Word boundaries are based on whether a character is alphanumeric or
not. For the PG_UNICODE_FAST collation, alphanumeric includes
non-ASCII digits; whereas for the PG_C_UTF8 collation, it only
includes digits 0-9. Pass down the right information from the
pg_locale_t into initcap_wbnext to differentiate the behavior.
Reported-by: Noah Misch <noah@leadboat.com>
Reviewed-by: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20250417135841.33.nmisch@google.com
Useful for caseless matching. Similar to LOWER(), but avoids edge-case
problems with using LOWER() for caseless matching.
For collations that support it, CASEFOLD() handles characters with
more than two case variations or multi-character case variations. Some
characters may fold to uppercase. The results of case folding are also
more stable across Unicode versions than LOWER() or UPPER().
Discussion: https://postgr.es/m/a1886ddfcd8f60cb3e905c93009b646b4cfb74c5.camel%40j-davis.com
Reviewed-by: Ian Lawrence Barwick
The PG_UNICODE_FAST locale uses code point sort order (fast,
memcmp-based) combined with Unicode character semantics. The character
semantics are based on Unicode full case mapping.
Full case mapping can map a single codepoint to multiple codepoints,
such as "ß" uppercasing to "SS". Additionally, it handles
context-sensitive mappings like the "final sigma", and it uses
titlecase mappings such as "Dž" when titlecasing (rather than plain
uppercase mappings).
Importantly, the uppercasing of "ß" as "SS" is specifically mentioned
by the SQL standard. In Postgres, UCS_BASIC uses plain ASCII semantics
for case mapping and pattern matching, so if we changed it to use the
PG_UNICODE_FAST locale, it would offer better compliance with the
standard. For now, though, do not change the behavior of UCS_BASIC.
Discussion: https://postgr.es/m/ddfd67928818f138f51635712529bc5e1d25e4e7.camel@j-davis.com
Discussion: https://postgr.es/m/27bb0e52-801d-4f73-a0a4-02cfdd4a9ada@eisentraut.org
Reviewed-by: Peter Eisentraut, Daniel Verite
Now that the result of pg_newlocale_from_collation() is always
non-NULL, then we can move the collate_is_c and ctype_is_c flags into
pg_locale_t. That simplifies the logic in lc_collate_is_c() and
lc_ctype_is_c(), removing the dependence on setlocale().
This commit also eliminates the multi-stage initialization of the
collation cache.
As long as we have catalog access, then it's now safe to call
pg_newlocale_from_collation() without checking lc_collate_is_c()
first.
Discussion: https://postgr.es/m/cfd9eb85-c52a-4ec9-a90e-a5e4de56e57d@eisentraut.org
Reviewed-by: Peter Eisentraut, Andreas Karlsson
The builtin C.UTF-8 locale has similar semantics to the libc locale of
the same name. That is, code point sort order (fast, memcmp-based)
combined with Unicode semantics for character operations such as
pattern matching, regular expressions, and
LOWER()/INITCAP()/UPPER(). The character semantics are based on
Unicode simple case mappings.
The builtin provider's C.UTF-8 offers several important advantages
over libc:
* faster sorting -- benefits from additional optimizations such as
abbreviated keys and varstrfastcmp_c
* faster case conversion, e.g. LOWER(), at least compared with some
libc implementations
* available on all platforms with identical semantics, and the
semantics are stable, testable, and documentable within a given
Postgres major version
Being based on memcmp, the builtin C.UTF-8 locale does not offer
natural language sort order. But it is an improvement for most use
cases that might otherwise use libc's "C.UTF-8" locale, as well as
many use cases that use libc's "C" locale.
Discussion: https://postgr.es/m/ff4c2f2f9c8fc7ca27c1c24ae37ecaeaeaff6b53.camel%40j-davis.com
Reviewed-by: Daniel Vérité, Peter Eisentraut, Jeremy Schneider
