Fix #20458: do not expose ClassInfo in quotes reflect widenTermRefByName

[jchyb]

Previously ClassInfo could easily be exposed with calls like TypeRepr.of[T].termRef.widenTermRefByName.

Fixes #20458

[dwijnand]

This doesn't seem like the right fix. The term reference for the Any companion object has an underlying Any companion module class (with nothing interesting). Widening the term to that class info is correct.

The original issue just seems invalid. Don't call asType on a term type.

Perhaps the user wanted to call .namedType, which might be a useful addition to the Quotes API:

    def namedType(using Context): NamedType =
      if (isType) typeRef else termRef

[jchyb]

I see where you are coming from, but there is a conscious effort in the design of the quotes reflect API to never expose ClassInfo to users. At this point, there are no tools there for users to be able to work with ClassInfo. Here, since ClassInfo is not supported, we will instead return a TermRef reference to a symbol of that class (which users can work on and analyze with the tools provided to them).

Additionally, calling any.termRef (like in the minimization) will give us TermRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any), any.termRef.asType will also work, as TermRef is a TypeRepr (in the quotes reflect API), which can be converted into a Type. The issue here is specifically about the unexpected ClassInfo crashing the compiler, as it was not supposed to be exposed here. Even outside of that I really do not think we should at any point allow to return an incorrect type from a quotes reflect API method (widenTermRefByName is supposed to return TypeRepr, but ClassInfo is not that).

About the original issue minimization itself, usually with the typeRepr.widen methods (like widen, widenByName, and widenTermRefByName), we would expect them to either widen, or if that is not possible, stay the same. Because of this, they can be a little overused, like what I imagine happened in the original issue minimisation (after this fix, in practice, the type stays the same - TermRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any), since it is not possible to widen it in the quotes reflect API).

[dwijnand]

In processing case _: Any I'm not sure why you want to end up with the term reference to the Any object. The user code just doesn't seem right to me.

The issue here is specifically about the unexpected ClassInfo crashing the compiler, as it was not supposed to be exposed here. Even outside of that I really do not think we should at any point allow to return an incorrect type from a quotes reflect API method (widenTermRefByName is supposed to return TypeRepr, but ClassInfo is not that).

I could get behind something like that, but that's not what your patch is doing.