BTW, I had a thought about this patch, which I wanted to write down
before it disappears again (I'm not offering to code it right now).
I think we should split array_subscript_handler into two functions,
one for "regular" varlena arrays and one for the fixed-length
pseudo-array types like "name" and "point". This needn't have a lot
of impact on the execution code. In fact, for the first version both
handlers could just return the same set of method pointers, and then
if we feel like it we could tease apart the code paths later. The
value of doing this is that then typsubshandler could be used as a
bulletproof designator of the type's semantics. Instead of weird
implementation-dependent tests on typlen and so on, the rule could be
"it's a regular array if typsubshandler == F_ARRAY_SUBSCRIPT_HANDLER".
Later on, we could even allow the "fixed length" array semantics to
be applied to varlena types perhaps, so long as their contents are
just N copies of some fixed-size type. The point here is that we
now have a tool for recognizing the subscripting semantics reliably,
instead of having to back into an understanding of what they are.
But for the tool to be useful, we don't want the same handler
implementing significantly different behaviors.
regards, tom lane