Bug: formatting deeply indented `if` is not idempotent and breaks code

[black-puppydog]

Checklist prior to opening an issue

• I have followed fully the installation steps laid out in the documentation site.
• I have restarted jupyterlab.
• I have read the FAQ section in the documentation site.

First off, despite what I am writing below, I want to thank Ryan and all the other contributors for making this! The extension has saved me a ton of trouble and nerves and has just been an all-round quality of life improvement! 😊

Describe the bug

I have a cell in one of my notebooks that breaks on formatting. Not sure what is going wrong yet, but I managed to get a minimal breaking example:

lm_tokenizer = object()
def f():
    while True:
        while True:
            while True:
                if (
                    lm_tokenizer.convert_tokens_to_ids(name) != lm_tokenizer.unk_token_id
                ):
                    pass

The key here is the if statement in combination with the deep nesting. In real life, this is of course a combination of class, function, and if/else nesting.

The bug happens upon formatting twice. Here's what the first saving produces, which matches what the black online formatter produces:

lm_tokenizer = object()


def f():
    while True:
        while True:
            while True:
                if (
                    lm_tokenizer.convert_tokens_to_ids(name)
                    != lm_tokenizer.unk_token_id
                ):
                    pass

Note that the second part of the if statement is now the start of the line, beginning with a ! character. Now, if I paste this version into the black online formatter, it correctly produces the exact same output. However, both on my local JupyterLab and on saturncloud.io, I get this output on the second pass:

lm_tokenizer = object()


def f():
    while True:
        while True:
            while True:
                if (
                    lm_tokenizer.convert_tokens_to_ids(name)
# �                     != lm_tokenizer.unk_token_id
                ):
                    pass

The second part of the if has been commented out, and I don't know where that extra unicode symbol comes from either. In Jupyter it shows up as a red dot.
In any case, this obviously changes the code significantly, so something is going wrong... Since black itself seems to be doing just fine, I'd expect this to be a downstream issue, hence I'm filing this here.

Workaround

For the time being, I just disabled formatting for the code inside the if with #fmt:off. So I'm not blocked by this, but it took me a while to spot this since my code didn't break, it "just" produced incorrect results.

Diagnostic commands

Most relevant here, both black and jupyterlab_code_formatter are up to date:

black==22.10.0
jupyterlab-code-formatter==1.5.3

Full diagnostics

$ pip freeze
absl-py==1.2.0
aiohttp==3.8.3
aioitertools==0.11.0
aiosignal==1.2.0
anyio==3.6.1
argon2-cffi==21.3.0
argon2-cffi-bindings==21.2.0
arrow==1.2.3
asttokens==2.0.8
astunparse==1.6.3
async-timeout==4.0.2
attrs==22.1.0
Babel==2.10.3
backcall==0.2.0
beautifulsoup4==4.11.1
bencoder.pyx==3.0.0
black==22.10.0
bleach==5.0.1
boto3==1.24.87
botocore==1.27.59
cachetools==5.2.0
certifi @ file:///croot/certifi_1665076670883/work/certifi
cffi==1.15.1
charset-normalizer==2.1.1
click==8.1.3
commonmark==0.9.1
ConfigArgParse==1.5.3
contourpy==1.0.5
croniter==1.3.7
cycler==0.11.0
datasets==2.6.0
debugpy==1.6.3
decorator==5.1.1
deepdiff==5.8.1
defusedxml==0.7.1
dill==0.3.5.1
dnspython==2.2.1
dottorrent==1.10.1
dottorrent-gui==1.3.11
email-validator==1.3.0
entrypoints==0.4
execnb==0.1.4
executing==1.1.0
fastcore==1.5.27
fastjsonschema==2.16.2
filelock==3.8.0
fire==0.4.0
fonttools==4.37.4
frozenlist==1.3.1
fsspec==2022.8.2
ghapi==1.0.3
google-auth==2.12.0
google-auth-oauthlib==0.4.6
grpcio==1.49.1
h11==0.14.0
httptools==0.5.0
huggingface-hub==0.10.0
humanfriendly==10.0
idna==3.4
ipykernel==6.16.0
ipython==8.5.0
ipython-genutils==0.2.0
ipywidgets==8.0.2
isort==5.10.1
itsdangerous==2.1.2
jedi==0.18.1
Jinja2==3.1.2
jmespath==1.0.1
joblib==1.2.0
json5==0.9.10
jsonschema==4.16.0
jupyter==1.0.0
jupyter-console==6.4.4
jupyter-core==4.11.1
jupyter-server==1.19.1
jupyter_client==7.3.5
jupyterlab==3.4.8
jupyterlab-code-formatter==1.5.3
jupyterlab-pygments==0.2.2
jupyterlab-widgets==3.0.3
jupyterlab_server==2.15.2
kiwisolver==1.4.4
lxml==4.9.1
Markdown==3.4.1
MarkupSafe==2.1.1
matplotlib==3.6.0
matplotlib-inline==0.1.6
mistune==2.0.4
multidict==6.0.2
multiprocess==0.70.13
mypy-extensions==0.4.3
nbclassic==0.4.4
nbclient==0.7.0
nbconvert==7.1.0
nbdev==2.3.7
nbformat==5.6.1
nest-asyncio==1.5.6
nltk==3.7
notebook==6.4.12
notebook-shim==0.1.0
numpy==1.23.3
oauthlib==3.2.1
ordered-set==4.1.0
orjson==3.8.0
packaging==21.3
pandas==1.5.0
pandocfilters==1.5.0
parso==0.8.3
pathspec==0.10.1
pexpect==4.8.0
pickleshare==0.7.5
Pillow==9.2.0
platformdirs==2.5.2
prometheus-client==0.14.1
prompt-toolkit==3.0.31
protobuf==3.19.6
psutil==5.9.2
ptyprocess==0.7.0
pudb==2022.1.2
pure-eval==0.2.2
pyarrow==9.0.0
pyasn1==0.4.8
pyasn1-modules==0.2.8
pycparser==2.21
pydantic==1.10.2
pyDeprecate==0.3.2
Pygments==2.13.0
PyJWT==2.5.0
pyparsing==3.0.9
pyrsistent==0.18.1
python-dateutil==2.8.2
python-dotenv==0.21.0
python-multipart==0.0.5
pytorch-lightning==1.7.7
pytorch-pretrained-biggan==0.1.1
pytz==2022.4
PyYAML==6.0
pyzmq==24.0.1
qtconsole==5.3.2
QtPy==2.2.1
regex==2022.9.13
requests==2.28.1
requests-oauthlib==1.3.1
responses==0.18.0
rich==12.6.0
rofimoji==5.6.0
rsa==4.9
s3transfer==0.6.0
scikit-learn==1.1.2
scipy==1.9.1
Send2Trash==1.8.0
six==1.16.0
sniffio==1.3.0
soupsieve==2.3.2.post1
speedtest-cli==2.1.3
stack-data==0.5.1
starlette==0.20.4
tensorboard==2.10.1
tensorboard-data-server==0.6.1
tensorboard-plugin-wit==1.8.1
termcolor==2.0.1
terminado==0.16.0
threadpoolctl==3.1.0
tinycss2==1.1.1
tokenizers==0.12.1
tomli==2.0.1
torch==1.12.1
torchmetrics==0.10.0
torchvision==0.13.1+cpu
tornado==6.2
tqdm==4.64.1
traitlets==5.4.0
transformers==4.22.2
typing_extensions==4.3.0
ujson==5.5.0
urllib3==1.26.12
urwid==2.1.2
urwid-readline==0.13
uvicorn==0.18.3
uvloop==0.17.0
watchdog==2.1.9
watchfiles==0.17.0
wcwidth==0.2.5
webencodings==0.5.1
websocket-client==1.4.1
websockets==10.3
Werkzeug==2.2.2
widgetsnbextension==4.0.3
wrapt==1.14.1
xxhash==3.0.0
yarl==1.8.1
youtube-dl==2021.12.17
yt-dlp==2022.8.19

$ jupyter labextension list
JupyterLab v3.4.8
/home/daan/miniconda3/envs/hfc/share/jupyter/labextensions
        jupyterlab_pygments v0.2.2 enabled OK (python, jupyterlab_pygments)
        @jupyter-widgets/jupyterlab-manager v5.0.3 enabled OK (python, jupyterlab_widgets)
        @ryantam626/jupyterlab_code_formatter v1.5.3 enabled OK (python, jupyterlab-code-formatter)

$ jupyter serverextension list
config dir: /home/daan/miniconda3/envs/hfc/etc/jupyter
    jupyterlab  enabled
    - Validating...
      jupyterlab 3.4.8 OK
    jupyterlab_code_formatter  enabled
    - Validating...
      jupyterlab_code_formatter 1.5.3 OK

[ryantam626]

Sorry for the late reply, I haven't given this project much love, I just kinda lost steam over the years as I got increasingly burnt out, but lately I have gotten a second wind (perhaps only for a brief period...)

Oh boy this is not great.

FWIW I am in middle to a big refactor for the project (mostly due to the evolution of jupyterlab's plugin tooling), I can look into this bug after that.

Without the the refactor, the development envrionment for this plugin is just nightmare-ish to use, so that is currently trumping all tasks.