wurfapi 9.1.2
C++ Documentation generator.
License: BSD 3-clause "New" or "Revised" License
Keywords: wurfapi

wurfapi
=======

|PyPi| |Waf Python Tests| |Black| |Flake8| |Pip Install|

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We wanted to have a configurable and easy-to-use Sphinx API documentation
generator for our C++ projects. To achieve this we leaned on others for
inspiration:

* Breathe (https://github.com/michaeljones/breathe): Excellent extension
  and the default choice for many.
* Gasp (https://github.com/troelsfr/Gasp): Gasp inspired us by allowing
  templates to control the output. Unfortunately development of Gaps
  seems to have stopped.

So what is ``wurfapi``:

* Essentially we picked up where Gasp let go. We have
  borrowed the idea of templates to make it highly configurable.

* We made it easy to use by automatically running Doxygen to generate the
  initial API documentation.

* We parse the Doxygen XML into an easy to use Python dictionary. Which can
  be consumed in the templates.

* We prepared the extension for other backends (replacing Doxygen) e.g.
  https://github.com/foonathan/standardese once they become ready.

.. contents:: Table of Contents:
   :local:


Status
======

We currently use wurfapi in the following projects:

* https://rely.steinwurf.com/docs/10.0.0/
* https://kodo.steinwurf.com/docs/11.0.0/
* https://otacast.steinwurf.com/docs/6.0.0/

... and many more.

Usage
=====

We recommend that you install wurfapi and sphinx in a virtual environment.
To use the extension, the following steps are needed:

1. Create a virtual environment::

    Follow the https://docs.python.org/3/tutorial/venv.html

2. Install the extension::

    pip install sphinx
    pip install wurfapi

3. Generate the initial ``Sphinx`` documentation by running::

      mkdir docs
      cd docs
      python sphinx-quickstart

   You will need to enter some basic information about your project such
   as the project name etc.

4. Open the ``conf.py`` generated by ``sphinx-quickstart`` and add the
   the following::

      # Append or insert 'wurfapi' in the extensions list
      extensions = ['wurfapi']

      # wurfapi options - relative to your docs dir
      wurfapi = {
        'source_paths': ['../src'],
        'recursive': True,
        'parser': {'type': 'doxygen', 'download': True,  'warnings_as_error': True}
      }

   .. note::

    ``source_path``
        If you separate source and build dir in sphinx your 'source_path'
        should be something like '../../src'.

    ``recursive``
        Set recursive ``True`` if you want recursively scan the ``source_paths``

    ``download``
        If you do not want to automatically download Doxygen, set
        ``download`` to ``False``. In that case ``wurfapi`` will try to invoke
        plain ``doxygen`` without specifying any path or similar. This means
        it ``doxygen`` must be available in the path.

    ``warnings_as_error``
        If Doxygen emits many warnings you might want to set warnings_as_error
        to False until they have been fixed.

5. To generate the API documentation for a class open a ``.rst`` file
   e.g. ``index.rst`` if you ran ``sphinx-quickstart``. Say we want to
   generate docs for a class called ``test`` in the namespace ``project``.

   To do this we add the following directive to the rst file::

      .. wurfapi:: class_synopsis.rst
        :selector: project::coffee::machine

   Such that ``index.rst`` becomes something like::

      Welcome to Coffee's documentation!
      ===================================

      .. toctree::
        :maxdepth: 2
        :caption: Contents:

      .. wurfapi:: class_synopsis.rst
          :selector: project::coffee::machine

      .. wurfapi:: class_synopsis.rst
          :selector: project::coffee::recipe


      Indices and tables
      ==================

      * :ref:`genindex`
      * :ref:`modindex`
      * :ref:`search`


    To do this we use the ``class_synopsis.rst`` template.

6. Generate the Documentation

    make html

Labels and References
---------------------

To reference different elements in the API, we have added a custom Sphinx role ``:wurfapi:``

The ``:wurfapi:`` role will try to deduce the ``unique-name`` from the text given.
E.g if you want to reference the ``unique-name`` ``foo::bar::baz::func(std::string var)`` and there are
no other member functions in ``foo::bar::baz`` named ``func``, you can reference it
by writing ``:wurfapi:`foo::bar::baz::func```.

On the other hand if there was a function with ``unique-name`` ``foo::bar::baz::function(std::string var)``
``:wurfapi:`foo::bar::baz::func``` could match with both func and function and will throw an error. In This
case this can be fixed by adding the left parenthesis: ``:wurfapi:`foo::bar::baz::func(```.

You can read more about unique names later in this README.

Running on readthedocs.org
--------------------------

To use this on readthedocs.org you need to have the ``wurfapi`` Sphinx
extension installed. This can be done by adding a ``requirements.txt`` in the
documentation folder. readthedocs.org can be configured to use the
``requirements.txt`` when building a project. Simply put ``wurfapi`` in to the
``requirements.txt``.

Doxygen issues
--------------

Nothing is perfect, neither is Doxygen. Sometimes Doxygen gets it wrong e.g. in
the following example::

    class foo
    {
    private:
        class bar;
    };

Doxygen incorrectly reports that ``bar`` has public scope (also reported here
https://bit.ly/2BWPllZ). To deal with such issues, until a fix lands in
Doxygen, you can do the following:

Add a list of *patches* to the API to your ``conf.py`` file. Extending the
example from before, we can add the following fix::

      wurfapi = {
        'source_paths': ['../src'],
        'recursive': True,
        'parser': {
          'type': 'doxygen', 'download': True,  'warnings_as_error': True,
           'patch_api': [
            {'selector': 'foo::bar', 'key': 'access', 'value': 'private'}
          ]
        }
      }

The ``patch_api`` allows you to reach in to the parsed API information and
update certain values. The ``selector`` is the ``unique-name`` of the
entity you want to update. Check the "Dictionary layout" section further down
for more information.

Collapse inline namespaces
--------------------------

For symbol versioning you may use ``inline namespaces``, however typically
you don't want these to show up in the docs, as these are mostly
invisible for your users.

With ``wurfapi`` you can collapse the inline namespace such that it
is removed form the scopes etc.

Example::

  namespace foo { inline namespace v1_2_3 { struct bar{}; } }

The scope to bar is ``foo::v1_2_3``. If you collapse the inline namespace it will
just be ``foo``.

First issue you have to deal with is that Doxygen currently does not
support inline namespaces. So we need to patch the API first::

      wurfapi = {
        'source_paths': ['../src'],
        'recursive': True,
        'parser': {
          'type': 'doxygen', 'download': True,  'warnings_as_error': True,
           'patch_api': [
            {'selector': 'foo::v1_2_3', 'key': 'inline', 'value': True}
          ]
        }
      }

After this we can collapse the namespace::

      wurfapi = {
        'source_paths': ['../src'],
        'recursive': True,
        'parser': {
          'type': 'doxygen', 'download': True,  'warnings_as_error': True,
           'patch_api': [
            {'selector': 'foo::v1_2_3', 'key': 'inline', 'value': True}
          ],
          'collapse_inline_namespaces': [
            "foo::v1_2_3"
          ]
        }
      }


Now you will be able to refer to ``bar`` as ``foo::bar``. Note, that
collapsing the namespace will affect the selectors you write when
generating the documentation.

Custom templates
----------------

You can write your own custom templates for generating the rst output.
To this you simply write a Jinja2 compatible rst template and place
it in some folder. Adding the ``user_templates`` key to the ``wurfapi``
configuration dictionary in the ``conf.py`` file will make it available.

For example::

    wurfapi = {
        'source_paths': ['../src', '../examples/header/header.h'],
        'recursive': True,
        'user_templates': 'rst_templates',
        'parser': {
            'type': 'doxygen', 'download': True, 'warnings_as_error': True
        }
    }

    exclude_patterns = ['rst_templates/*.rst']

Now we can use ``*.rst`` files inside the ``rst_templates`` folder e.g. if
we had a ``class_list.rst`` template we could use it like this::

    .. wurfapi:: class_list.rst
        :selector: project::coffee

Release new version
===================

1. Edit ``NEWS.rst``, ``wscript`` and ``src/wurfapi/wurfapi.py`` (set
   correct ``VERSION``)

2. Run ::

    ./waf upload


Source code
===========


Tests
=====

The tests will run automatically by passing ``--run_tests`` to waf::

    ./waf --run_tests

This follows what seems to be "best practice" advice, namely to install the
package in editable mode in a virtualenv.

Recordings
----------

A bunch of the tests use a library called ``pytest-datarecorder``.
The library is used to store the output as files from different parsing and
rendering operations.

E.g. say we want to make sure that a parser function returns a certain
``dict`` object. Then we can record that ``dict``::

    datarecorder.record_data(
        data={'foo': 2, 'bar': 3},
        recording_file="/tmp/recording/test.json"
    )

If ``data`` changes compared to a previous recording a mismatch will be
detected. To update a recording simply delete the recording file.

Test directories
----------------

You will also notice that a bunch of the tests take a parameter called
``testdirectory``. The ``testdirectory`` is a pytest fixture, which
represents a temporary directory on the filesystem. When running the tests
you will notice these temporary test directories pop up under the
``pytest_temp`` directory in the project root.

You can read more about that here:

* https://github.com/steinwurf/pytest-testdirectory

Developer Notes
===============

The `sphinx` documentation on creating extensions:
http://www.sphinx-doc.org/en/stable/extdev/index.html#dev-extensions

* An extension is a Python module. When an extension loads, Sphinx will import
  it and execute its ``setup()`` function.

* Understanding how to put together docutils nodes seems pretty difficult. One
  suggesting form the mailinglist was to look at the following document:
  https://github.com/docutils-mirror/docutils/blob/master/test/functional/expected/standalone_rst_pseudoxml.txt

* While researching how to do this, there seem to be three potential approaches:

  1. Use the standard Sphinx approach and operate with the doctree.
  2. Create RST based on jinja templates
  3. Create HTML based on jinja templates

* Inspiration - Sphinx extensions that were used as inspiration while
  developing this extension.

  * Breathe
  * Gasp
  * https://github.com/Robpol86/sphinxcontrib-imgur
  * https://github.com/djungelorm/sphinx-tabs

* Understanding how to write stuff with docutils:
  * http://agateau.com/2015/docutils-snippets/

* Creating a custom directive
  * http://www.xavierdupre.fr/blog/2015-06-07_nojs.html

* Nice looking Sphinx extensions
  * https://github.com/bokeh/bokeh/tree/master/bokeh/sphinxext

* This part of the documentation was useful in order to understand the need
  for ViewLists etc. in the directives run(...) function.
  http://www.sphinx-doc.org/en/stable/extdev/markupapi.html

* This link provided inspiration for the text json format: https://github.com/micnews/html-to-article-json
* More xml->json for the text: https://www.xml.com/pub/a/2006/05/31/converting-between-xml-and-json.html

Dictionary layout
-----------------

We want to support different "backends" like Doxygen to parse the source
code. To make this possible we define an internal source code description
format. We then translate e.g. Doxygen XML to this and use that to render
the API documentation.

This way a different "backend" e.g. Doxygen2 could be use used as the source
code parser and the API documentation could be generated.


``unique-name``
...............

In order to be able to reference the different entities in the API we need
to assign them a name.

We use a similar approach here as described in standardese_.

This means that the ``unique-name`` of an entity is the name with all
scopes e.g. ``foo::bar::baz``.

* For functions the unique name contains the signature (parameter types and for
  member functions cv-qualifier and ref-qualifier) e.g. ``foo::bar::baz::func()``
  or ``foo::bar::baz::func(int a, char*) const``. See cppreference_ for more
  information.

* For class template specializations the unique name includes the specialization
  arguments. For example::

      // Here the unique-name is just 'foo'
      template<class T>
      class foo {};

      // Here the unique name is foo<int>
      template<>
      class foo<int> {};

* In addition to types, we also have entries for the parsed files. For files
  the unique name will be the relative path from the project root.

* For defines we will use the name of the define. As an example::

      #define PROJECT_VERSION "1.0.0"

  Here ``unique-name`` will be ``PROJECT_VERSION``.

.. _cppreference: http://en.cppreference.com/w/cpp/language/member_functions
.. _standardese: https://github.com/foonathan/standardese#linking



The API dictionary
...................

The internal structure is a dicts with the different API entities. The
``unique-name`` of the entity is the key and the entity type also a
Python dictionary is the value e.g::


    api = {
      'unique-name': { ... },
      'unique-name': { ... },
      ...
    }

To make this a bit more concrete consider the following code::

    namespace ns1
    {
      class shape
      {
        void print(int a) const;
      };

      namespace ns2
      {
        struct box
        {
          void hello();
        };

        void print();
      }
    }

Parsing the above code would produce the following API dictionary::

      api = {
        'ns1': { 'kind': 'namespace', ...},
        'ns1::shape': { 'kind': 'class', ... },
        'ns1::shape::print(int) const': { kind': function' ... },
        'ns1::ns2': { 'kind': 'namespace', ... },
        'ns1::ns2::box': { 'kind': 'struct', ... },
        'ns1::ns2::box::hello()': { kind': function' ... },
        'ns1::ns2::print()': { 'kind': 'function', ...},
        'ns1.hpp': { 'kind': 'file', ...}
      }

The different entity kinds expose different information about the
API. We will document the different kinds in the following.

We make some keys *optional* this is marked in the following way::

    api = {
      'unique-name': {
        'some_key': ...
        Optional('an_optional_key'): ...
      },
      ...
    }

``namespace`` Kind
..................

Python dictionary representing a C++ namespace::

    info = {
      'kind': 'namespace',
      'name': 'unqualified-name',
      'scope': 'unique-name' | None,
      'members: [ 'unique-name', 'unique-name' ],
      'briefdescription': paragraphs,
      'detaileddescription': paragraphs,
      'inline': True | False
    }

Note: Currently Doxygen does not support parsing ``inline namespaces``. So
you need to use the patch API to change the value from ``False`` to ``True``
manually. Maybe at some point https://github.com/doxygen/doxygen/issues/6741
it will be supported.

``class`` | ``struct`` Kind
...........................

Python dictionary representing a C++ class or struct::

    info = {
      'kind': 'class' | 'struct',
      'name': 'unqualified-name',
      'location': location,
      'scope': 'unique-name' | None,
      'access': 'public' | 'protected' | 'private',
      Optional('template_parameters'): template_parameters,
      'members: [ 'unique-name', 'unique-name' ],
      'briefdescription': paragraphs,
      'detaileddescription': paragraphs
    }


``enum`` | ``enum class`` Kind
..............................

Python dictionary representing a C++ enum or enum class::

    info = {
      'kind': 'enum',
      'name': 'unqualified-name',
      'location': location,
      'scope': 'unique-name' | None,
      'access': 'public' | 'protected' | 'private',
      'values: [
        {
          'name': 'somename',
          'briefdescription': paragraphs,
          'detaileddescription': paragraphs,
          Optional('value'): 'some value'
        }
       ],
      'briefdescription': paragraphs,
      'detaileddescription': paragraphs
    }

``typedef`` | ``using`` Kind
............................

Python dictionary representing a C++ using or typedef statement::

    info = {
      'kind': 'typedef' | 'using',
      'name': 'unqualified-name',
      'location': location,
      'scope': 'unique-name' | None,
      'access': 'public' | 'protected' | 'private',
      'type': type,
      'briefdescription': paragraphs,
      'detaileddescription': paragraphs
    }

``define`` Kind
...............

Python dictionary representing a C/C++ define::

    info = {
      'kind': 'define',
      'name': 'name',
      'location': location,
      Optional('initializer'): 'some_value',
      Optional('parameters'): [{
          'name': 'somestring',
          Optional('description'): paragraphs
      }],
      'briefdescription': paragraphs,
      'detaileddescription': paragraphs
    }

The content of the define will be in the ``initializer`` field. If the define
takes documented paremeters these will be under the ``parameter`` key.

Examples:

1. Define initializer::

      #define VERSION "1.0.2"

2. Define initalizer with parameters::

      #define min(X, Y)  ((X) < (Y) ? (X) : (Y))


``file`` Kind
............................

Python dictionary representing a file in the project::

    info = {
      'kind': 'file',
      'name': 'somefile.hpp',
      'path': 'relative/path/to/somefile.hpp',
    }

``function`` Kind
.................

Python dictionary representing a C++ function::

    info = {
      'kind': 'function',
      'name': 'unqualified-name',
      'location': location,
      'scope': 'unique-name' | None,
      Optional('return'): {
        'type': type,
        'description': paragraphs
      }
      Optional('template_parameters'): template_parameters,
      'is_const': True | False,
      'is_static': True | False,
      'is_virtual': True | False,
      'is_explicit': True | False,
      'is_inline': True | False,
      'is_constructor': True | False,
      'is_destructor': True | False,
      'trailing_return': True | False,
      'access': 'public' | 'protected' | 'private',
      'briefdescription: paragraphs,
      'detaileddescription: paragraphs,
      'parameters': [
        { 'type': type, Optional('name'): 'somename', 'description': paragraphs },
        ...
      ]
  }

The `return` key is optional if the function is either a constructor or
destructor.

``variable`` Kind
.................

Python dictionary representing a C++ variable::

    info = {
      'kind': 'variable',
      'name': 'unqualified-name',
      Optional('value'): 'some value',
      'type': type,
      'location': location,
      'is_static': True | False,
      'is_mutable': True | False,
      'is_volatile': True | False,
      'is_const': True | False,
      'is_constexpr': True | False,
      'scope': 'unique-name' | None,
      'access': 'public' | 'protected' | 'private',
      'briefdescription: paragraphs,
      'detaileddescription: paragraphs,
    }

``location`` item
.................

Python dictionary representing a location::

    location = {
      Optional('include'): 'some/header.h',
      'path': 'src/project/header.h',
      'line': 10
      }

* The ``include`` will be relative to any ``include_paths`` specified in the
  ``wurfapi`` dictionary in your Sphinx ``conf.py``.

* The ``path`` will be relative to the project root folder.

``type`` item
.............

Python list representing a C++ type::

    type = [
      {
        'value': 'sometext',
        Optional('link'): link
      }, ...
    ]

Having the type as a list of items we can create links to nested types e.g.
say we have a `std::unique_ptr<impl>` and we would like to make `impl` a link.
This could look like::

    "type": [
      {
        "value": "std::unique_ptr<"
      },
      {
        "link": {"url": False, "value": "project::impl"},
        "value": "impl"
      },
      {
        "value": ">"
      }
    ]

Any spaces in the type list should be preserved all the way from the Doxygen
output and into the type list. In the rst it should be sufficient to simply
output the values of the type. No spaces or other stuff should be injected.

``link`` item
.............

Python dictionary representing a link::

    link = { 'url': True | False, 'value': 'somestring' }

If `url` is `True` we have a basic extrenal reference otherwise we have a
link to an internal type in the API.

``parameter`` item
...................

Dictionary representing a function parameter::

    parameter = {
      'type': type,
      Optional('name'): 'somestring',
      Optional('description'): paragraphs
    }

For the parameter, the name is also included in the type list. The reason
is that some parameters can be pretty complex, with the name embedded
inside the type e.g.::

    void function(int (*(*foo)())[3]);

This is a function that takes one parameter `foo` which is a pointer
function returning a pointer to array 3 of int - nice right? Anyway, in
such cases the parameter name is embedded inside the type of the parameter.
We therefore took the easy way out and `wurfapi` will always include the
parameter name in the type.

As an example the parameter dictionary for a function `void test(int b)`
could be::

    {
       'type': [{'value': 'int '}, {'value': 'b'}],
       'name': 'b'
    }

``template_parameters`` item
.............................

Python list of dictionaries representing template parameters::

    template_parameters = [{
      'type': type,
      'name': 'somestring',
      Optional('default'): type,
      Optional('description'): paragraphs
    }]

Text Information
................

Text information is stored in a list of paragraphs::

    paragraphs = [paragraph]

A paragraph consists of a list of paragraph elements::

    paragraph = [
          {
            "kind": "text" | "code" | "list" | "bold" | "italic",
            ...
          },
        ]

Paragraph elements can be one of three kinds, "text", "code" or "list"::

    text = {
      'kind': 'text',
      'content': 'hello',
      Optional('link'): link
      }

    code = {
      'kind': 'code',
      'content': 'void print();',
      'is_block': true | false
    }

    list = {
      'kind': 'list',
      'ordered': true | false,
      'items': [paragraphs] # Each item is a list of paragraphs
    }


Problem with ``unique-name`` for functions
..........................................

Issue equivalent C++ function signatures can be written in a number of
different ways::

  void hello(const int *x); // x is a pointer to const int
  void hello(int const *x); // x is a pointer to const int

We can also move the asterisk (``*``) to the left::

  void hello(const int* x); // x is a pointer to const int
  void hello(int const* x); // x is a pointer to const int

So we need some way to normalize the function signature when transforming it
to ``unique-name``. We cannot simply rely on sting comparisons.

According to the numerous google searches it is hard to write a regex for this.
Instead we will try to use a parser:

* Python parser: https://github.com/erezsh/lark
* C++ Grammar: http://www.externsoft.ch/media/swf/cpp11-iso.html#parameters_and_qualifiers

We only need to parse the function parameter list denoted as the
``http://www.externsoft.ch/media/swf/cpp11-iso.html#parameters_and_qualifiers``.


Generated output
----------------

Since we are going to be using Doxygen's XML output as input to the
extension we need a place to store it. We store it system temporary folder e.g.
if the project name is "foobar" on Linux this would be
``/tmp/wurfapi-foobar-123456`` where ``123456`` is a hash of the source
directory paths. In addition to Doxygen's XML we also store the generated rst
for the different directives there. This is nice for debugging to see whether
we generate broken rst.

The API in json format can be found in the ``_build/.doctree/wurfapi_api.json``.

Paths and directories
---------------------


* Source directory: In Sphinx the source directory is where our .rst files are
  located. This is what you pass to ``sphinx-build`` when building your
  documentation. We will use this in our extension to find the C++ source code
  and output customization templates.


Notes
=====

* Why use an ``src`` folder (https://hynek.me/articles/testing-packaging/).
  tl;dr you should run your tests in the same environment as your users would
  run your code. So by placing the source files in a non-importable folder you
  avoid accidentally having access to resources not added to the Python
  package your users will install...
* Python packaging guide: https://packaging.python.org/distributing/