Revised build importer implementations (#5428)

This PR rewrites importer implementations using a new architecture that
is easy to maintain and extend.

## Motivation
While working on adding support for cross projects, the build models
used in the existing implementations turned out to be insufficient for
the use-case.
This prompted work on an alternate architecture that culminated in this
pull request.

## Solution
New data models are introduced to define a build specification. This
includes an ADT whose members have a one-to-one correspondence with
module types defined within Mill. Importer implementations were updated
to target the new models.

## New and dropped features
- Added support for converting cross-platform and cross version SBT
projects.
- Added support for configuring `ErrorProneModule` for Gradle and Maven
projects.
- Added support for configuring `jvmId`.
- Dropped support for mapping `resources`.
- Redundant command line options were removed.

## Other improvements
- Fixed mapping for `PomSettings` in Maven conversion.
- Fixed mapping for `artifactName` in SBT conversion.
- Publish is skipped for Maven modules where it is explicitly disabled.
Example, `testsuite-osgi` module in [netty](https://github.com/netty/)
project.
- Prevent runtime failure by handling Maven `ModelBuildingException`.

## Limitations
- As before, build customizations are not supported. This includes
custom sources, custom Gradle configurations, and Maven profiles.
- SBT cross-platform support is limited to projects using
`sbt-crossproject` plugin.

## Summary of code changes
The previous implementation has been completely removed. Source files
for application entry points and some tests were retained, but the
contents have changed.
- The new shared models are housed in the `buildgen.api` module.
Together with new code in `buildgen` these account for ~1300 LOC.
- The new Gradle plugin is isolated in the `gradle.exportplugin` module.
The Gradle importer implementation and unit tests account for ~430 and
~700 LOC, respectively.
- The Maven importer implementation and unit tests account for ~500 and
~1350 LOC, respectively.
- The SBT importer implementation and unit tests account for ~600 and
~2200 LOC, respectively.
- The integration tests and golden files account for ~150 and ~11500
LOC, respectively.
- The manual integration tests account for ~400 LOC.

## Testing
- Updated integration tests to use golden testing for checking settings.
- Added `integration.manual[migrating]` module to develop and test the
conversions against real world projects.

Summary of fixes/enhancements made to improve support for test projects.
- Fixed `init` error in path handling for `spring-ai`.
- Fixed `init`/configuration error by removing custom resources for
`byte-buddy`/`joda-beans`.
- Added `spring-boot-dependencies` BOM dependency for `microconfig`.
- Generated `ErrorPluginModule` configurations for `mockito`.
- Generated cross-platform/version configurations for `Airstream`,
`cats`, `enumeratum`, `fs2`, `nscala-time`, `refined`, `scala-logging`,
`scopt`, `scrypto`.

## Future work
- Add support for converting Kotlin/Android projects.
- Add support for converting SBT projects that use the
`sbt-projectmatrix` plugin.

Author: ajaychandran

.scalafmt.conf

@@ -29,6 +29,9 @@ project {
     "glob:**/example/**/*-spotless*/**",
     "glob:**/javalib/test/resources/checkstyle/**",
     "glob:**/init/test/resources/giter8/hello.g8/src/main/g8/build.mill",
+    "glob:**/init/gradle/test/resources/**",
+    "glob:**/init/maven/test/resources/**",
+    "glob:**/init/sbt/test/resources/**",
     "glob:**/javalib/test/resources/javalib/palantirformat/**",
     "glob:**/integration/failure/parse-error/**",
     "glob:**/testkit/test/resources/example-test-example-project/build.mill",

example/migrating/javalib/3-maven-complete-large/build.mill

@@ -6,7 +6,9 @@
 > git remote add -f origin https://github.com/iluwatar/java-design-patterns
 > git checkout ede37bd05568b1b8b814d8e9a1d2bbd71d9d615d
 
-> ./mill init --jvm-id 21 # Repo needs Java >=21 to build and test
+> ./mill init
+
+> echo 21 > .mill-jvm-version # Repo needs Java >=21 to build and test
 
 > rm twin/src/test/java/com/iluwatar/twin/BallThreadTest.java # skip flaky test
 > rm actor-model/src/test/java/com/iluwatar/actor/ActorModelTest.java # skip flaky test

example/migrating/javalib/4-gradle-complete/build.mill

@@ -6,7 +6,7 @@
 > git remote add -f origin https://github.com/komamitsu/fluency.git
 > git checkout 2.7.3 # multi-module Java project that requires Java 16+
 
-> ./mill init --base-module FluencyModule --jvm-id 16
+> ./mill init
 converting Gradle build
 ...
 init completed, run "mill resolve _" to list available tasks

example/migrating/javalib/5-gradle-incomplete/build.mill

@@ -4,13 +4,12 @@
 
 > git init .
 > git remote add -f origin https://github.com/mockito/mockito.git
-> git checkout v5.15.2 # multi-module Java project that requires Java 17+
+> git checkout v5.19.0 # multi-module Java project
 
-> ./mill init --base-module MockitoModule --jvm-id 17   # init ignores custom dependency configurations
+> ./mill init --gradle-jvm-id 17  # imported modules are not fully functional
 converting Gradle build
-ignoring errorprone dependency (com.google.errorprone,error_prone_core,2.23.0)
 init completed, run "mill resolve _" to list available tasks
 
-> ./mill __.compile   # compilation error can be by fixed by using the Mill plugin for ErrorProne
-error: plug-in not found: ErrorProne
+> ./mill mockito-core.compile   # module jvmId needs tweaking
+error: java.lang.UnsupportedClassVersionError: com/google/errorprone/ErrorProneJavacPlugin has been compiled by a more recent version...
 */

example/migrating/scalalib/2-sbt-incomplete/build.mill

@@ -3,17 +3,15 @@
 > rm build.mill # remove any existing build file
 
 > git init .
-> git remote add -f origin https://github.com/tototoshi/scala-csv.git
-> git checkout 2.0.0
+> git remote add -f origin https://github.com/fthomas/refined.git
+> git checkout v0.11.3
 
 > ./mill init
 converting sbt build
 ...
 init completed, run "mill resolve _" to list available tasks
 
-> ./mill compile # You will have to further configure the `CrossScalaModule` for different Scala versions
-compiling 7 Scala sources and 3 Java sources to ...
-error: class CSVReader protected (private val lineReader: LineReader)(implicit format: CSVFormat) extends Closeable with CSVReaderCompat {
-error:                                                                                                                   ^
-error: one error found
+> ./mill modules.core.jvm[2.12.20].compile # source roots for custom version ranges need tweaking
+compiling 22 Scala sources to ...
+error: ...object boolean is not a member of package eu.timepit.refined
 */

integration/manual/migrating/src/MillInitGradleAsmTests.scala

@@ -0,0 +1,13 @@
+package mill.integration
+import utest.*
+object MillInitGradleAsmTests extends MillInitTestSuite {
+  def tests = Tests {
+    test - checkImport(
+      gitUrl = "https://gitlab.ow2.org/asm/asm.git",
+      gitBranch = "ASM_9_8",
+      initArgs = Seq("--gradle-jvm-id", "11"),
+      passingTasks = Seq("asm.compile"),
+      failingTasks = Seq("tools.retrofitter.compile")
+    )
+  }
+}

integration/manual/migrating/src/MillInitGradleEhcache3Tests.scala

@@ -0,0 +1,12 @@
+package mill.integration
+import utest.*
+object MillInitGradleEhcache3Tests extends MillInitTestSuite {
+  def tests = Tests {
+    test - checkImport(
+      gitUrl = "https://github.com/ehcache/ehcache3.git",
+      gitBranch = "v3.10.8",
+      initArgs = Seq("--gradle-jvm-id", "11"),
+      failingTasks = Seq("ehcache-api.compile")
+    )
+  }
+}

integration/manual/migrating/src/MillInitGradleFastCsvTests.scala

@@ -0,0 +1,12 @@
+package mill.integration
+import utest.*
+object MillInitGradleFastCsvTests extends MillInitTestSuite {
+  def tests = Tests {
+    test - checkImport(
+      gitUrl = "https://github.com/osiegmar/FastCSV.git",
+      gitBranch = "v4.0.0",
+      initArgs = Seq("--gradle-jvm-id", "24"),
+      failingTasks = Seq("lib.compile")
+    )
+  }
+}

integration/manual/migrating/src/MillInitGradleJCommanderTests.scala

@@ -0,0 +1,12 @@
+package mill.integration
+import utest.*
+object MillInitGradleJCommanderTests extends MillInitTestSuite {
+  def tests = Tests {
+    test - checkImport(
+      gitUrl = "https://github.com/cbeust/jcommander.git",
+      gitBranch = "2.0",
+      initArgs = Seq("--gradle-jvm-id", "11"),
+      failingTasks = Seq("test.compile")
+    )
+  }
+}

integration/manual/migrating/src/MillInitGradleMicroconfigTests.scala

@@ -0,0 +1,12 @@
+package mill.integration
+import utest.*
+object MillInitGradleMicroconfigTests extends MillInitTestSuite {
+  def tests = Tests {
+    test - checkImport(
+      gitUrl = "https://github.com/microconfig/microconfig.git",
+      gitBranch = "v4.9.5",
+      initArgs = Seq("--merge"),
+      passingTasks = Seq("_.test")
+    )
+  }
+}