From 5287e138176bc7ea18cb12f6e6e2aa821e1eefb7 Mon Sep 17 00:00:00 2001
From: MrSpider <philippfriedenberger@gmail.com>
Date: Fri, 10 Mar 2017 20:41:03 +0100
Subject: [PATCH] Fix replacing function declaration in export default (fixes
 #4468) (#5444)

---
 .../babel-traverse/src/path/replacement.js    |  3 +-
 packages/babel-traverse/test/replacement.js   | 28 +++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 packages/babel-traverse/test/replacement.js

diff --git a/packages/babel-traverse/src/path/replacement.js b/packages/babel-traverse/src/path/replacement.js
index a2028e6d8b..e82bba5b39 100644
--- a/packages/babel-traverse/src/path/replacement.js
+++ b/packages/babel-traverse/src/path/replacement.js
@@ -125,7 +125,8 @@ export function replaceWith(replacement) {
   if (this.isNodeType("Statement") && t.isExpression(replacement)) {
     if (
       !this.canHaveVariableDeclarationOrExpression() &&
-      !this.canSwapBetweenExpressionAndStatement(replacement)
+      !this.canSwapBetweenExpressionAndStatement(replacement) &&
+      !this.parentPath.isExportDefaultDeclaration()
     ) {
       // replacing a statement with an expression so wrap it in an expression statement
       replacement = t.expressionStatement(replacement);
diff --git a/packages/babel-traverse/test/replacement.js b/packages/babel-traverse/test/replacement.js
new file mode 100644
index 0000000000..eb29364f2f
--- /dev/null
+++ b/packages/babel-traverse/test/replacement.js
@@ -0,0 +1,28 @@
+import traverse from "../lib";
+import assert from "assert";
+import { parse } from "babylon";
+import * as t from "babel-types";
+
+describe("path/replacement", function () {
+  describe("replaceWith", function () {
+    const ast = parse("export default function() {};", { sourceType: "module" });
+
+    it("replaces declaration in ExportDefaultDeclaration node", function() {
+      traverse(ast, {
+        FunctionDeclaration(path) {
+          path.replaceWith(t.arrayExpression([
+            t.functionExpression(
+              path.node.id,
+              path.node.params,
+              path.node.body,
+              path.node.generator,
+              path.node.async
+            ),
+          ]));
+        },
+      });
+
+      assert(ast.program.body[0].declaration.type == "ArrayExpression");
+    });
+  });
+});