Mark traits coming from Scala 2.12+ with flag

Author: odersky

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

@@ -402,6 +402,9 @@ object Flags {
   /** A definition that's initialized before the super call (Scala 2.x only) */
   final val Scala2PreSuper = termFlag(58, "<presuper>")
 
+  /** A Scala 2.12 or higher trait */
+  final val Scala_2_12_Trait = typeFlag(58, "<scala12trait>")
+
   /** A macro (Scala 2.x only) */
   final val Macro = commonFlag(59, "<macro>")
 

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

@@ -70,26 +70,29 @@ object Mode {
   /** We are currently unpickling Scala2 info */
   val Scala2Unpickling = newMode(13, "Scala2Unpickling")
 
+  /** We are currently unpickling from Java 8 or higher */
+  val Java8Unpickling = newMode(14, "Java8Unpickling")
+
   /** Use Scala2 scheme for overloading and implicit resolution */
-  val OldOverloadingResolution = newMode(14, "OldOverloadingResolution")
+  val OldOverloadingResolution = newMode(15, "OldOverloadingResolution")
 
   /** Allow hk applications of type lambdas to wildcard arguments;
    *  used for checking that such applications do not normally arise
    */
-  val AllowLambdaWildcardApply = newMode(15, "AllowHKApplyToWildcards")
+  val AllowLambdaWildcardApply = newMode(16, "AllowHKApplyToWildcards")
 
   /** Read original positions when unpickling from TASTY */
-  val ReadPositions = newMode(16, "ReadPositions")
+  val ReadPositions = newMode(17, "ReadPositions")
 
   /** Don't suppress exceptions thrown during show */
-  val PrintShowExceptions = newMode(17, "PrintShowExceptions")
+  val PrintShowExceptions = newMode(18, "PrintShowExceptions")
 
   val PatternOrType = Pattern | Type
 
   /** We are elaborating the fully qualified name of a package clause.
    *  In this case, identifiers should never be imported.
    */
-  val InPackageClauseName = newMode(18, "InPackageClauseName")
+  val InPackageClauseName = newMode(19, "InPackageClauseName")
 
   /** We are in the IDE */
   val Interactive = newMode(20, "Interactive")

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

@@ -10,6 +10,8 @@ object ClassfileConstants {
   final val JAVA_MAJOR_VERSION = 45
   final val JAVA_MINOR_VERSION = 3
 
+  final val JAVA8_MAJOR_VERSION = 52
+
   /** (see http://java.sun.com/docs/books/jvms/second_edition/jvms-clarify.html)
    *
    *  If the `ACC_INTERFACE` flag is set, the `ACC_ABSTRACT` flag must also

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

@@ -42,6 +42,8 @@ class ClassfileParser(
   protected var currentClassName: SimpleName = _      // JVM name of the current class
   protected var classTParams = Map[Name,Symbol]()
 
+  private var Scala2UnpicklingMode = Mode.Scala2Unpickling
+
   classRoot.info = (new NoCompleter).withDecls(instanceScope)
   moduleRoot.info = (new NoCompleter).withDecls(staticScope).withSourceModule(_ => staticModule)
 
@@ -69,6 +71,8 @@ class ClassfileParser(
       throw new IOException(s"class file '${in.file}' has wrong magic number 0x${toHexString(magic)}, should be 0x${toHexString(JAVA_MAGIC)}")
     val minorVersion = in.nextChar.toInt
     val majorVersion = in.nextChar.toInt
+    if (majorVersion >= JAVA8_MAJOR_VERSION)
+      Scala2UnpicklingMode |= Mode.Java8Unpickling
     if ((majorVersion < JAVA_MAJOR_VERSION) ||
         ((majorVersion == JAVA_MAJOR_VERSION) &&
          (minorVersion < JAVA_MINOR_VERSION)))
@@ -714,7 +718,7 @@ class ClassfileParser(
 
       def unpickleScala(bytes: Array[Byte]): Some[Embedded] = {
         val unpickler = new unpickleScala2.Scala2Unpickler(bytes, classRoot, moduleRoot)(ctx)
-        unpickler.run()(ctx.addMode(Mode.Scala2Unpickling))
+        unpickler.run()(ctx.addMode(Scala2UnpicklingMode))
         Some(unpickler)
       }
 

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -466,7 +466,11 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
     }
 
     def finishSym(sym: Symbol): Symbol = {
-      if (sym.isClass) sym.setFlag(Scala2x)
+      if (sym.isClass) {
+        sym.setFlag(Scala2x)
+        if (flags.is(Trait) && ctx.mode.is(Mode.Java8Unpickling))
+          sym.setFlag(Scala_2_12_Trait)
+      }
       if (!(isRefinementClass(sym) || isUnpickleRoot(sym) || (sym is Scala2Existential))) {
         val owner = sym.owner
         if (owner.isClass)

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -362,7 +362,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
   protected def keyString(sym: Symbol): String = {
     val flags = sym.flagsUNSAFE
     if (flags is JavaTrait) "interface"
-    else if ((flags is Trait) && !(flags is ImplClass)) "trait"
+    else if (flags is Trait) "trait"
     else if (sym.isClass) "class"
     else if (sym.isType) "type"
     else if (flags is Mutable) "var"