Fix ExecMakeTableFunctionResult to verify that all rows returned by a SRF

returning "record" actually do have the same rowtype.  This is needed because
the parser can't realistically enforce that they will all have the same typmod,
as seen in a recent example from David Wheeler.

Back-patch to 8.0, which is as far back as we have the notion of RECORD
subtypes being distinguished by typmod.  Wheeler's example depends on
8.4-and-up features, but I suspect there may be ways to provoke similar
failures before 8.4.

src/backend/executor/execQual.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.264 2010/07/12 17:01:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.265 2010/08/26 18:54:37 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2143,6 +2143,16 @@ ExecMakeTableFunctionResult(ExprState *funcexpr,
 
 				td = DatumGetHeapTupleHeader(result);
 
+				/*
+				 * Verify all returned rows have same subtype; necessary in
+				 * case the type is RECORD.
+				 */
+				if (HeapTupleHeaderGetTypeId(td) != tupdesc->tdtypeid ||
+					HeapTupleHeaderGetTypMod(td) != tupdesc->tdtypmod)
+					ereport(ERROR,
+							(errcode(ERRCODE_DATATYPE_MISMATCH),
+							 errmsg("rows returned by function are not all of the same row type")));
+
 				/*
 				 * tuplestore_puttuple needs a HeapTuple not a bare
 				 * HeapTupleHeader, but it doesn't need all the fields.