Add support for Scala 3

[anatoliykmetyuk]

This PR is a blocker for scala/scala3#9917. We have a bunch of libraries compiled with Mill in the Dotty community build, and we'd rather not disable them during the artefacts naming change.

@lihaoyi what's the policy on the Mill nightly builds? How soon will we be able to use this change in a nightly build once this is merged?

[anatoliykmetyuk]

Travis fails with:

[78/1994] publishVersion 
fatal: 7617235c325bd0ed51922b6f8535a8b1e6869034 is not a valid 'commit' object
fatal: bad object 7617235c325bd0ed51922b6f8535a8b1e6869034
1 targets failed

Any idea what causes it?

[joan38]

We need to rerun CI. I usually git reset HEAD~ and commit/push again since I don't have the rights to rerun.

[lefou]

Unfortunately, reruning the Travis-CI jobs won't resolve the issue. Only chance is to rebase the branch on latest master.

P.S. I'm working on a GitHub Actions setup to overcome these limitations.

[lefou]

Seeing this test failure in the CI logs:

X mill.scalalib.HelloWorldTests.dotty213 399ms 
  scala.MatchError: Left(Failure(
  Resolution failed for 1 modules:
  --------------------------------------------
    org.scala-lang.modules:scala-xml_0.18:1.2.0 
  	not found: /home/travis/.ivy2/local/org.scala-lang.modules/scala-xml_0.18/1.2.0/ivys/ivy.xml
  	not found: https://repo1.maven.org/maven2/org/scala-lang/modules/scala-xml_0.18/1.2.0/scala-xml_0.18-1.2.0.pom
  ,None)) (of class scala.util.Left)
    mill.scalalib.HelloWorldTests$.$anonfun$tests$250(HelloWorldTests.scala:960)
    mill.scalalib.HelloWorldTests$.$anonfun$tests$250$adapted(HelloWorldTests.scala:959)
    mill.scalalib.HelloWorldTests$.workspaceTest(HelloWorldTests.scala:314)
    mill.scalalib.HelloWorldTests$.$anonfun$tests$249(HelloWorldTests.scala:320)

[anatoliykmetyuk]

Unfortunately, reruning the Travis-CI jobs won't resolve the issue. Only chance is to rebase the branch on latest master.

I believe my branch is already on top of the latest master. I'm trying the trick with git reset HEAD~, but the past two times it didn't work...

[lefou]

Unfortunately, reruning the Travis-CI jobs won't resolve the issue. Only chance is to rebase the branch on latest master.

I believe my branch is already on top of the latest master. I'm trying the trick with git reset HEAD~, but the past two times it didn't work...

Tests are running, some are already green. No need to rebase again (for now). I restarted the second, which fails alsmost any second time but outside of our control.

[anatoliykmetyuk]

Is there a chance of this getting reviewed & merged soon? Scala 3.0.0-M1 release is blocked by this PR since we are using Mill projects in our community build. /cc @lihaoyi @lefou

[lefou]

Looks good to me. Tests are green. Merging now...

Thank you!

[anatoliykmetyuk]

Thanks, @lefou! Will it be available somewhere as a nightly so that we can use it?

[lefou]

Yes, see http://www.lihaoyi.com/mill/#development-releases.