Fix overriding a Java method with varargs

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -48,9 +48,9 @@ class Compiler {
       List(new Pickler),            // Generate TASTY info
       List(new FirstTransform,      // Some transformations to put trees into a canonical form
            new CheckReentrant),     // Internal use only: Check that compiled program has no data races involving global vars
-      List(new RefChecks,           // Various checks mostly related to abstract members and overriding
-           new CheckStatic,         // Check restrictions that apply to @static members
+      List(new CheckStatic,         // Check restrictions that apply to @static members
            new ElimRepeated,        // Rewrite vararg parameters and arguments
+           new RefChecks,           // Various checks mostly related to abstract members and overriding
            new NormalizeFlags,      // Rewrite some definition flags
            new ExtensionMethods,    // Expand methods of value classes with extension methods
            new ExpandSAMs,          // Expand single abstract method closures to anonymous classes

compiler/src/dotty/tools/dotc/transform/ElimRepeated.scala

@@ -32,8 +32,21 @@ class ElimRepeated extends MiniPhaseTransform with InfoTransformer with Annotati
   def transformInfo(tp: Type, sym: Symbol)(implicit ctx: Context): Type =
     elimRepeated(tp)
 
+
+  override def transform(ref: SingleDenotation)(implicit ctx: Context): SingleDenotation =
+    super.transform(ref) match {
+      case ref1: SymDenotation if (ref1 ne ref) && overridesJava(ref1.symbol) =>
+        // This method won't override the corresponding Java method at the end of this phase,
+        // only the bridge added by `addVarArgsBridge` will.
+        ref1.copySymDenotation(initFlags = ref1.flags &~ Override)
+      case ref1 =>
+        ref1
+    }
+
   override def mayChange(sym: Symbol)(implicit ctx: Context): Boolean = sym is Method
 
+  private def overridesJava(sym: Symbol)(implicit ctx: Context) = sym.allOverriddenSymbols.exists(_ is JavaDefined)
+
   private def elimRepeated(tp: Type)(implicit ctx: Context): Type = tp.stripTypeVar match {
     case tp @ MethodType(paramNames, paramTypes) =>
       val resultType1 = elimRepeated(tp.resultType)
@@ -93,10 +106,9 @@ class ElimRepeated extends MiniPhaseTransform with InfoTransformer with Annotati
    */
   override def transformDefDef(tree: DefDef)(implicit ctx: Context, info: TransformerInfo): Tree = {
     assert(ctx.phase == thisTransformer)
-    def overridesJava = tree.symbol.allOverriddenSymbols.exists(_ is JavaDefined)
-    if (tree.symbol.info.isVarArgsMethod && overridesJava)
-        addVarArgsBridge(tree)(ctx.withPhase(thisTransformer.next))
-     else
+    if (tree.symbol.info.isVarArgsMethod && overridesJava(tree.symbol))
+      addVarArgsBridge(tree)
+    else
       tree
   }
 
@@ -120,6 +132,7 @@ class ElimRepeated extends MiniPhaseTransform with InfoTransformer with Annotati
         .appliedToArgs(vrefs :+ TreeGen.wrapArray(varArgRef, elemtp))
         .appliedToArgss(vrefss1)
     })
+
     Thicket(ddef, bridgeDef)
   }
 

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

@@ -766,6 +766,9 @@ class RefChecks extends MiniPhase { thisTransformer =>
 
   override def phaseName: String = "refchecks"
 
+  // Needs to run after ElimRepeated for override checks involving varargs methods
+  override def runsAfter = Set(classOf[ElimRepeated])
+
   val treeTransform = new Transform(NoLevelInfo)
 
   class Transform(currentLevel: RefChecks.OptLevelInfo = RefChecks.NoLevelInfo) extends TreeTransform {

tests/pos-java-interop/varargsOverride/Base.java

@@ -0,0 +1,5 @@
+class Base {
+  public Object foo(Object... x) {
+    return x;
+  }
+}

tests/pos-java-interop/varargsOverride/Sub.scala

@@ -0,0 +1,3 @@
+class Sub extends Base {
+  override def foo(x: Object*): Object = x
+}