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?