How to properly handle migration errors I've got some migrations and they are basically doing their job. My problem is that errors in the data source end up in a WSOD in Migrate Tools UI, without any human readable error message (when I click on "List migration").

E.g. my source usually responds something like

{success: true, result: {my_dataset: {data1: 'Alice', data2: 'Bob'}}}

and in my YML I've got something like

source:
  plugin: url
  data_parser_plugin: json
  item_selector: /result/my_dataset
  fields:
    -
      name: data1
      label: 'Just an example'
      selector: data1


Today my source went down and returns a HTTP 500 with

{success: false, message: 'We are working on it, try later...'}

How can I force the Migrate Tools UI to display an error message and stay in the admin theme, instead of a WSOD?
Came across this question trying to resolve a similar migration error -- try using the Drush command line tools instead of the UI and use the -d flag so it shows all of the errors during a migrate command, ex:

drush -d migrate:status