Why doesn't this predicate get pushed down in a function?

1.sql

create or replace function matcher()
returns table(user_id int, match int) as $$
  
    select o.user_id, 1 as match
    from (
      select u.id as user_id, u.gender
      from users as u
    ) as o
    cross join
    (
      select u.id as user_id, u.gender
      from users as u
      where u.id = 1
    ) as my;

$$ language sql stable;

2a-as-function.sql

select * from matcher() where user_id = 2;

2b-explain.sql

LOG:  duration: 1.242 ms  plan:
	Query Text: 
	  
	    select o.user_id, 1 as match
	    from (
	      select u.id as user_id, u.gender
	      from users as u
	    ) as o
	    cross join
	    (
	      select u.id as user_id, u.gender
	      from users as u
	      where u.id = 1
	    ) as my;
	
	
	Nested Loop  (cost=0.00..118.39 rows=1656 width=4) (actual time=0.022..0.888 rows=1613 loops=1)
	  Output: u.id, 1
	  ->  Index Scan using users_pkey on public.users u  (cost=0.00..8.27 rows=1 width=0) (actual time=0.013..0.015 rows=1 loops=1)
	        Index Cond: (u.id = 1)
	  ->  Seq Scan on public.users u  (cost=0.00..93.56 rows=1656 width=4) (actual time=0.004..0.479 rows=1613 loops=1)
	        Output: u.id
CONTEXT:  SQL function "matcher" statement 1
LOG:  duration: 1.951 ms  plan:
	Query Text: select * from matcher() where user_id = 2;
	Function Scan on public.matcher  (cost=0.25..12.75 rows=5 width=8) (actual time=1.687..1.940 rows=1 loops=1)
	  Output: user_id, match
	  Filter: (matcher.user_id = 2)

3a-inline.sql

select * from
(
  select o.user_id, 1 as match
  from (
    select u.id as user_id, u.gender
    from users as u
  ) as o
  cross join
  (
    select u.id as user_id, u.gender
    from users as u
    where u.id = 1
  ) as my
) as matcher
where user_id = 2;

3b-explain.sql

LOG:  duration: 0.044 ms  plan:
	Query Text: select * from
	(
	  select o.user_id, 1 as match
	  from (
	    select u.id as user_id, u.gender
	    from users as u
	  ) as o
	  cross join
	  (
	    select u.id as user_id, u.gender
	    from users as u
	    where u.id = 1
	  ) as my
	) as matcher
	where user_id = 2;
	Nested Loop  (cost=0.00..16.55 rows=1 width=4) (actual time=0.028..0.031 rows=1 loops=1)
	  Output: u.id, 1
	  ->  Index Scan using users_pkey on public.users u  (cost=0.00..8.27 rows=1 width=4) (actual time=0.021..0.022 rows=1 loops=1)
	        Output: u.id
	        Index Cond: (u.id = 2)
	  ->  Index Scan using users_pkey on public.users u  (cost=0.00..8.27 rows=1 width=0) (actual time=0.004..0.006 rows=1 loops=1)
	        Index Cond: (u.id = 1)

4a-view.sql

-- It gets pushed down in a view, too!

create view matchview as
select o.user_id, 1 as match
  from (
    select u.id as user_id, u.gender
    from users as u
  ) as o
  cross join
  (
    select u.id as user_id, u.gender
    from users as u
    where u.id = 1
  ) as my;

4b-explain.sql

select * from matchview where user_id = 2;


LOG:  duration: 0.044 ms  plan:
	Query Text: select * from matchview where user_id = 2;
	Nested Loop  (cost=0.00..16.55 rows=1 width=4) (actual time=0.028..0.031 rows=1 loops=1)
	  Output: u.id, 1
	  ->  Index Scan using users_pkey on public.users u  (cost=0.00..8.27 rows=1 width=4) (actual time=0.021..0.022 rows=1 loops=1)
	        Output: u.id
	        Index Cond: (u.id = 2)
	  ->  Index Scan using users_pkey on public.users u  (cost=0.00..8.27 rows=1 width=0) (actual time=0.005..0.007 rows=1 loops=1)
	        Index Cond: (u.id = 1)

The answer from Tom Lane, for all you Googlers:

the answer seems to be that inline_set_returning_function needs some work to handle cases with declared OUT parameters. I will see about fixing that going forward, but in existing releases what you need to do is declare the function as returning SETOF some named composite type, eg

create type matcher_result as (user_id int, match int);

create or replace function matcher() returns setof matcher_result as ...