Fix #1209: Skip redundant superclasses\supertraits.

1 files changed, 37 insertions, 0 deletions

diff --git a/src/dotty/tools/backend/jvm/CollectSuperCalls.scala b/src/dotty/tools/backend/jvm/CollectSuperCalls.scala
new file mode 100644
index 000000000..d19228364
--- /dev/null
+++ b/src/dotty/tools/backend/jvm/CollectSuperCalls.scala
@@ -0,0 +1,37 @@
+package dotty.tools.backend.jvm
+
+import dotty.tools.dotc.ast.tpd._
+import dotty.tools.dotc.ast.Trees
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.Symbols._
+import dotty.tools.dotc.transform.TreeTransforms.{MiniPhaseTransform, TransformerInfo}
+
+/** Collect all super calls except to the parent class.
+ *
+ *  This information is used to know if it is safe to remove a redundant mixin class.
+ *  A redundant mixin class is one that is implemented by another mixin class. As the
+ *  methods in a redundant mixin class could be implemented with a default abstract method,
+ *  the redundant mixin class could be required as a parent by the JVM.
+ */
+class CollectSuperCalls extends MiniPhaseTransform {
+
+  def phaseName: String = "collectSuperCalls"
+
+  override def transformSuper(tree: Super)(implicit ctx: Context, info: TransformerInfo): Tree = {
+    tree match {
+      case Trees.Super(qual: This, mix) if mix.nonEmpty =>
+        val classSymbol = qual.symbol.asClass.classSymbol
+        registerSuperCall(classSymbol, tree.tpe.baseClasses.head)
+      case _ =>
+    }
+    super.transformSuper(tree)
+  }
+
+  private def registerSuperCall(sym: ClassSymbol, calls: ClassSymbol)(implicit ctx: Context) = {
+    ctx.genBCodePhase match {
+      case genBCodePhase: GenBCode =>
+        genBCodePhase.registerSuperCall(sym, calls)
+      case _ =>
+    }
+  }
+}