How can I auto-format Rust (and C++) code on commit automatically?

Question

I would like to automatically format the code when I do commit using rustfmt the same way as I did it before for clang-format -i. I.e. format only the lines of code which has been updated in the commit without touching other code. How to do it?

Answer 1

It might be done using git pre-commit hook in the following way:

1. Add file pre-commit to the folder .githooks in your repo with the following text:

#!/bin/bash

exe=$(which rustfmt)

if [ -n "$exe" ]
then
    # field separator to the new line
    IFS=$'\n'

    for line in $(git status -s)
    do
        # if added or modified
        if [[ $line == A* || $line == M* ]]
        then
            # check file extension
            if [[ $line == *.rs ]]
            then
                # format file
                rustfmt $(pwd)/${line:3}
                # add changes
                git add $(pwd)/${line:3}
            fi
        fi
    done

else
    echo "rustfmt was not found"
fi

2. Run in your repo folder:

chmod +x .githooks/pre-commit
git config core.hooksPath .githooks

To make it work for clang-format you need to replace rustfmt with clang-format -i and do corresponding modifications in the check for file extension (cpp\h\hpp\etc).