bpo-44335: Fix a regression when identifying invalid characters in sy…

…ntax errors (GH-26589)

(cherry picked from commit d334c73)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>

Lib/test/test_exceptions.py

@@ -211,6 +211,7 @@ def testSyntaxErrorOffset(self):
         check('lambda x: x = 2', 1, 1)
         check('f{a + b + c}', 1, 2)
         check('[file for str(file) in []\n])', 2, 2)
+        check('a = « hello » « world »', 1, 5)
         check('[\nfile\nfor str(file)\nin\n[]\n]', 3, 5)
         check('[file for\n str(file) in []]', 2, 2)
         check("ages = {'Alice'=22, 'Bob'=23}", 1, 16)

Misc/NEWS.d/next/Core and Builtins/2021-06-08-01-13-47.bpo-44335.GQTTkl.rst

@@ -0,0 +1,2 @@
+Fix a regression when identifying incorrect characters in syntax errors.
+Patch by Pablo Galindo

Parser/pegen.c

@@ -1288,7 +1288,9 @@ _PyPegen_run_parser(Parser *p)
         reset_parser_state(p);
         _PyPegen_parse(p);
         if (PyErr_Occurred()) {
-            if (PyErr_ExceptionMatches(PyExc_SyntaxError)) {
+            // Prioritize tokenizer errors to custom syntax errors raised
+            // on the second phase only if the errors come from the parser.
+            if (p->tok->done != E_ERROR && PyErr_ExceptionMatches(PyExc_SyntaxError)) {
                 _PyPegen_check_tokenizer_errors(p);
             }
             return NULL;