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Add missing impl Fn for &mut F where F: Fn #148271

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10 changes: 10 additions & 0 deletions library/core/src/ops/async_function.rs
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Expand Up @@ -126,6 +126,16 @@ mod impls {
F::async_call_mut(self, args)
}
}

#[stable(feature = "async_closure", since = "1.85.0")]

@thomcc thomcc Oct 20, 2026

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This attribute is wrong too.

impl<'a, A: Tuple, F: ?Sized> AsyncFn<A> for &'a mut F
where
F: AsyncFn<A>,
{
extern "rust-call" fn async_call(&self, args: A) -> Self::CallRefFuture<'_> {
F::async_call(*self, args)
}
}
}

mod internal_implementation_detail {
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11 changes: 11 additions & 0 deletions library/core/src/ops/function.rs
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Expand Up @@ -310,4 +310,15 @@ mod impls {
(*self).call_mut(args)
}
}

#[stable(feature = "rust1", since = "1.0.0")]

@theemathas theemathas Oct 30, 2025

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Is this "since" line correct?

@Kivooeo Kivooeo Oct 30, 2025 •
edited
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This is going to be insta stable so I think so and it should be available on all versions

@theemathas theemathas Oct 30, 2025

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What do you mean by "should be available on all versions"?

@Kivooeo Kivooeo Oct 30, 2025

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Ah, you mean that if I make it since = 1.91 it will work not only in 1.91+? because in my opinion this should be available in all versions since 1.0

@Noratrieb Noratrieb Oct 30, 2025

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This attribute is only describing when it was added for docs. We cannot add things to old versions.

@Kivooeo Kivooeo Oct 30, 2025

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oh, ok then, I will change it after crater

@Kivooeo Kivooeo Nov 8, 2025

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huh, seems like I can't?

error[E0711]: feature `async_closure` is declared stable since 1.93.0, but was previously declared stable since 1.85.0
   --> library/core/src/ops/async_function.rs:130:5
    |
130 |     #[stable(feature = "async_closure", since = "1.93.0")]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0711]: feature `rust1` is declared stable since 1.93.0, but was previously declared stable since 1.0.0
   --> library/core/src/ops/function.rs:314:5
    |
314 |     #[stable(feature = "rust1", since = "1.93.0")]
    |

@Kivooeo Kivooeo Nov 8, 2025

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it don't feel correct to change stable since for all impls

@teor2345 teor2345 Mar 9, 2026

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What you've done might be fine, I've seen other PRs that just re-use an existing stable feature name and version for small gaps like this.

But for other PRs, if you want to declare them stable in the version where the PR merges, use:

Suggested change
#[stable(feature = "rust1", since = "1.0.0")]
#[stable(feature = "new_feature_name", since = "CURRENT_RUSTC_VERSION")]

This does two things:

  • makes the "consistent feature stable version" check pass (because it's a new feature)
  • when the code is promoted to beta, CURRENT_RUSTC_VERSION will automatically get replaced with the current version

https://std-dev-guide.rust-lang.org/development/stabilization.html#stabilization-pr-checklist

#[rustc_const_unstable(feature = "const_trait_impl", issue = "143874")]
impl<A: Tuple, F: ?Sized> const Fn<A> for &mut F
where
F: [const] Fn<A>,
{
extern "rust-call" fn call(&self, args: A) -> F::Output {
(**self).call(args)
}
}
}
2 changes: 2 additions & 0 deletions tests/ui/const-generics/adt_const_params/non_valtreeable_const_arg-2.stderr
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Expand Up @@ -29,6 +29,8 @@ LL | Wrapper::<function>::call;
= note: the following trait bounds were not satisfied:
`Wrapper<function>: Fn<_>`
which is required by `&Wrapper<function>: Fn<_>`
`Wrapper<function>: Fn<_>`
which is required by `&mut Wrapper<function>: Fn<_>`
note: the trait `Fn` must be implemented
--> $SRC_DIR/core/src/ops/function.rs:LL:COL
= help: items from traits can only be used if the trait is implemented and in scope
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2 changes: 2 additions & 0 deletions tests/ui/impl-trait/where-allowed.stderr
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Expand Up @@ -385,6 +385,8 @@ LL | fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { pani
= note: multiple `impl`s satisfying `_: Fn()` found in the following crates: `alloc`, `core`:
- impl<A, F> Fn<A> for &F
where A: Tuple, F: Fn<A>, F: ?Sized;
- impl<A, F> Fn<A> for &mut F
where A: Tuple, F: Fn<A>, F: ?Sized;
- impl<Args, F, A> Fn<Args> for Box<F, A>
where Args: Tuple, F: Fn<Args>, A: Allocator, F: ?Sized;
- impl<F, Args> Fn<Args> for Exclusive<F>
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2 changes: 2 additions & 0 deletions tests/ui/traits/next-solver/well-formed-in-relate.stderr
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Expand Up @@ -10,6 +10,8 @@ LL | x = unconstrained_map();
= note: multiple `impl`s satisfying `_: Fn()` found in the following crates: `alloc`, `core`:
- impl<A, F> Fn<A> for &F
where A: Tuple, F: Fn<A>, F: ?Sized;
- impl<A, F> Fn<A> for &mut F
where A: Tuple, F: Fn<A>, F: ?Sized;
- impl<Args, F, A> Fn<Args> for Box<F, A>
where Args: Tuple, F: Fn<Args>, A: Allocator, F: ?Sized;
- impl<F, Args> Fn<Args> for Exclusive<F>
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