Special case C_COLLATION_OID in pg_newlocale_from_collation().

Allow pg_newlocale_from_collation(C_COLLATION_OID) to work even if
there's no catalog access, which some extensions expect.

Not known to be a bug without extensions involved, but backport to 18.

Also corrects an issue in master with dummy_c_locale (introduced in
commit 5a38104b36) where deterministic was not set. That wasn't a bug,
but could have been if that structure was used more widely.

Reported-by: Alexander Kukushkin <cyberdemn@gmail.com>
Reviewed-by: Alexander Kukushkin <cyberdemn@gmail.com>
Discussion: https://postgr.es/m/CAFh8B=nj966ECv5vi_u3RYij12v0j-7NPZCXLYzNwOQp9AcPWQ@mail.gmail.com
Backpatch-through: 18

1 files changed, 5 insertions, 31 deletions

diff --git a/src/backend/regex/regc_pg_locale.c b/src/backend/regex/regc_pg_locale.c
index e0c892db713..4698f110a0c 100644
--- a/src/backend/regex/regc_pg_locale.c
+++ b/src/backend/regex/regc_pg_locale.c
@@ -23,11 +23,6 @@
 
 static pg_locale_t pg_regex_locale;
 
-static struct pg_locale_struct dummy_c_locale = {
-	.collate_is_c = true,
-	.ctype_is_c = true,
-};
-
 
 /*
  * pg_set_regex_collation: set collation for these functions to obey
@@ -53,33 +48,12 @@ pg_set_regex_collation(Oid collation)
 				 errhint("Use the COLLATE clause to set the collation explicitly.")));
 	}
 
-	if (collation == C_COLLATION_OID)
-	{
-		/*
-		 * Some callers expect regexes to work for C_COLLATION_OID before
-		 * catalog access is available, so we can't call
-		 * pg_newlocale_from_collation().
-		 */
-		locale = &dummy_c_locale;
-	}
-	else
-	{
-		locale = pg_newlocale_from_collation(collation);
-
-		if (!locale->deterministic)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("nondeterministic collations are not supported for regular expressions")));
+	locale = pg_newlocale_from_collation(collation);
 
-		if (locale->ctype_is_c)
-		{
-			/*
-			 * C/POSIX collations use this path regardless of database
-			 * encoding
-			 */
-			locale = &dummy_c_locale;
-		}
-	}
+	if (!locale->deterministic)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("nondeterministic collations are not supported for regular expressions")));
 
 	pg_regex_locale = locale;
 }