docs: Add shim Sphinx config for readthedocs

This adds a faux Sphinx project under host/docs. When invoking sphinx,
it will in fact forward the generator request to Doxygen. This is useful
for generating the UHD manual, e.g., on readthedocs.

To enable the latter service, .readthedocs.yaml and environment.yml
files were added as well.

5 files changed, 223 insertions, 0 deletions

diff --git a/host/docs/sphinx/.gitignore b/host/docs/sphinx/.gitignore
new file mode 100644
index 000000000..ce8c7a876
--- /dev/null
+++ b/host/docs/sphinx/.gitignore
@@ -0,0 +1,2 @@
+build/
+build_doxygen/
diff --git a/host/docs/sphinx/Makefile b/host/docs/sphinx/Makefile
new file mode 100644
index 000000000..69fe55ecf
--- /dev/null
+++ b/host/docs/sphinx/Makefile
@@ -0,0 +1,19 @@
+# Minimal makefile for Sphinx documentation
+#
+
+# You can set these variables from the command line.
+SPHINXOPTS    =
+SPHINXBUILD   = sphinx-build
+SOURCEDIR     = source
+BUILDDIR      = build
+
+# Put it first so that "make" without argument is like "make help".
+help:
+	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+
+.PHONY: help Makefile
+
+# Catch-all target: route all unknown targets to Sphinx using the new
+# "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
+%: Makefile
+	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
\ No newline at end of file
diff --git a/host/docs/sphinx/environment.yml b/host/docs/sphinx/environment.yml
new file mode 100644
index 000000000..16a5c10d5
--- /dev/null
+++ b/host/docs/sphinx/environment.yml
@@ -0,0 +1,7 @@
+name: UHD
+channels:
+  - conda-forge
+  - defaults
+dependencies:
+  - cmake
+  - compilers
diff --git a/host/docs/sphinx/source/conf.py b/host/docs/sphinx/source/conf.py
new file mode 100644
index 000000000..e8a7c413c
--- /dev/null
+++ b/host/docs/sphinx/source/conf.py
@@ -0,0 +1,185 @@
+# -*- coding: utf-8 -*-
+#
+# Configuration file for the Sphinx documentation builder.
+#
+# This file does only contain a selection of the most common options. For a
+# full list see the documentation:
+# http://www.sphinx-doc.org/en/master/config
+
+# -- 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 = 'UHD'
+copyright = '2022, Ettus Research, an NI Brand'
+author = 'Ettus Research, an NI Brand'
+
+# The short X.Y version
+version = ''
+# The full version, including alpha/beta/rc tags
+release = ''
+
+
+# -- General configuration ---------------------------------------------------
+
+# If your documentation needs a minimal Sphinx version, state it here.
+#
+# needs_sphinx = '1.0'
+
+# 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 = ['_templates']
+
+# The suffix(es) of source filenames.
+# You can specify multiple suffix as a list of string:
+#
+# source_suffix = ['.rst', '.md']
+source_suffix = '.rst'
+
+# The master toctree document. Note that this file (index.rst) does not actually
+# get used in the deployed documentation, because we overwrite the Sphinx output
+# further down.
+master_doc = 'index'
+
+# The language for content autogenerated by Sphinx. Refer to documentation
+# for a list of supported languages.
+#
+# This is also used if you do content translation via gettext catalogs.
+# Usually you set "language" from the command line for these cases.
+language = None
+
+# 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 = []
+
+# The name of the Pygments (syntax highlighting) style to use.
+pygments_style = None
+
+
+# -- 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'
+
+# Theme options are theme-specific and customize the look and feel of a theme
+# further.  For a list of options available for each theme, see the
+# documentation.
+#
+# html_theme_options = {}
+
+# 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 = ['_static']
+
+# Custom sidebar templates, must be a dictionary that maps document names
+# to template names.
+#
+# The default sidebars (for documents that don't match any pattern) are
+# defined by theme itself.  Builtin themes are using these templates by
+# default: ``['localtoc.html', 'relations.html', 'sourcelink.html',
+# 'searchbox.html']``.
+#
+# html_sidebars = {}
+
+
+# -- Options for HTMLHelp output ---------------------------------------------
+
+# Output file base name for HTML help builder.
+htmlhelp_basename = 'UHDdoc'
+
+
+# -- Options for LaTeX output ------------------------------------------------
+
+latex_elements = {
+    # The paper size ('letterpaper' or 'a4paper').
+    #
+    # 'papersize': 'letterpaper',
+
+    # The font size ('10pt', '11pt' or '12pt').
+    #
+    # 'pointsize': '10pt',
+
+    # Additional stuff for the LaTeX preamble.
+    #
+    # 'preamble': '',
+
+    # Latex figure (float) alignment
+    #
+    # 'figure_align': 'htbp',
+}
+
+# Grouping the document tree into LaTeX files. List of tuples
+# (source start file, target name, title,
+#  author, documentclass [howto, manual, or own class]).
+latex_documents = [
+    (master_doc, 'UHD.tex', 'UHD Documentation',
+     'Ettus Research, an NI Brand', 'manual'),
+]
+
+
+# -- Options for manual page output ------------------------------------------
+
+# One entry per manual page. List of tuples
+# (source start file, name, description, authors, manual section).
+man_pages = [
+    (master_doc, 'uhd', 'UHD Documentation',
+     [author], 1)
+]
+
+
+# -- Options for Texinfo output ----------------------------------------------
+
+# Grouping the document tree into Texinfo files. List of tuples
+# (source start file, target name, title, author,
+#  dir menu entry, description, category)
+texinfo_documents = [
+    (master_doc, 'UHD', 'UHD Documentation',
+     author, 'UHD', 'One line description of project.',
+     'Miscellaneous'),
+]
+
+
+# -- Options for Epub output -------------------------------------------------
+
+# Bibliographic Dublin Core info.
+epub_title = project
+
+# The unique identifier of the text. This can be a ISBN number
+# or the project homepage.
+#
+# epub_identifier = ''
+
+# A unique identification for the text.
+#
+# epub_uid = ''
+
+# A list of files that should not be packed into the epub file.
+epub_exclude_files = ['search.html']
+
+## Now we cheat Sphinx by running Doxygen instead. This will overwrite the
+# Sphinx output with the Doxygen output.
+_doxy_dir = '../build_doxygen'
+import subprocess
+subprocess.call(
+    f"mkdir -p {_doxy_dir} && "
+    f"cmake ../../.. -DUHD_BOOST_REQUIRED=OFF -DENABLE_LIBUHD=OFF -DENABLE_MAN_PAGES=OFF -B {_doxy_dir} && "
+    f"make -C {_doxy_dir} doxygen_docs", shell=True)
+html_extra_path = [f'{_doxy_dir}/docs/doxygen/html']
diff --git a/host/docs/sphinx/source/index.rst b/host/docs/sphinx/source/index.rst
new file mode 100644
index 000000000..f62125e5f
--- /dev/null
+++ b/host/docs/sphinx/source/index.rst
@@ -0,0 +1,10 @@
+.. UHD documentation master file, created by sphinx-quickstart.
+   This is a dummy file, it will be ignored and its result will be overwritten.
+
+Welcome to UHD's documentation!
+===============================
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Contents:
+