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.