Git hook pre-commit

pre-commit hook of Git

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A Git hook is a function in Git that executes a specific script at an event. Git pre-commit hook automatically executes certain tasks every time we commit our code. So basically it is called before we actually write a commit message. We can automate code checking before commit with pre-commit. This can be used to check for grammar errors, style, alignment, and type errors before committing. Many projects use this to run a Code Formatter to unify the code style and run a Linter to find potential problems in the code. It can even be customized according to the developer’s preference. And also the biggest advantage of pre-commit is that just as Git is language-agnostic, this can be used regardless of programming language.

Getting started with pre-commit

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1. Initialize git

git init

2-1. When python is installed.

When there is Python installed already then you can just use pip.

pip install pre-commit
pre-commit -V

2-2. On MacOS

If Python is not installed, you can also install it through package manager from your operating system. MacOS users can use homebrew.

brew install pre-commit
pre-commit -V

3. Config setting

pre-commit needs it’s own config file. We can create a configuration file using a command that outputs sample settings to the terminal.

pre-commit sample-config > .pre-commit-config.yaml
cat .pre-commit-config.yaml

We can check out that four hooks have been set.

The pre-commit tool downloads and executes hooks from Git repositories. So, we need to know which Git repository the hook is located in. You can see various pre-commit hooks on the Supported hooks page on the pre-commit official website.

Another example of .pre-commit-config.yaml file

repos:
  - repo: https://github.com/ambv/black
    rev: ''  # you also can set the version for repo
    hooks:
      - id: black
        language_version: python3.8  # please change the python version
  - repo: https://gitlab.com/pycqa/flake8
    rev: ''
    hooks:
      - id: flake8
  - repo: https://github.com/pycqa/isort
    rev: ''
    hooks:
      - id: isort
  - repo: https://github.com/necaris/pre-commit-pyright
    rev: ''
    hooks:
      - id: pyright

You can update rev version automatically by pre-commit autoupdate.

4. Add and run

git add .pre-commit-config.yaml
pre-commit run -a

5. Git commit

git commit -m "creates .pre-commit-config.yaml"

6. Test

To check whether it is set properly, let’s try intentionally adding a trailing-whitespace. If you stage the created file by add and run the pre-commit, the trailing-whitespace hook will fail.

echo "Testing trailing whitespace.   " > text.txt
git add test.txt
pre-commit run

But you don’t have to worry!😺 Files where hooks fail will be automatically modified, so if you stage the changes and run pre-commit again, then all hooks will pass!

git status. # check the changes
git add test.txt
pre-commit run

7. Automation

The ultimate purpose of using pre-commit is to automatically execute a specific task every time a commit is made, so all developers in the project must run the pre-commit.

With the command below, pre-commit will be automatically executed every time you try to commit, without running it manually.

pre-commit install

References

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• https://www.daleseo.com/pre-commit/