Update language only on HEAD of the repository

app/services/git_push_service.rb

@@ -55,6 +55,9 @@ class GitPushService < BaseService
   end
 
   def update_main_language
+    return unless is_default_branch?
+    return unless push_to_new_branch? || push_to_existing_branch?
+
     current_language = @project.repository.main_language
 
     unless current_language == @project.main_language

spec/services/git_push_service_spec.rb

@@ -159,18 +159,28 @@ describe GitPushService, services: true do
   end
 
   describe "Updates main language" do
-
     context "before push" do
       it { expect(project.main_language).to eq(nil) }
     end
 
     context "after push" do
       before do
-        @service = execute_service(project, user, @oldrev, @newrev, @ref)
+        @service = execute_service(project, user, @oldrev, @newrev, ref)
+      end
+
+      context "to master" do
+        let(:ref) { @ref }
+
+        it { expect(@service.update_main_language).to eq(true) }
+        it { expect(project.main_language).to eq("Ruby") }
       end
 
-      it { expect(@service.update_main_language).to eq(true) }
-      it { expect(project.main_language).to eq("Ruby") }
+      context "to other branch" do
+        let(:ref) { 'refs/heads/feature/branch' }
+
+        it { expect(@service.update_main_language).to eq(nil) }
+        it { expect(project.main_language).to eq(nil) }
+      end
     end
   end