Automatic conversion of anonymous records returned from an UDF to well known table-type
There is a way.

Given a table t and a function f() that returns an anonymous record that would match that table type:

CREATE TABLE t (id int, d date);


You cannot just cast the anonymous record, since a column definition list is required for

SELECT * FROM f()


Quoting the manual on the SELECT command:


  If the function has been defined as returning the record data type,
  then an alias or the key word AS must be present, followed by a column
  definition list in the form ...


Bold emphasis mine.

So, while all of these queries work:

SELECT '(1,2013-11-11)'::t;
SELECT ('(1,2013-11-11)'::t).*;
SELECT f();                      -- returning anonymous record
SELECT * FROM f() AS f(id int, d date);


Neither of these do:

SELECT * FROM f();
SELECT * FROM f()::t;


The latter raising an exception:


  ERROR:  cannot cast type record to t


You could wrap the SELECT with column definition list into a VIEW or function like @a_horse and @deszo suggested. That would work just fine:

CREATE OR REPLACE VIEW v1 AS
SELECT * FROM f() AS f(id int, d date);


But that wouldn't answer your question:


  convert the record (or setof record return type) into the T rowtype
  without listing the attributes?


Solution for single row

While a cast fails, an assignment in plpgsql works.

CREATE OR REPLACE function f1(OUT rec t) AS
$func$
BEGIN
rec := f();   -- assignment succeeds where cast failed (!)
END
$func$ LANGUAGE plpgsql;


Call:

SELECT * FROM f1();


While you can also write a set returning function with that pattern I did not find a way to SELECT from a set returning function without supplying a column definition list ...

->SQLfiddle