[officialasishkumar]

Fixes #424.

Postgres functions that return rows of a table could not be queried. RETURNS TABLE (LIKE users) was discovered as one output column named like, so selecting a real column failed with field 'id' is not a column or a function; available columns: like. RETURNS SETOF users and RETURNS users were discovered with no output columns and were not exposed at all.

The cause is in function discovery: row columns came from information_schema.attributes, which only lists standalone composite types (CREATE TYPE ... AS (...)), never the row type of a table or view.

Changes

• postgres_functions.sql reads row columns from pg_attribute through the return type's typrelid. It covers tables, views, materialized views, foreign and partitioned tables and composite types, skips dropped columns, and uses format_type for column types, as table discovery does. The single OUT parameter that holds the whole row (the like column above) is not reported, because Postgres expands it into the row's columns. Enum and domain RETURNS TABLE outputs behave as before.
• Function output columns now carry the array flag (so filters like contains work on text[] columns) and honour the configured blocklist. A function returning users no longer bypasses a blocklist entry such as password.
• Array-typed function parameters are written to the schema DDL with the same [Type] syntax as table columns, and the DDL parser reads them back. The old Text[] output was not valid DDL. It never showed up before because Postgres reported array parameters as ARRAY. With real types it broke reloading db.ddl under enable_schema (TestEnableSchema).

Function names in the blocklist still decide whether a function is exposed. The function's return type does not, which matches how RETURNS TABLE (...) functions already work.

Tests

• tests/postgres.sql adds get_users_up_to (RETURNS TABLE (LIKE users)), get_products_up_to (RETURNS SETOF products) and get_user_row (RETURNS users).
• New examples in tests/query_pg_test.go cover each form, including an array contains filter and a blocklisted column. They fail on master and pass with this change.
• New unit tests: TestNewDBInfoFunctionOutputColumns (blocklist and array flag) and TestCreateSchemaFunctionArrayParams (DDL round trip).
• I ran the full tests suite with -db=postgres on Postgres 15, before and after the change. The only new results are the four new examples passing. The geo tests fail in both runs because my local database had no PostGIS. I also ran the function examples and TestEnableSchema on Postgres 12, plus the core, sdata, qcode, introspection and psql packages.
• On the test database the new discovery query takes about 20 ms, compared with 40 ms for the old one.