1 use crate::reexport::*;
2 use if_chain::if_chain;
3 use itertools::Itertools;
4 use rustc::hir::def::{DefKind, Res};
5 use rustc::hir::def_id;
6 use rustc::hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
8 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
9 use rustc::middle::region;
10 use rustc::{declare_lint_pass, declare_tool_lint};
11 // use rustc::middle::region::CodeExtent;
12 use crate::consts::{constant, Constant};
13 use crate::utils::usage::mutated_variables;
14 use crate::utils::{in_macro_or_desugar, sext, sugg};
15 use rustc::middle::expr_use_visitor::*;
16 use rustc::middle::mem_categorization::cmt_;
17 use rustc::middle::mem_categorization::Categorization;
18 use rustc::ty::subst::Subst;
19 use rustc::ty::{self, Ty};
20 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
21 use rustc_errors::Applicability;
22 use std::iter::{once, Iterator};
25 use syntax::source_map::Span;
26 use syntax_pos::BytePos;
28 use crate::utils::paths;
30 get_enclosing_block, get_parent_expr, has_iter_method, higher, is_integer_literal, is_refutable, last_path_segment,
31 match_trait_method, match_type, match_var, multispan_sugg, snippet, snippet_opt, snippet_with_applicability,
32 span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then, SpanlessEq,
35 declare_clippy_lint! {
36 /// **What it does:** Checks for for-loops that manually copy items between
37 /// slices that could be optimized by having a memcpy.
39 /// **Why is this bad?** It is not as fast as a memcpy.
41 /// **Known problems:** None.
45 /// for i in 0..src.len() {
46 /// dst[i + 64] = src[i];
51 "manually copying items between slices"
54 declare_clippy_lint! {
55 /// **What it does:** Checks for looping over the range of `0..len` of some
56 /// collection just to get the values by index.
58 /// **Why is this bad?** Just iterating the collection itself makes the intent
59 /// more clear and is probably faster.
61 /// **Known problems:** None.
65 /// let vec = vec!['a', 'b', 'c'];
66 /// for i in 0..vec.len() {
67 /// println!("{}", vec[i]);
70 /// Could be written as:
72 /// let vec = vec!['a', 'b', 'c'];
74 /// println!("{}", i);
77 pub NEEDLESS_RANGE_LOOP,
79 "for-looping over a range of indices where an iterator over items would do"
82 declare_clippy_lint! {
83 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
84 /// suggests the latter.
86 /// **Why is this bad?** Readability.
88 /// **Known problems:** False negatives. We currently only warn on some known
93 /// // with `y` a `Vec` or slice:
94 /// for x in y.iter() {
98 /// can be rewritten to
104 pub EXPLICIT_ITER_LOOP,
106 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
109 declare_clippy_lint! {
110 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
111 /// suggests the latter.
113 /// **Why is this bad?** Readability.
115 /// **Known problems:** None
119 /// // with `y` a `Vec` or slice:
120 /// for x in y.into_iter() {
124 /// can be rewritten to
130 pub EXPLICIT_INTO_ITER_LOOP,
132 "for-looping over `_.into_iter()` when `_` would do"
135 declare_clippy_lint! {
136 /// **What it does:** Checks for loops on `x.next()`.
138 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
139 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
140 /// implements `IntoIterator`, so that possibly one value will be iterated,
141 /// leading to some hard to find bugs. No one will want to write such code
142 /// [except to win an Underhanded Rust
143 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
145 /// **Known problems:** None.
149 /// for x in y.next() {
155 "for-looping over `_.next()` which is probably not intended"
158 declare_clippy_lint! {
159 /// **What it does:** Checks for `for` loops over `Option` values.
161 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
164 /// **Known problems:** None.
168 /// for x in option {
175 /// if let Some(x) = option {
179 pub FOR_LOOP_OVER_OPTION,
181 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
184 declare_clippy_lint! {
185 /// **What it does:** Checks for `for` loops over `Result` values.
187 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
190 /// **Known problems:** None.
194 /// for x in result {
201 /// if let Ok(x) = result {
205 pub FOR_LOOP_OVER_RESULT,
207 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
210 declare_clippy_lint! {
211 /// **What it does:** Detects `loop + match` combinations that are easier
212 /// written as a `while let` loop.
214 /// **Why is this bad?** The `while let` loop is usually shorter and more
217 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
222 /// let x = match y {
226 /// // .. do something with x
228 /// // is easier written as
229 /// while let Some(x) = y {
230 /// // .. do something with x
235 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
238 declare_clippy_lint! {
239 /// **What it does:** Checks for using `collect()` on an iterator without using
242 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
243 /// iterator instead.
245 /// **Known problems:** None.
249 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
253 "`collect()`ing an iterator without using the result; this is usually better written as a for loop"
256 declare_clippy_lint! {
257 /// **What it does:** Checks for functions collecting an iterator when collect
260 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
261 /// when this allocation may not be needed.
263 /// **Known problems:**
268 /// let len = iterator.collect::<Vec<_>>().len();
270 /// let len = iterator.count();
272 pub NEEDLESS_COLLECT,
274 "collecting an iterator when collect is not needed"
277 declare_clippy_lint! {
278 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
279 /// are constant and `x` is greater or equal to `y`, unless the range is
280 /// reversed or has a negative `.step_by(_)`.
282 /// **Why is it bad?** Such loops will either be skipped or loop until
283 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
286 /// **Known problems:** The lint cannot catch loops over dynamically defined
287 /// ranges. Doing this would require simulating all possible inputs and code
288 /// paths through the program, which would be complex and error-prone.
292 /// for x in 5..10 - 5 {
294 /// } // oops, stray `-`
296 pub REVERSE_RANGE_LOOP,
298 "iteration over an empty range, such as `10..0` or `5..5`"
301 declare_clippy_lint! {
302 /// **What it does:** Checks `for` loops over slices with an explicit counter
303 /// and suggests the use of `.enumerate()`.
305 /// **Why is it bad?** Not only is the version using `.enumerate()` more
306 /// readable, the compiler is able to remove bounds checks which can lead to
307 /// faster code in some instances.
309 /// **Known problems:** None.
313 /// for i in 0..v.len() { foo(v[i]);
314 /// for i in 0..v.len() { bar(i, v[i]); }
316 pub EXPLICIT_COUNTER_LOOP,
318 "for-looping with an explicit counter when `_.enumerate()` would do"
321 declare_clippy_lint! {
322 /// **What it does:** Checks for empty `loop` expressions.
324 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
325 /// anything. Think of the environment and either block on something or at least
326 /// make the thread sleep for some microseconds.
328 /// **Known problems:** None.
336 "empty `loop {}`, which should block or sleep"
339 declare_clippy_lint! {
340 /// **What it does:** Checks for `while let` expressions on iterators.
342 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
343 /// the intent better.
345 /// **Known problems:** None.
349 /// while let Some(val) = iter() {
353 pub WHILE_LET_ON_ITERATOR,
355 "using a while-let loop instead of a for loop on an iterator"
358 declare_clippy_lint! {
359 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
360 /// ignoring either the keys or values.
362 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
363 /// can be used to express that don't need the values or keys.
365 /// **Known problems:** None.
369 /// for (k, _) in &map {
374 /// could be replaced by
377 /// for k in map.keys() {
383 "looping on a map using `iter` when `keys` or `values` would do"
386 declare_clippy_lint! {
387 /// **What it does:** Checks for loops that will always `break`, `return` or
388 /// `continue` an outer loop.
390 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
393 /// **Known problems:** None
404 "any loop that will always `break` or `return`"
407 declare_clippy_lint! {
408 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
410 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
412 /// **Known problems:** None
416 /// let mut foo = 42;
417 /// for i in 0..foo {
419 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
424 "for loop over a range where one of the bounds is a mutable variable"
427 declare_clippy_lint! {
428 /// **What it does:** Checks whether variables used within while loop condition
429 /// can be (and are) mutated in the body.
431 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
432 /// will lead to an infinite loop.
434 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
435 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
436 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
442 /// println!("let me loop forever!");
445 pub WHILE_IMMUTABLE_CONDITION,
447 "variables used within while expression are not mutated in the body"
450 declare_lint_pass!(Loops => [
454 EXPLICIT_INTO_ITER_LOOP,
456 FOR_LOOP_OVER_RESULT,
457 FOR_LOOP_OVER_OPTION,
462 EXPLICIT_COUNTER_LOOP,
464 WHILE_LET_ON_ITERATOR,
468 WHILE_IMMUTABLE_CONDITION,
471 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
472 #[allow(clippy::too_many_lines)]
473 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
474 // we don't want to check expanded macros
475 if in_macro_or_desugar(expr.span) {
479 if let Some((pat, arg, body)) = higher::for_loop(expr) {
480 check_for_loop(cx, pat, arg, body, expr);
483 // check for never_loop
485 ExprKind::While(_, ref block, _) | ExprKind::Loop(ref block, _, _) => {
486 match never_loop_block(block, expr.hir_id) {
487 NeverLoopResult::AlwaysBreak => {
488 span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops")
490 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
496 // check for `loop { if let {} else break }` that could be `while let`
497 // (also matches an explicit "match" instead of "if let")
498 // (even if the "match" or "if let" is used for declaration)
499 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
500 // also check for empty `loop {}` statements
501 if block.stmts.is_empty() && block.expr.is_none() {
506 "empty `loop {}` detected. You may want to either use `panic!()` or add \
507 `std::thread::sleep(..);` to the loop body.",
511 // extract the expression from the first statement (if any) in a block
512 let inner_stmt_expr = extract_expr_from_first_stmt(block);
513 // or extract the first expression (if any) from the block
514 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
515 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
516 // ensure "if let" compatible match structure
518 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
520 && arms[0].pats.len() == 1
521 && arms[0].guard.is_none()
522 && arms[1].pats.len() == 1
523 && arms[1].guard.is_none()
524 && is_simple_break_expr(&arms[1].body)
526 if in_external_macro(cx.sess(), expr.span) {
530 // NOTE: we used to build a body here instead of using
531 // ellipsis, this was removed because:
532 // 1) it was ugly with big bodies;
533 // 2) it was not indented properly;
534 // 3) it wasn’t very smart (see #675).
535 let mut applicability = Applicability::HasPlaceholders;
540 "this loop could be written as a `while let` loop",
543 "while let {} = {} {{ .. }}",
544 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
545 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
556 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
557 let pat = &arms[0].pats[0].node;
559 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
560 &ExprKind::MethodCall(ref method_path, _, ref method_args),
561 ) = (pat, &match_expr.node)
563 let iter_expr = &method_args[0];
564 let lhs_constructor = last_path_segment(qpath);
565 if method_path.ident.name == sym!(next)
566 && match_trait_method(cx, match_expr, &paths::ITERATOR)
567 && lhs_constructor.ident.name == sym!(Some)
568 && (pat_args.is_empty()
569 || !is_refutable(cx, &pat_args[0])
570 && !is_used_inside(cx, iter_expr, &arms[0].body)
571 && !is_iterator_used_after_while_let(cx, iter_expr)
572 && !is_nested(cx, expr, &method_args[0]))
574 let iterator = snippet(cx, method_args[0].span, "_");
575 let loop_var = if pat_args.is_empty() {
578 snippet(cx, pat_args[0].span, "_").into_owned()
582 WHILE_LET_ON_ITERATOR,
584 "this loop could be written as a `for` loop",
586 format!("for {} in {} {{ .. }}", loop_var, iterator),
587 Applicability::HasPlaceholders,
593 // check for while loops which conditions never change
594 if let ExprKind::While(ref cond, _, _) = expr.node {
595 check_infinite_loop(cx, cond, expr);
598 check_needless_collect(expr, cx);
601 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
602 if let StmtKind::Semi(ref expr) = stmt.node {
603 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
605 && method.ident.name == sym!(collect)
606 && match_trait_method(cx, expr, &paths::ITERATOR)
612 "you are collect()ing an iterator and throwing away the result. \
613 Consider using an explicit for loop to exhaust the iterator",
621 enum NeverLoopResult {
622 // A break/return always get triggered but not necessarily for the main loop.
624 // A continue may occur for the main loop.
629 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
631 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
632 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
636 // Combine two results for parts that are called in order.
637 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
639 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
640 NeverLoopResult::Otherwise => second,
644 // Combine two results where both parts are called but not necessarily in order.
645 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
646 match (left, right) {
647 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
648 NeverLoopResult::MayContinueMainLoop
650 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
651 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
655 // Combine two results where only one of the part may have been executed.
656 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
658 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
659 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
660 NeverLoopResult::MayContinueMainLoop
662 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
666 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
667 let stmts = block.stmts.iter().map(stmt_to_expr);
668 let expr = once(block.expr.as_ref().map(|p| &**p));
669 let mut iter = stmts.chain(expr).filter_map(|e| e);
670 never_loop_expr_seq(&mut iter, main_loop_id)
673 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
675 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
676 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
681 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
684 | ExprKind::Unary(_, ref e)
685 | ExprKind::Cast(ref e, _)
686 | ExprKind::Type(ref e, _)
687 | ExprKind::Field(ref e, _)
688 | ExprKind::AddrOf(_, ref e)
689 | ExprKind::Struct(_, _, Some(ref e))
690 | ExprKind::Repeat(ref e, _)
691 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
692 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
693 never_loop_expr_all(&mut es.iter(), main_loop_id)
695 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
696 ExprKind::Binary(_, ref e1, ref e2)
697 | ExprKind::Assign(ref e1, ref e2)
698 | ExprKind::AssignOp(_, ref e1, ref e2)
699 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
700 ExprKind::Loop(ref b, _, _) => {
701 // Break can come from the inner loop so remove them.
702 absorb_break(&never_loop_block(b, main_loop_id))
704 ExprKind::While(ref e, ref b, _) => {
705 let e = never_loop_expr(e, main_loop_id);
706 let result = never_loop_block(b, main_loop_id);
707 // Break can come from the inner loop so remove them.
708 combine_seq(e, absorb_break(&result))
710 ExprKind::Match(ref e, ref arms, _) => {
711 let e = never_loop_expr(e, main_loop_id);
715 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
719 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
720 ExprKind::Continue(d) => {
723 .expect("target ID can only be missing in the presence of compilation errors");
724 if id == main_loop_id {
725 NeverLoopResult::MayContinueMainLoop
727 NeverLoopResult::AlwaysBreak
730 ExprKind::Break(_, _) => NeverLoopResult::AlwaysBreak,
731 ExprKind::Ret(ref e) => {
732 if let Some(ref e) = *e {
733 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
735 NeverLoopResult::AlwaysBreak
738 ExprKind::Struct(_, _, None)
739 | ExprKind::Yield(_, _)
740 | ExprKind::Closure(_, _, _, _, _)
741 | ExprKind::InlineAsm(_, _, _)
744 | ExprKind::Err => NeverLoopResult::Otherwise,
748 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
749 es.map(|e| never_loop_expr(e, main_loop_id))
750 .fold(NeverLoopResult::Otherwise, combine_seq)
753 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
754 es.map(|e| never_loop_expr(e, main_loop_id))
755 .fold(NeverLoopResult::Otherwise, combine_both)
758 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
759 e.map(|e| never_loop_expr(e, main_loop_id))
760 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
763 fn check_for_loop<'a, 'tcx>(
764 cx: &LateContext<'a, 'tcx>,
770 check_for_loop_range(cx, pat, arg, body, expr);
771 check_for_loop_reverse_range(cx, arg, expr);
772 check_for_loop_arg(cx, pat, arg, expr);
773 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
774 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
775 check_for_mut_range_bound(cx, arg, body);
776 detect_manual_memcpy(cx, pat, arg, body, expr);
779 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
781 if let ExprKind::Path(ref qpath) = expr.node;
782 if let QPath::Resolved(None, ref path) = *qpath;
783 if path.segments.len() == 1;
784 if let Res::Local(local_id) = cx.tables.qpath_res(qpath, expr.hir_id);
801 fn negative(s: String) -> Self {
802 Self { value: s, negate: true }
805 fn positive(s: String) -> Self {
813 struct FixedOffsetVar {
818 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
819 let is_slice = match ty.sty {
820 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
821 ty::Slice(..) | ty::Array(..) => true,
825 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
828 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
829 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
831 ExprKind::Lit(ref l) => match l.node {
832 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
835 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
840 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
841 let ty = cx.tables.expr_ty(seqexpr);
842 if !is_slice_like(cx, ty) {
846 let offset = match idx.node {
847 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
849 let offset_opt = if same_var(cx, lhs, var) {
850 extract_offset(cx, rhs, var)
851 } else if same_var(cx, rhs, var) {
852 extract_offset(cx, lhs, var)
857 offset_opt.map(Offset::positive)
859 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
862 ExprKind::Path(..) => {
863 if same_var(cx, idx, var) {
864 Some(Offset::positive("0".into()))
872 offset.map(|o| FixedOffsetVar {
873 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
881 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
882 cx: &LateContext<'a, 'tcx>,
885 ) -> Option<FixedOffsetVar> {
887 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
888 if method.ident.name == sym!(clone);
890 if let Some(arg) = args.get(0);
892 return get_fixed_offset_var(cx, arg, var);
896 get_fixed_offset_var(cx, expr, var)
899 fn get_indexed_assignments<'a, 'tcx>(
900 cx: &LateContext<'a, 'tcx>,
903 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
904 fn get_assignment<'a, 'tcx>(
905 cx: &LateContext<'a, 'tcx>,
908 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
909 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
911 get_fixed_offset_var(cx, lhs, var),
912 fetch_cloned_fixed_offset_var(cx, rhs, var),
914 (Some(offset_left), Some(offset_right)) => {
915 // Source and destination must be different
916 if offset_left.var_name == offset_right.var_name {
919 Some((offset_left, offset_right))
929 if let ExprKind::Block(ref b, _) = body.node {
931 ref stmts, ref expr, ..
936 .map(|stmt| match stmt.node {
937 StmtKind::Local(..) | StmtKind::Item(..) => None,
938 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
940 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
942 .collect::<Option<Vec<_>>>()
943 .unwrap_or_else(|| vec![])
945 get_assignment(cx, body, var).into_iter().collect()
949 /// Checks for for loops that sequentially copy items from one slice-like
950 /// object to another.
951 fn detect_manual_memcpy<'a, 'tcx>(
952 cx: &LateContext<'a, 'tcx>,
958 if let Some(higher::Range {
962 }) = higher::range(cx, arg)
964 // the var must be a single name
965 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
966 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
967 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
968 ("0", _, "0", _) => "".into(),
969 ("0", _, x, false) | (x, false, "0", false) => x.into(),
970 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
971 (x, false, y, false) => format!("({} + {})", x, y),
972 (x, false, y, true) => {
976 format!("({} - {})", x, y)
979 (x, true, y, false) => {
983 format!("({} - {})", y, x)
986 (x, true, y, true) => format!("-({} + {})", x, y),
990 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
991 if let Some(end) = *end {
993 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
994 if method.ident.name == sym!(len);
995 if len_args.len() == 1;
996 if let Some(arg) = len_args.get(0);
997 if snippet(cx, arg.span, "??") == var_name;
999 return if offset.negate {
1000 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
1007 let end_str = match limits {
1008 ast::RangeLimits::Closed => {
1009 let end = sugg::Sugg::hir(cx, end, "<count>");
1010 format!("{}", end + sugg::ONE)
1012 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1015 print_sum(&Offset::positive(end_str), &offset)
1021 // The only statements in the for loops can be indexed assignments from
1022 // indexed retrievals.
1023 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1025 let big_sugg = manual_copies
1027 .map(|(dst_var, src_var)| {
1028 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1029 let dst_offset = print_sum(&start_str, &dst_var.offset);
1030 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1031 let src_offset = print_sum(&start_str, &src_var.offset);
1032 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1033 let dst = if dst_offset == "" && dst_limit == "" {
1036 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1040 "{}.clone_from_slice(&{}[{}..{}])",
1041 dst, src_var.var_name, src_offset, src_limit
1046 if !big_sugg.is_empty() {
1051 "it looks like you're manually copying between slices",
1052 "try replacing the loop by",
1054 Applicability::Unspecified,
1061 /// Checks for looping over a range and then indexing a sequence with it.
1062 /// The iteratee must be a range literal.
1063 #[allow(clippy::too_many_lines)]
1064 fn check_for_loop_range<'a, 'tcx>(
1065 cx: &LateContext<'a, 'tcx>,
1071 if in_macro_or_desugar(expr.span) {
1075 if let Some(higher::Range {
1079 }) = higher::range(cx, arg)
1081 // the var must be a single name
1082 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1083 let mut visitor = VarVisitor {
1086 indexed_mut: FxHashSet::default(),
1087 indexed_indirectly: FxHashMap::default(),
1088 indexed_directly: FxHashMap::default(),
1089 referenced: FxHashSet::default(),
1091 prefer_mutable: false,
1093 walk_expr(&mut visitor, body);
1095 // linting condition: we only indexed one variable, and indexed it directly
1096 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1097 let (indexed, (indexed_extent, indexed_ty)) = visitor
1101 .expect("already checked that we have exactly 1 element");
1103 // ensure that the indexed variable was declared before the loop, see #601
1104 if let Some(indexed_extent) = indexed_extent {
1105 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1106 let parent_def_id = cx.tcx.hir().local_def_id_from_hir_id(parent_id);
1107 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1108 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1109 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1114 // don't lint if the container that is indexed does not have .iter() method
1115 let has_iter = has_iter_method(cx, indexed_ty);
1116 if has_iter.is_none() {
1120 // don't lint if the container that is indexed into is also used without
1122 if visitor.referenced.contains(&indexed) {
1126 let starts_at_zero = is_integer_literal(start, 0);
1128 let skip = if starts_at_zero {
1131 format!(".skip({})", snippet(cx, start.span, ".."))
1134 let mut end_is_start_plus_val = false;
1136 let take = if let Some(end) = *end {
1137 let mut take_expr = end;
1139 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1140 if let BinOpKind::Add = op.node {
1141 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1142 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1144 if start_equal_left {
1146 } else if start_equal_right {
1150 end_is_start_plus_val = start_equal_left | start_equal_right;
1154 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1158 ast::RangeLimits::Closed => {
1159 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1160 format!(".take({})", take_expr + sugg::ONE)
1162 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1169 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1170 ("mut ", "iter_mut")
1175 let take_is_empty = take.is_empty();
1176 let mut method_1 = take;
1177 let mut method_2 = skip;
1179 if end_is_start_plus_val {
1180 mem::swap(&mut method_1, &mut method_2);
1183 if visitor.nonindex {
1186 NEEDLESS_RANGE_LOOP,
1188 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1192 "consider using an iterator".to_string(),
1194 (pat.span, format!("({}, <item>)", ident.name)),
1197 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1204 let repl = if starts_at_zero && take_is_empty {
1205 format!("&{}{}", ref_mut, indexed)
1207 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1212 NEEDLESS_RANGE_LOOP,
1215 "the loop variable `{}` is only used to index `{}`.",
1221 "consider using an iterator".to_string(),
1222 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1232 fn is_len_call(expr: &Expr, var: Name) -> bool {
1234 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1235 if len_args.len() == 1;
1236 if method.ident.name == sym!(len);
1237 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1238 if path.segments.len() == 1;
1239 if path.segments[0].ident.name == var;
1248 fn is_end_eq_array_len<'tcx>(
1249 cx: &LateContext<'_, 'tcx>,
1251 limits: ast::RangeLimits,
1252 indexed_ty: Ty<'tcx>,
1255 if let ExprKind::Lit(ref lit) = end.node;
1256 if let ast::LitKind::Int(end_int, _) = lit.node;
1257 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1258 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1260 return match limits {
1261 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1262 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1270 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1271 // if this for loop is iterating over a two-sided range...
1272 if let Some(higher::Range {
1276 }) = higher::range(cx, arg)
1278 // ...and both sides are compile-time constant integers...
1279 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1280 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1281 // ...and the start index is greater than the end index,
1282 // this loop will never run. This is often confusing for developers
1283 // who think that this will iterate from the larger value to the
1285 let ty = cx.tables.expr_ty(start);
1286 let (sup, eq) = match (start_idx, end_idx) {
1287 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1289 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1290 ty::Uint(_) => start_idx > end_idx,
1293 start_idx == end_idx,
1295 _ => (false, false),
1299 let start_snippet = snippet(cx, start.span, "_");
1300 let end_snippet = snippet(cx, end.span, "_");
1301 let dots = if limits == ast::RangeLimits::Closed {
1311 "this range is empty so this for loop will never run",
1315 "consider using the following if you are attempting to iterate over this \
1318 "({end}{dots}{start}).rev()",
1321 start = start_snippet
1323 Applicability::MaybeIncorrect,
1327 } else if eq && limits != ast::RangeLimits::Closed {
1328 // if they are equal, it's also problematic - this loop
1334 "this range is empty so this for loop will never run",
1342 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1343 let mut applicability = Applicability::MachineApplicable;
1344 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1345 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1350 "it is more concise to loop over references to containers instead of using explicit \
1352 "to write this more concisely, try",
1353 format!("&{}{}", muta, object),
1358 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1359 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1360 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1361 // just the receiver, no arguments
1362 if args.len() == 1 {
1363 let method_name = &*method.ident.as_str();
1364 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1365 if method_name == "iter" || method_name == "iter_mut" {
1366 if is_ref_iterable_type(cx, &args[0]) {
1367 lint_iter_method(cx, args, arg, method_name);
1369 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1370 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1371 let substs = cx.tables.node_substs(arg.hir_id);
1372 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1374 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1375 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1376 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1377 match cx.tables.expr_ty(&args[0]).sty {
1378 // If the length is greater than 32 no traits are implemented for array and
1379 // therefore we cannot use `&`.
1380 ty::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1381 _ => lint_iter_method(cx, args, arg, method_name),
1384 let mut applicability = Applicability::MachineApplicable;
1385 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1388 EXPLICIT_INTO_ITER_LOOP,
1390 "it is more concise to loop over containers instead of using explicit \
1391 iteration methods`",
1392 "to write this more concisely, try",
1397 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1402 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1403 probably not what you want",
1405 next_loop_linted = true;
1409 if !next_loop_linted {
1410 check_arg_type(cx, pat, arg);
1414 /// Checks for `for` loops over `Option`s and `Result`s.
1415 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1416 let ty = cx.tables.expr_ty(arg);
1417 if match_type(cx, ty, &paths::OPTION) {
1420 FOR_LOOP_OVER_OPTION,
1423 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1424 `if let` statement.",
1425 snippet(cx, arg.span, "_")
1428 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1429 snippet(cx, pat.span, "_"),
1430 snippet(cx, arg.span, "_")
1433 } else if match_type(cx, ty, &paths::RESULT) {
1436 FOR_LOOP_OVER_RESULT,
1439 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1440 `if let` statement.",
1441 snippet(cx, arg.span, "_")
1444 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1445 snippet(cx, pat.span, "_"),
1446 snippet(cx, arg.span, "_")
1452 fn check_for_loop_explicit_counter<'a, 'tcx>(
1453 cx: &LateContext<'a, 'tcx>,
1459 // Look for variables that are incremented once per loop iteration.
1460 let mut visitor = IncrementVisitor {
1462 states: FxHashMap::default(),
1466 walk_expr(&mut visitor, body);
1468 // For each candidate, check the parent block to see if
1469 // it's initialized to zero at the start of the loop.
1470 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1471 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1472 let mut visitor2 = InitializeVisitor {
1476 state: VarState::IncrOnce,
1481 walk_block(&mut visitor2, block);
1483 if visitor2.state == VarState::Warn {
1484 if let Some(name) = visitor2.name {
1485 let mut applicability = Applicability::MachineApplicable;
1488 EXPLICIT_COUNTER_LOOP,
1490 &format!("the variable `{}` is used as a loop counter.", name),
1493 "for ({}, {}) in {}.enumerate()",
1495 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1496 if higher::range(cx, arg).is_some() {
1499 snippet_with_applicability(cx, arg.span, "_", &mut applicability)
1504 sugg::Sugg::hir_with_applicability(cx, arg, "_", &mut applicability).maybe_par()
1516 /// Checks for the `FOR_KV_MAP` lint.
1517 fn check_for_loop_over_map_kv<'a, 'tcx>(
1518 cx: &LateContext<'a, 'tcx>,
1524 let pat_span = pat.span;
1526 if let PatKind::Tuple(ref pat, _) = pat.node {
1528 let arg_span = arg.span;
1529 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1530 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1531 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1532 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1537 let mutbl = match mutbl {
1539 MutMutable => "_mut",
1541 let arg = match arg.node {
1542 ExprKind::AddrOf(_, ref expr) => &**expr,
1546 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1551 &format!("you seem to want to iterate on a map's {}s", kind),
1553 let map = sugg::Sugg::hir(cx, arg, "map");
1556 "use the corresponding method".into(),
1558 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1559 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1569 struct MutatePairDelegate {
1570 hir_id_low: Option<HirId>,
1571 hir_id_high: Option<HirId>,
1572 span_low: Option<Span>,
1573 span_high: Option<Span>,
1576 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1577 fn consume(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1579 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1581 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1583 fn borrow(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1584 if let ty::BorrowKind::MutBorrow = bk {
1585 if let Categorization::Local(id) = cmt.cat {
1586 if Some(id) == self.hir_id_low {
1587 self.span_low = Some(sp)
1589 if Some(id) == self.hir_id_high {
1590 self.span_high = Some(sp)
1596 fn mutate(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1597 if let Categorization::Local(id) = cmt.cat {
1598 if Some(id) == self.hir_id_low {
1599 self.span_low = Some(sp)
1601 if Some(id) == self.hir_id_high {
1602 self.span_high = Some(sp)
1607 fn decl_without_init(&mut self, _: HirId, _: Span) {}
1610 impl<'tcx> MutatePairDelegate {
1611 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1612 (self.span_low, self.span_high)
1616 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1617 if let Some(higher::Range {
1621 }) = higher::range(cx, arg)
1623 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1624 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1625 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1626 mut_warn_with_span(cx, span_low);
1627 mut_warn_with_span(cx, span_high);
1632 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1633 if let Some(sp) = span {
1638 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1643 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1645 if let ExprKind::Path(ref qpath) = bound.node;
1646 if let QPath::Resolved(None, _) = *qpath;
1648 let res = cx.tables.qpath_res(qpath, bound.hir_id);
1649 if let Res::Local(node_id) = res {
1650 let node_str = cx.tcx.hir().get(node_id);
1652 if let Node::Binding(pat) = node_str;
1653 if let PatKind::Binding(bind_ann, ..) = pat.node;
1654 if let BindingAnnotation::Mutable = bind_ann;
1656 return Some(node_id);
1665 fn check_for_mutation(
1666 cx: &LateContext<'_, '_>,
1668 bound_ids: &[Option<HirId>],
1669 ) -> (Option<Span>, Option<Span>) {
1670 let mut delegate = MutatePairDelegate {
1671 hir_id_low: bound_ids[0],
1672 hir_id_high: bound_ids[1],
1676 let def_id = def_id::DefId::local(body.hir_id.owner);
1677 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1678 ExprUseVisitor::new(
1688 delegate.mutation_span()
1691 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1692 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1694 PatKind::Wild => true,
1695 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1696 let mut visitor = UsedVisitor {
1700 walk_expr(&mut visitor, body);
1707 struct UsedVisitor {
1708 var: ast::Name, // var to look for
1709 used: bool, // has the var been used otherwise?
1712 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1713 fn visit_expr(&mut self, expr: &'tcx Expr) {
1714 if match_var(expr, self.var) {
1717 walk_expr(self, expr);
1721 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1722 NestedVisitorMap::None
1726 struct LocalUsedVisitor<'a, 'tcx> {
1727 cx: &'a LateContext<'a, 'tcx>,
1732 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1733 fn visit_expr(&mut self, expr: &'tcx Expr) {
1734 if same_var(self.cx, expr, self.local) {
1737 walk_expr(self, expr);
1741 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1742 NestedVisitorMap::None
1746 struct VarVisitor<'a, 'tcx> {
1747 /// context reference
1748 cx: &'a LateContext<'a, 'tcx>,
1749 /// var name to look for as index
1751 /// indexed variables that are used mutably
1752 indexed_mut: FxHashSet<Name>,
1753 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1754 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1755 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1756 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1757 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1758 /// Any names that are used outside an index operation.
1759 /// Used to detect things like `&mut vec` used together with `vec[i]`
1760 referenced: FxHashSet<Name>,
1761 /// has the loop variable been used in expressions other than the index of
1764 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1765 /// takes `&mut self`
1766 prefer_mutable: bool,
1769 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1770 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1772 // the indexed container is referenced by a name
1773 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1774 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1775 if seqvar.segments.len() == 1;
1777 let index_used_directly = same_var(self.cx, idx, self.var);
1778 let indexed_indirectly = {
1779 let mut used_visitor = LocalUsedVisitor {
1784 walk_expr(&mut used_visitor, idx);
1788 if indexed_indirectly || index_used_directly {
1789 if self.prefer_mutable {
1790 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1792 let res = self.cx.tables.qpath_res(seqpath, seqexpr.hir_id);
1794 Res::Local(hir_id) => {
1795 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1796 let parent_def_id = self.cx.tcx.hir().local_def_id_from_hir_id(parent_id);
1797 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1798 if indexed_indirectly {
1799 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1801 if index_used_directly {
1802 self.indexed_directly.insert(
1803 seqvar.segments[0].ident.name,
1804 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1807 return false; // no need to walk further *on the variable*
1809 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1810 if indexed_indirectly {
1811 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1813 if index_used_directly {
1814 self.indexed_directly.insert(
1815 seqvar.segments[0].ident.name,
1816 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1819 return false; // no need to walk further *on the variable*
1830 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1831 fn visit_expr(&mut self, expr: &'tcx Expr) {
1834 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1835 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1836 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1837 if !self.check(&args[1], &args[0], expr);
1843 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1844 if !self.check(idx, seqexpr, expr);
1849 // directly using a variable
1850 if let ExprKind::Path(ref qpath) = expr.node;
1851 if let QPath::Resolved(None, ref path) = *qpath;
1852 if path.segments.len() == 1;
1854 if let Res::Local(local_id) = self.cx.tables.qpath_res(qpath, expr.hir_id) {
1855 if local_id == self.var {
1856 self.nonindex = true;
1858 // not the correct variable, but still a variable
1859 self.referenced.insert(path.segments[0].ident.name);
1865 let old = self.prefer_mutable;
1867 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1868 self.prefer_mutable = true;
1869 self.visit_expr(lhs);
1870 self.prefer_mutable = false;
1871 self.visit_expr(rhs);
1873 ExprKind::AddrOf(mutbl, ref expr) => {
1874 if mutbl == MutMutable {
1875 self.prefer_mutable = true;
1877 self.visit_expr(expr);
1879 ExprKind::Call(ref f, ref args) => {
1882 let ty = self.cx.tables.expr_ty_adjusted(expr);
1883 self.prefer_mutable = false;
1884 if let ty::Ref(_, _, mutbl) = ty.sty {
1885 if mutbl == MutMutable {
1886 self.prefer_mutable = true;
1889 self.visit_expr(expr);
1892 ExprKind::MethodCall(_, _, ref args) => {
1893 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1894 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1895 self.prefer_mutable = false;
1896 if let ty::Ref(_, _, mutbl) = ty.sty {
1897 if mutbl == MutMutable {
1898 self.prefer_mutable = true;
1901 self.visit_expr(expr);
1904 ExprKind::Closure(_, _, body_id, ..) => {
1905 let body = self.cx.tcx.hir().body(body_id);
1906 self.visit_expr(&body.value);
1908 _ => walk_expr(self, expr),
1910 self.prefer_mutable = old;
1912 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1913 NestedVisitorMap::None
1917 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1918 let def_id = match var_def_id(cx, expr) {
1920 None => return false,
1922 if let Some(used_mutably) = mutated_variables(container, cx) {
1923 if used_mutably.contains(&def_id) {
1930 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1931 let def_id = match var_def_id(cx, iter_expr) {
1933 None => return false,
1935 let mut visitor = VarUsedAfterLoopVisitor {
1938 iter_expr_id: iter_expr.hir_id,
1939 past_while_let: false,
1940 var_used_after_while_let: false,
1942 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1943 walk_block(&mut visitor, enclosing_block);
1945 visitor.var_used_after_while_let
1948 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1949 cx: &'a LateContext<'a, 'tcx>,
1951 iter_expr_id: HirId,
1952 past_while_let: bool,
1953 var_used_after_while_let: bool,
1956 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1957 fn visit_expr(&mut self, expr: &'tcx Expr) {
1958 if self.past_while_let {
1959 if Some(self.def_id) == var_def_id(self.cx, expr) {
1960 self.var_used_after_while_let = true;
1962 } else if self.iter_expr_id == expr.hir_id {
1963 self.past_while_let = true;
1965 walk_expr(self, expr);
1967 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1968 NestedVisitorMap::None
1972 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1973 /// for `&T` and `&mut T`, such as `Vec`.
1975 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1976 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1977 // will allow further borrows afterwards
1978 let ty = cx.tables.expr_ty(e);
1979 is_iterable_array(ty, cx) ||
1980 match_type(cx, ty, &paths::VEC) ||
1981 match_type(cx, ty, &paths::LINKED_LIST) ||
1982 match_type(cx, ty, &paths::HASHMAP) ||
1983 match_type(cx, ty, &paths::HASHSET) ||
1984 match_type(cx, ty, &paths::VEC_DEQUE) ||
1985 match_type(cx, ty, &paths::BINARY_HEAP) ||
1986 match_type(cx, ty, &paths::BTREEMAP) ||
1987 match_type(cx, ty, &paths::BTREESET)
1990 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1991 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1993 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1998 /// If a block begins with a statement (possibly a `let` binding) and has an
1999 /// expression, return it.
2000 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
2001 if block.stmts.is_empty() {
2004 if let StmtKind::Local(ref local) = block.stmts[0].node {
2005 if let Some(ref expr) = local.init {
2015 /// If a block begins with an expression (with or without semicolon), return it.
2016 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2018 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2019 None if !block.stmts.is_empty() => match block.stmts[0].node {
2020 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2021 StmtKind::Local(..) | StmtKind::Item(..) => None,
2027 /// Returns `true` if expr contains a single break expr without destination label
2029 /// passed expression. The expression may be within a block.
2030 fn is_simple_break_expr(expr: &Expr) -> bool {
2032 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2033 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2034 Some(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_literal(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(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2091 } else if is_loop(expr) || is_conditional(expr) {
2093 walk_expr(self, expr);
2096 } else if let ExprKind::Continue(_) = expr.node {
2100 walk_expr(self, expr);
2102 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2103 NestedVisitorMap::None
2107 /// Checks whether a variable is initialized to zero at the start of a loop.
2108 struct InitializeVisitor<'a, 'tcx> {
2109 cx: &'a LateContext<'a, 'tcx>, // context reference
2110 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2114 depth: u32, // depth of conditional expressions
2118 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2119 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2120 // Look for declarations of the variable
2121 if let StmtKind::Local(ref local) = stmt.node {
2122 if local.pat.hir_id == self.var_id {
2123 if let PatKind::Binding(.., ident, _) = local.pat.node {
2124 self.name = Some(ident.name);
2126 self.state = if let Some(ref init) = local.init {
2127 if is_integer_literal(init, 0) {
2138 walk_stmt(self, stmt);
2141 fn visit_expr(&mut self, expr: &'tcx Expr) {
2142 if self.state == VarState::DontWarn {
2145 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2146 self.past_loop = true;
2149 // No need to visit expressions before the variable is
2151 if self.state == VarState::IncrOnce {
2155 // If node is the desired variable, see how it's used
2156 if var_def_id(self.cx, expr) == Some(self.var_id) {
2157 if let Some(parent) = get_parent_expr(self.cx, expr) {
2159 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2160 self.state = VarState::DontWarn;
2162 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2163 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2169 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2175 self.state = VarState::DontWarn;
2178 } else if !self.past_loop && is_loop(expr) {
2179 self.state = VarState::DontWarn;
2181 } else if is_conditional(expr) {
2183 walk_expr(self, expr);
2187 walk_expr(self, expr);
2189 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2190 NestedVisitorMap::None
2194 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2195 if let ExprKind::Path(ref qpath) = expr.node {
2196 let path_res = cx.tables.qpath_res(qpath, expr.hir_id);
2197 if let Res::Local(node_id) = path_res {
2198 return Some(node_id);
2204 fn is_loop(expr: &Expr) -> bool {
2206 ExprKind::Loop(..) | ExprKind::While(..) => true,
2211 fn is_conditional(expr: &Expr) -> bool {
2213 ExprKind::Match(..) => true,
2218 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2220 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2221 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2222 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2224 return is_loop_nested(cx, loop_expr, iter_expr)
2230 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2231 let mut id = loop_expr.hir_id;
2232 let iter_name = if let Some(name) = path_name(iter_expr) {
2238 let parent = cx.tcx.hir().get_parent_node(id);
2242 match cx.tcx.hir().find(parent) {
2243 Some(Node::Expr(expr)) => match expr.node {
2244 ExprKind::Loop(..) | ExprKind::While(..) => {
2249 Some(Node::Block(block)) => {
2250 let mut block_visitor = LoopNestVisitor {
2252 iterator: iter_name,
2255 walk_block(&mut block_visitor, block);
2256 if block_visitor.nesting == RuledOut {
2260 Some(Node::Stmt(_)) => (),
2269 #[derive(PartialEq, Eq)]
2271 Unknown, // no nesting detected yet
2272 RuledOut, // the iterator is initialized or assigned within scope
2273 LookFurther, // no nesting detected, no further walk required
2276 use self::Nesting::{LookFurther, RuledOut, Unknown};
2278 struct LoopNestVisitor {
2284 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2285 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2286 if stmt.hir_id == self.hir_id {
2287 self.nesting = LookFurther;
2288 } else if self.nesting == Unknown {
2289 walk_stmt(self, stmt);
2293 fn visit_expr(&mut self, expr: &'tcx Expr) {
2294 if self.nesting != Unknown {
2297 if expr.hir_id == self.hir_id {
2298 self.nesting = LookFurther;
2302 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2303 if match_var(path, self.iterator) {
2304 self.nesting = RuledOut;
2307 _ => walk_expr(self, expr),
2311 fn visit_pat(&mut self, pat: &'tcx Pat) {
2312 if self.nesting != Unknown {
2315 if let PatKind::Binding(.., span_name, _) = pat.node {
2316 if self.iterator == span_name.name {
2317 self.nesting = RuledOut;
2324 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2325 NestedVisitorMap::None
2329 fn path_name(e: &Expr) -> Option<Name> {
2330 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2331 let segments = &path.segments;
2332 if segments.len() == 1 {
2333 return Some(segments[0].ident.name);
2339 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2340 if constant(cx, cx.tables, cond).is_some() {
2341 // A pure constant condition (e.g., `while false`) is not linted.
2345 let mut var_visitor = VarCollectorVisitor {
2347 ids: FxHashSet::default(),
2348 def_ids: FxHashMap::default(),
2351 var_visitor.visit_expr(cond);
2352 if var_visitor.skip {
2355 let used_in_condition = &var_visitor.ids;
2356 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2357 used_in_condition.is_disjoint(&used_mutably)
2361 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2362 if no_cond_variable_mutated && !mutable_static_in_cond {
2365 WHILE_IMMUTABLE_CONDITION,
2367 "Variable in the condition are not mutated in the loop body. \
2368 This either leads to an infinite or to a never running loop.",
2373 /// Collects the set of variables in an expression
2374 /// Stops analysis if a function call is found
2375 /// Note: In some cases such as `self`, there are no mutable annotation,
2376 /// All variables definition IDs are collected
2377 struct VarCollectorVisitor<'a, 'tcx> {
2378 cx: &'a LateContext<'a, 'tcx>,
2379 ids: FxHashSet<HirId>,
2380 def_ids: FxHashMap<def_id::DefId, bool>,
2384 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2385 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2387 if let ExprKind::Path(ref qpath) = ex.node;
2388 if let QPath::Resolved(None, _) = *qpath;
2389 let res = self.cx.tables.qpath_res(qpath, ex.hir_id);
2392 Res::Local(node_id) => {
2393 self.ids.insert(node_id);
2395 Res::Def(DefKind::Static, def_id) => {
2396 let mutable = self.cx.tcx.is_mutable_static(def_id);
2397 self.def_ids.insert(def_id, mutable);
2406 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2407 fn visit_expr(&mut self, ex: &'tcx Expr) {
2409 ExprKind::Path(_) => self.insert_def_id(ex),
2410 // If there is any function/method call… we just stop analysis
2411 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2413 _ => walk_expr(self, ex),
2417 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2418 NestedVisitorMap::None
2422 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2424 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2426 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2427 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2428 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2429 if let Some(ref generic_args) = chain_method.args;
2430 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2432 let ty = cx.tables.node_type(ty.hir_id);
2433 if match_type(cx, ty, &paths::VEC) ||
2434 match_type(cx, ty, &paths::VEC_DEQUE) ||
2435 match_type(cx, ty, &paths::BTREEMAP) ||
2436 match_type(cx, ty, &paths::HASHMAP) {
2437 if method.ident.name == sym!(len) {
2438 let span = shorten_needless_collect_span(expr);
2439 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2443 ".count()".to_string(),
2444 Applicability::MachineApplicable,
2448 if method.ident.name == sym!(is_empty) {
2449 let span = shorten_needless_collect_span(expr);
2450 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2454 ".next().is_none()".to_string(),
2455 Applicability::MachineApplicable,
2459 if method.ident.name == sym!(contains) {
2460 let contains_arg = snippet(cx, args[1].span, "??");
2461 let span = shorten_needless_collect_span(expr);
2462 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2467 ".any(|&x| x == {})",
2468 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2470 Applicability::MachineApplicable,
2479 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2481 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2482 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2484 return expr.span.with_lo(span.lo() - BytePos(1));