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🛠️ Developer documentation

This is a documentation file for Code Highlighter's developers.

Dev environment setup

This section describes how to setup your development environment.

This project requires the following tools:

  1. Install the required Python version:

    pyenv install

  2. Set up Poetry:

    poetry install

  3. Install Lefthook:

    lefthook install

Updating highlight.js

Anki code highlighter comes in bundled with the highlight.js JavaScript package. The JS package's files are included in assets, e.g., assets/_ch-highlight.js contains the single-file implementation of highlight.js.

To update highlight.js:

  1. Set HLJS_VERSION in tools/hljs.py.
  2. Run python tools/hljs.py.

Updating Pygments

Anki code hightlighter comes in bundled with the [Pygments] library, and its version is tracked as a Git submodule inside this repository.

To update Pygments, go to the submodule and pull the desired version. For example:

cd pydeps/pygments
git fetch
git checkout 2.15.1

Generating Pygment stylesheets

In assets/_ch-pygment-solarized.css I keep the stylesheet for code formatted with pygments plus a few lines for general styles. I generated the style there with dev/bin/pygutils.py with some minor adjustments by hand:

  1. There are some tech debt lines relevant for all <pre><code> tags.
  2. I have added some custom styles for borders.

Testing

  1. Run unit tests and mypy with just test.
  2. Test supported Anki versions (2.1.49 and latest) by packaging the plugin and importing the plugin into the lowest and the newest support Anki.

Release & distribution

  1. Create a release commit.
    1. Bump up the package version in codehighlighter/manifest.json and pyproject.toml.
    2. Tag the release commit git tag vx.y.z && git push origin vx.y.z.
  2. Use the dev/bin/package tool to create codehighlighter.ankiaddon.
  3. Create a GitHub release: gh release create vx.y.z codehighlighter.ankiaddon.
  4. Share the package on Anki.

Design Decisions

This section discuss some design decisions made for this plugin.

Highlighter concept

One fundamental abstraction is that of highlighter. A highlighter is essentially a function that produces an HTML representing a highlighted code snippet given the following:

  • A string with the unmarked code snippet.
  • A language that code snippet represents.
  • Additional styling options.

For code clarity and modularity, I keep such pure highlighters in separate modules (hljs and pygments). A highlighter does not implement any logic related to Anki including sanitising input from HTML markup.

Using assets/_ch* files for CSS and JS

The asset files start with an underscore, because then Anki ignores them (source).

This plugin saves its assets directly in the global assets directory.

  • The only way to share files across desktop and mobile seems to be through collection.media.
  • Anki does not support file directories in collection.media.

Alternatives considered

Fetching CSS and JS assets from Internet

Loading files from Internet has the disadvantage of making my Anki solving experience depend on Internet, which I don't think is reasonable on mobile.

Card template instrumentation mode

The plugin instruments all card templates by default, because that's what most people will want. It requires zero-effort from a user to get to what they want, which is being able to highlight code. It's non-intrusive, the added styles should not interfere with users' preexisting settings as they are namespaced by a class (hljs or pygments).

Alternative methods of using highlight.js

I've added each highlight.js language as a separate script to assets/, and then used another JS script to dynamically load languages. This method led to visible lag in rendering as the number of languages grew, so I abandoned this.

I've then tried detecting which languages are used in the card. I had a bug, where I did not properly account for language aliases. I've abandoned this way, because I figured that it would way more fool-proof to just use a single highlight.js bundle that has all languages. Loading that single file seems to be fast.

Updating Python

This package sets up a specific Python version to keep the dev environment in sync with what Anki uses. To update this Python version, you need to:

  1. If in the Poetry venv, deactive and remove it.
  2. Update Python spec in .python-version and pyproject.toml.
  3. Install the new Python version with pyenv install.
  4. Install the new virtual environment with poetry install.