fix #10884: eliminate JavaMethodType from exported info

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1716,6 +1716,19 @@ object Types {
         else funType
     }
 
+    final def dropJavaMethod(using Context): Type = this match
+      case pt: PolyType => pt.derivedLambdaType(resType = pt.resType.dropJavaMethod)
+
+      case mt: MethodType =>
+        if mt.isJavaMethod then
+          MethodType.apply(mt.paramNames, mt.paramInfos, mt.resType.dropJavaMethod)
+        else
+          mt.derivedLambdaType(resType = mt.resType.dropJavaMethod)
+
+      case _ => this
+
+    end dropJavaMethod
+
     /** The signature of this type. This is by default NotAMethod,
      *  but is overridden for PolyTypes, MethodTypes, and TermRef types.
      *  (the reason why we deviate from the "final-method-with-pattern-match-in-base-class"

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

@@ -111,15 +111,8 @@ object ErrorReporting {
 
     /** A subtype log explaining why `found` does not conform to `expected` */
     def whyNoMatchStr(found: Type, expected: Type): String = {
-      def dropJavaMethod(tp: Type): Type = tp match {
-        case tp: PolyType =>
-          tp.derivedLambdaType(resType = dropJavaMethod(tp.resultType))
-        case tp: MethodType if tp.isJavaMethod =>
-          MethodType(tp.paramNames, tp.paramInfos, dropJavaMethod(tp.resultType))
-        case tp => tp
-      }
-      val found1 = dropJavaMethod(found)
-      val expected1 = dropJavaMethod(expected)
+      val found1 = found.dropJavaMethod
+      val expected1 = expected.dropJavaMethod
       if ((found1 eq found) != (expected eq expected1) && (found1 <:< expected1))
         i"""
            |(Note that Scala's and Java's representation of this type differs)"""

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

@@ -1024,7 +1024,7 @@ class Namer { typer: Typer =>
                   if sym.isStableMember && sym.isPublic && !refersToPrivate(path.tpe) then
                     (StableRealizable, ExprType(path.tpe.select(sym)))
                   else
-                    (EmptyFlags, mbr.info.ensureMethodic)
+                    (EmptyFlags, mbr.info.ensureMethodic.dropJavaMethod)
                 var mbrFlags = Exported | Method | Final | maybeStable | sym.flags & RetainedExportFlags
                 if sym.is(ExtensionMethod) then mbrFlags |= ExtensionMethod
                 val forwarderName = checkNoConflict(alias, isPrivate = false, span)

tests/run/i10884/JavaExporter_1.java

@@ -0,0 +1,7 @@
+import java.util.Arrays;
+
+public class JavaExporter_1 {
+  public static String varargExample(String... args) {
+    return Arrays.toString(args);
+  }
+}

tests/run/i10884/Test_2.scala

@@ -0,0 +1,7 @@
+object Exporter:
+  export JavaExporter_1._
+
+import Exporter._
+
+@main def Test =
+  println(varargExample("a", "b", "c"))