From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Regina Obe" <lr@pcorp.us>
cc: "'Gregory Stark \(as CFM\)'" <stark.cfm@gmail.com>,
        "'Sandro Santilli'" <strk@kbt.io>, pgsql-hackers@lists.postgresql.org,
        "'Regina Obe'" <r@pcorp.us>
Subject: Re: Ability to reference other extensions by schema in extension scripts
In-reply-to: <005501d953a0$906c4df0$b144e9d0$@pcorp.us>
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Comments: In-reply-to "Regina Obe" <lr@pcorp.us>
	message dated "Fri, 10 Mar 2023 17:35:05 -0500"
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Date: Fri, 10 Mar 2023 17:47:17 -0500
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"Regina Obe" <lr@pcorp.us> writes:
>> requires = 'extfoo, extbar'
>> no_relocate = 'extfoo'

> So when no_relocate is specified, where would that live?

In the control file.

> Would I mark the extfoo as not relocatable on CREATE / ALTER of said
> extension?
> Or add an extra field to pg_extension

We don't record dependent extensions in pg_extension now, so that
doesn't seem like it would fit well.  I was envisioning that
ALTER EXTENSION SET SCHEMA would do something along the lines of

(1) scrape the list of dependent extensions out of pg_depend
(2) open and parse each of their control files
(3) fail if any of their control files mentions the target one in
    no_relocate.

Admittedly, this'd be a bit slow, but I doubt that ALTER EXTENSION
SET SCHEMA is a performance bottleneck for anybody.

> I had tried to do that originally, e.g. instead of even bothering with such
> an extra arg, just mark it as not relocatable if the extension's script
> contains references to the required extension's schema.

I don't think that's a great approach, because those references might
appear in places that can track a rename (ie, in an object name that's
resolved to a stored OID).  Short of fully parsing the script file you
aren't going to get a reliable answer.  I'm content to lay that problem
off on the extension authors.

> But then what if extfoo is upgraded?

We already have mechanisms for version-dependent control files, so
I don't see where there's a problem.

			regards, tom lane