[libgpiod][PATCH] doc: add configuration to generate doxygen documentation on readthedocs.

[Kent Gibson <warthog618@gmail.com>]

Having the libgpiod documentation available online would be helpful, so
add the configuration required to generate the existing doxygen C/C++
documentation on readthedocs.

Signed-off-by: Kent Gibson <warthog618@gmail.com>

---

This is intended to be a minimal change that can be applied to both
master and v1.6.x and have zero impact on existing builds.
It has been tested on RTD using the current v1.6.3 release[1].
The approach used here is to replace any Sphinx documentation generated
by RTD with the doxygen documentation.
A subsequent patch for v2 can switch to using Breathe/Sphinx to include
the documentation for the Python bindings as well.  And relocate the
Sphinx configuration into the doc directory.

Cheers,
Kent.
[1] https://libgpiod.readthedocs.io/en/latest/

 .readthedocs.yaml | 29 ++++++++++++++++++++
 sphinx/conf.py    | 70 +++++++++++++++++++++++++++++++++++++++++++++++
 sphinx/index.rst  | 24 ++++++++++++++++
 3 files changed, 123 insertions(+)
 create mode 100644 .readthedocs.yaml
 create mode 100644 sphinx/conf.py
 create mode 100644 sphinx/index.rst

diff --git a/.readthedocs.yaml b/.readthedocs.yaml
new file mode 100644
index 0000000..976496c
--- /dev/null
+++ b/.readthedocs.yaml
@@ -0,0 +1,29 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+#
+# This file is part of libgpiod.
+#
+# Copyright (C) 2022 Bartosz Golaszewski <bartekgola@gmail.com>
+#
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+version: 2
+
+build:
+  os: ubuntu-20.04
+  tools:
+    python: "3.9"
+  # doxygen is available by default, but just in case.
+  # others are definitely missing.
+  apt_packages:
+      - autoconf
+      - autoconf-archive
+      - libtool
+      - m4
+      - doxygen
+      - graphviz
+
+sphinx:
+   configuration: sphinx/conf.py
+
diff --git a/sphinx/conf.py b/sphinx/conf.py
new file mode 100644
index 0000000..7022ff9
--- /dev/null
+++ b/sphinx/conf.py
@@ -0,0 +1,70 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+#
+# This file is part of libgpiod.
+#
+# Copyright (C) 2022 Bartosz Golaszewski <bartekgola@gmail.com>
+#
+# Configuration file for the Sphinx documentation builder.
+#
+# This file only contains a selection of the most common options. For a full
+# list see the documentation:
+# https://www.sphinx-doc.org/en/master/usage/configuration.html
+
+import subprocess
+
+subprocess.run('cd .. ; ./autogen.sh ; make doc', shell=True)
+
+# -- Path setup --------------------------------------------------------------
+
+# If extensions (or modules to document with autodoc) are in another directory,
+# add these directories to sys.path here. If the directory is relative to the
+# documentation root, use os.path.abspath to make it absolute, like shown here.
+#
+# import os
+# import sys
+# sys.path.insert(0, os.path.abspath('.'))
+
+
+# -- Project information -----------------------------------------------------
+
+project = 'libgpiod'
+copyright = '2022, Bartosz Golaszewski'
+author = 'Bartosz Golaszewski'
+
+# The full version, including alpha/beta/rc tags
+release = subprocess.run(
+            ['git', 'describe', '--dirty'],
+            capture_output=True).stdout.decode().strip()
+
+# -- General configuration ---------------------------------------------------
+
+# Add any Sphinx extension module names here, as strings. They can be
+# extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
+# ones.
+extensions = [
+]
+
+# Add any paths that contain templates here, relative to this directory.
+templates_path = []
+
+# List of patterns, relative to source directory, that match files and
+# directories to ignore when looking for source files.
+# This pattern also affects html_static_path and html_extra_path.
+exclude_patterns = []
+
+
+# -- Options for HTML output -------------------------------------------------
+
+# The theme to use for HTML and HTML Help pages.  See the documentation for
+# a list of builtin themes.
+#
+html_theme = 'alabaster'
+
+# Add any paths that contain custom static files (such as style sheets) here,
+# relative to this directory. They are copied after the builtin static files,
+# so a file named "default.css" will overwrite the builtin "default.css".
+html_static_path = []
+
+html_extra_path = ['../doc/html']
+
diff --git a/sphinx/index.rst b/sphinx/index.rst
new file mode 100644
index 0000000..e38fad7
--- /dev/null
+++ b/sphinx/index.rst
@@ -0,0 +1,24 @@
+.. SPDX-License-Identifier: LGPL-2.1-or-later
+
+..
+   This file is part of libgpiod.
+
+   Copyright (C) 2022 Bartosz Golaszewski <bartekgola@gmail.com>
+
+   libgpiod documentation master file.
+
+Welcome to libgpiod's documentation!
+====================================
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Contents:
+
+
+
+Indices and tables
+==================
+
+* :ref:`genindex`
+* :ref:`modindex`
+* :ref:`search`
-- 
2.35.1