fix rest parameter array allocation loop being incorrectly aliased - fixes #1800

CHANGELOG.md

@@ -13,6 +13,11 @@ _Note: Gaps between patch versions are faulty/broken releases._
 
 See [CHANGELOG - 6to5](CHANGELOG-6to5.md) for the pre-4.0.0 version changelog.
 
+## 5.6.3
+
+ * **Bug Fix**
+  * Fix rest parameter array allocation loop being incorrectly aliased.
+
 ## 5.6.2
 
  * **Bug Fix**

src/babel/transformation/transformers/es6/parameters.rest.js

@@ -100,7 +100,6 @@ export var visitor = {
     }
 
     // check and optimise for extremely common cases
-
     var state = {
       references: [],
       offset:     node.params.length,
@@ -135,6 +134,9 @@ export var visitor = {
       state.references = state.references.concat(state.candidates);
     }
 
+    // deopt shadowed functions as transforms like regenerator may try touch the allocation loop
+    state.deopted = state.deopted || !!node.shadow;
+
     //
 
     var start = t.literal(node.params.length);
@@ -173,13 +175,13 @@ export var visitor = {
       LEN:        len
     });
 
-    if (!state.deopted) {
+    if (state.deopted) {
+      loop._blockHoist = node.params.length + 1;
+      node.body.body.unshift(loop);
+    } else {
       // perform allocation at the lowest common denominator of all references
+      loop._blockHoist = 1;
       this.getEarliestCommonAncestorFrom(state.references).getStatementParent().insertBefore(loop);
-      return;
     }
-
-    loop._blockHoist = node.params.length + 1;
-    node.body.body.unshift(loop);
   }
 };

test/core/fixtures/transformation/es6.parameters.rest/async-function/actual.js

@@ -0,0 +1,7 @@
+var fn = async (...rest) => rest;
+
+var fn = async (...rest) => {
+  if (true) {
+    rest;
+  }
+};

test/core/fixtures/transformation/es6.parameters.rest/async-function/expected.js

@@ -0,0 +1,39 @@
+"use strict";
+
+var _this = this;
+
+var fn = function fn() {
+  for (var _len = arguments.length, rest = Array(_len), _key = 0; _key < _len; _key++) {
+    rest[_key] = arguments[_key];
+  }
+
+  return regeneratorRuntime.async(function fn$(context$1$0) {
+    while (1) switch (context$1$0.prev = context$1$0.next) {
+      case 0:
+        return context$1$0.abrupt("return", rest);
+
+      case 1:
+      case "end":
+        return context$1$0.stop();
+    }
+  }, null, _this);
+};
+
+var fn = function fn() {
+  for (var _len2 = arguments.length, rest = Array(_len2), _key2 = 0; _key2 < _len2; _key2++) {
+    rest[_key2] = arguments[_key2];
+  }
+
+  return regeneratorRuntime.async(function fn$(context$1$0) {
+    while (1) switch (context$1$0.prev = context$1$0.next) {
+      case 0:
+        if (true) {
+          rest;
+        }
+
+      case 1:
+      case "end":
+        return context$1$0.stop();
+    }
+  }, null, _this);
+};

test/core/fixtures/transformation/es6.parameters.rest/async-function/options.json

@@ -0,0 +1,3 @@
+{
+  "stage": 0
+}