Documentation and readme

contrib/errorprone/readme.adoc

@@ -1,2 +1,30 @@
 = Mill ErrorProne Plugin
 
+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

@@ -6,19 +6,37 @@ 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(
@@ -42,8 +60,16 @@ trait ErrorProneModule extends JavaModule {
     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