Rework order of checks in ALTER / SET SCHEMA

When attempting to move an object into the schema in which it already
was, for most objects classes we were correctly complaining about
exactly that ("object is already in schema"); but for some other object
classes, such as functions, we were instead complaining of a name
collision ("object already exists in schema").  The latter is wrong and
misleading, per complaint from Robert Haas in
CA+TgmoZ0+gNf7RDKRc3u5rHXffP=QjqPZKGxb4BsPz65k7qnHQ@mail.gmail.com

To fix, refactor the way these checks are done.  As a bonus, the
resulting code is smaller and can also share some code with Rename
cases.

While at it, remove use of getObjectDescriptionOids() in error messages.
These are normally disallowed because of translatability considerations,
but this one had slipped through since 9.1.  (Not sure that this is
worth backpatching, though, as it would create some untranslated
messages in back branches.)

This is loosely based on a patch by KaiGai Kohei, heavily reworked by
me.

3 files changed, 4 insertions, 7 deletions

diff --git a/src/include/commands/alter.h b/src/include/commands/alter.h
index 37e095efa56..b9400a98128 100644
--- a/src/include/commands/alter.h
+++ b/src/include/commands/alter.h
@@ -21,9 +21,8 @@
 extern Oid ExecRenameStmt(RenameStmt *stmt);
 
 extern Oid ExecAlterObjectSchemaStmt(AlterObjectSchemaStmt *stmt);
-extern Oid	AlterObjectNamespace_oid(Oid classId, Oid objid, Oid nspOid,
+extern Oid AlterObjectNamespace_oid(Oid classId, Oid objid, Oid nspOid,
 						 ObjectAddresses *objsMoved);
-extern Oid	AlterObjectNamespace_internal(Relation rel, Oid objid, Oid nspOid);
 
 extern Oid ExecAlterOwnerStmt(AlterOwnerStmt *stmt);
 extern void AlterObjectOwner_internal(Relation catalog, Oid objectId,
diff --git a/src/include/commands/collationcmds.h b/src/include/commands/collationcmds.h
index c7b536a6358..5aaa1781726 100644
--- a/src/include/commands/collationcmds.h
+++ b/src/include/commands/collationcmds.h
@@ -19,7 +19,6 @@
 
 extern Oid DefineCollation(List *names, List *parameters);
 extern Oid RenameCollation(List *name, const char *newname);
-extern Oid AlterCollationNamespace(List *name, const char *newschema);
-extern Oid	AlterCollationNamespace_oid(Oid collOid, Oid newNspOid);
+extern void IsThereCollationInNamespace(const char *collname, Oid newNspOid);
 
 #endif   /* COLLATIONCMDS_H */
diff --git a/src/include/commands/defrem.h b/src/include/commands/defrem.h
index c327136a36d..7de6d5de979 100644
--- a/src/include/commands/defrem.h
+++ b/src/include/commands/defrem.h
@@ -50,9 +50,8 @@ extern Oid RenameFunction(List *name, List *argtypes, const char *newname);
 extern Oid AlterFunction(AlterFunctionStmt *stmt);
 extern Oid CreateCast(CreateCastStmt *stmt);
 extern void DropCastById(Oid castOid);
-extern Oid AlterFunctionNamespace(List *name, List *argtypes, bool isagg,
-								  const char *newschema);
-extern Oid	AlterFunctionNamespace_oid(Oid procOid, Oid nspOid);
+extern void IsThereFunctionInNamespace(const char *proname, int pronargs,
+						   oidvector proargtypes, Oid nspOid);
 extern void ExecuteDoStmt(DoStmt *stmt);
 extern Oid	get_cast_oid(Oid sourcetypeid, Oid targettypeid, bool missing_ok);