Rustdoc does not show documentation on empty impl blocks

[jyn514]

I tried this code:

struct Ty {}
/// Documentation 1
impl Ty {}

I expected to see this happen: Either the comment should show up in the generated docs, or rustdoc/rustc should issue a warning.

Instead, this happened: The documentation is silently ignored.

I think we should show the documentation, since people like to use impl blocks for grouping and it's possible that all the items in the impl have a #[cfg()] macro that's false.

Thanks @WaffleLapkin for the bug report and @GuillaumeGomez for giving feedback on the proper fix.

Meta

rustdoc --version --verbose: rustdoc 1.58.0-nightly (e90c5fb 2021-11-12)

[GuillaumeGomez]

I'll write the fix in the next days.

[kpreid]

A suggestion: Since this is such an unusual case, add a special note like

This impl TypeName {} contains no items.

after the displayed documentation. This will help people parse the structure of the documentation page, understand what it means that the thing is said to be an implementation, and understand that it's not purely a rustdoc bug/infelicity that it's showing an empty section.

[GuillaumeGomez]

Good idea!