Create the infrastructure for planner support functions.

Rename/repurpose pg_proc.protransform as "prosupport".  The idea is
still that it names an internal function that provides knowledge to
the planner about the behavior of the function it's attached to;
but redesign the API specification so that it's not limited to doing
just one thing, but can support an extensible set of requests.

The original purpose of simplifying a function call is handled by
the first request type to be invented, SupportRequestSimplify.
Adjust all the existing transform functions to handle this API,
and rename them fron "xxx_transform" to "xxx_support" to reflect
the potential generalization of what they do.  (Since we never
previously provided any way for extensions to add transform functions,
this change doesn't create an API break for them.)

Also add DDL and pg_dump support for attaching a support function to a
user-defined function.  Unfortunately, DDL access has to be restricted
to superusers, at least for now; but seeing that support functions
will pretty much have to be written in C, that limitation is just
theoretical.  (This support is untested in this patch, but a follow-on
patch will add cases that exercise it.)

Discussion: https://postgr.es/m/15193.1548028093@sss.pgh.pa.us

1 files changed, 36 insertions, 16 deletions

diff --git a/src/backend/catalog/pg_depend.c b/src/backend/catalog/pg_depend.c
index 2b8f651c99..23b01f841e 100644
--- a/src/backend/catalog/pg_depend.c
+++ b/src/backend/catalog/pg_depend.c
@@ -286,9 +286,12 @@ deleteDependencyRecordsForClass(Oid classId, Oid objectId,
  * newRefObjectId is the new referenced object (must be of class refClassId).
  *
  * Note the lack of objsubid parameters.  If there are subobject references
- * they will all be readjusted.
+ * they will all be readjusted.  Also, there is an expectation that we are
+ * dealing with NORMAL dependencies: if we have to replace an (implicit)
+ * dependency on a pinned object with an explicit dependency on an unpinned
+ * one, the new one will be NORMAL.
  *
- * Returns the number of records updated.
+ * Returns the number of records updated -- zero indicates a problem.
  */
 long
 changeDependencyFor(Oid classId, Oid objectId,
@@ -301,35 +304,52 @@ changeDependencyFor(Oid classId, Oid objectId,
 	SysScanDesc scan;
 	HeapTuple	tup;
 	ObjectAddress objAddr;
+	ObjectAddress depAddr;
+	bool		oldIsPinned;
 	bool		newIsPinned;
 
 	depRel = table_open(DependRelationId, RowExclusiveLock);
 
 	/*
-	 * If oldRefObjectId is pinned, there won't be any dependency entries on
-	 * it --- we can't cope in that case.  (This isn't really worth expending
-	 * code to fix, in current usage; it just means you can't rename stuff out
-	 * of pg_catalog, which would likely be a bad move anyway.)
+	 * Check to see if either oldRefObjectId or newRefObjectId is pinned.
+	 * Pinned objects should not have any dependency entries pointing to them,
+	 * so in these cases we should add or remove a pg_depend entry, or do
+	 * nothing at all, rather than update an entry as in the normal case.
 	 */
 	objAddr.classId = refClassId;
 	objAddr.objectId = oldRefObjectId;
 	objAddr.objectSubId = 0;
 
-	if (isObjectPinned(&objAddr, depRel))
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("cannot remove dependency on %s because it is a system object",
-						getObjectDescription(&objAddr))));
+	oldIsPinned = isObjectPinned(&objAddr, depRel);
 
-	/*
-	 * We can handle adding a dependency on something pinned, though, since
-	 * that just means deleting the dependency entry.
-	 */
 	objAddr.objectId = newRefObjectId;
 
 	newIsPinned = isObjectPinned(&objAddr, depRel);
 
-	/* Now search for dependency records */
+	if (oldIsPinned)
+	{
+		table_close(depRel, RowExclusiveLock);
+
+		/*
+		 * If both are pinned, we need do nothing.  However, return 1 not 0,
+		 * else callers will think this is an error case.
+		 */
+		if (newIsPinned)
+			return 1;
+
+		/*
+		 * There is no old dependency record, but we should insert a new one.
+		 * Assume a normal dependency is wanted.
+		 */
+		depAddr.classId = classId;
+		depAddr.objectId = objectId;
+		depAddr.objectSubId = 0;
+		recordDependencyOn(&depAddr, &objAddr, DEPENDENCY_NORMAL);
+
+		return 1;
+	}
+
+	/* There should be existing dependency record(s), so search. */
 	ScanKeyInit(&key[0],
 				Anum_pg_depend_classid,
 				BTEqualStrategyNumber, F_OIDEQ,