Hook validation errors should be displayed to enduser

app/controllers/projects/merge_requests_controller.rb

@@ -199,7 +199,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
 
     merge_request_service = MergeRequests::MergeService.new(@project, current_user, merge_params)
     unless merge_request_service.hooks_validation_pass?(@merge_request)
-      @status = :failed
+      @status = :hook_validation_error
       return
     end
 

app/services/merge_requests/merge_service.rb

@@ -30,6 +30,7 @@ module MergeRequests
 
     def hooks_validation_pass?(merge_request)
       git_hook = merge_request.project.git_hook
+      return true unless git_hook
 
       unless git_hook.commit_message_allowed?(params[:commit_message])
         merge_request.update(merge_error: "Commit message does not follow the pattern '#{git_hook.commit_message_regex}'")

app/views/projects/merge_requests/merge.js.haml

@@ -5,6 +5,9 @@
 - when :merge_when_build_succeeds
   :plain
     $('.mr-widget-body').html("#{escape_javascript(render('projects/merge_requests/widget/open/merge_when_build_succeeds'))}");
+- when :hook_validation_error
+  :plain
+    $('.mr-widget-body').html("#{escape_javascript(render('projects/merge_requests/widget/open/error'))}");
 - else
   :plain
     $('.mr-widget-body').html("#{escape_javascript(render('projects/merge_requests/widget/open/reload'))}");

app/views/projects/merge_requests/widget/open/_error.html.haml

+%h4
+  = icon('exclamation-triangle')
+  This merge request failed to be merged automatically
+
+%p
+  = @merge_request.merge_error