fix fuzz test failed

Author: lpyu001

Lib/test/test_tstring.py

@@ -162,6 +162,18 @@ def test_debug_specifier(self):
         )
         self.assertEqual(fstring(t), "Value: value = 42")
 
+    def test_debug_specifier_with_reconstructed_metadata(self):
+        regular = t'''{(
+            1,  # Force lexer metadata reconstruction.
+            "\"#")}'''
+        debug = t'''{(
+            1,  # Force lexer metadata reconstruction.
+            "\"#")=}'''
+        self.assertEqual(
+            debug.interpolations[0].expression,
+            regular.interpolations[0].expression,
+        )
+
     def test_raw_tstrings(self):
         path = r"C:\Users"
         t = rt"{path}\Documents"

Parser/action_helpers.c

@@ -1552,7 +1552,10 @@ _strip_interpolation_debug_expr(PyObject *exprstr)
         }
         len--;
     }
-    assert(len > 0 && PyUnicode_READ_CHAR(exprstr, len - 1) == '=');
+    /* The debug marker may be absent from reconstructed lexer metadata. */
+    if (len == 0 || PyUnicode_READ_CHAR(exprstr, len - 1) != '=') {
+        return Py_NewRef(exprstr);
+    }
 
     return PyUnicode_Substring(exprstr, 0, len - 1);
 }