Merge branch 'i-#25814-500-error' into 'master'

app/controllers/projects/compare_controller.rb

@@ -25,8 +25,17 @@ class Projects::CompareController < Projects::ApplicationController
   end
 
   def create
-    redirect_to namespace_project_compare_path(@project.namespace, @project,
+    if params[:from].blank? || params[:to].blank?
+      flash[:alert] = "You must select from and to branches"
+      from_to_vars = {
+        from: params[:from].presence,
+        to: params[:to].presence
+      }
+      redirect_to namespace_project_compare_index_path(@project.namespace, @project, from_to_vars)
+    else
+      redirect_to namespace_project_compare_path(@project.namespace, @project,
                                                params[:from], params[:to])
+    end
   end
 
   private

changelogs/unreleased/i--25814-500-error.yml

+---
+title: Fix Compare page throws 500 error when any branch/reference is not selected
+merge_request: 8492
+author: Martin Cabrera

spec/controllers/projects/compare_controller_spec.rb

@@ -64,6 +64,36 @@ describe Projects::CompareController do
       expect(assigns(:diffs)).to eq(nil)
       expect(assigns(:commits)).to eq(nil)
     end
+
+    it 'redirects back to index when params[:from] is empty and preserves params[:to]' do
+      post(:create,
+           namespace_id: project.namespace.to_param,
+           project_id: project.to_param,
+           from: '',
+           to: 'master')
+
+      expect(response).to redirect_to(namespace_project_compare_index_path(project.namespace, project, to: 'master'))
+    end
+
+    it 'redirects back to index when params[:to] is empty and preserves params[:from]' do
+      post(:create,
+           namespace_id: project.namespace.to_param,
+           project_id: project.to_param,
+           from: 'master',
+           to: '')
+
+      expect(response).to redirect_to(namespace_project_compare_index_path(project.namespace, project, from: 'master'))
+    end
+
+    it 'redirects back to index when params[:from] and params[:to] are empty' do
+      post(:create,
+           namespace_id: project.namespace.to_param,
+           project_id: project.to_param,
+           from: '',
+           to: '')
+
+      expect(response).to redirect_to(namespace_project_compare_index_path)
+    end
   end
 
   describe 'GET diff_for_path' do