Re: JIT performance bug/regression & JIT EXPLAIN

>But that's pretty crappy, because it means that the 'shape' of the output depends on the jit_details option.

Yeah, that would be hard to work with. What about adding it as a sibling group?

"Filter": "(lineitem.l_shipdate <= '1998-09-18 00:00:00'::timestamp
without time zone)",
"Filter JIT": {
  "Expr": "evalexpr_0_2",
  "Deform Scan": "deform_0_3",
  "Deform Outer": null,
  "Deform Inner": null
}

Also not that pretty, but at least it's easier to work with (I also
changed the dashes to spaces since that's what the rest of EXPLAIN is
doing as a matter of style).

>But the compat break due to that change is not small- perhaps we could instead mark that in another way?

We could add a "Projects" boolean key instead? Of course that's more
awkward in text mode. Maybe compat break is less of an issue in text
mode and we can treat this differently?

>I'm not sure that 'TRANS' is the best placeholder for the transition value here. Maybe $TRANS would be clearer?

+1, I think the `$` makes it clearer that this is not a literal expression.

>For HashJoin/Hash I've added 'Outer Hash Key' and 'Hash Key' for each key, but only in verbose mode.

That reads pretty well to me. What does the structured output look like?