Allow main class to be non-public. Fixes #883.

compile/api/src/main/scala/xsbt/api/Discovery.scala

@@ -14,7 +14,13 @@ class Discovery(baseClasses: Set[String], annotations: Set[String])
 	def apply(d: Definition): Discovered =
 		d match
 		{
-			case c: ClassLike if isPublic(c) && isConcrete(c.modifiers) => discover(c)
+			case c: ClassLike if isConcrete(c.modifiers) => 
+				if(isPublic(c))
+					discover(c)
+				else if(isModule(c) && hasMainMethod(c)) // jvm does not require a main class to be public
+					new Discovered(Set.empty, Set.empty, true, true)
+				else
+					Discovered.empty
 			case _ => Discovered.empty
 		}
 	def discover(c: ClassLike): Discovered =
@@ -24,6 +30,7 @@ class Discovery(baseClasses: Set[String], annotations: Set[String])
 		val module = isModule(c)
 		new Discovered( bases(c.name, c.structure.parents), onClass ++ onDefs, module && hasMainMethod(c), module )
 	}
+
 	def bases(own: String, c: Seq[Type]): Set[String] =
 		(own +: c.flatMap(simpleName)).filter(baseClasses).toSet
 

run/src/main/scala/sbt/Run.scala

@@ -76,6 +76,9 @@ class Run(instance: ScalaInstance, trapExit: Boolean, nativeTmp: File) extends S
 	{
 		val mainClass = Class.forName(mainClassName, true, loader)
 		val method = mainClass.getMethod("main", classOf[Array[String]])
+		// jvm allows the actual main class to be non-public and to run a method in the non-public class,
+		//  we need to make it accessible
+		method.setAccessible(true)
 		val modifiers = method.getModifiers
 		if(!isPublic(modifiers)) throw new NoSuchMethodException(mainClassName + ".main is not public")
 		if(!isStatic(modifiers)) throw new NoSuchMethodException(mainClassName + ".main is not static")

sbt/src/sbt-test/java/varargs-main/A.java

@@ -1,4 +1,5 @@
-public class A{
+// Java allows the main class to have default access, test that here
+class A{
   public static void main(String... args){
 
   }