Extended `mill init` to support an existing Maven project #3756

ajaychandran · 2024-10-16T16:40:02Z

This PR adds support to convert a Maven build to Mill by generating Mill build file(s) from POM file(s).
The generator output should be considered scaffolding and will likely require edits to complete conversion.

Capabilities

The conversion

handles deeply nested modules
captures project metadata
configures dependencies for scopes:
- compile
- provided
- runtime
- test
configures testing frameworks:
- JUnit 4
- JUnit 5
- TestNG
configures multiple, compile and test, resource directories

Limitations

The conversion does not support:

build extensions
build profiles
plugins, other than maven-compiler-plugin

Future work

Add support for:

Resolves #3449.

lihaoyi · 2024-10-17T05:19:38Z

For a multi-module project the package.mill files are generated for sub-modules but they are not recognized by Mill. See integration test MillInitMavenTests for details.

@ajaychandran for package.mill files to be recognized, you need the magic import import $packages._ in the top-level `build.mill

Should a new task be defined for provided dependencies? JavaModule.providedIvyDeps?

IIRC provided dependencies correspond to Mill's compileIvyDeps

ajaychandran · 2024-10-17T17:01:25Z

@lihaoyi Thanks for the tips.

Now, the conversion fails with

super-csv/package.mill:7:71: type BaseMavenModule is not a member of object build_.package_

I am not sure why this is happening. Could it be because build.mill has a package RootModule (for publishing the Maven parent module)?

Below is the output of generatedScriptSources.
build.mill

package build_
import _root_.{build_ => $file}
import build_.{package_ => build}
import _root_.mill.runner.MillBuildRootModule
@_root_.scala.annotation.nowarn
object MillMiscInfo extends mill.main.RootModule.Info(
  Vector("/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.14/scala-library-2.13.14.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/mill-moduledefs_2.13/0.11.1/mill-moduledefs_2.13-0.11.1.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scalameta/scalafmt-dynamic_2.13/3.8.3/scalafmt-dynamic_2.13-3.8.3.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/modules/scala-xml_2.13/2.3.0/scala-xml_2.13-2.3.0.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/io/github/alexarchambault/windows-ansi/windows-ansi/0.0.5/windows-ansi-0.0.5.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/io/get-coursier/interface/1.0.19/interface-1.0.19.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/mainargs_2.13/0.7.6/mainargs_2.13-0.7.6.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/requests_2.13/0.9.0/requests_2.13-0.9.0.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/ch/qos/logback/logback-classic/1.5.7/logback-classic-1.5.7.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/org/jgrapht/jgrapht-core/1.4.0/jgrapht-core-1.4.0.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/guru/nidi/graphviz-java-min-deps/0.18.1/graphviz-java-min-deps-0.18.1.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/com/lihaoyi/sourcecode_2.13/0.4.0/sourcecode_2.13-0.4.0.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/net/java/dev/jna/jna/5.14.0/jna-5.14.0.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/net/java/dev/jna/jna-platform/5.14.0/jna-platform-5.14.0.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/com/eed3si9n/jarjarabrams/jarjar-abrams-core_2.13/1.14.0/jarjar-abrams-core_2.13-1.14.0.jar", 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"/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/com/github/luben/zstd-jni/1.5.5-10/zstd-jni-1.5.5-10.jar", "/home/aj/.cache/coursier/v1/https/repo1.maven.org/maven2/org/apache/xbean/xbean-reflect/3.7/xbean-reflect-3.7.jar", "/home/aj/github/ajaychandran/mill/out/runner/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/runner/client/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/server/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/codesig/compile.dest/classes", "/home/aj/github/ajaychandran/mill/runner/linenumbers/resources", "/home/aj/github/ajaychandran/mill/out/runner/linenumbers/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/bsp/buildInfoResources.dest", "/home/aj/github/ajaychandran/mill/out/bsp/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/scalanativelib/worker-api/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/scalanativelib/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/scalajslib/worker-api/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/scalajslib/buildInfoResources.dest", "/home/aj/github/ajaychandran/mill/out/scalajslib/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/kotlinlib/worker/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/kotlinlib/buildInfoResources.dest", "/home/aj/github/ajaychandran/mill/out/kotlinlib/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/testrunner/entrypoint/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/testrunner/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/scalalib/api/buildInfoResources.dest", "/home/aj/github/ajaychandran/mill/out/scalalib/api/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/resolve/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/util/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/client/buildInfoResources.dest", "/home/aj/github/ajaychandran/mill/out/main/client/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/api/buildInfoResources.dest", "/home/aj/github/ajaychandran/mill/out/main/api/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/define/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/eval/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/buildInfoResources.dest", "/home/aj/github/ajaychandran/mill/out/main/compile.dest/classes", "/home/aj/github/ajaychandran/mill/scalalib/resources", "/home/aj/github/ajaychandran/mill/out/scalalib/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/idea/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/main/init/exampleList.dest", "/home/aj/github/ajaychandran/mill/out/main/init/compile.dest/classes", "/home/aj/github/ajaychandran/mill/out/dist/runClasspath.dest"),
  "/home/aj/github/ajaychandran/mill/out/integration/feature/init/local/testOnly.dest/sandbox/run-2",
  "/home/aj/github/ajaychandran/mill/out/integration/feature/init/local/testOnly.dest/sandbox/run-2/out",
  "/home/aj/github/ajaychandran/mill/out/integration/feature/init/local/testOnly.dest/sandbox/run-2"
)
import MillMiscInfo._

//MILL_ORIGINAL_FILE_PATH=/home/aj/github/ajaychandran/mill/out/integration/feature/init/local/testOnly.dest/sandbox/run-2/build.mill
//MILL_USER_CODE_START_MARKER


import mill._
import mill.javalib._
import mill.javalib.publish._
import _root_._

trait BaseMavenModule extends MavenModule with PublishModule {

  override def pomSettings = PomSettings(
    s"""Super CSV parent project""".stripMargin,
    "Super CSV",
    "https://github.com/super-csv/super-csv",
    Seq(
      License("Apache License, Version 2.0", "Apache License, Version 2.0", "http://www.apache.org/licenses/LICENSE-2.0.html", false, false, "repo")
    ),
    VersionControl(
      Option("https://github.com/super-csv/super-csv"),
      Option("scm:git:[email protected]:super-csv/super-csv.git"),
      Option("scm:git:[email protected]:super-csv/super-csv.git"),
      Option("v2.4.0")
    ),
    Seq(
      Developer("kbg", "Kasper Graversen", "", Option(null), Option(null)),
      Developer("jamesbassett", "James Bassett", "", Option(null), Option(null)),
      Developer("ddv36a78", "Dominique De Vito", "", Option(null), Option(null))
    )
  )

  override def publishVersion = "2.4.0"

  trait Tests extends TestModule.Junit4 with MavenTests {

    override def defaultCommandName() = "test"

    override def ivyDeps = super.ivyDeps() ++ Agg(
      ivy"com.novocode:junit-interface:0.11"
    )
  }
}

abstract class package_  extends RootModule with BaseMavenModule {

  override def artifactName = "super-csv-parent"

  override def pomPackagingType = PackagingType.Pom
}

object package_ extends package_ {
  final lazy val `super-csv-distribution`: _root_.build_.`super-csv-distribution`.package_.type = _root_.build_.`super-csv-distribution`.package_ // subfolder module reference
final lazy val `super-csv-dozer`: _root_.build_.`super-csv-dozer`.package_.type = _root_.build_.`super-csv-dozer`.package_ // subfolder module reference
final lazy val `super-csv-joda`: _root_.build_.`super-csv-joda`.package_.type = _root_.build_.`super-csv-joda`.package_ // subfolder module reference
final lazy val `super-csv`: _root_.build_.`super-csv`.package_.type = _root_.build_.`super-csv`.package_ // subfolder module reference
final lazy val `super-csv-java8`: _root_.build_.`super-csv-java8`.package_.type = _root_.build_.`super-csv-java8`.package_ // subfolder module reference
final lazy val `super-csv-benchmark`: _root_.build_.`super-csv-benchmark`.package_.type = _root_.build_.`super-csv-benchmark`.package_ // subfolder module reference
  override lazy val millDiscover: _root_.mill.define.Discover = _root_.mill.define.Discover[this.type]

}

super-csv/package.mill

package build_.`super-csv`
import _root_.{build_ => $file}
import build_.{package_ => build}
object MillMiscSubFolderInfo
extends mill.main.SubfolderModule.Info(
  os.Path("/home/aj/github/ajaychandran/mill/out/integration/feature/init/local/testOnly.dest/sandbox/run-2/super-csv"),
  _root_.scala.Seq("super-csv")
)
import MillMiscSubFolderInfo._

//MILL_ORIGINAL_FILE_PATH=/home/aj/github/ajaychandran/mill/out/integration/feature/init/local/testOnly.dest/sandbox/run-2/super-csv/package.mill
//MILL_USER_CODE_START_MARKER


import mill._
import mill.javalib._
import mill.javalib.publish._

abstract class package_  extends mill.main.SubfolderModule with build.BaseMavenModule {

  override def artifactName = "super-csv"

  override def javacOptions = Seq(
    "-source",
    "1.5",
    "-target",
    "1.5"
  )


  object test extends Tests {

    override def ivyDeps = super.ivyDeps() ++ Agg(
      ivy"junit:junit:4.12"
    )
  }

}
object package_ extends package_ {
  
  
}

lihaoyi · 2024-10-18T00:51:39Z

@ajaychandran looks like the issue is trait BaseMavenModule needs to live within the object package for it to get picked up correctly

ajaychandran · 2024-10-18T06:23:29Z

@lihaoyi This is ready for review.

The issue was resolved by adding the $file import in package.mill files.

One criticism of this solution is that the root task namespace (mill resolve _) gets cluttered with the tasks of the root module. This could be a problem if a "name collision" occurs.
On the upside, this allows running tasks like mill compile (post initialization). IMO this offers a better user experience.

main/init/src/mill/init/maven/codegen.scala

main/init/test/src/mill/init/maven/InitModuleTests.scala

main/init/src/mill/init/maven/PomReader.scala

main/init/src/mill/init/maven/codegen.scala

integration/feature/init/src/MillInitMavenTests.scala

main/init/src/mill/init/maven/codegen.scala

lihaoyi · 2024-10-19T11:07:22Z

@ajaychandran did a pass and left some comments. Probably will take a few more passes to get it merged, but looks promising.

Some high-level comments:

Please update the PR description with details of what future maintainers or users would want to read.
- For me, I am most interested in the scope of this feature: it obviously cannot convert every Maven build under the sun with all possible plugins, but it can convert simple maven builds, so where is the line drawn for this particular implementation?
- There are probably other things that you would expect others sending you a large PR to write in the description
Add an integration test that takes the Netty codebase we use in https://github.com/com-lihaoyi/mill/blob/main/example/thirdparty/netty/build.mill, runs your converter, and then runs the subset of the netty module tests that work.
- Not everything will work - some of the modules require calling make and compiling C code or running an H2Spec or Autobahn server - and that is expected.
- But we should assert that the modules that are supported do compile, the tests which are supported do pass, and the correct number of test suites are being run (by looking at show __.discoveredTestClasses).
- We should also have comments enumerating the modules/tests that not pass, and why it is expected they do not pass (e.g. native C dependencies, requiring external servers running, etc.)
Let's move all this maven logic and dependencies out of the main classpath into an isolated subprocess or classloader. This will avoid risking artifact collisions in the main classpath
- You can see how it is done for GraphvizTools https://github.com/com-lihaoyi/mill/blob/main/main/graphviz/src/mill/main/graphviz/GraphvizTools.scala, which downloads the relevant classpath during the build (rather than as part of Mill's distribution) and runs the classpath in a Jvm.subprocess

- Reorganized documentation

ajaychandran · 2024-11-11T20:51:20Z

@lihaoyi Please review.

Notably,

added option to merge generated build files
added "Future work" section in PR description

CI failures on Windows are due to EOL differences in golden files. Any tips on how to fix this?

lihaoyi · 2024-11-11T23:20:05Z

@ajaychandran for the golden files, we've typically just done .replaceAll("\r\n", "\n") to fix up line endings before comparison. Typically needs to be done on both the expected and actual output, but otherwise works great

lihaoyi · 2024-11-11T23:56:38Z

I think this looks good overall. I tried it out on https://github.com/iluwatar/java-design-patterns, and apart from parts of the codebase that needed compiler plugins (e.g. @lombok.extern.slf4j.Slf4j) or maven plugins (e.g. spring-boot-maven-plugin) it seems that it mostly worked and I got most of the codebase compiling and testing. Nice work!

Notably, I needed one upstream patch to avoid class file size limitations to get things compiling:

--- a/main/define/src/mill/define/Discover.scala
+++ b/main/define/src/mill/define/Discover.scala
@@ -147,7 +147,7 @@ object Discover {
         // by wrapping the `overridesRoutes` in a lambda function we kind of work around
         // the problem of generating a *huge* macro method body that finally exceeds the
         // JVM's maximum allowed method size
-        val overridesLambda = q"(() => $overridesRoutes)()"
+        val overridesLambda = q"(new Function0[(Seq[String], Seq[mainargs.MainData[_, _]], Seq[String])]{def apply() = $overridesRoutes})()"
         q"$lhs -> $overridesLambda"
       }

ajaychandran · 2024-11-12T17:41:13Z

Investigating the CI failure with act.
Changed the PR to Draft.

Extended mill init to support an existing Maven project

ab80850

ajaychandran added 3 commits October 17, 2024 22:06

Renamed variable

9cfa813

Added magic import to generated build.mill

6b1d573

Added provided dependencies to compileIvyDeps

0e1dbe6

ajaychandran added 4 commits October 17, 2024 23:04

Extended mill init to support an existing Maven project

6c4ad41

Renamed variable

b60147e

Added magic import to generated build.mill

db77ae6

Added provided dependencies to compileIvyDeps

e28b83f

ajaychandran force-pushed the main branch from 0e1dbe6 to e28b83f Compare October 17, 2024 17:34

Merge remote-tracking branch 'origin/main'

6fc9eb2

ajaychandran added 3 commits October 18, 2024 10:08

Added magic import to resolve base module in package build files

229e95c

Fix test

4b7948c

Refactored out code generation

6e7061e

ajaychandran marked this pull request as ready for review October 18, 2024 06:23