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derive(Clone, Debug) should not prevent "field is never read" from firing #84647

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matklad opened this issue Apr 28, 2021 · 1 comment · Fixed by #85200
Closed

derive(Clone, Debug) should not prevent "field is never read" from firing #84647

matklad opened this issue Apr 28, 2021 · 1 comment · Fixed by #85200
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A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. C-enhancement Category: An issue proposing an enhancement or a PR with one.

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@matklad
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matklad commented Apr 28, 2021

struct A { f: () }
#[derive(Clone)]
struct B { f: () }

fn main() {
    let _ = A { f: () };
    let _ = B { f: () };
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=ddbb661ad3a117642c4f750b31da4b18

Only A's field triggers the warning. It's clear why B doesn't do this, but it clearly should. Doesn't seem easy to fix though :(

@matklad matklad changed the title derive(Clone) should not prevent "field is never read" from firing derive(Clone, Debug) should not prevent "field is never read" from firing Apr 28, 2021
matklad added a commit to matklad/rust-analyzer that referenced this issue Apr 28, 2021
matklad added a commit to matklad/rust-analyzer that referenced this issue Apr 28, 2021
@jonas-schievink jonas-schievink added A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. C-enhancement Category: An issue proposing an enhancement or a PR with one. labels Apr 28, 2021
@bors bors closed this as completed in acfe7c4 Sep 11, 2021
@est31
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est31 commented Sep 15, 2021

There is discussion in #88900 whether the desired (and now implemented on nightly) behaviour is good for Debug or not.

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Labels
A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. C-enhancement Category: An issue proposing an enhancement or a PR with one.
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3 participants