Detect breaking changes

Adds a gradle task and github action to check for breaking changes made
to the APIs in server by running comparison against most resent snapshot
build on sonotype maven repository.

Uses japicmp to perform the comparison against the jar files, learn
more https://siom79.github.io/japicmp/

- Related opensearch-project#8982

Signed-off-by: Peter Nied <[email protected]>

.github/workflows/detect-breaking-change.yml

@@ -0,0 +1,20 @@
+name: "Detect Breaking Changes"
+on: [push, pull_request]
+jobs:
+  detect-breaking-change:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/setup-java@v2
+      with:
+        distribution: temurin # Temurin is a distribution of adoptium
+        java-version: 17
+
+    - uses: actions/checkout@v2
+
+    - uses: gradle/gradle-build-action@v2
+      with:
+        arguments: japicmp
+        build-root-directory: server
+
+    - if: failure()
+      run: cat server/build/reports/japi.txt

server/build.gradle

@@ -36,6 +36,7 @@ plugins {
   id('opensearch.publish')
   id('opensearch.internal-cluster-test')
   id('opensearch.optional-dependencies')
+  id('me.champeau.gradle.japicmp') version '0.4.2'
 }
 
 publishing {
@@ -408,3 +409,38 @@ tasks.named("sourcesJar").configure {
     duplicatesStrategy = DuplicatesStrategy.EXCLUDE
   }
 }
+
+/** Compares the current build against a snapshot build */
+tasks.register("japicmp", me.champeau.gradle.japicmp.JapicmpTask) {
+    oldClasspath.from(files("${buildDir}/snapshot/opensearch-${version}.jar"))
+    newClasspath.from(tasks.named('jar'))
+    onlyModified = true
+    failOnModification = true
+    ignoreMissingClasses = true
+    txtOutputFile = layout.buildDirectory.file("reports/japi.txt")
+    dependsOn downloadSnapshot
+}
+
+/** Downloads latest snapshot from maven repository */
+tasks.register("downloadSnapshot", Copy) {
+    def mavenSnapshotRepoUrl = "https://aws.oss.sonatype.org/content/repositories/snapshots/"
+    def groupId = "org.opensearch"
+    def artifactId = "opensearch"
+
+    repositories {
+        maven {
+            url mavenSnapshotRepoUrl
+        }
+    }
+
+    configurations {
+        snapshotArtifact
+    }
+
+    dependencies {
+        snapshotArtifact("${groupId}:${artifactId}:${version}:")
+    }
+
+    from configurations.snapshotArtifact
+    into "$buildDir/snapshot"
+}