Move methods shared between Mixin and Backend to SymUtils.

Author: DarkDimius

src/dotty/tools/dotc/transform/MixinOps.scala

@@ -4,15 +4,14 @@ package transform
 import core._
 import Symbols._, Types._, Contexts._, SymDenotations._, DenotTransformers._, Flags._
 import util.Positions._
+import SymUtils._
 import StdNames._, NameOps._
 
 class MixinOps(cls: ClassSymbol, thisTransform: DenotTransformer)(implicit ctx: Context) {
   import ast.tpd._
 
-  val superCls: Symbol = cls.classInfo.parents.head.symbol
-  val mixins: List[ClassSymbol] =
-    if (cls is Trait) Nil
-    else cls.baseClasses.tail.takeWhile(_ ne superCls).reverse
+  val superCls: Symbol = cls.superClass
+  val mixins: List[ClassSymbol] = cls.mixins
 
   def implementation(member: TermSymbol): TermSymbol =
     member.copy(

src/dotty/tools/dotc/transform/SymUtils.scala

@@ -24,6 +24,23 @@ object SymUtils {
 class SymUtils(val self: Symbol) extends AnyVal {
   import SymUtils._
 
+  def superClass(implicit ctx: Context) = {
+    val parents = self.asClass.classInfo.parents
+    if (parents.isEmpty) NoSymbol
+    else parents.head.symbol
+  }
+
+  /** All interfaces implemented by a class, except for those inherited through the superclass. */
+  def mixins(implicit ctx: Context) = {
+    val superCls = self.superClass
+    if (self is Trait) Nil
+    else {
+      val baseClasses = self.asClass.baseClasses
+      if (baseClasses.isEmpty) Nil
+      else baseClasses.tail.takeWhile(_ ne superCls).reverse
+    }
+  }
+
   def isTypeTestOrCast(implicit ctx: Context): Boolean =
     self == defn.Any_asInstanceOf || self == defn.Any_isInstanceOf