Pre-commit : Making Commits Safer

Shivam Bhatnagar

It’s certain that as you go about developing code in your regular workflow you will end up pushing mistakes into your git commits. The result of a mistake can be either a small slip-up or a more major issue which causes issues with the application that you are working on.

Pre-commit is a simple to use tool with which you can manage hooks in your project that will run with every commit that you make

References

1. pre-commit
2. How to install pre-commit

Why pre-commit

Git has a built-in concept of hooks that allow you to define and run hooks by creating a folder named hooks inside the .git directory.

The .git directory must NOT be checked into your source control, so the down-side of this approach is that you are required to manually copy hooks to another project / developer if need be

pre-commit is a package manager for hooks. It allows you to specify, using a config file, the hooks you need and it will make sure that these are installed and executed before any commit

How to install pre-commit

Make sure you are working in a git directory, if you don’t then you can initialise one using git init

1. Install pre-commit : pip install pre-commit
2. Create pre-commit config : Create a file that is named pre-commit-config.yaml
3. Install the pre-commit hooks : pre-commit install

Suggested pre-commit config

For a python project

repos:
  - repo: 'https://github.com/pre-commit/pre-commit-hooks'
    rev: v4.4.0
    hooks:
      - id: end-of-file-fixer
      - id: check-added-large-files
      - id: check-toml
      - id: check-ast
      - id: check-json
        exclude: .devcontainer/devcontainer.json
      - id: check-case-conflict
      - id: double-quote-string-fixer
      - id: check-executables-have-shebangs
      - id: check-merge-conflict
      - id: trailing-whitespace
  - repo: 'https://github.com/adrienverge/yamllint'
    rev: v1.32.0
    hooks:
      - id: yamllint
        args:
          - '--config-file'
          - .yamllint.yaml
  - repo: https://github.com/astral-sh/ruff-pre-commit
    rev: 'v0.3.4'
    hooks:
      - id: ruff
      - id: ruff-format

Running pre-commit

Local Assuming pre-commit is installed in your repo, then it will run whenever you make a commit. Crucially hooks will only run against files that have been changed and added to a given commit

CI/CD It is recommended to have a CI/CD job which runs pre-commit on all files in the project. This can be achieved by running the following command from within a job

pre-commit run --all-files --show-diff-on-failure

This will ensure that all files follow the hooks defined in the pre-commit-config.yaml