Lambda capture types aren't inferred correctly

[SeanTAllen]

This issue comes from a short discussion with @sylvanc.

I have a method fun _index_for(id: SeqId): USize ?.

I add a lambda capture such as

{
        ()(_seq_id_to_incoming, index, id): Bool ? =>
        _seq_id_to_incoming(index)._1 <= id
}

where _seq_id_to_incoming is Array[(SeqId, (Producer tag, U64 val, U64 val))] ref.

The method no longer compiles.

I get an error...

Array[(U64 val, (Producer tag, U64 val, U64 val))] box is not a subtype of Array[(U64 val, (Producer tag, U64 val, U64 val))] ref: box is not a subtype of ref

This can be addressed by specifying a type for the capture such as:

{()(x: Array[(SeqId, (Producer tag, U64 val, U64 val))] box = _seq_id_to_incoming) Bool ? => ... }

However, in the end, the capture should use the type in the current context (val, box or ref) and not require the programmer to specify the type (which is redundant info at that point).

[jemc]

As discussed on the sync call, in expr/lambda, for fields that get captured, we need to use the type of how this sees the field. Right now it's not making a distinction between locals and fields.

[Praetonus]

@jemc Will #2168 fix this?

[jemc]

@Praetonus No, #2168 has not touched captures at all because they aren't part of the antecedent for the lambda. This would be a separate unit of work.