Re: Window functions can be created with defaults, but they don't work

I wrote:
> I noticed this while poking at the variadic-aggregates issue:
> regression=# create function nth_value_def(anyelement, integer = 1) returns anyelement language internal window immutable strict as 'window_nth_value';
> CREATE FUNCTION
> regression=# SELECT nth_value_def(ten) OVER (PARTITION BY four), ten, four
> FROM (SELECT * FROM tenk1 WHERE unique2 < 10 ORDER BY four, ten)s;
> The connection to the server was lost. Attempting reset: Failed.

Attached is a proposed patch against HEAD that fixes this by supporting
default arguments properly for window functions. In passing, it also
allows named-argument notation in window function calls, since that's
free once the other thing works (because the same subroutine fixes up
both things).

> The reason this crashes is that the planner doesn't apply
> default-insertion to WindowFunc nodes, only to FuncExprs. We could make
> it do that, probably, but that seems to me like a feature addition.
> I think a more reasonable approach for back-patching is to fix function
> creation to disallow attaching defaults to window functions (or
> aggregates, for that matter, which would have the same issue if CREATE
> AGGREGATE had the syntax option to specify defaults). ProcedureCreate
> seems like an appropriate place, since it already contains a lot of sanity
> checks of this sort.

Having now done the patch to fix it properly, I'm more inclined to think
that maybe we should just back-patch this rather than inserting an error
check. It seems pretty low-risk.

Comments?

regards, tom lane