rustdoc: how does `#[doc(hidden)]` interact with `--document-private-items`?

[hdevalence]

I have types Public (which is exported) and Private (which isn't) and an impl Add<Private> for Public. I would like the impl Add<Private> for Public to appear in the Rustdoc output only when using --document-private-items.

As far as I can tell, the impl Add<Private> for Public appears in the normal rustdoc output unless it has a #[doc(hidden)] attribute. But this prevents the impl from appearing with --document-private-items.

Is --document-private-items supposed to override #[doc(hidden)]? Is there another way to hide impl Add<Private> for Public from the public rustdoc output?

[QuietMisdreavus]

So it seems like there's two things going on here:

• --document-private-items runs the strip-hidden pass, which i would consider a bug. #[doc(hidden)] items are private implementation details and fall under the same camp, conceptually, as regular items that aren't public. (Removing the String::from("strip-hidden"), line from that block will fix that.)
• Trait impls whose trait's type parameters include private items still appear in the docs, because the type it's impl'd for is public. Again, i would consider this a bug, but a separate one. The fix for that is more involved, though. >_>

[QuietMisdreavus]

To fix the second note in my previous comment, you'd need to unpack imp.trait_ in here, iterate through the contained Type's .generics() and check each of those (via .def_id()) against self.retained the same way that imp.for_ is. Something like this:

if let Some(generics) = imp.trait_.and_then(|t| t.generics()) {
    for typaram in generics {
        if let Some(did) = typaram.def_id() {
            if did.is_local() && !self.retained.contains(did) {
                return None;
            }
        }
    }
}

Right after that linked block.

This is technically not part of the issue (at least it sounds like the issue was more about --document-private-items) but would also be a nice thing to add, probably separately from the other proposed change.

[QuietMisdreavus]

Fixed in #46412