Pre-commit

Overview

Questions

• What quality assurance checks can I run using pre-commit checks?

Objectives

• Explain what pre-commit hooks are.
• Install and run a pre-commit hook.

Git hooks let you run certain scripts before git actions. In this optional episode we are going to set up a pre-commit hook which runs quality assurance checks on our code before we are allowed to make a commit.

pre-commit is a Python package that makes it easier to set up git hooks. To install it using pip or conda:

pip

conda

BASH

$ pip install pre-commit

BASH

$ conda install pre-commit

In the git-training-demo we provided an example pre-commit configuration. These pre-commit checks were run as part of your pull requests. We can install the pre-commit hook scripts so they run before we can commit locally:

BASH

[git-training-demo]:(main =)$ pre-commit install

OUTPUT

pre-commit installed at .git/hooks/pre-commit

It’s good practice to run the pre-commit checks on all your files after installing them.

BASH

[git-training-demo]:(main =)$ pre-commit run --all-files

OUTPUT

[INFO] Initializing environment for https://github.com/pre-commit/pre-commit-hooks.
[INFO] Installing environment for https://github.com/pre-commit/pre-commit-hooks.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
don't commit to branch ...................................................Passed
check for added large files ..............................................Passed
check for case conflicts .................................................Passed
check for merge conflicts ................................................Passed
check toml ...........................................(no files to check)Skipped
check yaml ...............................................................Passed
fix end of files .........................................................Passed
trim trailing whitespace .................................................Passed

The next time the pre-commit scripts run they will re-use the Python environment that was just installed, making the run faster.

The pre-commit.com site has a reference of useful hooks. Your organisation may have their own pre-commit hooks which you can use and or block third party hooks for security.

Committing to Main

With the pre-commit installed try adding any change to the main branch and then run git commit.

What happens with the pre-commit hooks installed?

Show me the solution

The pre-commit check for not committing to main fails so git commit wasn’t run. Your changes are still staged.

BASH

[git-training-demo]:(main +=)$ git commit -m "Attempts to commit to main"

OUTPUT

don't commit to branch...................................................Failed
- hook id: no-commit-to-branch
- exit code: 1
check for added large files..............................................Passed
check for case conflicts.................................................Passed
check for merge conflicts................................................Passed
check toml...........................................(no files to check)Skipped
check yaml...............................................................Passed
fix end of files.........................................................Passed
trim trailing whitespace.................................................Passed

To move the staged changes to a new branch use git switch:

BASH

[git-training-demo]:(main +=)$ git switch -c <branch-name>

OUTPUT

Switched to a new branch 'challenge'

BASH

[git-training-demo]:(challenge +)$ git status

OUTPUT

On branch challenge
Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
	modified:   .pre-commit-config.yaml

Key Points

• pre-commit checks help prevent accidental commits to main and provide an extra layer of quality assurance.