Topic on Talk:Stable interface policy

The policy currently states:

• Obsolete behavior MAY be removed right away if it appears to have never been used within the Wikimedia maintained code and the MediaWiki ecosystem (except in the repo that defines it), and seems unlikely to be used elsewhere.

This misses the point that code that has been in use only in the repo it is defined in, and perhaps in extensions maintained by the same entity, should allowed to be removed.

Perhaps this point should be rewritten as follows:

• Obsolete behavior MAY be removed right away if it appears to have never been used within the MediaWiki Ecosystem in a repository other than the one it is defined in. Even then, it MAY be removed right away if it has only been used in repositories maintained by the same entity.

Also, perhaps it would make sense to clarify how this provision interacts with another part of the policy, namely:

• If it is not reasonably possible for the deprecated code to emit deprecation warnings, hard deprecation can be applied by announcing the removal on wikitech-l in a timely manner.

Taken together, this means that certain breaking changes may only require an email to wikitech-l and a brief wait. This may be useful e.g. when it is desirable to change the return type of a method in a way that does not break any known callers: there is no way to deprecate a return type, so if nothing seems to rely on the old type, it's ok to change it after asking about concerns on the mailing list.