Quick spike of how to show a bit more detailed missing dependency message

app/presenters/commit_status_presenter.rb

@@ -25,6 +25,8 @@ def self.callout_failure_messages
   end
 
   def callout_failure_message
+    return missing_dependencies_message if failure_reason.to_sym == :missing_dependency_failure
+
     self.class.callout_failure_messages.fetch(failure_reason.to_sym)
   end
 
@@ -35,4 +37,17 @@ def recoverable?
   def unrecoverable?
     script_failure? || missing_dependency_failure? || archived_failure?
   end
+
+  private
+
+  def missing_dependencies_message
+    [
+      "There were missing dependencies from the following stage(s): #{invalid_stages}",
+      "Please refer to https://docs.gitlab.com/ce/ci/yaml/README.html#when-a-dependent-job-will-fail"
+    ].join("\n")
+  end
+
+  def invalid_stages
+    dependencies.reject(&:valid_dependency?).map(&:name).join(', ')
+  end
 end

app/serializers/build_details_entity.rb

@@ -56,6 +56,10 @@ class BuildDetailsEntity < JobEntity
 
   expose :failure_reason, if: -> (*) { build.failed? }
 
+  expose :missing_dependencies, using: BuildDetailsEntity do |b|
+    b.dependencies.reject(&:valid_dependency?)
+  end
+
   expose :terminal_path, if: -> (*) { can_create_build_terminal? } do |build|
     terminal_project_job_path(project, build)
   end