Add a hook for future systems to get the Graphviz diagnostic

Author: retronym

src/main/scala/scala/async/internal/AsyncTransform.scala

@@ -115,6 +115,7 @@ trait AsyncTransform {
     if(AsyncUtils.verbose) {
       logDiagnostics(anfTree, asyncBlock, asyncBlock.asyncStates.map(_.toString))
     }
+    futureSystemOps.dot(enclosingOwner, body).foreach(f => f(asyncBlock.toDot))
     cleanupContainsAwaitAttachments(result)
   }
 

src/main/scala/scala/async/internal/FutureSystem.scala

@@ -71,6 +71,9 @@ trait FutureSystem {
 
     /** A hook for custom macros to transform the tree post-ANF transform */
     def postAnfTransform(tree: Block): Block = tree
+
+    /** A hook for custom macros to selectively generate and process a Graphviz visualization of the transformed state machine */
+    def dot(enclosingOwner: Symbol, macroApplication: Tree): Option[(String => Unit)] = None
   }
 
   def mkOps(c0: Context): Ops { val c: c0.type }