Use a loop to collect args in the parser instead of recursion

[pablogsal]

BPO	41690
Nosy	@pablogsal
PRs	bpo-41690: Use a loop to collect args in the parser instead of recursion #22053 [3.9] bpo-41690: Use a loop to collect args in the parser instead of recursion (GH-22053) #22067

^{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 = None
closed_at = <Date 2020-09-02.20:31:14.576>
created_at = <Date 2020-09-02.10:59:21.311>
labels = ['3.9', '3.10']
title = 'Use a loop to collect args in the parser instead of recursion'
updated_at = <Date 2020-09-02.20:31:14.576>
user = 'https://github.com/pablogsal'

bugs.python.org fields:

activity = <Date 2020-09-02.20:31:14.576>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2020-09-02.20:31:14.576>
closer = 'pablogsal'
components = []
creation = <Date 2020-09-02.10:59:21.311>
creator = 'pablogsal'
dependencies = []
files = []
hgrepos = []
issue_num = 41690
keywords = ['patch']
message_count = 3.0
messages = ['376225', '376255', '376263']
nosy_count = 1.0
nosy_names = ['pablogsal']
pr_nums = ['22053', '22067']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue41690'
versions = ['Python 3.9', 'Python 3.10']

[pablogsal]

This program can segfault the parser by stackoverflow:

import ast

code = "f(" + ",".join(['a' for _ in range(100000)]) + ")"
print("Ready!")
ast.parse(code)

the reason is that the rule for arguments has a simple recursion when collecting args:

args[expr_ty]:
[...]
| a=named_expression b=[',' c=args { c }] {
[...] }

Check https://github.com/we-like-parsers/pegen/issues/245 for more context and informaton

[pablogsal]

New changeset 4a97b15 by Pablo Galindo in branch 'master':
bpo-41690: Use a loop to collect args in the parser instead of recursion (GH-22053)
4a97b15

[pablogsal]

New changeset 8de34cd by Pablo Galindo in branch '3.9':
[3.9] bpo-41690: Use a loop to collect args in the parser instead of recursion (GH-22053) (GH-22067)
8de34cd