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

2 files changed, 2 insertions, 2 deletions

diff --git a/src/test/modules/test_ddl_deparse/expected/create_transform.out b/src/test/modules/test_ddl_deparse/expected/create_transform.out
index 0d1cc360f4e..da7fea2d091 100644
--- a/src/test/modules/test_ddl_deparse/expected/create_transform.out
+++ b/src/test/modules/test_ddl_deparse/expected/create_transform.out
@@ -7,7 +7,7 @@
 -- internal and as return argument the datatype of the transform done.
 -- pl/plpgsql does not authorize the use of internal as data type.
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-    FROM SQL WITH FUNCTION varchar_transform(internal),
+    FROM SQL WITH FUNCTION varchar_support(internal),
     TO SQL WITH FUNCTION int4recv(internal));
 NOTICE:  DDL test: type simple, tag CREATE TRANSFORM
 DROP TRANSFORM FOR int LANGUAGE SQL;
diff --git a/src/test/modules/test_ddl_deparse/sql/create_transform.sql b/src/test/modules/test_ddl_deparse/sql/create_transform.sql
index 096870233f8..132fc5af049 100644
--- a/src/test/modules/test_ddl_deparse/sql/create_transform.sql
+++ b/src/test/modules/test_ddl_deparse/sql/create_transform.sql
@@ -8,7 +8,7 @@
 -- internal and as return argument the datatype of the transform done.
 -- pl/plpgsql does not authorize the use of internal as data type.
 CREATE TRANSFORM FOR int LANGUAGE SQL (
-    FROM SQL WITH FUNCTION varchar_transform(internal),
+    FROM SQL WITH FUNCTION varchar_support(internal),
     TO SQL WITH FUNCTION int4recv(internal));
 
 DROP TRANSFORM FOR int LANGUAGE SQL;