Document Generator for Lean 4


doc-gen4 is the easiest to use via its custom Lake facet, in order to do this you have to add it to your lakefile.lean like this:

meta if get_config? env = some "dev" then -- dev is so not everyone has to build it
require «doc-gen4» from git "" @ "main"

Then update your dependencies:

lake -R -Kenv=dev update

Then you can generate documentation for an entire library and all files imported by that library using:

lake -R -Kenv=dev build Test:docs

If you have multiple libraries you want to generate full documentation for:

lake -R -Kenv=dev build Test:docs Foo:docs

Note that doc-gen4 currently always generates documentation for Lean, Init and Lake in addition to the provided targets.

The root of the built docs will be .lake/build/doc/index.html. However, due to the "Same Origin Policy", the generated website will be partially broken if you just open the generated html files in your browser. You need to serve them from a proper http server for it to work. An easy way to do that is to run python3 -m http.server from the .lake/build/doc directory.

Requirements to run doc-gen4

In order to compile itself doc-gen4 requires:

  • a Lean 4 or elan installation
  • a C compiler if on Linux or MacOS (on Windows it will use Lean's built-in clang compiler)

Apart from this the only requirement for lake -Kenv=dev build Test:docs to work is that your target library builds, that is lake build Test exits without an error. If this requirement is not fulfilled, the documentation generation will fail and you will end up with partial build artefacts in .lake/build/doc. Note that doc-gen4 is perfectly capable of generating documentation for Lean code that contains sorry, just not for code that doesn't compile.

If you are working on a project that only partially compiles but can't fix the errors from the top of your head, you can try to remove imports of both the failing files and all files that refer to the failing ones from your top level library file. Like this you will end up with an incomplete documentation but at least working documentation of your project.

Note that we do not recommend this approach and suggest to instead make sure your projects always compile by using CI to prevent broken code from being added and sorry-ing out things that you intend to complete later.

Source locations

Source locations default to guessing the Github repo for the library, but different different schemas can be used by setting the DOCGEN_SRC environment variable. For example, one can use links that open the local source file in VSCode by running lake with:

DOCGEN_SRC="vscode" lake -R -Kenv=dev ...

The different options are:

  • DOCGEN_SRC="github" infers the Github project for each library and uses source links to the Github source view. This is the default if DOCGEN_SRC is unset.
  • DOCGEN_SRC="file" creates references to local file references.
  • DOCGEN_SRC="vscode" creates VSCode URLs to local files.

How does docs#Nat.add from the Lean Zulip work?

If someone sends a message that contains docs#Nat.add on the Lean Zulip this will automatically link to Nat.add from the mathlib4 documentation. The way that this feature is implemented is by linking to /find of generated documentation in the following way: in the case of the mathlib4 documentation this ends up being to: If you wish to provide a similar feature to docs#Nat.add from the Lean Zulip for your documentation, this is the way to go.

Development of doc-gen4

You can build docs using a modified doc-gen4 as follows: Replace the from git "..." @ "main" in the lakefile.lean with just from "..." using the path to the modified version of doc-gen4. E.g. if the path to the modified version of doc-gen4 is ../doc-gen4, it would be:

meta if get_config? env = some "dev" then -- dev is so not everyone has to build it
require «doc-gen4» from "../doc-gen4"

Note that if you modify the .js or .css files in doc-gen4, they won't necessarily be copied over when you rebuild the documentation. You can manually copy the changes to the .lake/build/doc directory to make sure the changes appear, or just do a full recompilation (lake clean and lake build inside the doc-gen4 directory.)