The additional thing that seems to cause the reported error is that once the subquery is pulled up, the run condition also needs a round of constant folding done. See subquery_planner() around line 827. The problem is that the target list's WindowFunc ends up with count(1) over .., but the run condition's one is left as count(case 1 when 1 then 1 else null end), which preprocess_expression() will fold into the same as what's in the target list.
Yes exactly. That's what we also have to do. I was debugging with a simplified version of the query with the WindowFunc as count(t1.a) over (...) and did not realize constant folding is also needed for the runCondition.
I'm now wondering if WindowClause.runCondition should be of type Node * instead of List *. I'd have imagined I should be passing the type of EXPRKIND_QUAL to preprocess_expression's type, but canonicalize_qual() does not like Lists.
I'm not sure about this. From how the runCondition is constructed in find_window_run_conditions, it seems there is no need to canonicalize it.