0102: Consistent Module Documentation#

Status: Open for Comments Intent Approved Last Call Accepted Rejected

Proposal Date: 2023-02-10

CL: pwrev/128811, pwrev/130410

Author: Chad Norvell

Facilitator: Kayce Basques

Status (October 2023)#

If you’re looking for guidelines on how to author module docs, use these: Module docs


SEED-0102 is still considered accepted because we are still using some parts of it in our current module docs guidelines. However, over the course of 2023 we discovered that other parts of the SEED-0102 plan didn’t achieve our goals. Therefore, at this point you should only read SEED-0102 for historical context on how our docs guidelines have evolved.


Pigweed modules ought to have documentation that is reasonably comprehensive, that has a consistent and predictable format, and that provides the reader with sufficient information to judge whether using the module is the right choice for them. This SEED proposes a documentation philosophy applicable to all Pigweed modules and a flexible yet consistent structure to which all module docs should conform.


In this SEED, we define users as developers using Pigweed in downstream projects, and maintainers as developers working on upstream Pigweed. The primary focus of this SEED is to improve the documentation experience for users.


Currently, each Pigweed module is required to have, at minimum, a single docs.rst file that contains the module’s documentation. This gives the module maintainer considerable discretion to provide as much or as little documentation as they would like. However, this approach fails for Pigweed maintainers by providing no guidance or structure to help them write effective documentation, and certainly fails Pigweed users who struggle to find the information they’re looking for. So a solution needs to make it easier for Pigweed maintainers to write good documentation, thereby making Pigweed much more accessible to its users.

Pigweed’s design is inherently and intentionally modular. So documentation at the level of the module is the most natural place to make impactful improvements, while avoiding a fundamental restructuring of the Pigweed documentation. Module docs are also what the majority of Pigweed users rely on most. As a result, this SEED is focused exclusively on improving module documentation.

Diátaxis proposes a four-mode framework for technical documentation, illustrated below with terminology altered to better match Pigweed’s needs:

Serve our study

Serve our work

Practical steps

Tutorials (learning-oriented)

Guides (task-oriented)

Theoretical knowledge

Concept & design docs (understanding-oriented)

Interface reference (information-oriented)

Pigweed needs a framework that ensures modules have coverage across these four quadrants. That framework should provide a structure that makes it easier for maintainers to write effective documentation, and a single page that provides the most basic information a user needs to understand the module.


There are risks to focusing on module docs:

  • The most useful docs are those that focus on tasks rather than system features. The module-focused approach risks producing feature-focused docs rather than task-focused docs, since the tasks users need to complete may not fit within the boundaries of a module.

  • Likewise, focusing on module documentation reduces focus on content that integrates across multiple modules.

The justification for focusing on module documentation doesn’t imply that module docs are the only docs that matter. Higher level introductory and guidance material that integrates Pigweed as a system and covers cross cutting concerns is also important, and would arguably be more effective at bringing new developers into the Pigweed ecosystem. However, this SEED proposes focusing on module docs for two primary reasons:

  1. Improving module docs and providing them with a consistent structure will have the largest impact with the least amount of investment.

  2. It will be easier to construct higher-level and cross-cutting documentation from well-developed module docs compared to going the other direction.

While not a primary consideration, a bonus of a module-focused approach is that modules already have owners, and those owners are natural candidates to be the maintainers of their modules’ docs.


This change would require each module directory to match this structure:

module root directory/
├── docs.rst
├── concepts.rst [or concepts/...] [when needed]
├── design.rst [or design/...] [when needed]
├── guides.rst [or guides/...] [when needed]
├── tutorials/ [aspirational]
│   ├── index.rst
│   └── ...
├── api.rst [or api/...] [if applicable]
├── cli.rst [if applicable]
└── gui.rst [if applicable]

Fundamental module docs#

These three documents are the minimum required of every Pigweed module.

The basics: docs.rst#

Basic, structured information about the module, including what it does, what problems it’s designed solve, and information that lets a user quickly evaluate if the module is useful to them.

How it works and why: design.rst & concepts.rst (understanding-oriented)#

Background on the design goals, assumptions, limitations, and implementation details of a module, and may contrast the design of the module with alternative solutions.

This content can start in the “Design considerations” section of the index, and grow into this separate document as the module matures. If that document becomes too large, the single design.rst file can be replaced by a design subdirectory containing more than one nested doc.

Some modules may need documentation on fundamental concepts that are independent of the module’s solution. For example, a module that provides a reliable transport layer may include a conceptual description of reliable transport in general in a concepts.rst file or concepts subdirectory.

How to get stuff done: guides.rst (task-oriented)#

These are focused on specific outcomes and should be produced as soon as we see a question being answered multiple times. Each module should have at least one guide on integrating the module into a project, and one guide on the most common use case.

This content can start in the “Getting started” section of the index, and grow into this separate document as the module matures. If that document becomes too large, it can be replaced with a guides subdirectory containing more than one doc.

Interface docs (information-oriented)#

These docs describe the module’s interfaces. Each of these docs may be omitted if the module doesn’t include an applicable interface.

api.rst: External API reference#

Modules should have reference documentation for their user-facing APIs. Modules that have APIs for multiple languages should replace the single api.rst with an api subdirectory with docs for each supported language.

How API docs should be structured, generated, and maintained is a complex topic that this SEED will not determine.

cli.rst & gui.rst: Developer tools reference#

A user-facing command line interface (CLI) should be documented in cli.rst if the module provides one. It’s ideal if this documentation closely matches the output of the CLI tool’s “help” command.

If the module provides a graphical user interface (GUI) (including text mode interfaces and web front-ends), its documentation should be included in gui.rst.

Tutorials (learning-oriented)#

We keep these as separate files in tutorials. These take considerable effort to develop, so they aren’t required, but we aspire to develop them for all but the most trivial modules.

When one size does not fit all#

Pigweed modules span a spectrum of complexity, from relatively simple embedded libraries to sophisticated communication protocols and host-side developer tooling. The structure described above should be the starting point for each module’s documentation and should be appropriate to the vast majority of modules. But this proposal is not strictly prescriptive; modules with documentation needs that are not met by this structure are free to deviate from it by adding docs that are not mentioned here.


A template for implementing this structure can be found docs/templates/docs.