simplify_function() mustn't try to evaluate functions that return

composite types, because TupleTableSlots aren't Datums and can't be
stored in Const nodes.  We can remove this restriction if we ever
adopt a cleaner runtime representation for whole-tuple results, but
at the moment it's broken.  Per example from Thomas Hallgren.

src/backend/optimizer/util/clauses.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.162 2004/01/12 20:48:15 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.163 2004/01/28 00:05:04 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -1711,6 +1711,7 @@ evaluate_function(Oid funcid, Oid result_type, List *args,
 	bool		has_null_input = false;
 	List	   *arg;
 	FuncExpr   *newexpr;
+	char		result_typtype;
 
 	/*
 	 * Can't simplify if it returns a set.
@@ -1747,6 +1748,15 @@ evaluate_function(Oid funcid, Oid result_type, List *args,
 		has_nonconst_input)
 		return NULL;
 
+	/*
+	 * Can't simplify functions returning composite types (mainly because
+	 * datumCopy() doesn't cope; FIXME someday when we have a saner
+	 * representation for whole-tuple results).
+	 */
+	result_typtype = get_typtype(funcform->prorettype);
+	if (result_typtype == 'c')
+		return NULL;
+
 	/*
 	 * OK, looks like we can simplify this operator/function.
 	 *