Re: pg_get_functiondef forgets about most GUC_LIST_INPUT GUCs

On Thu, Jan 11, 2018 at 10:42:38AM -0500, Tom Lane wrote:
> Michael Paquier <michael.paquier@gmail.com> writes:
>> guc.c already holds a find_option()
>> which can be used to retrieve the flags of a parameter. What about using
>> that and filtering by GUC_LIST_INPUT? This requires exposing the
>> function, and I am not sure what people think about that.
> 
> Don't like exposing find_option directly, but I think it would make
> sense to provide an API along the lines of
> int GetConfigOptionFlags(const char *name, bool missing_ok).

OK, I can live with that. What do you think about the attached? I'll be
happy to produce patches for back-branches as necessary. When an option
is not found, I have made the function return 0 as value for the flags,
which is consistent with flatten_set_variable_args(). To make things
behave more consistently with GUC_LIST_QUOTE GUCs, it seems to me that
those should not be quoted as well (ALTER SYSTEM shares the same
compatibility). And attached is a patch.

While reviewing more the code, I have noticed the same code pattern in
pg_dump.c and pg_dumpall.c. In the patch attached, I have corrected
things so as all parameters marked as GUC_LIST_QUOTE are correctly not
quoted because we have no generic solution to know from frontends what's
a GUC type (it would make sense to me to expose a text[] with this
information in pg_settings). However, let's be honest, it does not make
sense to update all those parameters because who is really going to use
them for functions! Two things that make sense to me are just
wal_consistency_checking and synchronous_standby_names for developers
which could use it to tune WAL generated within a set of SQL or plpgsql
functions. As it is easier to delete than add code here, I have added
all of them to ease the production of a committable version. For
correctness, still having them may make sense.
--
Michael