Self::EnumVariant not considered const fn

[marmistrz]

When using Self to create an enum variant in Rust 1.37+, we get an error:

const VAL: Self = Self::X(42);

results in:

error: `Foo::X` is not yet stable as a const fn

but if the enum is constructed explicitly, the compilation succeeds:

const VAL: Self = Foo::X(42)

Looking at #53555, it looks like Self::EnumVariant should be considered a const fn with min_const_fn.

Playground links for both variants: error, no-error

[Centril]

Duplicate of #61456 (will close in a bit).

@oli-obk It seems like folks open this issue because on stable, the error message does not point to the tracking issue, e.g. you don't see:

  = note: for more information, see https://github.com/rust-lang/rust/issues/61456

can we fix this?

[oli-obk]

I think we should just stabilize it

[Centril]

@oli-obk Is this diagnostics problem specific to this feature gate? I meant a more general fix to const-fn related gates.

[oli-obk]

Not sure. I thought we're using the normal feature gate infra

[Centril]

Reopening this to make sure we add a test per #61456 (comment).