Enable returning classes from MacroAnnotations (part 3)

[nicolasstucki]

Enable the addition of classes from a MacroAnnotation:

• Can add new class/object definitions next to the annotated definition

Special cases:

• An annotated top-level def, val, var, lazy val can return a class/object
  definition that is owned by the package or package object.

Related PRs:

• Follows Macro annotations class modifications (part 2)  #16454

[smarter]

Suggested change

	/** Generates a new module symbol with an associated module class symbol.
	/** Generates a new module symbol with an associated module class symbol,
	* this is equivalent to an `object` declaration in source code.

[smarter]

It looks like this change was not applied.

[smarter]

Unfortunately I think this isn't sufficient because package objects can be nested:

package foo {
  val x = 1
  package bar {
    val y = 2
  }
}

Instead, maybe the MemberDef case of transform should return a Thicket with the top-level classes, and we should add an extra case to transform to handle the package object module class itself, where we should also return a Thicket with the top-level classes

[nicolasstucki]

This use case was considered and works. I added tests for it in tests/run-macros/annot-add-global-class.

[nicolasstucki]

Note that after after post typer the tree is

package foo {
  package bar {
    val y = 2
  }
  val x = 1
}

This implies that nested classes are processed first and the buffer never overlaps and is emptied just after transforming the nested package.

[smarter]

This implies that nested classes are processed first and the buffer never overlaps and is emptied just after transforming the nested package.

This is subtle, so this precondition should be documented in the code (and ideally checked somewhere, in case it breaks)

[nicolasstucki]

I found cases where this precondition does not hold. I updated the implementation to handle such cases.

[smarter]

Otherwise LGTM.