plpgsql redesign (related to plpgsql check function)

Hello all

I am searching way how to push our plpgsql_check_function to upstream.
One possibility is redesign of plpgsql architecture.

Now, we have two stages -> compilation and execution, and almost all
compilation logic is in gram file. If I understand to this design
well, then a reason for it is a possibility to raise user friendly
error messages with location specification. Now, we are able to raise
messages with location info outside gram file, so we can little bit
cleanup architecture by dividing current compilation to parsing and
compilation stage (recursive).

A new compilation stage can be good place for placing current checks
and deep (sql semantic) check.

This redesign contains lot of work, so I would to know all opinions
and I would to know, if this idea is acceptable.

Regards

Pavel Stehule