match: nonlinear pat refs in list-no-order

[AlexKnauth]

Allows patterns inside list-no-order to refer to nonlinear patterns declared prior, such as in (cons a (list-no-order a rst ...)).

Includes nonlinear patterns declared under ellipses, such as in (list (cons a (list-no-order a rst ...)) ...).

This also makes nonlinear pattern declarations syntax errors if the first use is in the scope of a ... pattern that doesn't encompass all uses.

[samth]

If this is supposed to work now this log should be removed.

[AlexKnauth]

I didn't want things like this to change for now:

(match '(1 2 3 4)
  [(list a ... a) a])

Order matters. When the a without ellipses comes first, that's when it works as a nonlinear pattern:

(match '(1 1 1 1)
  [(list a a ...) a])

[samth]

We should try to make the set of things that works clearer and simpler, not adding more weird exceptions.

[AlexKnauth]

I've updated the PR, it now makes nonlinear pattern declarations syntax errors if the first use is in the scope of a ... pattern that doesn't encompass all uses.

[samth]

1. I think this needs a lot more testing if it's going to work.
2. In particular, the problems that led to the warnings should be definitely checked.

[AlexKnauth]

I have an idea for checking the problems that lead to warnings:

Track ellipsis depth, and when merging pattern-variables together into non-linear patterns, only accept them when the ellipsis-depth of the first one, the declaration, is less than or equal to the ellipsis-depth of the later ones, the references.

So (list a a ...) would be allowed because the declaration ellipsis-depth 0 is less than the reference ellipsis-depth 1, but (list a ... a) would be an error because the declaration ellipsis-depth 1 is greater than the reference ellipsis-depth 0.