Fix ClassfileParser

#2158 has uncovered flaws in the classfile parser. Matches that used
to always miss led to code that made no sense. The function naming was terrible
too, that's why nobody understood what was going on. `findSourceFile` to find
the class file, seriously?

Author: odersky

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

@@ -661,7 +661,7 @@ class ClassfileParser(
     for (entry <- innerClasses.values) {
       // create a new class member for immediate inner classes
       if (entry.outerName == currentClassName) {
-        val file = ctx.platform.classPath.findSourceFile(entry.externalName.toString) getOrElse {
+        val file = ctx.platform.classPath.findBinaryFile(entry.externalName.toString) getOrElse {
           throw new AssertionError(entry.externalName)
         }
         enterClassAndModule(entry, file, entry.jflags)

compiler/src/dotty/tools/io/ClassPath.scala

@@ -240,20 +240,13 @@ abstract class ClassPath {
   def findClass(name: String): Option[AnyClassRep] =
     name.splitWhere(_ == '.', doDropIndex = true) match {
       case Some((pkg, rest)) =>
-        val rep = packages find (_.name == pkg) flatMap (_ findClass rest)
-        rep map {
-          case x: AnyClassRep => x
-          case x              => throw new FatalError("Unexpected ClassRep '%s' found searching for name '%s'".format(x, name))
-        }
+        packages find (_.name == pkg) flatMap (_ findClass rest)
       case _ =>
         classes find (_.name == name)
     }
 
-  def findSourceFile(name: String): Option[AbstractFile] =
-    findClass(name) match {
-      case Some(ClassRep(Some(x: AbstractFile), _)) => Some(x)
-      case _                                        => None
-    }
+  def findBinaryFile(name: String): Option[AbstractFile] =
+    findClass(name).flatMap(_.binary)
 
   def sortString = join(split(asClasspathString).sorted: _*)