Re: Refactor: allow pg_strncoll(), etc., to accept -1 length for NUL-terminated cstrings.

On Thu, 2024-08-22 at 11:00 -0700, Jeff Davis wrote:
> Like ICU, allow -1 length to mean that the input string is NUL-
> terminated for pg_strncoll(), pg_strnxfrm(), and
> pg_strnxfrm_prefix().

To better illustrate the direction I'm going, I roughly implemented
some patches that implement collation using a table of methods rather
than lots branching based on the provider.

This more cleanly separates the API for a provider, which will enable
us to use a hook to create a custom provider with arbitrary methods,
that may have nothing to do with ICU or libc. Or, we could go so far as
to implement a "CREATE LOCALE PROVIDER" that would provide the methods
using a handler function, and "datlocprovider" would be an OID rather
than a char.

From a practical perspective, I expect that extensions would use this
to lock down the version of a particular provider rather than implement
a completely arbitrary one. But the API is good for either case, and
offers quite a bit of code cleanup.

There are quite a few loose ends, of course:

  * There is still a lot of branching on the provider for DDL and
catalog access. I'm not sure if we will ever eliminate all of this, or
if we would even want to.

  * I haven't done anything with get_collation_actual_version().
Perhaps that should be a method, too, but it requires some extra
thought if we want this to be useful for "multilib" (having multiple
versions of a provider library at once).

  * I didn't add methods for formatting.c yet.

  * initdb -- should it offer a way to preload a library and then use
that for the provider?

  * I need to allow an arbitrary per-provider context, rather than the
current union designed for the existing providers.

Again, the patches are rough and there's a lot of code churn. I'd like
some feedback on whether people generally like the direction this is
going. If so I will clean up the patch series into smaller, more
reviewable chunks.

Regards,
	Jeff Davis