[Jeff Davis <pgsql@j-davis.com>]

On Sat, 2023-03-11 at 15:47 -0500, Tom Lane wrote:
> In general, I see no good reason for our regression tests to be
> making
> assumptions about exactly how ICU's root locale behaves, so I'd
> suggest
> just lobotomizing this test case so it doesn't depend on upper/lower
> sort order.

[ Looks like Peter already found the answer, but I had some additional
commentary so I'll send this anyway. ]

Mystery solved: "und" was not a valid spelling of "root" until version
55. So it fell back to the default locale, which is sensitive to the
environment.

With this in mind, I think we should take the opposite lesson and keep
this test as-is. We don't have to promise the behavior in the docs, but
it did catch a real issue. In fact, it caught a dangerous issue,
because a change to lc_messages could cause a corrupt index.

I'd like to see if there's a way to reliably detect that a fallback to
the environment-sensitive default locale has happened, and throw an
error. I don't think that happens in versions 55 and later, but it
would be nice to have a test because earlier versions of ICU seem
dangerous to me.

Regards,
	Jeff Davis