Add checkstyle enforcement to build and CI

- Add maven-checkstyle-plugin (3.6.0, Checkstyle 10.23.1) to pluginManagement
- Configure google_checks.xml with suppressions, fail on warnings
- Run checkstyle:check in Java 17+ profile (verify phase)
- Add checkstyle step to CI format job
- Add check-style Makefile target
- Replace spotbugs-annotations with jsr305 (for javax.annotation.Nullable)

Author: bramp

.github/workflows/test.yml

@@ -23,6 +23,9 @@ jobs:
       - name: Check formatting (Google Java Style)
         run: mvn --batch-mode fmt:check
 
+      - name: Check style (Google Java Style)
+        run: mvn --batch-mode checkstyle:check
+
   test:
     runs-on: ubuntu-latest
     strategy:

Makefile

@@ -7,6 +7,7 @@ help:
 	@echo "  make compile        - Run clean compile on all supported JDKs ($(JDK_VERSIONS))"
 	@echo "  make format         - Auto-format code (Google Java Style)"
 	@echo "  make check-format   - Check code formatting (Google Java Style)"
+	@echo "  make check-style    - Run checkstyle (Google Java Style)"
 	@echo "  make examples       - Regenerate EXAMPLES.md and README.md from test source code"
 	@echo "  make check-examples - Verify EXAMPLES.md and README.md are up to date"
 	@echo "  make version        - Show current project version"
@@ -73,6 +74,10 @@ format:
 check-format:
 	mvn fmt:check
 
+.PHONY: check-style
+check-style:
+	mvn checkstyle:check
+
 .PHONY: examples
 examples:
 	python3 tools/generate_examples.py

pom.xml

@@ -284,6 +284,25 @@
                     <artifactId>fmt-maven-plugin</artifactId>
                     <version>2.29</version>
                 </plugin>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-checkstyle-plugin</artifactId>
+                    <version>3.6.0</version>
+                    <dependencies>
+                        <dependency>
+                            <groupId>com.puppycrawl.tools</groupId>
+                            <artifactId>checkstyle</artifactId>
+                            <version>10.23.1</version>
+                        </dependency>
+                    </dependencies>
+                    <configuration>
+                        <configLocation>google_checks.xml</configLocation>
+                        <suppressionsLocation>checkstyle-suppressions.xml</suppressionsLocation>
+                        <violationSeverity>warning</violationSeverity>
+                        <failOnViolation>true</failOnViolation>
+                        <consoleOutput>true</consoleOutput>
+                    </configuration>
+                </plugin>
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-enforcer-plugin</artifactId>
@@ -525,6 +544,19 @@
                             </execution>
                         </executions>
                     </plugin>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-checkstyle-plugin</artifactId>
+                        <executions>
+                            <execution>
+                                <id>checkstyle</id>
+                                <phase>verify</phase>
+                                <goals>
+                                    <goal>check</goal>
+                                </goals>
+                            </execution>
+                        </executions>
+                    </plugin>
                 </plugins>
             </build>
         </profile>