Merge branch 'fix/14388' into 'master'

CHANGELOG

@@ -43,6 +43,7 @@ v 8.6.0 (unreleased)
   - Increase the notes polling timeout over time (Roberto Dip)
   - Add shortcut to toggle markdown preview (Florent Baldino)
   - Show labels in dashboard and group milestone views
+  - Fix an issue when the target branch of a MR had been deleted
   - Add main language of a project in the list of projects (Tiago Botelho)
   - Add #upcoming filter to Milestone filter (Tiago Botelho)
   - Add ability to show archived projects on dashboard, explore and group pages

app/models/merge_request.rb

@@ -516,7 +516,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def target_sha
-    @target_sha ||= target_project.repository.commit(target_branch).sha
+    @target_sha ||= target_project.repository.commit(target_branch).try(:sha)
   end
 
   def source_sha
@@ -572,8 +572,11 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def compute_diverged_commits_count
+    return 0 unless source_sha && target_sha
+
     Gitlab::Git::Commit.between(target_project.repository.raw_repository, source_sha, target_sha).size
   end
+  private :compute_diverged_commits_count
 
   def diverged_from_target_branch?
     diverged_commits_count > 0

spec/models/merge_request_spec.rb

@@ -86,6 +86,16 @@ describe MergeRequest, models: true do
     end
   end
 
+  describe '#target_sha' do
+    context 'when the target branch does not exist anymore' do
+      subject { create(:merge_request).tap { |mr| mr.update_attribute(:target_branch, 'deleted') } }
+
+      it 'returns nil' do
+        expect(subject.target_sha).to be_nil
+      end
+    end
+  end
+
   describe '#source_sha' do
     let(:last_branch_commit) { subject.source_project.repository.commit(subject.source_branch) }
 
@@ -310,6 +320,18 @@ describe MergeRequest, models: true do
     let(:project)      { create(:project) }
     let(:fork_project) { create(:project, forked_from_project: project) }
 
+    context 'when the target branch does not exist anymore' do
+      subject { create(:merge_request).tap { |mr| mr.update_attribute(:target_branch, 'deleted') } }
+
+      it 'does not crash' do
+        expect{ subject.diverged_commits_count }.not_to raise_error
+      end
+
+      it 'returns 0' do
+        expect(subject.diverged_commits_count).to eq(0)
+      end
+    end
+
     context 'diverged on same repository' do
       subject(:merge_request_with_divergence) { create(:merge_request, :diverged, source_project: project, target_project: project) }