bpo-44143: Fix crash in the parser when raising tokenizer errors with an exception set (GH-26144) (GH-26148)

(cherry picked from commit 80b0891)

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

Author: miss-islington

Lib/test/test_exceptions.py

@@ -242,6 +242,7 @@ def baz():
             """, 9, 24)
         check("pass\npass\npass\n(1+)\npass\npass\npass", 4, 4)
         check("(1+)", 1, 4)
+        check("[interesting\nfoo()\n", 1, 1)
 
         # Errors thrown by symtable.c
         check('x = [(yield i) for i in range(3)]', 1, 5)

Misc/NEWS.d/next/Core and Builtins/2021-05-15-17-30-57.bpo-44143.7UTS6H.rst

@@ -0,0 +1,2 @@
+Fixed a crash in the parser that manifest when raising tokenizer errors when
+an existing exception was present. Patch by Pablo Galindo.

Parser/pegen.c

@@ -1259,6 +1259,7 @@ _PyPegen_check_tokenizer_errors(Parser *p) {
                 if (p->tok->level != 0) {
                     int error_lineno = p->tok->parenlinenostack[p->tok->level-1];
                     if (current_err_line > error_lineno) {
+                        PyErr_Clear();
                         raise_unclosed_parentheses_error(p);
                         return -1;
                     }