PEG Parser: Invalid targets for augassign and except succeed

[lysnikolaou]

BPO	40618
Nosy	@gvanrossum, @lysnikolaou, @pablogsal
PRs	bpo-40618: Disallow invalid targets in augassign and except clauses #20083

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/lysnikolaou'
closed_at = <Date 2020-05-14.22:54:13.450>
created_at = <Date 2020-05-14.00:15:04.010>
labels = ['interpreter-core', 'type-bug', '3.9']
title = 'PEG Parser: Invalid targets for augassign and except succeed'
updated_at = <Date 2020-05-14.22:54:13.449>
user = 'https://github.com/lysnikolaou'

bugs.python.org fields:

activity = <Date 2020-05-14.22:54:13.449>
actor = 'lys.nikolaou'
assignee = 'lys.nikolaou'
closed = True
closed_date = <Date 2020-05-14.22:54:13.450>
closer = 'lys.nikolaou'
components = ['Interpreter Core']
creation = <Date 2020-05-14.00:15:04.010>
creator = 'lys.nikolaou'
dependencies = []
files = []
hgrepos = []
issue_num = 40618
keywords = ['patch']
message_count = 2.0
messages = ['368809', '368866']
nosy_count = 3.0
nosy_names = ['gvanrossum', 'lys.nikolaou', 'pablogsal']
pr_nums = ['20083']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40618'
versions = ['Python 3.9']

[lysnikolaou]

Tuples and lists, which are invalid augmented assignment targets, currently get successfully parsed, without failing.

➜  cpython git:(targets-fix) ✗ ./python -X oldparser              
Python 3.9.0a6+ (heads/master-dirty:75cd8e48c6, May 14 2020, 03:01:42) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> (a, b) += (1, 2)
  File "<stdin>", line 1
SyntaxError: illegal expression for augmented assignment


➜  cpython git:(pr/20076) ./python             
Python 3.9.0a6+ (heads/pr/20076:bcf5be2772, May 14 2020, 02:15:37) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> (a, b) += 1
SystemError: invalid node type (26) for augmented assignment

We also accept arbitrary targets in except clauses, while we should only be accepting NAME nodes:

➜  cpython git:(master) ./python 
Python 3.9.0a6+ (heads/master:75cd8e48c6, May 14 2020, 03:14:03) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> try:
...     pass
... except Exception as a.b:
...     pass
... 
[1]    135956 segmentation fault (core dumped)  ./python

[pablogsal]

New changeset ce21cfc by Lysandros Nikolaou in branch 'master':
bpo-40618: Disallow invalid targets in augassign and except clauses (GH-20083)
ce21cfc