From bffa415b83e7cef21cb43b05cc05fc93cf0ac782 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hu=C3=A1ng=20J=C3=B9nli=C3=A0ng?= <jlhwung@gmail.com>
Date: Fri, 13 Dec 2019 08:39:37 -0500
Subject: [PATCH] Check shadow variable to identifier in default parameters
 (#10053)

When there is a variable declaration inside the function body, which shares its name to a referenced identifier in default parameter expression, the function body should be wrapped into iife, otherwise the binding in default parameter scope will be shadowed by function body.
---
 .../babel-plugin-transform-parameters/src/params.js |  6 +++++-
 .../fixtures/parameters/default-iife-9947/input.js  |  6 ++++++
 .../fixtures/parameters/default-iife-9947/output.js | 13 +++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-iife-9947/input.js
 create mode 100644 packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-iife-9947/output.js

diff --git a/packages/babel-plugin-transform-parameters/src/params.js b/packages/babel-plugin-transform-parameters/src/params.js
index 000a8505a581..4bf346b5be7b 100644
--- a/packages/babel-plugin-transform-parameters/src/params.js
+++ b/packages/babel-plugin-transform-parameters/src/params.js
@@ -32,7 +32,11 @@ function isSafeBinding(scope, node) {
 const iifeVisitor = {
   ReferencedIdentifier(path, state) {
     const { scope, node } = path;
-    if (node.name === "eval" || !isSafeBinding(scope, node)) {
+    if (
+      node.name === "eval" ||
+      !isSafeBinding(scope, node) ||
+      !isSafeBinding(state.scope, node)
+    ) {
       state.iife = true;
       path.stop();
     }
diff --git a/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-iife-9947/input.js b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-iife-9947/input.js
new file mode 100644
index 000000000000..e2ca36c7ddb2
--- /dev/null
+++ b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-iife-9947/input.js
@@ -0,0 +1,6 @@
+let x = "outside";
+function outer(a = () => x) {
+  let x = "inside";
+  return a();
+}
+outer();
diff --git a/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-iife-9947/output.js b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-iife-9947/output.js
new file mode 100644
index 000000000000..74ff50c2df94
--- /dev/null
+++ b/packages/babel-plugin-transform-parameters/test/fixtures/parameters/default-iife-9947/output.js
@@ -0,0 +1,13 @@
+var x = "outside";
+
+function outer() {
+  var a = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : function () {
+    return x;
+  };
+  return function () {
+    var x = "inside";
+    return a();
+  }();
+}
+
+outer();