Merge branch 'mk-fix-wiki-backup' into 'master'

Fix improperly skipped backups of wikis

Closes #28854

See merge request !13096

changelogs/unreleased/mk-fix-wiki-backup.yml

+---
+title: Fix improperly skipped backups of wikis.
+merge_request: 13096
+author:

lib/backup/repository.rb

@@ -189,6 +189,7 @@ module Backup
     end
 
     def empty_repo?(project_or_wiki)
+      project_or_wiki.repository.expire_exists_cache # protect backups from stale cache
       project_or_wiki.repository.empty_repo?
     rescue => e
       progress.puts "Ignoring repository error and continuing backing up project: #{project_or_wiki.path_with_namespace} - #{e.message}".color(:orange)

spec/lib/gitlab/backup/repository_spec.rb

@@ -60,4 +60,58 @@ describe Backup::Repository do
       end
     end
   end
+
+  describe '#empty_repo?' do
+    context 'for a wiki' do
+      let(:wiki) { create(:project_wiki) }
+
+      context 'wiki repo has content' do
+        let!(:wiki_page) { create(:wiki_page, wiki: wiki) }
+
+        before do
+          wiki.repository.exists? # initial cache
+        end
+
+        context '`repository.exists?` is incorrectly cached as false' do
+          before do
+            repo = wiki.repository
+            repo.send(:cache).expire(:exists?)
+            repo.send(:cache).fetch(:exists?) { false }
+            repo.send(:instance_variable_set, :@exists, false)
+          end
+
+          it 'returns false, regardless of bad cache value' do
+            expect(described_class.new.send(:empty_repo?, wiki)).to be_falsey
+          end
+        end
+
+        context '`repository.exists?` is correctly cached as true' do
+          it 'returns false' do
+            expect(described_class.new.send(:empty_repo?, wiki)).to be_falsey
+          end
+        end
+      end
+
+      context 'wiki repo does not have content' do
+        context '`repository.exists?` is incorrectly cached as true' do
+          before do
+            repo = wiki.repository
+            repo.send(:cache).expire(:exists?)
+            repo.send(:cache).fetch(:exists?) { true }
+            repo.send(:instance_variable_set, :@exists, true)
+          end
+
+          it 'returns true, regardless of bad cache value' do
+            expect(described_class.new.send(:empty_repo?, wiki)).to be_truthy
+          end
+        end
+
+        context '`repository.exists?` is correctly cached as false' do
+          it 'returns true' do
+            expect(described_class.new.send(:empty_repo?, wiki)).to be_truthy
+          end
+        end
+      end
+    end
+  end
 end