Pretty code with pre-commit

Do you have programming OCD like I do? Do you have nightmares if your code is not perfectly formatted and consistent between all developers? If you don’t even want a single commit in the repo with not properly indent code then there are 2 options:

1. Try to cure your programming OCD.
   or more realistically
2. Create pre-commit hooks that will format your code before it is committed.

This article will not cure your OCD rather we will focus on learning about properly configuring pre-commit hooks for your project.

pre-commit

pre-commit is a framework for managing and maintaining multi-language pre-commit hooks. It allows the community to maintain a set of hooks that can be shared across multiple projects. For example instead of recreating a hook that will run terraform fmt and recreate this hook in every terraform project you create, the community can share a project with pre-commit hooks that will integrate with the pre-commit framework. You create a pre-commit configuration under the file .pre-commit-config.yaml in the root of your project, you specify in that config the repositories that are containing the hooks that you want to run before commiting your code, you run pre-commit install and from now on every time you commit your code the hooks will run. Pretty simple, and luckily the community already created a Terraform/OpenTofu/Terragrunt pre-commit hooks that you can use.

pre-commit-terraform

pre-commit-terraform is a collection of git hooks to be used with pre-commit. We simply place the repository in the .pre-commit-config.yaml and choose the hooks that we want to run. For now we will use a simple hook that will format our terragrunt code before committing it.

terragrunt fmt

Reformats all Terragrunt configuration files to a canonical format, meaning the reformat is according to officially defined, standard and consistent way of organizing and formatting our configuration files according to terraform and community standards. It is based on terraform fmt or tofu fmt commands and it will format the .hcl files in the project. Among the things it will do:

• Indentation (two spaces no tabs)
• Alignment
• Spacing between blocks
• Key ordering
• Block structure
• string are quoted with double quotes
• Remove redundant spaces

The code becomes more readable and consistent between all developers.

Install pre-commit

Let’s start by installing pre-commit on our machine, we will follow the instructions from the pre-commit website.

pip install pre-commit

If the installation was successful you should be able to run the following command to check the version of pre-commit:

pre-commit --version

Create a .pre-commit-config.yaml file

We can integrate the community terraform hooks by creating a .pre-commit-config.yaml file in the root of our project and including the pre-commit-terraform hooks that we want to use.
For now we will only use the terragrunt fmt hook we is under the id terragrunt_fmt.

.pre-commit-config.yaml

repos:
  - repo: https://github.com/antonbabenko/pre-commit-terraform
    rev: v1.96.2
    hooks:
      - id: terragrunt_fmt

For now we only have one hook that will run terragrunt fmt before committing our code. But we can add more hooks from pre-commit-terraform or from other repositories as we move along in the project.

Install the hooks

After our config file is ready we can install the hooks by running the following command:

pre-commit install

This command will install the hooks in the .git/hooks directory of our project. Now every time we stage files for commit and run git commit the hooks will run before the commit is completed.

Run on all the files

since we already commited a lot of files before we installed the hooks we can run the hooks on all the files in the project by running the following command:

pre-commit run --all-files

After that commit and push our files to the repository.

CONTRIBUTING.md

Let’s update the CONTRIBUTING.md file to include the pre-commit hooks that we are using in the project.

Summary

We learned how to use pre-commit hooks in our project to format our code before committing it. We used the pre-commit-terraform hooks to format our terragrunt code before committing it. We created a .pre-commit-config.yaml file in the root of our project and included the hooks that we want to use. We installed the hooks by running pre-commit install and ran the hooks on all the files in the project by running pre-commit run --all-files.