Scala ASTs & Annotations

[Matthias Langer]

Hello everybody,

I'm already discussing this on scala-ide-dev, but I thought that it might be helpful to bring this issue to broader attention: I'm currently working on #1001793 (a minimal example can be found here), which is about classes used in expressions like "@AnAnnotation(classOf[Foo]) not being handled properly. The problem is, that for example "@AnAnnotation(classOf[Foo])" is represented by

Apply(
  Select(New(Ident(AnAnnotation)), termNames.CONSTRUCTOR), List(
    AssignOrNamedArg(
      Ident(TermName("value")), TypeApply(
        Ident(TermName("classOf")), List(Ident(TypeName("Foo")))
      )
    )
  )
)

The "Ident(TypeName("Foo"))" has neither a tpe nor a symbol, and so it is not handled by the traverser in scala.tools.refactoring.analysis.CompilationUnitDependencies, that would otherwise use these properties to build a "fakeSelectTree". So my questions are:

1) Why are tpe and symbol not set in this case?
2) How can I obtain these properties?

Thank you very much,
Matthias

[Eugene Burmako]

Iirc typedAnnotation does some unconventional tree manipulation to transform a Tree that represents an annotation into an Annotation. 

I wouldn't be surprised if the typechecker doesn't attribute the original tree, because originals (originals of TypeTrees and originals of Annotations alike) typically receive subpar treatment - they aren't immediately used by anyone, so they are considered second-class (at least, that's what I inferred from working with the code).

In scalahost [1], I obtain the corresponding instance of Annotation by inspecting `memberDef.symbol.annotation` and then correlate the original tree and the annotation to fill in the blanks. That's quite a hack, but I don't know of a better strategy.

[1] https://github.com/scalameta/scalahost/blob/4b991258b9de0137a74e7c8a1089f8832eeffefa/foundation/src/main/scala/org/scalameta/reflection/Ensugar.scala#L299

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[Matthias Langer]

Thanks a lot for your comment; I'll look at this at the coming weekend!

Matthias