Support a way to run Scalafmt on the build files

[lolgab]

Is there a way to lint the build files?
In my projects I usually define a target like:

def buildSources = T.sources(os.pwd / "build.sc")

And then I run Scalafmt with:

mill mill.scalalib.scalafmt.ScalafmtModule/reformatAll buildSources

It would be nice if there was a way to access the build sources without having to define them manually.

[lefou]

Currently there is no such target, but I think it is a good idea to have it. It should probably also contain all included files, which we need also in other places like e.g. IDE/BSP support.

[lefou]

I opened a RFC which might affect this issue.

• Consolidating `Tasks` and `Task`s as command parameters (RFC) #1857

[lefou]

I opened two PR to support running targets on meta-builds (#2719) and to look up the .scalafmt.conf in the current working directory (#2720). After merging both, the following should work to format the build.sc and it's included files:

$ mill --meta-level 1 mill.scalalib.scalafmt.ScalafmtModule/reformatAll sources
Formatting 3 Scala sources
parsed config (v3.7.10): /home/lefou/work/opensource/mill/.scalafmt.conf

[lolgab]

Thank you very much for this @lefou! 👏👏👏👏