[3.12] gh-105938: Emit a SyntaxWarning for escaped braces in an f-string (GH-105939) (#105941)

(cherry picked from commit 6586cee27f32f0354fe4e77c7b8c6e399329b5e2)

Co-authored-by: Lysandros Nikolaou <lisandrosnik@gmail.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/Lib/test/test_fstring.py b/Lib/test/test_fstring.py
index 8f6b576..ad5ac6a 100644
--- a/Lib/test/test_fstring.py
+++ b/Lib/test/test_fstring.py
@@ -13,6 +13,7 @@ import re
 import types
 import decimal
 import unittest
+import warnings
 from test import support
 from test.support.os_helper import temp_cwd
 from test.support.script_helper import assert_python_failure, assert_python_ok
@@ -904,7 +905,7 @@ x = (
         self.assertEqual(f'2\x203', '2 3')
         self.assertEqual(f'\x203', ' 3')
 
-        with self.assertWarns(DeprecationWarning):  # invalid escape sequence
+        with self.assertWarns(SyntaxWarning):  # invalid escape sequence
             value = eval(r"f'\{6*7}'")
         self.assertEqual(value, '\\42')
         with self.assertWarns(SyntaxWarning):  # invalid escape sequence
@@ -1037,7 +1038,7 @@ x = (
         ]
         for case, expected_result in deprecated_cases:
             with self.subTest(case=case, expected_result=expected_result):
-                with self.assertWarns(DeprecationWarning):
+                with self.assertWarns(SyntaxWarning):
                     result = eval(case)
                 self.assertEqual(result, expected_result)
         self.assertEqual(fr'\{{\}}', '\\{\\}')
@@ -1046,6 +1047,12 @@ x = (
         self.assertEqual(fr'\}}{1+1}', '\\}2')
         self.assertEqual(fr'{1+1}\}}', '2\\}')
 
+    def test_fstring_backslash_before_double_bracket_warns_once(self):
+        with warnings.catch_warnings(record=True) as w:
+            eval(r"f'\{{'")
+        self.assertEqual(len(w), 1)
+        self.assertEqual(w[0].category, SyntaxWarning)
+
     def test_fstring_backslash_prefix_raw(self):
         self.assertEqual(f'\\', '\\')
         self.assertEqual(f'\\\\', '\\\\')