Implement rules in darglint

[edgarrmondragon]

This might be superseded by #12434

---

https://pypi.org/project/darglint/

Darglint's primary focus is to identify incorrect and missing documentationd
of a function's signature. Checking style is a stretch goal, and is supported
on a best-effort basis. Darglint does not check stylistic preferences expressed
by tools in the Python Code Quality Authority (through tools such as pydocstyle).
So when using Darglint, it may be a good idea to also use pydocstyle, if you
want to enforce style. (For example, pydocstyle requires the short summary
to be separated from other sections by a line break. Darglint makes no such check.)

Error Codes

• DAR001: The docstring was not parsed correctly due to a syntax error.
• DAR002: An argument/exception lacks a description
• DAR003: A line is under-indented or over-indented.
• DAR004: The docstring contains an extra newline where it shouldn't.
• DAR005: The item contains a type section (parentheses), but no type.
• DAR101: The docstring is missing a parameter in the definition.
• DAR102: The docstring contains a parameter not in function.
• DAR103: The docstring parameter type doesn't match function.
• DAR104: (disabled) The docstring parameter has no type specified
• DAR105: The docstring parameter type is malformed.
• DAR201: The docstring is missing a return from definition.
• DAR202: The docstring has a return not in definition.
• DAR203: The docstring parameter type doesn't match function.
• DAR301: The docstring is missing a yield present in definition.
• DAR302: The docstring has a yield not in definition.
• DAR401: The docstring is missing an exception raised.
• DAR402: The docstring describes an exception not explicitly raised.
• DAR501: The docstring describes a variable which is not defined.

[charliermarsh]

Cool, I've never used but looks useful. Would this be an impactful plugin for you? Would it unblock any Ruff adoption? :)

[edgarrmondragon]

Hey @charliermarsh, yeah. I maintain a few packages with public APIs that would benefit from contributors being informed about documentation for arguments or exceptions raised being missing.

A number of features would make Ruff a nice replacement for flake8: speed, compatibility with the rest of the Python ecosystem, pyproject.toml support.

[lsorber]

FWIW, darglint is the main blocker [1] for us to migrate Poetry Cookiecutter [2] from flake8 to ruff.

[1] superlinear-ai/poetry-cookiecutter#125
[2] https://github.com/radix-ai/poetry-cookiecutter

[charliermarsh]

👍 Helpful to hear! darglint is probably the most popular unimplemented plugin. I'd like to get around to it soon. If there's a subset of rules that are most impactful, that'd be helpful to know too for prioritization.

[edgarrmondragon]

If there's a subset of rules that are most impactful, that'd be helpful to know too for prioritization.

For me personally, they're probably DAR101, DAR102, DAR201, DAR202 and to a lesser extent DAR301, DAR302, DAR401 and DAR402

[strickvl]

For me, I use darglint together with pydocstyle since they don't do quite the same thing. Having darglint absorbed into the ruff world would be really great.

[erwann-met]

We just discovered ruff in my team. It's amazing, and I'd like to thank you for all the great work!

We used to run flake8 along with darglint. Unfortunately since ruff does not yet implement darglint rules we still have to keep darglint alongside ruff which is a shame given how slow darglint is.

Reimplementing darglint within ruff is definitely the feature we are most looking forward to!

For us the most important rules are probably those related to the parameters (and returns) and their types: DAR101, DAR102, DAR103, DAR201, DAR202, DAR203 and DAR501. I hope this helps!

We understand that maintaining an open-source project can be a lot of work and we want to express our appreciation for all the effort that goes into it. We were wondering if there's any update on when this issue might be addressed? Any information would be greatly appreciated. Thank you!

[charliermarsh]

Very helpful, thank you! It's not something I've started working on actively (and would make for a good contribution if there are any eager contributors reading this :)), but that set of rules at least is probably not too much work to support, and this issue has a lot of thumbs-up votes so I'll try to get to it soon-ish. I'll post here when I'm able to take it on.

[charliermarsh]

Looking into starting on this. darglint has a lot of code because it defines entire grammars for the docstrings, and then lexes and parses according to those grammars. pydocstyle, on the other hand, does it all with regular expressions. Wondering if we could get away with the latter.

[anthonyburdi]

Super exciting to hear that this is in the works. We just switched to ruff instead of pydocstyle and are eager to replace darglint as well. Here are the error codes we are most interested (least overlap with pydocstyle):

• DAR102: The docstring contains a parameter not in function.
• DAR201: The docstring is missing a return from definition.
• DAR202: The docstring has a return not in definition.
• DAR301: The docstring is missing a yield present in definition.
• DAR302: The docstring has a yield not in definition.
• DAR401: The docstring is missing an exception raised.
• DAR402: The docstring describes an exception not explicitly raised.
• DAR501: The docstring describes a variable which is not defined.

[rbebb]

It would be great if it could add darglint’s feature that checks if docstrings match a particular style (whether it be Sphinx, Google, or something else)

[baggiponte]

Implementing darglint could handle some flake8 exceptions, as well as part of docformatter I guess?

[rbebb]

@charliermarsh Is there an update on implementing darglint features in ruff? Thank you for all of your work on this project!

[finswimmer]

Hey,

unfortunately darglint is unmaintained since December 2022. So I would be very happy to see something similar in ruff.

Thanks a lot for all your very good work!

fin swimmer

[charliermarsh]

I'm currently considering taking this on as a project over the next few weeks, but it's competing with some other priorities so not a firm commitment yet :) I definitely hear that this something users want, and it's something I want Ruff to support too -- just a question of when, will post here when I have a clear decision.

[leandro-lucarella-frequenz]

Great to hear work is close to being started. We also rely a lot on darglint and are concerned about is current abandoned state, and were also looking to start using ruff, so it would be very good news if it can be a replacement for darglint. The rules that most often catch error in the documentation for us are:

• DAR101: The docstring is missing a parameter in the definition.
• DAR102: The docstring contains a parameter not in function.
• DAR201: The docstring is missing a return from definition.
• DAR202: The docstring has a return not in definition.
• DAR301: The docstring is missing a yield present in definition.
• DAR302: The docstring has a yield not in definition.
• DAR401: The docstring is missing an exception raised.
• DAR402: The docstring describes an exception not explicitly raised.

[BigForLy]

Hello @charliermarsh! I manage to convert almost all checks to ruff, except for Darling, do you have any idea whether this will be done?

[strickvl]

As mentioned in Discord, registering my interest in taking a stab at this.

[Spenhouet]

Using pydocstyle we are using the google style with typing. We strictly use typing in python, so repeating the types in the Doc string serves no purpose and is just redundant. Having rules like DAR103: The docstring parameter type doesn't match function. or DAR105: The docstring parameter type is malformed. certainly would help to keep Doc string and parameter declaration aligned, it's still redundant and we'd rather enforce that no types are specified in the Doc string. Seems darglint doesn't provide such a rule.

Edit: Just found this issue which raises the same wish: #9070

[AloizioMacedo]

Hoping to see this as well! Ruff already encompasses most of my CI linting checks, this would be a great addition.

Meanwhile, in case it is useful for other people, I decided to take a stab and implement a version that is sufficient for my needs: https://github.com/AloizioMacedo/pystaleds.

It intends primarily to check for mismatches of the parameters in the function signature and the arguments in the docstring. It is very experimental, but I can already use it in my projects while ruff doesn't support a similar feature : )

[ddelange]

we'd rather enforce that no types are specified in the Doc string

@Spenhouet fwiw pydoclint has an --arg-type-hints-in-signature flag ref https://jsh9.github.io/pydoclint/violation_codes.html

see also my config above

[Spenhouet]

@ddelange Thanks for sharing, that would introduce a new tool just for this small requirement. Would much more prefer if this would be covered by a linting rule within ruff.

[aeturrell]

Just wanted to add my voice to those saying that this would be a really useful feature. Thanks for all the amazing work on Ruff!

[tmke8]

I wonder if at this point, it would be better to implement pydoclint in ruff instead of darglint? (This is prompted by the recent PR #11471.)

Pydoclint has

• more error codes (e.g., DOC104 in pydoclint checks for the order of the parameters; darglint doesn't have that AFAICT),
• more config options (like arg-type-hints-in-signature which lets you decide whether you want to include types in the docstring),
• and the config options of pydoclint also seem more well-thought-out to me than darglint's. (E.g., pydoclint has skip-checking-short-docstrings which makes sense to me, but darglint's strictness=short vs strictness=long is a bit confusing)

[Goldziher]

I wonder if at this point, it would be better to implement pydoclint in ruff instead of darglint? (This is prompted by the recent PR #11471.)

Pydoclint has

• more error codes (e.g., DOC104 in pydoclint checks for the order of the parameters; darglint doesn't have that AFAICT),
• more config options (like arg-type-hints-in-signature which lets you decide whether you want to include types in the docstring),
• and the config options of pydoclint also seem more well-thought-out to me than darglint's. (E.g., pydoclint has skip-checking-short-docstrings which makes sense to me, but darglint's strictness=short vs strictness=long is a bit confusing)

Strong +1 for this. pydoclint is really great and pretty fast already, but ruff could improve on this and extend it further. Also some issues might be autofixable.

[charliermarsh]

Are there rules that are present in darglint but not pydoclint?

[Apakottur]

Are there rules that are present in darglint but not pydoclint?

I know of at least two:

1. DAR401: The docstring is missing an exception raised.
2. DAR402: The docstring describes an exception not explicitly raised.

These two rules are the only reason we use darglint, everything else that we want is covered by pydoclint.

[charliermarsh]

Interesting, ok. Those are the exact rules added in #11471.

[jsh9]

Are there rules that are present in darglint but not pydoclint?

I know of at least two:

1. DAR401: The docstring is missing an exception raised.
2. DAR402: The docstring describes an exception not explicitly raised.

These two rules are the only reason we use darglint, everything else that we want is covered by pydoclint.

I'm the author of pydoclint.

I think these two pydoclint violation codes cover DAR401 and 402:

Code	Explanation
DOC501	Function/method has “raise” statements, but the docstring does not have a “Raises” section
DOC502	Function/method has a “Raises” section in the docstring, but there are not “raise” statements in the body

If they don't cover what you want, please feel free to open an issue.

[AndydeCleyre]

@jsh9 I don't think those check the exception types. For example, if I have a function like this, which sometimes raises a ValueError, but incorrectly document that it raises a ZeroDivisionError, darglint will report the problem while pydoclint won't:

def _str_to_bool(informal_bool: str) -> bool:
    """
    Translate a commonly used boolean ``str`` into a real ``bool``.

    Args:
        informal_bool: A boolean represented as ``str``, like ``"true"``, ``"no"``, ``"off"``, etc.

    Returns:
        ``True`` or ``False`` to match the intent of ``informal_bool``.

    Raises:
        ZeroDivisionError: This doesn't look like enough like a ``bool`` to translate.
    """
    if informal_bool.lower() in ('true', 't', 'yes', 'y', 'on', '1'):
        return True
    if informal_bool.lower() in ('false', 'f', 'no', 'n', 'off', '0'):
        return False
    raise ValueError(f"{informal_bool} doesn't look like a boolean")  # pragma: no cover

$ darglint nt2
nt2/casters.py:_str_to_bool:29: DAR401: -r ValueError
nt2/casters.py:_str_to_bool:39: DAR402: +r ZeroDivisionError

$ pydoclint nt2
Loading config from user-specified .toml file: pyproject.toml
No config found in pyproject.toml.
Skipping files that match this pattern: \.git|\.tox
nt2/__init__.py
nt2/casters.py
nt2/converters.py
nt2/dumpers.py
nt2/ui.py
nt2/yamlpath_tools.py
🎉 No violations 🎉

[jsh9]

Thanks @AndydeCleyre !

I've opened a new issue (jsh9/pydoclint#158) on pydoclint to add this feature.