DROP OWNED: don't try to drop tablespaces/databases

My "fix" for bugs #7578 and #6116 on DROP OWNED at fe3b5eb not only
misstated that it applied to REASSIGN OWNED (which it did not affect),
but it also failed to fix the problems fully, because I didn't test the
case of owned shared objects.  Thus I created a new bug, reported by
Thomas Kellerer as #7748, which would cause DROP OWNED to fail with a
not-for-user-consumption error message.  The code would attempt to drop
the database, which not only fails to work because the underlying code
does not support that, but is a pretty dangerous and undesirable thing
to be doing as well.

This patch fixes that bug by having DROP OWNED only attempt to process
shared objects when grants on them are found, ignoring ownership.

Backpatch to 8.3, which is as far as the previous bug was backpatched.

Author: alvherre

doc/src/sgml/ref/drop_owned.sgml

@@ -29,10 +29,11 @@ DROP OWNED BY <replaceable class="PARAMETER">name</replaceable> [, ...] [ CASCAD
   <title>Description</title>
 
   <para>
-   <command>DROP OWNED</command> drops all the objects in the current
+   <command>DROP OWNED</command> drops all the objects within the current
    database that are owned by one of the specified roles. Any
    privileges granted to the given roles on objects in the current
-   database will also be revoked.
+   database and on shared objects (databases, tablespaces) will also be
+   revoked.
   </para>
  </refsect1>
 
@@ -93,7 +94,7 @@ DROP OWNED BY <replaceable class="PARAMETER">name</replaceable> [, ...] [ CASCAD
   </para>
 
   <para>
-   Databases owned by the role(s) will not be removed.
+   Databases and tablespaces owned by the role(s) will not be removed.
   </para>
  </refsect1>
 

src/backend/catalog/pg_shdepend.c

@@ -1240,11 +1240,14 @@ shdepDropOwned(List *roleids, DropBehavior behavior)
 											sdepForm->objid);
 					break;
 				case SHARED_DEPENDENCY_OWNER:
-					/* Save it for deletion below */
-					obj.classId = sdepForm->classid;
-					obj.objectId = sdepForm->objid;
-					obj.objectSubId = sdepForm->objsubid;
-					add_exact_object_address(&obj, deleteobjs);
+					/* If a local object, save it for deletion below */
+					if (sdepForm->dbid == MyDatabaseId)
+					{
+						obj.classId = sdepForm->classid;
+						obj.objectId = sdepForm->objid;
+						obj.objectSubId = sdepForm->objsubid;
+						add_exact_object_address(&obj, deleteobjs);
+					}
 					break;
 			}
 		}