Horton

Re: Built-in CTYPE provider

Jeff Davis <pgsql@j-davis.com>

View thread View on postgr.es
From: Jeff Davis <pgsql@j-davis.com>
To: Jeremy Schneider <schneider@ardentperf.com>, pgsql-hackers@lists.postgresql.org, "Davis, Jeff" <jefdavj@amazon.com>
Date: 2023-12-21T23:00:26Z
Lists: pgsql-hackers 
On Wed, 2023-12-20 at 15:47 -0800, Jeremy Schneider wrote:

> One other thing that comes to mind: how does the parser do case
> folding
> for relation names? Is that using OS-provided libc as of today? Or
> did
> we code it to use ICU if that's the DB default? I'm guessing libc,
> and
> global catalogs probably need to be handled in a consistent manner,
> even
> across different encodings.

The code is in downcase_identifier():

  /*                                                                  
   * SQL99 specifies Unicode-aware case normalization, which we don't 
   * yet have the infrastructure for...
   */
  if (ch >= 'A' && ch <= 'Z')
    ch += 'a' - 'A';
  else if (enc_is_single_byte && IS_HIGHBIT_SET(ch) && isupper(ch))
    ch = tolower(ch);
  result[i] = (char) ch;

My proposal would add the infrastructure that the comment above says is
missing.

It seems like we should be using the database collation at this point
because you don't want inconsistency between the catalogs and the
parser here. Then again, the SQL spec doesn't seem to support tailoring
of case conversions, so maybe we are avoiding it for that reason? Or
maybe we're avoiding catalog access? Or perhaps the work for ICU just
wasn't done here yet?

> (Kindof related... did you ever see the demo where I create a user
> named
> '🏃' and then I try to connect to a database with non-unicode
> encoding?
> 💥😜  ...at least it seems to be able to walk the index without
> decoding
> strings to find other users - but the way these global catalogs work
> scares me a little bit)

I didn't see that specific demo, but in general we seem to change
between pg_wchar and unicode code points too freely, so I'm not
surprised that something went wrong.

Regards,
	Jeff Davis

Commits

  1. Support PG_UNICODE_FAST locale in the builtin collation provider.

  2. Support Unicode full case mapping and conversion.

  3. Fix test failures when language environment is not UTF-8.

  4. Add unicode_strtitle() for Unicode Default Case Conversion.

  5. Use version for builtin collations.

  6. Fix convert_case(), introduced in 5c40364dd6.

  7. Inline basic UTF-8 functions.

  8. Support C.UTF-8 locale in the new builtin collation provider.

  9. Fix another warning, introduced by 846311051e.

  10. Address more review comments on commit 2d819a08a1.

  11. Fix unreachable code warning from commit 2d819a08a1.

  12. Introduce "builtin" collation provider.

  13. Catalog changes preparing for builtin collation provider.

  14. Unicode case mapping tables and functions.

  15. Add Unicode property tables.

  16. Documentation update for Standard Collations.

  17. Cleanup for unicode-update build target and test.

  18. Shrink Unicode category table.

  19. Make some error strings more generic

  20. pg_upgrade: copy locale and encoding information to new cluster.

  21. Update Unicode data to Unicode 15.0.0

  22. Create a new type category for "internal use" types.