Un-break whole-row Vars referencing domain-over-composite types.

In commit ec62cb0aa, I foolishly replaced ExecEvalWholeRowVar's
lookup_rowtype_tupdesc_domain call with just lookup_rowtype_tupdesc,
because I didn't see how a domain could be involved there, and
there were no regression test cases to jog my memory.  But the
existing code was correct, so revert that change and add a test
case showing why it's necessary.  (Note: per comment in struct
DatumTupleFields, it is correct to produce an output tuple that's
labeled with the base composite type, not the domain; hence just
blindly looking through the domain is correct here.)

Per bug #17515 from Dan Kubb.  Back-patch to v11 where domains over
composites became a thing.

Discussion: https://postgr.es/m/17515-a24737438363aca0@postgresql.org

1 files changed, 5 insertions, 1 deletions

diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index 0999bba4217..3e0751c9236 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -3917,8 +3917,12 @@ ExecEvalWholeRowVar(ExprState *state, ExprEvalStep *op, ExprContext *econtext)
 			 * generates an INT4 NULL regardless of the dropped column type).
 			 * If we find a dropped column and cannot verify that case (1)
 			 * holds, we have to use the slow path to check (2) for each row.
+			 *
+			 * If vartype is a domain over composite, just look through that
+			 * to the base composite type.
 			 */
-			var_tupdesc = lookup_rowtype_tupdesc(variable->vartype, -1);
+			var_tupdesc = lookup_rowtype_tupdesc_domain(variable->vartype,
+														-1, false);
 
 			slot_tupdesc = slot->tts_tupleDescriptor;