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Canonicalize ICU locale names to language tags.

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Convert to BCP47 language tags before storing in the catalog, except
during binary upgrade or when the locale comes from an existing
collation or template database.

The resulting language tags can vary slightly between ICU
versions. For instance, "@colBackwards=yes" is converted to
"und-u-kb-true" in older versions of ICU, and to the simpler (but
equivalent) "und-u-kb" in newer versions.

The process of canonicalizing to a language tag also understands more
input locale string formats than ucol_open(). For instance,
"fr_CA.UTF-8" is misinterpreted by ucol_open() and the region is
ignored; effectively treating it the same as the locale "fr" and
opening the wrong collator. Canonicalization properly interprets the
language and region, resulting in the language tag "fr-CA", which can
then be understood by ucol_open().

This commit fixes a problem in prior versions due to ucol_open()
misinterpreting locale strings as described above. For instance,
creating an ICU collation with locale "fr_CA.UTF-8" would store that
string directly in the catalog, which would later be passed to (and
misinterpreted by) ucol_open(). After this commit, the locale string
will be canonicalized to language tag "fr-CA" in the catalog, which
will be properly understood by ucol_open(). Because this fix affects
the resulting collator, we cannot change the locale string stored in
the catalog for existing databases or collations; otherwise we'd risk
corrupting indexes. Therefore, only canonicalize locales for
newly-created (not upgraded) collations/databases. For similar
reasons, do not backport.

Discussion: https://postgr.es/m/8c7af6820aed94dc7bc259d2aa7f9663518e6137.camel@j-davis.com
Reviewed-by: Peter Eisentraut
This commit is contained in:
Jeff Davis
2023-04-04 10:28:08 -07:00
parent d3d53f955c
commit ea1db8ae70
10 changed files with 258 additions and 27 deletions
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doc/src/sgml/charset.sgml
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@ -893,7 +893,7 @@ CREATE COLLATION german (provider = libc, locale = 'de_DE');
The first example selects the ICU locale using a <quote>language
tag</quote> per BCP 47. The second example uses the traditional
ICU-specific locale syntax. The first style is preferred going
forward, but it is not supported by older ICU versions.
forward, and is used internally to store locales.
</para>
<para>
Note that you can name the collation objects in the SQL environment