summonInline/summonFrom does not work on field types

[propensive]

A proper test is required, but it seems like inline summoning does not work inside polymorphic lambdas, e.g. in

fields(value): [FieldType] =>
  field =>
    summonFrom:
      case given Show[FieldType] => 2
      case _                     => 4

The default case will always match, even if there are Show instances available for each field type.

I think this is a limitation of Scala, because even after inlining, FieldType is a abstract type parameter, and there's never a typeclass instance in-scope for exactly that type parameter.

We could mitigate this by first resolving an IArray of typeclass instances for each field type, and then accessing it by index (which is available in the polymorphic lambda.

[propensive]

It is worth checking whether making some of Wisteria's macros transparent inline helps.

[propensive]

From a similar test, it appears not to help, and the problem lies in the Scala compiler.

[propensive]

One possibility workaround could be to provide a new method, summonPoly, which will summon a specified typeclass corresponding to the particular field type. So instead of writing, summonInline[Show[fieldType]], you could write, summonPoly[Show]. It's not entirely clear whether this would work.