I still not happy with plugin_info - it is only per plugin now and should be per plugin and per function.
I'm not sure I understand the point of plugin_info in the first place, but what would having a separate info per (plugin, function) achieve that can't be done otherwise?
First use case - I would to protect repeated call of plpgsql_check_function in passive mode. Where I have to store information about successful first start? It is related to the function instance, so function oid can be ambiguous (for function with polymorphic parameters). When function instance is destroyed, then this information should be destroyed. It is impossible do this check from plugin. Second use case - attach session life cycle plugin data with some function - for example for coverage calculation. Inside plugin without function specific data you have to hold a hash of all used function, and you have to search again and again. When plpgsql hold this info in internal plpgsql function structures, then you don't need search anything.
Regards
Pavel
As for the current patch, I'd like to see improvements on a few things:
1) It doesn't currently compile because of extra semicolons in the PLpgSQL_plugin struct.
2) The previous comment above the same struct still talk about the rendezvous variable which is now gone. The comment should be updated to reflect the new API.
3) The same comment talks about how important it is to unregister a plugin if its _PG_fini() is ever called, but the current API does not support unregistering. That should probably be added? I'm not sure when _PG_fini() would be called.
4) The comment /* reserved for use by optional plugin */ seems a bit weird in its new context.