[CI] Automatically apply spotless changes in pull request CI (elastic…

…#118701) (elastic#118711)

(cherry picked from commit f900ae6)

.buildkite/pipelines/pull-request/part-1.yml

@@ -1,6 +1,8 @@
 steps:
   - label: part-1
-    command: .ci/scripts/run-gradle.sh -Dignore.tests.seed checkPart1
+    command: |
+      .buildkite/scripts/spotless.sh # This doesn't have to be part of part-1, it was just a convenient place to put it
+      .ci/scripts/run-gradle.sh -Dignore.tests.seed checkPart1
     timeout_in_minutes: 300
     agents:
       provider: gcp

.buildkite/pipelines/pull-request/precommit.yml

@@ -3,7 +3,9 @@ config:
   skip-labels: []
 steps:
   - label: precommit
-    command: .ci/scripts/run-gradle.sh -Dignore.tests.seed precommit
+    command: |
+      .buildkite/scripts/spotless.sh
+      .ci/scripts/run-gradle.sh -Dignore.tests.seed precommit
     timeout_in_minutes: 300
     agents:
       provider: gcp

.buildkite/scripts/spotless.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+
+if [[ -z "${BUILDKITE_PULL_REQUEST:-}" ]]; then
+  echo "Not a pull request, skipping spotless"
+  exit 0
+fi
+
+if ! git diff --exit-code; then
+  echo "Changes are present before running spotless, not running"
+  git status
+  exit 0
+fi
+
+NEW_COMMIT_MESSAGE="[CI] Auto commit changes from spotless"
+PREVIOUS_COMMIT_MESSAGE="$(git log -1 --pretty=%B)"
+
+echo "--- Running spotless"
+.ci/scripts/run-gradle.sh -Dscan.tag.NESTED spotlessApply
+
+if git diff --exit-code; then
+  echo "No changes found after running spotless. Don't need to auto commit."
+  exit 0
+fi
+
+if [[ "$NEW_COMMIT_MESSAGE" == "$PREVIOUS_COMMIT_MESSAGE" ]]; then
+  echo "Changes found after running spotless"
+  echo "CI already attempted to commit these changes, but the file(s) seem to have changed again."
+  echo "Please review and fix manually."
+  exit 1
+fi
+
+git config --global user.name elasticsearchmachine
+git config --global user.email '[email protected]'
+
+gh pr checkout "${BUILDKITE_PULL_REQUEST}"
+git add -u .
+git commit -m "$NEW_COMMIT_MESSAGE"
+git push
+
+# After the git push, the new commit will trigger a new build within a few seconds and this build should get cancelled
+# So, let's just sleep to give the build time to cancel itself without an error
+# If it doesn't get cancelled for some reason, then exit with an error, because we don't want this build to be green (we just don't want it to generate an error either)
+sleep 300
+exit 1