.. _module-pw_docgen: --------- pw_docgen --------- The docgen module provides tools to generate documentation for Pigweed-based projects, and for Pigweed itself. Pigweed-based projects typically use a subset of Pigweed's modules and add their own product-specific modules on top of that, which may have product-specific documentation. Docgen provides a convenient way to combine all of the relevant documentation for a project into one place, allowing downstream consumers of release bundles (e.g. factory teams, QA teams, beta testers, etc.) to have a unified source of documentation early on. The documentation generation is integrated directly into the build system. Any build target can depend on documentation, which allows it to be included as part of a factory release build, for example. Additionally, documentation itself can depend on other build targets, such as report cards for binary size/profiling. Any time the code is changed, documentation will be regenerated with the updated reports. Documentation Overview ====================== Each Pigweed module provides documentation describing its functionality, use cases, and programming API. Included in a module's documentation are report cards which show an overview of the module's size cost and performance benchmarks. These allow prospective users to evaluate the impact of including the module in their projects. Build Integration ================= Pigweed documentation files are written in `reStructuredText`_ format and rendered to HTML using `Sphinx`_ through Pigweed's GN build system. .. _reStructuredText: http://docutils.sourceforge.net/rst.html .. inclusive-language: ignore .. _Sphinx: http://www.sphinx-doc.org/en/master There are additonal Sphinx plugins used for rendering diagrams within reStructuredText files including: * `mermaid `_ via the `sphinxcontrib-mermaid `_ package. Documentation source and asset files are placed alongside code within a module and registered as a ``pw_doc_group`` target within a ``BUILD.gn`` file. These groups become available for import within a special documentation generation target, which accumulates all of them and renders the resulting HTML. This system can either be used directly within Pigweed, or integrated into a downstream project. GN Templates ------------ pw_doc_group ____________ The main template for defining documentation files is ``pw_doc_group``. It is used to logically group a collection of documentation source files and assets. Each Pigweed module is expected to provide at least one ``pw_doc_group`` target defining the module's documentation. A ``pw_doc_group`` can depend on other groups, causing them to be built with it. **Arguments** * ``sources``: RST documentation source files. * ``inputs``: Additional resources required for the docs (images, data files, etc.) * ``group_deps``: Other ``pw_doc_group`` targets required by this one. * ``report_deps``: Report card generating targets (e.g. ``pw_size_diff``) on which the docs depend. * ``other_deps``: Any other GN targets that should be run before this ``pw_doc_group`` runs that is not included in one of the above ``dep`` categories. **Example** .. code-block:: pw_doc_group("my_doc_group") { sources = [ "docs.rst" ] inputs = [ "face-with-tears-of-joy-emoji.svg" ] group_deps = [ ":sub_doc_group" ] report_deps = [ ":my_size_report" ] } pw_doc_gen __________ The ``pw_doc_gen`` template creates a target which renders complete HTML documentation for a project. It depends on registered ``pw_doc_group`` targets and creates an action which collects and renders them. To generate the complete docs, the template also requires a ``conf.py`` file configuring Sphinx's output, and a top level ``index.rst`` for the main page of the documentation. These are added at the root level of the built documentation to tie everything together. **Arguments** * ``conf``: Path to the ``conf.py`` to use for Sphinx. * ``index``: Path to the top-level ``index.rst`` file. * ``output_directory``: Directory in which to render HTML output. * ``deps``: List of all ``pw_doc_group`` targets required for the documentation. * ``python_metadata_deps``: Python-related dependencies that are only used as deps for generating Python package metadata list, not the overall documentation generation. This should rarely be used by non-Pigweed code. **Example** .. code-block:: pw_doc_gen("my_docs") { conf = "//my_docs/conf.py" index = "//my_docs/index.rst" output_directory = target_gen_dir deps = [ "//my_module:my_doc_group", ] } Generating Documentation ------------------------ All source files listed under a ``pw_doc_gen`` target and its ``pw_doc_group`` dependencies get copied out into a directory structure mirroring the original layout of the modules in which the sources appear. This is demonstrated below using a subset of Pigweed's core documentation. Consider the following target in ``$dir_pigweed/docs/BUILD.gn``: .. code-block:: pw_doc_gen("docs") { conf = "conf.py" index = "index.rst" output_directory = target_gen_dir deps = [ "$dir_pw_bloat:docs", "$dir_pw_docgen:docs", "$dir_pw_preprocessor:docs", ] } A documentation tree is created under the output directory. Each of the sources and inputs in the target's dependency graph is copied under this tree in the same directory structure as they appear under the root GN build directory (``$dir_pigweed`` in this case). The ``conf.py`` and ``index.rst`` provided directly to the ``pw_doc_gen`` template are copied in at the root of the tree. .. code-block:: out/gen/docs/pw_docgen_tree/ ├── conf.py ├── index.rst ├── pw_bloat │ ├── bloat.rst │ └── examples │ └── simple_bloat.rst ├── pw_docgen │ └── docgen.rst └── pw_preprocessor └── docs.rst This is the documentation tree which gets passed to Sphinx to build HTML output. Imports within documentation files must be relative to this structure. In practice, relative imports from within modules' documentation groups are identical to the project's directory structure. The only special case is the top-level ``index.rst`` file's imports; they must start from the project's build root. Sphinx Extensions ================= This module houses Pigweed-specific extensions for the Sphinx documentation generator. Extensions are included and configured in ``docs/conf.py``. module_metadata --------------- Per :ref:`SEED-0102 `, Pigweed module documentation has a standard format. The ``pigweed-module`` Sphinx directive provides that format and registers module metadata that can be used elsewhere in the Sphinx build. We need to add the directive after the document title, and add a class *to* the document title to achieve the title & subtitle formatting. Here's an example: .. code-block:: rst .. rst-class:: with-subtitle ========= pw_string ========= .. pigweed-module:: :name: pw_string :tagline: Efficient, easy, and safe string manipulation :status: stable :languages: C++17, Rust :code-size-impact: 500 to 1500 bytes Module sales pitch goes here! Directive options _________________ - ``name``: The module name (required) - ``tagline``: A very short tagline that summarizes the module (required) - ``status``: One of ``experimental``, ``unstable``, and ``stable`` (required) - ``is-deprecated``: A flag indicating that the module is deprecated - ``languages``: A comma-separated list of languages the module supports. If the language has API docs (Rust), they will be linked from the metadata block. - ``code-size-impact``: A summarize of the average code size impact google_analytics ---------------- When this extension is included and a ``google_analytics_id`` is set in the Sphinx configuration, a Google Analytics tracking tag will be added to each page of the documentation when it is rendered to HTML. By default, the Sphinx configuration's ``google_analytics_id`` is set automatically based on the value of the GN argument ``pw_docs_google_analytics_id``, allowing you to control whether tracking is enabled or not in your build configuration. Typically, you would only enable this for documentation builds intended for deployment on the web. Debugging Pigweed's Sphinx extensions ------------------------------------- To step through your Pigweed extension code with `pdb `_: #. Set a breakpoint in your extension code: .. code-block:: breakpoint() #. Build ``python.install`` to install the code change into the bootstrap venv (``environment/pigweed-venv/lib/python3.8/site-packages/pw_docgen``): .. code-block:: ninja -C out python.install #. Manually invoke Sphinx to build the docs and trigger your breakpoint: .. code-block:: cd out sphinx-build -W -b html -d docs/gen/docs/help docs/gen/docs/pw_docgen_tree docs/gen/docs/html -v -v -v You should see build output from Sphinx. The build should pause at your breakpoint and you should then see pdb's prompt (``(Pdb)``).