Hide internal error for pg_collation_actual_version(<bad OID>).

Instead of an unsightly internal "cache lookup failed" message, just
return NULL for bad OIDs, as is the convention for other similar things.
Reported-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com

src/backend/catalog/index.c

@@ -1290,7 +1290,8 @@ do_collation_version_check(const ObjectAddress *otherObject,
 		return false;
 
 	/* Ask the provider for the current version.  Give up if unsupported. */
-	current_version = get_collation_version_for_oid(otherObject->objectId);
+	current_version = get_collation_version_for_oid(otherObject->objectId,
+													false);
 	if (!current_version)
 		return false;
 
@@ -1369,7 +1370,7 @@ do_collation_version_update(const ObjectAddress *otherObject,
 	if (OidIsValid(*coll) && otherObject->objectId != *coll)
 		return false;
 
-	*new_version = get_collation_version_for_oid(otherObject->objectId);
+	*new_version = get_collation_version_for_oid(otherObject->objectId, false);
 
 	return true;
 }

src/backend/catalog/pg_depend.c

@@ -116,7 +116,8 @@ recordMultipleDependencies(const ObjectAddress *depender,
 					referenced->objectId == POSIX_COLLATION_OID)
 					continue;
 
-				version = get_collation_version_for_oid(referenced->objectId);
+				version = get_collation_version_for_oid(referenced->objectId,
+														false);
 
 				/*
 				 * Default collation is pinned, so we need to force recording

src/backend/commands/collationcmds.c

@@ -273,7 +273,7 @@ pg_collation_actual_version(PG_FUNCTION_ARGS)
 	Oid			collid = PG_GETARG_OID(0);
 	char	   *version;
 
-	version = get_collation_version_for_oid(collid);
+	version = get_collation_version_for_oid(collid, true);
 
 	if (version)
 		PG_RETURN_TEXT_P(cstring_to_text(version));

src/backend/utils/adt/pg_locale.c

@@ -1726,10 +1726,11 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 /*
  * Get provider-specific collation version string for a given collation OID.
  * Return NULL if the provider doesn't support versions, or the collation is
- * unversioned (for example "C").
+ * unversioned (for example "C").  Unknown OIDs result in NULL if missing_ok is
+ * true.
  */
 char *
-get_collation_version_for_oid(Oid oid)
+get_collation_version_for_oid(Oid oid, bool missing_ok)
 {
 	HeapTuple	tp;
 	char	   *version;
@@ -1751,7 +1752,11 @@ get_collation_version_for_oid(Oid oid)
 
 		tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(oid));
 		if (!HeapTupleIsValid(tp))
+		{
+			if (missing_ok)
+				return NULL;
 			elog(ERROR, "cache lookup failed for collation %u", oid);
+		}
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 		version = get_collation_actual_version(collform->collprovider,
 											   NameStr(collform->collcollate));

src/include/utils/pg_locale.h

@@ -103,7 +103,7 @@ typedef struct pg_locale_struct *pg_locale_t;
 
 extern pg_locale_t pg_newlocale_from_collation(Oid collid);
 
-extern char *get_collation_version_for_oid(Oid collid);
+extern char *get_collation_version_for_oid(Oid collid, bool missing_ok);
 
 #ifdef USE_ICU
 extern int32_t icu_to_uchar(UChar **buff_uchar, const char *buff, size_t nbytes);

src/test/regress/expected/collate.icu.utf8.out

@@ -2155,3 +2155,17 @@ DROP SCHEMA collate_tests CASCADE;
 RESET client_min_messages;
 -- leave a collation for pg_upgrade test
 CREATE COLLATION coll_icu_upgrade FROM "und-x-icu";
+-- Test user-visible function for inspecting versions
+SELECT pg_collation_actual_version('"en-x-icu"'::regcollation) is not null;
+ ?column? 
+----------
+ t
+(1 row)
+
+-- Invalid OIDs are silently ignored
+SELECT pg_collation_actual_version(0) is null;
+ ?column? 
+----------
+ t
+(1 row)
+

src/test/regress/sql/collate.icu.utf8.sql

@@ -883,3 +883,8 @@ RESET client_min_messages;
 
 -- leave a collation for pg_upgrade test
 CREATE COLLATION coll_icu_upgrade FROM "und-x-icu";
+
+-- Test user-visible function for inspecting versions
+SELECT pg_collation_actual_version('"en-x-icu"'::regcollation) is not null;
+-- Invalid OIDs are silently ignored
+SELECT pg_collation_actual_version(0) is null;