Migrate to mill 0.12.5 and refactor mill scripts

[unlsycn]

This PR migrates to Mill 0.12.5 and refactors the Mill build scripts according to the recommended practice, which includes the following changes:

1. All modules except chisel have been split into separate package.mill in subfolders, and the publish flow has been separated into release.mill. build.mill contains only
   the utility traits and modules for easy reuse in packages and the chisel module, which Mill requires to be declared inside the top-level module.

2. Due to RootModule and Cross cannot be applied to the same module com-lihaoyi/mill#3693, CrossModule have been moved to {module}.cross (e.g. firrtl[2.13.15] => firrtl.cross[2.13.15] as a workaround, and it does not affect the directory hierarchy.

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• Internal or build-related (includes code refactoring/cleanup)

Desired Merge Strategy

• Squash: The PR will be squashed and merged (choose this if you have no preference).
• Rebase: You will rebase the PR onto master and it will be merged with a merge commit.

Release Notes

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
• Did you mark the proper milestone (Bug fix: 3.6.x, 5.x, or 6.x depending on impact, API modification or big change: 7.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you do one of the following when ready to merge:
  • Squash: You/ the contributor Enable auto-merge (squash), clean up the commit message, and label with Please Merge.
  • Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.

[sequencer]

I didn't expect introduced so many package.mill files, but anyway that looks good to me since it's recommended by the official mill.

But My key concern is package.mill always requires importing from the root build.mill, I understand this is because the cross dependencies of these modules. But is possible to only declare the dependencies requirements from each sub-folder and fill by the build.mill, like what my common.sc originally did.

The second nit is, I think the build.mill is still too much of things, please reduce it by splitting it into multiple files, I think the core build.mill should only maintain the publish flow.

[sequencer]

HasJextractGeneratedSources, you can add a panama.mill file storing it, In the future, a contribution point is push our Jextract + Panama as plugin to official mill plugin.

[seldridge]

Thanks for this.

I'm seeing both failures during the publish step [1], during nightly ci [2], and locally when switching branches. The switching branches I'm confused about, but this is acting like there is a stale file that it is trying to compile which was removed:

# ./mill 'chisel[2.13.15].test.testOnly' chiselTests.LayerSpec  
[372/372] ============================== chisel[2.13.15].test.testOnly chiselTests.LayerSpec ==============================
1 tasks failed
chisel[2.13.15].test.discoveredTestClasses java.lang.NoClassDefFoundError: chisel3/Placeholder
    java.base/java.lang.Class.getDeclaredMethods0(Native Method)
    java.base/java.lang.Class.privateGetDeclaredMethods(Class.java:3166)
    java.base/java.lang.Class.getDeclaredMethods(Class.java:2309)
    mill.testrunner.TestRunnerUtils$.$anonfun$matchFingerprints$1(TestRunnerUtils.scala:99)
    mill.testrunner.TestRunnerUtils$.$anonfun$matchFingerprints$1$adapted(TestRunnerUtils.scala:89)
    scala.collection.ArrayOps$.find$extension(ArrayOps.scala:694)
    mill.testrunner.TestRunnerUtils$.matchFingerprints(TestRunnerUtils.scala:89)
    mill.testrunner.TestRunnerUtils$.$anonfun$discoverTests$3(TestRunnerUtils.scala:64)
    geny.Generator$Mapped.$anonfun$generate$4(Generator.scala:288)
    geny.Generator$Mapped.$anonfun$generate$4(Generator.scala:288)
    geny.Generator$Filtered.$anonfun$generate$3(Generator.scala:281)
    geny.Generator$Mapped.$anonfun$generate$4(Generator.scala:288)
    os.walk$stream$$anon$2$$anon$3.visitFile(ListOps.scala:258)
    os.walk$stream$$anon$2$$anon$3.visitFile(ListOps.scala:239)
    java.base/java.nio.file.Files.walkFileTree(Files.java:2725)
    os.walk$stream$$anon$2.generate(ListOps.scala:239)
    geny.Generator$Mapped.generate(Generator.scala:288)
    geny.Generator$Filtered.generate(Generator.scala:281)
    geny.Generator$Mapped.generate(Generator.scala:288)
    geny.Generator$Mapped.generate(Generator.scala:288)
    geny.Generator.foreach(Generator.scala:49)
    geny.Generator.foreach$(Generator.scala:49)
    geny.Generator$Mapped.foreach(Generator.scala:286)
    geny.Generator.toBuffer(Generator.scala:132)
    geny.Generator.toBuffer$(Generator.scala:130)
    geny.Generator$Mapped.toBuffer(Generator.scala:286)
    geny.Generator.toVector(Generator.scala:140)
    geny.Generator.toVector$(Generator.scala:140)
    geny.Generator$Mapped.toVector(Generator.scala:286)
    geny.Generator.toSeq(Generator.scala:137)
    geny.Generator.toSeq$(Generator.scala:137)
    geny.Generator$Mapped.toSeq(Generator.scala:286)
    mill.testrunner.TestRunnerUtils$.$anonfun$discoverTests$2(TestRunnerUtils.scala:49)
    mill.api.AggWrapper$Agg$Mutable.$anonfun$flatMap$1(AggWrapper.scala:114)
    mill.api.AggWrapper$Agg$Mutable.$anonfun$flatMap$1$adapted(AggWrapper.scala:114)
    scala.collection.IterableOnceOps.foreach(IterableOnce.scala:619)
    scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:617)
    scala.collection.AbstractIterator.foreach(Iterator.scala:1303)
    mill.api.AggWrapper$Agg$Mutable.flatMap(AggWrapper.scala:114)
    mill.api.AggWrapper$Agg$Mutable.flatMap(AggWrapper.scala:76)
    mill.testrunner.TestRunnerUtils$.discoverTests(TestRunnerUtils.scala:47)
    mill.testrunner.DiscoverTestsMain$.$anonfun$main0$1(DiscoverTestsMain.scala:22)
    mill.util.Jvm$.inprocess(Jvm.scala:480)
    mill.testrunner.DiscoverTestsMain$.main0(DiscoverTestsMain.scala:30)
    mill.scalalib.TestModule.$anonfun$discoveredTestClasses$3(TestModule.scala:43)
java.lang.ClassNotFoundException: chisel3.Placeholder
    java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:476)
    mill.api.ClassLoader$$anon$1.findClass(ClassLoader.scala:27)
    java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:589)
    java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
    java.base/java.lang.Class.getDeclaredMethods0(Native Method)
    java.base/java.lang.Class.privateGetDeclaredMethods(Class.java:3166)
    java.base/java.lang.Class.getDeclaredMethods(Class.java:2309)
    mill.testrunner.TestRunnerUtils$.$anonfun$matchFingerprints$1(TestRunnerUtils.scala:99)
    mill.testrunner.TestRunnerUtils$.$anonfun$matchFingerprints$1$adapted(TestRunnerUtils.scala:89)
    scala.collection.ArrayOps$.find$extension(ArrayOps.scala:694)
    mill.testrunner.TestRunnerUtils$.matchFingerprints(TestRunnerUtils.scala:89)
    mill.testrunner.TestRunnerUtils$.$anonfun$discoverTests$3(TestRunnerUtils.scala:64)
    geny.Generator$Mapped.$anonfun$generate$4(Generator.scala:288)
    geny.Generator$Mapped.$anonfun$generate$4(Generator.scala:288)
    geny.Generator$Filtered.$anonfun$generate$3(Generator.scala:281)
    geny.Generator$Mapped.$anonfun$generate$4(Generator.scala:288)
    os.walk$stream$$anon$2$$anon$3.visitFile(ListOps.scala:258)
    os.walk$stream$$anon$2$$anon$3.visitFile(ListOps.scala:239)
    java.base/java.nio.file.Files.walkFileTree(Files.java:2725)
    os.walk$stream$$anon$2.generate(ListOps.scala:239)
    geny.Generator$Mapped.generate(Generator.scala:288)
    geny.Generator$Filtered.generate(Generator.scala:281)
    geny.Generator$Mapped.generate(Generator.scala:288)
    geny.Generator$Mapped.generate(Generator.scala:288)
    geny.Generator.foreach(Generator.scala:49)
    geny.Generator.foreach$(Generator.scala:49)
    geny.Generator$Mapped.foreach(Generator.scala:286)
    geny.Generator.toBuffer(Generator.scala:132)
    geny.Generator.toBuffer$(Generator.scala:130)
    geny.Generator$Mapped.toBuffer(Generator.scala:286)
    geny.Generator.toVector(Generator.scala:140)
    geny.Generator.toVector$(Generator.scala:140)
    geny.Generator$Mapped.toVector(Generator.scala:286)
    geny.Generator.toSeq(Generator.scala:137)
    geny.Generator.toSeq$(Generator.scala:137)
    geny.Generator$Mapped.toSeq(Generator.scala:286)
    mill.testrunner.TestRunnerUtils$.$anonfun$discoverTests$2(TestRunnerUtils.scala:49)
    mill.api.AggWrapper$Agg$Mutable.$anonfun$flatMap$1(AggWrapper.scala:114)
    mill.api.AggWrapper$Agg$Mutable.$anonfun$flatMap$1$adapted(AggWrapper.scala:114)
    scala.collection.IterableOnceOps.foreach(IterableOnce.scala:619)
    scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:617)
    scala.collection.AbstractIterator.foreach(Iterator.scala:1303)
    mill.api.AggWrapper$Agg$Mutable.flatMap(AggWrapper.scala:114)
    mill.api.AggWrapper$Agg$Mutable.flatMap(AggWrapper.scala:76)
    mill.testrunner.TestRunnerUtils$.discoverTests(TestRunnerUtils.scala:47)
    mill.testrunner.DiscoverTestsMain$.$anonfun$main0$1(DiscoverTestsMain.scala:22)
    mill.util.Jvm$.inprocess(Jvm.scala:480)
    mill.testrunner.DiscoverTestsMain$.main0(DiscoverTestsMain.scala:30)
    mill.scalalib.TestModule.$anonfun$discoveredTestClasses$3(TestModule.scala:43)

chisel3.Placeholder is something I have committed on a branch, but is now gone after changing and building on main.

Any idea what is going on?

Given that CI is actually broken, can this be blamelessly reverted while it gets figured out?

[sequencer]

Any idea what is going on?

I think it was blamed to random issue from mill side, may GitHub Action + mill don't work well together.

Given that CI is actually broken, can this be blamelessly reverted while it gets figured out?

I personally think it just only a small tweak on CI, ask @unlsycn fix this today, otherwise revert this.