Add ErrorProne plugin (#3460)

This adds a new `ErrorProne` plugin to the `contrib` section of Mill.

It provides the `ErrorProneModule` `trait`, which can be mixed into
`JavaModule`s. Derived modules like `ScalaModule` are also supported, as
long as they support the `javacOptions` task to configure the Java
compiler.

We use the [Error Prone](https://errorprone.info/index) project as a
compiler plugin. Although this is a simple javac compiler plugin, it's
usage isn't trivial. Fetching the correct classpath and supplying
options can be tricky, since they need to be provided in a special form.
Also using with JVMs starting from version 16 requires special options
handling due to the new more restrictive module classpath. This plugin
is handling all of the known issues and make its use easy for the user.

Additional configuration options are supported via the
`errorProneOptions` target.

Here is a usage example:

```scala
package build
import mill._, javalib._
import mill.contrib.errorprone._

import $ivy.`com.lihaoyi::mill-contrib-errorprone:`

object `package` extends RootModule with JavaModule with ErrorProneModule {
  def errorProneOptions = Seq("-XepAllErrorsAsWarnings")
}
```

Fix #3447

Pull request: #3460
---------

Co-authored-by: Li Haoyi <haoyi.sg@gmail.com>

build.mill

@@ -190,9 +190,10 @@ 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. */
@@ -729,6 +730,7 @@ object dist0 extends MillPublishJavaModule {
     build.contrib.jmh.testDep(),
     build.contrib.playlib.testDep(),
     build.contrib.playlib.worker("2.8").testDep(),
+    build.contrib.errorprone.testDep(),
     build.bsp.worker.testDep(),
     build.testkit.testDep()
   )

contrib/errorprone/readme.adoc

@@ -0,0 +1,31 @@
+= Mill ErrorProne Plugin
+:page-aliases: Plugin_ErrorProne.adoc
+
+https://errorprone.info/index[Error Prone] augments the Java compiler's type checker and detect common mistakes at compile time.
+
+You just need to mix the `ErrorProneModule` into your `JavaModule` and it will automatically run with every compilation.
+
+.`build.mill.sc`: Enable `ErrorProne` in a module
+[source,scala]
+----
+package build
+import mill._, scalalib._
+
+import $ivy.`com.lihaoyi::mill-contrib-errorprone:`
+import mill.contrib.errorprone.ErrorProneModule
+
+object foo extends JavaModule with ErrorProneModule {
+}
+----
+
+== Configuration
+
+The following configuration options exist:
+
+`def errorProneVersion: T[String]`::
+The `error-prone` version to use. Defaults to [[BuildInfo.errorProneVersion]], the version used to build and test the module.
+Find the latest at https://mvnrepository.com/artifact/com.google.errorprone/error_prone_core[mvnrepository.com]
+
+`def errorProneOptions: T[Seq[String]]`::
+ Options directly given to the `error-prone` processor.
+Those are documented as "flags" at https://errorprone.info/docs/flags

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

@@ -0,0 +1,81 @@
+package mill.contrib.errorprone
+
+import mill.api.PathRef
+import mill.{Agg, T}
+import mill.scalalib.{Dep, DepSyntax, JavaModule}
+
+import java.io.File
+
+/**
+ * Integrated Error Prone into a [[JavaModule]].
+ *
+ * See https://errorprone.info/index
+ */
+trait ErrorProneModule extends JavaModule {
+
+  /** The `error-prone` version to use. Defaults to [[BuildInfo.errorProneVersion]]. */
+  def errorProneVersion: T[String] = T.input {
+    BuildInfo.errorProneVersion
+  }
+
+  /**
+   * The dependencies of the `error-prone` compiler plugin.
+   */
+  def errorProneDeps: T[Agg[Dep]] = T {
+    Agg(
+      ivy"com.google.errorprone:error_prone_core:${errorProneVersion()}"
+    )
+  }
+
+  /**
+   * The classpath of the `error-prone` compiler plugin.
+   */
+  def errorProneClasspath: T[Agg[PathRef]] = T {
+    resolveDeps(T.task { errorProneDeps().map(bindDependency()) })()
+  }
+
+  /**
+   * Options used to enable and configure the `eror-prone` plugin in the Java compiler.
+   */
+  def errorProneJavacEnableOptions: T[Seq[String]] = T {
+    val processorPath = errorProneClasspath().map(_.path).mkString(File.pathSeparator)
+    val enableOpts = Seq(
+      "-XDcompilePolicy=simple",
+      "-processorpath",
+      processorPath,
+      (Seq("-Xplugin:ErrorProne") ++ errorProneOptions()).mkString(" ")
+    )
+    val java17Options = Option.when(scala.util.Properties.isJavaAtLeast(16))(Seq(
+      "--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED",
+      "--add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED",
+      "--add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED",
+      "--add-exports=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED",
+      "--add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED",
+      "--add-exports=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED",
+      "--add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED",
+      "--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED",
+      "--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED",
+      "--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED"
+    ).map(o => s"-J${o}")).toSeq.flatten
+    java17Options ++ enableOpts
+  }
+
+  /**
+   * Options directly given to the `error-prone` processor.
+   *
+   * Those are documented as "flags" at https://errorprone.info/docs/flags
+   */
+  def errorProneOptions: T[Seq[String]] = T { Seq.empty[String] }
+
+  /**
+   * Appends the [[errorProneJavacEnableOptions]] to the Java compiler options.
+   */
+  override def javacOptions: T[Seq[String]] = T {
+    val supOpts = super.javacOptions()
+    val enableOpts = Option
+      .when(!supOpts.exists(o => o.startsWith("-Xplugin:ErrorProne")))(
+        errorProneJavacEnableOptions()
+      )
+    supOpts ++ enableOpts.toSeq.flatten
+  }
+}

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 +1,44 @@
+package mill.contrib.errorprone
+
+import mill.T
+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 {}
+  object errorProneCustom extends TestBaseModule with JavaModule with ErrorProneModule {
+    override def errorProneOptions: T[Seq[String]] = T(Seq(
+      "-XepAllErrorsAsWarnings"
+    ))
+  }
+
+  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") {
+        val eval = UnitTester(errorProne, testModuleSourcesPath)
+        val res = eval(errorProne.compile)
+        assert(res.isLeft)
+      }
+      test("compileWarn") {
+        val eval = UnitTester(errorProneCustom, testModuleSourcesPath, debugEnabled = true)
+        val Right(opts) = eval(errorProneCustom.javacOptions)
+        assert(opts.value.exists(_.contains("-XepAllErrorsAsWarnings")))
+        val res = eval(errorProneCustom.compile)
+        assert(res.isRight)
+      }
+    }
+  }
+}

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))
+  }
 }

docs/modules/ROOT/pages/Java_Module_Config.adoc

@@ -88,3 +88,6 @@ If you are using millw, a more permanent solution could be to set the environmen
 
 include::example/javalib/module/13-jni.adoc[]
 
+== Using the ErrorProne plugin to detect code problems
+
+include::example/javalib/module/14-error-prone.adoc[]

example/javalib/module/14-error-prone/build.mill

@@ -0,0 +1,31 @@
+// When adding the `ErrorPromeModule` to your `JavaModule`,
+// the `error-prone` compiler plugin automatically detects various kind of programming errors.
+
+package build
+import mill._, javalib._
+import mill.contrib.errorprone._
+
+import $ivy.`com.lihaoyi::mill-contrib-errorprone:`
+
+object `package` extends RootModule with JavaModule with ErrorProneModule {
+  def errorProneOptions = Seq("-XepAllErrorsAsWarnings")
+}
+
+/** See Also: src/example/ShortSet.java */
+
+/** Usage
+
+> ./mill show errorProneOptions
+[
+  "-XepAllErrorsAsWarnings"
+]
+
+> ./mill compile
+[warn] .../src/example/ShortSet.java:11:15:  [CollectionIncompatibleType] Argument 'i - 1' should not be passed to this method; its type int is not compatible with its collection's type argument Short
+[warn]       s.remove(i - 1);
+[warn]               ^    (see https://errorprone.info/bugpattern/CollectionIncompatibleType)
+[warn] 1 warning
+[warn]               ^
+*/
+
+

example/javalib/module/14-error-prone/src/example/ShortSet.java

@@ -0,0 +1,16 @@
+package example;
+
+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());
+  }
+}
+

scalalib/worker/src/mill/scalalib/worker/ZincWorkerImpl.scala

@@ -496,6 +496,22 @@ class ZincWorkerImpl(
   )(implicit ctx: ZincWorkerApi.Ctx): Result[CompilationResult] = {
     os.makeDir.all(ctx.dest)
 
+    val classesDir =
+      if (compileToJar) ctx.dest / "classes.jar"
+      else ctx.dest / "classes"
+
+    if (ctx.log.debugEnabled) {
+      ctx.log.debug(
+        s"""Compiling:
+           |  javacOptions: ${javacOptions.map("'" + _ + "'").mkString(" ")}
+           |  scalacOptions: ${scalacOptions.map("'" + _ + "'").mkString(" ")}
+           |  sources: ${sources.map("'" + _ + "'").mkString(" ")}
+           |  classpath: ${compileClasspath.map("'" + _ + "'").mkString(" ")}
+           |  output: ${classesDir}"""
+          .stripMargin
+      )
+    }
+
     reporter.foreach(_.start())
 
     val consoleAppender = ConsoleAppender(
@@ -549,10 +565,6 @@ class ZincWorkerImpl(
 
     val lookup = MockedLookup(analysisMap)
 
-    val classesDir =
-      if (compileToJar) ctx.dest / "classes.jar"
-      else ctx.dest / "classes"
-
     val store = fileAnalysisStore(ctx.dest / zincCache)
 
     // Fix jdk classes marked as binary dependencies, see https://github.com/com-lihaoyi/mill/pull/1904

testkit/src/mill/testkit/ExampleTester.scala

@@ -25,7 +25,7 @@ import utest._
  * 2. Output lines can be prefixed by `error: ` to indicate we expect that
  *    command to fail.
  *
- * 3. `..` can be used to indicate wildcards, which match anything. These can
+ * 3. `...` can be used to indicate wildcards, which match anything. These can
  *    be used alone as the entire line, or in the middle of another line
  *
  * 4. Every line of stdout/stderr output by the command must match at least