RE: [bug?] Missed parallel safety checks, and wrong parallel safety

> >>> I'm curious. The FmgrBuiltin struct includes the "strict" flag, so
> >>> that would "lock down the value" of the strict flag, wouldn't it?
>
> >> It does, but that's much more directly a property of the function's C
> >> code than parallel-safety is.
>
> > I'm not sure I agree with that, but I think having the "strict" flag
> > in FmgrBuiltin isn't that nice either.
>
> Yeah, if we could readily do without it, we probably would. But the function
> call mechanism itself is responsible for implementing strictness, so it *has* to
> have that flag available.

So, If we do not want to lock down the parallel safety of built-in functions.
It seems we can try to fetch the proparallel from pg_proc for built-in function
in fmgr_info_cxt_security too. To avoid recursive safety check when fetching
proparallel from pg_proc, we can add a Global variable to mark is it in a recursive state.
And we skip safety check in a recursive state, In this approach, parallel safety
will not be locked, and there are no new members in FmgrBuiltin.

Attaching the patch about this approach [0001-approach-1].
Thoughts ?

I also attached another approach patch [0001-approach-2] about adding
parallel safety in FmgrBuiltin, because this approach seems faster and
we can combine some bool member into a bitflag to avoid enlarging the
FmgrBuiltin array, though this approach will lock down the parallel safety
of built-in function.

Best regards,
houzj