gh-105938: Emit a SyntaxWarning for escaped braces in an f-string (#105939)

2 files changed, 9 insertions, 4 deletions

diff --git a/Parser/string_parser.c b/Parser/string_parser.c
index d4ce338..20459e8 100644
--- a/Parser/string_parser.c
+++ b/Parser/string_parser.c
@@ -12,6 +12,11 @@ static int
 warn_invalid_escape_sequence(Parser *p, const char *first_invalid_escape, Token *t)
 {
     unsigned char c = *first_invalid_escape;
+    if ((t->type == FSTRING_MIDDLE || t->type == FSTRING_END) && (c == '{' || c == '}')) {  // in this case the tokenizer has already emitted a warning,
+                                                                                            // see tokenizer.c:warn_invalid_escape_sequence
+        return 0;
+    }
+
     int octal = ('4' <= c && c <= '7');
     PyObject *msg =
         octal
@@ -31,7 +36,7 @@ warn_invalid_escape_sequence(Parser *p, const char *first_invalid_escape, Token
     if (PyErr_WarnExplicitObject(category, msg, p->tok->filename,
                                  t->lineno, NULL, NULL) < 0) {
         if (PyErr_ExceptionMatches(category)) {
-            /* Replace the DeprecationWarning exception with a SyntaxError
+            /* Replace the Syntax/DeprecationWarning exception with a SyntaxError
                to get a more accurate error report */
             PyErr_Clear();
 
diff --git a/Parser/tokenizer.c b/Parser/tokenizer.c
index 4f7b1f8..6bdf371 100644
--- a/Parser/tokenizer.c
+++ b/Parser/tokenizer.c
@@ -1559,12 +1559,12 @@ warn_invalid_escape_sequence(struct tok_state *tok, int first_invalid_escape_cha
         return -1;
     }
 
-    if (PyErr_WarnExplicitObject(PyExc_DeprecationWarning, msg, tok->filename,
+    if (PyErr_WarnExplicitObject(PyExc_SyntaxWarning, msg, tok->filename,
                                  tok->lineno, NULL, NULL) < 0) {
         Py_DECREF(msg);
 
-        if (PyErr_ExceptionMatches(PyExc_DeprecationWarning)) {
-            /* Replace the DeprecationWarning exception with a SyntaxError
+        if (PyErr_ExceptionMatches(PyExc_SyntaxWarning)) {
+            /* Replace the SyntaxWarning exception with a SyntaxError
                to get a more accurate error report */
             PyErr_Clear();
             return syntaxerror(tok, "invalid escape sequence '\\%c'", (char) first_invalid_escape_char);