Git hooks for Go fmt

A common problem when reviewing pull requests is large diffs of formatting changes. You end up with pages of formatting changes that people waste time looking at when in reality it was just a 3 line PR. Go has a tool called fmt which can format any Go code into the standard Go format. What happens in my project is that some of the team has their IDE configured to automatically run go fmt when they save a file, while the rest do not. So our codebase is in an inconsistently formatted state. What I am attempting to do is to setup a git-hook that will run go fmt before any commits.

The .git/hooks directory contains samples of git hooks that can be triggered on various git actions like pre-commit, post-commit, post-receive, etc. The files need to be executable, with no extension and named after the appropriate hook. This digital ocean link has a table of the available hooks if you scroll down a bit https://www.digitalocean.com/community/tutorials/how-to-use-git-hooks-to-automate-development-and-deployment-tasks#basic-idea-with-git-hooks. 

The hooks are just executable files and it may be possible to run compiled binaries as well as shell scripts. Here is my working go fmt pre-commit hook. I edited the example script in .git/hooks/pre-commit.sample to run go fmt and renamed it to pre-commit.

 

#!/bin/sh
#
# A  hook script to verify what is about to be committed.
# Called by "git commit" with no arguments.  The hook should
# exit with non-zero status after issuing an appropriate message if
# it wants to stop the commit.
# This hook runs 'go fmt ./...' on the project
# To enable this hook, rename this file to "pre-commit".

if git rev-parse --verify HEAD >/dev/null 2>&1
then
        against=HEAD
else
        # Initial commit: diff against an empty tree object
        against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

# If you want to allow non-ASCII filenames set this variable to true.
allownonascii=$(git config --bool hooks.allownonascii)

# Redirect output to stderr.
exec 1>&2

echo "Running go fmt"
go fmt -x ./...

 

 

Here are some further references.

An Example Git-Enforced Policy

https://git-scm.com/book/en/v2/Customizing-Git-An-Example-Git-Enforced-Policy#_an_example_git_enforced_policy

Pre-Commit    NPM based git-hook installer https://github.com/observing/pre-commit

Githooks 

https://githooks.com

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