Fix async-to-generator ForAwait transform (#5932)

The old transform called an external `babel-traverse`, which doesn’t
does something funky.

packages/babel-helper-remap-async-to-generator/src/for-await.js

@@ -1,8 +1,7 @@
 import * as t from "babel-types";
 import template from "babel-template";
-import traverse from "babel-traverse";
 
-const buildForAwait = template(`
+const awaitTemplate = `
   function* wrapper() {
     var ITERATOR_COMPLETION = true;
     var ITERATOR_HAD_ERROR_KEY = false;
@@ -33,30 +32,11 @@ const buildForAwait = template(`
       }
     }
   }
-`);
-
-const forAwaitVisitor = {
-  noScope: true,
-
-  Identifier(path, replacements) {
-    if (path.node.name in replacements) {
-      path.replaceInline(replacements[path.node.name]);
-    }
-  },
-
-  CallExpression(path, replacements) {
-    const callee = path.node.callee;
-
-    // if no await wrapping is being applied, unwrap the call expression
-    if (
-      t.isIdentifier(callee) &&
-      callee.name === "AWAIT" &&
-      !replacements.AWAIT
-    ) {
-      path.replaceWith(path.node.arguments[0]);
-    }
-  },
-};
+`;
+const buildForAwait = template(awaitTemplate);
+const buildForAwaitWithoutWrapping = template(
+  awaitTemplate.replace(/\bAWAIT\b/g, ""),
+);
 
 export default function(path, helpers) {
   const { node, scope, parent } = path;
@@ -78,9 +58,10 @@ export default function(path, helpers) {
     ]);
   }
 
-  let template = buildForAwait();
-
-  traverse(template, forAwaitVisitor, null, {
+  const build = helpers.wrapAwait
+    ? buildForAwait
+    : buildForAwaitWithoutWrapping;
+  let template = build({
     ITERATOR_HAD_ERROR_KEY: scope.generateUidIdentifier("didIteratorError"),
     ITERATOR_COMPLETION: scope.generateUidIdentifier(
       "iteratorNormalCompletion",

packages/babel-helper-remap-async-to-generator/src/index.js

@@ -65,7 +65,6 @@ const awaitVisitor = {
 
     if (build.replaceParent) {
       path.parentPath.replaceWithMultiple(build.node);
-      path.remove();
     } else {
       path.replaceWithMultiple(build.node);
     }

packages/babel-plugin-transform-async-to-generator/test/fixtures/regression/5880/actual.js

@@ -0,0 +1,3 @@
+(async () => {
+  for await (const [value] of iterable) {}
+})()

packages/babel-plugin-transform-async-to-generator/test/fixtures/regression/5880/expected.js

@@ -0,0 +1,26 @@
+babelHelpers.asyncToGenerator(function* () {
+  var _iteratorNormalCompletion = true;
+  var _didIteratorError = false;
+  var _iteratorError = undefined;
+
+  try {
+    for (var _iterator = babelHelpers.asyncIterator(iterable), _step, _value; _step = yield _iterator.next(), _iteratorNormalCompletion = _step.done, _value = yield _step.value, !_iteratorNormalCompletion; _iteratorNormalCompletion = true) {
+      const _value2 = _value,
+            _value3 = babelHelpers.slicedToArray(_value2, 1),
+            value = _value3[0];
+    }
+  } catch (err) {
+    _didIteratorError = true;
+    _iteratorError = err;
+  } finally {
+    try {
+      if (!_iteratorNormalCompletion && _iterator.return) {
+        yield _iterator.return();
+      }
+    } finally {
+      if (_didIteratorError) {
+        throw _iteratorError;
+      }
+    }
+  }
+})();

packages/babel-plugin-transform-async-to-generator/test/fixtures/regression/5880/options.json

@@ -0,0 +1,8 @@
+{
+  "plugins": [
+    "external-helpers",
+    "transform-async-to-generator",
+    "transform-es2015-destructuring",
+    "syntax-async-generators"
+  ]
+}