ExplicitResultTypes: backquote types when needed

[danicheg]

This fixes #1219. I was struggled with a working fix for all type-symbols but didn't succeed. I'd be glad to get help in moving this onward.

[bjaglin]

Thanks for the PR, that's already a step forward! I didn't have a look at it yet, but can you maybe elaborate what challenges you faced with other type symbols? You can open a draft PR with failing tests as a starting point, it's always valuable for others to pick up where you left off.

[mlachkar]

Hello!
thanks for your contribution.
This code should not be outside of the method g.shortType(preProcessed, history), because this method is recursive.
There is a test example that would break with your fix:

object ExplicitResultTypesBackQuote {
  case class `Foo-Bar`(i: Int)
}

object TestBackQuote {
  val foobar = ExplicitResultTypesBackQuote.`Foo-Bar`(42)
}

it would output:

object TestBackQuote {
  val foobar: `ExplicitResultTypesBackQuote.Foo-Bar` = ExplicitResultTypesBackQuote.`Foo-Bar`(42)

}

It's tempting to fix the issue, by taking the shortType and pattern match on it, but it can't work, because you need to do that recursively as it's done in the method def shortType. You can check this PR, where we discussed how to fix issues on this rule #1495

If you have any question, don't hesitate!

[danicheg]

@mlachkar Thanks for the review. I moved impl to ScalafixGlobal#shortType, so now traits and nested case classes/traits support backticks.

[bjaglin]

Thanks for the iteration, it's shaping up! Don't forget to run ./bin/scalafmt.

[danicheg]

Thank you for your review, @bjaglin!

[tgodzik]

Thanks for the great work @danicheg ! I managed to backport the changes to Metals also https://github.com/scalameta/metals/pull/3829/files