Dotty pickles type trees of | and & to applied type tree of fictional symbols

[bishabosha]

minimized code

Because intersection types and union types are pickled in TASTy to applied type trees of imaginary types scala.& and scala.|, all implementations must intercept these names, when they could be reified as the intrinsic types that they are.

trait A
trait B

type AwithB = A with B // pickles to scala.&[A,B]
type AandB  = A & B    // pickles to scala.&[A,B]

type AorB = A | B      // pickles to scala.|[A,B]

expectation

maybe new tags ANDtpt and ORtpt

[smarter]

These tags were actually removed in #5935 but it might make sense to bring them back, the main benefit of #5935 is that it simplifies dotty internals, but that doesn't mean we can't represent & and | explicitly in Tasty itself. Also I think that this PR removed all the logic in tasty-reflect for constructing & and | types which is something people actually want to do in macros (cf. https://contributors.scala-lang.org/t/union-types-and-generalisations/3820/6?u=smarter) /cc @nicolasstucki

[bishabosha]

I took a stab at this, but preserving the positions for the idempotency test seems hard

[smarter]

do you mean that the positions are lost somewhere ?

[bishabosha]

So I pickled just the type arguments of the AppliedTypeTree, with ANDtpt length tag, then when I reconstruct an AppliedTypeTree from the args and a ref(defn.andType), the range was off by one

[bishabosha]

so I need to preserve the position of the tycon that is thrown away

[smarter]

Right, the typetree itself should have a position, but I don't think that's any different from other type trees.

[smarter]

Or do you mean the position of & itself in A & B ? I don't think that one matters for anything (you can't rename & to something else) so preserving it is not important.

[bishabosha]

$ diff before-pickling.txt after-pickling.txt
53c53
<                 ):scala.quoted.Expr[$t0 & T2@tests/pos/i7264c.scala<113..116>]@tests/pos/i7264c.scala<113..116>@
---
>                 ):scala.quoted.Expr[$t0 & T2@tests/pos/i7264c.scala<114..116>]@tests/pos/i7264c.scala<113..116>@