privacy: no nominal visibility for assoc fns

[davidtwco]

Fixes #113860.

When staged_api is enabled, effective visibilities are computed earlier and this can trigger an ICE in some cases.

In particular, if a impl of a trait method has a visibility then an error will be reported for that, but when privacy invariants are being checked, the effective visibility will still be greater than the nominal visbility and that will trigger a span_bug!.

However, this invariant - that effective visibilites are limited to nominal visibility - doesn't make sense for associated functions.

[rustbot]

r? @fee1-dead

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[petrochenkov]

I'd like too look in more detail why the invariant is broken in this scenario, maybe it can affect non-erroneous cases too.
r? @petrochenkov

[petrochenkov]

Minimized reproduction:

#![feature(staged_api)]

pub trait Trait {
    fn fun() {}
}

impl Trait for u8 {
    pub(self) fn fun() {}
}

fn main() {}

When staged_api is enabled, effective visibilities are computed for a greater number of items

That shouldn't be the case, from what I remember the effective_visibilities query just runs at a different (earlier) point in compilation in this case.

[petrochenkov]

@bors r+ rollup

[bors]

📌 Commit e051a32 has been approved by petrochenkov

It is now in the queue for this repository.