Fix for macro annotation that resolves macro-based implicit crashing the compiler

[pweisenburger]

When (1) macro-annotating a class or object nested in another class or object and (2) the annotation macro tries to summon an implicit value using Implicits.search and (3) the implicit search needs to expand a given macro, the compiler crashes with:

Failed to evaluate macro.
  Caused by class dotty.tools.dotc.CompilationUnit$SuspendException

I found that the reason for the crash is macroDependencies returning locally defined variables, which, I believe, it should not. In particular it returns a list containing $anonfun for trees of the following shape that appear when resolving implicit macros:

{
  def $anonfun(using contextual$1: scala.quoted.Quotes): scala.quoted.Expr[<type for implicit search>] =
    <given macro for implicit value>(contextual$1)
  closure($anonfun)
}

This PR skips over such Closure nodes, which should be the correct behavior. Not sure if there are other cases that macroDependencies handles incorrectly and that should be fixed ...

[hamzaremmal]

Hey, to fix the CI run, can you rebase your work on the latest commit in main ?

[pweisenburger]

I rebased on the main branch.

[hamzaremmal]

Hi, I've been investigating this for the past few days and I'm not sure why the closure is created. I wasn't able to reproduce the behavior with other constructs. I'm still looking into it and I will answer back here when I have a final answer.

[pweisenburger]

Thanks! 🙂

I assumed this was normal behavior for expanding macro givens, as at some point you probably want a context function Quotes ?=> T (to inject the implicit Quotes argument), hence the given is eta-expanded, hence the closure. But this guess could be wrong ...

[hamzaremmal]

@pweisenburger Sorry for the very late review 😅 , I had some weird behaviour in the compiler when I was playing with your changes, everything should be fixed now !