Re: new environment variable INITDB_LOCALE_PROVIDER

On Tue, 2025-07-29 at 16:55 -0700, Jeff Davis wrote:
> $SUBJECT makes it easier to test other providers, especially the
> regression tests.

Rebased.

Changes:

* Use environment variable name PG_LOCALE_PROVIDER, which seems more
consistent.

* Updated doc.

* If the provider is builtin and the LC_CTYPE or LC_COLLATE environment
variables aren't compatible with UTF-8, it can override those to "C".
But if --locale, --lc-ctype, or --lc-collate are specified and
incompatible, they will throw an error instead.

Note: when the provider is builtin, the overriding of LC_CTYPE and
LC_COLLATE don't matter a lot. LC_CTYPE affects the translation of
messages from the OS (but not Postgres messages), as well as a few
other places that are likely to be fixed soon (e.g. [1]). LC_COLLATE
has no effect when the provider is builtin. In any case, it only
happens when those environment variables aren't compatible with UTF-8,
and the user hasn't specified any locale settings on the command line.
I see this as more of a detail about how the defaults work together
that can easily be corrected if the user specifies something different.

Also note: if PG_LOCALE_PROVIDER=libc (or is unset), there should be no
behavior change with this patch.

I am planning to commit this soon.

Regards,
    Jeff Davis

[1]
https://www.postgresql.org/message-id/0151ad01239e2cc7b3139644358cf8f7b9622ff7.camel@j-davis.com