rustdoc: Correctly handle reexports when --document-private-items is used

[GuillaumeGomez]

Fixes #159109.

This PR makes the (private) reexport work like the public ones when the --document-private-items option is used. I still differentiate between imports (use) and reexports (pub(...) use) in this PR as I don't think we should display imports.

r? @Urgau

[GuillaumeGomez]

Fun fact: this test was added in 2016 in #37773. :)

View changes since the review

[Urgau]

I don't like this hack. I think we would be better of checking if the visibility of the use item is different from where the use item is defined.

I'm thinking of something like this:

let parent_module = tcx.parent_module_from_def_id(def_id);
let is_exported = tcx.visibility(def_id) != Visibility::Restricted(parent_module.to_mod_id());
// or maybe call Visibility::greater_than

View changes since the review

[GuillaumeGomez]

That's... strange. With this code:

pub(crate) mod foo {
    pub(crate) use self::x::Y;

    #[doc(hidden)]
    mod x {
        struct Y;
    }
}

It means we would not see Y. I think the only thing we want to care about is whether it's a reexport or not. And the only way to see that is if there is a pub(), which we know with vis_span. Not a trick imo.

[Urgau]

It means we would not see Y

I think we would, parent_module should be mod foo and tcx.visibility(def_id) should be CRATE_DEF_ID and those do not match, implying that there is a pub(...) token. It's possible my logic is wrong and should be adjusted, but I think something like that should work.

And the only way to see that is if there is a pub(), which we know with vis_span. Not a trick imo.

Spans can be arbitrarily manipulated by proc-macros, a proc-macro could assign a empty span to the pub(...) tokens and your check would be bypassed. We should never rely on spans for correctness.

[GuillaumeGomez]

Fair point. I'll test locally and we'll see if use without visibility are correctly handled.

[Urgau]

I was wondering if this was a breaking change, but our documentation clearly states:

--document-private-items includes all non-public items in the generated documentation except for #[doc(hidden)] items.

as such, this seems clearly like a bug fix.

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