Re: PL/pgSQL, RAISE and error context

Entering the discussion because this is a huge pain for me in my daily
work as well.

This is not a reply to any specific post in this thread, but my first
message in the thread.

I see a great value in providing both a GUC and a new RAISE syntax.
The different benefits of the two are maybe obvious, but perhaps worth
pointing out:
GUC: Good because you don't have to change any existing code.
RAISE syntax: Good because you can control exactly what message should
be emitted or not be emitted at that line of code.

I think preserving backwards compatibility is very important.
Not changing the default is not a problem for me, as long as it can be
overridden.

Whatever the default behaviour is, I think the need expressed by all
users in this thread boils down to any of these two sentences:

"I want CONTEXT to be (DISPLAYED|SUPPRESSED) for (ALL|ONLY THIS LINE)
RAISE (NOTICE|WARNING|ERROR)"
OR
"I don't want to change the default current behaviour of CONTEXT"

So we basically need a boolean setting value, where:
NULL means the default behaviour
TRUE means DISPLAY CONTEXT
FALSE means SUPPRESS CONTEXT

And the (ALL|ONLY THIS) part translates into using,
* a GUC to change behaviour for ALL lines of code,
* or using the RAISE syntax to change the behaviour of ONLY THIS line of code.

And then we have the different message levels, for which CONTEXT is
sometimes desirable in some situations:
* The RAISE syntax allows controlling any message level in a natural
way, as the message level is part of the syntax.
* Allowing the same control using GUC would mean the message level
would need to be part of the GUC key name, which means either add
multiple GUCs, one for each message level, or only allow controlling
the most important one and ignore the possibly need to control the
other message levels.

If it would be possible to somehow combine multiple message levels in
the same GUC, that would solve the latter problem.

We already have comma separated values for many GUCs, so maybe we
could use that approach here as well.

It looks like adding these two GUCs would meet the demands of all users:

suppress_context_messages (enum)
display_context_messages (enum)

This would allow doing something crazy as:

suppress_context_messages = warning,error
display_context_messages = notice