Fix handling of defaults in Java annotations

 - Java-defined annotation constructors need to have JavaDefined set.
 - Change the points where we suppress lifting. One case slipped through before.
 - Also: Add test.

Author: odersky

compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala

@@ -637,7 +637,7 @@ class ClassfileParser(
           val constr = ctx.newSymbol(
             owner = classRoot.symbol,
             name = nme.CONSTRUCTOR,
-            flags = Flags.Synthetic,
+            flags = Flags.Synthetic | Flags.JavaDefined,
             info = constrType
           ).entered
           for ((attr, i) <- attrs.zipWithIndex)

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -394,6 +394,10 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
       }
     }
 
+    /** Is `sym` a constructor of a Java-defined annotation? */
+    def isJavaAnnotConstr(sym: Symbol) =
+      sym.is(JavaDefined) && sym.isConstructor && sym.owner.derivesFrom(defn.AnnotationClass)
+
     /** Match re-ordered arguments against formal parameters
      *  @param n   The position of the first parameter in formals in `methType`.
      */
@@ -419,7 +423,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
           }
 
           def tryDefault(n: Int, args1: List[Arg]): Unit = {
-            liftFun()
+            if (!isJavaAnnotConstr(methRef.symbol)) liftFun()
             val getter = findDefaultGetter(n + numArgs(normalizedFun))
             if (getter.isEmpty) missingArg(n)
             else {
@@ -571,11 +575,8 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
 
     def normalizedFun = myNormalizedFun
 
-    private def isJavaAnnotConstr(sym: Symbol) =
-      sym.is(JavaDefined) && sym.isConstructor && sym.owner.derivesFrom(defn.AnnotationClass)
-
     override def liftFun(): Unit =
-      if (liftedDefs == null && !isJavaAnnotConstr(methRef.symbol)) {
+      if (liftedDefs == null) {
         liftedDefs = new mutable.ListBuffer[Tree]
         myNormalizedFun = liftApp(liftedDefs, myNormalizedFun)
       }
@@ -606,7 +607,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
       val app1 =
         if (!success) app0.withType(UnspecifiedErrorType)
         else {
-          if (!sameSeq(args, orderedArgs)) {
+          if (!sameSeq(args, orderedArgs) && !isJavaAnnotConstr(methRef.symbol)) {
             // need to lift arguments to maintain evaluation order in the
             // presence of argument reorderings.
             liftFun()

tests/pos/i2797/Fork.java

@@ -0,0 +1,4 @@
+public @interface Fork {
+  int value() default -1;
+  String[] jvmArgs() default { "nope" };
+}

tests/pos/i2797/Test.scala

@@ -0,0 +1,2 @@
+@Fork(jvmArgs = Array("I'm", "hot"))
+class Test