Custom Sphinx extensions

To ease the effort required to keep the documentation up to date, and improve the writing experience, we developed a few custom Sphinx extensions. This page documents the features of each extension.

ferrocene_qualification extension

This extension implements “global” features that are not tied to any specific document, and should be imported in each document.

Defining and linking to IDs

Our qualification documents contain IDs defining every concept and item referenced across our qualification material for example - ERR_DRIVER_04. The ferrocene_qualification Sphinx extension provides a directive and a role to respectively declare and link to an ID.

To declare a new ID, you can use the id directive:

.. id:: FOO

That directive will define an ID named FOO, and it will render it as “Identifier: FOO” (inside of tables it will just render it as “FOO” to reduce clutter).

To link to an ID, you can use the id role:


This will create a link pointing to the definition you created earlier. Note that linking to IDs works transparently across all of our qualification material, without having to mention the document the ID was defined in. You can just reference an ID defined in a different document like you would link to an ID defined in the same document.


The id role and directive are both defined in the qualification Sphinx domain. To use them, you must either prefix their name with qualification:, or put this at the top of the file:

.. default-domain:: qualification

Using substitutions

Across our documentation there are terms or phrases referenced multiple times. Substitutions allow you to create “aliases” for common phrases you can include in any qualification document.

Substitutions are defined in the ferrocene/doc/sphinx-substitutions.toml file. There are also the following substitutions, which are calculated dynamically:

  • doc_title: the name of the document (e.g. Safety Manual)

  • doc_short_title: the acronym of the document (e.g. SM)

  • ferrocene_version: the Ferrocene version number (e.g. 23.06.0)

  • rust_version: the Rust version number (e.g. 1.68.2)

  • channel: the Ferrocene channel of this release (e.g. stable-23.06)

You can refer to substitutions by surrounding the substitution name with |:


Mentioning targets

When you need to refer to targets across the documentation, it’s better to use a human-readable name (like “Armv8-A bare-metal”) than the target triple, as the latter is often inconsistent between similar targets and could be confusing to customers.

To keep the target names consistent, you can use the :target: role with the target triple as its content, which will be rendered as the human-readable name:


The :target-with-triple: role will also add the triple following the human-readable name, which is best used when customers then need to copy/paste the triple:


The human-readable names are stored in ferrocene/doc/target-names.toml, and referring to a target not defined in that file will emit a warning.

Document ID

The extension is responsible for generating the ID of the document, which is displayed at the bottom of every page. The ID contains the acronym of the document and a hash of the content, uniquely identifying the revision of the document. This is enabled by default and requires no maintainer action.

Signature outcome page

The extension is responsible for generating the dynamic page showing the signature status of the document (see Digital signatures for more information about signatures). This is enabled by default and requires no maintainer action.

ferrocene_domain_cli extension

The extension adds a custoom cli Sphinx domain that can be used to document the CLI options of a program. Compared to Sphinx’s builtin domain, our cli domain supports options with spaces in their name (like -C option), and emits metadata compatible with our traceability matrix tooling.

The extension only needs to be added to documents either defining or linking to CLI options.

Defining CLI options

CLI options can be defined with the cli:program directive, whose argument is the name of the binary being documented.

Within it, you need to define one or more cli:option directives. The argument of the directive is the name of the option, with the user-provided value wrapped between <>. The body of the directive is the documentation of the CLI option:

.. cli::program: rustc

   .. cli::option: --target <name>

      Used to specify the target triple.

   .. cli::option: --help

      Show the help message.

Linking to CLI options

It’s possible to link to CLI options (even defined in other documents) with the :cli:option: role. Options are identified with both the program name and the option name, separated by a space. It works like a normal link role, so you can either put the option name as the role value, or arbitrary text (with the option name between <>).

:cli:option:`rustc --help`
:cli:option:`the target flag <rustc --target <name>>`

ferrocene_toctrees extension

This extension tweaks Sphinx’s table of contents support to better suit our style of documents. It must be enabled in all of our documents.

Continuous numbering of sections

By default Sphinx numbers pages within a toctree directive without considering other directives. This means adding multiple toctrees (for example to group some pages together) would reset the numbering, potentially having multiple pages numbered “1”.

The extension patches Sphinx to fix this, and ensure that the page numbers constantly increase even when multiple toctree directives are present.

Appendices support

The extension adds a new appendices directive, with the same syntax and functionality as the toctree directive. The only difference is that pages are numbered with letters rather than digits.

ferrocene_autoglossary extension

This extension eases the maintenance of the glossary, and should be enabled for each document containing a glossary. It serves two purposes:

  • Prunes from glossary directives all items that are not mentioned anywhere in the current document. This allows sharing the same glossary file across documents without adding extra content to documents not referring to some terms.

  • Automatically adds links to terms defined in glossary directives across the document, without the need to manually use the builtin :term: role.

ferrocene_intersphinx_support extension

This extension is required by the build system to enable interlinking between documents. It must be added to all documents and requires no maintainer action.

ferrocene_document_list extension

This extension is specific to the Ferrocene Document List document. It provides the document-id role, which injects the Document ID of the requested document:

The ID of the qualification plan is :document-id:`qualification-plan`.

ferrocene_test_outcomes extension

This extension is specific to the Ferrocene Qualification Report.

Rendering a template with the test outcomes

The render-outcomes-template directive allows rendering a Jinja template with the test outcomes of a tested target. The directive accepts a single argument, the path to the template to render. It also accepts multiple options:

  • host (required): the target triple of the host platform

  • target (required): the target triple of the compilation target

  • bare_metal_test_target (optional): the target triple of the special target used for bare metal testing; it should be omitted if no special target was used

  • remote_testing (optional): whether the tests were executed on CI or on a remote machine/emulator; its presence without a value means true, while its absence means false

.. render-outcomes-template:: templates/tests.jinja2
   :host: x86_64-unknown-linux-gnu
   :target: x86_64-unknown-linux-gnu

.. render-outcomes-template:: templates/tests.jinja2
   :host: x86_64-unknown-linux-gnu
   :target: aarch64-unknown-none
   :bare_metal_test_target: aarch64-unknown-ferrocenecoretest

Rendering a summary of all test outcome pages

The render-summary directive renders a table with all render-outcomes-template invocations present in the rest of the document. It accepts no arguments nor options.

ferrocene_relnotes extension

This extension is specific to the Ferrocene Release Notes.

Marking releases as upcoming

The extension allows marking a page as upcoming by adding :upcoming-release: before any content of the page (except for comments). This adds an “upcoming” badge next to the title, and a caution message just below the title.

Including Rust changelogs

It is possible to inject the Rust changelog for a range of versions with the rust-changelog directive. The directive requires the :from: and :to: options to define the (inclusive) range of releases to include:

.. rust-changelog::
   :from: 1.68.2
   :to: 1.76.0