Dealias quoted types when staging

[nicolasstucki]

This change improves the code generation of the contents of splices. In the splicing phase, we have to find all types that are defined in the quote but used in the splice. When there are type aliases, we can end up with several Type[T] for the different aliases of T. By dealiasing during the staging phase (just before splicing phase) we make sure that the splicer phase will only generate one Type[T].

By dealiasing we also optimize some situations where a type from outside a quote is inserted in the quoted code and then used in one of its splice through an alias. In this situation we can use the outer Type[T] directly.

Example

After staging the following code should get what is in the comments

import scala.quoted.*

def f[T](using t: Type[T])(using Quotes) =
  '{
    // @SplicedType type t$1 = t.Underlying 
    type T2 = T // type T2 = t$1
    ${

      val t0: T = ???
      val t1: T2 = ??? //  val t1: T = ???
      val tp1 = Type.of[T] // val tp1 = t
      val tp2 = Type.of[T2] //  val tp2 = t
      '{
        // @SplicedType type t$2 = t.Underlying 
        val t3: T = ??? // val t3: t$2 = ???
        val t4: T2 = ???  // val t4: t$2 = ???
      }
    }
  }

def g(using Quotes) =
  '{
    type U
    type U2 = U
    ${

      val u1: U = ???
      val u2: U2 = ??? //  val u2: U = ???

      val tp1 = Type.of[U] // val tp1 = Type.of[U]
      val tp2 = Type.of[U2]  // val tp2 = Type.of[U]
      '{
        val u3: U = ???
        val u4: U2 = ??? // val u4: U = ???
      }
    }
  }

[natsukagami]

lgtm!

[nicolasstucki]

Rebased, conflicts were automatically resolved.

[xuwei-k]

• 🤔 does not match '{ new String($x: Array[Byte]) } since 3.3.1-RC1 #17606