Implement the transformation as a PathVisitor.

Author: benjamn

visitor.js

@@ -0,0 +1,61 @@
+var recast = require("recast");
+var types = recast.types;
+var b = types.builders;
+
+exports.visitFunction = function(path) {
+  // Calling this.traverse(path) first makes for a post-order traversal.
+  this.traverse(path);
+
+  var node = path.value;
+  if (node.async) {
+    node.async = false;
+  } else {
+    return;
+  }
+
+  awaitVisitor.visit(path.get("body"));
+
+  var resultExpr = b.callExpression(
+    b.memberExpression(
+      this.getRuntime(),
+      b.identifier("async"),
+      false
+    ),
+    [b.callExpression(
+      b.functionExpression(
+        null, // Anonymous.
+        [], // No parameters.
+        node.body, // Body without await.
+        true, // Generator.
+        node.expression
+      ),
+      [] // Immediately invoked.
+    )]
+  );
+
+  if (node.expression) {
+    node.body = resultExpr;
+  } else {
+    node.body = b.blockStatement([
+      b.returnStatement(resultExpr)
+    ]);
+  }
+};
+
+exports.getRuntime = function() {
+  return b.callExpression(
+    b.identifier("require"),
+    [b.literal("es7-async-await/runtime")]
+  );
+};
+
+var awaitVisitor = types.PathVisitor.fromMethodsObject({
+  visitFunction: function(path) {
+    return false; // Don't descend into nested function scopes.
+  },
+
+  visitAwaitExpression: function(path) {
+    // Convert await expressions to yield expressions.
+    return b.yieldExpression(path.value.argument, false);
+  }
+});