contrib BuildInfo plugin: fix generatedSources, it must be a folder (#589)

* fix BuildInfo generatedSources, it must be a folder

generatedSources must be a folder,
but till now it was a reference to a generated file
This commit fixes this issue.

There are 2 reasons for this fix:
(1) Because generatedSources must be folders by the definition:
Folders containing source files that are generated
(2) If you use intellij IDEA and build your project from the IDE,
building module, which includes BuildInfo plugin, fails.

* test: make explicit check that generatedSources is a folder

* correct T.ctx -> T.ctx()

* workaround to get `dest` property of the task into other

2 files changed, 51 insertions, 39 deletions

diff --git a/contrib/buildinfo/src/BuildInfo.scala b/contrib/buildinfo/src/BuildInfo.scala
index fe252b97..0804b9a5 100644
--- a/contrib/buildinfo/src/BuildInfo.scala
+++ b/contrib/buildinfo/src/BuildInfo.scala
@@ -1,8 +1,8 @@
 package mill.contrib.buildinfo
 
 import mill.T
-import mill.define.Target
-import mill.api.{Ctx, Logger, PathRef}
+import mill.api.Logger
+import mill.api.PathRef
 import mill.scalalib.ScalaModule
 
 trait BuildInfo extends ScalaModule {
@@ -15,33 +15,35 @@ trait BuildInfo extends ScalaModule {
     Map.empty[String, String]
   }
 
-  private def generateBuildInfo(members: Map[String, Any])(implicit dest: Ctx.Dest, log: Ctx.Log): Seq[PathRef] =
-    if (!members.isEmpty) {
-      val outputFile = dest.dest / "BuildInfo.scala"
+  def generatedBuildInfo: T[(Seq[PathRef], PathRef)] = T {
+    val logger: Logger = T.ctx().log
+    val members: Map[String, String] = buildInfoMembers()
+    if (members.nonEmpty) {
+      val outputFile = T.ctx().dest / "BuildInfo.scala"
       val internalMembers =
         members
           .map {
             case (name, value) => s"""  def ${name} = "${value}""""
           }
           .mkString("\n")
-      log.log.debug(s"Generating object [${buildInfoPackageName.map(_ + ".").getOrElse("")}${buildInfoObjectName}] with [${members.size}] members to [${outputFile}]")
+      logger.debug(s"Generating object [${buildInfoPackageName.map(_ + ".").getOrElse("")}${buildInfoObjectName}] with [${members.size}] members to [${outputFile}]")
       os.write(
         outputFile,
-        s"""|${buildInfoPackageName.map(p => s"package ${p}").getOrElse("")}
-          |object ${buildInfoObjectName} {
-          |$internalMembers
-          |}""".stripMargin
+        s"""|${buildInfoPackageName.map(packageName => s"package ${packageName}\n").getOrElse("")}
+            |object ${buildInfoObjectName} {
+            |$internalMembers
+            |}""".stripMargin
       )
-      Seq(PathRef(outputFile))
+      (Seq(PathRef(outputFile)), PathRef(T.ctx().dest))
     } else {
-      log.log.debug("No build info member defined, skipping code generation")
-      Seq.empty[PathRef]
+      logger.debug("No build info member defined, skipping code generation")
+      (Seq.empty[PathRef], PathRef(T.ctx().dest))
     }
-
-  def buildInfo = T {
-    generateBuildInfo(buildInfoMembers())
   }
 
-  override def generatedSources: Target[Seq[PathRef]] = T { super.generatedSources() ++ buildInfo() }
+  override def generatedSources = T {
+    val (_, destPathRef) = generatedBuildInfo()
+    super.generatedSources() :+ destPathRef
+  }
 
 }
diff --git a/contrib/buildinfo/test/src/BuildInfoTests.scala b/contrib/buildinfo/test/src/BuildInfoTests.scala
index c6d0256d..9b840ed9 100644
--- a/contrib/buildinfo/test/src/BuildInfoTests.scala
+++ b/contrib/buildinfo/test/src/BuildInfoTests.scala
@@ -1,15 +1,12 @@
 package mill.contrib.buildinfo
 
-import java.util.jar.JarFile
 import mill._
+import mill.define.Sources
 import mill.define.Target
-import mill.api.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 mill.scalalib.ScalaModule
+import mill.util.TestEvaluator
+import mill.util.TestUtil
+import os.Path
 import utest._
 import utest.framework.TestPath
 
@@ -18,8 +15,9 @@ 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
+    // override build root to test custom builds/modules
+    override def millSourcePath: Path = TestUtil.getSrcPathStatic()
+    override def scalaVersion = scalaVersionString
   }
 
   object EmptyBuildInfo extends BuildInfoModule
@@ -42,16 +40,16 @@ object BuildInfoTests extends TestSuite {
     }
   }
 
-  val resourcePath = os.pwd / 'contrib / 'buildinfo / 'test / 'resources / "buildinfo"
+  val testModuleSourcesPath: Path = os.pwd / 'contrib / 'buildinfo / 'test / 'resources / "buildinfo"
 
-  def workspaceTest[T](m: TestUtil.BaseModule, resourcePath: os.Path = resourcePath)
+  def workspaceTest[T](m: TestUtil.BaseModule)
                       (t: TestEvaluator => T)
                       (implicit tp: TestPath): T = {
     val eval = new TestEvaluator(m)
     os.remove.all(m.millSourcePath)
     os.remove.all(eval.outPath)
     os.makeDir.all(m.millSourcePath / os.up)
-    os.copy(resourcePath, m.millSourcePath)
+    os.copy(testModuleSourcesPath, m.millSourcePath)
     t(eval)
   }
 
@@ -59,36 +57,37 @@ object BuildInfoTests extends TestSuite {
 
     'buildinfo - {
       'createSourcefile - workspaceTest(BuildInfo){ eval =>
-        val expected = 
+        val expected =
           s"""|
               |object BuildInfo {
               |  def scalaVersion = "2.12.4"
               |}""".stripMargin
-        val Right((result, evalCount)) = eval.apply(BuildInfo.buildInfo)
+        val Right(((result, _), evalCount)) = eval.apply(BuildInfo.generatedBuildInfo)
         assert(
-          result.head.path == eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala" &&
+          result.head.path == eval.outPath / 'generatedBuildInfo / 'dest / "BuildInfo.scala" &&
             os.exists(result.head.path) &&
             os.read(result.head.path) == expected
         )
       }
 
       'notCreateEmptySourcefile - workspaceTest(EmptyBuildInfo){ eval =>
-        val Right((result, evalCount)) = eval.apply(EmptyBuildInfo.buildInfo)
+        val Right(((result, _), evalCount)) = eval.apply(EmptyBuildInfo.generatedBuildInfo)
         assert(
           result.isEmpty &&
-            !os.exists(eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala")
+            !os.exists(eval.outPath / 'generatedBuildInfo / 'dest / "BuildInfo.scala")
         )
       }
 
       'supportCustomSettings - workspaceTest(BuildInfoSettings){ eval =>
-        val expected = 
+        val expected =
           s"""|package foo
+              |
               |object bar {
               |  def scalaVersion = "2.12.4"
               |}""".stripMargin
-        val Right((result, evalCount)) = eval.apply(BuildInfoSettings.buildInfo)
+        val Right(((result, _), evalCount)) = eval.apply(BuildInfoSettings.generatedBuildInfo)
         assert(
-          result.head.path == eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala" &&
+          result.head.path == eval.outPath / 'generatedBuildInfo / 'dest / "BuildInfo.scala" &&
             os.exists(result.head.path) &&
             os.read(result.head.path) == expected
         )
@@ -104,7 +103,18 @@ object BuildInfoTests extends TestSuite {
         val Right((result, evalCount)) = eval.apply(BuildInfo.run(runResult.toString))
         assert(
           os.exists(runResult),
-          os.read(runResult) == scalaVersionString)
+          os.read(runResult) == scalaVersionString
+        )
+      }
+
+      "generatedSources must be a folder" - workspaceTest(BuildInfo) { eval =>
+        val buildInfoGeneratedSourcesFolder = eval.outPath / 'generatedBuildInfo / 'dest
+        val Right((result, evalCount)) = eval.apply(BuildInfo.generatedSources)
+        assert(
+          result.size == 1,
+          os.isDir(result.head.path),
+          result.head.path == buildInfoGeneratedSourcesFolder
+        )
       }
     }
   }