[WIP] intersphinx, allow an inventory to be a self ref

[jakobandersen]

Feature or Bugfix

• Feature

Purpose

A resolution for #9169 where a new config variable intersphinx_self_mapping can be used to specify an inventory name which will make corresponding :external+thatName:domain:role: references to fall back as if the user wrote :domain:role:.
This is useful for Python projects where a docstring can be inherited from an external project. That external project would need to write :external: references in those docstrings and use this self-mapping mechanism.

TODOs:

• Name of config variable?
• Does it need an env_version bump?
• Documentation
• CHANGES entry

Relates

Fixes #9169

[tk0miya]

I can understand the case. But I feel very strange to annotate "local" reference as an "external" reference... I'm not sure this should be implemented as a built-in feature.

[jakobandersen]

I can understand the case. But I feel very strange to annotate "local" reference as an "external" reference... I'm not sure this should be implemented as a built-in feature.

It is indeed a bit of a hax. Ideally the root of the problem, that docstrings are copied from external projects, should be addressed directly.