fixup! bpo-40619: Correctly handle error text and offset for <string> input

Author: pablogsal

Lib/test/test_exceptions.py

@@ -229,6 +229,7 @@ def baz():
                 '''quux'''
             """, 9, 20)
         check("pass\npass\npass\n(1+)\npass\npass\npass", 4, 4)
+        check("(1+)", 1, 4)
 
         # Errors thrown by symtable.c
         check('x = [(yield i) for i in range(3)]', 1, 5)

Parser/pegen/pegen.c

@@ -399,7 +399,9 @@ _PyPegen_raise_error_known_location(Parser *p, PyObject *errtype,
 
     if (!error_line) {
         Py_ssize_t size = p->tok->inp - p->tok->buf;
-        error_line = PyUnicode_DecodeUTF8(p->tok->buf, size ? size - 1: size, "replace");
+        error_line = PyUnicode_DecodeUTF8(p->tok->buf,
+                                          p->tok->buf[size-1] == '\n' ? size - 1 : size,
+                                          "replace");
         if (!error_line) {
             goto error;
         }