feat: add git pre-commit hook for automatic code formatting (#23384)

 Add a Husky-based pre-commit hook that runs Spotless on staged files, so code is automatically formatted before each commit.                      
 - Use Husky (via npx) for cross-platform git hook management
 - Auto-install hooks via Maven profile activated when .husky/_ is missing
 - Use ratchetFrom with the upstream merge-base to only format changed files
 - Stash unstaged changes before formatting to preserve partial staging
 - Use a filesystem lock to prevent races during parallel Maven builds
 - Skip formatting during rebase when no upstream is set

Author: Artur-

.husky/pre-commit

@@ -0,0 +1,25 @@
+# Get staged files that spotless can format
+STAGED_FILES=$(git diff --cached --name-only --diff-filter=ACM | grep -E '\.(java|js|ts|css)$|pom\.xml$' || true)
+
+if [ -n "$STAGED_FILES" ]; then
+    # Skip formatting during rebase (detached HEAD, no upstream)
+    UPSTREAM_REF="$(git rev-parse --abbrev-ref --symbolic-full-name @{u} 2>/dev/null)" || exit 0
+    BASE_SHA="$(git merge-base HEAD "$UPSTREAM_REF")"
+
+    # Stash unstaged changes to avoid re-staging partial hunks
+    git stash push --keep-index --quiet --message "pre-commit-hook-unstaged"
+
+    echo "Formatting with Spotless..."
+    if ! mvn spotless:apply -q -Dspotless.ratchetFrom="$BASE_SHA"; then
+        echo "Spotless formatting failed."
+        git stash pop --quiet 2>/dev/null || true
+        exit 1
+    fi
+
+    echo "$STAGED_FILES" | xargs git add
+
+    # Restore unstaged changes
+    git stash pop --quiet 2>/dev/null || true
+
+    echo "Formatting complete."
+fi

pom.xml

@@ -113,6 +113,7 @@
     <maven-plugin-annotations.version>3.15.2</maven-plugin-annotations.version>
     <spotless.plugin.version>3.2.1</spotless.plugin.version>
     <spotless.license-header>${maven.multiModuleProjectDirectory}/eclipse/apache2-license-header.txt</spotless.license-header>
+    <spotless.ratchetFrom/>
 
     <!-- Frontend -->
     <flow.dev.dependencies.folder>generatedDeps</flow.dev.dependencies.folder>
@@ -593,6 +594,7 @@
         <artifactId>spotless-maven-plugin</artifactId>
         <version>${spotless.plugin.version}</version>
         <configuration>
+          <ratchetFrom>${spotless.ratchetFrom}</ratchetFrom>
           <java>
             <eclipse>
               <file>${maven.multiModuleProjectDirectory}/eclipse/VaadinJavaConventions.xml</file>
@@ -769,6 +771,39 @@
     </extensions>
   </build>
   <profiles>
+    <profile>
+      <id>install-git-hooks</id>
+      <activation>
+        <file>
+          <missing>${maven.multiModuleProjectDirectory}/.husky/_</missing>
+        </file>
+      </activation>
+      <build>
+        <plugins>
+          <plugin>
+            <groupId>org.codehaus.mojo</groupId>
+            <artifactId>exec-maven-plugin</artifactId>
+            <version>${maven.exec.plugin.version}</version>
+            <executions>
+              <execution>
+                <id>install-git-hooks</id>
+                <goals>
+                  <goal>exec</goal>
+                </goals>
+                <phase>initialize</phase>
+                <configuration>
+                  <executable>node</executable>
+                  <workingDirectory>${maven.multiModuleProjectDirectory}</workingDirectory>
+                  <arguments>
+                    <argument>${maven.multiModuleProjectDirectory}/scripts/installHusky.js</argument>
+                  </arguments>
+                </configuration>
+              </execution>
+            </executions>
+          </plugin>
+        </plugins>
+      </build>
+    </profile>
     <profile>
       <id>default</id>
       <activation>

scripts/installHusky.js

@@ -0,0 +1,15 @@
+#!/usr/bin/env node
+const fs = require("fs");
+const { execSync } = require("child_process");
+
+const lockDir = ".husky/_lock";
+try {
+  fs.mkdirSync(lockDir);
+} catch (e) {
+  return; // another process or already set up
+}
+try {
+  execSync("npx husky@9.1.7", { stdio: "inherit" });
+} finally {
+  fs.rmSync(lockDir, { recursive: true });
+}