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, which is done here by tweaking the
`accessibleFrom` predicate. I tried to not load them in ClassfileParser in the
first place, but that caused lots of errors because we do need the methods after
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 Java bridge method */
+  final val JavaBridge = allOf(JavaDefined, Bridge)
+
   /** A Java enum */
   final val JavaEnum = allOf(JavaDefined, Enum)
 

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

@@ -720,6 +720,13 @@ object SymDenotations {
         else true
       }
 
+      /** True if we refer to a Java bridge before erasure. In this case we should
+       *  pretend the bridge is not there. Scala bridge methods get created during erasure
+       *  and are therefore not visible before. But Java bridge methods are visible as
+       *  soon as the class is loaded, so we need to compensate for that difference.
+       */
+      def isEarlyJavaBridgeAccess = is(JavaBridge) && !ctx.erasedTypes
+
       if (pre eq NoPrefix) true
       else if (info eq NoType) false
       else {
@@ -740,7 +747,7 @@ object SymDenotations {
              || ctx.phase.erasedTypes
              || isProtectedAccessOK
              )
-        )
+        ) && !isEarlyJavaBridgeAccess
       }
     }
 

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)
+  }
+}