Add explanation to NoInitClasses

1 files changed, 10 insertions, 0 deletions

diff --git a/compiler/src/dotty/tools/dotc/core/Definitions.scala b/compiler/src/dotty/tools/dotc/core/Definitions.scala
index 7eb3d9d47..18e2b883c 100644
--- a/compiler/src/dotty/tools/dotc/core/Definitions.scala
+++ b/compiler/src/dotty/tools/dotc/core/Definitions.scala
@@ -766,6 +766,16 @@ class Definitions {
 
   lazy val PhantomClasses = Set[Symbol](AnyClass, AnyValClass, NullClass, NothingClass)
 
+  /** Classes that are known not to have an initializer irrespective of
+   *  whether NoInits is set. Note: FunctionXXLClass is in this set
+   *  because if it is compiled by Scala2, it does not get a NoInit flag.
+   *  But since it is introduced only at erasure, there's no chance
+   *  for augmentScala2Traits to do anything on a class that inherits it. So
+   *  it also misses an implementation class, which means that the usual scheme
+   *  of calling a superclass init in the implementation class of a Scala2
+   *  trait gets screwed up. Therefore, it is mandatory that FunctionXXL
+   *  is treated as a NoInit trait.
+   */
   lazy val NoInitClasses = PhantomClasses + FunctionXXLClass
 
   def isPolymorphicAfterErasure(sym: Symbol) =