Re: Built-in CTYPE provider

On Tue, 2024-03-26 at 08:04 +0100, Peter Eisentraut wrote:
> The patch set v27 is ok with me, modulo (a) discussion about initcap
> semantics, and (b) what collation to assign to ucs_basic, which can
> be
> revisited later.

I held off on the refactoring patch for lc_{ctype|collate}_is_c().
There's an explicit "NB: pg_newlocale_from_collation is only supposed
to be called on non-C-equivalent locales" comment in DefineCollation().

What I'd like to do is make it possible to create valid pg_locale_t
objects out of C locales, which can be used anywhere a real locale can
be used. Callers can still check lc_{collate|ctype}_is_c() for various
reasons; but if they did call pg_newlocale_from_collation on a C locale
it would at least work for the pg_locale.h APIs. That would be a
slightly simpler and safer API, and make it easier to do the collation
version check consistently.

That's not very complicated, but it's a bit invasive and probably out
of scope for v17. It might be part of another change I had intended for
a while, which is to make NULL an invalid pg_locale_t, and use a
different representation to mean "use the server environment". That
would clean up a lot of checks for NULL.

For now, we'd still like to add the version number to the builtin
collations, so that leaves us with two options:

(a) Perform the version check in lc_{collate|ctype}_is_c(), which
duplicates some code and creates some inconsistency in how the version
is checked for different providers.

(b) Don't worry about it and just commit the version change in v27-
0001. The version check is already performed correctly on the database
without changes, even if the locale is "C". And there are already three
built-in "C" collations: "C", "POSIX", and UCS_BASIC; so it's not clear
why someone would create even more of them. And even if they did, there
would be no reason to give them a warning because we haven't
incremented the version, so there's no chance of a mismatch.

I'm inclined toward (b). Thoughts?

Regards,
Jeff Davis