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Improve needless_pass_by_value suggestion #13880

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Improve needless_pass_by_value suggestion #13880

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10 changes: 9 additions & 1 deletion clippy_lints/src/needless_pass_by_value.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -275,10 +275,18 @@ impl<'tcx> LateLintPass<'tcx> for NeedlessPassByValue {
}
}

let suggestion = if is_type_diagnostic_item(cx, ty, sym::Option)
&& let snip = snippet(cx, input.span, "_")
&& let Some((first, rest)) = snip.split_once('<')
{
format!("{first}<&{rest}")
} else {
format!("&{}", snippet(cx, input.span, "_"))
};
diag.span_suggestion(
input.span,
"consider taking a reference instead",
format!("&{}", snippet(cx, input.span, "_")),
suggestion,
Applicability::MaybeIncorrect,
);
};
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7 changes: 7 additions & 0 deletions tests/ui/needless_pass_by_value.rs
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Expand Up @@ -182,6 +182,13 @@ struct Obj(String);

fn prefix_test(_unused_with_prefix: Obj) {}

// Regression test for <https://github.com/rust-lang/rust-clippy/issues/13744>.
// It's more idiomatic to write `Option<&T>` rather than `&Option<T>`.
fn option_inner_ref(x: Option<String>) {
//~^ ERROR: this argument is passed by value, but not consumed in the function body
assert!(x.is_some());
}

fn main() {
// This should not cause an ICE either
// https://github.com/rust-lang/rust-clippy/issues/3144
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10 changes: 8 additions & 2 deletions tests/ui/needless_pass_by_value.stderr
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Expand Up @@ -29,7 +29,7 @@ error: this argument is passed by value, but not consumed in the function body
--> tests/ui/needless_pass_by_value.rs:56:18
|
LL | fn test_match(x: Option<Option<String>>, y: Option<Option<String>>) {
| ^^^^^^^^^^^^^^^^^^^^^^ help: consider taking a reference instead: `&Option<Option<String>>`
| ^^^^^^^^^^^^^^^^^^^^^^ help: consider taking a reference instead: `Option<&Option<String>>`
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Should you run this several times?

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I was wondering about that. Is it better to propose for the inner most T to be behind a reference or just the direct top child?


error: this argument is passed by value, but not consumed in the function body
--> tests/ui/needless_pass_by_value.rs:70:24
Expand Down Expand Up @@ -175,5 +175,11 @@ error: this argument is passed by value, but not consumed in the function body
LL | fn more_fun(items: impl Club<'static, i32>) {}
| ^^^^^^^^^^^^^^^^^^^^^^^ help: consider taking a reference instead: `&impl Club<'static, i32>`

error: aborting due to 22 previous errors
error: this argument is passed by value, but not consumed in the function body
--> tests/ui/needless_pass_by_value.rs:187:24
|
LL | fn option_inner_ref(x: Option<String>) {
| ^^^^^^^^^^^^^^ help: consider taking a reference instead: `Option<&String>`

error: aborting due to 23 previous errors

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