Simple BuildInfo plugin (#325)

* Simple BuildInfo plugin
* BuildInfo readme
   include other known yet external plugins
* Add tests

5 files changed, 234 insertions, 0 deletions

diff --git a/build.sc b/build.sc
index 27914803..d9b357f7 100755
--- a/build.sc
+++ b/build.sc
@@ -238,6 +238,16 @@ object contrib extends MillModule {
     def moduleDeps = Seq(scalalib)
   }
 
+  object buildinfo extends MillModule {
+    def moduleDeps = Seq(scalalib)
+    // why do I need this?
+    def testArgs = T{
+      Seq("-Djna.nosys=true") ++
+      scalalib.worker.testArgs() ++
+      scalalib.backgroundwrapper.testArgs()
+    }
+   }
+
 }
 
 
diff --git a/contrib/buildinfo/src/mill/contrib/BuildInfo.scala b/contrib/buildinfo/src/mill/contrib/BuildInfo.scala
new file mode 100644
index 00000000..0eb94a6d
--- /dev/null
+++ b/contrib/buildinfo/src/mill/contrib/BuildInfo.scala
@@ -0,0 +1,45 @@
+package mill.contrib
+
+import ammonite.ops.write
+import mill.T
+import mill.define.Target
+import mill.eval.PathRef
+import mill.scalalib.ScalaModule
+import mill.util.Ctx
+
+trait BuildInfo extends ScalaModule {
+
+  def buildInfoPackageName: Option[String] = None
+
+  def buildInfoObjectName: String = "BuildInfo"
+
+  def buildInfoMembers: T[Map[String, String]] = T {
+    Map.empty[String, String]
+  }
+
+  private def generateBuildInfo(members: Map[String, Any])(implicit dest: Ctx.Dest): Seq[PathRef] =
+  if(!members.isEmpty){
+    val outputFile = dest.dest / "BuildInfo.scala"
+    val internalMembers =
+      members
+        .map {
+          case (name, value) => s"""  def ${name} = "${value}""""
+        }
+        .mkString("\n")
+    write(outputFile,
+      s"""|${buildInfoPackageName.map(p => s"package ${p}").getOrElse("")}
+          |object ${buildInfoObjectName} {
+          |$internalMembers
+          |}""".stripMargin)
+    Seq(PathRef(outputFile))
+  } else {
+    Seq.empty[PathRef]
+  }
+
+  def buildInfo = T {
+    generateBuildInfo(buildInfoMembers())
+  }
+
+  override def generatedSources: Target[Seq[PathRef]] = super.generatedSources() ++ buildInfo()
+
+}
diff --git a/contrib/buildinfo/test/resources/buildinfo/src/Main.scala b/contrib/buildinfo/test/resources/buildinfo/src/Main.scala
new file mode 100644
index 00000000..3d672668
--- /dev/null
+++ b/contrib/buildinfo/test/resources/buildinfo/src/Main.scala
@@ -0,0 +1,9 @@
+import java.nio.file.{Files, Paths}
+
+object Main extends App {
+
+  val resultPath = Paths.get(args(0))
+  Files.createDirectories(resultPath.getParent)
+  Files.write(resultPath, BuildInfo.scalaVersion.getBytes)
+
+}
diff --git a/contrib/buildinfo/test/src/mill/contrib/BuildInfoTests.scala b/contrib/buildinfo/test/src/mill/contrib/BuildInfoTests.scala
new file mode 100644
index 00000000..9e1549de
--- /dev/null
+++ b/contrib/buildinfo/test/src/mill/contrib/BuildInfoTests.scala
@@ -0,0 +1,112 @@
+package mill.contrib
+
+import ammonite.ops._
+import java.util.jar.JarFile
+import mill._
+import mill.define.Target
+import mill.eval.Result._
+import mill.eval.{Evaluator, Result}
+import mill.modules.Assembly
+import mill.scalalib.publish.VersionControl
+import mill.scalalib.publish._
+import mill.util.{TestEvaluator, TestUtil}
+import scala.collection.JavaConverters._
+import utest._
+import utest.framework.TestPath
+
+
+object BuildInfoTests extends TestSuite {
+
+  val scalaVersionString = "2.12.4"
+  trait BuildInfoModule extends TestUtil.BaseModule with scalalib.ScalaModule with BuildInfo {
+    def millSourcePath =  TestUtil.getSrcPathBase() / millOuterCtx.enclosing.split('.')
+    def scalaVersion = scalaVersionString
+  }
+
+  object EmptyBuildInfo extends BuildInfoModule
+
+  object BuildInfo extends BuildInfoModule {
+    def buildInfoMembers=T{
+      Map(
+        "scalaVersion" -> scalaVersion(),
+      )
+    }
+  }
+
+  object BuildInfoSettings extends BuildInfoModule {
+    def buildInfoPackageName = Some("foo")
+    def buildInfoObjectName = "bar"
+    def buildInfoMembers=T{
+      Map(
+        "scalaVersion" -> scalaVersion()
+      )
+    }
+  }
+
+  val resourcePath = pwd / 'contrib / 'buildinfo / 'test / 'resources / "buildinfo"
+
+  def workspaceTest[T, M <: TestUtil.BaseModule](m: M, resourcePath: Path = resourcePath)
+                                                (t: TestEvaluator[M] => T)
+                                                (implicit tp: TestPath): T = {
+    val eval = new TestEvaluator(m)
+    rm(m.millSourcePath)
+    rm(eval.outPath)
+    mkdir(m.millSourcePath / up)
+    cp(resourcePath, m.millSourcePath)
+    t(eval)
+  }
+
+  def tests: Tests = Tests {
+
+    'buildinfo - {
+      'createSourcefile - workspaceTest(BuildInfo){ eval =>
+        val expected = 
+          s"""|
+              |object BuildInfo {
+              |  def scalaVersion = "2.12.4"
+              |}""".stripMargin
+        val Right((result, evalCount)) = eval.apply(BuildInfo.buildInfo)
+        assert(
+          result.head.path == eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala" &&
+            exists(result.head.path) &&
+            read! result.head.path == expected
+        )
+      }
+
+      'notCreateEmptySourcefile - workspaceTest(EmptyBuildInfo){ eval =>
+        val Right((result, evalCount)) = eval.apply(EmptyBuildInfo.buildInfo)
+        assert(
+          result.isEmpty &&
+            !exists(eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala")
+        )
+      }
+
+      'supportCustomSettings - workspaceTest(BuildInfoSettings){ eval =>
+        val expected = 
+          s"""|package foo
+              |object bar {
+              |  def scalaVersion = "2.12.4"
+              |}""".stripMargin
+        val Right((result, evalCount)) = eval.apply(BuildInfoSettings.buildInfo)
+        assert(
+          result.head.path == eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala" &&
+            exists(result.head.path) &&
+            read! result.head.path == expected
+        )
+      }
+
+      'compile - workspaceTest(BuildInfo){ eval =>
+        val Right((result, evalCount)) = eval.apply(BuildInfo.compile)
+        assert(true)
+      }
+
+      'run - workspaceTest(BuildInfo){ eval =>
+        val runResult = eval.outPath / "hello-mill"
+        val Right((result, evalCount)) = eval.apply(BuildInfo.run(runResult.toString))
+        assert(
+          exists(runResult),
+          read(runResult) == scalaVersionString)
+      }
+    }
+  }
+}
diff --git a/docs/pages/9 - Contrib Modules.md b/docs/pages/9 - Contrib Modules.md
index 0360cc75..c49f6238 100644
--- a/docs/pages/9 - Contrib Modules.md
+++ b/docs/pages/9 - Contrib Modules.md
@@ -49,3 +49,61 @@ object example extends ScalaPBModule {
   override def scalaPBOptions = "flat_package,java_conversions"
 }
 ```
+
+### BuildInfo
+
+Generate scala code from your buildfile.  
+This plugin generates a single object containing information from your build.
+  
+To declare a module that uses BuildInfo you must extend the `mill.contrib.BuildInfo` trait when defining your module.
+
+Quickstart:
+  ```scala
+  object project extends BuildInfo {
+    val name = "poject-name"
+    def  buildInfoMembers: T[Map[String, String]] = T {
+      Map(
+        "name" -> name),
+        "scalaVersion" -> scalaVersion()
+      )
+    }
+  }
+  ```
+  
+#### Configuration options
+
+* `def buildInfoMembers: T[Map[String, String]]`  
+  The map containing all member names and values for the generated info object.
+
+* `def buildInfoObjectName: String`, default: `BuildInfo`  
+  The name of the object which contains all the members from `buildInfoMembers`.
+
+* `def buildInfoPackageName: Option[String]`, default: `None`  
+  The package name of the object.
+
+
+### Other Mill Plugins
+
+- [ensime](https://github.com/yyadavalli/mill-ensime "mill-ensime")
+
+  Create an [.ensime](http://ensime.github.io/ "ensime") file for your build.
+  
+  Quickstart:
+  ```scala
+  import $ivy.`fun.valycorp::mill-ensime:0.0.1`
+  ```
+  ```sh
+  sh> mill fun.valycorp.mill.GenEnsime/ensimeConfig
+  ```
+  
+- [dgraph](https://github.com/ajrnz/mill-dgraph "mill-dgraph")
+
+  Show transitive dependencies of your build in your browser.
+  
+  Quickstart:
+  ```scala
+  import $ivy.`com.github.ajrnz::mill-dgraph:0.2.0`
+  ```
+  ```sh
+  sh> mill plugin.dgraph.browseDeps(proj)()
+  ```