Introduce await

runtime/vm/ast_transformer.h

Index: runtime/vm/ast_transformer.h
diff --git a/runtime/vm/ast_transformer.h b/runtime/vm/ast_transformer.h
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+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef VM_AST_TRANSFORMER_H_
+#define VM_AST_TRANSFORMER_H_
+
+#include "platform/assert.h"
+#include "vm/ast.h"
+
+namespace dart {
+
+class ParsedFunction;
+
+// Translate an AstNode containing an expression (that itself contains one or
+// more awaits) into a sequential representation where subexpressions are
+// evaluated sequentially into intermediates. Those intermediates are stored
+// within a context.
+//
+// This allows a function to be suspended and resumed from within evaluating an
+// expression. The evaluation is split among a so-called preamble and the
+// evaluation of the resulting expression (which is only a single load).
+//
+// Example (minimalistic):
+//
+//   var a = (await bar()) + foo();
+//
+// This translates to a premable similar to:
+//
+//   var t_1, t_2, t_3, t_4; // All stored in a context.
+//   t_1 = bar();
+//   :result_param = t_1;
+//   <continuation logic>
+//   t_2 = :result_param;
+//   t_3 = foo();
+//   t_4 = t_2.operator+(t_3);
+//
+// and a resulting expression of a load of t_4.
+//
+class AwaitTransformer : public AstNodeVisitor {
+ public:
+  AwaitTransformer(SequenceNode* preamble,
+                   const Library& library,
+                   ParsedFunction* const parsed_function)
+    : preamble_(preamble),
+      temp_cnt_(0),
+      library_(library),
+      parsed_function_(parsed_function),
+      isolate_(Isolate::Current()) {}
+
+#define DECLARE_VISIT(BaseName)                                                \
+  virtual void Visit##BaseName##Node(BaseName##Node* node);
+
+  FOR_EACH_NODE(DECLARE_VISIT)
+#undef DECLARE_VISIT
+
+  AstNode* Transform(AstNode* expr);
+
+ private:
+  LocalVariable* EnsureCurrentTempVar();
+  LocalVariable* AddToPreambleNewTempVar(AstNode* node);
+  ArgumentListNode* TransformArguments(ArgumentListNode* node);
+  AstNode* LazyTransform(const Token::Kind kind,
+                         AstNode* new_left,
+                         AstNode* right);
+
+  void NextTempVar() { temp_cnt_++; }
+
+  Isolate* isolate() const { return isolate_; }
+
+  SequenceNode* preamble_;
+  int temp_cnt_;
+  AstNode* result_;
+  const Library& library_;
+  ParsedFunction* const parsed_function_;
+
+  Isolate* isolate_;
+
+  DISALLOW_COPY_AND_ASSIGN(AwaitTransformer);
+};
+
+}  // namespace dart
+
+#endif  // VM_AST_TRANSFORMER_H_