Replace empty locale name with implied value in CREATE DATABASE and initdb.

setlocale() accepts locale name "" as meaning "the locale specified by the
process's environment variables".  Historically we've accepted that for
Postgres' locale settings, too.  However, it's fairly unsafe to store an
empty string in a new database's pg_database.datcollate or datctype fields,
because then the interpretation could vary across postmaster restarts,
possibly resulting in index corruption and other unpleasantness.

Instead, we should expand "" to whatever it means at the moment of calling
CREATE DATABASE, which we can do by saving the value returned by
setlocale().

For consistency, make initdb set up the initial lc_xxx parameter values the
same way.  initdb was already doing the right thing for empty locale names,
but it did not replace non-empty names with setlocale results.  On a
platform where setlocale chooses to canonicalize the spellings of locale
names, this would result in annoying inconsistency.  (It seems that popular
implementations of setlocale don't do such canonicalization, which is a
pity, but the POSIX spec certainly allows it to be done.)  The same risk
of inconsistency leads me to not venture back-patching this, although it
could certainly be seen as a longstanding bug.

Per report from Jeff Davis, though this is not his proposed patch.

1 files changed, 6 insertions, 3 deletions

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 91d74815287..9721ce9e0a6 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -123,6 +123,7 @@ createdb(const CreatedbStmt *stmt)
 	const char *dbtemplate = NULL;
 	char	   *dbcollate = NULL;
 	char	   *dbctype = NULL;
+	char	   *canonname;
 	int			encoding = -1;
 	int			dbconnlimit = -1;
 	int			notherbackends;
@@ -318,15 +319,17 @@ createdb(const CreatedbStmt *stmt)
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("invalid server encoding %d", encoding)));
 
-	/* Check that the chosen locales are valid */
-	if (!check_locale(LC_COLLATE, dbcollate))
+	/* Check that the chosen locales are valid, and get canonical spellings */
+	if (!check_locale(LC_COLLATE, dbcollate, &canonname))
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("invalid locale name %s", dbcollate)));
-	if (!check_locale(LC_CTYPE, dbctype))
+	dbcollate = canonname;
+	if (!check_locale(LC_CTYPE, dbctype, &canonname))
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("invalid locale name %s", dbctype)));
+	dbctype = canonname;
 
 	check_encoding_locale_matches(encoding, dbcollate, dbctype);