Await it!

runtime/vm/ast.h

Index: runtime/vm/ast.h
diff --git a/runtime/vm/ast.h b/runtime/vm/ast.h
index 7c1279b4fa58df4e01c3b4a5025664d3e6afa18f..d10e50c28f57ac0f4c41fc83a2e5df5406be03ba 100644
--- a/runtime/vm/ast.h
+++ b/runtime/vm/ast.h
@@ -17,6 +17,7 @@ namespace dart {
 
 #define FOR_EACH_NODE(V)                                                       \
   V(Await)                                                                     \
+  V(AwaitMarker)                                                               \
   V(Return)                                                                    \
   V(Literal)                                                                   \
   V(Type)                                                                      \
@@ -168,6 +169,45 @@ class AwaitNode : public AstNode {
 };
 
 
+// AwaitMarker nodes are used to generate markers that the FlowGraphBuilder
+// relies on. They can occur in two kinds:
+// 1) kNewContinuationState: A marker indicating that a new await state needs to
+//    be added to a function preamble. This type also triggers storing of the
+//    current context.
+// 2) kTargetForContinuation: A marker indicating an entry point for the most
+//    recent generated state.
+//
+// In general it is expected (ASSERT) that the different kinds of markers reach
+// the FlowGraphBuilder in alternating order. That is:
+//   <new state> -> <other nodes> -> <target> -> <other nodes> ->
+//   <new state> -> ...
+class AwaitMarkerNode : public AstNode {
+ public:
+  enum Type {
+    kNewContinuationState,
+    kTargetForContinuation,
+  };
+
+  explicit AwaitMarkerNode(Type type)
+    : AstNode(Scanner::kNoSourcePos), type_(type) { }
+
+  void VisitChildren(AstNodeVisitor* visitor) const { }
+
+  Type type() const { return type_; }
+
+  LocalScope* scope() const { return scope_; }
+  void set_scope(LocalScope* scope) { scope_ = scope; }
+
+  DECLARE_COMMON_NODE_FUNCTIONS(AwaitMarkerNode);
+
+ private:
+  Type type_;
+  LocalScope* scope_;
+
+  DISALLOW_COPY_AND_ASSIGN(AwaitMarkerNode);
+};
+
+
 class SequenceNode : public AstNode {
  public:
   SequenceNode(intptr_t token_pos, LocalScope* scope)
@@ -536,24 +576,31 @@ class PrimaryNode : public AstNode {
   DISALLOW_IMPLICIT_CONSTRUCTORS(PrimaryNode);
 };
 
-
-// TODO(mlippautz): Implement return nodes that are used to return from a
-// continuation.
+// Return nodes can be of different types:
+// * A regular return node that in the case of async functions gets replaced
+//   with appropriate completer calls. This kind is generated by dart code.
+// * A continuation return that just returns from a function. This kind is
+//   generated by AST transformers.
 class ReturnNode : public AstNode {
  public:
+  enum ReturnType {
+    kRegular,
+    kContinuation,
+  };
+
   // Return from a void function returns the null object.
   explicit ReturnNode(intptr_t token_pos)
       : AstNode(token_pos),
         value_(new LiteralNode(token_pos, Instance::ZoneHandle())),
         inlined_finally_list_(),
-        is_regular_return_(true) { }
+        return_type_(kRegular) { }
   // Return from a non-void function.
   ReturnNode(intptr_t token_pos,
              AstNode* value)
       : AstNode(token_pos),
         value_(value),
         inlined_finally_list_(),
-        is_regular_return_(true) {
+        return_type_(kRegular) {
     ASSERT(value_ != NULL);
   }
 
@@ -578,8 +625,8 @@ class ReturnNode : public AstNode {
   void set_scope(LocalScope* scope) { scope_ = scope; }
   LocalScope* scope() const { return scope_; }
 
-  // Returns false if the return node is used to return from a continuation.
-  bool is_regular_return() const { return is_regular_return_; }
+  ReturnType return_type() const { return return_type_; }
+  void set_return_type(ReturnType type) { return_type_ = type; }
 
   DECLARE_COMMON_NODE_FUNCTIONS(ReturnNode);
 
@@ -587,7 +634,7 @@ class ReturnNode : public AstNode {
   AstNode* value_;
   GrowableArray<InlinedFinallyNode*> inlined_finally_list_;
   LocalScope* scope_;
-  bool is_regular_return_;
+  ReturnType return_type_;
 
   DISALLOW_COPY_AND_ASSIGN(ReturnNode);
 };