1 use crate::reexport::*;
2 use if_chain::if_chain;
3 use itertools::Itertools;
4 use rustc::declare_lint_pass;
5 use rustc::hir::def::{DefKind, Res};
6 use rustc::hir::def_id;
7 use rustc::hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
9 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
10 use rustc::middle::region;
11 use rustc_session::declare_tool_lint;
12 // use rustc::middle::region::CodeExtent;
13 use crate::consts::{constant, Constant};
14 use crate::utils::usage::mutated_variables;
15 use crate::utils::{is_type_diagnostic_item, qpath_res, sext, sugg};
16 use rustc::ty::subst::Subst;
17 use rustc::ty::{self, Ty};
18 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
19 use rustc_errors::Applicability;
20 use rustc_typeck::expr_use_visitor::*;
21 use std::iter::{once, Iterator};
24 use syntax::source_map::Span;
25 use syntax_pos::{BytePos, Symbol};
27 use crate::utils::paths;
29 get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
30 is_integer_const, is_refutable, last_path_segment, match_trait_method, match_type, match_var, multispan_sugg,
31 snippet, snippet_opt, snippet_with_applicability, span_help_and_lint, span_lint, span_lint_and_sugg,
32 span_lint_and_then, SpanlessEq,
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// # let src = vec![1];
46 /// # let mut dst = vec![0; 65];
47 /// for i in 0..src.len() {
48 /// dst[i + 64] = src[i];
51 /// Could be written as:
53 /// # let src = vec![1];
54 /// # let mut dst = vec![0; 65];
55 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
59 "manually copying items between slices"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for looping over the range of `0..len` of some
64 /// collection just to get the values by index.
66 /// **Why is this bad?** Just iterating the collection itself makes the intent
67 /// more clear and is probably faster.
69 /// **Known problems:** None.
73 /// let vec = vec!['a', 'b', 'c'];
74 /// for i in 0..vec.len() {
75 /// println!("{}", vec[i]);
78 /// Could be written as:
80 /// let vec = vec!['a', 'b', 'c'];
82 /// println!("{}", i);
85 pub NEEDLESS_RANGE_LOOP,
87 "for-looping over a range of indices where an iterator over items would do"
90 declare_clippy_lint! {
91 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
92 /// suggests the latter.
94 /// **Why is this bad?** Readability.
96 /// **Known problems:** False negatives. We currently only warn on some known
101 /// // with `y` a `Vec` or slice:
102 /// # let y = vec![1];
103 /// for x in y.iter() {
107 /// can be rewritten to
109 /// # let y = vec![1];
114 pub EXPLICIT_ITER_LOOP,
116 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
119 declare_clippy_lint! {
120 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
121 /// suggests the latter.
123 /// **Why is this bad?** Readability.
125 /// **Known problems:** None
129 /// # let y = vec![1];
130 /// // with `y` a `Vec` or slice:
131 /// for x in y.into_iter() {
135 /// can be rewritten to
137 /// # let y = vec![1];
142 pub EXPLICIT_INTO_ITER_LOOP,
144 "for-looping over `_.into_iter()` when `_` would do"
147 declare_clippy_lint! {
148 /// **What it does:** Checks for loops on `x.next()`.
150 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
151 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
152 /// implements `IntoIterator`, so that possibly one value will be iterated,
153 /// leading to some hard to find bugs. No one will want to write such code
154 /// [except to win an Underhanded Rust
155 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
157 /// **Known problems:** None.
161 /// for x in y.next() {
167 "for-looping over `_.next()` which is probably not intended"
170 declare_clippy_lint! {
171 /// **What it does:** Checks for `for` loops over `Option` values.
173 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
176 /// **Known problems:** None.
180 /// for x in option {
187 /// if let Some(x) = option {
191 pub FOR_LOOP_OVER_OPTION,
193 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
196 declare_clippy_lint! {
197 /// **What it does:** Checks for `for` loops over `Result` values.
199 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
202 /// **Known problems:** None.
206 /// for x in result {
213 /// if let Ok(x) = result {
217 pub FOR_LOOP_OVER_RESULT,
219 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
222 declare_clippy_lint! {
223 /// **What it does:** Detects `loop + match` combinations that are easier
224 /// written as a `while let` loop.
226 /// **Why is this bad?** The `while let` loop is usually shorter and more
229 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
233 /// # let y = Some(1);
235 /// let x = match y {
239 /// // .. do something with x
241 /// // is easier written as
242 /// while let Some(x) = y {
243 /// // .. do something with x
248 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
251 declare_clippy_lint! {
252 /// **What it does:** Checks for functions collecting an iterator when collect
255 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
256 /// when this allocation may not be needed.
258 /// **Known problems:**
263 /// # let iterator = vec![1].into_iter();
264 /// let len = iterator.clone().collect::<Vec<_>>().len();
266 /// let len = iterator.count();
268 pub NEEDLESS_COLLECT,
270 "collecting an iterator when collect is not needed"
273 declare_clippy_lint! {
274 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
275 /// are constant and `x` is greater or equal to `y`, unless the range is
276 /// reversed or has a negative `.step_by(_)`.
278 /// **Why is it bad?** Such loops will either be skipped or loop until
279 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
282 /// **Known problems:** The lint cannot catch loops over dynamically defined
283 /// ranges. Doing this would require simulating all possible inputs and code
284 /// paths through the program, which would be complex and error-prone.
288 /// for x in 5..10 - 5 {
290 /// } // oops, stray `-`
292 pub REVERSE_RANGE_LOOP,
294 "iteration over an empty range, such as `10..0` or `5..5`"
297 declare_clippy_lint! {
298 /// **What it does:** Checks `for` loops over slices with an explicit counter
299 /// and suggests the use of `.enumerate()`.
301 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
302 /// declutters the code and may be faster in some instances.
304 /// **Known problems:** None.
308 /// # let v = vec![1];
309 /// # fn bar(bar: usize, baz: usize) {}
316 /// Could be written as
318 /// # let v = vec![1];
319 /// # fn bar(bar: usize, baz: usize) {}
320 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
322 pub EXPLICIT_COUNTER_LOOP,
324 "for-looping with an explicit counter when `_.enumerate()` would do"
327 declare_clippy_lint! {
328 /// **What it does:** Checks for empty `loop` expressions.
330 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
331 /// anything. Think of the environment and either block on something or at least
332 /// make the thread sleep for some microseconds.
334 /// **Known problems:** None.
342 "empty `loop {}`, which should block or sleep"
345 declare_clippy_lint! {
346 /// **What it does:** Checks for `while let` expressions on iterators.
348 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
349 /// the intent better.
351 /// **Known problems:** None.
355 /// while let Some(val) = iter() {
359 pub WHILE_LET_ON_ITERATOR,
361 "using a while-let loop instead of a for loop on an iterator"
364 declare_clippy_lint! {
365 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
366 /// ignoring either the keys or values.
368 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
369 /// can be used to express that don't need the values or keys.
371 /// **Known problems:** None.
375 /// for (k, _) in &map {
380 /// could be replaced by
383 /// for k in map.keys() {
389 "looping on a map using `iter` when `keys` or `values` would do"
392 declare_clippy_lint! {
393 /// **What it does:** Checks for loops that will always `break`, `return` or
394 /// `continue` an outer loop.
396 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
399 /// **Known problems:** None
410 "any loop that will always `break` or `return`"
413 declare_clippy_lint! {
414 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
416 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
418 /// **Known problems:** None
422 /// let mut foo = 42;
423 /// for i in 0..foo {
425 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
430 "for loop over a range where one of the bounds is a mutable variable"
433 declare_clippy_lint! {
434 /// **What it does:** Checks whether variables used within while loop condition
435 /// can be (and are) mutated in the body.
437 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
438 /// will lead to an infinite loop.
440 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
441 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
442 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
448 /// println!("let me loop forever!");
451 pub WHILE_IMMUTABLE_CONDITION,
453 "variables used within while expression are not mutated in the body"
456 declare_lint_pass!(Loops => [
460 EXPLICIT_INTO_ITER_LOOP,
462 FOR_LOOP_OVER_RESULT,
463 FOR_LOOP_OVER_OPTION,
467 EXPLICIT_COUNTER_LOOP,
469 WHILE_LET_ON_ITERATOR,
473 WHILE_IMMUTABLE_CONDITION,
476 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
477 #[allow(clippy::too_many_lines)]
478 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
479 if let Some((pat, arg, body)) = higher::for_loop(expr) {
480 // we don't want to check expanded macros
481 // this check is not at the top of the function
482 // since higher::for_loop expressions are marked as expansions
483 if body.span.from_expansion() {
486 check_for_loop(cx, pat, arg, body, expr);
489 // we don't want to check expanded macros
490 if expr.span.from_expansion() {
494 // check for never_loop
495 if let ExprKind::Loop(ref block, _, _) = expr.kind {
496 match never_loop_block(block, expr.hir_id) {
497 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
498 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
502 // check for `loop { if let {} else break }` that could be `while let`
503 // (also matches an explicit "match" instead of "if let")
504 // (even if the "match" or "if let" is used for declaration)
505 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
506 // also check for empty `loop {}` statements
507 if block.stmts.is_empty() && block.expr.is_none() {
512 "empty `loop {}` detected. You may want to either use `panic!()` or add \
513 `std::thread::sleep(..);` to the loop body.",
517 // extract the expression from the first statement (if any) in a block
518 let inner_stmt_expr = extract_expr_from_first_stmt(block);
519 // or extract the first expression (if any) from the block
520 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
521 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
522 // ensure "if let" compatible match structure
524 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
526 && arms[0].guard.is_none()
527 && arms[1].guard.is_none()
528 && is_simple_break_expr(&arms[1].body)
530 if in_external_macro(cx.sess(), expr.span) {
534 // NOTE: we used to build a body here instead of using
535 // ellipsis, this was removed because:
536 // 1) it was ugly with big bodies;
537 // 2) it was not indented properly;
538 // 3) it wasn’t very smart (see #675).
539 let mut applicability = Applicability::HasPlaceholders;
544 "this loop could be written as a `while let` loop",
547 "while let {} = {} {{ .. }}",
548 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
549 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
560 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
561 let pat = &arms[0].pat.kind;
563 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
564 &ExprKind::MethodCall(ref method_path, _, ref method_args),
565 ) = (pat, &match_expr.kind)
567 let iter_expr = &method_args[0];
568 let lhs_constructor = last_path_segment(qpath);
569 if method_path.ident.name == sym!(next)
570 && match_trait_method(cx, match_expr, &paths::ITERATOR)
571 && lhs_constructor.ident.name == sym!(Some)
572 && (pat_args.is_empty()
573 || !is_refutable(cx, &pat_args[0])
574 && !is_used_inside(cx, iter_expr, &arms[0].body)
575 && !is_iterator_used_after_while_let(cx, iter_expr)
576 && !is_nested(cx, expr, &method_args[0]))
578 let iterator = snippet(cx, method_args[0].span, "_");
579 let loop_var = if pat_args.is_empty() {
582 snippet(cx, pat_args[0].span, "_").into_owned()
586 WHILE_LET_ON_ITERATOR,
588 "this loop could be written as a `for` loop",
590 format!("for {} in {} {{ .. }}", loop_var, iterator),
591 Applicability::HasPlaceholders,
597 if let Some((cond, body)) = higher::while_loop(&expr) {
598 check_infinite_loop(cx, cond, body);
601 check_needless_collect(expr, cx);
605 enum NeverLoopResult {
606 // A break/return always get triggered but not necessarily for the main loop.
608 // A continue may occur for the main loop.
614 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
616 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
617 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
621 // Combine two results for parts that are called in order.
623 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
625 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
626 NeverLoopResult::Otherwise => second,
630 // Combine two results where both parts are called but not necessarily in order.
632 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
633 match (left, right) {
634 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
635 NeverLoopResult::MayContinueMainLoop
637 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
638 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
642 // Combine two results where only one of the part may have been executed.
644 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
646 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
647 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
648 NeverLoopResult::MayContinueMainLoop
650 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
654 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
655 let stmts = block.stmts.iter().map(stmt_to_expr);
656 let expr = once(block.expr.as_ref().map(|p| &**p));
657 let mut iter = stmts.chain(expr).filter_map(|e| e);
658 never_loop_expr_seq(&mut iter, main_loop_id)
661 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
663 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
664 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
669 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
672 | ExprKind::Unary(_, ref e)
673 | ExprKind::Cast(ref e, _)
674 | ExprKind::Type(ref e, _)
675 | ExprKind::Field(ref e, _)
676 | ExprKind::AddrOf(_, _, ref e)
677 | ExprKind::Struct(_, _, Some(ref e))
678 | ExprKind::Repeat(ref e, _)
679 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
680 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
681 never_loop_expr_all(&mut es.iter(), main_loop_id)
683 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
684 ExprKind::Binary(_, ref e1, ref e2)
685 | ExprKind::Assign(ref e1, ref e2)
686 | ExprKind::AssignOp(_, ref e1, ref e2)
687 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
688 ExprKind::Loop(ref b, _, _) => {
689 // Break can come from the inner loop so remove them.
690 absorb_break(&never_loop_block(b, main_loop_id))
692 ExprKind::Match(ref e, ref arms, _) => {
693 let e = never_loop_expr(e, main_loop_id);
697 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
701 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
702 ExprKind::Continue(d) => {
705 .expect("target ID can only be missing in the presence of compilation errors");
706 if id == main_loop_id {
707 NeverLoopResult::MayContinueMainLoop
709 NeverLoopResult::AlwaysBreak
712 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
713 if let Some(ref e) = *e {
714 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
716 NeverLoopResult::AlwaysBreak
719 ExprKind::Struct(_, _, None)
720 | ExprKind::Yield(_, _)
721 | ExprKind::Closure(_, _, _, _, _)
722 | ExprKind::InlineAsm(_)
725 | ExprKind::Err => NeverLoopResult::Otherwise,
729 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
730 es.map(|e| never_loop_expr(e, main_loop_id))
731 .fold(NeverLoopResult::Otherwise, combine_seq)
734 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
735 es.map(|e| never_loop_expr(e, main_loop_id))
736 .fold(NeverLoopResult::Otherwise, combine_both)
739 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
740 e.map(|e| never_loop_expr(e, main_loop_id))
741 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
744 fn check_for_loop<'a, 'tcx>(
745 cx: &LateContext<'a, 'tcx>,
751 check_for_loop_range(cx, pat, arg, body, expr);
752 check_for_loop_reverse_range(cx, arg, expr);
753 check_for_loop_arg(cx, pat, arg, expr);
754 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
755 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
756 check_for_mut_range_bound(cx, arg, body);
757 detect_manual_memcpy(cx, pat, arg, body, expr);
760 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
762 if let ExprKind::Path(ref qpath) = expr.kind;
763 if let QPath::Resolved(None, ref path) = *qpath;
764 if path.segments.len() == 1;
765 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
782 fn negative(s: String) -> Self {
783 Self { value: s, negate: true }
786 fn positive(s: String) -> Self {
794 struct FixedOffsetVar {
799 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
800 let is_slice = match ty.kind {
801 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
802 ty::Slice(..) | ty::Array(..) => true,
806 is_slice || is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) || match_type(cx, ty, &paths::VEC_DEQUE)
809 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
810 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
812 ExprKind::Lit(ref l) => match l.node {
813 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
816 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
821 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind {
822 let ty = cx.tables.expr_ty(seqexpr);
823 if !is_slice_like(cx, ty) {
827 let offset = match idx.kind {
828 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
830 let offset_opt = if same_var(cx, lhs, var) {
831 extract_offset(cx, rhs, var)
832 } else if same_var(cx, rhs, var) {
833 extract_offset(cx, lhs, var)
838 offset_opt.map(Offset::positive)
840 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
843 ExprKind::Path(..) => {
844 if same_var(cx, idx, var) {
845 Some(Offset::positive("0".into()))
853 offset.map(|o| FixedOffsetVar {
854 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
862 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
863 cx: &LateContext<'a, 'tcx>,
866 ) -> Option<FixedOffsetVar> {
868 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
869 if method.ident.name == sym!(clone);
871 if let Some(arg) = args.get(0);
873 return get_fixed_offset_var(cx, arg, var);
877 get_fixed_offset_var(cx, expr, var)
880 fn get_indexed_assignments<'a, 'tcx>(
881 cx: &LateContext<'a, 'tcx>,
884 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
885 fn get_assignment<'a, 'tcx>(
886 cx: &LateContext<'a, 'tcx>,
889 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
890 if let ExprKind::Assign(ref lhs, ref rhs) = e.kind {
892 get_fixed_offset_var(cx, lhs, var),
893 fetch_cloned_fixed_offset_var(cx, rhs, var),
895 (Some(offset_left), Some(offset_right)) => {
896 // Source and destination must be different
897 if offset_left.var_name == offset_right.var_name {
900 Some((offset_left, offset_right))
910 if let ExprKind::Block(ref b, _) = body.kind {
912 ref stmts, ref expr, ..
917 .map(|stmt| match stmt.kind {
918 StmtKind::Local(..) | StmtKind::Item(..) => None,
919 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
921 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
923 .collect::<Option<Vec<_>>>()
924 .unwrap_or_else(|| vec![])
926 get_assignment(cx, body, var).into_iter().collect()
930 /// Checks for for loops that sequentially copy items from one slice-like
931 /// object to another.
932 fn detect_manual_memcpy<'a, 'tcx>(
933 cx: &LateContext<'a, 'tcx>,
939 if let Some(higher::Range {
943 }) = higher::range(cx, arg)
945 // the var must be a single name
946 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
947 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
948 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
949 ("0", _, "0", _) => "".into(),
950 ("0", _, x, false) | (x, false, "0", false) => x.into(),
951 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
952 (x, false, y, false) => format!("({} + {})", x, y),
953 (x, false, y, true) => {
957 format!("({} - {})", x, y)
960 (x, true, y, false) => {
964 format!("({} - {})", y, x)
967 (x, true, y, true) => format!("-({} + {})", x, y),
971 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
972 if let Some(end) = *end {
974 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.kind;
975 if method.ident.name == sym!(len);
976 if len_args.len() == 1;
977 if let Some(arg) = len_args.get(0);
978 if snippet(cx, arg.span, "??") == var_name;
980 return if offset.negate {
981 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
988 let end_str = match limits {
989 ast::RangeLimits::Closed => {
990 let end = sugg::Sugg::hir(cx, end, "<count>");
991 format!("{}", end + sugg::ONE)
993 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
996 print_sum(&Offset::positive(end_str), &offset)
1002 // The only statements in the for loops can be indexed assignments from
1003 // indexed retrievals.
1004 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1006 let big_sugg = manual_copies
1008 .map(|(dst_var, src_var)| {
1009 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1010 let dst_offset = print_sum(&start_str, &dst_var.offset);
1011 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1012 let src_offset = print_sum(&start_str, &src_var.offset);
1013 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1014 let dst = if dst_offset == "" && dst_limit == "" {
1017 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1021 "{}.clone_from_slice(&{}[{}..{}])",
1022 dst, src_var.var_name, src_offset, src_limit
1027 if !big_sugg.is_empty() {
1032 "it looks like you're manually copying between slices",
1033 "try replacing the loop by",
1035 Applicability::Unspecified,
1042 /// Checks for looping over a range and then indexing a sequence with it.
1043 /// The iteratee must be a range literal.
1044 #[allow(clippy::too_many_lines)]
1045 fn check_for_loop_range<'a, 'tcx>(
1046 cx: &LateContext<'a, 'tcx>,
1052 if let Some(higher::Range {
1056 }) = higher::range(cx, arg)
1058 // the var must be a single name
1059 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1060 let mut visitor = VarVisitor {
1063 indexed_mut: FxHashSet::default(),
1064 indexed_indirectly: FxHashMap::default(),
1065 indexed_directly: FxHashMap::default(),
1066 referenced: FxHashSet::default(),
1068 prefer_mutable: false,
1070 walk_expr(&mut visitor, body);
1072 // linting condition: we only indexed one variable, and indexed it directly
1073 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1074 let (indexed, (indexed_extent, indexed_ty)) = visitor
1078 .expect("already checked that we have exactly 1 element");
1080 // ensure that the indexed variable was declared before the loop, see #601
1081 if let Some(indexed_extent) = indexed_extent {
1082 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1083 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1084 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1085 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1086 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1091 // don't lint if the container that is indexed does not have .iter() method
1092 let has_iter = has_iter_method(cx, indexed_ty);
1093 if has_iter.is_none() {
1097 // don't lint if the container that is indexed into is also used without
1099 if visitor.referenced.contains(&indexed) {
1103 let starts_at_zero = is_integer_const(cx, start, 0);
1105 let skip = if starts_at_zero {
1108 format!(".skip({})", snippet(cx, start.span, ".."))
1111 let mut end_is_start_plus_val = false;
1113 let take = if let Some(end) = *end {
1114 let mut take_expr = end;
1116 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1117 if let BinOpKind::Add = op.node {
1118 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1119 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1121 if start_equal_left {
1123 } else if start_equal_right {
1127 end_is_start_plus_val = start_equal_left | start_equal_right;
1131 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1135 ast::RangeLimits::Closed => {
1136 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1137 format!(".take({})", take_expr + sugg::ONE)
1139 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1146 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1147 ("mut ", "iter_mut")
1152 let take_is_empty = take.is_empty();
1153 let mut method_1 = take;
1154 let mut method_2 = skip;
1156 if end_is_start_plus_val {
1157 mem::swap(&mut method_1, &mut method_2);
1160 if visitor.nonindex {
1163 NEEDLESS_RANGE_LOOP,
1165 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1169 "consider using an iterator".to_string(),
1171 (pat.span, format!("({}, <item>)", ident.name)),
1174 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1181 let repl = if starts_at_zero && take_is_empty {
1182 format!("&{}{}", ref_mut, indexed)
1184 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1189 NEEDLESS_RANGE_LOOP,
1192 "the loop variable `{}` is only used to index `{}`.",
1198 "consider using an iterator".to_string(),
1199 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1209 fn is_len_call(expr: &Expr, var: Name) -> bool {
1211 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.kind;
1212 if len_args.len() == 1;
1213 if method.ident.name == sym!(len);
1214 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1215 if path.segments.len() == 1;
1216 if path.segments[0].ident.name == var;
1225 fn is_end_eq_array_len<'tcx>(
1226 cx: &LateContext<'_, 'tcx>,
1228 limits: ast::RangeLimits,
1229 indexed_ty: Ty<'tcx>,
1232 if let ExprKind::Lit(ref lit) = end.kind;
1233 if let ast::LitKind::Int(end_int, _) = lit.node;
1234 if let ty::Array(_, arr_len_const) = indexed_ty.kind;
1235 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1237 return match limits {
1238 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1239 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1247 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1248 // if this for loop is iterating over a two-sided range...
1249 if let Some(higher::Range {
1253 }) = higher::range(cx, arg)
1255 // ...and both sides are compile-time constant integers...
1256 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1257 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1258 // ...and the start index is greater than the end index,
1259 // this loop will never run. This is often confusing for developers
1260 // who think that this will iterate from the larger value to the
1262 let ty = cx.tables.expr_ty(start);
1263 let (sup, eq) = match (start_idx, end_idx) {
1264 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1266 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1267 ty::Uint(_) => start_idx > end_idx,
1270 start_idx == end_idx,
1272 _ => (false, false),
1276 let start_snippet = snippet(cx, start.span, "_");
1277 let end_snippet = snippet(cx, end.span, "_");
1278 let dots = if limits == ast::RangeLimits::Closed {
1288 "this range is empty so this for loop will never run",
1292 "consider using the following if you are attempting to iterate over this \
1295 "({end}{dots}{start}).rev()",
1298 start = start_snippet
1300 Applicability::MaybeIncorrect,
1304 } else if eq && limits != ast::RangeLimits::Closed {
1305 // if they are equal, it's also problematic - this loop
1311 "this range is empty so this for loop will never run",
1319 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1320 let mut applicability = Applicability::MachineApplicable;
1321 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1322 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1327 "it is more concise to loop over references to containers instead of using explicit \
1329 "to write this more concisely, try",
1330 format!("&{}{}", muta, object),
1335 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1336 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1337 if let ExprKind::MethodCall(ref method, _, ref args) = arg.kind {
1338 // just the receiver, no arguments
1339 if args.len() == 1 {
1340 let method_name = &*method.ident.as_str();
1341 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1342 if method_name == "iter" || method_name == "iter_mut" {
1343 if is_ref_iterable_type(cx, &args[0]) {
1344 lint_iter_method(cx, args, arg, method_name);
1346 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1347 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1348 let substs = cx.tables.node_substs(arg.hir_id);
1349 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1351 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1352 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1353 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1354 match cx.tables.expr_ty(&args[0]).kind {
1355 // If the length is greater than 32 no traits are implemented for array and
1356 // therefore we cannot use `&`.
1357 ty::Array(_, size) if size.eval_usize(cx.tcx, cx.param_env) > 32 => {},
1358 _ => lint_iter_method(cx, args, arg, method_name),
1361 let mut applicability = Applicability::MachineApplicable;
1362 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1365 EXPLICIT_INTO_ITER_LOOP,
1367 "it is more concise to loop over containers instead of using explicit \
1368 iteration methods`",
1369 "to write this more concisely, try",
1374 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1379 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1380 probably not what you want",
1382 next_loop_linted = true;
1386 if !next_loop_linted {
1387 check_arg_type(cx, pat, arg);
1391 /// Checks for `for` loops over `Option`s and `Result`s.
1392 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1393 let ty = cx.tables.expr_ty(arg);
1394 if match_type(cx, ty, &paths::OPTION) {
1397 FOR_LOOP_OVER_OPTION,
1400 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1401 `if let` statement.",
1402 snippet(cx, arg.span, "_")
1405 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1406 snippet(cx, pat.span, "_"),
1407 snippet(cx, arg.span, "_")
1410 } else if match_type(cx, ty, &paths::RESULT) {
1413 FOR_LOOP_OVER_RESULT,
1416 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1417 `if let` statement.",
1418 snippet(cx, arg.span, "_")
1421 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1422 snippet(cx, pat.span, "_"),
1423 snippet(cx, arg.span, "_")
1429 fn check_for_loop_explicit_counter<'a, 'tcx>(
1430 cx: &LateContext<'a, 'tcx>,
1436 // Look for variables that are incremented once per loop iteration.
1437 let mut visitor = IncrementVisitor {
1439 states: FxHashMap::default(),
1443 walk_expr(&mut visitor, body);
1445 // For each candidate, check the parent block to see if
1446 // it's initialized to zero at the start of the loop.
1447 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1448 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1449 let mut visitor2 = InitializeVisitor {
1453 state: VarState::IncrOnce,
1458 walk_block(&mut visitor2, block);
1460 if visitor2.state == VarState::Warn {
1461 if let Some(name) = visitor2.name {
1462 let mut applicability = Applicability::MachineApplicable;
1464 // for some reason this is the only way to get the `Span`
1465 // of the entire `for` loop
1466 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1474 EXPLICIT_COUNTER_LOOP,
1475 for_span.with_hi(arg.span.hi()),
1476 &format!("the variable `{}` is used as a loop counter.", name),
1479 "for ({}, {}) in {}.enumerate()",
1481 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1482 make_iterator_snippet(cx, arg, &mut applicability),
1492 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1493 /// actual `Iterator` that the loop uses.
1494 fn make_iterator_snippet(cx: &LateContext<'_, '_>, arg: &Expr, applic_ref: &mut Applicability) -> String {
1495 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR)
1496 .map_or(false, |id| implements_trait(cx, cx.tables.expr_ty(arg), id, &[]));
1500 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1503 // (&x).into_iter() ==> x.iter()
1504 // (&mut x).into_iter() ==> x.iter_mut()
1506 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1507 if has_iter_method(cx, cx.tables.expr_ty(&arg_inner)).is_some() =>
1509 let meth_name = match mutability {
1510 Mutability::Mut => "iter_mut",
1511 Mutability::Not => "iter",
1515 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1521 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1527 /// Checks for the `FOR_KV_MAP` lint.
1528 fn check_for_loop_over_map_kv<'a, 'tcx>(
1529 cx: &LateContext<'a, 'tcx>,
1535 let pat_span = pat.span;
1537 if let PatKind::Tuple(ref pat, _) = pat.kind {
1539 let arg_span = arg.span;
1540 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).kind {
1541 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1542 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1543 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Not),
1548 let mutbl = match mutbl {
1549 Mutability::Not => "",
1550 Mutability::Mut => "_mut",
1552 let arg = match arg.kind {
1553 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1557 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1562 &format!("you seem to want to iterate on a map's {}s", kind),
1564 let map = sugg::Sugg::hir(cx, arg, "map");
1567 "use the corresponding method".into(),
1569 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1570 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1580 struct MutatePairDelegate {
1581 hir_id_low: Option<HirId>,
1582 hir_id_high: Option<HirId>,
1583 span_low: Option<Span>,
1584 span_high: Option<Span>,
1587 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1588 fn consume(&mut self, _: &Place<'tcx>, _: ConsumeMode) {}
1590 fn borrow(&mut self, cmt: &Place<'tcx>, bk: ty::BorrowKind) {
1591 if let ty::BorrowKind::MutBorrow = bk {
1592 if let PlaceBase::Local(id) = cmt.base {
1593 if Some(id) == self.hir_id_low {
1594 self.span_low = Some(cmt.span)
1596 if Some(id) == self.hir_id_high {
1597 self.span_high = Some(cmt.span)
1603 fn mutate(&mut self, cmt: &Place<'tcx>) {
1604 if let PlaceBase::Local(id) = cmt.base {
1605 if Some(id) == self.hir_id_low {
1606 self.span_low = Some(cmt.span)
1608 if Some(id) == self.hir_id_high {
1609 self.span_high = Some(cmt.span)
1615 impl<'tcx> MutatePairDelegate {
1616 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1617 (self.span_low, self.span_high)
1621 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1622 if let Some(higher::Range {
1626 }) = higher::range(cx, arg)
1628 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1629 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1630 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1631 mut_warn_with_span(cx, span_low);
1632 mut_warn_with_span(cx, span_high);
1637 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1638 if let Some(sp) = span {
1643 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1648 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1650 if let ExprKind::Path(ref qpath) = bound.kind;
1651 if let QPath::Resolved(None, _) = *qpath;
1653 let res = qpath_res(cx, qpath, bound.hir_id);
1654 if let Res::Local(node_id) = res {
1655 let node_str = cx.tcx.hir().get(node_id);
1657 if let Node::Binding(pat) = node_str;
1658 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1659 if let BindingAnnotation::Mutable = bind_ann;
1661 return Some(node_id);
1670 fn check_for_mutation(
1671 cx: &LateContext<'_, '_>,
1673 bound_ids: &[Option<HirId>],
1674 ) -> (Option<Span>, Option<Span>) {
1675 let mut delegate = MutatePairDelegate {
1676 hir_id_low: bound_ids[0],
1677 hir_id_high: bound_ids[1],
1681 let def_id = def_id::DefId::local(body.hir_id.owner);
1682 cx.tcx.infer_ctxt().enter(|infcx| {
1683 ExprUseVisitor::new(&mut delegate, &infcx, def_id, cx.param_env, cx.tables).walk_expr(body);
1685 delegate.mutation_span()
1688 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1689 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1691 PatKind::Wild => true,
1692 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1693 let mut visitor = UsedVisitor {
1697 walk_expr(&mut visitor, body);
1704 struct UsedVisitor {
1705 var: ast::Name, // var to look for
1706 used: bool, // has the var been used otherwise?
1709 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1710 fn visit_expr(&mut self, expr: &'tcx Expr) {
1711 if match_var(expr, self.var) {
1714 walk_expr(self, expr);
1718 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1719 NestedVisitorMap::None
1723 struct LocalUsedVisitor<'a, 'tcx> {
1724 cx: &'a LateContext<'a, 'tcx>,
1729 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1730 fn visit_expr(&mut self, expr: &'tcx Expr) {
1731 if same_var(self.cx, expr, self.local) {
1734 walk_expr(self, expr);
1738 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1739 NestedVisitorMap::None
1743 struct VarVisitor<'a, 'tcx> {
1744 /// context reference
1745 cx: &'a LateContext<'a, 'tcx>,
1746 /// var name to look for as index
1748 /// indexed variables that are used mutably
1749 indexed_mut: FxHashSet<Name>,
1750 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1751 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1752 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1753 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1754 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1755 /// Any names that are used outside an index operation.
1756 /// Used to detect things like `&mut vec` used together with `vec[i]`
1757 referenced: FxHashSet<Name>,
1758 /// has the loop variable been used in expressions other than the index of
1761 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1762 /// takes `&mut self`
1763 prefer_mutable: bool,
1766 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1767 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1769 // the indexed container is referenced by a name
1770 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
1771 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1772 if seqvar.segments.len() == 1;
1774 let index_used_directly = same_var(self.cx, idx, self.var);
1775 let indexed_indirectly = {
1776 let mut used_visitor = LocalUsedVisitor {
1781 walk_expr(&mut used_visitor, idx);
1785 if indexed_indirectly || index_used_directly {
1786 if self.prefer_mutable {
1787 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1789 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
1791 Res::Local(hir_id) => {
1792 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1793 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1794 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1795 if indexed_indirectly {
1796 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1798 if index_used_directly {
1799 self.indexed_directly.insert(
1800 seqvar.segments[0].ident.name,
1801 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1804 return false; // no need to walk further *on the variable*
1806 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1807 if indexed_indirectly {
1808 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1810 if index_used_directly {
1811 self.indexed_directly.insert(
1812 seqvar.segments[0].ident.name,
1813 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1816 return false; // no need to walk further *on the variable*
1827 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1828 fn visit_expr(&mut self, expr: &'tcx Expr) {
1831 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.kind;
1832 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1833 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1834 if !self.check(&args[1], &args[0], expr);
1840 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
1841 if !self.check(idx, seqexpr, expr);
1846 // directly using a variable
1847 if let ExprKind::Path(ref qpath) = expr.kind;
1848 if let QPath::Resolved(None, ref path) = *qpath;
1849 if path.segments.len() == 1;
1851 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
1852 if local_id == self.var {
1853 self.nonindex = true;
1855 // not the correct variable, but still a variable
1856 self.referenced.insert(path.segments[0].ident.name);
1862 let old = self.prefer_mutable;
1864 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1865 self.prefer_mutable = true;
1866 self.visit_expr(lhs);
1867 self.prefer_mutable = false;
1868 self.visit_expr(rhs);
1870 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
1871 if mutbl == Mutability::Mut {
1872 self.prefer_mutable = true;
1874 self.visit_expr(expr);
1876 ExprKind::Call(ref f, ref args) => {
1879 let ty = self.cx.tables.expr_ty_adjusted(expr);
1880 self.prefer_mutable = false;
1881 if let ty::Ref(_, _, mutbl) = ty.kind {
1882 if mutbl == Mutability::Mut {
1883 self.prefer_mutable = true;
1886 self.visit_expr(expr);
1889 ExprKind::MethodCall(_, _, ref args) => {
1890 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1891 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1892 self.prefer_mutable = false;
1893 if let ty::Ref(_, _, mutbl) = ty.kind {
1894 if mutbl == Mutability::Mut {
1895 self.prefer_mutable = true;
1898 self.visit_expr(expr);
1901 ExprKind::Closure(_, _, body_id, ..) => {
1902 let body = self.cx.tcx.hir().body(body_id);
1903 self.visit_expr(&body.value);
1905 _ => walk_expr(self, expr),
1907 self.prefer_mutable = old;
1909 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1910 NestedVisitorMap::None
1914 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1915 let def_id = match var_def_id(cx, expr) {
1917 None => return false,
1919 if let Some(used_mutably) = mutated_variables(container, cx) {
1920 if used_mutably.contains(&def_id) {
1927 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1928 let def_id = match var_def_id(cx, iter_expr) {
1930 None => return false,
1932 let mut visitor = VarUsedAfterLoopVisitor {
1935 iter_expr_id: iter_expr.hir_id,
1936 past_while_let: false,
1937 var_used_after_while_let: false,
1939 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1940 walk_block(&mut visitor, enclosing_block);
1942 visitor.var_used_after_while_let
1945 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1946 cx: &'a LateContext<'a, 'tcx>,
1948 iter_expr_id: HirId,
1949 past_while_let: bool,
1950 var_used_after_while_let: bool,
1953 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1954 fn visit_expr(&mut self, expr: &'tcx Expr) {
1955 if self.past_while_let {
1956 if Some(self.def_id) == var_def_id(self.cx, expr) {
1957 self.var_used_after_while_let = true;
1959 } else if self.iter_expr_id == expr.hir_id {
1960 self.past_while_let = true;
1962 walk_expr(self, expr);
1964 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1965 NestedVisitorMap::None
1969 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1970 /// for `&T` and `&mut T`, such as `Vec`.
1972 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1973 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1974 // will allow further borrows afterwards
1975 let ty = cx.tables.expr_ty(e);
1976 is_iterable_array(ty, cx) ||
1977 is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) ||
1978 match_type(cx, ty, &paths::LINKED_LIST) ||
1979 match_type(cx, ty, &paths::HASHMAP) ||
1980 match_type(cx, ty, &paths::HASHSET) ||
1981 match_type(cx, ty, &paths::VEC_DEQUE) ||
1982 match_type(cx, ty, &paths::BINARY_HEAP) ||
1983 match_type(cx, ty, &paths::BTREEMAP) ||
1984 match_type(cx, ty, &paths::BTREESET)
1987 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1988 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1990 ty::Array(_, n) => {
1991 if let Some(val) = n.try_eval_usize(cx.tcx, cx.param_env) {
1992 (0..=32).contains(&val)
2001 /// If a block begins with a statement (possibly a `let` binding) and has an
2002 /// expression, return it.
2003 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
2004 if block.stmts.is_empty() {
2007 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2008 if let Some(ref expr) = local.init {
2018 /// If a block begins with an expression (with or without semicolon), return it.
2019 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2021 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2022 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2023 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2024 StmtKind::Local(..) | StmtKind::Item(..) => None,
2030 /// Returns `true` if expr contains a single break expr without destination label
2032 /// passed expression. The expression may be within a block.
2033 fn is_simple_break_expr(expr: &Expr) -> bool {
2035 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2036 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2041 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2042 // incremented exactly once in the loop body, and initialized to zero
2043 // at the start of the loop.
2044 #[derive(Debug, PartialEq)]
2046 Initial, // Not examined yet
2047 IncrOnce, // Incremented exactly once, may be a loop counter
2048 Declared, // Declared but not (yet) initialized to zero
2053 /// Scan a for loop for variables that are incremented exactly once.
2054 struct IncrementVisitor<'a, 'tcx> {
2055 cx: &'a LateContext<'a, 'tcx>, // context reference
2056 states: FxHashMap<HirId, VarState>, // incremented variables
2057 depth: u32, // depth of conditional expressions
2061 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2062 fn visit_expr(&mut self, expr: &'tcx Expr) {
2067 // If node is a variable
2068 if let Some(def_id) = var_def_id(self.cx, expr) {
2069 if let Some(parent) = get_parent_expr(self.cx, expr) {
2070 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2073 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2074 if lhs.hir_id == expr.hir_id {
2075 if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) {
2076 *state = match *state {
2077 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2078 _ => VarState::DontWarn,
2081 // Assigned some other value
2082 *state = VarState::DontWarn;
2086 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2087 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2088 *state = VarState::DontWarn
2093 } else if is_loop(expr) || is_conditional(expr) {
2095 walk_expr(self, expr);
2098 } else if let ExprKind::Continue(_) = expr.kind {
2102 walk_expr(self, expr);
2104 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2105 NestedVisitorMap::None
2109 /// Checks whether a variable is initialized to zero at the start of a loop.
2110 struct InitializeVisitor<'a, 'tcx> {
2111 cx: &'a LateContext<'a, 'tcx>, // context reference
2112 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2116 depth: u32, // depth of conditional expressions
2120 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2121 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2122 // Look for declarations of the variable
2123 if let StmtKind::Local(ref local) = stmt.kind {
2124 if local.pat.hir_id == self.var_id {
2125 if let PatKind::Binding(.., ident, _) = local.pat.kind {
2126 self.name = Some(ident.name);
2128 self.state = if let Some(ref init) = local.init {
2129 if is_integer_const(&self.cx, init, 0) {
2140 walk_stmt(self, stmt);
2143 fn visit_expr(&mut self, expr: &'tcx Expr) {
2144 if self.state == VarState::DontWarn {
2147 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2148 self.past_loop = true;
2151 // No need to visit expressions before the variable is
2153 if self.state == VarState::IncrOnce {
2157 // If node is the desired variable, see how it's used
2158 if var_def_id(self.cx, expr) == Some(self.var_id) {
2159 if let Some(parent) = get_parent_expr(self.cx, expr) {
2161 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2162 self.state = VarState::DontWarn;
2164 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2165 self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 {
2171 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
2172 self.state = VarState::DontWarn
2179 self.state = VarState::DontWarn;
2182 } else if !self.past_loop && is_loop(expr) {
2183 self.state = VarState::DontWarn;
2185 } else if is_conditional(expr) {
2187 walk_expr(self, expr);
2191 walk_expr(self, expr);
2194 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2195 NestedVisitorMap::OnlyBodies(&self.cx.tcx.hir())
2199 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2200 if let ExprKind::Path(ref qpath) = expr.kind {
2201 let path_res = qpath_res(cx, qpath, expr.hir_id);
2202 if let Res::Local(node_id) = path_res {
2203 return Some(node_id);
2209 fn is_loop(expr: &Expr) -> bool {
2211 ExprKind::Loop(..) => true,
2216 fn is_conditional(expr: &Expr) -> bool {
2218 ExprKind::Match(..) => true,
2223 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2225 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2226 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2227 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2229 return is_loop_nested(cx, loop_expr, iter_expr)
2235 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2236 let mut id = loop_expr.hir_id;
2237 let iter_name = if let Some(name) = path_name(iter_expr) {
2243 let parent = cx.tcx.hir().get_parent_node(id);
2247 match cx.tcx.hir().find(parent) {
2248 Some(Node::Expr(expr)) => {
2249 if let ExprKind::Loop(..) = expr.kind {
2253 Some(Node::Block(block)) => {
2254 let mut block_visitor = LoopNestVisitor {
2256 iterator: iter_name,
2259 walk_block(&mut block_visitor, block);
2260 if block_visitor.nesting == RuledOut {
2264 Some(Node::Stmt(_)) => (),
2273 #[derive(PartialEq, Eq)]
2275 Unknown, // no nesting detected yet
2276 RuledOut, // the iterator is initialized or assigned within scope
2277 LookFurther, // no nesting detected, no further walk required
2280 use self::Nesting::{LookFurther, RuledOut, Unknown};
2282 struct LoopNestVisitor {
2288 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2289 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2290 if stmt.hir_id == self.hir_id {
2291 self.nesting = LookFurther;
2292 } else if self.nesting == Unknown {
2293 walk_stmt(self, stmt);
2297 fn visit_expr(&mut self, expr: &'tcx Expr) {
2298 if self.nesting != Unknown {
2301 if expr.hir_id == self.hir_id {
2302 self.nesting = LookFurther;
2306 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2307 if match_var(path, self.iterator) {
2308 self.nesting = RuledOut;
2311 _ => walk_expr(self, expr),
2315 fn visit_pat(&mut self, pat: &'tcx Pat) {
2316 if self.nesting != Unknown {
2319 if let PatKind::Binding(.., span_name, _) = pat.kind {
2320 if self.iterator == span_name.name {
2321 self.nesting = RuledOut;
2328 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2329 NestedVisitorMap::None
2333 fn path_name(e: &Expr) -> Option<Name> {
2334 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2335 let segments = &path.segments;
2336 if segments.len() == 1 {
2337 return Some(segments[0].ident.name);
2343 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2344 if constant(cx, cx.tables, cond).is_some() {
2345 // A pure constant condition (e.g., `while false`) is not linted.
2349 let mut var_visitor = VarCollectorVisitor {
2351 ids: FxHashSet::default(),
2352 def_ids: FxHashMap::default(),
2355 var_visitor.visit_expr(cond);
2356 if var_visitor.skip {
2359 let used_in_condition = &var_visitor.ids;
2360 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2361 used_in_condition.is_disjoint(&used_mutably)
2365 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2367 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2368 has_break_or_return: false,
2370 has_break_or_return_visitor.visit_expr(expr);
2371 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2373 if no_cond_variable_mutated && !mutable_static_in_cond {
2376 WHILE_IMMUTABLE_CONDITION,
2378 "variables in the condition are not mutated in the loop body",
2380 db.note("this may lead to an infinite or to a never running loop");
2382 if has_break_or_return {
2383 db.note("this loop contains `return`s or `break`s");
2384 db.help("rewrite it as `if cond { loop { } }`");
2391 struct HasBreakOrReturnVisitor {
2392 has_break_or_return: bool,
2395 impl<'a, 'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2396 fn visit_expr(&mut self, expr: &'tcx Expr) {
2397 if self.has_break_or_return {
2402 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2403 self.has_break_or_return = true;
2409 walk_expr(self, expr);
2412 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2413 NestedVisitorMap::None
2417 /// Collects the set of variables in an expression
2418 /// Stops analysis if a function call is found
2419 /// Note: In some cases such as `self`, there are no mutable annotation,
2420 /// All variables definition IDs are collected
2421 struct VarCollectorVisitor<'a, 'tcx> {
2422 cx: &'a LateContext<'a, 'tcx>,
2423 ids: FxHashSet<HirId>,
2424 def_ids: FxHashMap<def_id::DefId, bool>,
2428 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2429 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2431 if let ExprKind::Path(ref qpath) = ex.kind;
2432 if let QPath::Resolved(None, _) = *qpath;
2433 let res = qpath_res(self.cx, qpath, ex.hir_id);
2436 Res::Local(node_id) => {
2437 self.ids.insert(node_id);
2439 Res::Def(DefKind::Static, def_id) => {
2440 let mutable = self.cx.tcx.is_mutable_static(def_id);
2441 self.def_ids.insert(def_id, mutable);
2450 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2451 fn visit_expr(&mut self, ex: &'tcx Expr) {
2453 ExprKind::Path(_) => self.insert_def_id(ex),
2454 // If there is any function/method call… we just stop analysis
2455 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2457 _ => walk_expr(self, ex),
2461 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2462 NestedVisitorMap::None
2466 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2468 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2470 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
2471 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].kind;
2472 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2473 if let Some(ref generic_args) = chain_method.args;
2474 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2476 let ty = cx.tables.node_type(ty.hir_id);
2477 if is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) ||
2478 match_type(cx, ty, &paths::VEC_DEQUE) ||
2479 match_type(cx, ty, &paths::BTREEMAP) ||
2480 match_type(cx, ty, &paths::HASHMAP) {
2481 if method.ident.name == sym!(len) {
2482 let span = shorten_needless_collect_span(expr);
2483 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2487 ".count()".to_string(),
2488 Applicability::MachineApplicable,
2492 if method.ident.name == sym!(is_empty) {
2493 let span = shorten_needless_collect_span(expr);
2494 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2498 ".next().is_none()".to_string(),
2499 Applicability::MachineApplicable,
2503 if method.ident.name == sym!(contains) {
2504 let contains_arg = snippet(cx, args[1].span, "??");
2505 let span = shorten_needless_collect_span(expr);
2506 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2507 let (arg, pred) = if contains_arg.starts_with('&') {
2508 ("x", &contains_arg[1..])
2510 ("&x", &*contains_arg)
2516 ".any(|{}| x == {})",
2519 Applicability::MachineApplicable,
2528 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2530 if let ExprKind::MethodCall(_, _, ref args) = expr.kind;
2531 if let ExprKind::MethodCall(_, ref span, _) = args[0].kind;
2533 return expr.span.with_lo(span.lo() - BytePos(1));