Doesn't synchronize default branch for push mirrors

We should not synchronize the source repository with
the target root ref while updating a push mirror.

app/models/project.rb

@@ -2076,12 +2076,6 @@ class Project < ActiveRecord::Base
     auto_cancel_pending_pipelines == 'enabled'
   end
-  # Update the default branch querying the remote to determine its HEAD
-  def update_root_ref(remote_name)
-    root_ref = repository.find_remote_root_ref(remote_name)
-    change_head(root_ref) if root_ref.present? && root_ref != default_branch
-  end
-
   private
   # rubocop: disable CodeReuse/ServiceClass

app/models/repository.rb

@@ -24,7 +24,6 @@ class Repository
   delegate :ref_name_for_sha, to: :raw_repository
   delegate :bundle_to_disk, to: :raw_repository
-  delegate :find_remote_root_ref, to: :raw_repository
   CreateTreeError = Class.new(StandardError)

app/services/projects/update_remote_mirror_service.rb

@@ -12,7 +12,6 @@ module Projects
       begin
         remote_mirror.ensure_remote!
         repository.fetch_remote(remote_mirror.remote_name, no_tags: true)
-        project.update_root_ref(remote_mirror.remote_name)
         opts = {}
         if remote_mirror.only_protected_branches?

spec/models/project_spec.rb

@@ -3983,40 +3983,6 @@ describe Project do
     end
   end
-  describe '#update_root_ref' do
-    let(:project) { create(:project, :repository) }
-
-    it 'updates the default branch when HEAD has changed' do
-      stub_find_remote_root_ref(project, ref: 'feature')
-
-      expect { project.update_root_ref('origin') }
-        .to change { project.default_branch }
-        .from('master')
-        .to('feature')
-    end
-
-    it 'does not update the default branch when HEAD does not change' do
-      stub_find_remote_root_ref(project, ref: 'master')
-
-      expect { project.update_root_ref('origin') }
-        .not_to change { project.default_branch }
-    end
-
-    it 'does not update the default branch when HEAD does not exist' do
-      stub_find_remote_root_ref(project, ref: 'foo')
-
-      expect { project.update_root_ref('origin') }
-        .not_to change { project.default_branch }
-    end
-
-    def stub_find_remote_root_ref(project, ref:)
-      allow(project.repository)
-        .to receive(:find_remote_root_ref)
-        .with('origin')
-        .and_return(ref)
-    end
-  end
-
   def rugged_config
     Gitlab::GitalyClient::StorageSettings.allow_disk_access do
       project.repository.rugged.config

spec/services/projects/update_remote_mirror_service_spec.rb

@@ -17,7 +17,6 @@ describe Projects::UpdateRemoteMirrorService do
     it "ensures the remote exists" do
       stub_fetch_remote(project, remote_name: remote_name)
-      stub_find_remote_root_ref(project, remote_name: remote_name)
       expect(remote_mirror).to receive(:ensure_remote!)
@@ -25,8 +24,6 @@ describe Projects::UpdateRemoteMirrorService do
     end
     it "fetches the remote repository" do
-      stub_find_remote_root_ref(project, remote_name: remote_name)
-
       expect(project.repository)
         .to receive(:fetch_remote)
         .with(remote_mirror.remote_name, no_tags: true)
@@ -34,26 +31,8 @@ describe Projects::UpdateRemoteMirrorService do
       service.execute(remote_mirror)
     end
-    it "updates the default branch when HEAD has changed" do
-      stub_fetch_remote(project, remote_name: remote_name)
-      stub_find_remote_root_ref(project, remote_name: remote_name, ref: "existing-branch")
-
-      expect { service.execute(remote_mirror) }
-        .to change { project.default_branch }
-        .from("master")
-        .to("existing-branch")
-    end
-
-    it "does not update the default branch when HEAD does not change" do
-      stub_fetch_remote(project, remote_name: remote_name)
-      stub_find_remote_root_ref(project, remote_name: remote_name, ref: "master")
-
-      expect { service.execute(remote_mirror) }.not_to change { project.default_branch }
-    end
-
     it "returns success when updated succeeds" do
       stub_fetch_remote(project, remote_name: remote_name)
-      stub_find_remote_root_ref(project, remote_name: remote_name)
       result = service.execute(remote_mirror)
@@ -63,7 +42,6 @@ describe Projects::UpdateRemoteMirrorService do
     context 'when syncing all branches' do
       it "push all the branches the first time" do
         stub_fetch_remote(project, remote_name: remote_name)
-        stub_find_remote_root_ref(project, remote_name: remote_name)
         expect(remote_mirror).to receive(:update_repository).with({})
@@ -74,7 +52,6 @@ describe Projects::UpdateRemoteMirrorService do
     context 'when only syncing protected branches' do
       it "sync updated protected branches" do
         stub_fetch_remote(project, remote_name: remote_name)
-        stub_find_remote_root_ref(project, remote_name: remote_name)
         protected_branch = create_protected_branch(project)
         remote_mirror.only_protected_branches = true
@@ -92,13 +69,6 @@ describe Projects::UpdateRemoteMirrorService do
     end
   end
-  def stub_find_remote_root_ref(project, ref: 'master', remote_name:)
-    allow(project.repository)
-      .to receive(:find_remote_root_ref)
-      .with(remote_name)
-      .and_return(ref)
-  end
-
   def stub_fetch_remote(project, remote_name:)
     allow(project.repository)
       .to receive(:fetch_remote)