Allow setting of feature gates per project

For features the feature gates are sometimes projects, not groups or
users. For example for git object pools:
https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5872

This commit allows for setting feature group gates based on projects, by its
path as that seems most convenient.

changelogs/unreleased/zj-feature-gate-set-project-path.yml

+---
+title: Allow setting of feature gates per project
+merge_request: 24184
+author:
+type: added

doc/api/features.md

@@ -60,9 +60,10 @@ POST /features/:name
 | `value` | integer/string | yes | `true` or `false` to enable/disable, or an integer for percentage of time |
 | `feature_group` | string | no | A Feature group name |
 | `user` | string | no | A GitLab username |
+| `project` | string | no | A projects path, for example 'gitlab-org/gitlab-ce' |
 
-Note that you can enable or disable a feature for both a `feature_group` and a
-`user` with a single API call.
+Note that you can enable or disable a feature for a `feature_group`, a `user`,
+and a `project` in a single API call.
 
 ```bash
 curl --data "value=30" --header "PRIVATE-TOKEN: <your_access_token>" https://gitlab.example.com/api/v4/features/new_library

lib/api/features.rb

@@ -16,15 +16,13 @@ module API
         end
       end
 
-      # rubocop: disable CodeReuse/ActiveRecord
       def gate_targets(params)
-        targets = []
-        targets << Feature.group(params[:feature_group]) if params[:feature_group]
-        targets << UserFinder.new(params[:user]).find_by_username if params[:user]
+        Feature::Target.new(params).targets
+      end
 
-        targets
+      def gate_specified?(params)
+        Feature::Target.new(params).gate_specified?
       end
-      # rubocop: enable CodeReuse/ActiveRecord
     end
 
     resource :features do
@@ -44,6 +42,7 @@ module API
         requires :value, type: String, desc: '`true` or `false` to enable/disable, an integer for percentage of time'
         optional :feature_group, type: String, desc: 'A Feature group name'
         optional :user, type: String, desc: 'A GitLab username'
+        optional :project, type: String, desc: 'A projects path, like gitlab-org/gitlab-ce'
       end
       post ':name' do
         feature = Feature.get(params[:name])
@@ -52,13 +51,13 @@ module API
 
         case value
         when true
-          if targets.present?
+          if gate_specified?(params)
             targets.each { |target| feature.enable(target) }
           else
             feature.enable
           end
         when false
-          if targets.present?
+          if gate_specified?(params)
             targets.each { |target| feature.disable(target) }
           else
             feature.disable

lib/feature.rb

@@ -102,4 +102,42 @@ class Feature
         expires_in: 1.hour)
     end
   end
+
+  class Target
+    attr_reader :params
+
+    def initialize(params)
+      @params = params
+    end
+
+    def gate_specified?
+      %i(user project feature_group).any? { |key| params.key?(key) }
+    end
+
+    def targets
+      [feature_group, user, project].compact
+    end
+
+    private
+
+    # rubocop: disable CodeReuse/ActiveRecord
+    def feature_group
+      return unless params.key?(:feature_group)
+
+      Feature.group(params[:feature_group])
+    end
+    # rubocop: enable CodeReuse/ActiveRecord
+
+    def user
+      return unless params.key?(:user)
+
+      UserFinder.new(params[:user]).find_by_username!
+    end
+
+    def project
+      return unless params.key?(:project)
+
+      Project.find_by_full_path(params[:project])
+    end
+  end
 end

spec/lib/feature_spec.rb

@@ -182,4 +182,18 @@ describe Feature do
       expect(described_class.disabled?(:enabled_feature_flag)).to be_falsey
     end
   end
+
+  describe Feature::Target do
+    describe '#targets' do
+      let(:project) { create(:project) }
+      let(:user_name) { project.owner.username }
+
+      subject { described_class.new(user: user_name, project: project.full_path) }
+
+      it 'returns all found targets' do
+        expect(subject.targets).to be_an(Array)
+        expect(subject.targets).to eq([project.owner, project])
+      end
+    end
+  end
 end

spec/requests/api/features_spec.rb

@@ -129,6 +129,40 @@ describe API::Features do
         end
       end
 
+      context 'when enabling for a project by path' do
+        context 'when the project exists' do
+          let!(:project) { create(:project) }
+
+          it 'sets the feature gate' do
+            post api("/features/#{feature_name}", admin), params: { value: 'true', project: project.full_path }
+
+            expect(response).to have_gitlab_http_status(201)
+            expect(json_response).to eq(
+              'name' => 'my_feature',
+              'state' => 'conditional',
+              'gates' => [
+                { 'key' => 'boolean', 'value' => false },
+                { 'key' => 'actors', 'value' => ["Project:#{project.id}"] }
+              ])
+          end
+        end
+
+        context 'when the project does not exist' do
+          it 'sets no new values' do
+            post api("/features/#{feature_name}", admin), params: { value: 'true', project: 'mep/to/the/mep/mep' }
+
+            expect(response).to have_gitlab_http_status(201)
+            expect(json_response).to eq(
+              "name" => "my_feature",
+              "state" => "off",
+              "gates" => [
+                { "key" => "boolean", "value" => false }
+              ]
+            )
+          end
+        end
+      end
+
       it 'creates a feature with the given percentage if passed an integer' do
         post api("/features/#{feature_name}", admin), params: { value: '50' }