From b6328ca05030d815222b25d208cc59a964623bf9 Mon Sep 17 00:00:00 2001
From: bashonly <bashonly@protonmail.com>
Date: Sat, 5 Jul 2025 16:55:36 -0500
Subject: [PATCH] [jsinterp] Fix variable scoping (#13639)

Authored by: bashonly, seproDev

Co-authored-by: sepro <sepro@sepr0.com>
---
 test/test_jsinterp.py | 46 +++++++++++++++++++++++++++++++++++++++++++
 yt_dlp/jsinterp.py    | 31 +++++++++++++++++++++++++----
 2 files changed, 73 insertions(+), 4 deletions(-)

diff --git a/test/test_jsinterp.py b/test/test_jsinterp.py
index 4268e890b8..a1088cea49 100644
--- a/test/test_jsinterp.py
+++ b/test/test_jsinterp.py
@@ -490,6 +490,52 @@ class TestJSInterpreter(unittest.TestCase):
         self._test('function f() { var a = "test--"; return a; }', 'test--')
         self._test('function f() { var b = 1; var a = "b--"; return a; }', 'b--')
 
+    def test_nested_function_scoping(self):
+        self._test(R'''
+            function f() {
+                var g = function() {
+                    var P = 2;
+                    return P;
+                };
+                var P = 1;
+                g();
+                return P;
+            }
+        ''', 1)
+        self._test(R'''
+            function f() {
+                var x = function() {
+                    for (var w = 1, M = []; w < 2; w++) switch (w) {
+                        case 1:
+                            M.push("a");
+                        case 2:
+                            M.push("b");
+                    }
+                    return M
+                };
+                var w = "c";
+                var M = "d";
+                var y = x();
+                y.push(w);
+                y.push(M);
+                return y;
+            }
+        ''', ['a', 'b', 'c', 'd'])
+        self._test(R'''
+            function f() {
+                var P, Q;
+                var z = 100;
+                var g = function() {
+                    var P, Q; P = 2; Q = 15;
+                    z = 0;
+                    return P+Q;
+                };
+                P = 1; Q = 10;
+                var x = g(), y = 3;
+                return P+Q+x+y+z;
+            }
+        ''', 31)
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/yt_dlp/jsinterp.py b/yt_dlp/jsinterp.py
index b49f0cf30a..5b3b33f456 100644
--- a/yt_dlp/jsinterp.py
+++ b/yt_dlp/jsinterp.py
@@ -222,6 +222,14 @@ class LocalNameSpace(collections.ChainMap):
     def __delitem__(self, key):
         raise NotImplementedError('Deleting is not supported')
 
+    def set_local(self, key, value):
+        self.maps[0][key] = value
+
+    def get_local(self, key):
+        if key in self.maps[0]:
+            return self.maps[0][key]
+        return JS_Undefined
+
 
 class Debugger:
     import sys
@@ -381,7 +389,7 @@ class JSInterpreter:
             return self._named_object(namespace, obj)
 
     @Debugger.wrap_interpreter
-    def interpret_statement(self, stmt, local_vars, allow_recursion=100):
+    def interpret_statement(self, stmt, local_vars, allow_recursion=100, _is_var_declaration=False):
         if allow_recursion < 0:
             raise self.Exception('Recursion limit reached')
         allow_recursion -= 1
@@ -401,6 +409,7 @@ class JSInterpreter:
             if m.group('throw'):
                 raise JS_Throw(self.interpret_expression(expr, local_vars, allow_recursion))
             should_return = not m.group('var')
+            _is_var_declaration = _is_var_declaration or bool(m.group('var'))
         if not expr:
             return None, should_return
 
@@ -585,7 +594,8 @@ class JSInterpreter:
         sub_expressions = list(self._separate(expr))
         if len(sub_expressions) > 1:
             for sub_expr in sub_expressions:
-                ret, should_abort = self.interpret_statement(sub_expr, local_vars, allow_recursion)
+                ret, should_abort = self.interpret_statement(
+                    sub_expr, local_vars, allow_recursion, _is_var_declaration=_is_var_declaration)
                 if should_abort:
                     return ret, True
             return ret, False
@@ -599,8 +609,12 @@ class JSInterpreter:
             left_val = local_vars.get(m.group('out'))
 
             if not m.group('index'):
-                local_vars[m.group('out')] = self._operator(
+                eval_result = self._operator(
                     m.group('op'), left_val, m.group('expr'), expr, local_vars, allow_recursion)
+                if _is_var_declaration:
+                    local_vars.set_local(m.group('out'), eval_result)
+                else:
+                    local_vars[m.group('out')] = eval_result
                 return local_vars[m.group('out')], should_return
             elif left_val in (None, JS_Undefined):
                 raise self.Exception(f'Cannot index undefined variable {m.group("out")}', expr)
@@ -654,7 +668,16 @@ class JSInterpreter:
             return float('NaN'), should_return
 
         elif m and m.group('return'):
-            return local_vars.get(m.group('name'), JS_Undefined), should_return
+            var = m.group('name')
+            # Declared variables
+            if _is_var_declaration:
+                ret = local_vars.get_local(var)
+                # Register varname in local namespace
+                # Set value as JS_Undefined or its pre-existing value
+                local_vars.set_local(var, ret)
+            else:
+                ret = local_vars.get(var, JS_Undefined)
+            return ret, should_return
 
         with contextlib.suppress(ValueError):
             return json.loads(js_to_json(expr, strict=True)), should_return