Added pre-commit hooks

Author: Zabuzard

build.gradle

@@ -21,6 +21,14 @@ sonarqube {
     }
 }
 
+// Install git hooks
+task installLocalGitHook(type: Copy) {
+    from new File(rootProject.rootDir, 'scripts/pre-commit')
+    into new File(rootProject.rootDir, '.git/hooks')
+    fileMode 0775
+}
+build.dependsOn installLocalGitHook
+
 subprojects {
     apply plugin: "java"
     apply plugin: "com.diffplug.spotless"
@@ -54,9 +62,6 @@ subprojects {
     def compileTasks = {
         options.encoding = 'UTF-8'
 
-        // Makes spotlessApply task run on every compile/build.
-        dependsOn 'spotlessApply'
-
         // Nails the Java-Version of every Subproject
         sourceCompatibility = JavaVersion.VERSION_17
         targetCompatibility = JavaVersion.VERSION_17

scripts/pre-commit

@@ -0,0 +1,52 @@
+#!/bin/sh
+
+create_stash() {
+  # Stash unstaged changes, if any
+  previous_stash=$(git rev-parse -q --verify refs/stash)
+  git stash push -q
+  new_stash=$(git rev-parse -q --verify refs/stash)
+}
+
+pop_stash() {
+  # Restore unstaged changes, if any
+  if [ "$previous_stash" != "$new_stash" ]; then
+    git stash apply -q && git stash drop -q
+  fi
+}
+
+echo "****Running pre-commit hooks****"
+# We want to apply spotless on all staged files. Therefore, we have to first draft a
+# WIP-commit for the staged changes and put the unstaged changes aside using stash
+# (otherwise spotless would apply on them as well, see https://github.com/diffplug/spotless/issues/623).
+# There are a few edge cases to handle here; for example if there are no unstaged changes, stash would not create a stash.
+# Hence, the following pop of the stash must be guarded (see https://stackoverflow.com/a/20480591/2411243).
+
+# Mini commit for staged changes, so that we can stash away unstaged in the next step (bypass hook with "no-verify" to avoid recursion)
+git commit --no-verify --message "WIP"
+commitExitCode=$?
+if [ "$commitExitCode" -ne 0 ]; then
+  # Commit failed (for example if there is nothing staged), early-out
+  exit "$commitExitCode"
+fi
+
+# Put unstaged away
+create_stash
+# Get back staged changes
+git reset --soft HEAD^
+
+# Apply spotless on the staged changes only (rest has been put away)
+echo "**Applying spotless**"
+./gradlew spotlessApply
+spotlessExitCode=$?
+if [ "$spotlessExitCode" -ne 0 ]; then
+  # Spotless failed, restore unstaged
+  pop_stash
+  exit "$spotlessExitCode"
+fi
+
+# Spotless possibly found changes, apply them
+git add -A
+
+# Restore back the unstaged changes
+pop_stash
+echo "****Done pre-commit hooks****"