Resolve "Incorrect merge request title when Jira activated and multiple commits on branch"

app/services/merge_requests/build_service.rb

 module MergeRequests
   class BuildService < MergeRequests::BaseService
+    include Gitlab::Utils::StrongMemoize
+
     def execute
-      @issue_iid = params.delete(:issue_iid)
+      @params_issue_iid = params.delete(:issue_iid)
       self.merge_request = MergeRequest.new(params)
       merge_request.compare_commits = []
@@ -123,7 +125,7 @@ module MergeRequests
     #
     def assign_title_and_description
       assign_title_and_description_from_single_commit
-      assign_title_from_issue
+      assign_title_from_issue if target_project.issues_enabled? || target_project.external_issue_tracker
       merge_request.title ||= source_branch.titleize.humanize
       merge_request.title = wip_title if compare_commits.empty?
@@ -132,9 +134,9 @@ module MergeRequests
     end
     def append_closes_description
-      return unless issue_iid
-      closes_issue = "Closes ##{issue_iid}"
+      return unless issue
+      closes_issue = "Closes #{issue.to_reference}"
       if description.present?
         merge_request.description += closes_issue.prepend("\n\n")
@@ -154,13 +156,27 @@ module MergeRequests
     end
     def assign_title_from_issue
-      return unless issue && issue.is_a?(Issue)
-      merge_request.title = "Resolve \"#{issue.title}\""
+      return unless issue
+
+      merge_request.title = "Resolve \"#{issue.title}\"" if issue.is_a?(Issue)
+      unless merge_request.title
+        branch_title = source_branch.downcase.remove(issue_iid.downcase).titleize.humanize
+        merge_request.title = "Resolve #{issue_iid}"
+        merge_request.title += " \"#{branch_title}\"" unless branch_title.empty?
+      end
     end
     def issue_iid
-      @issue_iid ||= source_branch.match(/\A(\d+)-/).try(:[], 1)
+      strong_memoize(:issue_iid) do
+        @params_issue_iid || begin
+          id = if target_project.external_issue_tracker
+                 source_branch.match(target_project.external_issue_reference_pattern).try(:[], 0)
+               end
+
+          id || source_branch.match(/\A(\d+)-/).try(:[], 1)
+        end
+      end
     end
     def issue

changelogs/unreleased/40793-fix-mr-title-for-jira.yml

+---
+title: Prevent JIRA issue identifier from being humanized.
+merge_request: 16491
+author: Andrew McCallum
+type: fixed

spec/services/merge_requests/build_service_spec.rb

@@ -172,11 +172,32 @@ describe MergeRequests::BuildService do
         end
       end
-      context 'branch starts with external issue IID followed by a hyphen' do
+      context 'branch starts with numeric characters followed by a hyphen with no issue tracker' do
         let(:source_branch) { '12345-fix-issue' }
+        before do
+          allow(project).to receive(:external_issue_tracker).and_return(false)
+          allow(project).to receive(:issues_enabled?).and_return(false)
+        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' do
+          commit_description = commit_1.safe_message.split(/\n+/, 2).last
+
+          expect(merge_request.description).to eq("#{commit_description}")
+        end
+      end
+
+      context 'branch starts with JIRA-formatted external issue IID followed by a hyphen' do
+        let(:source_branch) { 'EXMPL-12345-fix-issue' }
+
         before do
           allow(project).to receive(:external_issue_tracker).and_return(true)
+          allow(project).to receive(:issues_enabled?).and_return(false)
+          allow(project).to receive(:external_issue_reference_pattern).and_return(IssueTrackerService.reference_pattern)
         end
         it 'uses the title of the commit as the title of the merge request' do
@@ -186,7 +207,7 @@ describe MergeRequests::BuildService do
         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")
+          expect(merge_request.description).to eq("#{commit_description}\n\nCloses EXMPL-12345")
         end
       end
     end
@@ -252,19 +273,46 @@ describe MergeRequests::BuildService do
         end
       end
-      context 'branch starts with external issue IID followed by a hyphen' do
+      context 'branch starts with numeric characters followed by a hyphen with no issue tracker' do
         let(:source_branch) { '12345-fix-issue' }
         before do
-          allow(project).to receive(:external_issue_tracker).and_return(true)
+          allow(project).to receive(:external_issue_tracker).and_return(false)
+          allow(project).to receive(:issues_enabled?).and_return(false)
         end
         it 'sets the title to the humanized branch title' do
           expect(merge_request.title).to eq('12345 fix issue')
         end
+      end
+
+      context 'branch starts with JIRA-formatted external issue IID' do
+        let(:source_branch) { 'EXMPL-12345' }
+
+        before do
+          allow(project).to receive(:external_issue_tracker).and_return(true)
+          allow(project).to receive(:issues_enabled?).and_return(false)
+          allow(project).to receive(:external_issue_reference_pattern).and_return(IssueTrackerService.reference_pattern)
+        end
+
+        it 'sets the title to the humanized branch title' do
+          expect(merge_request.title).to eq('Resolve EXMPL-12345')
+        end
         it 'appends the closes text' do
-          expect(merge_request.description).to eq('Closes #12345')
+          expect(merge_request.description).to eq('Closes EXMPL-12345')
+        end
+
+        context 'followed by hyphenated text' do
+          let(:source_branch) { 'EXMPL-12345-fix-issue' }
+
+          it 'sets the title to the humanized branch title' do
+            expect(merge_request.title).to eq('Resolve EXMPL-12345 "Fix issue"')
+          end
+
+          it 'appends the closes text' do
+            expect(merge_request.description).to eq('Closes EXMPL-12345')
+          end
         end
       end
     end