[mutter] gitlab-ci.yml: Add check for issue or MR URL

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit b70c0eb9a5db9479408ed5102b1bf346749aec1f
Author: Jonas Ådahl <jadahl gmail com>
Date:   Tue Feb 5 18:19:43 2019 +0100

    gitlab-ci.yml: Add check for issue or MR URL
    
    This adds a pipeline stage for merge requests that checks that the
    commit message contains an URL to either a issue or a merge request.
    This means that for merge requests without corresponding issues will
    always fail initially, as the merge request URL is not known until after
    it is created. This is still arguably better than accidentally merging
    merge requests without URLs.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/440

 .gitlab-ci.yml                 | 14 ++++++++++++++
 .gitlab-ci/check-commit-log.sh | 31 +++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 07348238d..09b0052c5 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,9 +1,17 @@
 image: registry.gitlab.gnome.org/gnome/mutter/master:v1
 
 stages:
+ - review
  - build
  - test
 
+check-commit-log:
+  stage: review
+  script:
+    - ./.gitlab-ci/check-commit-log.sh
+  only:
+    - merge_requests
+
 build-mutter:
   stage: build
   script:
@@ -14,6 +22,9 @@ build-mutter:
     expire_in: 1 day
     paths:
       - build
+  only:
+    - merge_requests
+    - /^.*$/
 
 test-mutter:
   stage: test
@@ -28,3 +39,6 @@ test-mutter:
     - >
       dbus-run-session -- xvfb-run -s '+iglx -noreset'
       meson test -C build --no-rebuild -t 10 --verbose --no-stdsplit --wrap catchsegv
+  only:
+    - merge_requests
+    - /^.*$/
diff --git a/.gitlab-ci/check-commit-log.sh b/.gitlab-ci/check-commit-log.sh
new file mode 100755
index 000000000..cc3bcee60
--- /dev/null
+++ b/.gitlab-ci/check-commit-log.sh
@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+
+if [ -z "$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" ]; then
+  echo Cannot review non-merge request
+  exit 1
+fi
+
+git fetch $CI_MERGE_REQUEST_PROJECT_URL.git $CI_MERGE_REQUEST_TARGET_BRANCH_NAME
+
+branch_point=$(git merge-base HEAD FETCH_HEAD)
+
+commits=$(git log --format='format:%H' $branch_point..$CI_COMMIT_SHA)
+
+if [ -z "$commits" ]; then
+  echo Commit range empty
+  exit 1
+fi
+
+function commit_message_has_url() {
+  commit=$1
+  commit_message=$(git show -s --format='format:%b' $commit)
+  echo "$commit_message" | grep -qe 
"\($CI_MERGE_REQUEST_PROJECT_URL/\(issues\|merge_requests\)/[0-9]\+\|https://bugzilla.gnome.org/show_bug.cgi?id=[0-9]\+\)"
+  return $?
+}
+
+for commit in $commits; do
+  if ! commit_message_has_url $commit; then
+    echo "Missing merge request or issue URL on commit $(echo $commit | cut -c -8)"
+    exit 1
+  fi
+done