Merge branch 'Ben305/gitlab-ce-36669-default-mr-title-with-external-issues' into 'master'

Resolve "Incorrect default merge request title when Jira activated"

Closes #36669

See merge request gitlab-org/gitlab-ce!16356

(cherry picked from commit e726644123c70eb8f62a6b6b433c2e4fea8e8a52)

44c8f919 Fix incorrect default merge request title when external issue tracker is activated
ca275561 Never set special MR titles for external issues
f9cf2f99 Give appropriate credit to Ben305 in the changelog

3 files changed, 31 insertions, 8 deletions

diff --git a/app/services/merge_requests/build_service.rb b/app/services/merge_requests/build_service.rb
index 9622a5c5462..22b9b91a957 100644
--- a/app/services/merge_requests/build_service.rb
+++ b/app/services/merge_requests/build_service.rb
@@ -154,13 +154,9 @@ module MergeRequests
     end
 
     def assign_title_from_issue
-      return unless issue
+      return unless issue && issue.is_a?(Issue)
 
-      merge_request.title =
-        case issue
-        when Issue         then "Resolve \"#{issue.title}\""
-        when ExternalIssue then "Resolve #{issue.title}"
-        end
+      merge_request.title = "Resolve \"#{issue.title}\""
     end
 
     def issue_iid
diff --git a/changelogs/unreleased/36669-default-mr-title-with-external-issues.yml b/changelogs/unreleased/36669-default-mr-title-with-external-issues.yml
new file mode 100644
index 00000000000..6af9ac4b099
--- /dev/null
+++ b/changelogs/unreleased/36669-default-mr-title-with-external-issues.yml
@@ -0,0 +1,5 @@
+---
+title: Default merge request title is set correctly again when external issue tracker is activated
+merge_request: 16356
+author: Ben305
+type: fixed
diff --git a/spec/services/merge_requests/build_service_spec.rb b/spec/services/merge_requests/build_service_spec.rb
index b5c92e681fb..44f12bf2745 100644
--- a/spec/services/merge_requests/build_service_spec.rb
+++ b/spec/services/merge_requests/build_service_spec.rb
@@ -171,6 +171,24 @@ describe MergeRequests::BuildService do
           end
         end
       end
+
+      context 'branch starts with external issue IID followed by a hyphen' do
+        let(:source_branch) { '12345-fix-issue' }
+
+        before do
+          allow(project).to receive(:external_issue_tracker).and_return(true)
+        end
+
+        it 'uses the title of the commit as the title of the merge request' do
+          expect(merge_request.title).to eq(commit_1.safe_message.split("\n").first)
+        end
+
+        it 'uses the description of the commit as the description of the merge request and appends the closes text' do
+          commit_description = commit_1.safe_message.split(/\n+/, 2).last
+
+          expect(merge_request.description).to eq("#{commit_description}\n\nCloses #12345")
+        end
+      end
     end
 
     context 'more than one commit in the diff' do
@@ -241,8 +259,12 @@ describe MergeRequests::BuildService do
           allow(project).to receive(:external_issue_tracker).and_return(true)
         end
 
-        it 'sets the title to: Resolves External Issue $issue-iid' do
-          expect(merge_request.title).to eq('Resolve External Issue 12345')
+        it 'sets the title to the humanized branch title' do
+          expect(merge_request.title).to eq('12345 fix issue')
+        end
+
+        it 'appends the closes text' do
+          expect(merge_request.description).to eq('Closes #12345')
         end
       end
     end