}",
549 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
550 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
561 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
562 let pat = &arms[0].pat.kind;
564 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
565 &ExprKind::MethodCall(ref method_path, _, ref method_args),
566 ) = (pat, &match_expr.kind)
568 let iter_expr = &method_args[0];
569 let lhs_constructor = last_path_segment(qpath);
570 if method_path.ident.name == sym!(next)
571 && match_trait_method(cx, match_expr, &paths::ITERATOR)
572 && lhs_constructor.ident.name == sym!(Some)
573 && (pat_args.is_empty()
574 || !is_refutable(cx, &pat_args[0])
575 && !is_used_inside(cx, iter_expr, &arms[0].body)
576 && !is_iterator_used_after_while_let(cx, iter_expr)
577 && !is_nested(cx, expr, &method_args[0]))
579 let iterator = snippet(cx, method_args[0].span, "_");
580 let loop_var = if pat_args.is_empty() {
583 snippet(cx, pat_args[0].span, "_").into_owned()
587 WHILE_LET_ON_ITERATOR,
589 "this loop could be written as a `for` loop",
591 format!("for {} in {} {{ .. }}", loop_var, iterator),
592 Applicability::HasPlaceholders,
598 if let Some((cond, body)) = higher::while_loop(&expr) {
599 check_infinite_loop(cx, cond, body);
602 check_needless_collect(expr, cx);
606 enum NeverLoopResult {
607 // A break/return always get triggered but not necessarily for the main loop.
609 // A continue may occur for the main loop.
615 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
617 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
618 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
622 // Combine two results for parts that are called in order.
624 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
626 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
627 NeverLoopResult::Otherwise => second,
631 // Combine two results where both parts are called but not necessarily in order.
633 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
634 match (left, right) {
635 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
636 NeverLoopResult::MayContinueMainLoop
638 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
639 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
643 // Combine two results where only one of the part may have been executed.
645 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
647 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
648 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
649 NeverLoopResult::MayContinueMainLoop
651 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
655 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
656 let stmts = block.stmts.iter().map(stmt_to_expr);
657 let expr = once(block.expr.as_ref().map(|p| &**p));
658 let mut iter = stmts.chain(expr).filter_map(|e| e);
659 never_loop_expr_seq(&mut iter, main_loop_id)
662 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
664 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
665 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
670 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
673 | ExprKind::Unary(_, ref e)
674 | ExprKind::Cast(ref e, _)
675 | ExprKind::Type(ref e, _)
676 | ExprKind::Field(ref e, _)
677 | ExprKind::AddrOf(_, ref e)
678 | ExprKind::Struct(_, _, Some(ref e))
679 | ExprKind::Repeat(ref e, _)
680 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
681 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
682 never_loop_expr_all(&mut es.iter(), main_loop_id)
684 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
685 ExprKind::Binary(_, ref e1, ref e2)
686 | ExprKind::Assign(ref e1, ref e2)
687 | ExprKind::AssignOp(_, ref e1, ref e2)
688 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
689 ExprKind::Loop(ref b, _, _) => {
690 // Break can come from the inner loop so remove them.
691 absorb_break(&never_loop_block(b, main_loop_id))
693 ExprKind::Match(ref e, ref arms, _) => {
694 let e = never_loop_expr(e, main_loop_id);
698 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
702 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
703 ExprKind::Continue(d) => {
706 .expect("target ID can only be missing in the presence of compilation errors");
707 if id == main_loop_id {
708 NeverLoopResult::MayContinueMainLoop
710 NeverLoopResult::AlwaysBreak
713 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
714 if let Some(ref e) = *e {
715 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
717 NeverLoopResult::AlwaysBreak
720 ExprKind::Struct(_, _, None)
721 | ExprKind::Yield(_, _)
722 | ExprKind::Closure(_, _, _, _, _)
723 | ExprKind::InlineAsm(_)
726 | ExprKind::Err => NeverLoopResult::Otherwise,
730 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
731 es.map(|e| never_loop_expr(e, main_loop_id))
732 .fold(NeverLoopResult::Otherwise, combine_seq)
735 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
736 es.map(|e| never_loop_expr(e, main_loop_id))
737 .fold(NeverLoopResult::Otherwise, combine_both)
740 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
741 e.map(|e| never_loop_expr(e, main_loop_id))
742 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
745 fn check_for_loop<'a, 'tcx>(
746 cx: &LateContext<'a, 'tcx>,
752 check_for_loop_range(cx, pat, arg, body, expr);
753 check_for_loop_reverse_range(cx, arg, expr);
754 check_for_loop_arg(cx, pat, arg, expr);
755 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
756 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
757 check_for_mut_range_bound(cx, arg, body);
758 detect_manual_memcpy(cx, pat, arg, body, expr);
761 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
763 if let ExprKind::Path(ref qpath) = expr.kind;
764 if let QPath::Resolved(None, ref path) = *qpath;
765 if path.segments.len() == 1;
766 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
783 fn negative(s: String) -> Self {
784 Self { value: s, negate: true }
787 fn positive(s: String) -> Self {
795 struct FixedOffsetVar {
800 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
801 let is_slice = match ty.kind {
802 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
803 ty::Slice(..) | ty::Array(..) => true,
807 is_slice || is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) || match_type(cx, ty, &paths::VEC_DEQUE)
810 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
811 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
813 ExprKind::Lit(ref l) => match l.node {
814 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
817 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
822 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind {
823 let ty = cx.tables.expr_ty(seqexpr);
824 if !is_slice_like(cx, ty) {
828 let offset = match idx.kind {
829 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
831 let offset_opt = if same_var(cx, lhs, var) {
832 extract_offset(cx, rhs, var)
833 } else if same_var(cx, rhs, var) {
834 extract_offset(cx, lhs, var)
839 offset_opt.map(Offset::positive)
841 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
844 ExprKind::Path(..) => {
845 if same_var(cx, idx, var) {
846 Some(Offset::positive("0".into()))
854 offset.map(|o| FixedOffsetVar {
855 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
863 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
864 cx: &LateContext<'a, 'tcx>,
867 ) -> Option<FixedOffsetVar> {
869 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
870 if method.ident.name == sym!(clone);
872 if let Some(arg) = args.get(0);
874 return get_fixed_offset_var(cx, arg, var);
878 get_fixed_offset_var(cx, expr, var)
881 fn get_indexed_assignments<'a, 'tcx>(
882 cx: &LateContext<'a, 'tcx>,
885 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
886 fn get_assignment<'a, 'tcx>(
887 cx: &LateContext<'a, 'tcx>,
890 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
891 if let ExprKind::Assign(ref lhs, ref rhs) = e.kind {
893 get_fixed_offset_var(cx, lhs, var),
894 fetch_cloned_fixed_offset_var(cx, rhs, var),
896 (Some(offset_left), Some(offset_right)) => {
897 // Source and destination must be different
898 if offset_left.var_name == offset_right.var_name {
901 Some((offset_left, offset_right))
911 if let ExprKind::Block(ref b, _) = body.kind {
913 ref stmts, ref expr, ..
918 .map(|stmt| match stmt.kind {
919 StmtKind::Local(..) | StmtKind::Item(..) => None,
920 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
922 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
924 .collect::<Option<Vec<_>>>()
925 .unwrap_or_else(|| vec![])
927 get_assignment(cx, body, var).into_iter().collect()
931 /// Checks for for loops that sequentially copy items from one slice-like
932 /// object to another.
933 fn detect_manual_memcpy<'a, 'tcx>(
934 cx: &LateContext<'a, 'tcx>,
940 if let Some(higher::Range {
944 }) = higher::range(cx, arg)
946 // the var must be a single name
947 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
948 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
949 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
950 ("0", _, "0", _) => "".into(),
951 ("0", _, x, false) | (x, false, "0", false) => x.into(),
952 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
953 (x, false, y, false) => format!("({} + {})", x, y),
954 (x, false, y, true) => {
958 format!("({} - {})", x, y)
961 (x, true, y, false) => {
965 format!("({} - {})", y, x)
968 (x, true, y, true) => format!("-({} + {})", x, y),
972 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
973 if let Some(end) = *end {
975 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.kind;
976 if method.ident.name == sym!(len);
977 if len_args.len() == 1;
978 if let Some(arg) = len_args.get(0);
979 if snippet(cx, arg.span, "??") == var_name;
981 return if offset.negate {
982 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
989 let end_str = match limits {
990 ast::RangeLimits::Closed => {
991 let end = sugg::Sugg::hir(cx, end, "<count>");
992 format!("{}", end + sugg::ONE)
994 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
997 print_sum(&Offset::positive(end_str), &offset)
1003 // The only statements in the for loops can be indexed assignments from
1004 // indexed retrievals.
1005 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1007 let big_sugg = manual_copies
1009 .map(|(dst_var, src_var)| {
1010 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1011 let dst_offset = print_sum(&start_str, &dst_var.offset);
1012 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1013 let src_offset = print_sum(&start_str, &src_var.offset);
1014 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1015 let dst = if dst_offset == "" && dst_limit == "" {
1018 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1022 "{}.clone_from_slice(&{}[{}..{}])",
1023 dst, src_var.var_name, src_offset, src_limit
1028 if !big_sugg.is_empty() {
1033 "it looks like you're manually copying between slices",
1034 "try replacing the loop by",
1036 Applicability::Unspecified,
1043 /// Checks for looping over a range and then indexing a sequence with it.
1044 /// The iteratee must be a range literal.
1045 #[allow(clippy::too_many_lines)]
1046 fn check_for_loop_range<'a, 'tcx>(
1047 cx: &LateContext<'a, 'tcx>,
1053 if let Some(higher::Range {
1057 }) = higher::range(cx, arg)
1059 // the var must be a single name
1060 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1061 let mut visitor = VarVisitor {
1064 indexed_mut: FxHashSet::default(),
1065 indexed_indirectly: FxHashMap::default(),
1066 indexed_directly: FxHashMap::default(),
1067 referenced: FxHashSet::default(),
1069 prefer_mutable: false,
1071 walk_expr(&mut visitor, body);
1073 // linting condition: we only indexed one variable, and indexed it directly
1074 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1075 let (indexed, (indexed_extent, indexed_ty)) = visitor
1079 .expect("already checked that we have exactly 1 element");
1081 // ensure that the indexed variable was declared before the loop, see #601
1082 if let Some(indexed_extent) = indexed_extent {
1083 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1084 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1085 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1086 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1087 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1092 // don't lint if the container that is indexed does not have .iter() method
1093 let has_iter = has_iter_method(cx, indexed_ty);
1094 if has_iter.is_none() {
1098 // don't lint if the container that is indexed into is also used without
1100 if visitor.referenced.contains(&indexed) {
1104 let starts_at_zero = is_integer_const(cx, start, 0);
1106 let skip = if starts_at_zero {
1109 format!(".skip({})", snippet(cx, start.span, ".."))
1112 let mut end_is_start_plus_val = false;
1114 let take = if let Some(end) = *end {
1115 let mut take_expr = end;
1117 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1118 if let BinOpKind::Add = op.node {
1119 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1120 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1122 if start_equal_left {
1124 } else if start_equal_right {
1128 end_is_start_plus_val = start_equal_left | start_equal_right;
1132 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1136 ast::RangeLimits::Closed => {
1137 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1138 format!(".take({})", take_expr + sugg::ONE)
1140 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1147 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1148 ("mut ", "iter_mut")
1153 let take_is_empty = take.is_empty();
1154 let mut method_1 = take;
1155 let mut method_2 = skip;
1157 if end_is_start_plus_val {
1158 mem::swap(&mut method_1, &mut method_2);
1161 if visitor.nonindex {
1164 NEEDLESS_RANGE_LOOP,
1166 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1170 "consider using an iterator".to_string(),
1172 (pat.span, format!("({}, <item>)", ident.name)),
1175 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1182 let repl = if starts_at_zero && take_is_empty {
1183 format!("&{}{}", ref_mut, indexed)
1185 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1190 NEEDLESS_RANGE_LOOP,
1193 "the loop variable `{}` is only used to index `{}`.",
1199 "consider using an iterator".to_string(),
1200 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1210 fn is_len_call(expr: &Expr, var: Name) -> bool {
1212 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.kind;
1213 if len_args.len() == 1;
1214 if method.ident.name == sym!(len);
1215 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1216 if path.segments.len() == 1;
1217 if path.segments[0].ident.name == var;
1226 fn is_end_eq_array_len<'tcx>(
1227 cx: &LateContext<'_, 'tcx>,
1229 limits: ast::RangeLimits,
1230 indexed_ty: Ty<'tcx>,
1233 if let ExprKind::Lit(ref lit) = end.kind;
1234 if let ast::LitKind::Int(end_int, _) = lit.node;
1235 if let ty::Array(_, arr_len_const) = indexed_ty.kind;
1236 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1238 return match limits {
1239 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1240 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1248 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1249 // if this for loop is iterating over a two-sided range...
1250 if let Some(higher::Range {
1254 }) = higher::range(cx, arg)
1256 // ...and both sides are compile-time constant integers...
1257 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1258 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1259 // ...and the start index is greater than the end index,
1260 // this loop will never run. This is often confusing for developers
1261 // who think that this will iterate from the larger value to the
1263 let ty = cx.tables.expr_ty(start);
1264 let (sup, eq) = match (start_idx, end_idx) {
1265 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1267 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1268 ty::Uint(_) => start_idx > end_idx,
1271 start_idx == end_idx,
1273 _ => (false, false),
1277 let start_snippet = snippet(cx, start.span, "_");
1278 let end_snippet = snippet(cx, end.span, "_");
1279 let dots = if limits == ast::RangeLimits::Closed {
1289 "this range is empty so this for loop will never run",
1293 "consider using the following if you are attempting to iterate over this \
1296 "({end}{dots}{start}).rev()",
1299 start = start_snippet
1301 Applicability::MaybeIncorrect,
1305 } else if eq && limits != ast::RangeLimits::Closed {
1306 // if they are equal, it's also problematic - this loop
1312 "this range is empty so this for loop will never run",
1320 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1321 let mut applicability = Applicability::MachineApplicable;
1322 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1323 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1328 "it is more concise to loop over references to containers instead of using explicit \
1330 "to write this more concisely, try",
1331 format!("&{}{}", muta, object),
1336 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1337 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1338 if let ExprKind::MethodCall(ref method, _, ref args) = arg.kind {
1339 // just the receiver, no arguments
1340 if args.len() == 1 {
1341 let method_name = &*method.ident.as_str();
1342 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1343 if method_name == "iter" || method_name == "iter_mut" {
1344 if is_ref_iterable_type(cx, &args[0]) {
1345 lint_iter_method(cx, args, arg, method_name);
1347 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1348 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1349 let substs = cx.tables.node_substs(arg.hir_id);
1350 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1352 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1353 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1354 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1355 match cx.tables.expr_ty(&args[0]).kind {
1356 // If the length is greater than 32 no traits are implemented for array and
1357 // therefore we cannot use `&`.
1358 ty::Array(_, size) if size.eval_usize(cx.tcx, cx.param_env) > 32 => {},
1359 _ => lint_iter_method(cx, args, arg, method_name),
1362 let mut applicability = Applicability::MachineApplicable;
1363 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1366 EXPLICIT_INTO_ITER_LOOP,
1368 "it is more concise to loop over containers instead of using explicit \
1369 iteration methods`",
1370 "to write this more concisely, try",
1375 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1380 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1381 probably not what you want",
1383 next_loop_linted = true;
1387 if !next_loop_linted {
1388 check_arg_type(cx, pat, arg);
1392 /// Checks for `for` loops over `Option`s and `Result`s.
1393 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1394 let ty = cx.tables.expr_ty(arg);
1395 if match_type(cx, ty, &paths::OPTION) {
1398 FOR_LOOP_OVER_OPTION,
1401 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1402 `if let` statement.",
1403 snippet(cx, arg.span, "_")
1406 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1407 snippet(cx, pat.span, "_"),
1408 snippet(cx, arg.span, "_")
1411 } else if match_type(cx, ty, &paths::RESULT) {
1414 FOR_LOOP_OVER_RESULT,
1417 "for loop over `{0}`, which is a `Result`. 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 Ok({0}) = {1}`",
1423 snippet(cx, pat.span, "_"),
1424 snippet(cx, arg.span, "_")
1430 fn check_for_loop_explicit_counter<'a, 'tcx>(
1431 cx: &LateContext<'a, 'tcx>,
1437 // Look for variables that are incremented once per loop iteration.
1438 let mut visitor = IncrementVisitor {
1440 states: FxHashMap::default(),
1444 walk_expr(&mut visitor, body);
1446 // For each candidate, check the parent block to see if
1447 // it's initialized to zero at the start of the loop.
1448 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1449 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1450 let mut visitor2 = InitializeVisitor {
1454 state: VarState::IncrOnce,
1459 walk_block(&mut visitor2, block);
1461 if visitor2.state == VarState::Warn {
1462 if let Some(name) = visitor2.name {
1463 let mut applicability = Applicability::MachineApplicable;
1465 // for some reason this is the only way to get the `Span`
1466 // of the entire `for` loop
1467 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1475 EXPLICIT_COUNTER_LOOP,
1476 for_span.with_hi(arg.span.hi()),
1477 &format!("the variable `{}` is used as a loop counter.", name),
1480 "for ({}, {}) in {}.enumerate()",
1482 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1483 make_iterator_snippet(cx, arg, &mut applicability),
1493 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1494 /// actual `Iterator` that the loop uses.
1495 fn make_iterator_snippet(cx: &LateContext<'_, '_>, arg: &Expr, applic_ref: &mut Applicability) -> String {
1496 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR)
1497 .map_or(false, |id| implements_trait(cx, cx.tables.expr_ty(arg), id, &[]));
1501 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1504 // (&x).into_iter() ==> x.iter()
1505 // (&mut x).into_iter() ==> x.iter_mut()
1507 ExprKind::AddrOf(mutability, arg_inner) if has_iter_method(cx, cx.tables.expr_ty(&arg_inner)).is_some() => {
1508 let meth_name = match mutability {
1509 Mutability::Mutable => "iter_mut",
1510 Mutability::Immutable => "iter",
1514 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1520 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1526 /// Checks for the `FOR_KV_MAP` lint.
1527 fn check_for_loop_over_map_kv<'a, 'tcx>(
1528 cx: &LateContext<'a, 'tcx>,
1534 let pat_span = pat.span;
1536 if let PatKind::Tuple(ref pat, _) = pat.kind {
1538 let arg_span = arg.span;
1539 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).kind {
1540 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1541 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1542 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Immutable),
1547 let mutbl = match mutbl {
1548 Mutability::Immutable => "",
1549 Mutability::Mutable => "_mut",
1551 let arg = match arg.kind {
1552 ExprKind::AddrOf(_, ref expr) => &**expr,
1556 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1561 &format!("you seem to want to iterate on a map's {}s", kind),
1563 let map = sugg::Sugg::hir(cx, arg, "map");
1566 "use the corresponding method".into(),
1568 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1569 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1579 struct MutatePairDelegate {
1580 hir_id_low: Option<HirId>,
1581 hir_id_high: Option<HirId>,
1582 span_low: Option<Span>,
1583 span_high: Option<Span>,
1586 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1587 fn consume(&mut self, _: &cmt_<'tcx>, _: ConsumeMode) {}
1589 fn borrow(&mut self, cmt: &cmt_<'tcx>, bk: ty::BorrowKind) {
1590 if let ty::BorrowKind::MutBorrow = bk {
1591 if let Categorization::Local(id) = cmt.cat {
1592 if Some(id) == self.hir_id_low {
1593 self.span_low = Some(cmt.span)
1595 if Some(id) == self.hir_id_high {
1596 self.span_high = Some(cmt.span)
1602 fn mutate(&mut self, cmt: &cmt_<'tcx>) {
1603 if let Categorization::Local(id) = cmt.cat {
1604 if Some(id) == self.hir_id_low {
1605 self.span_low = Some(cmt.span)
1607 if Some(id) == self.hir_id_high {
1608 self.span_high = Some(cmt.span)
1614 impl<'tcx> MutatePairDelegate {
1615 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1616 (self.span_low, self.span_high)
1620 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1621 if let Some(higher::Range {
1625 }) = higher::range(cx, arg)
1627 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1628 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1629 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1630 mut_warn_with_span(cx, span_low);
1631 mut_warn_with_span(cx, span_high);
1636 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1637 if let Some(sp) = span {
1642 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1647 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1649 if let ExprKind::Path(ref qpath) = bound.kind;
1650 if let QPath::Resolved(None, _) = *qpath;
1652 let res = qpath_res(cx, qpath, bound.hir_id);
1653 if let Res::Local(node_id) = res {
1654 let node_str = cx.tcx.hir().get(node_id);
1656 if let Node::Binding(pat) = node_str;
1657 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1658 if let BindingAnnotation::Mutable = bind_ann;
1660 return Some(node_id);
1669 fn check_for_mutation(
1670 cx: &LateContext<'_, '_>,
1672 bound_ids: &[Option<HirId>],
1673 ) -> (Option<Span>, Option<Span>) {
1674 let mut delegate = MutatePairDelegate {
1675 hir_id_low: bound_ids[0],
1676 hir_id_high: bound_ids[1],
1680 let def_id = def_id::DefId::local(body.hir_id.owner);
1681 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1682 ExprUseVisitor::new(
1691 delegate.mutation_span()
1694 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1695 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1697 PatKind::Wild => true,
1698 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1699 let mut visitor = UsedVisitor {
1703 walk_expr(&mut visitor, body);
1710 struct UsedVisitor {
1711 var: ast::Name, // var to look for
1712 used: bool, // has the var been used otherwise?
1715 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1716 fn visit_expr(&mut self, expr: &'tcx Expr) {
1717 if match_var(expr, self.var) {
1720 walk_expr(self, expr);
1724 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1725 NestedVisitorMap::None
1729 struct LocalUsedVisitor<'a, 'tcx> {
1730 cx: &'a LateContext<'a, 'tcx>,
1735 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1736 fn visit_expr(&mut self, expr: &'tcx Expr) {
1737 if same_var(self.cx, expr, self.local) {
1740 walk_expr(self, expr);
1744 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1745 NestedVisitorMap::None
1749 struct VarVisitor<'a, 'tcx> {
1750 /// context reference
1751 cx: &'a LateContext<'a, 'tcx>,
1752 /// var name to look for as index
1754 /// indexed variables that are used mutably
1755 indexed_mut: FxHashSet<Name>,
1756 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1757 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1758 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1759 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1760 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1761 /// Any names that are used outside an index operation.
1762 /// Used to detect things like `&mut vec` used together with `vec[i]`
1763 referenced: FxHashSet<Name>,
1764 /// has the loop variable been used in expressions other than the index of
1767 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1768 /// takes `&mut self`
1769 prefer_mutable: bool,
1772 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1773 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1775 // the indexed container is referenced by a name
1776 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
1777 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1778 if seqvar.segments.len() == 1;
1780 let index_used_directly = same_var(self.cx, idx, self.var);
1781 let indexed_indirectly = {
1782 let mut used_visitor = LocalUsedVisitor {
1787 walk_expr(&mut used_visitor, idx);
1791 if indexed_indirectly || index_used_directly {
1792 if self.prefer_mutable {
1793 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1795 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
1797 Res::Local(hir_id) => {
1798 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1799 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1800 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1801 if indexed_indirectly {
1802 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1804 if index_used_directly {
1805 self.indexed_directly.insert(
1806 seqvar.segments[0].ident.name,
1807 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1810 return false; // no need to walk further *on the variable*
1812 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1813 if indexed_indirectly {
1814 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1816 if index_used_directly {
1817 self.indexed_directly.insert(
1818 seqvar.segments[0].ident.name,
1819 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1822 return false; // no need to walk further *on the variable*
1833 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1834 fn visit_expr(&mut self, expr: &'tcx Expr) {
1837 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.kind;
1838 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1839 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1840 if !self.check(&args[1], &args[0], expr);
1846 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
1847 if !self.check(idx, seqexpr, expr);
1852 // directly using a variable
1853 if let ExprKind::Path(ref qpath) = expr.kind;
1854 if let QPath::Resolved(None, ref path) = *qpath;
1855 if path.segments.len() == 1;
1857 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
1858 if local_id == self.var {
1859 self.nonindex = true;
1861 // not the correct variable, but still a variable
1862 self.referenced.insert(path.segments[0].ident.name);
1868 let old = self.prefer_mutable;
1870 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1871 self.prefer_mutable = true;
1872 self.visit_expr(lhs);
1873 self.prefer_mutable = false;
1874 self.visit_expr(rhs);
1876 ExprKind::AddrOf(mutbl, ref expr) => {
1877 if mutbl == Mutability::Mutable {
1878 self.prefer_mutable = true;
1880 self.visit_expr(expr);
1882 ExprKind::Call(ref f, ref args) => {
1885 let ty = self.cx.tables.expr_ty_adjusted(expr);
1886 self.prefer_mutable = false;
1887 if let ty::Ref(_, _, mutbl) = ty.kind {
1888 if mutbl == Mutability::Mutable {
1889 self.prefer_mutable = true;
1892 self.visit_expr(expr);
1895 ExprKind::MethodCall(_, _, ref args) => {
1896 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1897 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1898 self.prefer_mutable = false;
1899 if let ty::Ref(_, _, mutbl) = ty.kind {
1900 if mutbl == Mutability::Mutable {
1901 self.prefer_mutable = true;
1904 self.visit_expr(expr);
1907 ExprKind::Closure(_, _, body_id, ..) => {
1908 let body = self.cx.tcx.hir().body(body_id);
1909 self.visit_expr(&body.value);
1911 _ => walk_expr(self, expr),
1913 self.prefer_mutable = old;
1915 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1916 NestedVisitorMap::None
1920 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1921 let def_id = match var_def_id(cx, expr) {
1923 None => return false,
1925 if let Some(used_mutably) = mutated_variables(container, cx) {
1926 if used_mutably.contains(&def_id) {
1933 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1934 let def_id = match var_def_id(cx, iter_expr) {
1936 None => return false,
1938 let mut visitor = VarUsedAfterLoopVisitor {
1941 iter_expr_id: iter_expr.hir_id,
1942 past_while_let: false,
1943 var_used_after_while_let: false,
1945 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1946 walk_block(&mut visitor, enclosing_block);
1948 visitor.var_used_after_while_let
1951 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1952 cx: &'a LateContext<'a, 'tcx>,
1954 iter_expr_id: HirId,
1955 past_while_let: bool,
1956 var_used_after_while_let: bool,
1959 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1960 fn visit_expr(&mut self, expr: &'tcx Expr) {
1961 if self.past_while_let {
1962 if Some(self.def_id) == var_def_id(self.cx, expr) {
1963 self.var_used_after_while_let = true;
1965 } else if self.iter_expr_id == expr.hir_id {
1966 self.past_while_let = true;
1968 walk_expr(self, expr);
1970 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1971 NestedVisitorMap::None
1975 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1976 /// for `&T` and `&mut T`, such as `Vec`.
1978 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1979 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1980 // will allow further borrows afterwards
1981 let ty = cx.tables.expr_ty(e);
1982 is_iterable_array(ty, cx) ||
1983 is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) ||
1984 match_type(cx, ty, &paths::LINKED_LIST) ||
1985 match_type(cx, ty, &paths::HASHMAP) ||
1986 match_type(cx, ty, &paths::HASHSET) ||
1987 match_type(cx, ty, &paths::VEC_DEQUE) ||
1988 match_type(cx, ty, &paths::BINARY_HEAP) ||
1989 match_type(cx, ty, &paths::BTREEMAP) ||
1990 match_type(cx, ty, &paths::BTREESET)
1993 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1994 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1996 ty::Array(_, n) => {
1997 if let Some(val) = n.try_eval_usize(cx.tcx, cx.param_env) {
1998 (0..=32).contains(&val)
2007 /// If a block begins with a statement (possibly a `let` binding) and has an
2008 /// expression, return it.
2009 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
2010 if block.stmts.is_empty() {
2013 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2014 if let Some(ref expr) = local.init {
2024 /// If a block begins with an expression (with or without semicolon), return it.
2025 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2027 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2028 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2029 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2030 StmtKind::Local(..) | StmtKind::Item(..) => None,
2036 /// Returns `true` if expr contains a single break expr without destination label
2038 /// passed expression. The expression may be within a block.
2039 fn is_simple_break_expr(expr: &Expr) -> bool {
2041 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2042 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2047 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2048 // incremented exactly once in the loop body, and initialized to zero
2049 // at the start of the loop.
2050 #[derive(Debug, PartialEq)]
2052 Initial, // Not examined yet
2053 IncrOnce, // Incremented exactly once, may be a loop counter
2054 Declared, // Declared but not (yet) initialized to zero
2059 /// Scan a for loop for variables that are incremented exactly once.
2060 struct IncrementVisitor<'a, 'tcx> {
2061 cx: &'a LateContext<'a, 'tcx>, // context reference
2062 states: FxHashMap<HirId, VarState>, // incremented variables
2063 depth: u32, // depth of conditional expressions
2067 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2068 fn visit_expr(&mut self, expr: &'tcx Expr) {
2073 // If node is a variable
2074 if let Some(def_id) = var_def_id(self.cx, expr) {
2075 if let Some(parent) = get_parent_expr(self.cx, expr) {
2076 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2079 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2080 if lhs.hir_id == expr.hir_id {
2081 if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) {
2082 *state = match *state {
2083 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2084 _ => VarState::DontWarn,
2087 // Assigned some other value
2088 *state = VarState::DontWarn;
2092 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2093 ExprKind::AddrOf(mutability, _) if mutability == Mutability::Mutable => *state = VarState::DontWarn,
2097 } else if is_loop(expr) || is_conditional(expr) {
2099 walk_expr(self, expr);
2102 } else if let ExprKind::Continue(_) = expr.kind {
2106 walk_expr(self, expr);
2108 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2109 NestedVisitorMap::None
2113 /// Checks whether a variable is initialized to zero at the start of a loop.
2114 struct InitializeVisitor<'a, 'tcx> {
2115 cx: &'a LateContext<'a, 'tcx>, // context reference
2116 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2120 depth: u32, // depth of conditional expressions
2124 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2125 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2126 // Look for declarations of the variable
2127 if let StmtKind::Local(ref local) = stmt.kind {
2128 if local.pat.hir_id == self.var_id {
2129 if let PatKind::Binding(.., ident, _) = local.pat.kind {
2130 self.name = Some(ident.name);
2132 self.state = if let Some(ref init) = local.init {
2133 if is_integer_const(&self.cx, init, 0) {
2144 walk_stmt(self, stmt);
2147 fn visit_expr(&mut self, expr: &'tcx Expr) {
2148 if self.state == VarState::DontWarn {
2151 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2152 self.past_loop = true;
2155 // No need to visit expressions before the variable is
2157 if self.state == VarState::IncrOnce {
2161 // If node is the desired variable, see how it's used
2162 if var_def_id(self.cx, expr) == Some(self.var_id) {
2163 if let Some(parent) = get_parent_expr(self.cx, expr) {
2165 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2166 self.state = VarState::DontWarn;
2168 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2169 self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 {
2175 ExprKind::AddrOf(mutability, _) if mutability == Mutability::Mutable => {
2176 self.state = VarState::DontWarn
2183 self.state = VarState::DontWarn;
2186 } else if !self.past_loop && is_loop(expr) {
2187 self.state = VarState::DontWarn;
2189 } else if is_conditional(expr) {
2191 walk_expr(self, expr);
2195 walk_expr(self, expr);
2198 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2199 NestedVisitorMap::OnlyBodies(&self.cx.tcx.hir())
2203 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2204 if let ExprKind::Path(ref qpath) = expr.kind {
2205 let path_res = qpath_res(cx, qpath, expr.hir_id);
2206 if let Res::Local(node_id) = path_res {
2207 return Some(node_id);
2213 fn is_loop(expr: &Expr) -> bool {
2215 ExprKind::Loop(..) => true,
2220 fn is_conditional(expr: &Expr) -> bool {
2222 ExprKind::Match(..) => true,
2227 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2229 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2230 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2231 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2233 return is_loop_nested(cx, loop_expr, iter_expr)
2239 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2240 let mut id = loop_expr.hir_id;
2241 let iter_name = if let Some(name) = path_name(iter_expr) {
2247 let parent = cx.tcx.hir().get_parent_node(id);
2251 match cx.tcx.hir().find(parent) {
2252 Some(Node::Expr(expr)) => {
2253 if let ExprKind::Loop(..) = expr.kind {
2257 Some(Node::Block(block)) => {
2258 let mut block_visitor = LoopNestVisitor {
2260 iterator: iter_name,
2263 walk_block(&mut block_visitor, block);
2264 if block_visitor.nesting == RuledOut {
2268 Some(Node::Stmt(_)) => (),
2277 #[derive(PartialEq, Eq)]
2279 Unknown, // no nesting detected yet
2280 RuledOut, // the iterator is initialized or assigned within scope
2281 LookFurther, // no nesting detected, no further walk required
2284 use self::Nesting::{LookFurther, RuledOut, Unknown};
2286 struct LoopNestVisitor {
2292 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2293 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2294 if stmt.hir_id == self.hir_id {
2295 self.nesting = LookFurther;
2296 } else if self.nesting == Unknown {
2297 walk_stmt(self, stmt);
2301 fn visit_expr(&mut self, expr: &'tcx Expr) {
2302 if self.nesting != Unknown {
2305 if expr.hir_id == self.hir_id {
2306 self.nesting = LookFurther;
2310 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2311 if match_var(path, self.iterator) {
2312 self.nesting = RuledOut;
2315 _ => walk_expr(self, expr),
2319 fn visit_pat(&mut self, pat: &'tcx Pat) {
2320 if self.nesting != Unknown {
2323 if let PatKind::Binding(.., span_name, _) = pat.kind {
2324 if self.iterator == span_name.name {
2325 self.nesting = RuledOut;
2332 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2333 NestedVisitorMap::None
2337 fn path_name(e: &Expr) -> Option<Name> {
2338 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2339 let segments = &path.segments;
2340 if segments.len() == 1 {
2341 return Some(segments[0].ident.name);
2347 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2348 if constant(cx, cx.tables, cond).is_some() {
2349 // A pure constant condition (e.g., `while false`) is not linted.
2353 let mut var_visitor = VarCollectorVisitor {
2355 ids: FxHashSet::default(),
2356 def_ids: FxHashMap::default(),
2359 var_visitor.visit_expr(cond);
2360 if var_visitor.skip {
2363 let used_in_condition = &var_visitor.ids;
2364 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2365 used_in_condition.is_disjoint(&used_mutably)
2369 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2371 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2372 has_break_or_return: false,
2374 has_break_or_return_visitor.visit_expr(expr);
2375 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2377 if no_cond_variable_mutated && !mutable_static_in_cond {
2380 WHILE_IMMUTABLE_CONDITION,
2382 "variables in the condition are not mutated in the loop body",
2384 db.note("this may lead to an infinite or to a never running loop");
2386 if has_break_or_return {
2387 db.note("this loop contains `return`s or `break`s");
2388 db.help("rewrite it as `if cond { loop { } }`");
2395 struct HasBreakOrReturnVisitor {
2396 has_break_or_return: bool,
2399 impl<'a, 'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2400 fn visit_expr(&mut self, expr: &'tcx Expr) {
2401 if self.has_break_or_return {
2406 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2407 self.has_break_or_return = true;
2413 walk_expr(self, expr);
2416 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2417 NestedVisitorMap::None
2421 /// Collects the set of variables in an expression
2422 /// Stops analysis if a function call is found
2423 /// Note: In some cases such as `self`, there are no mutable annotation,
2424 /// All variables definition IDs are collected
2425 struct VarCollectorVisitor<'a, 'tcx> {
2426 cx: &'a LateContext<'a, 'tcx>,
2427 ids: FxHashSet<HirId>,
2428 def_ids: FxHashMap<def_id::DefId, bool>,
2432 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2433 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2435 if let ExprKind::Path(ref qpath) = ex.kind;
2436 if let QPath::Resolved(None, _) = *qpath;
2437 let res = qpath_res(self.cx, qpath, ex.hir_id);
2440 Res::Local(node_id) => {
2441 self.ids.insert(node_id);
2443 Res::Def(DefKind::Static, def_id) => {
2444 let mutable = self.cx.tcx.is_mutable_static(def_id);
2445 self.def_ids.insert(def_id, mutable);
2454 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2455 fn visit_expr(&mut self, ex: &'tcx Expr) {
2457 ExprKind::Path(_) => self.insert_def_id(ex),
2458 // If there is any function/method call… we just stop analysis
2459 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2461 _ => walk_expr(self, ex),
2465 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2466 NestedVisitorMap::None
2470 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2472 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2474 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
2475 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].kind;
2476 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2477 if let Some(ref generic_args) = chain_method.args;
2478 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2480 let ty = cx.tables.node_type(ty.hir_id);
2481 if is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) ||
2482 match_type(cx, ty, &paths::VEC_DEQUE) ||
2483 match_type(cx, ty, &paths::BTREEMAP) ||
2484 match_type(cx, ty, &paths::HASHMAP) {
2485 if method.ident.name == sym!(len) {
2486 let span = shorten_needless_collect_span(expr);
2487 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2491 ".count()".to_string(),
2492 Applicability::MachineApplicable,
2496 if method.ident.name == sym!(is_empty) {
2497 let span = shorten_needless_collect_span(expr);
2498 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2502 ".next().is_none()".to_string(),
2503 Applicability::MachineApplicable,
2507 if method.ident.name == sym!(contains) {
2508 let contains_arg = snippet(cx, args[1].span, "??");
2509 let span = shorten_needless_collect_span(expr);
2510 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2511 let (arg, pred) = if contains_arg.starts_with('&') {
2512 ("x", &contains_arg[1..])
2514 ("&x", &*contains_arg)
2520 ".any(|{}| x == {})",
2523 Applicability::MachineApplicable,
2532 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2534 if let ExprKind::MethodCall(_, _, ref args) = expr.kind;
2535 if let ExprKind::MethodCall(_, ref span, _) = args[0].kind;
2537 return expr.span.with_lo(span.lo() - BytePos(1));