Retrieve ref from unborn HEAD for wikis

In order to allow working with different branches in wikis,
we need to change the way the gollum wiki is instantiated.

We need to pass the default branch in HEAD when we instantiate
the gollum wiki, otherwise it will always default to `master`.

Changelog: added

4 files changed, 66 insertions, 1 deletions

diff --git a/ruby/lib/gitlab/git/repository.rb b/ruby/lib/gitlab/git/repository.rb
index a05c25757..fa457cf92 100644
--- a/ruby/lib/gitlab/git/repository.rb
+++ b/ruby/lib/gitlab/git/repository.rb
@@ -440,6 +440,14 @@ module Gitlab
         rugged&.close if defined?(@rugged)
       end
 
+      def head_symbolic_ref
+        message, status = run_git(%w[symbolic-ref HEAD])
+
+        return 'main' if status.nonzero?
+
+        Ref.extract_branch_name(message.squish)
+      end
+
       private
 
       def sparse_checkout_empty?(output)
diff --git a/ruby/lib/gitlab/git/wiki.rb b/ruby/lib/gitlab/git/wiki.rb
index 452351afd..506b4489f 100644
--- a/ruby/lib/gitlab/git/wiki.rb
+++ b/ruby/lib/gitlab/git/wiki.rb
@@ -60,11 +60,18 @@ module Gitlab
       end
 
       def gollum_wiki
-        @gollum_wiki ||= Gollum::Wiki.new(@repository.path)
+        options = {}
+        options[:ref] = gollum_default_ref if gollum_default_ref
+
+        @gollum_wiki ||= Gollum::Wiki.new(@repository.path, options)
       end
 
       private
 
+      def gollum_default_ref
+        @gollum_default_ref ||= @repository.root_ref || @repository.head_symbolic_ref
+      end
+
       def new_page(gollum_page)
         Gitlab::Git::WikiPage.new(gollum_page, new_version(gollum_page, gollum_page.version.id))
       end
diff --git a/ruby/spec/lib/gitlab/git/repository_spec.rb b/ruby/spec/lib/gitlab/git/repository_spec.rb
index 70899d4c7..6bbf4bcff 100644
--- a/ruby/spec/lib/gitlab/git/repository_spec.rb
+++ b/ruby/spec/lib/gitlab/git/repository_spec.rb
@@ -470,6 +470,24 @@ describe Gitlab::Git::Repository do # rubocop:disable Metrics/BlockLength
     end
   end
 
+  describe '#head_symbolic_ref' do
+    subject { repository.head_symbolic_ref }
+
+    it 'returns the symbolic ref in HEAD' do
+      expect(subject).to eq('master')
+    end
+
+    context 'when repo is empty' do
+      let(:repository) { gitlab_git_from_gitaly(new_empty_test_repo) }
+
+      it 'returns the symbolic ref in HEAD' do
+        repository.rugged.head = 'refs/heads/foo'
+
+        expect(subject).to eq('foo')
+      end
+    end
+  end
+
   def create_remote_branch(remote_name, branch_name, source_branch_name)
     source_branch = repository.branches.find { |branch| branch.name == source_branch_name }
     repository_rugged.references.create("refs/remotes/#{remote_name}/#{branch_name}", source_branch.dereferenced_target.sha)
diff --git a/ruby/spec/lib/gitlab/git/wiki_spec.rb b/ruby/spec/lib/gitlab/git/wiki_spec.rb
index aca0f0dee..9240ed62c 100644
--- a/ruby/spec/lib/gitlab/git/wiki_spec.rb
+++ b/ruby/spec/lib/gitlab/git/wiki_spec.rb
@@ -132,6 +132,38 @@ describe Gitlab::Git::Wiki do
     end
   end
 
+  describe '#gollum_wiki' do
+    context 'when repository is empty' do
+      it 'instantiates the gollum wiki with the repo symbolic ref' do
+        repository.rugged.head = 'refs/heads/foo'
+
+        expect(Gollum::Wiki).to receive(:new).with(repository.path, hash_including(ref: 'foo'))
+
+        subject.gollum_wiki
+      end
+    end
+
+    context 'when repository is not empty' do
+      let(:repository) { gitlab_git_from_gitaly(new_mutable_git_test_repo) }
+
+      it 'instantiates the gollum wiki with the repo root_ref' do
+        expect(Gollum::Wiki).to receive(:new).with(repository.path, hash_including(ref: repository.root_ref))
+
+        subject.gollum_wiki
+      end
+    end
+
+    context 'when symbolic ref and root ref cannot be found' do
+      it 'instantiates the gollum wiki without any ref' do
+        allow(subject).to receive(:gollum_default_ref).and_return(nil)
+
+        expect(Gollum::Wiki).to receive(:new).with(repository.path, {})
+
+        subject.gollum_wiki
+      end
+    end
+  end
+
   def create_page(name, content)
     subject.write_page(name, :markdown, content, commit_details(name))
   end