Fix getTypeIOParam to support type record[].

Since record[] uses array_in, it needs to have its element type passed
as typioparam.  In HEAD and 9.1, this fix essentially reverts commit
9bc933b212, which was a hack that is no
longer needed since domains don't set their typelem anymore.  Before
that, adjust the logic so that only domains are excluded from being
treated like arrays, rather than assuming that only base types should
be included.  Add a regression test to demonstrate the need for this.
Per report from Maxim Boguk.

Back-patch to 8.4, where type record[] was added.

src/backend/utils/cache/lsyscache.c

@@ -1888,10 +1888,9 @@ getTypeIOParam(HeapTuple typeTuple)
 
 	/*
 	 * Array types get their typelem as parameter; everybody else gets their
-	 * own type OID as parameter.  (As of 8.2, domains must get their own OID
-	 * even if their base type is an array.)
+	 * own type OID as parameter.
 	 */
-	if (typeStruct->typtype == TYPTYPE_BASE && OidIsValid(typeStruct->typelem))
+	if (OidIsValid(typeStruct->typelem))
 		return typeStruct->typelem;
 	else
 		return HeapTupleGetOid(typeTuple);

src/test/regress/expected/polymorphism.out

@@ -578,6 +578,27 @@ select q2, sql_if(q2 > 0, q2, q2 + 1) from int8_tbl;
  -4567890123456789 | -4567890123456788
 (5 rows)
 
+-- another sort of polymorphic aggregate
+CREATE AGGREGATE array_cat_accum (anyarray)
+(
+    sfunc = array_cat,
+    stype = anyarray,
+    initcond = '{}'
+);
+SELECT array_cat_accum(i)
+FROM (VALUES (ARRAY[1,2]), (ARRAY[3,4])) as t(i);
+ array_cat_accum 
+-----------------
+ {1,2,3,4}
+(1 row)
+
+SELECT array_cat_accum(i)
+FROM (VALUES (ARRAY[row(1,2),row(3,4)]), (ARRAY[row(5,6),row(7,8)])) as t(i);
+          array_cat_accum          
+-----------------------------------
+ {"(1,2)","(3,4)","(5,6)","(7,8)"}
+(1 row)
+
 -- another kind of polymorphic aggregate
 create function add_group(grp anyarray, ad anyelement, size integer)
   returns anyarray

src/test/regress/sql/polymorphism.sql

@@ -392,6 +392,21 @@ select f1, sql_if(f1 > 0, bleat(f1), bleat(f1 + 1)) from int4_tbl;
 
 select q2, sql_if(q2 > 0, q2, q2 + 1) from int8_tbl;
 
+-- another sort of polymorphic aggregate
+
+CREATE AGGREGATE array_cat_accum (anyarray)
+(
+    sfunc = array_cat,
+    stype = anyarray,
+    initcond = '{}'
+);
+
+SELECT array_cat_accum(i)
+FROM (VALUES (ARRAY[1,2]), (ARRAY[3,4])) as t(i);
+
+SELECT array_cat_accum(i)
+FROM (VALUES (ARRAY[row(1,2),row(3,4)]), (ARRAY[row(5,6),row(7,8)])) as t(i);
+
 -- another kind of polymorphic aggregate
 
 create function add_group(grp anyarray, ad anyelement, size integer)