1 use crate::reexport::*;
2 use if_chain::if_chain;
3 use itertools::Itertools;
4 use rustc::hir::def::{DefKind, Res};
5 use rustc::hir::def_id;
6 use rustc::hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
8 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
9 use rustc::middle::region;
10 use rustc::{declare_lint_pass, declare_tool_lint};
11 // use rustc::middle::region::CodeExtent;
12 use crate::consts::{constant, Constant};
13 use crate::utils::usage::mutated_variables;
14 use crate::utils::{is_type_diagnostic_item, qpath_res, sext, sugg};
15 use rustc_typeck::expr_use_visitor::*;
16 use rustc::ty::subst::Subst;
17 use rustc::ty::{self, Ty};
18 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
19 use rustc_errors::Applicability;
20 use std::iter::{once, Iterator};
23 use syntax::source_map::Span;
24 use syntax_pos::{BytePos, Symbol};
26 use crate::utils::paths;
28 get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
29 is_integer_const, is_refutable, last_path_segment, match_trait_method, match_type, match_var, multispan_sugg,
30 snippet, snippet_opt, snippet_with_applicability, span_help_and_lint, span_lint, span_lint_and_sugg,
31 span_lint_and_then, SpanlessEq,
34 declare_clippy_lint! {
35 /// **What it does:** Checks for for-loops that manually copy items between
36 /// slices that could be optimized by having a memcpy.
38 /// **Why is this bad?** It is not as fast as a memcpy.
40 /// **Known problems:** None.
44 /// # let src = vec![1];
45 /// # let mut dst = vec![0; 65];
46 /// for i in 0..src.len() {
47 /// dst[i + 64] = src[i];
50 /// Could be written as:
52 /// # let src = vec![1];
53 /// # let mut dst = vec![0; 65];
54 /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
58 "manually copying items between slices"
61 declare_clippy_lint! {
62 /// **What it does:** Checks for looping over the range of `0..len` of some
63 /// collection just to get the values by index.
65 /// **Why is this bad?** Just iterating the collection itself makes the intent
66 /// more clear and is probably faster.
68 /// **Known problems:** None.
72 /// let vec = vec!['a', 'b', 'c'];
73 /// for i in 0..vec.len() {
74 /// println!("{}", vec[i]);
77 /// Could be written as:
79 /// let vec = vec!['a', 'b', 'c'];
81 /// println!("{}", i);
84 pub NEEDLESS_RANGE_LOOP,
86 "for-looping over a range of indices where an iterator over items would do"
89 declare_clippy_lint! {
90 /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
91 /// suggests the latter.
93 /// **Why is this bad?** Readability.
95 /// **Known problems:** False negatives. We currently only warn on some known
100 /// // with `y` a `Vec` or slice:
101 /// # let y = vec![1];
102 /// for x in y.iter() {
106 /// can be rewritten to
108 /// # let y = vec![1];
113 pub EXPLICIT_ITER_LOOP,
115 "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
118 declare_clippy_lint! {
119 /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
120 /// suggests the latter.
122 /// **Why is this bad?** Readability.
124 /// **Known problems:** None
128 /// # let y = vec![1];
129 /// // with `y` a `Vec` or slice:
130 /// for x in y.into_iter() {
134 /// can be rewritten to
136 /// # let y = vec![1];
141 pub EXPLICIT_INTO_ITER_LOOP,
143 "for-looping over `_.into_iter()` when `_` would do"
146 declare_clippy_lint! {
147 /// **What it does:** Checks for loops on `x.next()`.
149 /// **Why is this bad?** `next()` returns either `Some(value)` if there was a
150 /// value, or `None` otherwise. The insidious thing is that `Option<_>`
151 /// implements `IntoIterator`, so that possibly one value will be iterated,
152 /// leading to some hard to find bugs. No one will want to write such code
153 /// [except to win an Underhanded Rust
154 /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
156 /// **Known problems:** None.
160 /// for x in y.next() {
166 "for-looping over `_.next()` which is probably not intended"
169 declare_clippy_lint! {
170 /// **What it does:** Checks for `for` loops over `Option` values.
172 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
175 /// **Known problems:** None.
179 /// for x in option {
186 /// if let Some(x) = option {
190 pub FOR_LOOP_OVER_OPTION,
192 "for-looping over an `Option`, which is more clearly expressed as an `if let`"
195 declare_clippy_lint! {
196 /// **What it does:** Checks for `for` loops over `Result` values.
198 /// **Why is this bad?** Readability. This is more clearly expressed as an `if
201 /// **Known problems:** None.
205 /// for x in result {
212 /// if let Ok(x) = result {
216 pub FOR_LOOP_OVER_RESULT,
218 "for-looping over a `Result`, which is more clearly expressed as an `if let`"
221 declare_clippy_lint! {
222 /// **What it does:** Detects `loop + match` combinations that are easier
223 /// written as a `while let` loop.
225 /// **Why is this bad?** The `while let` loop is usually shorter and more
228 /// **Known problems:** Sometimes the wrong binding is displayed (#383).
232 /// # let y = Some(1);
234 /// let x = match y {
238 /// // .. do something with x
240 /// // is easier written as
241 /// while let Some(x) = y {
242 /// // .. do something with x
247 "`loop { if let { ... } else break }`, which can be written as a `while let` loop"
250 declare_clippy_lint! {
251 /// **What it does:** Checks for functions collecting an iterator when collect
254 /// **Why is this bad?** `collect` causes the allocation of a new data structure,
255 /// when this allocation may not be needed.
257 /// **Known problems:**
262 /// # let iterator = vec![1].into_iter();
263 /// let len = iterator.clone().collect::<Vec<_>>().len();
265 /// let len = iterator.count();
267 pub NEEDLESS_COLLECT,
269 "collecting an iterator when collect is not needed"
272 declare_clippy_lint! {
273 /// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
274 /// are constant and `x` is greater or equal to `y`, unless the range is
275 /// reversed or has a negative `.step_by(_)`.
277 /// **Why is it bad?** Such loops will either be skipped or loop until
278 /// wrap-around (in debug code, this may `panic!()`). Both options are probably
281 /// **Known problems:** The lint cannot catch loops over dynamically defined
282 /// ranges. Doing this would require simulating all possible inputs and code
283 /// paths through the program, which would be complex and error-prone.
287 /// for x in 5..10 - 5 {
289 /// } // oops, stray `-`
291 pub REVERSE_RANGE_LOOP,
293 "iteration over an empty range, such as `10..0` or `5..5`"
296 declare_clippy_lint! {
297 /// **What it does:** Checks `for` loops over slices with an explicit counter
298 /// and suggests the use of `.enumerate()`.
300 /// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
301 /// declutters the code and may be faster in some instances.
303 /// **Known problems:** None.
307 /// # let v = vec![1];
308 /// # fn bar(bar: usize, baz: usize) {}
315 /// Could be written as
317 /// # let v = vec![1];
318 /// # fn bar(bar: usize, baz: usize) {}
319 /// for (i, item) in v.iter().enumerate() { bar(i, *item); }
321 pub EXPLICIT_COUNTER_LOOP,
323 "for-looping with an explicit counter when `_.enumerate()` would do"
326 declare_clippy_lint! {
327 /// **What it does:** Checks for empty `loop` expressions.
329 /// **Why is this bad?** Those busy loops burn CPU cycles without doing
330 /// anything. Think of the environment and either block on something or at least
331 /// make the thread sleep for some microseconds.
333 /// **Known problems:** None.
341 "empty `loop {}`, which should block or sleep"
344 declare_clippy_lint! {
345 /// **What it does:** Checks for `while let` expressions on iterators.
347 /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
348 /// the intent better.
350 /// **Known problems:** None.
354 /// while let Some(val) = iter() {
358 pub WHILE_LET_ON_ITERATOR,
360 "using a while-let loop instead of a for loop on an iterator"
363 declare_clippy_lint! {
364 /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
365 /// ignoring either the keys or values.
367 /// **Why is this bad?** Readability. There are `keys` and `values` methods that
368 /// can be used to express that don't need the values or keys.
370 /// **Known problems:** None.
374 /// for (k, _) in &map {
379 /// could be replaced by
382 /// for k in map.keys() {
388 "looping on a map using `iter` when `keys` or `values` would do"
391 declare_clippy_lint! {
392 /// **What it does:** Checks for loops that will always `break`, `return` or
393 /// `continue` an outer loop.
395 /// **Why is this bad?** This loop never loops, all it does is obfuscating the
398 /// **Known problems:** None
409 "any loop that will always `break` or `return`"
412 declare_clippy_lint! {
413 /// **What it does:** Checks for loops which have a range bound that is a mutable variable
415 /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
417 /// **Known problems:** None
421 /// let mut foo = 42;
422 /// for i in 0..foo {
424 /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
429 "for loop over a range where one of the bounds is a mutable variable"
432 declare_clippy_lint! {
433 /// **What it does:** Checks whether variables used within while loop condition
434 /// can be (and are) mutated in the body.
436 /// **Why is this bad?** If the condition is unchanged, entering the body of the loop
437 /// will lead to an infinite loop.
439 /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
440 /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
441 /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
447 /// println!("let me loop forever!");
450 pub WHILE_IMMUTABLE_CONDITION,
452 "variables used within while expression are not mutated in the body"
455 declare_lint_pass!(Loops => [
459 EXPLICIT_INTO_ITER_LOOP,
461 FOR_LOOP_OVER_RESULT,
462 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 if let Some((pat, arg, body)) = higher::for_loop(expr) {
479 // we don't want to check expanded macros
480 // this check is not at the top of the function
481 // since higher::for_loop expressions are marked as expansions
482 if body.span.from_expansion() {
485 check_for_loop(cx, pat, arg, body, expr);
488 // we don't want to check expanded macros
489 if expr.span.from_expansion() {
493 // check for never_loop
494 if let ExprKind::Loop(ref block, _, _) = expr.kind {
495 match never_loop_block(block, expr.hir_id) {
496 NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
497 NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
501 // check for `loop { if let {} else break }` that could be `while let`
502 // (also matches an explicit "match" instead of "if let")
503 // (even if the "match" or "if let" is used for declaration)
504 if let ExprKind::Loop(ref block, _, LoopSource::Loop) = expr.kind {
505 // also check for empty `loop {}` statements
506 if block.stmts.is_empty() && block.expr.is_none() {
511 "empty `loop {}` detected. You may want to either use `panic!()` or add \
512 `std::thread::sleep(..);` to the loop body.",
516 // extract the expression from the first statement (if any) in a block
517 let inner_stmt_expr = extract_expr_from_first_stmt(block);
518 // or extract the first expression (if any) from the block
519 if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
520 if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
521 // ensure "if let" compatible match structure
523 MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
525 && arms[0].guard.is_none()
526 && arms[1].guard.is_none()
527 && is_simple_break_expr(&arms[1].body)
529 if in_external_macro(cx.sess(), expr.span) {
533 // NOTE: we used to build a body here instead of using
534 // ellipsis, this was removed because:
535 // 1) it was ugly with big bodies;
536 // 2) it was not indented properly;
537 // 3) it wasn’t very smart (see #675).
538 let mut applicability = Applicability::HasPlaceholders;
543 "this loop could be written as a `while let` loop",
546 "while let {} = {} {{ .. }}",
547 snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
548 snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
559 if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
560 let pat = &arms[0].pat.kind;
562 &PatKind::TupleStruct(ref qpath, ref pat_args, _),
563 &ExprKind::MethodCall(ref method_path, _, ref method_args),
564 ) = (pat, &match_expr.kind)
566 let iter_expr = &method_args[0];
567 let lhs_constructor = last_path_segment(qpath);
568 if method_path.ident.name == sym!(next)
569 && match_trait_method(cx, match_expr, &paths::ITERATOR)
570 && lhs_constructor.ident.name == sym!(Some)
571 && (pat_args.is_empty()
572 || !is_refutable(cx, &pat_args[0])
573 && !is_used_inside(cx, iter_expr, &arms[0].body)
574 && !is_iterator_used_after_while_let(cx, iter_expr)
575 && !is_nested(cx, expr, &method_args[0]))
577 let iterator = snippet(cx, method_args[0].span, "_");
578 let loop_var = if pat_args.is_empty() {
581 snippet(cx, pat_args[0].span, "_").into_owned()
585 WHILE_LET_ON_ITERATOR,
587 "this loop could be written as a `for` loop",
589 format!("for {} in {} {{ .. }}", loop_var, iterator),
590 Applicability::HasPlaceholders,
596 if let Some((cond, body)) = higher::while_loop(&expr) {
597 check_infinite_loop(cx, cond, body);
600 check_needless_collect(expr, cx);
604 enum NeverLoopResult {
605 // A break/return always get triggered but not necessarily for the main loop.
607 // A continue may occur for the main loop.
613 fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
615 NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
616 NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
620 // Combine two results for parts that are called in order.
622 fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
624 NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
625 NeverLoopResult::Otherwise => second,
629 // Combine two results where both parts are called but not necessarily in order.
631 fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
632 match (left, right) {
633 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
634 NeverLoopResult::MayContinueMainLoop
636 (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
637 (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
641 // Combine two results where only one of the part may have been executed.
643 fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
645 (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
646 (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
647 NeverLoopResult::MayContinueMainLoop
649 (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
653 fn never_loop_block(block: &Block, main_loop_id: HirId) -> NeverLoopResult {
654 let stmts = block.stmts.iter().map(stmt_to_expr);
655 let expr = once(block.expr.as_ref().map(|p| &**p));
656 let mut iter = stmts.chain(expr).filter_map(|e| e);
657 never_loop_expr_seq(&mut iter, main_loop_id)
660 fn stmt_to_expr(stmt: &Stmt) -> Option<&Expr> {
662 StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
663 StmtKind::Local(ref local) => local.init.as_ref().map(|p| &**p),
668 fn never_loop_expr(expr: &Expr, main_loop_id: HirId) -> NeverLoopResult {
671 | ExprKind::Unary(_, ref e)
672 | ExprKind::Cast(ref e, _)
673 | ExprKind::Type(ref e, _)
674 | ExprKind::Field(ref e, _)
675 | ExprKind::AddrOf(_, _, ref e)
676 | ExprKind::Struct(_, _, Some(ref e))
677 | ExprKind::Repeat(ref e, _)
678 | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
679 ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es) | ExprKind::Tup(ref es) => {
680 never_loop_expr_all(&mut es.iter(), main_loop_id)
682 ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
683 ExprKind::Binary(_, ref e1, ref e2)
684 | ExprKind::Assign(ref e1, ref e2)
685 | ExprKind::AssignOp(_, ref e1, ref e2)
686 | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
687 ExprKind::Loop(ref b, _, _) => {
688 // Break can come from the inner loop so remove them.
689 absorb_break(&never_loop_block(b, main_loop_id))
691 ExprKind::Match(ref e, ref arms, _) => {
692 let e = never_loop_expr(e, main_loop_id);
696 let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
700 ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
701 ExprKind::Continue(d) => {
704 .expect("target ID can only be missing in the presence of compilation errors");
705 if id == main_loop_id {
706 NeverLoopResult::MayContinueMainLoop
708 NeverLoopResult::AlwaysBreak
711 ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => {
712 if let Some(ref e) = *e {
713 combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
715 NeverLoopResult::AlwaysBreak
718 ExprKind::Struct(_, _, None)
719 | ExprKind::Yield(_, _)
720 | ExprKind::Closure(_, _, _, _, _)
721 | ExprKind::InlineAsm(_)
724 | ExprKind::Err => NeverLoopResult::Otherwise,
728 fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
729 es.map(|e| never_loop_expr(e, main_loop_id))
730 .fold(NeverLoopResult::Otherwise, combine_seq)
733 fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
734 es.map(|e| never_loop_expr(e, main_loop_id))
735 .fold(NeverLoopResult::Otherwise, combine_both)
738 fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
739 e.map(|e| never_loop_expr(e, main_loop_id))
740 .fold(NeverLoopResult::AlwaysBreak, combine_branches)
743 fn check_for_loop<'a, 'tcx>(
744 cx: &LateContext<'a, 'tcx>,
750 check_for_loop_range(cx, pat, arg, body, expr);
751 check_for_loop_reverse_range(cx, arg, expr);
752 check_for_loop_arg(cx, pat, arg, expr);
753 check_for_loop_explicit_counter(cx, pat, arg, body, expr);
754 check_for_loop_over_map_kv(cx, pat, arg, body, expr);
755 check_for_mut_range_bound(cx, arg, body);
756 detect_manual_memcpy(cx, pat, arg, body, expr);
759 fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> bool {
761 if let ExprKind::Path(ref qpath) = expr.kind;
762 if let QPath::Resolved(None, ref path) = *qpath;
763 if path.segments.len() == 1;
764 if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id);
781 fn negative(s: String) -> Self {
782 Self { value: s, negate: true }
785 fn positive(s: String) -> Self {
793 struct FixedOffsetVar {
798 fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'_>) -> bool {
799 let is_slice = match ty.kind {
800 ty::Ref(_, subty, _) => is_slice_like(cx, subty),
801 ty::Slice(..) | ty::Array(..) => true,
805 is_slice || is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) || match_type(cx, ty, &paths::VEC_DEQUE)
808 fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: HirId) -> Option<FixedOffsetVar> {
809 fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: HirId) -> Option<String> {
811 ExprKind::Lit(ref l) => match l.node {
812 ast::LitKind::Int(x, _ty) => Some(x.to_string()),
815 ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
820 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind {
821 let ty = cx.tables.expr_ty(seqexpr);
822 if !is_slice_like(cx, ty) {
826 let offset = match idx.kind {
827 ExprKind::Binary(op, ref lhs, ref rhs) => match op.node {
829 let offset_opt = if same_var(cx, lhs, var) {
830 extract_offset(cx, rhs, var)
831 } else if same_var(cx, rhs, var) {
832 extract_offset(cx, lhs, var)
837 offset_opt.map(Offset::positive)
839 BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
842 ExprKind::Path(..) => {
843 if same_var(cx, idx, var) {
844 Some(Offset::positive("0".into()))
852 offset.map(|o| FixedOffsetVar {
853 var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
861 fn fetch_cloned_fixed_offset_var<'a, 'tcx>(
862 cx: &LateContext<'a, 'tcx>,
865 ) -> Option<FixedOffsetVar> {
867 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
868 if method.ident.name == sym!(clone);
870 if let Some(arg) = args.get(0);
872 return get_fixed_offset_var(cx, arg, var);
876 get_fixed_offset_var(cx, expr, var)
879 fn get_indexed_assignments<'a, 'tcx>(
880 cx: &LateContext<'a, 'tcx>,
883 ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
884 fn get_assignment<'a, 'tcx>(
885 cx: &LateContext<'a, 'tcx>,
888 ) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
889 if let ExprKind::Assign(ref lhs, ref rhs) = e.kind {
891 get_fixed_offset_var(cx, lhs, var),
892 fetch_cloned_fixed_offset_var(cx, rhs, var),
894 (Some(offset_left), Some(offset_right)) => {
895 // Source and destination must be different
896 if offset_left.var_name == offset_right.var_name {
899 Some((offset_left, offset_right))
909 if let ExprKind::Block(ref b, _) = body.kind {
911 ref stmts, ref expr, ..
916 .map(|stmt| match stmt.kind {
917 StmtKind::Local(..) | StmtKind::Item(..) => None,
918 StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)),
920 .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var))))
922 .collect::<Option<Vec<_>>>()
923 .unwrap_or_else(|| vec![])
925 get_assignment(cx, body, var).into_iter().collect()
929 /// Checks for for loops that sequentially copy items from one slice-like
930 /// object to another.
931 fn detect_manual_memcpy<'a, 'tcx>(
932 cx: &LateContext<'a, 'tcx>,
938 if let Some(higher::Range {
942 }) = higher::range(cx, arg)
944 // the var must be a single name
945 if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
946 let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
947 match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
948 ("0", _, "0", _) => "".into(),
949 ("0", _, x, false) | (x, false, "0", false) => x.into(),
950 ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
951 (x, false, y, false) => format!("({} + {})", x, y),
952 (x, false, y, true) => {
956 format!("({} - {})", x, y)
959 (x, true, y, false) => {
963 format!("({} - {})", y, x)
966 (x, true, y, true) => format!("-({} + {})", x, y),
970 let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| {
971 if let Some(end) = *end {
973 if let ExprKind::MethodCall(ref method, _, ref len_args) = end.kind;
974 if method.ident.name == sym!(len);
975 if len_args.len() == 1;
976 if let Some(arg) = len_args.get(0);
977 if snippet(cx, arg.span, "??") == var_name;
979 return if offset.negate {
980 format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
987 let end_str = match limits {
988 ast::RangeLimits::Closed => {
989 let end = sugg::Sugg::hir(cx, end, "<count>");
990 format!("{}", end + sugg::ONE)
992 ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
995 print_sum(&Offset::positive(end_str), &offset)
1001 // The only statements in the for loops can be indexed assignments from
1002 // indexed retrievals.
1003 let manual_copies = get_indexed_assignments(cx, body, canonical_id);
1005 let big_sugg = manual_copies
1007 .map(|(dst_var, src_var)| {
1008 let start_str = Offset::positive(snippet(cx, start.span, "").to_string());
1009 let dst_offset = print_sum(&start_str, &dst_var.offset);
1010 let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
1011 let src_offset = print_sum(&start_str, &src_var.offset);
1012 let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
1013 let dst = if dst_offset == "" && dst_limit == "" {
1016 format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
1020 "{}.clone_from_slice(&{}[{}..{}])",
1021 dst, src_var.var_name, src_offset, src_limit
1026 if !big_sugg.is_empty() {
1031 "it looks like you're manually copying between slices",
1032 "try replacing the loop by",
1034 Applicability::Unspecified,
1041 /// Checks for looping over a range and then indexing a sequence with it.
1042 /// The iteratee must be a range literal.
1043 #[allow(clippy::too_many_lines)]
1044 fn check_for_loop_range<'a, 'tcx>(
1045 cx: &LateContext<'a, 'tcx>,
1051 if let Some(higher::Range {
1055 }) = higher::range(cx, arg)
1057 // the var must be a single name
1058 if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
1059 let mut visitor = VarVisitor {
1062 indexed_mut: FxHashSet::default(),
1063 indexed_indirectly: FxHashMap::default(),
1064 indexed_directly: FxHashMap::default(),
1065 referenced: FxHashSet::default(),
1067 prefer_mutable: false,
1069 walk_expr(&mut visitor, body);
1071 // linting condition: we only indexed one variable, and indexed it directly
1072 if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
1073 let (indexed, (indexed_extent, indexed_ty)) = visitor
1077 .expect("already checked that we have exactly 1 element");
1079 // ensure that the indexed variable was declared before the loop, see #601
1080 if let Some(indexed_extent) = indexed_extent {
1081 let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
1082 let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
1083 let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
1084 let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
1085 if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
1090 // don't lint if the container that is indexed does not have .iter() method
1091 let has_iter = has_iter_method(cx, indexed_ty);
1092 if has_iter.is_none() {
1096 // don't lint if the container that is indexed into is also used without
1098 if visitor.referenced.contains(&indexed) {
1102 let starts_at_zero = is_integer_const(cx, start, 0);
1104 let skip = if starts_at_zero {
1107 format!(".skip({})", snippet(cx, start.span, ".."))
1110 let mut end_is_start_plus_val = false;
1112 let take = if let Some(end) = *end {
1113 let mut take_expr = end;
1115 if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
1116 if let BinOpKind::Add = op.node {
1117 let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
1118 let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
1120 if start_equal_left {
1122 } else if start_equal_right {
1126 end_is_start_plus_val = start_equal_left | start_equal_right;
1130 if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
1134 ast::RangeLimits::Closed => {
1135 let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
1136 format!(".take({})", take_expr + sugg::ONE)
1138 ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
1145 let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
1146 ("mut ", "iter_mut")
1151 let take_is_empty = take.is_empty();
1152 let mut method_1 = take;
1153 let mut method_2 = skip;
1155 if end_is_start_plus_val {
1156 mem::swap(&mut method_1, &mut method_2);
1159 if visitor.nonindex {
1162 NEEDLESS_RANGE_LOOP,
1164 &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
1168 "consider using an iterator".to_string(),
1170 (pat.span, format!("({}, <item>)", ident.name)),
1173 format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
1180 let repl = if starts_at_zero && take_is_empty {
1181 format!("&{}{}", ref_mut, indexed)
1183 format!("{}.{}(){}{}", indexed, method, method_1, method_2)
1188 NEEDLESS_RANGE_LOOP,
1191 "the loop variable `{}` is only used to index `{}`.",
1197 "consider using an iterator".to_string(),
1198 vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
1208 fn is_len_call(expr: &Expr, var: Name) -> bool {
1210 if let ExprKind::MethodCall(ref method, _, ref len_args) = expr.kind;
1211 if len_args.len() == 1;
1212 if method.ident.name == sym!(len);
1213 if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
1214 if path.segments.len() == 1;
1215 if path.segments[0].ident.name == var;
1224 fn is_end_eq_array_len<'tcx>(
1225 cx: &LateContext<'_, 'tcx>,
1227 limits: ast::RangeLimits,
1228 indexed_ty: Ty<'tcx>,
1231 if let ExprKind::Lit(ref lit) = end.kind;
1232 if let ast::LitKind::Int(end_int, _) = lit.node;
1233 if let ty::Array(_, arr_len_const) = indexed_ty.kind;
1234 if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
1236 return match limits {
1237 ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
1238 ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
1246 fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr, expr: &'tcx Expr) {
1247 // if this for loop is iterating over a two-sided range...
1248 if let Some(higher::Range {
1252 }) = higher::range(cx, arg)
1254 // ...and both sides are compile-time constant integers...
1255 if let Some((start_idx, _)) = constant(cx, cx.tables, start) {
1256 if let Some((end_idx, _)) = constant(cx, cx.tables, end) {
1257 // ...and the start index is greater than the end index,
1258 // this loop will never run. This is often confusing for developers
1259 // who think that this will iterate from the larger value to the
1261 let ty = cx.tables.expr_ty(start);
1262 let (sup, eq) = match (start_idx, end_idx) {
1263 (Constant::Int(start_idx), Constant::Int(end_idx)) => (
1265 ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity),
1266 ty::Uint(_) => start_idx > end_idx,
1269 start_idx == end_idx,
1271 _ => (false, false),
1275 let start_snippet = snippet(cx, start.span, "_");
1276 let end_snippet = snippet(cx, end.span, "_");
1277 let dots = if limits == ast::RangeLimits::Closed {
1287 "this range is empty so this for loop will never run",
1291 "consider using the following if you are attempting to iterate over this \
1294 "({end}{dots}{start}).rev()",
1297 start = start_snippet
1299 Applicability::MaybeIncorrect,
1303 } else if eq && limits != ast::RangeLimits::Closed {
1304 // if they are equal, it's also problematic - this loop
1310 "this range is empty so this for loop will never run",
1318 fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr], arg: &Expr, method_name: &str) {
1319 let mut applicability = Applicability::MachineApplicable;
1320 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1321 let muta = if method_name == "iter_mut" { "mut " } else { "" };
1326 "it is more concise to loop over references to containers instead of using explicit \
1328 "to write this more concisely, try",
1329 format!("&{}{}", muta, object),
1334 fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr, expr: &Expr) {
1335 let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
1336 if let ExprKind::MethodCall(ref method, _, ref args) = arg.kind {
1337 // just the receiver, no arguments
1338 if args.len() == 1 {
1339 let method_name = &*method.ident.as_str();
1340 // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
1341 if method_name == "iter" || method_name == "iter_mut" {
1342 if is_ref_iterable_type(cx, &args[0]) {
1343 lint_iter_method(cx, args, arg, method_name);
1345 } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
1346 let def_id = cx.tables.type_dependent_def_id(arg.hir_id).unwrap();
1347 let substs = cx.tables.node_substs(arg.hir_id);
1348 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
1350 let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
1351 assert_eq!(fn_arg_tys.skip_binder().len(), 1);
1352 if fn_arg_tys.skip_binder()[0].is_region_ptr() {
1353 match cx.tables.expr_ty(&args[0]).kind {
1354 // If the length is greater than 32 no traits are implemented for array and
1355 // therefore we cannot use `&`.
1356 ty::Array(_, size) if size.eval_usize(cx.tcx, cx.param_env) > 32 => {},
1357 _ => lint_iter_method(cx, args, arg, method_name),
1360 let mut applicability = Applicability::MachineApplicable;
1361 let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
1364 EXPLICIT_INTO_ITER_LOOP,
1366 "it is more concise to loop over containers instead of using explicit \
1367 iteration methods`",
1368 "to write this more concisely, try",
1373 } else if method_name == "next" && match_trait_method(cx, arg, &paths::ITERATOR) {
1378 "you are iterating over `Iterator::next()` which is an Option; this will compile but is \
1379 probably not what you want",
1381 next_loop_linted = true;
1385 if !next_loop_linted {
1386 check_arg_type(cx, pat, arg);
1390 /// Checks for `for` loops over `Option`s and `Result`s.
1391 fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat, arg: &Expr) {
1392 let ty = cx.tables.expr_ty(arg);
1393 if match_type(cx, ty, &paths::OPTION) {
1396 FOR_LOOP_OVER_OPTION,
1399 "for loop over `{0}`, which is an `Option`. This is more readably written as an \
1400 `if let` statement.",
1401 snippet(cx, arg.span, "_")
1404 "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
1405 snippet(cx, pat.span, "_"),
1406 snippet(cx, arg.span, "_")
1409 } else if match_type(cx, ty, &paths::RESULT) {
1412 FOR_LOOP_OVER_RESULT,
1415 "for loop over `{0}`, which is a `Result`. This is more readably written as an \
1416 `if let` statement.",
1417 snippet(cx, arg.span, "_")
1420 "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
1421 snippet(cx, pat.span, "_"),
1422 snippet(cx, arg.span, "_")
1428 fn check_for_loop_explicit_counter<'a, 'tcx>(
1429 cx: &LateContext<'a, 'tcx>,
1435 // Look for variables that are incremented once per loop iteration.
1436 let mut visitor = IncrementVisitor {
1438 states: FxHashMap::default(),
1442 walk_expr(&mut visitor, body);
1444 // For each candidate, check the parent block to see if
1445 // it's initialized to zero at the start of the loop.
1446 if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
1447 for (id, _) in visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) {
1448 let mut visitor2 = InitializeVisitor {
1452 state: VarState::IncrOnce,
1457 walk_block(&mut visitor2, block);
1459 if visitor2.state == VarState::Warn {
1460 if let Some(name) = visitor2.name {
1461 let mut applicability = Applicability::MachineApplicable;
1463 // for some reason this is the only way to get the `Span`
1464 // of the entire `for` loop
1465 let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind {
1473 EXPLICIT_COUNTER_LOOP,
1474 for_span.with_hi(arg.span.hi()),
1475 &format!("the variable `{}` is used as a loop counter.", name),
1478 "for ({}, {}) in {}.enumerate()",
1480 snippet_with_applicability(cx, pat.span, "item", &mut applicability),
1481 make_iterator_snippet(cx, arg, &mut applicability),
1491 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
1492 /// actual `Iterator` that the loop uses.
1493 fn make_iterator_snippet(cx: &LateContext<'_, '_>, arg: &Expr, applic_ref: &mut Applicability) -> String {
1494 let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR)
1495 .map_or(false, |id| implements_trait(cx, cx.tables.expr_ty(arg), id, &[]));
1499 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1502 // (&x).into_iter() ==> x.iter()
1503 // (&mut x).into_iter() ==> x.iter_mut()
1505 ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
1506 if has_iter_method(cx, cx.tables.expr_ty(&arg_inner)).is_some() =>
1508 let meth_name = match mutability {
1509 Mutability::Mutable => "iter_mut",
1510 Mutability::Immutable => "iter",
1514 sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
1520 sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
1526 /// Checks for the `FOR_KV_MAP` lint.
1527 fn check_for_loop_over_map_kv<'a, 'tcx>(
1528 cx: &LateContext<'a, 'tcx>,
1534 let pat_span = pat.span;
1536 if let PatKind::Tuple(ref pat, _) = pat.kind {
1538 let arg_span = arg.span;
1539 let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).kind {
1540 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
1541 (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl),
1542 (_, value) if pat_is_wild(value, body) => (pat[0].span, "key", ty, Mutability::Immutable),
1547 let mutbl = match mutbl {
1548 Mutability::Immutable => "",
1549 Mutability::Mutable => "_mut",
1551 let arg = match arg.kind {
1552 ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
1556 if match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::BTREEMAP) {
1561 &format!("you seem to want to iterate on a map's {}s", kind),
1563 let map = sugg::Sugg::hir(cx, arg, "map");
1566 "use the corresponding method".into(),
1568 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
1569 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
1579 struct MutatePairDelegate {
1580 hir_id_low: Option<HirId>,
1581 hir_id_high: Option<HirId>,
1582 span_low: Option<Span>,
1583 span_high: Option<Span>,
1586 impl<'tcx> Delegate<'tcx> for MutatePairDelegate {
1587 fn consume(&mut self, _: &Place<'tcx>, _: ConsumeMode) {}
1589 fn borrow(&mut self, cmt: &Place<'tcx>, bk: ty::BorrowKind) {
1590 if let ty::BorrowKind::MutBorrow = bk {
1591 if let Categorization::Local(id) = cmt.cat {
1592 if Some(id) == self.hir_id_low {
1593 self.span_low = Some(cmt.span)
1595 if Some(id) == self.hir_id_high {
1596 self.span_high = Some(cmt.span)
1602 fn mutate(&mut self, cmt: &Place<'tcx>) {
1603 if let Categorization::Local(id) = cmt.cat {
1604 if Some(id) == self.hir_id_low {
1605 self.span_low = Some(cmt.span)
1607 if Some(id) == self.hir_id_high {
1608 self.span_high = Some(cmt.span)
1614 impl<'tcx> MutatePairDelegate {
1615 fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
1616 (self.span_low, self.span_high)
1620 fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr, body: &Expr) {
1621 if let Some(higher::Range {
1625 }) = higher::range(cx, arg)
1627 let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
1628 if mut_ids[0].is_some() || mut_ids[1].is_some() {
1629 let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
1630 mut_warn_with_span(cx, span_low);
1631 mut_warn_with_span(cx, span_high);
1636 fn mut_warn_with_span(cx: &LateContext<'_, '_>, span: Option<Span>) {
1637 if let Some(sp) = span {
1642 "attempt to mutate range bound within loop; note that the range of the loop is unchanged",
1647 fn check_for_mutability(cx: &LateContext<'_, '_>, bound: &Expr) -> Option<HirId> {
1649 if let ExprKind::Path(ref qpath) = bound.kind;
1650 if let QPath::Resolved(None, _) = *qpath;
1652 let res = qpath_res(cx, qpath, bound.hir_id);
1653 if let Res::Local(node_id) = res {
1654 let node_str = cx.tcx.hir().get(node_id);
1656 if let Node::Binding(pat) = node_str;
1657 if let PatKind::Binding(bind_ann, ..) = pat.kind;
1658 if let BindingAnnotation::Mutable = bind_ann;
1660 return Some(node_id);
1669 fn check_for_mutation(
1670 cx: &LateContext<'_, '_>,
1672 bound_ids: &[Option<HirId>],
1673 ) -> (Option<Span>, Option<Span>) {
1674 let mut delegate = MutatePairDelegate {
1675 hir_id_low: bound_ids[0],
1676 hir_id_high: bound_ids[1],
1680 let def_id = def_id::DefId::local(body.hir_id.owner);
1681 ExprUseVisitor::new(
1689 delegate.mutation_span()
1692 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
1693 fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
1695 PatKind::Wild => true,
1696 PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => {
1697 let mut visitor = UsedVisitor {
1701 walk_expr(&mut visitor, body);
1708 struct UsedVisitor {
1709 var: ast::Name, // var to look for
1710 used: bool, // has the var been used otherwise?
1713 impl<'tcx> Visitor<'tcx> for UsedVisitor {
1714 fn visit_expr(&mut self, expr: &'tcx Expr) {
1715 if match_var(expr, self.var) {
1718 walk_expr(self, expr);
1722 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1723 NestedVisitorMap::None
1727 struct LocalUsedVisitor<'a, 'tcx> {
1728 cx: &'a LateContext<'a, 'tcx>,
1733 impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> {
1734 fn visit_expr(&mut self, expr: &'tcx Expr) {
1735 if same_var(self.cx, expr, self.local) {
1738 walk_expr(self, expr);
1742 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1743 NestedVisitorMap::None
1747 struct VarVisitor<'a, 'tcx> {
1748 /// context reference
1749 cx: &'a LateContext<'a, 'tcx>,
1750 /// var name to look for as index
1752 /// indexed variables that are used mutably
1753 indexed_mut: FxHashSet<Name>,
1754 /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
1755 indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
1756 /// subset of `indexed` of vars that are indexed directly: `v[i]`
1757 /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
1758 indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
1759 /// Any names that are used outside an index operation.
1760 /// Used to detect things like `&mut vec` used together with `vec[i]`
1761 referenced: FxHashSet<Name>,
1762 /// has the loop variable been used in expressions other than the index of
1765 /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
1766 /// takes `&mut self`
1767 prefer_mutable: bool,
1770 impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
1771 fn check(&mut self, idx: &'tcx Expr, seqexpr: &'tcx Expr, expr: &'tcx Expr) -> bool {
1773 // the indexed container is referenced by a name
1774 if let ExprKind::Path(ref seqpath) = seqexpr.kind;
1775 if let QPath::Resolved(None, ref seqvar) = *seqpath;
1776 if seqvar.segments.len() == 1;
1778 let index_used_directly = same_var(self.cx, idx, self.var);
1779 let indexed_indirectly = {
1780 let mut used_visitor = LocalUsedVisitor {
1785 walk_expr(&mut used_visitor, idx);
1789 if indexed_indirectly || index_used_directly {
1790 if self.prefer_mutable {
1791 self.indexed_mut.insert(seqvar.segments[0].ident.name);
1793 let res = qpath_res(self.cx, seqpath, seqexpr.hir_id);
1795 Res::Local(hir_id) => {
1796 let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
1797 let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
1798 let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
1799 if indexed_indirectly {
1800 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
1802 if index_used_directly {
1803 self.indexed_directly.insert(
1804 seqvar.segments[0].ident.name,
1805 (Some(extent), self.cx.tables.node_type(seqexpr.hir_id)),
1808 return false; // no need to walk further *on the variable*
1810 Res::Def(DefKind::Static, ..) | Res::Def(DefKind::Const, ..) => {
1811 if indexed_indirectly {
1812 self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
1814 if index_used_directly {
1815 self.indexed_directly.insert(
1816 seqvar.segments[0].ident.name,
1817 (None, self.cx.tables.node_type(seqexpr.hir_id)),
1820 return false; // no need to walk further *on the variable*
1831 impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
1832 fn visit_expr(&mut self, expr: &'tcx Expr) {
1835 if let ExprKind::MethodCall(ref meth, _, ref args) = expr.kind;
1836 if (meth.ident.name == sym!(index) && match_trait_method(self.cx, expr, &paths::INDEX))
1837 || (meth.ident.name == sym!(index_mut) && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
1838 if !self.check(&args[1], &args[0], expr);
1844 if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
1845 if !self.check(idx, seqexpr, expr);
1850 // directly using a variable
1851 if let ExprKind::Path(ref qpath) = expr.kind;
1852 if let QPath::Resolved(None, ref path) = *qpath;
1853 if path.segments.len() == 1;
1855 if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) {
1856 if local_id == self.var {
1857 self.nonindex = true;
1859 // not the correct variable, but still a variable
1860 self.referenced.insert(path.segments[0].ident.name);
1866 let old = self.prefer_mutable;
1868 ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs) => {
1869 self.prefer_mutable = true;
1870 self.visit_expr(lhs);
1871 self.prefer_mutable = false;
1872 self.visit_expr(rhs);
1874 ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
1875 if mutbl == Mutability::Mutable {
1876 self.prefer_mutable = true;
1878 self.visit_expr(expr);
1880 ExprKind::Call(ref f, ref args) => {
1883 let ty = self.cx.tables.expr_ty_adjusted(expr);
1884 self.prefer_mutable = false;
1885 if let ty::Ref(_, _, mutbl) = ty.kind {
1886 if mutbl == Mutability::Mutable {
1887 self.prefer_mutable = true;
1890 self.visit_expr(expr);
1893 ExprKind::MethodCall(_, _, ref args) => {
1894 let def_id = self.cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
1895 for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
1896 self.prefer_mutable = false;
1897 if let ty::Ref(_, _, mutbl) = ty.kind {
1898 if mutbl == Mutability::Mutable {
1899 self.prefer_mutable = true;
1902 self.visit_expr(expr);
1905 ExprKind::Closure(_, _, body_id, ..) => {
1906 let body = self.cx.tcx.hir().body(body_id);
1907 self.visit_expr(&body.value);
1909 _ => walk_expr(self, expr),
1911 self.prefer_mutable = old;
1913 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1914 NestedVisitorMap::None
1918 fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr, container: &'tcx Expr) -> bool {
1919 let def_id = match var_def_id(cx, expr) {
1921 None => return false,
1923 if let Some(used_mutably) = mutated_variables(container, cx) {
1924 if used_mutably.contains(&def_id) {
1931 fn is_iterator_used_after_while_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
1932 let def_id = match var_def_id(cx, iter_expr) {
1934 None => return false,
1936 let mut visitor = VarUsedAfterLoopVisitor {
1939 iter_expr_id: iter_expr.hir_id,
1940 past_while_let: false,
1941 var_used_after_while_let: false,
1943 if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
1944 walk_block(&mut visitor, enclosing_block);
1946 visitor.var_used_after_while_let
1949 struct VarUsedAfterLoopVisitor<'a, 'tcx> {
1950 cx: &'a LateContext<'a, 'tcx>,
1952 iter_expr_id: HirId,
1953 past_while_let: bool,
1954 var_used_after_while_let: bool,
1957 impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
1958 fn visit_expr(&mut self, expr: &'tcx Expr) {
1959 if self.past_while_let {
1960 if Some(self.def_id) == var_def_id(self.cx, expr) {
1961 self.var_used_after_while_let = true;
1963 } else if self.iter_expr_id == expr.hir_id {
1964 self.past_while_let = true;
1966 walk_expr(self, expr);
1968 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
1969 NestedVisitorMap::None
1973 /// Returns `true` if the type of expr is one that provides `IntoIterator` impls
1974 /// for `&T` and `&mut T`, such as `Vec`.
1976 fn is_ref_iterable_type(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
1977 // no walk_ptrs_ty: calling iter() on a reference can make sense because it
1978 // will allow further borrows afterwards
1979 let ty = cx.tables.expr_ty(e);
1980 is_iterable_array(ty, cx) ||
1981 is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) ||
1982 match_type(cx, ty, &paths::LINKED_LIST) ||
1983 match_type(cx, ty, &paths::HASHMAP) ||
1984 match_type(cx, ty, &paths::HASHSET) ||
1985 match_type(cx, ty, &paths::VEC_DEQUE) ||
1986 match_type(cx, ty, &paths::BINARY_HEAP) ||
1987 match_type(cx, ty, &paths::BTREEMAP) ||
1988 match_type(cx, ty, &paths::BTREESET)
1991 fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'_, 'tcx>) -> bool {
1992 // IntoIterator is currently only implemented for array sizes <= 32 in rustc
1994 ty::Array(_, n) => {
1995 if let Some(val) = n.try_eval_usize(cx.tcx, cx.param_env) {
1996 (0..=32).contains(&val)
2005 /// If a block begins with a statement (possibly a `let` binding) and has an
2006 /// expression, return it.
2007 fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
2008 if block.stmts.is_empty() {
2011 if let StmtKind::Local(ref local) = block.stmts[0].kind {
2012 if let Some(ref expr) = local.init {
2022 /// If a block begins with an expression (with or without semicolon), return it.
2023 fn extract_first_expr(block: &Block) -> Option<&Expr> {
2025 Some(ref expr) if block.stmts.is_empty() => Some(expr),
2026 None if !block.stmts.is_empty() => match block.stmts[0].kind {
2027 StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
2028 StmtKind::Local(..) | StmtKind::Item(..) => None,
2034 /// Returns `true` if expr contains a single break expr without destination label
2036 /// passed expression. The expression may be within a block.
2037 fn is_simple_break_expr(expr: &Expr) -> bool {
2039 ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
2040 ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
2045 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
2046 // incremented exactly once in the loop body, and initialized to zero
2047 // at the start of the loop.
2048 #[derive(Debug, PartialEq)]
2050 Initial, // Not examined yet
2051 IncrOnce, // Incremented exactly once, may be a loop counter
2052 Declared, // Declared but not (yet) initialized to zero
2057 /// Scan a for loop for variables that are incremented exactly once.
2058 struct IncrementVisitor<'a, 'tcx> {
2059 cx: &'a LateContext<'a, 'tcx>, // context reference
2060 states: FxHashMap<HirId, VarState>, // incremented variables
2061 depth: u32, // depth of conditional expressions
2065 impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
2066 fn visit_expr(&mut self, expr: &'tcx Expr) {
2071 // If node is a variable
2072 if let Some(def_id) = var_def_id(self.cx, expr) {
2073 if let Some(parent) = get_parent_expr(self.cx, expr) {
2074 let state = self.states.entry(def_id).or_insert(VarState::Initial);
2077 ExprKind::AssignOp(op, ref lhs, ref rhs) => {
2078 if lhs.hir_id == expr.hir_id {
2079 if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) {
2080 *state = match *state {
2081 VarState::Initial if self.depth == 0 => VarState::IncrOnce,
2082 _ => VarState::DontWarn,
2085 // Assigned some other value
2086 *state = VarState::DontWarn;
2090 ExprKind::Assign(ref lhs, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn,
2091 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mutable => {
2092 *state = VarState::DontWarn
2097 } else if is_loop(expr) || is_conditional(expr) {
2099 walk_expr(self, expr);
2102 } else if let ExprKind::Continue(_) = expr.kind {
2106 walk_expr(self, expr);
2108 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2109 NestedVisitorMap::None
2113 /// Checks whether a variable is initialized to zero at the start of a loop.
2114 struct InitializeVisitor<'a, 'tcx> {
2115 cx: &'a LateContext<'a, 'tcx>, // context reference
2116 end_expr: &'tcx Expr, // the for loop. Stop scanning here.
2120 depth: u32, // depth of conditional expressions
2124 impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
2125 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2126 // Look for declarations of the variable
2127 if let StmtKind::Local(ref local) = stmt.kind {
2128 if local.pat.hir_id == self.var_id {
2129 if let PatKind::Binding(.., ident, _) = local.pat.kind {
2130 self.name = Some(ident.name);
2132 self.state = if let Some(ref init) = local.init {
2133 if is_integer_const(&self.cx, init, 0) {
2144 walk_stmt(self, stmt);
2147 fn visit_expr(&mut self, expr: &'tcx Expr) {
2148 if self.state == VarState::DontWarn {
2151 if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) {
2152 self.past_loop = true;
2155 // No need to visit expressions before the variable is
2157 if self.state == VarState::IncrOnce {
2161 // If node is the desired variable, see how it's used
2162 if var_def_id(self.cx, expr) == Some(self.var_id) {
2163 if let Some(parent) = get_parent_expr(self.cx, expr) {
2165 ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
2166 self.state = VarState::DontWarn;
2168 ExprKind::Assign(ref lhs, ref rhs) if lhs.hir_id == expr.hir_id => {
2169 self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 {
2175 ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mutable => {
2176 self.state = VarState::DontWarn
2183 self.state = VarState::DontWarn;
2186 } else if !self.past_loop && is_loop(expr) {
2187 self.state = VarState::DontWarn;
2189 } else if is_conditional(expr) {
2191 walk_expr(self, expr);
2195 walk_expr(self, expr);
2198 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2199 NestedVisitorMap::OnlyBodies(&self.cx.tcx.hir())
2203 fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<HirId> {
2204 if let ExprKind::Path(ref qpath) = expr.kind {
2205 let path_res = qpath_res(cx, qpath, expr.hir_id);
2206 if let Res::Local(node_id) = path_res {
2207 return Some(node_id);
2213 fn is_loop(expr: &Expr) -> bool {
2215 ExprKind::Loop(..) => true,
2220 fn is_conditional(expr: &Expr) -> bool {
2222 ExprKind::Match(..) => true,
2227 fn is_nested(cx: &LateContext<'_, '_>, match_expr: &Expr, iter_expr: &Expr) -> bool {
2229 if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
2230 let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
2231 if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
2233 return is_loop_nested(cx, loop_expr, iter_expr)
2239 fn is_loop_nested(cx: &LateContext<'_, '_>, loop_expr: &Expr, iter_expr: &Expr) -> bool {
2240 let mut id = loop_expr.hir_id;
2241 let iter_name = if let Some(name) = path_name(iter_expr) {
2247 let parent = cx.tcx.hir().get_parent_node(id);
2251 match cx.tcx.hir().find(parent) {
2252 Some(Node::Expr(expr)) => {
2253 if let ExprKind::Loop(..) = expr.kind {
2257 Some(Node::Block(block)) => {
2258 let mut block_visitor = LoopNestVisitor {
2260 iterator: iter_name,
2263 walk_block(&mut block_visitor, block);
2264 if block_visitor.nesting == RuledOut {
2268 Some(Node::Stmt(_)) => (),
2277 #[derive(PartialEq, Eq)]
2279 Unknown, // no nesting detected yet
2280 RuledOut, // the iterator is initialized or assigned within scope
2281 LookFurther, // no nesting detected, no further walk required
2284 use self::Nesting::{LookFurther, RuledOut, Unknown};
2286 struct LoopNestVisitor {
2292 impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
2293 fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
2294 if stmt.hir_id == self.hir_id {
2295 self.nesting = LookFurther;
2296 } else if self.nesting == Unknown {
2297 walk_stmt(self, stmt);
2301 fn visit_expr(&mut self, expr: &'tcx Expr) {
2302 if self.nesting != Unknown {
2305 if expr.hir_id == self.hir_id {
2306 self.nesting = LookFurther;
2310 ExprKind::Assign(ref path, _) | ExprKind::AssignOp(_, ref path, _) => {
2311 if match_var(path, self.iterator) {
2312 self.nesting = RuledOut;
2315 _ => walk_expr(self, expr),
2319 fn visit_pat(&mut self, pat: &'tcx Pat) {
2320 if self.nesting != Unknown {
2323 if let PatKind::Binding(.., span_name, _) = pat.kind {
2324 if self.iterator == span_name.name {
2325 self.nesting = RuledOut;
2332 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2333 NestedVisitorMap::None
2337 fn path_name(e: &Expr) -> Option<Name> {
2338 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
2339 let segments = &path.segments;
2340 if segments.len() == 1 {
2341 return Some(segments[0].ident.name);
2347 fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr, expr: &'tcx Expr) {
2348 if constant(cx, cx.tables, cond).is_some() {
2349 // A pure constant condition (e.g., `while false`) is not linted.
2353 let mut var_visitor = VarCollectorVisitor {
2355 ids: FxHashSet::default(),
2356 def_ids: FxHashMap::default(),
2359 var_visitor.visit_expr(cond);
2360 if var_visitor.skip {
2363 let used_in_condition = &var_visitor.ids;
2364 let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
2365 used_in_condition.is_disjoint(&used_mutably)
2369 let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
2371 let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
2372 has_break_or_return: false,
2374 has_break_or_return_visitor.visit_expr(expr);
2375 let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
2377 if no_cond_variable_mutated && !mutable_static_in_cond {
2380 WHILE_IMMUTABLE_CONDITION,
2382 "variables in the condition are not mutated in the loop body",
2384 db.note("this may lead to an infinite or to a never running loop");
2386 if has_break_or_return {
2387 db.note("this loop contains `return`s or `break`s");
2388 db.help("rewrite it as `if cond { loop { } }`");
2395 struct HasBreakOrReturnVisitor {
2396 has_break_or_return: bool,
2399 impl<'a, 'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
2400 fn visit_expr(&mut self, expr: &'tcx Expr) {
2401 if self.has_break_or_return {
2406 ExprKind::Ret(_) | ExprKind::Break(_, _) => {
2407 self.has_break_or_return = true;
2413 walk_expr(self, expr);
2416 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2417 NestedVisitorMap::None
2421 /// Collects the set of variables in an expression
2422 /// Stops analysis if a function call is found
2423 /// Note: In some cases such as `self`, there are no mutable annotation,
2424 /// All variables definition IDs are collected
2425 struct VarCollectorVisitor<'a, 'tcx> {
2426 cx: &'a LateContext<'a, 'tcx>,
2427 ids: FxHashSet<HirId>,
2428 def_ids: FxHashMap<def_id::DefId, bool>,
2432 impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
2433 fn insert_def_id(&mut self, ex: &'tcx Expr) {
2435 if let ExprKind::Path(ref qpath) = ex.kind;
2436 if let QPath::Resolved(None, _) = *qpath;
2437 let res = qpath_res(self.cx, qpath, ex.hir_id);
2440 Res::Local(node_id) => {
2441 self.ids.insert(node_id);
2443 Res::Def(DefKind::Static, def_id) => {
2444 let mutable = self.cx.tcx.is_mutable_static(def_id);
2445 self.def_ids.insert(def_id, mutable);
2454 impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
2455 fn visit_expr(&mut self, ex: &'tcx Expr) {
2457 ExprKind::Path(_) => self.insert_def_id(ex),
2458 // If there is any function/method call… we just stop analysis
2459 ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
2461 _ => walk_expr(self, ex),
2465 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
2466 NestedVisitorMap::None
2470 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
2472 fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr, cx: &LateContext<'a, 'tcx>) {
2474 if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind;
2475 if let ExprKind::MethodCall(ref chain_method, _, _) = args[0].kind;
2476 if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
2477 if let Some(ref generic_args) = chain_method.args;
2478 if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
2480 let ty = cx.tables.node_type(ty.hir_id);
2481 if is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) ||
2482 match_type(cx, ty, &paths::VEC_DEQUE) ||
2483 match_type(cx, ty, &paths::BTREEMAP) ||
2484 match_type(cx, ty, &paths::HASHMAP) {
2485 if method.ident.name == sym!(len) {
2486 let span = shorten_needless_collect_span(expr);
2487 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2491 ".count()".to_string(),
2492 Applicability::MachineApplicable,
2496 if method.ident.name == sym!(is_empty) {
2497 let span = shorten_needless_collect_span(expr);
2498 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2502 ".next().is_none()".to_string(),
2503 Applicability::MachineApplicable,
2507 if method.ident.name == sym!(contains) {
2508 let contains_arg = snippet(cx, args[1].span, "??");
2509 let span = shorten_needless_collect_span(expr);
2510 span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| {
2511 let (arg, pred) = if contains_arg.starts_with('&') {
2512 ("x", &contains_arg[1..])
2514 ("&x", &*contains_arg)
2520 ".any(|{}| x == {})",
2523 Applicability::MachineApplicable,
2532 fn shorten_needless_collect_span(expr: &Expr) -> Span {
2534 if let ExprKind::MethodCall(_, _, ref args) = expr.kind;
2535 if let ExprKind::MethodCall(_, ref span, _) = args[0].kind;
2537 return expr.span.with_lo(span.lo() - BytePos(1));