Don't choke during startup if the environment offers an invalid value

for LC_MESSAGES; instead, just press forward, leaving the effective setting
at 'C'.  There is not any very good reason to complain when we are going
to replace the value soon with whatever postgresql.conf says.  This change
should solve the occasionally-reported problem of initdb failing with
'failed to initialize lc_messages'; the current theory is that that is
a reflection of either wrong LANG/LC_MESSAGES or completely broken locale
support.

src/backend/utils/adt/pg_locale.c

@@ -4,7 +4,7 @@
  *
  * Portions Copyright (c) 2002-2006, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/backend/utils/adt/pg_locale.c,v 1.35 2006/03/05 15:58:43 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/adt/pg_locale.c,v 1.36 2006/06/03 17:36:10 tgl Exp $
  *
  *-----------------------------------------------------------------------
  */
@@ -182,6 +182,10 @@ pg_perm_setlocale(int category, const char *locale)
  * This is common code for several locale categories.  This doesn't
  * actually set the locale permanently, it only tests if the locale is
  * valid.  (See explanation at the top of this file.)
+ *
+ * Note: we accept value = "" as selecting the postmaster's environment
+ * value, whatever it was (so long as the environment setting is legal).
+ * This will have been locked down by an earlier call to pg_perm_setlocale.
  */
 static const char *
 locale_xxx_assign(int category, const char *value, bool doit, GucSource source)
@@ -230,10 +234,20 @@ locale_time_assign(const char *value, bool doit, GucSource source)
 
 /*
  * We allow LC_MESSAGES to actually be set globally.
+ *
+ * Note: we normally disallow value = "" because it wouldn't have consistent
+ * semantics (it'd effectively just use the previous value).  However, this
+ * is the value passed for PGC_S_DEFAULT, so don't complain in that case,
+ * not even if the attempted setting fails due to invalid environment value.
+ * The idea there is just to accept the environment setting *if possible*
+ * during startup, until we can read the proper value from postgresql.conf.
  */
 const char *
 locale_messages_assign(const char *value, bool doit, GucSource source)
 {
+	if (*value == '\0' && source != PGC_S_DEFAULT)
+		return NULL;
+
 	/*
 	 * LC_MESSAGES category does not exist everywhere, but accept it anyway
 	 *
@@ -244,7 +258,8 @@ locale_messages_assign(const char *value, bool doit, GucSource source)
 	if (doit)
 	{
 		if (!pg_perm_setlocale(LC_MESSAGES, value))
-			return NULL;
+			if (source != PGC_S_DEFAULT)
+				return NULL;
 	}
 #ifndef WIN32
 	else