Emit trait method bodies in statics

And use this as the target of the default methods or
statically resolved super or $init calls.

The call-site change is predicated on `-Yuse-trait-statics`
as a stepping stone for experimentation / bootstrapping.

I have performed this transformation in the backend,
rather than trying to reflect this in the view from
Scala symbols + ASTs.

We also need to add an restriction related to invokespecial to Java
parents: to support a super call to one of these to implement a
super accessor, the interface must be listed as a direct parent
of the class.

The static method names has a trailing $ added to avoid duplicate
name and signature errors in classfiles.

1 files changed, 12 insertions, 3 deletions

diff --git a/test/junit/scala/tools/testing/BytecodeTesting.scala b/test/junit/scala/tools/testing/BytecodeTesting.scala
index 4ddb6580df..c0fdb8010f 100644
--- a/test/junit/scala/tools/testing/BytecodeTesting.scala
+++ b/test/junit/scala/tools/testing/BytecodeTesting.scala
@@ -12,6 +12,7 @@ import scala.tools.asm.tree.{AbstractInsnNode, ClassNode, MethodNode}
 import scala.tools.cmd.CommandLineParser
 import scala.tools.nsc.backend.jvm.AsmUtils
 import scala.tools.nsc.backend.jvm.AsmUtils._
+import scala.tools.nsc.backend.jvm.opt.BytecodeUtils
 import scala.tools.nsc.io.AbstractFile
 import scala.tools.nsc.reporters.StoreReporter
 import scala.tools.nsc.{Global, Settings}
@@ -247,11 +248,19 @@ object BytecodeTesting {
 
   def getAsmMethod(c: ClassNode, name: String): MethodNode = {
     val methods = getAsmMethods(c, name)
+    def fail() = {
+      val allNames = getAsmMethods(c, _ => true).map(_.name)
+      throw new AssertionFailedError(s"Could not find method named $name among ${allNames}")
+    }
     methods match {
       case List(m) => m
-      case ms =>
-        val allNames = getAsmMethods(c, _ => true).map(_.name)
-        throw new AssertionFailedError(s"Could not find method named $name among ${allNames}")
+      case ms @ List(m1, m2) if BytecodeUtils.isInterface(c) =>
+        val (statics, nonStatics) = ms.partition(BytecodeUtils.isStaticMethod)
+        (statics, nonStatics) match {
+          case (List(staticMethod), List(_)) => m1 // prefer the static method of the pair if methods in traits
+          case _ => fail()
+        }
+      case ms => fail()
     }
   }