[PATCH v4 3/3] dts: add API doc generation

["Juraj Linkeš" <juraj.linkes@pantheon.tech>]

The tool used to generate DTS API docs is Sphinx, which is already in
use in DPDK. The same configuration is used to preserve style with one
DTS-specific configuration (so that the DPDK docs are unchanged) that
modifies how the sidebar displays the content.

Sphinx generates the documentation from Python docstrings. The docstring
format is the Google format [0] which requires the sphinx.ext.napoleon
extension. The other extension, sphinx.ext.intersphinx, enables linking
to object in external documentations, such as the Python documentation.

There are two requirements for building DTS docs:
* The same Python version as DTS or higher, because Sphinx imports the
  code.
* Also the same Python packages as DTS, for the same reason.

[0] https://google.github.io/styleguide/pyguide.html#38-comments-and-docstrings

Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>
Reviewed-by: Jeremy Spewock <jspewock@iol.unh.edu>
Tested-by: Nicholas Pratte <npratte@iol.unh.edu>
---
 buildtools/call-sphinx-build.py | 33 +++++++++++++++++++---------
 doc/api/doxy-api-index.md       |  3 +++
 doc/api/doxy-api.conf.in        |  2 ++
 doc/api/meson.build             | 11 +++++++---
 doc/guides/conf.py              | 39 ++++++++++++++++++++++++++++-----
 doc/guides/meson.build          |  1 +
 doc/guides/tools/dts.rst        | 34 +++++++++++++++++++++++++++-
 dts/doc/meson.build             | 27 +++++++++++++++++++++++
 dts/meson.build                 | 16 ++++++++++++++
 meson.build                     |  1 +
 10 files changed, 148 insertions(+), 19 deletions(-)
 create mode 100644 dts/doc/meson.build
 create mode 100644 dts/meson.build

diff --git a/buildtools/call-sphinx-build.py b/buildtools/call-sphinx-build.py
index 39a60d09fa..aea771a64e 100755
--- a/buildtools/call-sphinx-build.py
+++ b/buildtools/call-sphinx-build.py
@@ -3,37 +3,50 @@
 # Copyright(c) 2019 Intel Corporation
 #
 
+import argparse
 import sys
 import os
 from os.path import join
 from subprocess import run, PIPE, STDOUT
 from packaging.version import Version
 
-# assign parameters to variables
-(sphinx, version, src, dst, *extra_args) = sys.argv[1:]
+parser = argparse.ArgumentParser()
+parser.add_argument('sphinx')
+parser.add_argument('version')
+parser.add_argument('src')
+parser.add_argument('dst')
+parser.add_argument('--dts-root', default=None)
+args, extra_args = parser.parse_known_args()
 
 # set the version in environment for sphinx to pick up
-os.environ['DPDK_VERSION'] = version
+os.environ['DPDK_VERSION'] = args.version
+if args.dts_root:
+    os.environ['DTS_ROOT'] = args.dts_root
 
 # for sphinx version >= 1.7 add parallelism using "-j auto"
-ver = run([sphinx, '--version'], stdout=PIPE,
+ver = run([args.sphinx, '--version'], stdout=PIPE,
           stderr=STDOUT).stdout.decode().split()[-1]
-sphinx_cmd = [sphinx] + extra_args
+sphinx_cmd = [args.sphinx] + extra_args
 if Version(ver) >= Version('1.7'):
     sphinx_cmd += ['-j', 'auto']
 
 # find all the files sphinx will process so we can write them as dependencies
 srcfiles = []
-for root, dirs, files in os.walk(src):
+for root, dirs, files in os.walk(args.src):
     srcfiles.extend([join(root, f) for f in files])
 
+if not os.path.exists(args.dst):
+    os.makedirs(args.dst)
+
 # run sphinx, putting the html output in a "html" directory
-with open(join(dst, 'sphinx_html.out'), 'w') as out:
-    process = run(sphinx_cmd + ['-b', 'html', src, join(dst, 'html')],
-                  stdout=out)
+with open(join(args.dst, 'sphinx_html.out'), 'w') as out:
+    process = run(
+        sphinx_cmd + ['-b', 'html', args.src, join(args.dst, 'html')],
+        stdout=out
+    )
 
 # create a gcc format .d file giving all the dependencies of this doc build
-with open(join(dst, '.html.d'), 'w') as d:
+with open(join(args.dst, '.html.d'), 'w') as d:
     d.write('html: ' + ' '.join(srcfiles) + '\n')
 
 sys.exit(process.returncode)
diff --git a/doc/api/doxy-api-index.md b/doc/api/doxy-api-index.md
index 8c1eb8fafa..d5f823b7f0 100644
--- a/doc/api/doxy-api-index.md
+++ b/doc/api/doxy-api-index.md
@@ -243,3 +243,6 @@ The public API headers are grouped by topics:
   [experimental APIs](@ref rte_compat.h),
   [ABI versioning](@ref rte_function_versioning.h),
   [version](@ref rte_version.h)
+
+- **tests**:
+  [**DTS**](@dts_api_main_page)
diff --git a/doc/api/doxy-api.conf.in b/doc/api/doxy-api.conf.in
index 27afec8b3b..2e08c6a452 100644
--- a/doc/api/doxy-api.conf.in
+++ b/doc/api/doxy-api.conf.in
@@ -123,6 +123,8 @@ SEARCHENGINE            = YES
 SORT_MEMBER_DOCS        = NO
 SOURCE_BROWSER          = YES
 
+ALIASES                 = "dts_api_main_page=@DTS_API_MAIN_PAGE@"
+
 EXAMPLE_PATH            = @TOPDIR@/examples
 EXAMPLE_PATTERNS        = *.c
 EXAMPLE_RECURSIVE       = YES
diff --git a/doc/api/meson.build b/doc/api/meson.build
index 5b50692df9..ffc75d7b5a 100644
--- a/doc/api/meson.build
+++ b/doc/api/meson.build
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 # Copyright(c) 2018 Luca Boccassi <bluca@debian.org>
 
+doc_api_build_dir = meson.current_build_dir()
 doxygen = find_program('doxygen', required: get_option('enable_docs'))
 
 if not doxygen.found()
@@ -32,14 +33,18 @@ example = custom_target('examples.dox',
 # set up common Doxygen configuration
 cdata = configuration_data()
 cdata.set('VERSION', meson.project_version())
-cdata.set('API_EXAMPLES', join_paths(dpdk_build_root, 'doc', 'api', 'examples.dox'))
-cdata.set('OUTPUT', join_paths(dpdk_build_root, 'doc', 'api'))
+cdata.set('API_EXAMPLES', join_paths(doc_api_build_dir, 'examples.dox'))
+cdata.set('OUTPUT', doc_api_build_dir)
 cdata.set('TOPDIR', dpdk_source_root)
-cdata.set('STRIP_FROM_PATH', ' '.join([dpdk_source_root, join_paths(dpdk_build_root, 'doc', 'api')]))
+cdata.set('STRIP_FROM_PATH', ' '.join([dpdk_source_root, doc_api_build_dir]))
 cdata.set('WARN_AS_ERROR', 'NO')
 if get_option('werror')
     cdata.set('WARN_AS_ERROR', 'YES')
 endif
+# A local reference must be relative to the main index.html page
+# The path below can't be taken from the DTS meson file as that would
+# require recursive subdir traversal (doc, dts, then doc again)
+cdata.set('DTS_API_MAIN_PAGE', join_paths('..', 'dts', 'html', 'index.html'))
 
 # configure HTML Doxygen run
 html_cdata = configuration_data()
diff --git a/doc/guides/conf.py b/doc/guides/conf.py
index 0f7ff5282d..b442a1f76c 100644
--- a/doc/guides/conf.py
+++ b/doc/guides/conf.py
@@ -7,10 +7,9 @@
 from sphinx import __version__ as sphinx_version
 from os import listdir
 from os import environ
-from os.path import basename
-from os.path import dirname
+from os.path import basename, dirname
 from os.path import join as path_join
-from sys import argv, stderr
+from sys import argv, stderr, path
 
 import configparser
 
@@ -24,6 +23,37 @@
           file=stderr)
     pass
 
+# Napoleon enables the Google format of Python doscstrings, used in DTS
+# Intersphinx allows linking to external projects, such as Python docs, also used in DTS
+extensions = ['sphinx.ext.napoleon', 'sphinx.ext.intersphinx']
+
+# DTS Python docstring options
+autodoc_default_options = {
+    'members': True,
+    'member-order': 'bysource',
+    'show-inheritance': True,
+}
+autodoc_class_signature = 'separated'
+autodoc_typehints = 'both'
+autodoc_typehints_format = 'short'
+autodoc_typehints_description_target = 'documented'
+napoleon_numpy_docstring = False
+napoleon_attr_annotations = True
+napoleon_preprocess_types = True
+add_module_names = False
+toc_object_entries = True
+toc_object_entries_show_parents = 'hide'
+intersphinx_mapping = {'python': ('https://docs.python.org/3', None)}
+
+dts_root = environ.get('DTS_ROOT')
+if dts_root:
+    path.append(dts_root)
+    # DTS Sidebar config
+    html_theme_options = {
+        'collapse_navigation': False,
+        'navigation_depth': -1,
+    }
+
 stop_on_error = ('-W' in argv)
 
 project = 'Data Plane Development Kit'
@@ -35,8 +65,7 @@
 html_show_copyright = False
 highlight_language = 'none'
 
-release = environ.setdefault('DPDK_VERSION', "None")
-version = release
+version = environ.setdefault('DPDK_VERSION', "None")
 
 master_doc = 'index'
 
diff --git a/doc/guides/meson.build b/doc/guides/meson.build
index 51f81da2e3..8933d75f6b 100644
--- a/doc/guides/meson.build
+++ b/doc/guides/meson.build
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 # Copyright(c) 2018 Intel Corporation
 
+doc_guides_source_dir = meson.current_source_dir()
 sphinx = find_program('sphinx-build', required: get_option('enable_docs'))
 
 if not sphinx.found()
diff --git a/doc/guides/tools/dts.rst b/doc/guides/tools/dts.rst
index 47b218b2c6..d1c3c2af7a 100644
--- a/doc/guides/tools/dts.rst
+++ b/doc/guides/tools/dts.rst
@@ -280,7 +280,12 @@ and try not to divert much from it.
 The :ref:`DTS developer tools <dts_dev_tools>` will issue warnings
 when some of the basics are not met.
 
-The code must be properly documented with docstrings.
+The API documentation, which is a helpful reference when developing, may be accessed
+in the code directly or generated with the :ref:`API docs build steps <building_api_docs>`.
+When adding new files or modifying the directory structure, the corresponding changes must
+be made to DTS api doc sources in ``dts/doc``.
+
+Speaking of which, the code must be properly documented with docstrings.
 The style must conform to the `Google style
 <https://google.github.io/styleguide/pyguide.html#38-comments-and-docstrings>`_.
 See an example of the style `here
@@ -415,6 +420,33 @@ the DTS code check and format script.
 Refer to the script for usage: ``devtools/dts-check-format.sh -h``.
 
 
+.. _building_api_docs:
+
+Building DTS API docs
+---------------------
+
+To build DTS API docs, install the dependencies with Poetry, then enter its shell:
+
+.. code-block:: console
+
+   poetry install --no-root --with docs
+   poetry shell
+
+The documentation is built using the standard DPDK build system. After executing the meson command
+and entering Poetry's shell, build the documentation with:
+
+.. code-block:: console
+
+   ninja -C build dts-doc
+
+The output is generated in ``build/doc/api/dts/html``.
+
+.. Note::
+
+   Make sure to fix any Sphinx warnings when adding or updating docstrings. Also make sure to run
+   the ``devtools/dts-check-format.sh`` script and address any issues it finds.
+
+
 Configuration Schema
 --------------------
 
diff --git a/dts/doc/meson.build b/dts/doc/meson.build
new file mode 100644
index 0000000000..01b7b51034
--- /dev/null
+++ b/dts/doc/meson.build
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright(c) 2023 PANTHEON.tech s.r.o.
+
+sphinx = find_program('sphinx-build', required: false)
+sphinx_apidoc = find_program('sphinx-apidoc', required: false)
+
+if not sphinx.found() or not sphinx_apidoc.found()
+    subdir_done()
+endif
+
+dts_doc_api_build_dir = join_paths(doc_api_build_dir, 'dts')
+
+extra_sphinx_args = ['-E', '-c', doc_guides_source_dir, '--dts-root', dts_dir]
+if get_option('werror')
+    extra_sphinx_args += '-W'
+endif
+
+htmldir = join_paths(get_option('datadir'), 'doc', 'dpdk', 'dts')
+dts_api_html = custom_target('dts_api_html',
+        output: 'html',
+        command: [sphinx_wrapper, sphinx, meson.project_version(),
+            meson.current_source_dir(), dts_doc_api_build_dir, extra_sphinx_args],
+        build_by_default: false,
+        install: get_option('enable_docs'),
+        install_dir: htmldir)
+doc_targets += dts_api_html
+doc_target_names += 'DTS_API_HTML'
diff --git a/dts/meson.build b/dts/meson.build
new file mode 100644
index 0000000000..e8ce0f06ac
--- /dev/null
+++ b/dts/meson.build
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright(c) 2023 PANTHEON.tech s.r.o.
+
+doc_targets = []
+doc_target_names = []
+dts_dir = meson.current_source_dir()
+
+subdir('doc')
+
+if doc_targets.length() == 0
+    message = 'No docs targets found'
+else
+    message = 'Built docs:'
+endif
+run_target('dts-doc', command: [echo, message, doc_target_names],
+    depends: doc_targets)
diff --git a/meson.build b/meson.build
index 8b248d4505..835973a0ce 100644
--- a/meson.build
+++ b/meson.build
@@ -87,6 +87,7 @@ subdir('app')
 
 # build docs
 subdir('doc')
+subdir('dts')
 
 # build any examples explicitly requested - useful for developers - and
 # install any example code into the appropriate install path
-- 
2.34.1