Revert "Pull - Cut ties with BindBind, no need for the BuildR"

This reverts commit f63dd03.

Author: diesalbla

core/shared/src/main/scala/fs2/Pull.scala

@@ -654,10 +654,9 @@ object Pull extends PullLowPriority {
     def cont(r: Terminal[Unit]): Pull[Pure, INothing, Unit] = r
   }
 
-  private abstract class Bind[+F[_], +O, X, +R](misstep: Pull[F, O, X])
+  private abstract class Bind[+F[_], +O, X, +R](val step: Pull[F, O, X])
       extends Pull[F, O, R]
       with ContP[X, F, O, R] {
-    def step: Pull[F, O, X] = misstep
     def cont(r: Terminal[X]): Pull[F, O, R]
     def delegate: Bind[F, O, X, R] = this
   }
@@ -694,12 +693,12 @@ object Pull extends PullLowPriority {
 
   // This class is not created by combinators in public Pull API, only during compilation
   private class BindBind[F[_], O, X, Y](
-      var innerBind: Bind[F, O, X, Y],
-      var endBind: Bind[F, O, Y, Unit]
-  ) extends Bind[F, O, X, Unit](null) {
-    override def step: Pull[F, O, X] = innerBind.step
-    def cont(xterm: Terminal[X]): Pull[F, O, Unit] =
-      try bindBindAux(xterm, this)
+      step: Pull[F, O, X],
+      val bb: Bind[F, O, X, Y],
+      val del: Bind[F, O, Y, Unit]
+  ) extends Bind[F, O, X, Unit](step) {
+    def cont(tx: Terminal[X]): Pull[F, O, Unit] =
+      try bindBindAux(bb.cont(tx), del)
       catch { case NonFatal(e) => Fail(e) }
   }
 
@@ -712,12 +711,7 @@ object Pull extends PullLowPriority {
       case ty: Terminal[_] =>
         del match {
           case cici: BindBind[F, O, r, Y] =>
-            val innerBind = cici.innerBind
-            val endBind = cici.endBind
-            cici.innerBind = null
-            cici.endBind = null
-            val nextStep = innerBind.cont(ty)
-            bindBindAux[F, O, r, Y](nextStep, endBind)
+            bindBindAux[F, O, r, Y](cici.bb.cont(ty), cici.del)
           case _ => del.cont(ty)
         }
       case x => new DelegateBind(x, del)
@@ -871,7 +865,7 @@ object Pull extends PullLowPriority {
         case b: Bind[G, X, y, Unit] =>
           b.step match {
             case c: Bind[G, X, x, _] =>
-              viewL(new BindBind[G, X, x, y](c, b.delegate))
+              viewL(new BindBind[G, X, x, y](c.step, c.delegate, b.delegate))
             case e: Action[G, X, y2] =>
               contP = b.delegate
               e
@@ -910,6 +904,21 @@ object Pull extends PullLowPriority {
       def interrupted(inter: Interrupted): End
       def fail(e: Throwable): End
     }
+    type CallRun[+G[_], +X, End] = Run[G, X, End] => End
+
+    object TheBuildR extends Run[Pure, INothing, F[CallRun[Pure, Nothing, F[INothing]]]] {
+      type TheRun = Run[Pure, INothing, F[INothing]]
+      def fail(e: Throwable) = F.raiseError(e)
+      def done(scope: Scope[F]) =
+        F.pure((cont: TheRun) => cont.done(scope))
+      def out(head: Chunk[INothing], scope: Scope[F], tail: Pull[Pure, INothing, Unit]) =
+        F.pure((cont: TheRun) => cont.out(head, scope, tail))
+      def interrupted(i: Interrupted) =
+        F.pure((cont: TheRun) => cont.interrupted(i))
+    }
+
+    def buildR[G[_], X, End]: Run[G, X, F[CallRun[G, X, F[End]]]] =
+      TheBuildR.asInstanceOf[Run[G, X, F[CallRun[G, X, F[End]]]]]
 
     def go[G[_], X, End](
         scope: Scope[F],
@@ -1205,13 +1214,17 @@ object Pull extends PullLowPriority {
         case u: Uncons[G, y] @unchecked =>
           val v = getCont[Option[(Chunk[y], Pull[G, y, Unit])], G, X]
           // a Uncons is run on the same scope, without shifting.
-          F.unit >> go(scope, extendedTopLevelScope, translation, new UnconsRunR(v), u.stream)
+          val runr = buildR[G, y, End]
+          F.unit >> go(scope, extendedTopLevelScope, translation, runr, u.stream).attempt
+            .flatMap(_.fold(goErr(_, v), _.apply(new UnconsRunR(v))))
 
         case s: StepLeg[G, y] @unchecked =>
           val v = getCont[Option[Stream.StepLeg[G, y]], G, X]
+          val runr = buildR[G, y, End]
           scope
             .shiftScope(s.scope, s.toString)
-            .flatMap(go(_, extendedTopLevelScope, translation, new StepLegRunR(v), s.stream))
+            .flatMap(go(_, extendedTopLevelScope, translation, runr, s.stream).attempt)
+            .flatMap(_.fold(goErr(_, v), _.apply(new StepLegRunR(v))))
 
         case _: GetScope[_] =>
           go(scope, extendedTopLevelScope, translation, runner, getCont(Succeeded(scope)))