1 files changed, 22 insertions, 8 deletions
diff --git a/stage2/BuildBuild.scala b/stage2/BuildBuild.scala
index 798bd7d..2eebcbc 100644
--- a/stage2/BuildBuild.scala
+++ b/stage2/BuildBuild.scala
@@ -63,15 +63,29 @@ trait BuildBuildWithoutEssentials extends BaseBuild{
                 .invoke( null, ctx )
             }
           }.getOrElse{
-            try{
-              classLoader
-                .loadClass(lib.buildClassName)
-                .getConstructors.head
-                .newInstance(managedContext)
-              } catch {
-                case e: ClassNotFoundException if e.getMessage == lib.buildClassName =>
-                  throw new Exception("You need to define a class Build in build.scala in: "+projectDirectory)
+            val buildClasses =
+              lib.iterateClasses( compileTarget, classLoader, false )
+                .filter(_.getSimpleName == lib.buildClassName)
+                .filter(classOf[BaseBuild] isAssignableFrom _)
+            if( buildClasses.size == 0 ){
+              throw new Exception(
+                s"You need to define a class ${lib.buildClassName} extending an appropriate super class in\n"
+                + (projectDirectory / lib.buildFileName) ++ "\nbut none found."
+              )
+            } else if( buildClasses.size > 1 ){
+              throw new Exception(
+                s"You need to define exactly one class ${lib.buildClassName} extending an appropriate build super class, but multiple found in " + projectDirectory + ":\n" + buildClasses.mkString("\n")
+              )
+            } else {
+              val buildClass = buildClasses.head
+              if( !buildClass.getConstructors.exists(_.getParameterTypes.toList == List(classOf[Context])) ){
+                throw new Exception(
+                  s"Expected class ${lib.buildClassName}(val context: Context), but found different constructor in\n"
+                  + projectDirectory ++ "\n"
+                  + buildClass ++ "(" ++ buildClass.getConstructors.map(_.getParameterTypes.mkString(", ")).mkString("; ") + ")" )
               }
+              buildClass.getConstructors.head.newInstance(managedContext)
+            }
           }
       }
     )