Hover on annotation in Scala just shows the Ref it's on

[ckipp01]

Describe the bug

Having a minimal piece of code like this:

import scala.annotation.nowarn

@no@@warn
class Foo

When you attempt to do a hover on @nowarn you actually get the TypeRef of Foo shown instead of the information about @nowarn.

The tree that is returned here for this pos is:

TypeDef(
  name = Foo,
  rhs = Template(
    constr = DefDef(
      name = <init>,
      paramss = List(List()),
      tpt = TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Unit)],
      preRhs = Thicket(trees = List())
    ),
    parentsOrDerived = List(
      Apply(
        fun = Select(
          qualifier = New(
            tpt = TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,module class lang)),class Object)]
          ),
          name = <init>
        ),
        args = List()
      )
    ),
    self = ValDef(name = _, tpt = Thicket(trees = List()), preRhs = Thicket(trees = List())),
    preBody = List()
  )
)

I actually stumbled onto this because of something else (trying to understand when I'd see the Annotated tree) and then realizing I could never see it when testing with untyped trees or typed ones. Then I looked at how Metals would show this, and it also doesn't show the annotation. Is this actually an updates issue that Annotated is never in the tree?

Expected behavior

I'd expect that this show the signature and scaladocs for @nowarn instead of for Foo.

Operating system

macOS

Editor/Extension

Nvim (nvim-metals)

Version of Metals

0.11.1+47-66ea31ef-SNAPSHOT

Extra context or search terms

No response

[tgodzik]

I dug into that recently actually and it seems that the annotation tree is in the type.

I did fix an issue related to it in https://github.com/lampepfl/dotty/pull/13834/files

[rochala]

This was caused by a crash:

dotty.tools.dotc.ast.Trees$Tree.tpe(Trees.scala:72)
        dotty.tools.pc.utils.MtagsEnrichments$.tryTail$1(MtagsEnrichments.scala:262)
        dotty.tools.pc.utils.MtagsEnrichments$.expandRangeToEnclosingApply(MtagsEnrichments.scala:279)
        dotty.tools.pc.HoverProvider$.hover(HoverProvider.scala:51)
        dotty.tools.pc.ScalaPresentationCompiler.hover$$anonfun$1(ScalaPresentationCompiler.scala:326)

It was already solved by accident with scala/scala3#19488

It will also be backported in the future to LTS. Also this may hide the underlying problem so it may need a bit more investigation.