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Don't trigger while_let_on_iterator when the iterator is recreated every iteration #5525

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Apr 25, 2020
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Don't trigger while_let_on_iterator when the iterator is recreated every iteration #5525

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Don't trigger while_let_on_iterator when the iterator is recreated ev…
flip1995 Apr 25, 2020
a182622
Add tests for #1654
flip1995 Apr 25, 2020
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11 changes: 11 additions & 0 deletions clippy_lints/src/loops.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -566,6 +566,17 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops {
) = (pat, &match_expr.kind)
{
let iter_expr = &method_args[0];

// Don't lint when the iterator is recreated on every iteration
if_chain! {
if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
if implements_trait(cx, cx.tables.expr_ty(iter_expr), iter_def_id, &[]);
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@phansch phansch Apr 25, 2020 •
edited
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Just to make sure I understand correctly: this is checking that the scrutinee is not a call to an iter method, right?

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@flip1995 flip1995 Apr 25, 2020 •
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It is checking, that a (method) call before the next call does not return a type, that implements Iterator. Should I add a comment?

This does not cover this:

#[derive(Debug, Clone)]
struct S<'a> {
    chars: std::str::CharIndices<'a>,
}

while let Some(_) = s.clone().chars.next() {
    break;
}

But then again, if the struct is clonable, every field is clonable (in general), and this should be changed to s.chars.clone().next(), which prevents the lint from triggering.

then {
return;
}
}

let lhs_constructor = last_path_segment(qpath);
if method_path.ident.name == sym!(next)
&& match_trait_method(cx, match_expr, &paths::ITERATOR)
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24 changes: 20 additions & 4 deletions tests/ui/while_let_on_iterator.fixed
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Expand Up @@ -119,10 +119,7 @@ fn issue2965() {
let mut values = HashSet::new();
values.insert(1);

for _ in values.iter() {
// FIXME(flip1995): Linting this with the following line uncommented is a FP, see #1654
// values.remove(&1);
}
while let Some(..) = values.iter().next() {}
}

fn issue3670() {
Expand All @@ -134,11 +131,30 @@ fn issue3670() {
}
}

fn issue1654() {
// should not lint if the iterator is generated on every iteration
use std::collections::HashSet;
let mut values = HashSet::new();
values.insert(1);

while let Some(..) = values.iter().next() {
values.remove(&1);
}

while let Some(..) = values.iter().map(|x| x + 1).next() {}

let chars = "Hello, World!".char_indices();
while let Some((i, ch)) = chars.clone().next() {
println!("{}: {}", i, ch);
}
}

fn main() {
base();
refutable();
nested_loops();
issue1121();
issue2965();
issue3670();
issue1654();
}
24 changes: 20 additions & 4 deletions tests/ui/while_let_on_iterator.rs
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Expand Up @@ -119,10 +119,7 @@ fn issue2965() {
let mut values = HashSet::new();
values.insert(1);

while let Some(..) = values.iter().next() {
// FIXME(flip1995): Linting this with the following line uncommented is a FP, see #1654
// values.remove(&1);
}
while let Some(..) = values.iter().next() {}
}

fn issue3670() {
Expand All @@ -134,11 +131,30 @@ fn issue3670() {
}
}

fn issue1654() {
// should not lint if the iterator is generated on every iteration
use std::collections::HashSet;
let mut values = HashSet::new();
values.insert(1);

while let Some(..) = values.iter().next() {
values.remove(&1);
}

while let Some(..) = values.iter().map(|x| x + 1).next() {}

let chars = "Hello, World!".char_indices();
while let Some((i, ch)) = chars.clone().next() {
println!("{}: {}", i, ch);
}
}

fn main() {
base();
refutable();
nested_loops();
issue1121();
issue2965();
issue3670();
issue1654();
}
8 changes: 1 addition & 7 deletions tests/ui/while_let_on_iterator.stderr
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Expand Up @@ -24,11 +24,5 @@ error: this loop could be written as a `for` loop
LL | while let Some(_) = y.next() {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for _ in y`

error: this loop could be written as a `for` loop
--> $DIR/while_let_on_iterator.rs:122:5
|
LL | while let Some(..) = values.iter().next() {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for _ in values.iter()`

error: aborting due to 5 previous errors
error: aborting due to 4 previous errors