Scala3 style imports

[satorg]

Removes runner.dialectOverride.allowStarWildcardImport = false from .scalafmt.conf then applies scalafmtAll.

UPD.: also re-enables "-Xsource:3" for algebraCore and algebraLaws.

[satorg]

Looks like it is failing because in #4478 the "-Xsource:3" option was disabled for algebraCore and algebraLaws with the following commit message:

Workaround binary-compatibility issues

🤔

[satorg]

Hi @armanbilge,
Do you remember by chance what was the issue with "-Xsource:3" in #4478? I re-enabled it in this PR and all the checks seem passing. Do you think it is safe to leave "-Xsource:3" enabled then?
Thanks!

[armanbilge]

Huh, that surprises me. I do have a vague recollection of the issue, I believe it related to some methods that were lacking an explicit type, and under -Xsource:3 the type inference works differently, so this would break binary compatibility. And adding an explicit type is impossible, because the binary-compatible explicit type is different for Scala 2 and Scala 3.

If CI is happy, it's probably okay now (?) but it would be really good to understand why ...

[satorg]

Yes, it is puzzling quite a bit.. I'm going to convert this Draft to a complete PR and let it stay that way for a while.
Just in order to collect more thoughts and opinions on that and allow some time for pondering all the implications.

[satorg]

@danicheg @armanbilge does it make sense to proceed with this, wdyt? I personally feel, yes, it does, since it could be yet another step towards Scala3 syntax migration, but I wouldn't like to run ahead of the train anyway.

Just to keep things connected: there's another PR (yet draft) in the same direction: #4673 by @xuwei-k, which I'd really love to have merged once it's ready.

[danicheg]

I think this requires an accepted tactic among the team. Currently, we have a coherent Scala 2 codebase with few provisos. Personally, I'm in favour of keeping that order of things as long as possible. Cats is a Scala 2 project cross-compiling to Scala 3. I don't think braiding the syntaxes of these two languages would make sense. But that's an interesting approach, indeed. What if they invented a strategy to turn Scala 2 syntax into Scala 3 one day?

[satorg]

What if they invented a strategy to turn Scala 2 syntax into Scala 3 one day?

Hmm.. I don't know. For now it looks like Scala3 is moving in the opposite direction – it keeps gradually deprecating Scala2 style syntaxes from version to version.

My point is that if Cats already has -Xsource:3 enabled by default and rewrite.scala3.convertToNewSyntax = true configured in .scalafmt.conf, then why to hold on imports? Imo, recent versions of Scala2 were equipped with -Xsource:3 for the sake of gradual migration rather than do-everything-at-once approach.

[armanbilge]

I think this is the right direction. It seems to me that a lot of the syntax changes from 2->3 are addressing various "warts" (see also #4673). I think it's great that these improvements are being backported to Scala 2.

My only hesitation with this PR is trying to understand what was breaking bincompat previously, and why it no longer is, see #4677 (comment). I guess it shouldn't be a blocker, I would just feel better knowing why 😅

[joroKr21]

Could be about different type inference when overriding a method from the superclass