Add revapi binary and source backwards compatibility check to build.

Author: Diego Veralli

.github/fetch_to_tag.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+set -e
+
+# Github actions will do shallow clones which is great for performance, but some of our
+# tasks require a history going back to the most recent tag, so this script achieves
+# that, without pulling the full history
+
+function fetch_to_tag() {
+    n="$1"
+    if [ "$n" == "" ]; then
+        n=2
+    fi
+    
+    echo "Fetching commits with depth ${n}"
+
+    rev=$(git rev-list -n 1 HEAD)
+
+    git fetch origin --depth "$n" "$rev"
+
+    if ! git describe --tags --abbrev=0 HEAD^ 1>/dev/null 2>&1; then
+        fetch_to_tag "$(expr "$n" \* 2)"
+    fi
+}
+
+git fetch origin 'refs/tags/*:refs/tags/*'
+
+fetch_to_tag

.github/workflows/ci.yml

@@ -14,6 +14,10 @@ jobs:
         java: [8, 11]
     steps:
       - uses: actions/checkout@v2
+        
+      - name: Fetch git tags
+        run: ./.github/fetch_to_tag.sh
+          
       # Our build uses JDK7's rt.jar to make sure the artifact is fully
       # compatible with Java 7, so we let this action set Java 7 up for us
       # and we store its JAVA_HOME

build.gradle

@@ -8,6 +8,7 @@ buildscript {
         classpath "de.marcphilipp.gradle:nexus-publish-plugin:0.4.0"
         classpath "io.codearte.gradle.nexus:gradle-nexus-staging-plugin:0.21.2"
         classpath "gradle.plugin.com.github.spotbugs.snom:spotbugs-gradle-plugin:4.2.4"
+        classpath "com.palantir.gradle.revapi:gradle-revapi:1.4.4"
     }
 }
 
@@ -37,6 +38,8 @@ subprojects { project ->
         apply from: "$rootDir/gradle/release.gradle"
 
         apply from: "$rootDir/gradle/quality.gradle"
+        
+        apply from: "$rootDir/gradle/compatibility.gradle"
 
         repositories {
             mavenCentral()

gradle/compatibility.gradle

@@ -0,0 +1,10 @@
+apply plugin: 'com.palantir.revapi'
+
+revapi {
+    oldGroup = GROUP
+    // By default, revapi will check against the version matching the most recent
+    // git tag, so we don't need to specify anything else here.
+    // If an artifact with the given version doesn't exist on maven, it will skip
+    // the check, so new projects won't cause any failures, and after the first
+    // version of a project is published it will start checking it.
+}