Compiler MegaPhase isn't tranforming annotation trees and named arguments

[soronpo]

I noticed while working on a compiler plugin that the MegaPhase isn't transforming annotation trees and NamedArg.

Compiler version

v3.7.2

Minimized code

No particular minimization.

Output

No particular output.

Expectation

The transformation must also pass the annotation trees, and there should be transformNamedArg and prepareForNamedArg methods in the MegaPhase.

[som-snytt]

transformOther in https://github.com/scala/scala3/blob/3.7.2/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala#L215

such as NamedArg https://github.com/scala/scala3/blob/3.7.2/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala#L246

traverseAnnotations https://github.com/scala/scala3/blob/3.7.2/compiler/src/dotty/tools/dotc/transform/CheckUnused.scala#L202

I don't know if the "other" category is optimal or represents trees that are eliminated early.

[soronpo]

OK, so you say that MegaPhase shouldn't be including these transformations by default?

[Gedochao]

@sjrd

[sjrd]

For annotation trees, this is definitely expected. Most compiler phases do not want to transform annotation trees, so they are not transformed by default.

Judging by the existing phases that manipulate NamedArg, I guess this is also working as designed. I am less sure that it is the right call in that case. We could consider changing the default for that one, if there is sufficient evidence that it is better that way.