Fix main class discovery for KotlinModule (#4797)

lihaoyi · web-flow · commit e6d04a2144d2 · 2025-03-28T12:10:30.000+01:00
Fixes #4772 Previously it inherited the Zinc-based main class discovery via `JavaModule`, which overrode the generic classpath-scanning approach from `RunModule`. This PR adjusts the overrides such the `KotlinModule` uses the disk-based discovery API. Removed all the now-unnecessary `def mainClass` annotations in the kotlinlib example tests, except for the one in `example/kotlinlib/module/1-common-config` that is useful for educational purposes. @lefou do you know what the difference between the two implementations is? I'm wondering what the Zinc-based approach gives us, or whether we can just standardize on the disk-based approach that seems like it should work for all JVM languages
diff --git a/example/kotlinlib/basic/1-simple/build.mill b/example/kotlinlib/basic/1-simple/build.mill
@@ -6,8 +6,6 @@ import mill._, kotlinlib._
 object foo extends KotlinModule {
   def kotlinVersion = "1.9.24"
 
-  def mainClass = Some("foo.FooKt")
-
   def ivyDeps = Seq(
     ivy"com.github.ajalt.clikt:clikt-jvm:4.4.0",
     ivy"org.jetbrains.kotlinx:kotlinx-html-jvm:0.11.0"
diff --git a/example/kotlinlib/basic/3-multi-module/build.mill b/example/kotlinlib/basic/3-multi-module/build.mill
@@ -13,7 +13,6 @@ trait MyModule extends KotlinModule {
 }
 
 object foo extends MyModule {
-  def mainClass = Some("foo.FooKt")
   def moduleDeps = Seq(bar)
   def ivyDeps = Seq(
     ivy"com.github.ajalt.clikt:clikt-jvm:4.4.0"
diff --git a/example/kotlinlib/basic/6-realistic/build.mill b/example/kotlinlib/basic/6-realistic/build.mill
@@ -28,8 +28,6 @@ trait MyModule extends KotlinModule with PublishModule {
 object foo extends MyModule {
   def moduleDeps = Seq(bar, qux)
 
-  def mainClass = Some("foo.FooKt")
-
   def generatedSources = Task {
     os.write(
       Task.dest / "Version.kt",
diff --git a/example/kotlinlib/dependencies/1-ivy-deps/build.mill b/example/kotlinlib/dependencies/1-ivy-deps/build.mill
@@ -6,8 +6,6 @@ object `package` extends RootModule with KotlinModule {
 
   def kotlinVersion = "1.9.24"
 
-  def mainClass = Some("foo.FooKt")
-
   def ivyDeps = Seq(
     ivy"com.fasterxml.jackson.core:jackson-databind:2.13.4"
   )
diff --git a/example/kotlinlib/dependencies/3-unmanaged-jars/build.mill b/example/kotlinlib/dependencies/3-unmanaged-jars/build.mill
@@ -6,8 +6,6 @@ object `package` extends RootModule with KotlinModule {
 
   def kotlinVersion = "1.9.24"
 
-  def mainClass = Some("foo.FooKt")
-
   def unmanagedClasspath = Task {
     if (!os.exists(moduleDir / "lib")) Seq()
     else Seq.from(os.list(moduleDir / "lib").map(PathRef(_)))
diff --git a/example/kotlinlib/dependencies/4-downloading-unmanaged-jars/build.mill b/example/kotlinlib/dependencies/4-downloading-unmanaged-jars/build.mill
@@ -6,8 +6,6 @@ object `package` extends RootModule with KotlinModule {
 
   def kotlinVersion = "1.9.24"
 
-  def mainClass = Some("foo.FooKt")
-
   def unmanagedClasspath = Task {
     os.write(
       Task.dest / "fastjavaio.jar",
diff --git a/example/kotlinlib/dependencies/5-repository-config/build.mill b/example/kotlinlib/dependencies/5-repository-config/build.mill
@@ -11,8 +11,6 @@ val sonatypeReleases = Seq(
 
 object foo extends KotlinModule {
 
-  def mainClass = Some("foo.FooKt")
-
   def kotlinVersion = "1.9.24"
 
   def ivyDeps = Seq(
diff --git a/example/kotlinlib/module/2-custom-tasks/build.mill b/example/kotlinlib/module/2-custom-tasks/build.mill
@@ -6,8 +6,6 @@ object `package` extends RootModule with KotlinModule {
 
   def kotlinVersion = "1.9.24"
 
-  def mainClass = Some("foo.FooKt")
-
   def ivyDeps = Seq(ivy"com.github.ajalt.clikt:clikt-jvm:4.4.0")
 
   def generatedSources: T[Seq[PathRef]] = Task {
diff --git a/example/kotlinlib/module/3-override-tasks/build.mill b/example/kotlinlib/module/3-override-tasks/build.mill
@@ -6,8 +6,6 @@ object foo extends KotlinModule {
 
   def kotlinVersion = "1.9.24"
 
-  def mainClass = Some("foo.FooKt")
-
   def sources = Task {
     os.write(
       Task.dest / "Foo.kt",
diff --git a/example/kotlinlib/module/4-compilation-execution-flags/build.mill b/example/kotlinlib/module/4-compilation-execution-flags/build.mill
@@ -6,8 +6,6 @@ object `package` extends RootModule with KotlinModule {
 
   def kotlinVersion = "1.9.24"
 
-  def mainClass = Some("foo.FooKt")
-
   def forkArgs = Seq("-Xmx4g", "-Dmy.jvm.property=hello")
   def forkEnv = Map("MY_ENV_VAR" -> "WORLD")
 
diff --git a/example/kotlinlib/publishing/1-assembly-config/build.mill b/example/kotlinlib/publishing/1-assembly-config/build.mill
@@ -7,8 +7,6 @@ object foo extends KotlinModule {
 
   def kotlinVersion = "1.9.24"
 
-  def mainClass = Some("foo.FooKt")
-
   def moduleDeps = Seq(bar)
   def assemblyRules = Seq(
     // all application.conf files will be concatenated into single file
diff --git a/example/kotlinlib/publishing/2-publish-module/build.mill b/example/kotlinlib/publishing/2-publish-module/build.mill
@@ -4,8 +4,6 @@ import mill._, kotlinlib._, publish._
 
 object foo extends KotlinModule with PublishModule {
 
-  def mainClass = Some("foo.FooKt")
-
   def kotlinVersion = "1.9.24"
 
   def publishVersion = "0.0.1"
diff --git a/example/kotlinlib/publishing/8-native-image-libs/build.mill b/example/kotlinlib/publishing/8-native-image-libs/build.mill
@@ -6,8 +6,6 @@ import mill.define.ModuleRef
 object foo extends KotlinModule with NativeImageModule {
   def kotlinVersion = "1.9.24"
 
-  def mainClass = Some("foo.FooKt")
-
   def nativeImageOptions = Seq(
     "--no-fallback",
     "-Os",
diff --git a/example/kotlinlib/testing/1-test-suite/build.mill b/example/kotlinlib/testing/1-test-suite/build.mill
@@ -4,8 +4,6 @@ import mill._, kotlinlib._
 
 object foo extends KotlinModule {
 
-  def mainClass = Some("foo.FooKt")
-
   def kotlinVersion = "1.9.24"
 
   object test extends KotlinTests {
diff --git a/example/kotlinlib/testing/4-test-parallel/build.mill b/example/kotlinlib/testing/4-test-parallel/build.mill
@@ -4,8 +4,6 @@ import mill._, kotlinlib._
 
 object foo extends KotlinModule {
 
-  def mainClass = Some("foo.FooKt")
-
   def kotlinVersion = "1.9.24"
 
   object test extends KotlinTests {
diff --git a/example/kotlinlib/testing/5-test-grouping/build.mill b/example/kotlinlib/testing/5-test-grouping/build.mill
@@ -4,8 +4,6 @@ import mill._, kotlinlib._
 
 object foo extends KotlinModule {
 
-  def mainClass = Some("foo.FooKt")
-
   def kotlinVersion = "1.9.24"
 
   object test extends KotlinTests {
diff --git a/example/kotlinlib/testing/6-test-group-parallel/build.mill b/example/kotlinlib/testing/6-test-group-parallel/build.mill
@@ -4,8 +4,6 @@ import mill._, kotlinlib._
 
 object foo extends KotlinModule {
 
-  def mainClass = Some("foo.FooKt")
-
   def kotlinVersion = "1.9.24"
 
   object test extends KotlinTests {
diff --git a/kotlinlib/src/mill/kotlinlib/KotlinModule.scala b/kotlinlib/src/mill/kotlinlib/KotlinModule.scala
@@ -47,6 +47,10 @@ trait KotlinModule extends JavaModule { outer =>
    */
   def kotlinVersion: T[String]
 
+  def allLocalMainClasses0 = Task {
+    zincWorker().worker().discoverMainClasses(localRunClasspath().map(_.path))
+  }
+
   /**
    * The dependencies of this module.
    * Defaults to add the kotlin-stdlib dependency matching the [[kotlinVersion]].
diff --git a/scalalib/src/mill/scalalib/RunModule.scala b/scalalib/src/mill/scalalib/RunModule.scala
@@ -49,9 +49,7 @@ trait RunModule extends WithZincWorker {
    * Same as [[allLocalMainClasses]], but only for modules with a custom
    * JVM version configured
    */
-  def allLocalMainClasses0: T[Seq[String]] = Task {
-    zincWorker().worker().discoverMainClasses(localRunClasspath().map(_.path))
-  }
+  def allLocalMainClasses0: T[Seq[String]] = Task { Seq.empty[String] }
 
   /**
    * All main classes detected in this module that can serve as program entrypoints

Original file line number	Diff line number	Diff line change
`@@ -13,7 +13,6 @@ trait MyModule extends KotlinModule {`
`13`	`13`	`}`
`14`	`14`
`15`	`15`	`object foo extends MyModule {`
`16`		`- def mainClass = Some("foo.FooKt")`
`17`	`16`	`def moduleDeps = Seq(bar)`
`18`	`17`	`def ivyDeps = Seq(`
`19`	`18`	`ivy"com.github.ajalt.clikt:clikt-jvm:4.4.0"`
Original file line number	Diff line number	Diff line change
@@ -6,8 +6,6 @@ object `package` extends RootModule with KotlinModule {
`6`	`6`
`7`	`7`	`def kotlinVersion = "1.9.24"`
`8`	`8`
`9`		`- def mainClass = Some("foo.FooKt")`
`10`		`-`
`11`	`9`	`def ivyDeps = Seq(`
`12`	`10`	`ivy"com.fasterxml.jackson.core:jackson-databind:2.13.4"`
`13`	`11`	`)`