Cannot export extension methods from a generic type

[deusaquilus]

Compiler version

3.2.0

Minimized code

I'm not sure if this is a bug, a feature, or something else but it is impossible to export methods from a generic type. The important of this kind of feature is that if it existed, it would be (probably) be possible to replace Quill's implicit conversion Quoted[T] => T with implicit exports (so long as the exported method themselves are inline).

  class Wrapped[T](t: T) {
    def unwrap:T = ???
  }

  extension [T](t: Wrapped[T])
    def unwrapped: T = t.unwrap
    export unwrapped.*

Wrapped("blah").toUpperCase()

Output

[error] 27 |      PrintMac(Wrapped("blah").toUpperCase())
[error]    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
[error]    |value toUpperCase is not a member of org.deusaquilus.ImplicitConf.Wrapped[String], but could be made available as an extension method.

Expectation

It should recognize that .toUpperCase() exists on Wrapped[String] because it exists on String.

The functionality should be equivalent to this (which works):

  extension (t: Wrapped[String])
    def unwrapped: String = t.unwrap
    export unwrapped.*

  Wrapped("blah").toUpperCase()

Of if inline is used,

  extension (inline t: Wrapped[String])
    inline def unwrapped: String = t.unwrap
    export unwrapped.*

Wrapped("blah").toUpperCase()
// Which in the AST should be encoded as:
Wrapped("blah").unwrap.toUpperCase()

it should be equivalent to this:

extension (inline t: Wrapped[String])
    inline def unwrapped: String = t.unwrap
    inline def toUpperCase(): String = unwrapped.toUpperCase()

Wrapped("blah").toUpperCase()

Quill's unquotation Quoted[T] => T function specifically relies on this kind of pattern (i.e. the input t has to be directly spliced).

[odersky]

That will indeed not work. The exported members are chosen where the extension is defined. I don't see another possibility.

[deusaquilus]

@odersky I’m totally stuck then. Is there any other way I could potentially do automatic conversion of Quoted[T] => T without implicit conversion or in some way that is planned for long term support? Everything that is currently proposed wouldn’t work.

I need to somehow be able to implicitly convert Quoted[T] to T inside of Quill quote { … } blocks or the Quill API wouldn’t work.

My original thoughts were here.
https://contributors.scala-lang.org/t/proposed-changes-and-restrictions-for-implicit-conversions/4923/167?u=deusaquilus