Merge branch 'feature/fork-to-group-api' into 'master'

API: Add the ability to fork to a specific namespace

Browser interface allows forking to an owned grup.
This commit brings API up to speed by providing optional namespace
parameter to fork API. This allows forking to users and groups under
forker's control using their id or unique name.

Fixes #21591 

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !6213

4 files changed, 85 insertions, 3 deletions

diff --git a/CHANGELOG b/CHANGELOG
index 17388615908..2af2056979d 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,7 @@
 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.12.0 (unreleased)
+  - Add ability to fork to a specific namespace using API. (ritave)
   - Cleanup misalignments in Issue list view !6206
   - Prepend blank line to `Closes` message on merge request linked to issue (lukehowell)
   - Filter tags by name !6121
diff --git a/doc/api/projects.md b/doc/api/projects.md
index a62aaee14d7..fe3c8709d13 100644
--- a/doc/api/projects.md
+++ b/doc/api/projects.md
@@ -514,7 +514,7 @@ invalid, 400 is returned.
 
 ### Fork project
 
-Forks a project into the user namespace of the authenticated user.
+Forks a project into the user namespace of the authenticated user or the one provided.
 
 ```
 POST /projects/fork/:id
@@ -523,6 +523,7 @@ POST /projects/fork/:id
 Parameters:
 
 - `id` (required) - The ID or NAMESPACE/PROJECT_NAME of the project to be forked
+- `namespace` (optional) - The ID or path of the namespace that the project will be forked to
 
 ### Star a project
 
diff --git a/lib/api/projects.rb b/lib/api/projects.rb
index a1fd598414a..4033f597859 100644
--- a/lib/api/projects.rb
+++ b/lib/api/projects.rb
@@ -189,16 +189,30 @@ module API
         end
       end
 
-      # Fork new project for the current user.
+      # Fork new project for the current user or provided namespace.
       #
       # Parameters:
       #   id (required) - The ID of a project
+      #   namespace (optional) - The ID or name of the namespace that the project will be forked into.
       # Example Request
       #   POST /projects/fork/:id
       post 'fork/:id' do
+        attrs = {}
+        namespace_id = params[:namespace]
+
+        if namespace_id.present?
+          namespace = Namespace.find_by(id: namespace_id) || Namespace.find_by_path_or_name(namespace_id)
+
+          not_found!('Target Namespace') unless namespace
+
+          attrs[:namespace] = namespace
+        end
+
         @forked_project =
           ::Projects::ForkService.new(user_project,
-                                      current_user).execute
+                                      current_user,
+                                      attrs).execute
+
         if @forked_project.errors.any?
           conflict!(@forked_project.errors.messages)
         else
diff --git a/spec/requests/api/fork_spec.rb b/spec/requests/api/fork_spec.rb
index f802fcd2d2e..06e3a2183c0 100644
--- a/spec/requests/api/fork_spec.rb
+++ b/spec/requests/api/fork_spec.rb
@@ -6,6 +6,12 @@ describe API::API, api: true  do
   let(:user2) { create(:user) }
   let(:user3) { create(:user) }
   let(:admin) { create(:admin) }
+  let(:group) { create(:group) }
+  let(:group2) do
+    group = create(:group, name: 'group2_name')
+    group.add_owner(user2)
+    group
+  end
 
   let(:project) do
     create(:project, creator_id: user.id, namespace: user.namespace)
@@ -22,6 +28,7 @@ describe API::API, api: true  do
     context 'when authenticated' do
       it 'forks if user has sufficient access to project' do
         post api("/projects/fork/#{project.id}", user2)
+
         expect(response).to have_http_status(201)
         expect(json_response['name']).to eq(project.name)
         expect(json_response['path']).to eq(project.path)
@@ -32,6 +39,7 @@ describe API::API, api: true  do
 
       it 'forks if user is admin' do
         post api("/projects/fork/#{project.id}", admin)
+
         expect(response).to have_http_status(201)
         expect(json_response['name']).to eq(project.name)
         expect(json_response['path']).to eq(project.path)
@@ -42,12 +50,14 @@ describe API::API, api: true  do
 
       it 'fails on missing project access for the project to fork' do
         post api("/projects/fork/#{project.id}", user3)
+
         expect(response).to have_http_status(404)
         expect(json_response['message']).to eq('404 Project Not Found')
       end
 
       it 'fails if forked project exists in the user namespace' do
         post api("/projects/fork/#{project.id}", user)
+
         expect(response).to have_http_status(409)
         expect(json_response['message']['name']).to eq(['has already been taken'])
         expect(json_response['message']['path']).to eq(['has already been taken'])
@@ -55,14 +65,70 @@ describe API::API, api: true  do
 
       it 'fails if project to fork from does not exist' do
         post api('/projects/fork/424242', user)
+
         expect(response).to have_http_status(404)
         expect(json_response['message']).to eq('404 Project Not Found')
       end
+
+      it 'forks with explicit own user namespace id' do
+        post api("/projects/fork/#{project.id}", user2), namespace: user2.namespace.id
+
+        expect(response).to have_http_status(201)
+        expect(json_response['owner']['id']).to eq(user2.id)
+      end
+
+      it 'forks with explicit own user name as namespace' do
+        post api("/projects/fork/#{project.id}", user2), namespace: user2.username
+
+        expect(response).to have_http_status(201)
+        expect(json_response['owner']['id']).to eq(user2.id)
+      end
+
+      it 'forks to another user when admin' do
+        post api("/projects/fork/#{project.id}", admin), namespace: user2.username
+
+        expect(response).to have_http_status(201)
+        expect(json_response['owner']['id']).to eq(user2.id)
+      end
+
+      it 'fails if trying to fork to another user when not admin' do
+        post api("/projects/fork/#{project.id}", user2), namespace: admin.namespace.id
+
+        expect(response).to have_http_status(409)
+      end
+
+      it 'fails if trying to fork to non-existent namespace' do
+        post api("/projects/fork/#{project.id}", user2), namespace: 42424242
+
+        expect(response).to have_http_status(404)
+        expect(json_response['message']).to eq('404 Target Namespace Not Found')
+      end
+
+      it 'forks to owned group' do
+        post api("/projects/fork/#{project.id}", user2), namespace: group2.name
+
+        expect(response).to have_http_status(201)
+        expect(json_response['namespace']['name']).to eq(group2.name)
+      end
+
+      it 'fails to fork to not owned group' do
+        post api("/projects/fork/#{project.id}", user2), namespace: group.name
+
+        expect(response).to have_http_status(409)
+      end
+
+      it 'forks to not owned group when admin' do
+        post api("/projects/fork/#{project.id}", admin), namespace: group.name
+
+        expect(response).to have_http_status(201)
+        expect(json_response['namespace']['name']).to eq(group.name)
+      end
     end
 
     context 'when unauthenticated' do
       it 'returns authentication error' do
         post api("/projects/fork/#{project.id}")
+
         expect(response).to have_http_status(401)
         expect(json_response['message']).to eq('401 Unauthorized')
       end