fix runMain task. support JEP-512

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

@@ -10,7 +10,7 @@ package sbt
 
 import java.io.File
 import java.lang.reflect.Method
-import java.lang.reflect.Modifier.{ isPublic, isStatic }
+import java.lang.reflect.Modifier.{ isPrivate, isPublic, isStatic }
 import sbt.internal.inc.ScalaInstance
 import sbt.internal.inc.classpath.{ ClasspathFilter, ClasspathUtil }
 import sbt.internal.util.MessageOnlyException
@@ -133,10 +133,17 @@ class Run(private[sbt] val newLoader: Seq[File] => ClassLoader, trapExit: Boolea
     currentThread.setContextClassLoader(loader)
     try {
       if (main.isStatic) {
+        if (Run.isJava25Plus) {
+          main.method.setAccessible(true)
+        }
         if (main.parameterCount > 0) main.method.invoke(null, options.toArray[String])
         else main.method.invoke(null)
       } else {
-        val ref = main.mainClass.getDeclaredConstructor().newInstance().asInstanceOf[AnyRef]
+        val constructor = main.mainClass.getDeclaredConstructor()
+        if (Run.isJava25Plus) {
+          constructor.setAccessible(true)
+        }
+        val ref = constructor.newInstance().asInstanceOf[AnyRef]
         if (main.parameterCount > 0) main.method.invoke(ref, options.toArray[String])
         else main.method.invoke(ref)
       }
@@ -165,10 +172,24 @@ class Run(private[sbt] val newLoader: Seq[File] => ClassLoader, trapExit: Boolea
       val method = try {
         mainClass.getMethod("main", classOf[Array[String]])
       } catch {
-        case _: NoSuchMethodException => mainClass.getMethod("main")
+        case _: NoSuchMethodException =>
+          try {
+            mainClass.getMethod("main")
+          } catch {
+            case _: NoSuchMethodException =>
+              try {
+                mainClass.getDeclaredMethod("main", classOf[Array[String]])
+              } catch {
+                case _: NoSuchMethodException =>
+                  mainClass.getDeclaredMethod("main")
+              }
+          }
+      }
+      val modifiers = method.getModifiers
+      if (isPrivate(modifiers)) {
+        throw new NoSuchMethodException(s"${mainClassName}.main is private")
       }
       method.setAccessible(true)
-      val modifiers = method.getModifiers
       DetectedMain(mainClass, method, isStatic(modifiers), method.getParameterCount())
     } else {
       val method = mainClass.getMethod("main", classOf[Array[String]])

sbt-app/src/sbt-test/run/jep-512/a2/A.java

@@ -0,0 +1,7 @@
+package example;
+
+class A {
+  void main() {
+    System.out.println("package private no args");
+  }
+}

sbt-app/src/sbt-test/run/jep-512/a3/A.java

@@ -0,0 +1,7 @@
+package example;
+
+class A {
+  protected void main() {
+    System.out.println("protected no args");
+  }
+}

sbt-app/src/sbt-test/run/jep-512/a4/A.java

@@ -0,0 +1,7 @@
+package example;
+
+class A {
+  void main(String[] args) {
+    System.out.println("package private with args");
+  }
+}

sbt-app/src/sbt-test/run/jep-512/a5/A.java

@@ -0,0 +1,7 @@
+package example;
+
+class A {
+  private void main(String[] args) {
+    System.out.println("private");
+  }
+}

sbt-app/src/sbt-test/run/jep-512/a6/A.java

@@ -0,0 +1,3 @@
+void main() {
+  IO.println("compact source file with java.lang.IO");
+}

sbt-app/src/sbt-test/run/jep-512/build.sbt

@@ -1,11 +1,54 @@
-// 2.12.x uses Zinc's compiler bridge
-ThisBuild / scalaVersion := "2.12.20"
-
 @transient
 lazy val check = taskKey[Unit]("")
 
-check := {
+lazy val common = Def.settings(
-  if (scala.util.Properties.isJavaAtLeast("25"))
+  // 2.12.x uses Zinc's compiler bridge
-    (Compile / run).toTask(" ").value
+  scalaVersion := "2.12.20",
-  else ()
+)
-}
+
+// use `runMain` instead of `run` because discoveredMainClasses return empty
+// if JEP-512 java main method
+// TODO fix zinc
+// https://github.com/sbt/sbt/issues/7384#issuecomment-3361020003
+lazy val commonRunMainCheck = Def.settings(
+  check := {
+    if (scala.util.Properties.isJavaAtLeast("25")) {
+      (Compile / runMain).toTask(" example.A").value
+    } else ()
+  }
+)
+
+lazy val a1 = project
+  .settings(common)
+  .settings(
+    check := {
+      if (scala.util.Properties.isJavaAtLeast("25")) {
+        assert((Compile / discoveredMainClasses).value.size == 1)
+        (Compile / run).toTask(" ").value
+      } else ()
+    }
+  )
+
+lazy val a2 = project.settings(common, commonRunMainCheck)
+lazy val a3 = project.settings(common, commonRunMainCheck)
+lazy val a4 = project.settings(common, commonRunMainCheck)
+
+lazy val a5 = project.settings(
+  common,
+  check := {
+    if (scala.util.Properties.isJavaAtLeast("25")) {
+      (Compile / runMain).toTask(" example.A").value
+    } else {
+      sys.error("not jdk 25")
+    }
+  }
+)
+
+lazy val a6 = project.settings(
+  common,
+  check := {
+    if (scala.util.Properties.isJavaAtLeast("25")) {
+      (Compile / runMain).toTask(" A").value
+    } else ()
+  }
+)

sbt-app/src/sbt-test/run/jep-512/test

@@ -1,2 +1,7 @@
 # > run
-> check
+> a1/check
+> a2/check
+> a3/check
+> a4/check
+-> a5/check
+> a6/check