Fix #4430: Disallow access to Java bridge methods before typer

Scala bridge methods only come to existence during erasure, so are not visible
before. But Java bridge methods come with their class files. To get parity, we
have to ignore them before erasure. We do this by marking them as private
and turning off the private flag at erasure.

Author: odersky

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

@@ -632,6 +632,9 @@ object Flags {
   /** A Java companion object */
   final val JavaProtected = allOf(JavaDefined, Protected)
 
+  /** A private Java bridge method */
+  final val PrivateJavaBridge = allOf(Private, JavaDefined, Bridge)
+
   /** A Java enum */
   final val JavaEnum = allOf(JavaDefined, Enum)
 

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

@@ -212,8 +212,10 @@ class ClassfileParser(
       else fieldTranslation.flags(jflags)
     val name = pool.getName(in.nextChar)
     if (!(sflags is Flags.Private) || name == nme.CONSTRUCTOR) {
+      val sflags1 =
+        if (sflags.is(Flags.Bridge) && !ctx.erasedTypes) sflags | Flags.Private else sflags
       val member = ctx.newSymbol(
-        getOwner(jflags), name, sflags, memberCompleter, coord = start)
+        getOwner(jflags), name, sflags1, memberCompleter, coord = start)
       getScope(jflags).enter(member)
     }
     // skip rest of member for now

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -971,7 +971,7 @@ class TreeUnpickler(reader: TastyReader,
 
       def accessibleDenot(pre: Type, name: Name, sig: Signature) = {
         val d = pre.member(name).atSignature(sig)
-        if (!d.symbol.exists || d.symbol.isAccessibleFrom(pre)) d
+        if (d.exists && !d.symbol.exists || d.symbol.isAccessibleFrom(pre)) d
         else pre.nonPrivateMember(name).atSignature(sig)
       }
 

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

@@ -74,7 +74,8 @@ class Erasure extends Phase with DenotTransformer {
         val newInfo = transformInfo(oldSymbol, oldInfo)
         val oldFlags = ref.flags
         val newFlags =
-          if (oldSymbol.is(Flags.TermParam) && isCompacted(oldSymbol.owner)) oldFlags &~ Flags.Param
+          if (oldFlags.is(Flags.TermParam) && isCompacted(oldSymbol.owner)) oldFlags &~ Flags.Param
+          else if (oldFlags.is(Flags.PrivateJavaBridge)) oldFlags &~ Flags.Private
           else oldFlags &~ Flags.HasDefaultParams // HasDefaultParams needs to be dropped because overriding might become overloading
 
         // TODO: define derivedSymDenotation?

tests/pickling/i4430.scala

@@ -0,0 +1,5 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    (new java.lang.StringBuilder()).append(Array[Char](), 0, 0)
+  }
+}

tests/run/i4430.scala

@@ -0,0 +1,5 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    (new java.lang.StringBuilder()).append(Array[Char](), 0, 0)
+  }
+}