[9.16] new: ci: Automate parts of MR workflow

Backport of MR !9244

Merge branch 'backport-pspacek/post-merge-ci-9.16' into 'bind-9.16'

See merge request isc-projects/bind9!9403

.gitlab-ci.yml

@@ -65,6 +65,7 @@ stages:
   - performance
   - docs
   - postcheck
+  - postmerge
   - release
 
 ### Runner Tag Templates
@@ -1530,3 +1531,37 @@ pairwise:
     variables:
       - $PAIRWISE_TESTING
   needs: []
+
+.post_merge_template: &post_merge
+  <<: *base_image
+  stage: postmerge
+  needs: []
+  # post-merge processes should run even if another MR was merged while the job was running (or queued)
+  interruptible: false
+  variables:
+    # automated commits will inherit identification from the user who pressed Merge button
+    GIT_COMMITTER_NAME: $GITLAB_USER_NAME
+    GIT_COMMITTER_EMAIL: $GITLAB_USER_EMAIL
+    # avoid leftover branches from previous jobs
+    GIT_STRATEGY: clone
+    # assumed max depth of a MR for backport or a rebased force-push
+    GIT_DEPTH: 1000
+  before_script:
+    # force-pushes should not trigger process automation (happens only in -sub branches)
+    - >
+      echo "previous branch tip: $CI_COMMIT_BEFORE_SHA"
+    - set +o pipefail; git log --format='%H' | grep --silent "$CI_COMMIT_BEFORE_SHA" && PREVIOUS_TIP_REACHABLE=1
+    - test "$PREVIOUS_TIP_REACHABLE" != "1" && echo "force-push detected, stop" && exit 1
+    # non-fast-forward merges are disabled so we have to have merge commit on top
+    - MERGE_REQUEST_ID="$(git log -1 --format='%b' | sed --silent -e 's/^See merge request [^!]\+!//p')"
+    - >
+      : stop if this is not a merge request
+    - test "$MERGE_REQUEST_ID" -ge 0
+    - git clone --depth 1 https://gitlab.isc.org/isc-projects/bind9-qa.git
+
+merged-metadata:
+  <<: *post_merge
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "push" && ($CI_COMMIT_REF_NAME =~ /^bind-9.[0-9]+(-sub)?$/ || $CI_COMMIT_REF_NAME =~ /^bind-9.[0-9]+.[0-9]+-release$/ || $CI_COMMIT_REF_NAME == $CI_DEFAULT_BRANCH)'
+  script:
+    - bind9-qa/releng/after_merge.py "$CI_PROJECT_ID" "$MERGE_REQUEST_ID"

dangerfile.py

@@ -181,15 +181,6 @@ for commit in danger.git.commits:
                 f"```{line}``` ({len(line)} > 72 characters)."
             )
 
-###############################################################################
-# MILESTONE
-###############################################################################
-#
-# FAIL if the merge request is not assigned to any milestone.
-
-if not danger.gitlab.mr.milestone:
-    fail("Please assign this merge request to a milestone.")
-
 ###############################################################################
 # BACKPORT & VERSION LABELS
 ###############################################################################