How to setup spotless for a git pre commit hook that only check changed files

I’m using spotless with an android kotlin project now. And I have spotless set up like this

apply plugin: 'com.diffplug.gradle.spotless'
spotless {
    kotlin {
        target "**/*.kt"
        ktlint(versions.ktlint)
    }
}

What I want to do is set up a git pre commit hook that apply gradlew spotlessCheck before the commit but only on the commited files. It’s something like this eslint-pre-commit-check I have search around the repo but can’t figure out how to achieve this. Is there any way to do this? Thanks.

[lowwor]

Understood. Following is my workaround now. Hope it helps someone else who want to achieve this too.

#!/bin/sh
# From gist at https://gist.github.com/chadmaughan/5889802

echo '[git hook] executing gradle spotlessCheck before commit'

# stash any unstaged changes
git stash -q --keep-index

# run the spotlessCheck with the gradle wrapper
./gradlew spotlessCheck --daemon

# store the last exit code in a variable
RESULT=$?

# unstash the unstashed changes
git stash pop -q

# return the './gradlew spotlessCheck' exit code
exit $RESULT

[toefel18]

I created a pre-commit hook that formats the code and adds the formatted files that were initially in the staging area back to the staging area in order to commit the actual formatted code. It leaves the other files as is.

you can install it by running this in your repository root:

curl -o .git/hooks/pre-commit https://gist.githubusercontent.com/toefel18/23c8927e28b7e7cf600cb5cdd4d980e1/raw/163337f2ae596d4b3a55936c2652b1e8227db5b7/pre-commit && chmod +x ./.git/hooks/pre-commit

#!/bin/bash
set -e

filesToAddAfterFormatting=()
containsJavaOrKotlin=0

# Collect all files currently in staging area, and check if there are any java or kotlin files
for entry in $(git status --porcelain | sed -r 's/[ \t]+/-/g')
do
  # entry can be for example:
  # MM-src/main/java/net/project/MyController.java
  # -M-src/main/java/net/project/AnotherController.java

 if [[ $entry == M* ]] ; then
    filesToAddAfterFormatting+=(${entry:2}) # strips the prefix
 fi

 if [[ $entry == *.java ]] || [[ $entry == *.kt ]] ; then
    containsJavaOrKotlin=1
 fi
done;


# If any java or kotlin files are found, run spotlessApply
if [ "$containsJavaOrKotlin" == "1" ] ; then
  echo "Kotlin and/or Java found in staging, running:  ./gradlew -PdisableSpotlessCheck spotlessApply"
  ./gradlew -PdisableSpotlessCheck spotlessApply
else
  echo "Not running spotlessApply"
fi

# Add the files that were in the staging area
for fileToAdd in $filesToAddAfterFormatting
do
  echo "re-adding $fileToAdd after formatting"
  git add "$fileToAdd"
done;