Re: Allowing extensions to supply operator-/function-specific info

Paul Ramsey <pramsey(at)cleverelephant(dot)ca> writes:
>> On Mar 4, 2019, at 2:52 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> BTW, if you'd like me to review the code you added for this, I'd be happy
>> to do so. I've never looked at PostGIS' innards, but probably I can make
>> sense of the code for this despite that.

> I would be ecstatic for a review, I'm sure I've left a million loose threads dangling.

I took a look, and saw that you'd neglected to check pseudoconstantness
of the non-index argument, so this'd fail on cases like ST_DWithin(x, y)
where x is indexed and y is another column in the same table. Also
I thought the handling of commutation could be done better. Attached is
a suggested patch atop your f731c1b7022381dbf627cae311c3d37791bf40c3 to
fix those and a couple of nitpicky other things. (I haven't tested this,
mind you.)

One thing that makes me itch, but I didn't address in the attached,
is that expandFunctionOid() is looking up a function by name without
any schema-qualification. That'll fail outright if PostGIS isn't in
the search path, and even if it is, you've got security issues there.
One way to address this is to assume that the expandfn is in the same
schema as the ST_XXX function you're attached to, so you could
do "get_namespace_name(get_func_namespace(funcid))" and then include
that in the list passed to LookupFuncName.

Also, this might be as-intended but I was wondering: I'd sort of expected
you to make, eg, _ST_DWithin() and ST_DWithin() into exact synonyms.
They aren't, since the former is not connected to the support function.
Is that intentional? I guess if you had a situation where you wanted to
force non-use of an index, being able to use _ST_DWithin() for that would
be helpful.

regards, tom lane