From 50068cd4e04a61ac5bb7e8c2149d27145436b832 Mon Sep 17 00:00:00 2001
From: Ben Newman <ben@benjamn.com>
Date: Wed, 30 Nov 2016 22:48:40 -0500
Subject: [PATCH] Keep directive strings at top of original function.

Fixes #248.
---
 packages/regenerator-transform/package.json |  2 +-
 packages/regenerator-transform/src/visit.js | 17 +++++++++++++-
 test/tests.es6.js                           | 25 +++++++++++++++++++++
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/packages/regenerator-transform/package.json b/packages/regenerator-transform/package.json
index 3fcf4418e..0e9ae23ca 100644
--- a/packages/regenerator-transform/package.json
+++ b/packages/regenerator-transform/package.json
@@ -2,7 +2,7 @@
   "name": "regenerator-transform",
   "author": "Ben Newman <bn@cs.stanford.edu>",
   "description": "Explode async and generator functions into a state machine.",
-  "version": "0.9.6",
+  "version": "0.9.7",
   "main": "lib/index.js",
   "keywords": [
     "regenerator",
diff --git a/packages/regenerator-transform/src/visit.js b/packages/regenerator-transform/src/visit.js
index 8d96f2b40..15f6203dc 100644
--- a/packages/regenerator-transform/src/visit.js
+++ b/packages/regenerator-transform/src/visit.js
@@ -56,7 +56,15 @@ exports.visitor = {
 
       bodyBlockPath.get("body").forEach(function(childPath) {
         let node = childPath.node;
-        if (node && node._blockHoist != null) {
+        if (t.isExpressionStatement(node) &&
+            t.isStringLiteral(node.expression)) {
+          // Babylon represents directives like "use strict" as elements
+          // of a bodyBlockPath.node.directives array, but they could just
+          // as easily be represented (by other parsers) as traditional
+          // string-literal-valued expression statements, so we need to
+          // handle that here. (#248)
+          outerBody.push(node);
+        } else if (node && node._blockHoist != null) {
           outerBody.push(node);
         } else {
           innerBody.push(node);
@@ -117,6 +125,13 @@ exports.visitor = {
       outerBody.push(t.returnStatement(wrapCall));
       node.body = t.blockStatement(outerBody);
 
+      const oldDirectives = bodyBlockPath.node.directives;
+      if (oldDirectives) {
+        // Babylon represents directives like "use strict" as elements of
+        // a bodyBlockPath.node.directives array. (#248)
+        node.body.directives = oldDirectives;
+      }
+
       let wasGeneratorFunction = node.generator;
       if (wasGeneratorFunction) {
         node.generator = false;
diff --git a/test/tests.es6.js b/test/tests.es6.js
index a5902d303..e4a56c4c0 100644
--- a/test/tests.es6.js
+++ b/test/tests.es6.js
@@ -1484,6 +1484,31 @@ describe("the arguments object", function() {
   });
 });
 
+describe("directive strings", function () {
+  function *strict() {
+    "use strict";
+    yield ! this;
+  }
+
+  function *sloppy() {
+    yield ! this;
+  }
+
+  it("should be kept at top of outer function", function () {
+    var strictCode = String(strict);
+    var useStrictIndex = strictCode.indexOf("use strict");
+    var thisIndex = strictCode.indexOf("this");
+
+    assert.notStrictEqual(useStrictIndex, -1);
+    assert.ok(thisIndex > useStrictIndex);
+
+    assert.strictEqual(String(sloppy).indexOf("use strict"), -1);
+
+    check(strict(), [true]);
+    check(sloppy(), [false]);
+  });
+});
+
 describe("catch parameter shadowing", function() {
   it("should leave outer variables unmodified", function() {
     function *gen(x) {