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).
221 /// # let y = Some(1);
223 /// let x = match y {
227 /// // .. do something with x
229 /// // is easier written as
230 /// while let Some(x) = y {
231 /// // .. do something with x
236 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
239 declare_clippy_lint! {
240 /// **What it does:** Checks for using `collect()` on an iterator without using
243 /// **Why is this bad?** It is more idiomatic to use a `for` loop over the
244 /// iterator instead.
246 /// **Known problems:** None.
250 /// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
254 "`collect()`ing an iterator without using the result; this is usually better written as a for loop"
257 declare_clippy_lint! {
258 /// **What it does:** Checks for functions collecting an iterator when collect
261 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
262 /// when this allocation may not be needed.
264 /// **Known problems:**
269 /// let len = iterator.collect::<Vec<_>>().len();
271 /// let len = iterator.count();
273 pub NEEDLESS_COLLECT,
275 "collecting an iterator when collect is not needed"
278 declare_clippy_lint! {
279 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
280 /// are constant and `x` is greater or equal to `y`, unless the range is
281 /// reversed or has a negative `.step_by(_)`.
283 /// **Why is it bad?** Such loops will either be skipped or loop until
284 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
287 /// **Known problems:** The lint cannot catch loops over dynamically defined
288 /// ranges. Doing this would require simulating all possible inputs and code
289 /// paths through the program, which would be complex and error-prone.
293 /// for x in 5..10 - 5 {
295 /// } // oops, stray `-`
297 pub REVERSE_RANGE_LOOP,
299 "iteration over an empty range, such as `10..0` or `5..5`"
302 declare_clippy_lint! {
303 /// **What it does:** Checks `for` loops over slices with an explicit counter
304 /// and suggests the use of `.enumerate()`.
306 /// **Why is it bad?** Not only is the version using `.enumerate()` more
307 /// readable, the compiler is able to remove bounds checks which can lead to
308 /// faster code in some instances.
310 /// **Known problems:** None.
314 /// # let v = vec![1];
315 /// # fn foo(bar: usize) {}
316 /// # fn bar(bar: usize, baz: usize) {}
317 /// for i in 0..v.len() { foo(v[i]); }
318 /// for i in 0..v.len() { bar(i, v[i]); }
320 pub EXPLICIT_COUNTER_LOOP,
322 "for-looping with an explicit counter when `_.enumerate()` would do"
325 declare_clippy_lint! {
326 /// **What it does:** Checks for empty `loop` expressions.
328 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
329 /// anything. Think of the environment and either block on something or at least
330 /// make the thread sleep for some microseconds.
332 /// **Known problems:** None.
340 "empty `loop {}`, which should block or sleep"
343 declare_clippy_lint! {
344 /// **What it does:** Checks for `while let` expressions on iterators.
346 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
347 /// the intent better.
349 /// **Known problems:** None.
353 /// while let Some(val) = iter() {
357 pub WHILE_LET_ON_ITERATOR,
359 "using a while-let loop instead of a for loop on an iterator"
362 declare_clippy_lint! {
363 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
364 /// ignoring either the keys or values.
366 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
367 /// can be used to express that don't need the values or keys.
369 /// **Known problems:** None.
373 /// for (k, _) in &map {
378 /// could be replaced by
381 /// for k in map.keys() {
387 "looping on a map using `iter` when `keys` or `values` would do"
390 declare_clippy_lint! {
391 /// **What it does:** Checks for loops that will always `break`, `return` or
392 /// `continue` an outer loop.
394 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
397 /// **Known problems:** None
408 "any loop that will always `break` or `return`"
411 declare_clippy_lint! {
412 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
414 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
416 /// **Known problems:** None
420 /// let mut foo = 42;
421 /// for i in 0..foo {
423 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
428 "for loop over a range where one of the bounds is a mutable variable"
431 declare_clippy_lint! {
432 /// **What it does:** Checks whether variables used within while loop condition
433 /// can be (and are) mutated in the body.
435 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
436 /// will lead to an infinite loop.
438 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
439 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
440 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
446 /// println!("let me loop forever!");
449 pub WHILE_IMMUTABLE_CONDITION,
451 "variables used within while expression are not mutated in the body"
454 declare_lint_pass!(Loops => [
458 EXPLICIT_INTO_ITER_LOOP,
460 FOR_LOOP_OVER_RESULT,
461 FOR_LOOP_OVER_OPTION,
466 EXPLICIT_COUNTER_LOOP,
468 WHILE_LET_ON_ITERATOR,
472 WHILE_IMMUTABLE_CONDITION,
475 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
476 #[allow(clippy::too_many_lines)]
477 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
478 // we don't want to check expanded macros
479 if in_macro_or_desugar(expr.span) {
483 if let Some((pat, arg, body)) = higher::for_loop(expr) {
484 check_for_loop(cx, pat, arg, body, expr);
487 // check for never_loop
488 if let ExprKind::Loop(ref block, _, _) = expr.node {
489 match never_loop_block(block, expr.hir_id) {
490 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
491 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
495 // check for `loop { if let {} else break }` that could be `while let`
496 // (also matches an explicit "match" instead of "if let")
497 // (even if the "match" or "if let" is used for declaration)
498 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.node {
499 // also check for empty `loop {}` statements
500 if block.stmts.is_empty() && block.expr.is_none() {
505 "empty `loop {}` detected. You may want to either use `panic!()` or add \
506 `std::thread::sleep(..);` to the loop body.",
510 // extract the expression from the first statement (if any) in a block
511 let inner_stmt_expr = extract_expr_from_first_stmt(block);
512 // or extract the first expression (if any) from the block
513 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
514 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.node {
515 // ensure "if let" compatible match structure
517 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
519 && arms[0].pats.len() == 1
520 && arms[0].guard.is_none()
521 && arms[1].pats.len() == 1
522 && arms[1].guard.is_none()
523 && is_simple_break_expr(&arms[1].body)
525 if in_external_macro(cx.sess(), expr.span) {
529 // NOTE: we used to build a body here instead of using
530 // ellipsis, this was removed because:
531 // 1) it was ugly with big bodies;
532 // 2) it was not indented properly;
533 // 3) it wasn’t very smart (see #675).
534 let mut applicability = Applicability::HasPlaceholders;
539 "this loop could be written as a `while let` loop",
542 "while let {} = {} {{ .. }}",
543 snippet_with_applicability(cx, arms[0].pats[0].span, "..", &mut applicability),
544 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
555 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
556 let pat = &arms[0].pats[0].node;
558 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
559 &ExprKind::MethodCall(ref method_path, _, ref method_args),
560 ) = (pat, &match_expr.node)
562 let iter_expr = &method_args[0];
563 let lhs_constructor = last_path_segment(qpath);
564 if method_path.ident.name == sym!(next)
565 && match_trait_method(cx, match_expr, &paths::ITERATOR)
566 && lhs_constructor.ident.name == sym!(Some)
567 && (pat_args.is_empty()
568 || !is_refutable(cx, &pat_args[0])
569 && !is_used_inside(cx, iter_expr, &arms[0].body)
570 && !is_iterator_used_after_while_let(cx, iter_expr)
571 && !is_nested(cx, expr, &method_args[0]))
573 let iterator = snippet(cx, method_args[0].span, "_");
574 let loop_var = if pat_args.is_empty() {
577 snippet(cx, pat_args[0].span, "_").into_owned()
581 WHILE_LET_ON_ITERATOR,
583 "this loop could be written as a `for` loop",
585 format!("for {} in {} {{ .. }}", loop_var, iterator),
586 Applicability::HasPlaceholders,
592 if let Some((cond, body)) = higher::while_loop(&expr) {
593 check_infinite_loop(cx, cond, body);
596 check_needless_collect(expr, cx);
599 fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
600 if let StmtKind::Semi(ref expr) = stmt.node {
601 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node {
603 && method.ident.name == sym!(collect)
604 && match_trait_method(cx, expr, &paths::ITERATOR)
610 "you are collect()ing an iterator and throwing away the result. \
611 Consider using an explicit for loop to exhaust the iterator",
619 enum NeverLoopResult {
620 // A break/return always get triggered but not necessarily for the main loop.
622 // A continue may occur for the main loop.
627 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
629 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
630 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
634 // Combine two results for parts that are called in order.
635 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
637 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
638 NeverLoopResult::Otherwise => second,
642 // Combine two results where both parts are called but not necessarily in order.
643 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
644 match (left, right) {
645 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
646 NeverLoopResult::MayContinueMainLoop
648 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
649 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
653 // Combine two results where only one of the part may have been executed.
654 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
656 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
657 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
658 NeverLoopResult::MayContinueMainLoop
660 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
664 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
665 let stmts = block.stmts.iter().map(stmt_to_expr);
666 let expr = once(block.expr.as_ref().map(|p| &**p));
667 let mut iter = stmts.chain(expr).filter_map(|e| e);
668 never_loop_expr_seq(&mut iter, main_loop_id)
671 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
673 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
674 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
679 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
682 | ExprKind::Unary(_, ref e)
683 | ExprKind::Cast(ref e, _)
684 | ExprKind::Type(ref e, _)
685 | ExprKind::Field(ref e, _)
686 | ExprKind::AddrOf(_, ref e)
687 | ExprKind::Struct(_, _, Some(ref e))
688 | ExprKind::Repeat(ref e, _)
689 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
690 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
691 never_loop_expr_all(&mut es.iter(), main_loop_id)
693 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
694 ExprKind::Binary(_, ref e1, ref e2)
695 | ExprKind::Assign(ref e1, ref e2)
696 | ExprKind::AssignOp(_, ref e1, ref e2)
697 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
698 ExprKind::Loop(ref b, _, _) => {
699 // Break can come from the inner loop so remove them.
700 absorb_break(&never_loop_block(b, main_loop_id))
702 ExprKind::Match(ref e, ref arms, _) => {
703 let e = never_loop_expr(e, main_loop_id);
707 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
711 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
712 ExprKind::Continue(d) => {
715 .expect("target ID can only be missing in the presence of compilation errors");
716 if id == main_loop_id {
717 NeverLoopResult::MayContinueMainLoop
719 NeverLoopResult::AlwaysBreak
722 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
723 if let Some(ref e) = *e {
724 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
726 NeverLoopResult::AlwaysBreak
729 ExprKind::Struct(_, _, None)
730 | ExprKind::Yield(_, _)
731 | ExprKind::Closure(_, _, _, _, _)
732 | ExprKind::InlineAsm(_, _, _)
735 | ExprKind::Err => NeverLoopResult::Otherwise,
739 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
740 es.map(|e| never_loop_expr(e, main_loop_id))
741 .fold(NeverLoopResult::Otherwise, combine_seq)
744 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
745 es.map(|e| never_loop_expr(e, main_loop_id))
746 .fold(NeverLoopResult::Otherwise, combine_both)
749 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
750 e.map(|e| never_loop_expr(e, main_loop_id))
751 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
754 fn check_for_loop<'a, 'tcx>(
755 cx: &LateContext<'a, 'tcx>,
761 check_for_loop_range(cx, pat, arg, body, expr);
762 check_for_loop_reverse_range(cx, arg, expr);
763 check_for_loop_arg(cx, pat, arg, expr);
764 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
765 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
766 check_for_mut_range_bound(cx, arg, body);
767 detect_manual_memcpy(cx, pat, arg, body, expr);
770 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
772 if let ExprKind::Path(ref qpath) = expr.node;
773 if let QPath::Resolved(None, ref path) = *qpath;
774 if path.segments.len() == 1;
775 if let Res::Local(local_id) = cx.tables.qpath_res(qpath, expr.hir_id);
792 fn negative(s: String) -> Self {
793 Self { value: s, negate: true }
796 fn positive(s: String) -> Self {
804 struct FixedOffsetVar {
809 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
810 let is_slice = match ty.sty {
811 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
812 ty::Slice(..) | ty::Array(..) => true,
816 is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
819 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
820 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
822 ExprKind::Lit(ref l) => match l.node {
823 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
826 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
831 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node {
832 let ty = cx.tables.expr_ty(seqexpr);
833 if !is_slice_like(cx, ty) {
837 let offset = match idx.node {
838 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
840 let offset_opt = if same_var(cx, lhs, var) {
841 extract_offset(cx, rhs, var)
842 } else if same_var(cx, rhs, var) {
843 extract_offset(cx, lhs, var)
848 offset_opt.map(Offset::positive)
850 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
853 ExprKind::Path(..) => {
854 if same_var(cx, idx, var) {
855 Some(Offset::positive("0".into()))
863 offset.map(|o| FixedOffsetVar {
864 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
872 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
873 cx: &LateContext<'a, 'tcx>,
876 ) -> Option<FixedOffsetVar> {
878 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
879 if method.ident.name == sym!(clone);
881 if let Some(arg) = args.get(0);
883 return get_fixed_offset_var(cx, arg, var);
887 get_fixed_offset_var(cx, expr, var)
890 fn get_indexed_assignments<'a, 'tcx>(
891 cx: &LateContext<'a, 'tcx>,
894 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
895 fn get_assignment<'a, 'tcx>(
896 cx: &LateContext<'a, 'tcx>,
899 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
900 if let ExprKind::Assign(ref lhs, ref rhs) = e.node {
902 get_fixed_offset_var(cx, lhs, var),
903 fetch_cloned_fixed_offset_var(cx, rhs, var),
905 (Some(offset_left), Some(offset_right)) => {
906 // Source and destination must be different
907 if offset_left.var_name == offset_right.var_name {
910 Some((offset_left, offset_right))
920 if let ExprKind::Block(ref b, _) = body.node {
922 ref stmts, ref expr, ..
927 .map(|stmt| match stmt.node {
928 StmtKind::Local(..) | StmtKind::Item(..) => None,
929 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
931 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
933 .collect::<Option<Vec<_>>>()
934 .unwrap_or_else(|| vec![])
936 get_assignment(cx, body, var).into_iter().collect()
940 /// Checks for for loops that sequentially copy items from one slice-like
941 /// object to another.
942 fn detect_manual_memcpy<'a, 'tcx>(
943 cx: &LateContext<'a, 'tcx>,
949 if let Some(higher::Range {
953 }) = higher::range(cx, arg)
955 // the var must be a single name
956 if let PatKind::Binding(_, canonical_id, _, _) = pat.node {
957 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
958 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
959 ("0", _, "0", _) => "".into(),
960 ("0", _, x, false) | (x, false, "0", false) => x.into(),
961 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
962 (x, false, y, false) => format!("({} + {})", x, y),
963 (x, false, y, true) => {
967 format!("({} - {})", x, y)
970 (x, true, y, false) => {
974 format!("({} - {})", y, x)
977 (x, true, y, true) => format!("-({} + {})", x, y),
981 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
982 if let Some(end) = *end {
984 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.node;
985 if method.ident.name == sym!(len);
986 if len_args.len() == 1;
987 if let Some(arg) = len_args.get(0);
988 if snippet(cx, arg.span, "??") == var_name;
990 return if offset.negate {
991 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
998 let end_str = match limits {
999 ast::RangeLimits::Closed => {
1000 let end = sugg::Sugg::hir(cx, end, "<count>");
1001 format!("{}", end + sugg::ONE)
1003 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
1006 print_sum(&Offset::positive(end_str), &offset)
1012 // The only statements in the for loops can be indexed assignments from
1013 // indexed retrievals.
1014 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1016 let big_sugg = manual_copies
1018 .map(|(dst_var, src_var)| {
1019 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1020 let dst_offset = print_sum(&start_str, &dst_var.offset);
1021 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1022 let src_offset = print_sum(&start_str, &src_var.offset);
1023 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1024 let dst = if dst_offset == "" && dst_limit == "" {
1027 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1031 "{}.clone_from_slice(&{}[{}..{}])",
1032 dst, src_var.var_name, src_offset, src_limit
1037 if !big_sugg.is_empty() {
1042 "it looks like you're manually copying between slices",
1043 "try replacing the loop by",
1045 Applicability::Unspecified,
1052 /// Checks for looping over a range and then indexing a sequence with it.
1053 /// The iteratee must be a range literal.
1054 #[allow(clippy::too_many_lines)]
1055 fn check_for_loop_range<'a, 'tcx>(
1056 cx: &LateContext<'a, 'tcx>,
1062 if in_macro_or_desugar(expr.span) {
1066 if let Some(higher::Range {
1070 }) = higher::range(cx, arg)
1072 // the var must be a single name
1073 if let PatKind::Binding(_, canonical_id, ident, _) = pat.node {
1074 let mut visitor = VarVisitor {
1077 indexed_mut: FxHashSet::default(),
1078 indexed_indirectly: FxHashMap::default(),
1079 indexed_directly: FxHashMap::default(),
1080 referenced: FxHashSet::default(),
1082 prefer_mutable: false,
1084 walk_expr(&mut visitor, body);
1086 // linting condition: we only indexed one variable, and indexed it directly
1087 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1088 let (indexed, (indexed_extent, indexed_ty)) = visitor
1092 .expect("already checked that we have exactly 1 element");
1094 // ensure that the indexed variable was declared before the loop, see #601
1095 if let Some(indexed_extent) = indexed_extent {
1096 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1097 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1098 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1099 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1100 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1105 // don't lint if the container that is indexed does not have .iter() method
1106 let has_iter = has_iter_method(cx, indexed_ty);
1107 if has_iter.is_none() {
1111 // don't lint if the container that is indexed into is also used without
1113 if visitor.referenced.contains(&indexed) {
1117 let starts_at_zero = is_integer_literal(start, 0);
1119 let skip = if starts_at_zero {
1122 format!(".skip({})", snippet(cx, start.span, ".."))
1125 let mut end_is_start_plus_val = false;
1127 let take = if let Some(end) = *end {
1128 let mut take_expr = end;
1130 if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
1131 if let BinOpKind::Add = op.node {
1132 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1133 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1135 if start_equal_left {
1137 } else if start_equal_right {
1141 end_is_start_plus_val = start_equal_left | start_equal_right;
1145 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1149 ast::RangeLimits::Closed => {
1150 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1151 format!(".take({})", take_expr + sugg::ONE)
1153 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1160 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1161 ("mut ", "iter_mut")
1166 let take_is_empty = take.is_empty();
1167 let mut method_1 = take;
1168 let mut method_2 = skip;
1170 if end_is_start_plus_val {
1171 mem::swap(&mut method_1, &mut method_2);
1174 if visitor.nonindex {
1177 NEEDLESS_RANGE_LOOP,
1179 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1183 "consider using an iterator".to_string(),
1185 (pat.span, format!("({}, <item>)", ident.name)),
1188 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1195 let repl = if starts_at_zero && take_is_empty {
1196 format!("&{}{}", ref_mut, indexed)
1198 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1203 NEEDLESS_RANGE_LOOP,
1206 "the loop variable `{}` is only used to index `{}`.",
1212 "consider using an iterator".to_string(),
1213 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1223 fn is_len_call(expr: &Expr, var: Name) -> bool {
1225 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.node;
1226 if len_args.len() == 1;
1227 if method.ident.name == sym!(len);
1228 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].node;
1229 if path.segments.len() == 1;
1230 if path.segments[0].ident.name == var;
1239 fn is_end_eq_array_len<'tcx>(
1240 cx: &LateContext<'_, 'tcx>,
1242 limits: ast::RangeLimits,
1243 indexed_ty: Ty<'tcx>,
1246 if let ExprKind::Lit(ref lit) = end.node;
1247 if let ast::LitKind::Int(end_int, _) = lit.node;
1248 if let ty::Array(_, arr_len_const) = indexed_ty.sty;
1249 if let Some(arr_len) = arr_len_const.assert_usize(cx.tcx);
1251 return match limits {
1252 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1253 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1261 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1262 // if this for loop is iterating over a two-sided range...
1263 if let Some(higher::Range {
1267 }) = higher::range(cx, arg)
1269 // ...and both sides are compile-time constant integers...
1270 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1271 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1272 // ...and the start index is greater than the end index,
1273 // this loop will never run. This is often confusing for developers
1274 // who think that this will iterate from the larger value to the
1276 let ty = cx.tables.expr_ty(start);
1277 let (sup, eq) = match (start_idx, end_idx) {
1278 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1280 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1281 ty::Uint(_) => start_idx > end_idx,
1284 start_idx == end_idx,
1286 _ => (false, false),
1290 let start_snippet = snippet(cx, start.span, "_");
1291 let end_snippet = snippet(cx, end.span, "_");
1292 let dots = if limits == ast::RangeLimits::Closed {
1302 "this range is empty so this for loop will never run",
1306 "consider using the following if you are attempting to iterate over this \
1309 "({end}{dots}{start}).rev()",
1312 start = start_snippet
1314 Applicability::MaybeIncorrect,
1318 } else if eq && limits != ast::RangeLimits::Closed {
1319 // if they are equal, it's also problematic - this loop
1325 "this range is empty so this for loop will never run",
1333 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1334 let mut applicability = Applicability::MachineApplicable;
1335 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1336 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1341 "it is more concise to loop over references to containers instead of using explicit \
1343 "to write this more concisely, try",
1344 format!("&{}{}", muta, object),
1349 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1350 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1351 if let ExprKind::MethodCall(ref method, _, ref args) = arg.node {
1352 // just the receiver, no arguments
1353 if args.len() == 1 {
1354 let method_name = &*method.ident.as_str();
1355 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1356 if method_name == "iter" || method_name == "iter_mut" {
1357 if is_ref_iterable_type(cx, &args[0]) {
1358 lint_iter_method(cx, args, arg, method_name);
1360 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1361 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1362 let substs = cx.tables.node_substs(arg.hir_id);
1363 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1365 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1366 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1367 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1368 match cx.tables.expr_ty(&args[0]).sty {
1369 // If the length is greater than 32 no traits are implemented for array and
1370 // therefore we cannot use `&`.
1371 ty::Array(_, size) if size.assert_usize(cx.tcx).expect("array size") > 32 => (),
1372 _ => lint_iter_method(cx, args, arg, method_name),
1375 let mut applicability = Applicability::MachineApplicable;
1376 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1379 EXPLICIT_INTO_ITER_LOOP,
1381 "it is more concise to loop over containers instead of using explicit \
1382 iteration methods`",
1383 "to write this more concisely, try",
1388 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1393 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1394 probably not what you want",
1396 next_loop_linted = true;
1400 if !next_loop_linted {
1401 check_arg_type(cx, pat, arg);
1405 /// Checks for `for` loops over `Option`s and `Result`s.
1406 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1407 let ty = cx.tables.expr_ty(arg);
1408 if match_type(cx, ty, &paths::OPTION) {
1411 FOR_LOOP_OVER_OPTION,
1414 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1415 `if let` statement.",
1416 snippet(cx, arg.span, "_")
1419 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1420 snippet(cx, pat.span, "_"),
1421 snippet(cx, arg.span, "_")
1424 } else if match_type(cx, ty, &paths::RESULT) {
1427 FOR_LOOP_OVER_RESULT,
1430 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1431 `if let` statement.",
1432 snippet(cx, arg.span, "_")
1435 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1436 snippet(cx, pat.span, "_"),
1437 snippet(cx, arg.span, "_")
1443 fn check_for_loop_explicit_counter<'a, 'tcx>(
1444 cx: &LateContext<'a, 'tcx>,
1450 // Look for variables that are incremented once per loop iteration.
1451 let mut visitor = IncrementVisitor {
1453 states: FxHashMap::default(),
1457 walk_expr(&mut visitor, body);
1459 // For each candidate, check the parent block to see if
1460 // it's initialized to zero at the start of the loop.
1461 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1462 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1463 let mut visitor2 = InitializeVisitor {
1467 state: VarState::IncrOnce,
1472 walk_block(&mut visitor2, block);
1474 if visitor2.state == VarState::Warn {
1475 if let Some(name) = visitor2.name {
1476 let mut applicability = Applicability::MachineApplicable;
1479 EXPLICIT_COUNTER_LOOP,
1481 &format!("the variable `{}` is used as a loop counter.", name),
1484 "for ({}, {}) in {}.enumerate()",
1486 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1487 if higher::range(cx, arg).is_some() {
1490 snippet_with_applicability(cx, arg.span, "_", &mut applicability)
1495 sugg::Sugg::hir_with_applicability(cx, arg, "_", &mut applicability).maybe_par()
1507 /// Checks for the `FOR_KV_MAP` lint.
1508 fn check_for_loop_over_map_kv<'a, 'tcx>(
1509 cx: &LateContext<'a, 'tcx>,
1515 let pat_span = pat.span;
1517 if let PatKind::Tuple(ref pat, _) = pat.node {
1519 let arg_span = arg.span;
1520 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
1521 ty::Ref(_, ty, mutbl) => match (&pat[0].node, &pat[1].node) {
1522 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1523 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, MutImmutable),
1528 let mutbl = match mutbl {
1530 MutMutable => "_mut",
1532 let arg = match arg.node {
1533 ExprKind::AddrOf(_, ref expr) => &**expr,
1537 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1542 &format!("you seem to want to iterate on a map's {}s", kind),
1544 let map = sugg::Sugg::hir(cx, arg, "map");
1547 "use the corresponding method".into(),
1549 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1550 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1560 struct MutatePairDelegate {
1561 hir_id_low: Option<HirId>,
1562 hir_id_high: Option<HirId>,
1563 span_low: Option<Span>,
1564 span_high: Option<Span>,
1567 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1568 fn consume(&mut self, _: HirId, _: Span, _: &cmt_<'tcx>, _: ConsumeMode) {}
1570 fn matched_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: MatchMode) {}
1572 fn consume_pat(&mut self, _: &Pat, _: &cmt_<'tcx>, _: ConsumeMode) {}
1574 fn borrow(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: ty::Region<'_>, bk: ty::BorrowKind, _: LoanCause) {
1575 if let ty::BorrowKind::MutBorrow = bk {
1576 if let Categorization::Local(id) = cmt.cat {
1577 if Some(id) == self.hir_id_low {
1578 self.span_low = Some(sp)
1580 if Some(id) == self.hir_id_high {
1581 self.span_high = Some(sp)
1587 fn mutate(&mut self, _: HirId, sp: Span, cmt: &cmt_<'tcx>, _: MutateMode) {
1588 if let Categorization::Local(id) = cmt.cat {
1589 if Some(id) == self.hir_id_low {
1590 self.span_low = Some(sp)
1592 if Some(id) == self.hir_id_high {
1593 self.span_high = Some(sp)
1598 fn decl_without_init(&mut self, _: HirId, _: Span) {}
1601 impl<'tcx> MutatePairDelegate {
1602 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1603 (self.span_low, self.span_high)
1607 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1608 if let Some(higher::Range {
1612 }) = higher::range(cx, arg)
1614 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1615 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1616 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1617 mut_warn_with_span(cx, span_low);
1618 mut_warn_with_span(cx, span_high);
1623 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1624 if let Some(sp) = span {
1629 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1634 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1636 if let ExprKind::Path(ref qpath) = bound.node;
1637 if let QPath::Resolved(None, _) = *qpath;
1639 let res = cx.tables.qpath_res(qpath, bound.hir_id);
1640 if let Res::Local(node_id) = res {
1641 let node_str = cx.tcx.hir().get(node_id);
1643 if let Node::Binding(pat) = node_str;
1644 if let PatKind::Binding(bind_ann, ..) = pat.node;
1645 if let BindingAnnotation::Mutable = bind_ann;
1647 return Some(node_id);
1656 fn check_for_mutation(
1657 cx: &LateContext<'_, '_>,
1659 bound_ids: &[Option<HirId>],
1660 ) -> (Option<Span>, Option<Span>) {
1661 let mut delegate = MutatePairDelegate {
1662 hir_id_low: bound_ids[0],
1663 hir_id_high: bound_ids[1],
1667 let def_id = def_id::DefId::local(body.hir_id.owner);
1668 let region_scope_tree = &cx.tcx.region_scope_tree(def_id);
1669 ExprUseVisitor::new(
1679 delegate.mutation_span()
1682 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1683 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1685 PatKind::Wild => true,
1686 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1687 let mut visitor = UsedVisitor {
1691 walk_expr(&mut visitor, body);
1698 struct UsedVisitor {
1699 var: ast::Name, // var to look for
1700 used: bool, // has the var been used otherwise?
1703 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1704 fn visit_expr(&mut self, expr: &'tcx Expr) {
1705 if match_var(expr, self.var) {
1708 walk_expr(self, expr);
1712 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1713 NestedVisitorMap::None
1717 struct LocalUsedVisitor<'a, 'tcx> {
1718 cx: &'a LateContext<'a, 'tcx>,
1723 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1724 fn visit_expr(&mut self, expr: &'tcx Expr) {
1725 if same_var(self.cx, expr, self.local) {
1728 walk_expr(self, expr);
1732 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1733 NestedVisitorMap::None
1737 struct VarVisitor<'a, 'tcx> {
1738 /// context reference
1739 cx: &'a LateContext<'a, 'tcx>,
1740 /// var name to look for as index
1742 /// indexed variables that are used mutably
1743 indexed_mut: FxHashSet<Name>,
1744 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1745 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1746 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1747 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1748 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1749 /// Any names that are used outside an index operation.
1750 /// Used to detect things like `&mut vec` used together with `vec[i]`
1751 referenced: FxHashSet<Name>,
1752 /// has the loop variable been used in expressions other than the index of
1755 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1756 /// takes `&mut self`
1757 prefer_mutable: bool,
1760 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1761 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1763 // the indexed container is referenced by a name
1764 if let ExprKind::Path(ref seqpath) = seqexpr.node;
1765 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1766 if seqvar.segments.len() == 1;
1768 let index_used_directly = same_var(self.cx, idx, self.var);
1769 let indexed_indirectly = {
1770 let mut used_visitor = LocalUsedVisitor {
1775 walk_expr(&mut used_visitor, idx);
1779 if indexed_indirectly || index_used_directly {
1780 if self.prefer_mutable {
1781 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1783 let res = self.cx.tables.qpath_res(seqpath, seqexpr.hir_id);
1785 Res::Local(hir_id) => {
1786 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1787 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1788 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1789 if indexed_indirectly {
1790 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1792 if index_used_directly {
1793 self.indexed_directly.insert(
1794 seqvar.segments[0].ident.name,
1795 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1798 return false; // no need to walk further *on the variable*
1800 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1801 if indexed_indirectly {
1802 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1804 if index_used_directly {
1805 self.indexed_directly.insert(
1806 seqvar.segments[0].ident.name,
1807 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1810 return false; // no need to walk further *on the variable*
1821 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1822 fn visit_expr(&mut self, expr: &'tcx Expr) {
1825 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.node;
1826 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1827 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1828 if !self.check(&args[1], &args[0], expr);
1834 if let ExprKind::Index(ref seqexpr, ref idx) = expr.node;
1835 if !self.check(idx, seqexpr, expr);
1840 // directly using a variable
1841 if let ExprKind::Path(ref qpath) = expr.node;
1842 if let QPath::Resolved(None, ref path) = *qpath;
1843 if path.segments.len() == 1;
1845 if let Res::Local(local_id) = self.cx.tables.qpath_res(qpath, expr.hir_id) {
1846 if local_id == self.var {
1847 self.nonindex = true;
1849 // not the correct variable, but still a variable
1850 self.referenced.insert(path.segments[0].ident.name);
1856 let old = self.prefer_mutable;
1858 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1859 self.prefer_mutable = true;
1860 self.visit_expr(lhs);
1861 self.prefer_mutable = false;
1862 self.visit_expr(rhs);
1864 ExprKind::AddrOf(mutbl, ref expr) => {
1865 if mutbl == MutMutable {
1866 self.prefer_mutable = true;
1868 self.visit_expr(expr);
1870 ExprKind::Call(ref f, ref args) => {
1873 let ty = self.cx.tables.expr_ty_adjusted(expr);
1874 self.prefer_mutable = false;
1875 if let ty::Ref(_, _, mutbl) = ty.sty {
1876 if mutbl == MutMutable {
1877 self.prefer_mutable = true;
1880 self.visit_expr(expr);
1883 ExprKind::MethodCall(_, _, ref args) => {
1884 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1885 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1886 self.prefer_mutable = false;
1887 if let ty::Ref(_, _, mutbl) = ty.sty {
1888 if mutbl == MutMutable {
1889 self.prefer_mutable = true;
1892 self.visit_expr(expr);
1895 ExprKind::Closure(_, _, body_id, ..) => {
1896 let body = self.cx.tcx.hir().body(body_id);
1897 self.visit_expr(&body.value);
1899 _ => walk_expr(self, expr),
1901 self.prefer_mutable = old;
1903 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1904 NestedVisitorMap::None
1908 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1909 let def_id = match var_def_id(cx, expr) {
1911 None => return false,
1913 if let Some(used_mutably) = mutated_variables(container, cx) {
1914 if used_mutably.contains(&def_id) {
1921 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1922 let def_id = match var_def_id(cx, iter_expr) {
1924 None => return false,
1926 let mut visitor = VarUsedAfterLoopVisitor {
1929 iter_expr_id: iter_expr.hir_id,
1930 past_while_let: false,
1931 var_used_after_while_let: false,
1933 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1934 walk_block(&mut visitor, enclosing_block);
1936 visitor.var_used_after_while_let
1939 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1940 cx: &'a LateContext<'a, 'tcx>,
1942 iter_expr_id: HirId,
1943 past_while_let: bool,
1944 var_used_after_while_let: bool,
1947 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1948 fn visit_expr(&mut self, expr: &'tcx Expr) {
1949 if self.past_while_let {
1950 if Some(self.def_id) == var_def_id(self.cx, expr) {
1951 self.var_used_after_while_let = true;
1953 } else if self.iter_expr_id == expr.hir_id {
1954 self.past_while_let = true;
1956 walk_expr(self, expr);
1958 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1959 NestedVisitorMap::None
1963 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1964 /// for `&T` and `&mut T`, such as `Vec`.
1966 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1967 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1968 // will allow further borrows afterwards
1969 let ty = cx.tables.expr_ty(e);
1970 is_iterable_array(ty, cx) ||
1971 match_type(cx, ty, &paths::VEC) ||
1972 match_type(cx, ty, &paths::LINKED_LIST) ||
1973 match_type(cx, ty, &paths::HASHMAP) ||
1974 match_type(cx, ty, &paths::HASHSET) ||
1975 match_type(cx, ty, &paths::VEC_DEQUE) ||
1976 match_type(cx, ty, &paths::BINARY_HEAP) ||
1977 match_type(cx, ty, &paths::BTREEMAP) ||
1978 match_type(cx, ty, &paths::BTREESET)
1981 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1982 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1984 ty::Array(_, n) => (0..=32).contains(&n.assert_usize(cx.tcx).expect("array length")),
1989 /// If a block begins with a statement (possibly a `let` binding) and has an
1990 /// expression, return it.
1991 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
1992 if block.stmts.is_empty() {
1995 if let StmtKind::Local(ref local) = block.stmts[0].node {
1996 if let Some(ref expr) = local.init {
2006 /// If a block begins with an expression (with or without semicolon), return it.
2007 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2009 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2010 None if !block.stmts.is_empty() => match block.stmts[0].node {
2011 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2012 StmtKind::Local(..) | StmtKind::Item(..) => None,
2018 /// Returns `true` if expr contains a single break expr without destination label
2020 /// passed expression. The expression may be within a block.
2021 fn is_simple_break_expr(expr: &Expr) -> bool {
2023 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2024 ExprKind::Block(ref b, _) => match extract_first_expr(b) {
2025 Some(subexpr) => is_simple_break_expr(subexpr),
2032 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2033 // incremented exactly once in the loop body, and initialized to zero
2034 // at the start of the loop.
2035 #[derive(Debug, PartialEq)]
2037 Initial, // Not examined yet
2038 IncrOnce, // Incremented exactly once, may be a loop counter
2039 Declared, // Declared but not (yet) initialized to zero
2044 /// Scan a for loop for variables that are incremented exactly once.
2045 struct IncrementVisitor<'a, 'tcx> {
2046 cx: &'a LateContext<'a, 'tcx>, // context reference
2047 states: FxHashMap<HirId, VarState>, // incremented variables
2048 depth: u32, // depth of conditional expressions
2052 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2053 fn visit_expr(&mut self, expr: &'tcx Expr) {
2058 // If node is a variable
2059 if let Some(def_id) = var_def_id(self.cx, expr) {
2060 if let Some(parent) = get_parent_expr(self.cx, expr) {
2061 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2064 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2065 if lhs.hir_id == expr.hir_id {
2066 if op.node == BinOpKind::Add && is_integer_literal(rhs, 1) {
2067 *state = match *state {
2068 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2069 _ => VarState::DontWarn,
2072 // Assigned some other value
2073 *state = VarState::DontWarn;
2077 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2078 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
2082 } else if is_loop(expr) || is_conditional(expr) {
2084 walk_expr(self, expr);
2087 } else if let ExprKind::Continue(_) = expr.node {
2091 walk_expr(self, expr);
2093 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2094 NestedVisitorMap::None
2098 /// Checks whether a variable is initialized to zero at the start of a loop.
2099 struct InitializeVisitor<'a, 'tcx> {
2100 cx: &'a LateContext<'a, 'tcx>, // context reference
2101 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2105 depth: u32, // depth of conditional expressions
2109 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2110 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2111 // Look for declarations of the variable
2112 if let StmtKind::Local(ref local) = stmt.node {
2113 if local.pat.hir_id == self.var_id {
2114 if let PatKind::Binding(.., ident, _) = local.pat.node {
2115 self.name = Some(ident.name);
2117 self.state = if let Some(ref init) = local.init {
2118 if is_integer_literal(init, 0) {
2129 walk_stmt(self, stmt);
2132 fn visit_expr(&mut self, expr: &'tcx Expr) {
2133 if self.state == VarState::DontWarn {
2136 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2137 self.past_loop = true;
2140 // No need to visit expressions before the variable is
2142 if self.state == VarState::IncrOnce {
2146 // If node is the desired variable, see how it's used
2147 if var_def_id(self.cx, expr) == Some(self.var_id) {
2148 if let Some(parent) = get_parent_expr(self.cx, expr) {
2150 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2151 self.state = VarState::DontWarn;
2153 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2154 self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
2160 ExprKind::AddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
2166 self.state = VarState::DontWarn;
2169 } else if !self.past_loop && is_loop(expr) {
2170 self.state = VarState::DontWarn;
2172 } else if is_conditional(expr) {
2174 walk_expr(self, expr);
2178 walk_expr(self, expr);
2180 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2181 NestedVisitorMap::None
2185 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2186 if let ExprKind::Path(ref qpath) = expr.node {
2187 let path_res = cx.tables.qpath_res(qpath, expr.hir_id);
2188 if let Res::Local(node_id) = path_res {
2189 return Some(node_id);
2195 fn is_loop(expr: &Expr) -> bool {
2197 ExprKind::Loop(..) => true,
2202 fn is_conditional(expr: &Expr) -> bool {
2204 ExprKind::Match(..) => true,
2209 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2211 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2212 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2213 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2215 return is_loop_nested(cx, loop_expr, iter_expr)
2221 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2222 let mut id = loop_expr.hir_id;
2223 let iter_name = if let Some(name) = path_name(iter_expr) {
2229 let parent = cx.tcx.hir().get_parent_node(id);
2233 match cx.tcx.hir().find(parent) {
2234 Some(Node::Expr(expr)) => {
2235 if let ExprKind::Loop(..) = expr.node {
2239 Some(Node::Block(block)) => {
2240 let mut block_visitor = LoopNestVisitor {
2242 iterator: iter_name,
2245 walk_block(&mut block_visitor, block);
2246 if block_visitor.nesting == RuledOut {
2250 Some(Node::Stmt(_)) => (),
2259 #[derive(PartialEq, Eq)]
2261 Unknown, // no nesting detected yet
2262 RuledOut, // the iterator is initialized or assigned within scope
2263 LookFurther, // no nesting detected, no further walk required
2266 use self::Nesting::{LookFurther, RuledOut, Unknown};
2268 struct LoopNestVisitor {
2274 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2275 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2276 if stmt.hir_id == self.hir_id {
2277 self.nesting = LookFurther;
2278 } else if self.nesting == Unknown {
2279 walk_stmt(self, stmt);
2283 fn visit_expr(&mut self, expr: &'tcx Expr) {
2284 if self.nesting != Unknown {
2287 if expr.hir_id == self.hir_id {
2288 self.nesting = LookFurther;
2292 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2293 if match_var(path, self.iterator) {
2294 self.nesting = RuledOut;
2297 _ => walk_expr(self, expr),
2301 fn visit_pat(&mut self, pat: &'tcx Pat) {
2302 if self.nesting != Unknown {
2305 if let PatKind::Binding(.., span_name, _) = pat.node {
2306 if self.iterator == span_name.name {
2307 self.nesting = RuledOut;
2314 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2315 NestedVisitorMap::None
2319 fn path_name(e: &Expr) -> Option<Name> {
2320 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
2321 let segments = &path.segments;
2322 if segments.len() == 1 {
2323 return Some(segments[0].ident.name);
2329 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2330 if constant(cx, cx.tables, cond).is_some() {
2331 // A pure constant condition (e.g., `while false`) is not linted.
2335 let mut var_visitor = VarCollectorVisitor {
2337 ids: FxHashSet::default(),
2338 def_ids: FxHashMap::default(),
2341 var_visitor.visit_expr(cond);
2342 if var_visitor.skip {
2345 let used_in_condition = &var_visitor.ids;
2346 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2347 used_in_condition.is_disjoint(&used_mutably)
2351 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2352 if no_cond_variable_mutated && !mutable_static_in_cond {
2355 WHILE_IMMUTABLE_CONDITION,
2357 "Variable in the condition are not mutated in the loop body. \
2358 This either leads to an infinite or to a never running loop.",
2363 /// Collects the set of variables in an expression
2364 /// Stops analysis if a function call is found
2365 /// Note: In some cases such as `self`, there are no mutable annotation,
2366 /// All variables definition IDs are collected
2367 struct VarCollectorVisitor<'a, 'tcx> {
2368 cx: &'a LateContext<'a, 'tcx>,
2369 ids: FxHashSet<HirId>,
2370 def_ids: FxHashMap<def_id::DefId, bool>,
2374 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2375 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2377 if let ExprKind::Path(ref qpath) = ex.node;
2378 if let QPath::Resolved(None, _) = *qpath;
2379 let res = self.cx.tables.qpath_res(qpath, ex.hir_id);
2382 Res::Local(node_id) => {
2383 self.ids.insert(node_id);
2385 Res::Def(DefKind::Static, def_id) => {
2386 let mutable = self.cx.tcx.is_mutable_static(def_id);
2387 self.def_ids.insert(def_id, mutable);
2396 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2397 fn visit_expr(&mut self, ex: &'tcx Expr) {
2399 ExprKind::Path(_) => self.insert_def_id(ex),
2400 // If there is any function/method call… we just stop analysis
2401 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2403 _ => walk_expr(self, ex),
2407 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2408 NestedVisitorMap::None
2412 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2414 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2416 if let ExprKind::MethodCall(ref method, _, ref args) = expr.node;
2417 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].node;
2418 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2419 if let Some(ref generic_args) = chain_method.args;
2420 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2422 let ty = cx.tables.node_type(ty.hir_id);
2423 if match_type(cx, ty, &paths::VEC) ||
2424 match_type(cx, ty, &paths::VEC_DEQUE) ||
2425 match_type(cx, ty, &paths::BTREEMAP) ||
2426 match_type(cx, ty, &paths::HASHMAP) {
2427 if method.ident.name == sym!(len) {
2428 let span = shorten_needless_collect_span(expr);
2429 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2433 ".count()".to_string(),
2434 Applicability::MachineApplicable,
2438 if method.ident.name == sym!(is_empty) {
2439 let span = shorten_needless_collect_span(expr);
2440 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2444 ".next().is_none()".to_string(),
2445 Applicability::MachineApplicable,
2449 if method.ident.name == sym!(contains) {
2450 let contains_arg = snippet(cx, args[1].span, "??");
2451 let span = shorten_needless_collect_span(expr);
2452 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2457 ".any(|&x| x == {})",
2458 if contains_arg.starts_with('&') { &contains_arg[1..] } else { &contains_arg }
2460 Applicability::MachineApplicable,
2469 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2471 if let ExprKind::MethodCall(_, _, ref args) = expr.node;
2472 if let ExprKind::MethodCall(_, ref span, _) = args[0].node;
2474 return expr.span.with_lo(span.lo() - BytePos(1));