Parser stack overflows

[IsaacElliott]

BPO	33149
Nosy	@pablogsal
Superseder	bpo-3971: s_push: parser stack overflow MemoryError

^{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 2018-03-27.14:41:15.882>
created_at = <Date 2018-03-26.23:57:23.547>
labels = []
title = 'Parser stack overflows'
updated_at = <Date 2018-03-27.14:41:15.882>
user = 'https://bugs.python.org/IsaacElliott'

bugs.python.org fields:

activity = <Date 2018-03-27.14:41:15.882>
actor = 'ned.deily'
assignee = 'none'
closed = True
closed_date = <Date 2018-03-27.14:41:15.882>
closer = 'ned.deily'
components = []
creation = <Date 2018-03-26.23:57:23.547>
creator = 'Isaac Elliott'
dependencies = []
files = []
hgrepos = []
issue_num = 33149
keywords = []
message_count = 3.0
messages = ['314485', '314486', '314497']
nosy_count = 2.0
nosy_names = ['Isaac Elliott', 'pablogsal']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '3971'
type = None
url = 'https://bugs.python.org/issue33149'
versions = ['Python 3.6']

[IsaacElliott]

python3's parser stack overflows on deeply-nested expressions, for example:

[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]

or

aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa(aa()))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

These are both minimal examples, so if you remove one level of nesting from either then python3 will behave normally.

[IsaacElliott]

Because of the way recursive descent parsing works,

[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[

is actually the minimal input required to reproduce this in python3.

In python2, the bug is still present, but requires a slightly deeper nesting:

[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[

[pablogsal]

Duplicate of bpo-3971