Include full path of source and target branch names in New Merge Request page

Previous title would only show the group name, which could be confusing.

Closes #2875

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.1.0 (unreleased)
+  - Include full path of source and target branch names in New Merge Request page (Stan Hu)
   - Add user preference to view activities as default dashboard (Stan Hu)
   - Add option to admin area to sign in as a specific user (Pavel Forkert)
   - Show CI status on all pages where commits list is rendered

app/helpers/merge_requests_helper.rb

@@ -71,4 +71,17 @@ module MergeRequestsHelper
       merge_request.source_branch
     end
   end
+
+  def format_mr_branch_names(merge_request)
+    source_path = merge_request.source_project_path
+    target_path = merge_request.target_project_path
+    source_branch = merge_request.source_branch
+    target_branch = merge_request.target_branch
+
+    if source_path == target_path
+      [source_branch, target_branch]
+    else
+      ["#{source_path}:#{source_branch}", "#{target_path}:#{target_branch}"]
+    end
+  end
 end

app/views/projects/merge_requests/_new_submit.html.haml

 %h3.page-title
   New merge request
 %p.slead
+  - source_title, target_title = format_mr_branch_names(@merge_request)
   From
-  %strong.label-branch #{@merge_request.source_project_namespace}:#{@merge_request.source_branch}
+  %strong.label-branch #{source_title}
   %span into
-  %strong.label-branch #{@merge_request.target_project_namespace}:#{@merge_request.target_branch}
+  %strong.label-branch #{target_title}
 
   %span.pull-right
     = link_to 'Change branches', mr_change_branches_path(@merge_request)

spec/helpers/merge_requests_helper.rb

-require 'spec_helper'
-
-describe MergeRequestsHelper do
-  describe :issues_sentence do
-    subject { issues_sentence(issues) }
-    let(:issues) do
-      [build(:issue, iid: 1), build(:issue, iid: 2), build(:issue, iid: 3)]
-    end
-
-    it { is_expected.to eq('#1, #2, and #3') }
-  end
-end

spec/helpers/merge_requests_helper_spec.rb

+require 'spec_helper'
+
+describe MergeRequestsHelper do
+  describe "#issues_sentence" do
+    subject { issues_sentence(issues) }
+    let(:issues) do
+      [build(:issue, iid: 1), build(:issue, iid: 2), build(:issue, iid: 3)]
+    end
+
+    it { is_expected.to eq('#1, #2, and #3') }
+  end
+
+  describe "#format_mr_branch_names" do
+    describe "within the same project" do
+      let(:merge_request) { create(:merge_request) }
+      subject { format_mr_branch_names(merge_request) }
+
+      it { is_expected.to eq([merge_request.source_branch, merge_request.target_branch]) }
+    end
+
+    describe "within different projects" do
+      let(:project) { create(:project) }
+      let(:fork_project) { create(:project, forked_from_project: project) }
+      let(:merge_request) { create(:merge_request, source_project: fork_project, target_project: project) }
+      subject { format_mr_branch_names(merge_request) }
+      let(:source_title) { "#{fork_project.path_with_namespace}:#{merge_request.source_branch}" }
+      let(:target_title) { "#{project.path_with_namespace}:#{merge_request.target_branch}" }
+
+      it { is_expected.to eq([source_title, target_title]) }
+    end
+  end
+end