rustdoc: hide constness of fns in stable docs

[durka]

Rustdoc shows const fns as const, but you can't call them in a const context because they're still unstable. If you aren't in a const context, it doesn't matter whether the fn is const or not. So it's confusing and maybe it shouldn't be shown at all until the feature is stable.

cc @jethrogb

[jethrogb]

Compare 1.5.0 docs

fn new(v: bool) -> AtomicBool

and stable docs

const fn new(v: bool) -> AtomicBool

This documentation change suggests that this a stable change. Yet const fn is still unstable. The stable docs should hide the const qualifier on const fns.

[tomjakubowski]

This should a pretty straightforward change for someone looking to get into rustdoc development.

[durka]

@tomjakubowski is it? does rustdoc know whether it's documenting stable/beta vs nightly?

[tomjakubowski]

@tomjakubowski is it? does rustdoc know whether it's documenting stable/beta vs nightly?

If rustdoc is going to simply remove const from functions until the feature is stabilized, then it doesn't matter.

If not, there's a little more work but it's not too bad. I think simply checking option_env!("CFG_RELEASE_CHANNEL") or CFG_DISABLE_UNSTABLE_FEATURES would suffice; nightly rustdoc binaries would produce const in documentation and others would not.

[durka]

I think it should make that distinction. If you are on nightly, you can turn on the feature and use the const fns in const contexts, so you want that information.

[jethrogb]

I don't think this issue is fixed until the docs at /stable/ actually don't show the qualification.

[mitaa]

I think this is still an issue?