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Fri, 2 Oct 2020 11:19:48 +0200 (CEST) From: Markus Armbruster To: John Snow Subject: Re: [PATCH v4 04/46] qapi: modify docstrings to be sphinx-compatible References: <20200930043150.1454766-1-jsnow@redhat.com> <20200930043150.1454766-5-jsnow@redhat.com> <87wo0bejmy.fsf@dusky.pond.sub.org> <96ba9e08-9806-baa3-62d2-2df84a666e62@redhat.com> <87blhm49bk.fsf@dusky.pond.sub.org> <5f3e38fd-6d18-5d28-31cd-6c0faa8c675d@redhat.com> Date: Fri, 02 Oct 2020 11:19:48 +0200 In-Reply-To: <5f3e38fd-6d18-5d28-31cd-6c0faa8c675d@redhat.com> (John Snow's message of "Thu, 1 Oct 2020 10:48:35 -0400") Message-ID: <877ds9m1cb.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=63.128.21.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/01 23:37:29 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Thomas Huth , Eduardo Habkost , qemu-devel@nongnu.org, Markus Armbruster , Cleber Rosa , Alex =?utf-8?Q?Benn=C3=A9e?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" John Snow writes: > On 10/1/20 4:52 AM, Markus Armbruster wrote: >> John Snow writes: >> >>> On 9/30/20 4:47 AM, Markus Armbruster wrote: >>>> John Snow writes: >>>> >>>>> I did not say "sphinx beautiful", just "sphinx compatible". They will >>>>> not throw errors when parsed and interpreted as ReST. >>>> "Bang on the keyboard until Sphinx doesn't throw errors anymore" >>>> might >>>> be good enough for a certain kind of mathematician, but a constructive >>>> solution needs a bit more direction. Is there a specification to >>>> follow? Other useful resources? >>>> >>> >>> I don't know if you are asking this question rhetorically, or in good faith. >> I ask to make sure I understand goals and limitations of your doc >> string >> work in this series. >> Also, even a passing to Sphinx becomes more useful when accompanied >> by a >> link to relevant documentation. >> >>> Let me preface this by saying: This series, and these 119 patches, are >>> not about finding a style guide for our docstring utilization or about >>> proposing one. It is also not about rigorously adding such >>> documentation or about finding ways to meaningfully publish it with >>> e.g. Sphinx, or the styling of such pages. >>> >>> Why bother to add docstrings at all, then? Because I needed them for >>> my own sake when learning this code and I felt it would be a waste to >>> just delete them, and I am of sound mind and able body and believe >>> that some documentation was better than none. They are useful even >>> just as plaintext. >>> >>> Having said that, let's explore the actual style I tend to use. >>> >>> I mentioned before in response to a review comment that there isn't >>> really any standard for docstrings. There are a few competing >>> "styles", but none of which are able to be programmatically checked >>> and validated. >>> >>> The primary guide for docstrings is PEP 257, of which I follow some >>> but not all of the recommendations. >>> >>> https://www.python.org/dev/peps/pep-0257/ >> >> I find PEP 257 frustrating. It leaves me with more questions than >> answers. > > Yeah, sorry. That's what we're dealing with. It's very open-ended. > >>> In general, >>> >>> - Always use triple-double quotes (unenforced) >>> - Modules, classes, and functions should have docstrings (pylint) >>> - No empty lines before or after the docstring (unenforced) >>> - Multi-line docstrings should take the form (unenforced): >>> >>> """ >>> single-line summary of function. >>> >>> Additional prose if needed describing the function. >>> >>> :param x: Input such that blah blah. >>> :raises y: When input ``x`` is unsuitable because blah blah. >>> :returns: A value that blah blah. >> This paragraph is already not PEP 257. >> > > Right -- well, it isn't NOT PEP 257 either. It just suggests you have > to describe these features, but it doesn't say HOW. Yep. Frustrating. >>> """ >>> >>> PEP257 suggests a form where the single-line summary appears on the >>> same line as the opening triple quotes. I don't like this, and prefer >>> symmetry. PEP257 *also* suggests that writing it my way is equivalent >>> to their way, because any docstring processor should trim the first >>> line. I take this as tacit admission that my way is acceptable and has >>> merit. >> I prefer the symmetric form myself. >> >>> What about the syntax or markup inside the docstring itself? there is >>> *absolutely no standard*, but Sphinx autodoc recognizes a few field >>> lists as significant in its parsing, so I prefer using them: >> >> Doc link? > > Hard to search for in my opinion; More reason to provide a link! > you want to search for "sphinx > python domain", and then click on "field lists" on the sidebar. > > https://www.sphinx-doc.org/en/master/usage/restructuredtext/domains.html#info-field-lists > > It has a special understanding for: > > param/parameter/arg/argument/key/keyword: I prefer "param" > here. Possibly key/keyword if we use a **kwargs form with a key that > we specially recognize, but I've not tested that yet. I know pycharm > understands "param" in a semantic way, and that's been good enough for me. > > type: Defines the type of a parameter. In my opinion, do not use > this. Let native type hints do the lifting. Agree. > raises/raise/except/exception: I prefer "raises". "raises ErrorType > when...." is a good sentence. > > var/ivar/cvar: Describes a variable, presumably in the body of the > function below. I've never used this, I always describe it in prose > instead. > > vartype: Defines a type for a variable; I would again defer to the > native type system instead now. > > returns/return: I prefer "returns" for grammatical reasons > again. ("Returns such-and-such when...") "Return such-and-such when..." is just as correct: imperative mood. I prefer imperative mood for function contracts. > rtype: again, type information. Don't use. > > meta: For directives to sphinx, e.g. :meta private: or :meta public: > to toggle the visibility class from its default. I don't use this. > > > None of these are validated or checked in any meaningful way; you can > use arbitrarily field lists (and I do in a few places!) to define your > own terms and so on. > > > (I would like to improve autodoc in the future to validate your > docstrings such that you can enforce :param:, :raises: and :return: > and it uses the type hints and introspection information to raise an > error when you make an obvious mistake. I am not there yet, but I am > using Peter Maydell's work to help inform how I might write such an > extension to autodoc. This work is not critical, but it will likely > occur upstream, outside of the QEMU context because I believe this is > a good thing to do for the ecosystem in general, to allow autodoc to > function slightly more like e.g. Doxygen does.) Sounds useful, but yes, it's clearly outside QEMU context. >>> :param x: Denotes the parameter X. Do not use type information in the >>> string, we rely on mypy for that now. >>> >>> :raises y: explains a case in which an Exception type y may be raised >>> either directly by this code or anticipated to be allowed to be raised >>> by a helper call. (There's no standard here that I am aware of. I use >>> my judgment. Always document direct raise calls, but use your judgment >>> for sub-calls.) >>> >>> :returns: explains the semantics of the return value. >>> >>> That said, literally any sphinx/ReST markup is OK as long as it passes >>> make sphinxdocs. Some sphinx markup is prohibited, like adding new >>> full-throated sections. You can use arbitrary field lists, definition >>> lists, pre-formatted text, examples, code blocks, whatever. >>> >>> In general, you are not going to find the kind of semantic validation >>> you want to ensure that the parameter names are correct, or that you >>> spelled :param: right, or that you didn't miss a parameter or an >>> exception. None of that tooling exists for Python. >>> >>> Thus, it's all rather subjective. No right answers, no validation >>> tools. Just whatever seems reasonable to a human eye until such time >>> we actually decide to pursue publishing the API docs in the >>> development manual, if indeed we ever do so at all. >>> >>> That series sounds like a great opportunity to hash this all out. That >>> is when I would like to remove --missing-docstring, too. There will >>> absolutely be a "docstring series" in the future, but I am insisting >>> stubbornly it happen after strict typing. >> >> Okay. Nevertheless, I'd prefer a bit more information in the commit >> message. Here's my try: >> >> qapi: Modify docstrings to be sphinx-compatible >> >> I did not say "sphinx beautiful", just "sphinx compatible". They >> will not throw errors when parsed and interpreted as ReST. Finding >> a comprehensive style guide for our docstring utilization is left >> for another day. >> >> For now, use field lists recognized by Sphinx autodoc. >> FIXME link to their documentation > > That I can do -- and I will double down on my IOU for a more formal > style guide: https://gitlab.com/jsnow/qemu/-/issues/7 > > I didn't bother writing it in any of the commits because I felt like > it'd get lost there and would be mostly useless; but a .rst doc inside > the package folder would be hard to miss. > > I plan to check in something like ./python/README.rst or > ./python/CODING_STYLE.rst to try and formalize a lot of what I am > doing here, where it's going to be harder to miss. Makes sense. >>>>> >>>>> Signed-off-by: John Snow >>>>> --- >>>>> scripts/qapi/gen.py | 6 ++++-- >>>>> scripts/qapi/parser.py | 9 +++++---- >>>>> 2 files changed, 9 insertions(+), 6 deletions(-) >>>>> >>>>> diff --git a/scripts/qapi/gen.py b/scripts/qapi/gen.py >>>>> index ca66c82b5b8..fc19b2aeb9b 100644 >>>>> --- a/scripts/qapi/gen.py >>>>> +++ b/scripts/qapi/gen.py >>>>> @@ -154,9 +154,11 @@ def _bottom(self): >>>>> @contextmanager >>>>> def ifcontext(ifcond, *args): >>>>> - """A 'with' statement context manager to wrap with start_if()/end_if() >>>>> + """ >>>>> + A 'with' statement context manager that wraps with `start_if` and `end_if`. >>>> Sadly, the fact that start_if() and end_if() are functions isn't >>>> immediately obvious anymore. >>>> I've seen :func:`start_if` elsewhere. Is this something we should >>>> or >>>> want to use? >>>> >>> >>> We *could*. >>> >>> `start_if` relies on the default role, which I have provisionally set >>> to "any" here, so this is shorthand for :any:`start_if`. >>> >>> The :any: role means: "cross-reference any type of thing." If there is >>> not exactly one thing that matches, it results in an error during the >>> documentation build. >>> >>> I like this, because it's nice short-hand syntax that I think >>> communicates effectively to the reader that this is a symbol of some >>> kind without needing a premium of ReST-ese. >>> >>> CONSTANTS are capitalized, Classes are title cased, and functions are >>> lower_case. `lower_case` references can be assumed to be functions, >> >> `lower_case` could also refer to an attribute, variable, or >> parameter. > > Hm. Attribute yes, actually. variable and parameter no -- sphinx does > not presently provide syntax or roles for creating anchors to > parameter names or variables, so they are not able to be > cross-referenced. How would you mark up variable names in doc strings? Often, their "variableness" is obvious from context, but not always. In C comments, we tend to use @var [*]. > Attributes CAN be cross-referenced, but only when they are documented. > > Another style guide thing: > > #: x is a number that represents "The Answer". See `Douglas Adams`_. > self.x = 42 > > You can use the special comment form "#:" to add a one-line > description of an attribute that Sphinx will pick up. Sphinx skips > these attributes otherwise. If you consider them part of the interface > of the module, it's maybe a good idea to do this. > > You can also use docstrings, but the ordering changes: > > self.x = 42 > """x is a number that represents "The Answer". See `Douglas Adams`_. > > I kind of like the #: form because it announces what follows, but I > admit it's a bit of special sphinx magic. Are both equally available in Python IDEs and in interactive Python? >>> but I will admit that this is not enforced or necessarily true as we >>> add more cross reference types in the future. >>> >>> (I am trying to add QMP cross-reference syntax!) >>> >>> I still prefer `start_if` to :func:`start_if` simply because it's less >>> markup and is easier to read in plaintext contexts. You're right, it >>> doesn't look like a function anymore. >> Yes, :func:`start_if` is rather heavy. I asked because I wanted to >> understand what :func: buys us. Not meant as endorsement. >> > > It specifically targets only cross-references of that exact type. In > the case that the :any: reference is ambiguous, :func: is the > disambiguation. > >> GDK-Doc seems smart enough to recognize start_if(). Sphinx isn't, >> because it's built around reST syntax. We put our money on the Sphinx >> horse, so... >> >>> I'm not sure if another annotations would work -- `start_if`() or >>> `start_if()`. Both seem kind of clunky to me, to be honest. Personal >>> feeling is "not really worth the hassle." >> >> You later reported the latter works. >> I prefer `start_if()` to `start_if`. Matter of taste. > > Change made. Thanks! >>>>> - *args: any number of QAPIGenCCode >>>>> + :param ifcond: List of conditionals >>>>> + :param args: any number of `QAPIGenCCode`. >>>>> Example:: >>>>> diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py >>>>> index 9d1a3e2eea9..02983979965 100644 >>>>> --- a/scripts/qapi/parser.py >>>>> +++ b/scripts/qapi/parser.py >>>>> @@ -381,10 +381,11 @@ def append(self, line): >>>>> The way that the line is dealt with depends on which >>>>> part of >>>>> the documentation we're parsing right now: >>>>> - * The body section: ._append_line is ._append_body_line >>>>> - * An argument section: ._append_line is ._append_args_line >>>>> - * A features section: ._append_line is ._append_features_line >>>>> - * An additional section: ._append_line is ._append_various_line >>>>> + >>>>> + * The body section: ._append_line is ._append_body_line >>>>> + * An argument section: ._append_line is ._append_args_line >>>>> + * A features section: ._append_line is ._append_features_line >>>>> + * An additional section: ._append_line is ._append_various_line >>>>> """ >>>>> line = line[1:] >>>>> if not line: >>>> I understand why you insert a blank line (reST wants blank lines >>>> around >>>> lists), I don't understand why you indent. Can you explain? >>> >>> I was mistaken about it needing the indent! >> Easy enough to tidy up :) >> > > Already done! Thanks again! [*] GTK-Doc says @var is just for parameters, but since it offers nothing for variables, we sometimes use it for variables as well.