Scala 3 / Dotty support

[kalejami]

Hi,

the first RC for scala 3 was released. Any plans for scalaxb for supporting scala 3?

[kalejami]

Tried to compile against 3.0.0-RC1. Got some errors/migration warnings:

soap11_async.scala:47:26
[warn] 47 |      ftr map { s: String =>
[warn]    |                          ^
[warn]    |parentheses are required around the parameter of a lambda
[warn]    |This construct can be rewritten automatically under -rewrite -source 3.0-migration.

scalaxb.scala:703:24
[warn] 703 |          lookupSuccess(current, in) match {
[warn]     |                        ^^^^^^^
[warn]     |The conversion (ParserExt.this.ev : P => AnyElemNameParser.this.Parser[T]) will not be applied implicitly here in Scala 3 because only implicit methods and instances of Conversion class will continue to work as implicit views.

xmlprotocol.scala:2443:8
[error] 2443 |  trait [...]SoapBindings { this: scalaxb.Soap11ClientsAsync =>
[error]      |        ^
[error]      |missing requirement: self type scalaxb.Soap11ClientsAsync &
[error]      |  XMLProtocol.this.[...]SoapBindings of trait [...]SoapBindings does not conform to self type scalaxb.HttpClientsAsync

[Tristan Overney]

First official scala 3 release is out now: https://github.com/lampepfl/dotty/releases/tag/3.0.0

[Frank Thomas]

I tried scalaxb with Scala 3.2.2 today and could not reproduce the first two warnings @kalejami mentioned in #557 (comment). Unfortunately the third error is still there. After a closer look at the generated code, it seems that the error is caused by constructs like this:

object Test {
  trait HttpClients {}

  trait Soap11Clients { this: HttpClients => }

  trait FooSoapBindings { this: Soap11Clients => } // error

  // trait FooSoapBindings { this: Soap11Clients with HttpClients => } // ok
}

The complete error message with the -explain compiler option is:

[error] -- [E058] Type Mismatch Error: Test.scala:6:8
[error] 6 |  trait FooSoapBindings { this: Soap11Clients => } // error
[error]   |        ^
[error]   |missing requirement: self type Test.Soap11Clients & Test.FooSoapBindings of trait FooSoapBindings does not conform to self type Test.HttpClients
[error]   |of required trait Soap11Clients
[error]   |-----------------------------------------------------------------------------
[error]   | Explanation (enabled by `-explain`)
[error]   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
[error]   | I tried to show that
[error]   |   Test.Soap11Clients & Test.FooSoapBindings
[error]   | conforms to
[error]   |   Test.HttpClients
[error]   | but the comparison trace ended with `false`:
[error]   |
[error]   |   ==> Test.Soap11Clients & Test.FooSoapBindings  <:  Test.HttpClients
[error]   |     ==> glb(<notype>, <notype>)
[error]   |     <== glb(<notype>, <notype>) = <notype>
[error]   |     ==> Test.Soap11Clients  <:  Test.HttpClients
[error]   |     <== Test.Soap11Clients  <:  Test.HttpClients = false
[error]   |     ==> Test.FooSoapBindings  <:  Test.HttpClients
[error]   |     <== Test.FooSoapBindings  <:  Test.HttpClients = false
[error]   |   <== Test.Soap11Clients & Test.FooSoapBindings  <:  Test.HttpClients = false
[error]   |
[error]   | The tests were made under the empty constraint
[error]    -----------------------------------------------------------------------------

I don't know yet if it is expected that such constructs do not compile with Scala 3 or if it is a regression. This behaviour change is expected: scala/scala3#2467

One possible fix here is to extend the self type of FooSoapBindings with the self type of Soap11Clients as shown in the comment above (trait FooSoapBindings { this: Soap11Clients with HttpClients => }). The Scala 3 and Scala 2 compiler are both happy with this code.

[Frank Thomas]

One possible fix here is to extend the self type of FooSoapBindings with the self type of Soap11Clients as shown in the comment above (trait FooSoapBindings { this: Soap11Clients with HttpClients => }).

I've a branch with that change at develop...fthomas:scalaxb:topic/transitive-self-types. Changing the self type was easy but testing this here in scalaxb's build with Scala 3 seems to be the hard part.