.. _zephyr_doc:

Documentation Generation
########################

These instructions will walk you through generating the Zephyr Project's
documentation on your local system using the same documentation sources
as we use to create the online documentation found at
https://docs.zephyrproject.org

.. _documentation-overview:

Documentation overview
**********************

Zephyr Project content is written using the reStructuredText markup
language (.rst file extension) with Sphinx extensions, and processed
using Sphinx to create a formatted stand-alone website. Developers can
view this content either in its raw form as .rst markup files, or you
can generate the HTML content and view it with a web browser directly on
your workstation. This same .rst content is also fed into the Zephyr
Project's public website documentation area (with a different theme
applied).

You can read details about `reStructuredText`_, and `Sphinx`_ from
their respective websites.

The project's documentation contains the following items:

* ReStructuredText source files used to generate documentation found at the
  https://docs.zephyrproject.org website. Most of the reStructuredText sources
  are found in the ``/doc`` directory, but others are stored within the
  code source tree near their specific component (such as ``/samples`` and
  ``/boards``)

* Doxygen-generated material used to create all API-specific documents
  also found at https://docs.zephyrproject.org

* Script-generated material for kernel configuration options based on Kconfig
  files found in the source code tree

.. image:: images/doc-gen-flow.png
   :align: center

The reStructuredText files are processed by the Sphinx documentation system,
and make use of the breathe extension for including the doxygen-generated API
material.  Additional tools are required to generate the
documentation locally, as described in the following sections.

.. _documentation-processors:

Installing the documentation processors
***************************************

Our documentation processing has been tested to run with:

* Doxygen version 1.8.13
* Sphinx version 3.2.0
* Breathe version 4.20.0
* docutils version 0.16
* sphinx_rtd_theme version 0.4.0
* sphinxcontrib-svg2pdfconverter version 0.1.0
* Latexmk version 4.56

In order to install the documentation tools, first install Zephyr as
described in :ref:`getting_started`. Then install additional tools
that are only required to generate the documentation,
as described below:

On Ubuntu Linux:

.. code-block:: console

   sudo apt-get install --no-install-recommends doxygen librsvg2-bin \
     texlive-latex-base texlive-latex-extra latexmk texlive-fonts-recommended

On Fedora Linux:

.. code-block:: console

   sudo dnf install doxygen texlive-latex latexmk \
     texlive-collection-fontsrecommended librsvg2-tools

On Clear Linux:

.. code-block:: console

  sudo swupd bundle-add texlive

On Arch Linux:

.. code-block:: console

   sudo pacman -S doxygen librsvg texlive-core texlive-bin

On macOS:

.. code-block:: console

   brew install doxygen mactex librsvg
   tlmgr install latexmk
   tlmgr install collection-fontsrecommended

On Windows in an Administrator ``cmd.exe`` prompt:

.. code-block:: console

   choco install doxygen.install strawberryperl miktex rsvg-convert

.. note::
   On Windows, the Sphinx executable ``sphinx-build.exe`` is placed in
   the ``Scripts`` folder of your Python installation path.
   Dependending on how you have installed Python, you may need to
   add this folder to your ``PATH`` environment variable. Follow
   the instructions in `Windows Python Path`_ to add those if needed.

Documentation presentation theme
********************************

Sphinx supports easy customization of the generated documentation
appearance through the use of themes. Replace the theme files and do
another ``make htmldocs`` and the output layout and style is changed.
The ``read-the-docs`` theme is installed as part of the
:ref:`install_py_requirements` step you took in the getting started
guide.

Running the documentation processors
************************************

The ``/doc`` directory in your cloned copy of the Zephyr project git
repo has all the .rst source files, extra tools, and Makefile for
generating a local copy of the Zephyr project's technical documentation.
Assuming the local Zephyr project copy is in a folder ``zephyr`` in your home
folder, here are the commands to generate the html content locally:

.. code-block:: console

   # On Linux/macOS
   cd ~/zephyr/doc
   # On Windows
   cd %userprofile%\zephyr\doc

   # Use cmake to configure a Ninja-based build system:
   cmake -GNinja -B_build .

   # Enter the build directory
   cd _build

   # To generate HTML output, run ninja on the generated build system:
   ninja htmldocs
   # If you modify or add .rst files, run ninja again:
   ninja htmldocs

   # To generate PDF output, run ninja on the generated build system:
   ninja pdfdocs

.. warning::

   The documentation build system creates copies in the build
   directory of every .rst file used to generate the documentation,
   along with dependencies referenced by those .rst files.

   This means that Sphinx warnings and errors refer to the **copies**,
   and **not the version-controlled original files in Zephyr**. Be
   careful to make sure you don't accidentally edit the copy of the
   file in an error message, as these changes will not be saved.

Depending on your development system, it will take up to 15 minutes to
collect and generate the HTML content.  When done, you can view the HTML
output with your browser started at ``doc/_build/html/index.html`` and
if generated, the PDF file is available at ``doc/_build/pdf/zephyr.pdf``.

If you want to build the documentation from scratch just delete the contents
of the build folder and run ``cmake`` and then ``ninja`` again.

.. note::

   If you add or remove a file from the documentation, you need to re-run CMake.

On Unix platforms a convenience :zephyr_file:`Makefile` at the root folder
of the Zephyr repository can be used to build the documentation directly from
there:

.. code-block:: console

   cd ~/zephyr

   # To generate HTML output
   make htmldocs

   # To generate PDF output
   make pdfdocs

Filtering expected warnings
***************************

Alas, there are some known issues with the doxygen/Sphinx/Breathe
processing that generates warnings for some constructs, in particular
around unnamed structures in nested unions or structs.
While these issues are being considered for fixing in
Sphinx/Breathe, we've added a post-processing filter on the output of
the documentation build process to check for "expected" messages from the
generation process output.

The output from the Sphinx build is processed by the python script
``scripts/filter-known-issues.py`` together with a set of filter
configuration files in the ``.known-issues/doc`` folder.  (This
filtering is done as part of the ``doc/CMakeLists.txt`` CMake listfile.)

If you're contributing components included in the Zephyr API
documentation and run across these warnings, you can include filtering
them out as "expected" warnings by adding a conf file to the
``.known-issues/doc`` folder, following the example of other conf files
found there.

Developer-mode Document Building
********************************

Building the documentation for all the Kconfig options significantly
adds to the total doc build time.  When making and testing major changes
to the documentation, we provide an option to temporarily stub-out
the auto-generated configuration documentation so the doc build process
runs much faster.

To enable this mode, set the following option when invoking cmake::

   -DKCONFIG_TURBO_MODE=1

or invoke make with the following target::

   cd ~/zephyr

   # To generate HTML output without detailed Kconfig
   make htmldocs-fast


.. _reStructuredText: http://sphinx-doc.org/rest.html
.. _Sphinx: http://sphinx-doc.org/
.. _Windows Python Path: https://docs.python.org/3/using/windows.html#finding-the-python-executable