👷 Add Spotless Java linting to CI pipeline

Add automated Java code style checking using Spotless with:
- Google Java Format (AOSP style) for Android-friendly formatting
- Gradle project in pythonforandroid/bootstraps/ for linting
- New 'spotless' job in GitHub Actions workflow
- Makefile targets: java-lint, java-lint-fix, docker/java-lint
- Excludes third-party code (org/kamranzafar/jtar/)

Downstream CI jobs now depend on both flake8 and spotless checks.

Author: AndreMiras

.github/workflows/push.yml

@@ -30,9 +30,26 @@ jobs:
         pip install tox>=2.0
         tox -e pep8
 
+  spotless:
+    name: Java Spotless check
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout python-for-android
+      uses: actions/checkout@v5
+    - name: Set up Java 17
+      uses: actions/setup-java@v4
+      with:
+        distribution: 'temurin'
+        java-version: '17'
+    - name: Set up Gradle
+      uses: gradle/actions/setup-gradle@v4
+    - name: Run Spotless check
+      working-directory: pythonforandroid/bootstraps
+      run: ./common/build/gradlew spotlessCheck
+
   test:
     name: Pytest [Python ${{ matrix.python-version }} | ${{ matrix.os }}]
-    needs: flake8
+    needs: [flake8, spotless]
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
@@ -61,7 +78,7 @@ jobs:
 
   ubuntu_build:
     name: Build test APP [ ${{ matrix.runs_on }} | ${{ matrix.bootstrap.name }} ]
-    needs: [flake8]
+    needs: [flake8, spotless]
     runs-on: ${{ matrix.runs_on }}
     strategy:
       matrix:
@@ -120,7 +137,7 @@ jobs:
 
   macos_build:
     name: Build test APP [ ${{ matrix.runs_on }} | ${{ matrix.bootstrap.name }} ]
-    needs: [flake8]
+    needs: [flake8, spotless]
     runs-on: ${{ matrix.runs_on }}
     strategy:
       matrix:
@@ -194,7 +211,7 @@ jobs:
 
   ubuntu_rebuild_updated_recipes:
     name: Test updated recipes for arch ${{ matrix.android_arch }} [ ubuntu-latest ]
-    needs: [flake8]
+    needs: [flake8, spotless]
     runs-on: ubuntu-latest
     # continue on error to see failures across all architectures
     continue-on-error: true
@@ -227,7 +244,7 @@ jobs:
 
   macos_rebuild_updated_recipes:
     name: Test updated recipes for arch ${{ matrix.android_arch }} [ ${{ matrix.runs_on }} ]
-    needs: [flake8]
+    needs: [flake8, spotless]
     runs-on: ${{ matrix.runs_on }}
     # continue on error to see failures across all architectures
     continue-on-error: true

.gitignore

@@ -36,5 +36,9 @@ coverage.xml
 # testapp's build folder
 testapps/build/
 
+# Gradle build artifacts (Java linting)
+pythonforandroid/bootstraps/.gradle/
+pythonforandroid/bootstraps/build/
+
 # Dolphin (the KDE file manager autogenerates the file `.directory`)
 .directory

CONTRIBUTING.md

@@ -66,6 +66,60 @@ latest python-for-android release that supported building Python 2 was version
 On August 2021, we added support for Android App Bundle (aab). As a
 collateral benefit, we now support multi-arch apk.
 
+## Code Quality
+
+### Python Linting
+
+Python code is linted using flake8. Run it locally with:
+
+```bash
+tox -e pep8
+```
+
+### Java Linting
+
+Java source files in the bootstrap directories are linted using
+[Spotless](https://github.com/diffplug/spotless) with Google Java Format
+(AOSP style). The CI runs this check automatically.
+
+**Local execution** (requires Java 17+):
+
+```bash
+# Check for violations
+make java-lint
+
+# Auto-fix violations
+make java-lint-fix
+```
+
+The Makefile uses the Gradle wrapper (`gradlew`), which automatically downloads
+the correct Gradle version on first run. No manual Gradle installation is required.
+
+**Using Docker** (if you don't have Java 17):
+
+```bash
+# Check for violations
+make docker/java-lint
+
+# Auto-fix violations
+make docker/java-lint-fix
+```
+
+The Docker approach builds the project's Docker image (which includes Java 17)
+and runs the linting inside the container.
+
+**What gets linted:**
+
+- All `.java` files in `pythonforandroid/bootstraps/*/build/src/main/java/`
+- Excludes third-party code (`org/kamranzafar/jtar/`)
+
+**Formatting rules applied:**
+
+- Google Java Format with AOSP style (Android-friendly indentation)
+- Removal of unused imports
+- Trailing whitespace trimming
+- Files end with newline
+
 ## Creating a new release
 
 (These instructions are for core developers, not casual contributors.)

Makefile

@@ -24,6 +24,20 @@ virtualenv: $(VIRTUAL_ENV)
 test:
 	$(TOX) -- tests/ --ignore tests/test_pythonpackage.py
 
+# Java linting using Spotless (requires Java 17+, uses Gradle wrapper)
+java-lint:
+	cd pythonforandroid/bootstraps && ./common/build/gradlew spotlessCheck
+
+java-lint-fix:
+	cd pythonforandroid/bootstraps && ./common/build/gradlew spotlessApply
+
+# Java linting via Docker (no local Java required)
+docker/java-lint: docker/build
+	docker run --rm -v $(CURDIR):/home/user/app -w /home/user/app/pythonforandroid/bootstraps $(DOCKER_IMAGE) ./common/build/gradlew spotlessCheck
+
+docker/java-lint-fix: docker/build
+	docker run --rm -v $(CURDIR):/home/user/app -w /home/user/app/pythonforandroid/bootstraps $(DOCKER_IMAGE) ./common/build/gradlew spotlessApply
+
 # Also install and configure rust
 rebuild_updated_recipes: virtualenv
 	. $(ACTIVATE) && \

pythonforandroid/bootstraps/build.gradle

@@ -0,0 +1,60 @@
+// Java Lint Configuration for python-for-android
+// This file configures Spotless to lint Java source files across all bootstraps
+
+plugins {
+    id 'java'
+    id 'com.diffplug.spotless' version '6.25.0'
+}
+
+// Repositories for plugin dependencies (e.g., google-java-format)
+repositories {
+    mavenCentral()
+}
+
+// Define the root directory for bootstrap Java sources
+def bootstrapsDir = "${rootProject.projectDir}"
+
+// Collect all Java source directories from all bootstraps
+def javaSourceDirs = []
+file(bootstrapsDir).eachDir { bootstrapDir ->
+    def srcDir = new File(bootstrapDir, 'build/src/main/java')
+    if (srcDir.exists()) {
+        javaSourceDirs.add(srcDir.absolutePath)
+    }
+}
+
+sourceSets {
+    main {
+        java {
+            srcDirs = javaSourceDirs
+        }
+    }
+}
+
+spotless {
+    java {
+        // Target all Java files from the source directories
+        target fileTree(bootstrapsDir) {
+            include '**/build/src/main/java/**/*.java'
+            // Exclude third-party vendored code
+            exclude '**/org/kamranzafar/jtar/**'
+        }
+
+        // Use Google Java Format with AOSP style (Android-friendly, slightly relaxed)
+        googleJavaFormat('1.19.2').aosp()
+
+        // Remove unused imports
+        removeUnusedImports()
+
+        // Trim trailing whitespace
+        trimTrailingWhitespace()
+
+        // Ensure files end with a newline
+        endWithNewline()
+    }
+}
+
+// Disable compilation - we only want to lint, not build
+tasks.withType(JavaCompile).configureEach {
+    enabled = false
+}

pythonforandroid/bootstraps/gradle.properties

@@ -0,0 +1,9 @@
+# Gradle properties for Java lint project
+# Disable daemon for CI environments
+org.gradle.daemon=false
+
+# Use parallel execution where possible
+org.gradle.parallel=true
+
+# Configure JVM memory
+org.gradle.jvmargs=-Xmx512m

pythonforandroid/bootstraps/settings.gradle

@@ -0,0 +1,3 @@
+// Java Lint Project Settings
+// This project is used for linting Java source files in CI
+rootProject.name = 'p4a-java-lint'