Render stage dropdown in separate API call as HTML

```
Endpoint: /group/project/pipelines/id/stage.json?stage=name

Call: stage_namespace_project_pipeline_path(pipeline.project.namespace, pipeline.project, pipeline, stage: stage.name)
```

1 files changed, 12 insertions, 0 deletions

diff --git a/app/controllers/projects/pipelines_controller.rb b/app/controllers/projects/pipelines_controller.rb
index 85188cfdd4c..0147072b0f1 100644
--- a/app/controllers/projects/pipelines_controller.rb
+++ b/app/controllers/projects/pipelines_controller.rb
@@ -8,6 +8,7 @@ class Projects::PipelinesController < Projects::ApplicationController
   def index
     @scope = params[:scope]
     @pipelines = PipelinesFinder.new(project).execute(scope: @scope).page(params[:page]).per(30)
+    @pipelines = @pipelines.includes(project: :namespace)
 
     @running_or_pending_count = PipelinesFinder.new(project).execute(scope: 'running').count
     @pipelines_count = PipelinesFinder.new(project).execute.count
@@ -40,6 +41,17 @@ class Projects::PipelinesController < Projects::ApplicationController
     end
   end
 
+  def stage
+    @stage = pipeline.stages.find do |stage|
+      stage.name == params[:stage]
+    end
+    return not_found unless @stage
+
+    respond_to do |format|
+      format.json { render json: { html: view_to_html_string('projects/pipelines/_stage') } }
+    end
+  end
+
   def retry
     pipeline.retry_failed(current_user)