gh-110696: Fix incorrect syntax error message for incorrect argument unpacking (#110706)

Author: pablogsal

Grammar/python.gram

@@ -1128,7 +1128,8 @@ func_type_comment[Token*]:
 
 # From here on, there are rules for invalid syntax with specialised error messages
 invalid_arguments:
-    | a=args ',' '*' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "iterable argument unpacking follows keyword argument unpacking") }
+    | ((','.(starred_expression | ( assignment_expression | expression !':=') !'=')+ ',' kwargs) | kwargs) ',' b='*' {
+        RAISE_SYNTAX_ERROR_KNOWN_LOCATION(b, "iterable argument unpacking follows keyword argument unpacking") }
     | a=expression b=for_if_clauses ',' [args | expression for_if_clauses] {
         RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, _PyPegen_get_last_comprehension_item(PyPegen_last_item(b, comprehension_ty)), "Generator expression must be parenthesized") }
     | a=NAME b='=' expression for_if_clauses {

Lib/test/test_syntax.py

@@ -1955,6 +1955,17 @@ def f(x: *b)
       ...
    SyntaxError: yield expression cannot be used within the definition of a generic
 
+    >>> f(**x, *y)
+    Traceback (most recent call last):
+    SyntaxError: iterable argument unpacking follows keyword argument unpacking
+
+    >>> f(**x, *)
+    Traceback (most recent call last):
+    SyntaxError: iterable argument unpacking follows keyword argument unpacking
+
+    >>> f(x, *:)
+    Traceback (most recent call last):
+    SyntaxError: invalid syntax
 """
 
 import re

Misc/NEWS.d/next/Core and Builtins/2023-10-11-13-46-14.gh-issue-110696.J9kSzr.rst

@@ -0,0 +1,2 @@
+Fix incorrect error message for invalid argument unpacking. Patch by Pablo
+Galindo