From 61ce86c7f1b4d64ed0cc2ee970337f61622deab6 Mon Sep 17 00:00:00 2001
From: Vasilii Iakliushin <viakliushin@gitlab.com>
Date: Mon, 15 Sep 2025 11:24:58 +0200
Subject: [PATCH] Support full refs in `default_branch` for Projects API
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Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/516857

**Problem**

The Projects API doesn’t support full references for the
`default_branch` setting when creating a project via the Projects API.
This leads to a non-initialized state.

**Solution**

Allow the `default_branch` parameter to accept fully qualified
references (e.g., refs/heads/main) and automatically convert them to
branch names (e.g., main).

Changelog: fixed
---
 app/services/projects/create_service.rb       |  4 +++-
 spec/requests/api/projects_spec.rb            | 13 ++++++++++++
 spec/services/projects/create_service_spec.rb | 21 +++++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/app/services/projects/create_service.rb b/app/services/projects/create_service.rb
index aaa69597d09b4f..64761d659607ee 100644
--- a/app/services/projects/create_service.rb
+++ b/app/services/projects/create_service.rb
@@ -319,7 +319,9 @@ def extra_attributes_for_measurement
     private
 
     def default_branch
-      @default_branch.presence || @project.default_branch_or_main
+      return @project.default_branch_or_main if @default_branch.blank?
+
+      Gitlab::Git.ref_name(@default_branch)
     end
 
     def validate_import_source_enabled!
diff --git a/spec/requests/api/projects_spec.rb b/spec/requests/api/projects_spec.rb
index fc996a063dfad7..07d03234bf7ce0 100644
--- a/spec/requests/api/projects_spec.rb
+++ b/spec/requests/api/projects_spec.rb
@@ -134,6 +134,19 @@
       end
     end
 
+    context 'when branch name is fully qualified' do
+      let(:default_branch) { 'refs/heads/full_name' }
+
+      it 'creates project with provided default branch name without refs/heads prefix' do
+        expect { request }.to change { Project.count }.by(1)
+        expect(response).to have_gitlab_http_status(:created)
+
+        project = Project.find(json_response['id'])
+        expect(project.repository_exists?).to be_truthy
+        expect(project.default_branch).to eq('full_name')
+      end
+    end
+
     context 'when initialize with readme is not set' do
       let(:params) { super().merge(initialize_with_readme: nil) }
 
diff --git a/spec/services/projects/create_service_spec.rb b/spec/services/projects/create_service_spec.rb
index c853bc654f200f..6e551bd7c827af 100644
--- a/spec/services/projects/create_service_spec.rb
+++ b/spec/services/projects/create_service_spec.rb
@@ -875,6 +875,27 @@ def wiki_repo(project)
         end
       end
     end
+
+    context 'when default branch is a fully qualified ref' do
+      before do
+        opts[:default_branch] = 'refs/heads/example_branch'
+      end
+
+      it 'creates the correct branch' do
+        expect(project.repository.branch_names).to contain_exactly('example_branch')
+      end
+
+      it_behaves_like 'a repo with a README.md' do
+        let(:expected_content) do
+          <<~MARKDOWN
+            cd existing_repo
+            git remote add origin #{project.http_url_to_repo}
+            git branch -M example_branch
+            git push -uf origin example_branch
+          MARKDOWN
+        end
+      end
+    end
   end
 
   context 'when SAST initialization is requested' do
-- 
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