Introduce GitHub action workflow to automate backporting (#74659)

.backportrc.json

@@ -0,0 +1,15 @@
+{
+  "upstream": "elastic/elasticsearch",
+  "targetBranchChoices": [
+    { "name": "master", "checked": true },
+    { "name": "7.x", "checked": true },
+    "7.13",
+    "6.8"
+  ],
+  "targetPRLabels": ["backport"],
+  "branchLabelMapping": {
+    "^v8.0.0$": "master",
+    "^v7.14.0$": "7.x",
+    "^v(\\d+).(\\d+).\\d+$": "$1.$2"
+  }
+}

.github/workflows/backport.yml

@@ -0,0 +1,38 @@
+on:
+  pull_request_target:
+    branches:
+      - master
+    types:
+      - labeled
+      - closed
+
+jobs:
+  backport:
+    name: Backport PR
+    if: |
+      github.event.pull_request.merged == true
+      && contains(github.event.pull_request.labels.*.name, 'auto-backport')
+      && (
+        (github.event.action == 'labeled' && github.event.label.name == 'auto-backport')
+        || (github.event.action == 'closed')
+      )
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Actions
+        uses: actions/checkout@v2
+        with:
+          repository: 'elastic/kibana-github-actions'
+          ref: main
+          path: ./actions
+
+      - name: Install Actions
+        run: npm install --production --prefix ./actions
+
+      - name: Run Backport
+        uses: ./actions/backport
+        with:
+          github_token: ${{secrets.ELASTICSEARCHMACHINE_TOKEN}}
+          commit_user: elasticsearchmachine
+          commit_email: elasticsarchmachine@users.noreply.github.com
+          auto_merge: 'false'
+          manual_backport_command_template: 'backport --pr %pullNumber%'

build.gradle

@@ -7,11 +7,14 @@
  */
 
 import com.avast.gradle.dockercompose.tasks.ComposePull
+import com.fasterxml.jackson.databind.JsonNode
+import com.fasterxml.jackson.databind.ObjectMapper
 import com.github.jengelman.gradle.plugins.shadow.ShadowPlugin
 import de.thetaphi.forbiddenapis.gradle.ForbiddenApisPlugin
 import org.elasticsearch.gradle.internal.BuildPlugin
 import org.elasticsearch.gradle.Version
 import org.elasticsearch.gradle.VersionProperties
+import org.elasticsearch.gradle.internal.BwcVersions
 import org.elasticsearch.gradle.internal.info.BuildParams
 import org.elasticsearch.gradle.plugin.PluginBuildPlugin
 import org.gradle.plugins.ide.eclipse.model.AccessRule
@@ -107,6 +110,28 @@ tasks.register("verifyVersions") {
         throw new Exception(".ci/bwcVersions is outdated, run `./gradlew updateCIBwcVersions` and check in the results");
       }
     }
+
+    // Make sure backport bot config file is up to date
+    JsonNode backportConfig = new ObjectMapper().readTree(file(".backportrc.json"))
+    List<BwcVersions.UnreleasedVersionInfo> unreleased = BuildParams.bwcVersions.unreleased.collect { BuildParams.bwcVersions.unreleasedInfo(it) }
+    unreleased.each { unreleasedVersion ->
+      boolean valid = backportConfig.get("targetBranchChoices").elements().any { branchChoice ->
+        if (branchChoice.isObject()) {
+          return branchChoice.get("name").textValue() == unreleasedVersion.branch
+        } else {
+          return branchChoice.textValue() == unreleasedVersion.branch
+        }
+      }
+      if (valid == false) {
+        throw new GradleException("No branch choice exists for development branch ${unreleasedVersion.branch} in .backportrc.json.")
+      }
+    }
+    BwcVersions.UnreleasedVersionInfo nextMinor = unreleased.find { it.branch.endsWith("x") }
+    String versionMapping = backportConfig.get("branchLabelMapping").fields().find { it.value.textValue() == nextMinor.branch }.key
+    if (versionMapping != "^v${nextMinor.version}\$") {
+      throw new GradleException("Backport label mapping for branch ${nextMinor.branch} is '${versionMapping}' but should be " +
+        "'^v${nextMinor.version}\$'. Update .backportrc.json.")
+    }
   }
 }