Function array_agg(array)

Greetings,

While looking for easier items in PostgreSQL Wiki's Todo List (this will be
my 3rd patch), i found this TODO:

Add a built-in array_agg(anyarray) or similar, that can aggregate
> 1-dimensional arrays into a 2-dimensional array.
>

I've stumbled by this lack of array_agg(anyarray) sometimes ago in my work,
so i decided to explore this.

Currently, if we try array_agg(anyarray), PostgreSQL behaves like this:

# select array_agg('{1,2}'::int[]);
ERROR: could not find array type for data type integer[]

Reading implementation of array_agg, it looks like the array_agg function
is generic, and can process any input. The error comes from PostgreSQL not
finding array type for int[] (_int4 in pg_proc).

In PostgreSQL, any array is multidimensional, array type for any array is
the same:
- the type of {1,2} is int[]
- {{1,2}, {3,4}} is int[]
- {{{1},{2}, {3} ,{4}}} is still int[]

So, can't we just set the typarray of array types to its self oid? (patch
attached). So far:
- the array_agg is working and returning correct types:

backend> select array_agg('{1,2}'::int[]);
1: array_agg (typeid = 1007, len = -1, typmod = -1, byval = f)
----
1: array_agg = "{"{1,2}"}" (typeid = 1007, len = -1, typmod = -1,
byval = f)
----

select array_agg('{''a'',''b''}'::varchar[]);
1: array_agg (typeid = 1015, len = -1, typmod = -1, byval = f)
----
1: array_agg = "{"{'a','b'}"}" (typeid = 1015, len = -1, typmod =
-1, byval = f)
----

- Regression tests passed except for the pg_type sanity check while
checking typelem relation with typarray:

SELECT p1.oid, p1.typname as basetype, p2.typname as arraytype,
p2.typelem, p2.typlen
FROM pg_type p1 LEFT JOIN pg_type p2 ON (p1.typarray = p2.oid)
WHERE p1.typarray <> 0 AND
(p2.oid IS NULL OR p2.typelem <> p1.oid OR p2.typlen <> -1);
! oid | basetype | arraytype | typelem | typlen
! ------+----------------+----------------+---------+--------
! 143 | _xml | _xml | 142 | -1
! 199 | _json | _json | 114 | -1
! 629 | _line | _line | 628 | -1
! 719 | _circle | _circle | 718 | -1
... (cut)

Aside from the sanity check complaints, I don't see any problems in the
resulting array operations.

So, back to the question: Can't we just set the typarray of array types to
its self oid?

Regards,
--
Ali Akbar