Fix project creation with templates using /projects/user/:id API

Previously creation with an instance or group template with POST
`/api/v4/projects worked`, but `/api/v4/projects/user/:id` did not
because the latter did not accept the `use_custom_templates` parameter
due to an oversight.

This commit fixes this by adding the `optional_create_project_params`
Grape API and add tests for project creation via the user endpoint.

Closes https://gitlab.com/gitlab-org/gitlab/issues/37004

changelogs/unreleased/sh-fix-api-project-template-creation.yml

+---
+title: Fix project creation with templates using /projects/user/:id API
+merge_request: 20590
+author:
+type: fixed

ee/spec/requests/api/projects_spec.rb

@@ -182,7 +182,11 @@ describe API::Projects do
     end
   end
 
-  describe 'POST /projects' do
+  # Assumes the following variables are defined:
+  # group
+  # project
+  # new_project_name
+  # api_call
   shared_examples 'creates projects with templates' do
     before do
       group.add_maintainer(user)
@@ -194,8 +198,7 @@ describe API::Projects do
       expect(ProjectExportWorker).to receive(:perform_async).and_call_original
 
       Sidekiq::Testing.fake! do
-          expect { post api('/projects', user), params: project_params }
-            .to change { Project.count }.by(1)
+        expect { api_call }.to change { Project.count }.by(1)
       end
 
       expect(response).to have_gitlab_http_status(201)
@@ -208,8 +211,7 @@ describe API::Projects do
       project_params.delete(:template_project_id)
       project_params[:template_name] = 'bogus-template'
 
-        expect { post api('/projects', user), params: project_params }
-          .not_to change { Project.count }
+      expect { api_call }.not_to change { Project.count }
 
       expect(response).to have_gitlab_http_status(400)
       expect(json_response['message']['template_name']).to eq(["'bogus-template' is unknown or invalid"])
@@ -220,20 +222,22 @@ describe API::Projects do
       new_project = create(:project)
       project_params[:template_project_id] = new_project.id
 
-        expect { post api('/projects', user), params: project_params }
-          .not_to change { Project.count }
+      expect { api_call }.not_to change { Project.count }
 
       expect(response).to have_gitlab_http_status(400)
       expect(json_response['message']['template_project_id']).to eq(["#{new_project.id} is unknown or invalid"])
     end
   end
 
-    context 'with instance-level templates' do
+  shared_context 'base instance template models' do
     let(:group) { create(:group) }
     let!(:project) { create(:project, :public, namespace: group) }
     let(:new_project_name) { "project-#{SecureRandom.hex}" }
+  end
+
+  shared_context 'instance template name' do
+    include_context 'base instance template models'
 
-      context 'using template name' do
     let(:project_params) do
       {
         template_name: project.name,
@@ -243,11 +247,11 @@ describe API::Projects do
         namespace_id: group.id
       }
     end
-
-        it_behaves_like 'creates projects with templates'
   end
 
-      context 'using template project ID' do
+  shared_context 'instance template ID' do
+    include_context 'base instance template models'
+
     let(:project_params) do
       {
         template_project_id: project.id,
@@ -257,19 +261,19 @@ describe API::Projects do
         namespace_id: group.id
       }
     end
-
-        it_behaves_like 'creates projects with templates'
-      end
   end
 
-    context 'with group templates' do
+  shared_context 'base group template models' do
     let(:parent_group) { create(:group) }
     let(:subgroup) { create(:group, :public, parent: parent_group) }
     let(:group) { subgroup }
     let!(:project) { create(:project, :public, namespace: subgroup) }
     let(:new_project_name) { "project-#{SecureRandom.hex}" }
+  end
+
+  shared_context 'group template name' do
+    include_context 'base group template models'
 
-      context 'using template name' do
     let(:project_params) do
       {
         template_name: project.name,
@@ -280,11 +284,11 @@ describe API::Projects do
         namespace_id: subgroup.id
       }
     end
-
-        it_behaves_like 'creates projects with templates'
   end
 
-      context 'using template project ID' do
+  shared_context 'group template ID' do
+    include_context 'base group template models'
+
     let(:project_params) do
       {
         template_project_id: project.id,
@@ -295,7 +299,48 @@ describe API::Projects do
         namespace_id: subgroup.id
       }
     end
+  end
+
+  describe 'POST /projects/user/:id' do
+    let(:admin) { create(:admin) }
+    let(:api_call) { post api("/projects/user/#{user.id}", admin), params: project_params }
+
+    context 'with templates' do
+      include_context 'instance template name' do
+        it_behaves_like 'creates projects with templates'
+      end
+
+      include_context 'instance template ID' do
+        it_behaves_like 'creates projects with templates'
+      end
+
+      include_context 'group template name' do
+        it_behaves_like 'creates projects with templates'
+      end
+
+      include_context 'group template ID' do
+        it_behaves_like 'creates projects with templates'
+      end
+    end
+  end
+
+  describe 'POST /projects' do
+    let(:api_call) { post api('/projects', user), params: project_params }
+
+    context 'with templates' do
+      include_context 'instance template name' do
+        it_behaves_like 'creates projects with templates'
+      end
+
+      include_context 'instance template ID' do
+        it_behaves_like 'creates projects with templates'
+      end
+
+      include_context 'group template name' do
+        it_behaves_like 'creates projects with templates'
+      end
 
+      include_context 'group template ID' do
         it_behaves_like 'creates projects with templates'
       end
     end

lib/api/projects.rb

@@ -191,6 +191,7 @@ module API
         optional :path, type: String, desc: 'The path of the repository'
         optional :default_branch, type: String, desc: 'The default branch of the project'
         use :optional_project_params
+        use :optional_create_project_params
         use :create_params
       end
       # rubocop: disable CodeReuse/ActiveRecord