Add client methods for DisconnectGitAlternates rpc

DisconnectGitAlternates is a Gitaly RPC that will delete a repository's
objects/info/alternates file. This commit adds client support for that
RPC.

lib/gitlab/git/repository.rb

@@ -922,6 +922,12 @@ module Gitlab
         end
       end
 
+      def disconnect_alternates
+        wrapped_gitaly_errors do
+          gitaly_repository_client.disconnect_alternates
+        end
+      end
+
       def gitaly_repository
         Gitlab::GitalyClient::Util.repository(@storage, @relative_path, @gl_repository, @gl_project_path)
       end

lib/gitlab/gitaly_client/repository_service.rb

@@ -331,6 +331,14 @@ module Gitlab
         search_results_from_response(response)
       end
 
+      def disconnect_alternates
+        request = Gitaly::DisconnectGitAlternatesRequest.new(
+          repository: @gitaly_repo
+        )
+
+        GitalyClient.call(@storage, :object_pool_service, :disconnect_git_alternates, request)
+      end
+
       private
 
       def search_results_from_response(gitaly_response)

spec/lib/gitlab/git/object_pool_spec.rb

@@ -7,8 +7,6 @@ describe Gitlab::Git::ObjectPool do
 
   let(:pool_repository) { create(:pool_repository) }
   let(:source_repository) { pool_repository.source_project.repository }
-  let(:source_repository_path) { File.join(TestEnv.repos_path, source_repository.relative_path) }
-  let(:source_repository_rugged) { Rugged::Repository.new(source_repository_path) }
 
   subject { pool_repository.object_pool }
 
@@ -82,6 +80,8 @@ describe Gitlab::Git::ObjectPool do
   end
 
   describe '#fetch' do
+    let(:source_repository_path) { File.join(TestEnv.repos_path, source_repository.relative_path) }
+    let(:source_repository_rugged) { Rugged::Repository.new(source_repository_path) }
     let(:commit_count) { source_repository.commit_count }
 
     context "when the object's pool repository exists" do
@@ -98,7 +98,7 @@ describe Gitlab::Git::ObjectPool do
       it "re-creates the object pool's repository" do
         subject.fetch
 
-        expect(subject.repository.exists?).to be(true)
+        expect(subject.repository.exists?).to be true
       end
 
       it 'does not raise an error' do

spec/lib/gitlab/git/repository_spec.rb

@@ -2215,4 +2215,43 @@ describe Gitlab::Git::Repository, :seed_helper do
       line.split("\t").last
     end
   end
+
+  describe '#disconnect_alternates' do
+    let(:project) { create(:project, :repository) }
+    let(:pool_repository) { create(:pool_repository) }
+    let(:repository) { project.repository }
+    let(:repository_path) { File.join(TestEnv.repos_path, repository.relative_path) }
+    let(:object_pool) { pool_repository.object_pool }
+    let(:object_pool_path) { File.join(TestEnv.repos_path, object_pool.repository.relative_path) }
+    let(:object_pool_rugged) { Rugged::Repository.new(object_pool_path) }
+
+    before do
+      object_pool.create
+    end
+
+    it 'does not raise an error when disconnecting a non-linked repository' do
+      expect { repository.disconnect_alternates }.not_to raise_error
+    end
+
+    it 'removes the alternates file' do
+      object_pool.link(repository)
+
+      alternates_file = File.join(repository_path, "objects", "info", "alternates")
+      expect(File.exist?(alternates_file)).to be_truthy
+
+      repository.disconnect_alternates
+
+      expect(File.exist?(alternates_file)).to be_falsey
+    end
+
+    it 'can still access objects in the object pool' do
+      object_pool.link(repository)
+      new_commit = new_commit_edit_old_file(object_pool_rugged)
+      expect(repository.commit(new_commit.oid).id).to eq(new_commit.oid)
+
+      repository.disconnect_alternates
+
+      expect(repository.commit(new_commit.oid).id).to eq(new_commit.oid)
+    end
+  end
 end

spec/lib/gitlab/gitaly_client/repository_service_spec.rb

@@ -231,4 +231,34 @@ describe Gitlab::GitalyClient::RepositoryService do
       client.raw_changes_between('deadbeef', 'deadpork')
     end
   end
+
+  describe '#disconnect_alternates' do
+    let(:project) { create(:project, :repository) }
+    let(:repository) { project.repository }
+    let(:repository_path) { File.join(TestEnv.repos_path, repository.relative_path) }
+    let(:pool_repository) { create(:pool_repository) }
+    let(:object_pool) { pool_repository.object_pool }
+    let(:object_pool_service) { Gitlab::GitalyClient::ObjectPoolService.new(object_pool) }
+
+    before do
+      object_pool_service.create(repository)
+      object_pool_service.link_repository(repository)
+    end
+
+    it 'deletes the alternates file' do
+      repository.disconnect_alternates
+
+      alternates_file = File.join(repository_path, "objects", "info", "alternates")
+
+      expect(File.exist?(alternates_file)).to be_falsey
+    end
+
+    context 'when called twice' do
+      it "doesn't raise an error" do
+        repository.disconnect_alternates
+
+        expect { repository.disconnect_alternates }.not_to raise_error
+      end
+    end
+  end
 end