From f38831df2394d541e2e3dc34d2a1b7b43b32233c Mon Sep 17 00:00:00 2001
From: Nitin Kumar <snitin315@gmail.com>
Date: Wed, 11 Nov 2020 13:40:27 +0530
Subject: [PATCH] fix: arrow-fn transformation when  is defined as var

---
 .../arrow-functions/arguments/input.js        | 28 +++++++++++++
 .../arrow-functions/arguments/output.js       | 40 +++++++++++++++++++
 .../babel-traverse/src/path/conversion.js     | 18 +++++++--
 3 files changed, 82 insertions(+), 4 deletions(-)

diff --git a/packages/babel-plugin-transform-arrow-functions/test/fixtures/arrow-functions/arguments/input.js b/packages/babel-plugin-transform-arrow-functions/test/fixtures/arrow-functions/arguments/input.js
index 198ac999f6ae..1c267271b0f2 100644
--- a/packages/babel-plugin-transform-arrow-functions/test/fixtures/arrow-functions/arguments/input.js
+++ b/packages/babel-plugin-transform-arrow-functions/test/fixtures/arrow-functions/arguments/input.js
@@ -43,3 +43,31 @@ function six(obj) {
   return fn();
 }
 six();
+
+var seven = () => {
+    var arguments = 1;
+    return arguments;
+};
+seven();
+
+var eight = () => {
+    var arguments = 1;
+    return () => arguments;
+};
+eight();
+
+function nine() {
+    var arguments = 1;
+    var foo = () => {
+      return arguments;
+    };
+}
+nine();
+
+var arguments = 1;
+function ten() {
+  var foo = () => {
+    return arguments;
+  };
+}
+ten();
\ No newline at end of file
diff --git a/packages/babel-plugin-transform-arrow-functions/test/fixtures/arrow-functions/arguments/output.js b/packages/babel-plugin-transform-arrow-functions/test/fixtures/arrow-functions/arguments/output.js
index 84bbb58be445..ae6ed4618f55 100644
--- a/packages/babel-plugin-transform-arrow-functions/test/fixtures/arrow-functions/arguments/output.js
+++ b/packages/babel-plugin-transform-arrow-functions/test/fixtures/arrow-functions/arguments/output.js
@@ -1,3 +1,5 @@
+var _arguments6 = arguments;
+
 function one() {
   var _arguments = arguments;
 
@@ -81,3 +83,41 @@ function six(obj) {
 }
 
 six();
+
+var seven = function () {
+  var arguments = 1;
+  return arguments;
+};
+
+seven();
+
+var eight = function () {
+  var arguments = 1;
+  return function () {
+    return _arguments6;
+  };
+};
+
+eight();
+
+function nine() {
+  var _arguments7 = arguments;
+  var arguments = 1;
+
+  var foo = function () {
+    return _arguments7;
+  };
+}
+
+nine();
+var arguments = 1;
+
+function ten() {
+  var _arguments8 = arguments;
+
+  var foo = function () {
+    return _arguments8;
+  };
+}
+
+ten();
diff --git a/packages/babel-traverse/src/path/conversion.js b/packages/babel-traverse/src/path/conversion.js
index 2ca47297c9ab..65851253f393 100644
--- a/packages/babel-traverse/src/path/conversion.js
+++ b/packages/babel-traverse/src/path/conversion.js
@@ -223,10 +223,20 @@ function hoistFunctionEnvironment(
     );
 
     argumentsPaths.forEach(argumentsChild => {
-      const argsRef = t.identifier(argumentsBinding);
-      argsRef.loc = argumentsChild.node.loc;
-
-      argumentsChild.replaceWith(argsRef);
+      let currentScope = argumentsChild.scope;
+      do {
+        if (
+          !currentScope.hasOwnBinding("arguments") &&
+          !(
+            currentScope.path.isFunctionExpression() ||
+            currentScope.path.isFunctionDeclaration()
+          )
+        ) {
+          const argsRef = t.identifier(argumentsBinding);
+          argsRef.loc = argumentsChild.node.loc;
+          argumentsChild.replaceWith(argsRef);
+        }
+      } while ((currentScope = currentScope.parent));
     });
   }