Add API compatibility checking with japicmp

This adds a GitHub Actions workflow that runs on PRs to detect breaking
changes in the public API. The check uses japicmp with semantic versioning
support, so it will only fail if breaking changes are detected without a
major version bump.

ENG-3367

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: oschwald

.github/workflows/api-compat.yml

@@ -0,0 +1,20 @@
+name: API Compatibility Check
+on:
+  pull_request:
+permissions:
+  contents: read
+jobs:
+  api-compat:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+        with:
+          submodules: true
+          persist-credentials: false
+      - uses: actions/setup-java@f2beeb24e141e01a676f977032f5a29d81c9e27e # v5.1.0
+        with:
+          distribution: zulu
+          java-version: 17
+          cache: maven
+      - name: Check API Compatibility
+        run: mvn verify -P api-compat -DskipTests -Dgpg.skip=true

pom.xml

@@ -177,6 +177,8 @@
     </build>
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <!-- Baseline version for API compatibility checking. Update after each release. -->
+        <japicmp.baselineVersion>4.0.2</japicmp.baselineVersion>
     </properties>
     <profiles>
         <profile>
@@ -218,5 +220,66 @@
                 </plugins>
             </build>
         </profile>
+        <profile>
+            <id>api-compat</id>
+            <build>
+                <plugins>
+                    <!-- Download baseline JAR directly from Maven Central for API comparison -->
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-antrun-plugin</artifactId>
+                        <version>3.1.0</version>
+                        <executions>
+                            <execution>
+                                <id>download-baseline</id>
+                                <phase>package</phase>
+                                <goals>
+                                    <goal>run</goal>
+                                </goals>
+                                <configuration>
+                                    <target>
+                                        <mkdir dir="${project.build.directory}/japicmp"/>
+                                        <get src="https://repo1.maven.org/maven2/com/maxmind/db/maxmind-db/${japicmp.baselineVersion}/maxmind-db-${japicmp.baselineVersion}.jar"
+                                             dest="${project.build.directory}/japicmp/baseline.jar"
+                                             skipexisting="false"/>
+                                    </target>
+                                </configuration>
+                            </execution>
+                        </executions>
+                    </plugin>
+                    <plugin>
+                        <groupId>com.github.siom79.japicmp</groupId>
+                        <artifactId>japicmp-maven-plugin</artifactId>
+                        <version>0.25.1</version>
+                        <configuration>
+                            <oldVersion>
+                                <file>
+                                    <path>${project.build.directory}/japicmp/baseline.jar</path>
+                                </file>
+                            </oldVersion>
+                            <newVersion>
+                                <file>
+                                    <path>${project.build.directory}/${project.artifactId}-${project.version}.jar</path>
+                                </file>
+                            </newVersion>
+                            <parameter>
+                                <accessModifier>public</accessModifier>
+                                <breakBuildOnBinaryIncompatibleModifications>true</breakBuildOnBinaryIncompatibleModifications>
+                                <onlyBinaryIncompatible>false</onlyBinaryIncompatible>
+                                <onlyModified>true</onlyModified>
+                            </parameter>
+                        </configuration>
+                        <executions>
+                            <execution>
+                                <phase>verify</phase>
+                                <goals>
+                                    <goal>cmp</goal>
+                                </goals>
+                            </execution>
+                        </executions>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
     </profiles>
 </project>