build.mill files compiled by Scala 3

[bishabosha]

This is work in progress to fix #3152

Numerous fixes were also needed to com-lihaoyi/mainargs, com-lihaoyi/sourcecode, and com-lihaoyi/mill-moduledefs

With the current state, only 1 example/integration tests is still failing:

• integration.feature[plugin-classpath].local

known TODOs:

• Discover macro
• Applicative macro
• Caller macro
• Cross.Factory macro
• EnclosingClass macro
• Task macros
• Cacher macro
• Moduledefs compiler plugin (override inferrence)
• All core Mill modules compile with Scala 3.5.0
• Fix Zinc reporter patch linenumbers of build scripts
• Check that bytecode analyzers work with Scala 3
• cleanup library dependency conflicts
• Support new Scala 3 syntax in build.sc files
• Fix BSP reporter linenumbers for build scripts (Zinc reporter forwards to bsp)
• Cleanup compiler warnings for outdated syntax

known incompatibilities:

• can't use ExplicitResultTypes scalafix rule - need to upgrade mill-scalafix
• Cross.scala uses the new quoted type syntax which scalafmt crashes on, (and version is frozen) so skip the file upgraded Scalafmt so not skipped anymore
• skipping Mima currently due to 1000s of errors (perhaps we should generate filters?)
• filtered one flaky test from example.thirdparty[mockito]
• filtered out integration.feature[plugin-classpath] due to third party plugin dep

[lihaoyi]

Thanks @bishabosha ! Lets get your mainargs changes landed, that way we can cut a release and you can test your WIP in CI

[lefou]

+1 for switching over to using directives!

• Support an alternative to $-imports #3062

[bishabosha]

@lihaoyi see com-lihaoyi/mainargs#148

[bishabosha]

[Edit: after switching to depending on mainargs 0.7.2] in https://github.com/com-lihaoyi/mill/actions/runs/10418081276/job/28853542122?pr=3369 you can see integration tests like example/tasks/6-workers/local passing

[bishabosha]

Rebased and included the new mill-moduledefs 0.11.0-M1

[bishabosha]

@lihaoyi just recording here that the mockito third party test can be flaky (specifically StubbingLookupListenerCallbackTest.add_listeners_concurrently_sanity_check):

https://github.com/mockito/mockito/blob/1e337ed703ce2b78ce9ea40ff8b8c645f8219cf2/src/test/java/org/mockitousage/debugging/StubbingLookupListenerCallbackTest.java#L199-L202

as seen in the CI run https://github.com/com-lihaoyi/mill/actions/runs/10909315276/job/30277476457?pr=3369#step:9:4941

[lihaoyi]

merged in latest main and got most tests passing; there are still some stragglers but nothing blocking.

The main thing still missing is proper support for corrected line-numbers and file-names. This kinda-sorta works in certain cases and not others, e.g. sourcecode.Line and sourcecode.File gives the wrong values still

[bishabosha]

@lihaoyi maybe you can cherry-pick my plugin fixes from https://github.com/bishabosha/mill/tree/scala3-build-sc-reintroduce-linenumbers and https://github.com/bishabosha/mill/tree/scala3-build-sc-reintroduce-linenumbers-with-dotc-patch

From Scala 3.6.2 the backend will accept the line number fix from a plugin without needing hacks

Also I heard that the restriction on pre-typer plugins could potentially be lifted for non .scala files, if one were to make the PR to scala/scala3 - unsure if .sc still applies

[lihaoyi]

All tests are green. Probably more polish to do esp.w.r.t. error locations, and will need a few more rebases, but hopefully not too many before we merge this in January

[lihaoyi]

Seems like some of the new ./mill -w 'integration.invalidation[codesig-subfolder].fork.test' mill.integration.CodeSigSubfolderTests.simple tests are failing on Scala 3. Probably just need to adjust some of the codesig heuristics we added in #4116 to be compatible with Scala 3

[lihaoyi]

Seems like some lazy val initialization code in the <clinit> static initializer changes when you rename lazy vals in Scala 3