FunctionTypeAnnotations should not require names for parameters, but do today

[jakemac53]

Today the ParameterDeclaration class requires a name (it extends from Declaration). This type is then used in the FunctionTypeAnnotation class to represent the parameters, but in that context they don't require a name.

The name is also an Identifier, which probably doesn't make sense in the context of a function type either, it isn't anything you can reference afaik.

Proposal

Make a new class Parameter which does not extend from Declaration, and has all the fields that ParameterDeclaration has. The ParameterDeclaration class would now implement both Declaration and Parameter. And we would add an additional class FunctionTypeParameter which would implement Parameter, and also have a String? get name field, instead of the Identifier get name field on Declaration.

cc @scheglov @johnniwinther

[scheglov]

Another alternative design could be to have separate FunctionTypePositionalParameter with String? get name and FunctionTypeNamedParameter with String get name. And then we would not need isNamed. Currently we imply that isNamed means also that get name return non-nullable String. But with types we could prove it.

[jakemac53]

True, I worry a bit that it doesn't map very directly to ParameterDeclaration which does not have that distinction. But I could also create NamedParameterDeclaration and drop isNamed from that api?

[scheglov]

Yes, in my opinion NamedParameterDeclaration also would be nice, and consistency as well.

In the analyzer it might be slightly less convenient though, because we have another layer of options - default parameters, field formal parameters, super formal parameters, all of which can be [required, optional] * [positional, named].

[johnniwinther]

I would go for the original proposal.

[jakemac53]

I generally like having a simpler class hierarchy, so I think it will just opt for the original proposal. It isn't as ideal for named parameters in function types, but I think that is ok.

[scheglov]

Sounds good.