[WIP] Add ErrorProne plugin

Fix #3447

build.mill

@@ -191,9 +191,10 @@ object Deps {
   val sonatypeCentralClient = ivy"com.lumidion::sonatype-central-client-requests:0.3.0"
 
   object RuntimeDeps {
-    val sbtTestInterface = ivy"com.github.sbt:junit-interface:0.13.2"
+    val errorProneCore = ivy"com.google.errorprone:error_prone_core:2.31.0"
     val jupiterInterface = ivy"com.github.sbt.junit:jupiter-interface:0.11.4"
-    def all = Seq(sbtTestInterface, jupiterInterface)
+    val sbtTestInterface = ivy"com.github.sbt:junit-interface:0.13.2"
+    def all = Seq(errorProneCore, jupiterInterface, sbtTestInterface)
   }
 
   /** Used to manage transitive versions. */

contrib/errorprone/readme.adoc

@@ -0,0 +1,20 @@
+= Mill ErrorProne Plugin
+
+== Caveats / JVM Options
+
+If you're on Java 17 or newer, you need to add the following options to your `.mill-jvm-opts` file in your project directory.
+
+.Required options in `.mill-jvm-opts`
+----
+--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED
+--add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED
+--add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED
+--add-exports=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED
+--add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED
+--add-exports=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED
+--add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED
+--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
+--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED
+--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED
+----
+

contrib/errorprone/src/mill/contrib/errorprone/ErrorProneModule.scala

@@ -0,0 +1,43 @@
+package mill.contrib.errorprone
+
+import mill.api.PathRef
+import mill.{Agg, T}
+import mill.scalalib.{Dep, DepSyntax, JavaModule}
+
+import java.io.File
+
+trait ErrorProneModule extends JavaModule {
+  def errorProneVersion: T[String] = T.input {
+    BuildInfo.errorProneVersion
+  }
+  def errorProneDeps: T[Agg[Dep]] = T {
+    Agg(
+      ivy"com.google.errorprone:error_prone_core:${errorProneVersion()}"
+    )
+  }
+  def errorProneClasspath: T[Agg[PathRef]] = T {
+    resolveDeps(T.task { errorProneDeps().map(bindDependency()) })()
+  }
+  def errorProneJavacOptions: T[Seq[String]] = T {
+    val processorPath = errorProneClasspath().map(_.path).mkString(File.pathSeparator)
+    Seq(
+      "-XDcompilePolicy=simple",
+      "-processorpath",
+      processorPath,
+      "-Xplugin:ErrorProne"
+    )
+//    val java17Options = Seq(
+//      "--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED",
+//      "--add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED",
+//      "--add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED",
+//      "--add-exports=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED",
+//      "--add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED",
+//      "--add-exports=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED",
+//      "--add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED",
+//      "--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED",
+//      "--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED",
+//      "--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED"
+//    )
+  }
+  override def javacOptions: T[Seq[String]] = super.javacOptions() ++ errorProneJavacOptions()
+}

contrib/errorprone/test/resources/simple/src/ShortSet.java

@@ -0,0 +1,16 @@
+package simple.src;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class ShortSet {
+  public static void main (String[] args) {
+    Set<Short> s = new HashSet<>();
+    for (short i = 0; i < 100; i++) {
+      s.add(i);
+      s.remove(i - 1);
+    }
+    System.out.println(s.size());
+  }
+}
+

contrib/errorprone/test/src/mill/contrib/errorprone/ErrorProneTests.scala

@@ -0,0 +1,35 @@
+package mill.contrib.errorprone
+
+import mill.scalalib.JavaModule
+import mill.testkit.{TestBaseModule, UnitTester}
+import os.Path
+import utest._
+
+object ErrorProneTests extends TestSuite {
+
+  object noErrorProne extends TestBaseModule with JavaModule {}
+  object errorProne extends TestBaseModule with JavaModule with ErrorProneModule {}
+
+  val testModuleSourcesPath: Path = os.Path(sys.env("MILL_TEST_RESOURCE_FOLDER")) / "simple"
+
+  def tests = Tests {
+    test("reference") {
+      test("compile") {
+        val eval = UnitTester(noErrorProne, testModuleSourcesPath)
+        val res = eval(noErrorProne.compile)
+        assert(res.isRight)
+      }
+    }
+    test("errorprone") {
+      test("compileFail") {
+        // we require additional JVM options, which we can't set at runtime, see contrib/errorprone/readme.adoc
+        if (scala.util.Properties.isJavaAtLeast(16)) "skipping test on Java 16+"
+        else {
+          val eval = UnitTester(errorProne, testModuleSourcesPath)
+          val res = eval(errorProne.compile)
+          assert(res.isLeft)
+        }
+      }
+    }
+  }
+}

contrib/package.mill

@@ -17,6 +17,7 @@ import mill.resolve.SelectMode
 import mill.contrib.buildinfo.BuildInfo
 import mill.T
 import mill.define.Cross
+import build.Deps
 
 // plugins and dependencies
 import $meta._
@@ -226,4 +227,12 @@ object `package` extends RootModule {
     def compileModuleDeps = Seq(build.scalalib)
     def testModuleDeps = super.testModuleDeps ++ Seq(build.scalalib)
   }
+
+  object errorprone extends ContribModule with BuildInfo {
+    def compileModuleDeps = Seq(build.scalalib)
+    def testModuleDeps = super.testModuleDeps ++ Seq(build.scalalib)
+    def buildInfoPackageName = "mill.contrib.errorprone"
+    def buildInfoObjectName = "BuildInfo"
+    def buildInfoMembers = Seq(BuildInfo.Value("errorProneVersion", Deps.RuntimeDeps.errorProneCore.version))
+  }
 }