Using Hugo modules for themes

Hugo is one of the most popular static site generators. It’s a simple tool to start building a website with ready-to-use themes or your own templates. Let’s focus on using the themes.

Problem to solve

There are a few ways to handle storing and versioning themes in your Hugo project. Previously, I used simple vendoring by copying all of the content from the theme repository to mine, but that’s inefficient. It complicates being up-to-date with new versions of the used theme. Of course, it can be scripted. But then you have to maintain the script and handle edge cases. For example, rolling back versions. Also, storing vendored theme versions in the repository creates big diffs in the git repository in case of updates. It obscures progress in creating content. Who doesn’t like to watch a number of lines going up while writing content?

My second previous way to handle the theme in the Hugo project was git submodules. Pros: versioning handled by git. Cons: who understand how does it work? I worked with git submodules in multiple projects. They’re always a constant headache. Just do not.

Easy tool

Hugo embraced the usage of the go modules. Go modules is the official way to handle dependencies inside the go projects. They were introduced back in 2019 and presently are used in most of the go projects. In the case of Hugo, they can be used as a for:

static
content
layouts
data
assets
i18n
archetypes

Hugo comes with wrapped go mod commands inside. That means you don’t have to install go toolset.

Solution

Let’s use Hugo (go) module as a theme inside the project:

Initialize the project as a module.

The project also has to be a module itself to use modules. Run command to initialize the module inside your repository with your URL.

# Replace `github.com/kbetanski/blog` with your own repository
hugo mod init github.com/kbetanski/blog

The command will create a file go.mod inside the project.

module github.com/kbetanski/blog

go 1.17

Use theme repository as a module.

Disclaimer: It works only for a theme that is initialized as a module.

The module has to be defined inside the configuration file to use it inside the Hugo project. In my case, it’s config.yamlfile:

# Replace path with a theme of your choice
module:
    imports:
        - path: github.com/CaiJimmy/hugo-theme-stack/v3
          disable: false

Download used modules

The last step for using Hugo modules is to download them for usage:

hugo mod get

The go.mod file will be updated with the required dependency.

module github.com/kbetanski/blog

go 1.17

require github.com/CaiJimmy/hugo-theme-stack/v3 v3.11.0 // indirect

Also, it will create a go.sum file. That file contains direct and indirect dependencies to the project and stores checksums. Each time Hugo downloads the dependencies, it will validate checksums of what was downloaded against the stored checksum in that file. In my case file was generated with the following content:

github.com/CaiJimmy/hugo-theme-stack/v3 v3.11.0 h1:HyHdT59BYMdPSjDljIWpJY/DT+NPiZgfqMlJBQwOa1A=
github.com/CaiJimmy/hugo-theme-stack/v3 v3.11.0/go.mod h1:IPmCXiIxlFSLFYS0tOmYP6ySLviyeNVSabyvSuaxD+I=

Updating modules

So, how easy is updating a theme when used as a module? That’s how it looks:

# All modules
hugo mod get -u

# One module
hugo mod get -u github.com/CaiJimmy/hugo-theme-stack/v3

# One module with the specific version
hugo mod get -u github.com/CaiJimmy/hugo-theme-stack/v3@v3.11.0

Summary

Hugo modules are an easy way to handle dependencies in the Hugo project. As mentioned before: themes are only one of the possibilities to use them. Just make sure to use its potential for better content creation!