Parser/pegen.c:68: _PyPegen_check_barry_as_flufl: Assertion `t->type == NOTEQUAL' failed

[vstinner]

BPO	42214
Nosy	@gvanrossum, @warsaw, @vstinner, @lysnikolaou, @pablogsal, @isidentical
PRs	bpo-42214: Fix check for NOTEQUAL token in the PEG parser for the barry_as_flufl rule #23048 [3.9] bpo-42214: Fix check for NOTEQUAL token in the PEG parser for the barry_as_flufl rule (GH-23048). #23051
Files	pgen_bug.py

^{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 2020-10-31.00:40:51.564>
created_at = <Date 2020-10-30.22:05:31.222>
labels = ['interpreter-core', '3.10']
title = "Parser/pegen.c:68: _PyPegen_check_barry_as_flufl: Assertion `t->type == NOTEQUAL' failed"
updated_at = <Date 2020-10-31.00:40:51.564>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2020-10-31.00:40:51.564>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2020-10-31.00:40:51.564>
closer = 'pablogsal'
components = ['Interpreter Core']
creation = <Date 2020-10-30.22:05:31.222>
creator = 'vstinner'
dependencies = []
files = ['49555']
hgrepos = []
issue_num = 42214
keywords = ['patch']
message_count = 5.0
messages = ['380002', '380003', '380004', '380014', '380025']
nosy_count = 6.0
nosy_names = ['gvanrossum', 'barry', 'vstinner', 'lys.nikolaou', 'pablogsal', 'BTaskaya']
pr_nums = ['23048', '23051']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue42214'
versions = ['Python 3.10']

[vstinner]

When Python is built in debug mode, it fails with an assertion error on the following code:
---

def func1():
    if a != b:
        raise ValueError

def func2():
    try
        return 1
    finally:
        pass

---

Try attached pgen_bug.py:

$ ./python pgen_bug.py 
python: Parser/pegen.c:68: _PyPegen_check_barry_as_flufl: Assertion `t->type == NOTEQUAL' failed.
Abandon (core dumped)

[vstinner]

Barry: what did you do?

[vstinner]

In release mode, there is no assertion error:

$ python3.10 pgen_bug.py 
  File "/home/vstinner/python/master/pgen_bug.py", line 6
    try
       ^
SyntaxError: invalid syntax

[pablogsal]

New changeset 06f8c33 by Pablo Galindo in branch 'master':
bpo-42214: Fix check for NOTEQUAL token in the PEG parser for the barry_as_flufl rule (GH-23048)
06f8c33

[pablogsal]

New changeset ddcd57e by Pablo Galindo in branch '3.9':
[3.9] bpo-42214: Fix check for NOTEQUAL token in the PEG parser for the barry_as_flufl rule (GH-23048) (GH-23051)
ddcd57e