[Issue-#89] Fix call of main methods (refer to the actual method owner not just the method)

[arainko]

Fixes #89

[arainko]

For an example like this one:

trait CommandCopy {
  @main
  def copy(@arg from: String, @arg to: String): Unit = ???
}

class Joined extends  CommandCopy {
  @main
  def test(@arg from: String, @arg to: String): Unit = ???

  val parser = ParserForMethods(this)
}

The issue manifests itself as a compiler crash:

[error] ## Exception when compiling 23 sources to /home/aleksander/repos/mainargs/out/mainargs/jvm/3.3.1/test/compile.dest/classes
[error] java.lang.AssertionError: assertion failed: missing outer accessor in class Joined
[error] scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
[error] dotty.tools.dotc.transform.ExplicitOuter$.dotty$tools$dotc$transform$ExplicitOuter$$$outerParamAccessor(ExplicitOuter.scala:237)
[error] dotty.tools.dotc.transform.ExplicitOuter$OuterOps$.loop$1(ExplicitOuter.scala:474)
[error] dotty.tools.dotc.transform.ExplicitOuter$OuterOps$.path$extension(ExplicitOuter.scala:483)

The code that gets generated looks like this:

(new ParserForMethods[Joined](
  MethodMains.apply[Joined](
    List.apply[MainData[Any, Joined]](
      MainData.create[Any, Joined](
        "copy",
        new main(main.$lessinit$greater$default$1, main.$lessinit$greater$default$2),
        List.apply[ArgSig](
          ArgSig.create[String, Joined](
            "from",
            new arg(arg.$lessinit$greater$default$1, arg.$lessinit$greater$default$2, arg.$lessinit$greater$default$3, arg.$lessinit$greater$default$4, arg.$lessinit$greater$default$5, arg.$lessinit$greater$default$6),
            None
          )(StringRead), 
          ArgSig.create[String, Joined](
            "to",
            new arg(arg.$lessinit$greater$default$1, arg.$lessinit$greater$default$2, arg.$lessinit$greater$default$3, arg.$lessinit$greater$default$4, arg.$lessinit$greater$default$5, arg.$lessinit$greater$default$6),
            None
          )(StringRead)),
        ((b: Joined, params: [A >: Nothing <: Any] =>> Seq[A][Any]) =>
          CommandCopy.this.copy(
            Seq.apply[Seq[Any]](params).apply(0).apply(0).asInstanceOf[String],
            Seq.apply[Seq[Any]](params).apply(0).apply(1).asInstanceOf[String]
          )
        )),
      MainData.create[Any, Joined](
        "test",
        new main(main.$lessinit$greater$default$1, main.$lessinit$greater$default$2),
        List.apply[ArgSig](
          ArgSig.create[String, Joined](
            "from",
            new arg(arg.$lessinit$greater$default$1, arg.$lessinit$greater$default$2, arg.$lessinit$greater$default$3, arg.$lessinit$greater$default$4, arg.$lessinit$greater$default$5, arg.$lessinit$greater$default$6),
            None
          )(StringRead),
        ArgSig.create[String, Joined](
          "to",
          new arg(arg.$lessinit$greater$default$1, arg.$lessinit$greater$default$2, arg.$lessinit$greater$default$3, arg.$lessinit$greater$default$4, arg.$lessinit$greater$default$5, arg.$lessinit$greater$default$6),
          None
        )(StringRead)),
        ((`b₂`: Joined, `params₂`: [A >: Nothing <: Any] =>> Seq[A][Any]) =>
          Joined.this.test(
            Seq.apply[Seq[Any]](`params₂`).apply(0).apply(0).asInstanceOf[String],
            Seq.apply[Seq[Any]](`params₂`).apply(0).apply(1).asInstanceOf[String]
          )
        ))), (() => Joined.this))
    ): ParserForMethods[Joined])

The issue itself stems from this:

((b: Joined, params: [A >: Nothing <: Any] =>> Seq[A][Any]) =>
          CommandCopy.this.copy(
            Seq.apply[Seq[Any]](params).apply(0).apply(0).asInstanceOf[String],
            Seq.apply[Seq[Any]](params).apply(0).apply(1).asInstanceOf[String]
          )
        )),

...that is, CommandCopy.this.copy is not actually a valid reference, we should use the b: Joined instance to call this method, i.e. the final tree should look like b.copy(...).

[lihaoyi]

@arainko thanks!

Could you isolate the semantic change and skip the autoformatting? We can autoformat in a separate PR if we want, but as is it makes this PR very hard to review

Also please update the PR description to include your understanding of the problem and the fix. Presumably you already have all that in your head, so better to write it down so future maintainers do not need to reverse engineer that understanding based on the code change

[arainko]

methodOwner is the actual instance of an object that owns the main methods to call

[arainko]

we first select the method using its Symbol on the owner and apply all of its parameter lists using .appliedToArgss as opposed to handrolling this tree

[lihaoyi]

Thanks @arainko! Can send me your bank transfer details to [email protected] and I can close out the bounty