Self type inheritance check

Check that the self type of a class conforms to the self types of its parent classes.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/typer/RefChecks.scala b/src/dotty/tools/dotc/typer/RefChecks.scala
index 9b14fffc0..6a1f3652b 100644
--- a/src/dotty/tools/dotc/typer/RefChecks.scala
+++ b/src/dotty/tools/dotc/typer/RefChecks.scala
@@ -71,6 +71,17 @@ object RefChecks {
     }
   }
 
+  /** Check that self type of this class conforms to self types of parents */
+  private def checkSelfType(clazz: Symbol)(implicit ctx: Context): Unit = clazz.info match {
+    case cinfo: ClassInfo =>
+      for (parent <- cinfo.classParents) {
+        val pself = parent.givenSelfType.asSeenFrom(clazz.thisType, parent.classSymbol)
+        if (pself.exists && !(cinfo.selfType <:< pself))
+          ctx.error(d"illegal inheritance: self type ${cinfo.selfType} of $clazz does not conform to self type $pself of parent ${parent.classSymbol}", clazz.pos)
+      }
+    case _ =>
+  }
+
   // Override checking ------------------------------------------------------------
 
   /** 1. Check all members of class `clazz` for overriding conditions.
@@ -770,6 +781,7 @@ class RefChecks extends MiniPhase with SymTransformer { thisTransformer =>
     override def transformTemplate(tree: Template)(implicit ctx: Context, info: TransformerInfo) = {
       val cls = ctx.owner
       checkOverloadedRestrictions(cls)
+      checkSelfType(cls)
       checkAllOverrides(cls)
       checkAnyValSubclass(cls)
       tree