Pattern matching of tuples and Any

[Praetonus]

Initially reported on the mailing list by @sgebbie.

actor Main
  new create(env: Env) =>
    let x: (Any val | (None, None)) = None
    match x
    | (let n1: None, let n2: None) => None
    end

This code used to compile under the 0.14 version but doesn't compile anymore. This comes from #1937, which made tuples be subtypes of empty interfaces like Any. The above type, (Any val | (None, None)) is now folded into Any val, and then fails to match with the tuple type because it doesn't have the right cardinality. The pattern matching code should be updated to allow empty interfaces to match with tuples of any cardinality.

[Theodus]

A possible solution to this may come from ponylang/rfcs#105

[jemc]

@Theodus - I don't think this is the same issue as the one addressed by that RFRFC.