Add 'scalafmt' to the project

[satorg]

This PR:

• Adds sbt-scalafmt plugin.
• Creates .scalafmt.conf¹.
• Applies scalafmtSbt and +scalafmtAll commands².
• Creates .git-blame-ignore-revs to exclude commits with auto-reformatting and code auto-generation from git blame³.

---

1. The .scalafmt.conf mostly contains default settings with a few exceptions. The exceptions are to try minimizing further reformatting. In a case if some specific settings are more preferable for the project, let me know please – I am open to accommodate any configuration changes in here.
2. There's no manual formatting in the PR except the FreeGen2.scala file – the latter contains a lot of strings that turn into code and there are quite a lot of pretty long strings among them. Turns out scalafmt is not really great in such cases and can end up with weird formatting. Therefore, I added some manual reformatting so that after scalafmtSbt the reformatted code still looks pretty decent and readable. All the manually reformatted code is gathered in a single commit: fix formatting in FreeGen2.scala.
3. If this branch gets rebased then the content of the .git-blame-ignore-revs file has to be updated accordingly.

[jatcwang]

Thank you! I'll find an opportune time to run this and merge this in (to avoid conflicts in all other PRs)

[satorg]

@jatcwang , I've actualized the PR: rebased onto main, updated scalafmt version, re-applied formattings and .git-blame-ignore-revs

Let me know if you have any suggestions/concerns please.
Thank you!

[jatcwang]

Thanks @satorg. Originally I wanted to merge this after RC6 because I didn't know about .git-blame-ignore-revs. But now I think we can get this in before RC6. I have a change with quite some lines of changes I'm working on so I'll sort this one out after that 🙏

[satorg]

@jatcwang sure, np. Let me know please when I should update this PR to synchronize it with the upstream.

Also I think that once this PR gets settled in main, it would make sense to enforce scalafmt checks in CI/CD with a follow-up PR. I think I could take on that too – just let me know when to step in please. Thank you!

[jatcwang]

@satorg I agree about the enforcement in CI. Feel free to implement it as part of this PR :)

[satorg]

The PR is updated:

• Bump scalafmt up to v3.8.2
• Reformat with the new version
• add scalafmt checks to the CI workflow

[satorg]

@jatcwang , turns out the new Scalafmt version (3.8.2) started reformatting in multiline strings a little more aggressively.
It resulted in these changes: d8c3d1c

The changes don't break the build but look a bit awkward to me.
If you'd like to, I can either

• leave it as is and therefore add the commit to .git-blame-ignore-revs (not there yet), OR
• try to manually improve it (and keep outside of .git-blame-ignore-revs).

Wdyt?

[jatcwang]

Thanks @satorg. I agree it looks worse but happy to leave it as is, as that code will probably change as part of my work to fix #533

[satorg]

Looks like the CI failed because freeGen2 command updates auto-generated sources...

The problem here is that if I apply scalafmt to auto-generated sources and commit the changes (as it is done now in the PR), then freeGen2 reverts all the formatting and these files appear as uncommitted.

However, if I don't apply formatting to those files, then scalafmt checks will begin failing.

Perhaps the simplest way to resolve this conundrum could be excluding auto-generated files from scalafmt's scope. I'll try to accomplish it shortly.

[satorg]

The PR is updated:

1. Disable formatting in auto-generated files via adding // format: off to the beginning of each file.
2. Reformat again to apply the changes.

[satorg]

@jatcwang, hopefully, the CI issue has been resolved now.

[satorg]

@jatcwang , just in case – in regards to the auto-generated sources:

Perhaps, in makes sense to bring in an approach that is used in Cats for that:
https://github.com/typelevel/cats/blob/dd891334505b35e010a12da254924811de838c85/build.sbt#L114

I.e. all the auto-generated sources are written into directories like .../target/scala-2.13/src_managed/main and therefore never auto-formatted nor even committed to Git.

I feel, this PR is ready to go, so I would refrain from adopting this technique right in here. Just because doing that would require even more seemingly unrelated changes to this PR.

However, if you like such an approach and don't mind landing it in this repo, I could take on it in a follow-up PR.

[jatcwang]

@satorg Yes I do agree that we should use sourceGenerators. I did try it before when I was improving/fixing the code generation but I can't remember what was the show stopper 🤔 Perhaps I wanted to keep the generated code committed in git so people can look at it on github.

[jatcwang]

Big thanks for sorting this out @satorg!