Error page type with 404 code can’t preview in CMS

[pack254]

Module version(s) affected

7.1

Description

I have a SilverStripe\ErrorPage\ErrorPage page type in the project which sets the ErrorCode to 404. When I am in the CMS, to split view to preview the page. it shows the/admin/pages page instead. I have found this caused by LocaleSwitchRedirector.

How to reproduce

1. Create any two locales
2. Edit ErrorPage type with 404 code
3. Preview the page by split view, you will see it display the admin/pages instead of error page template.

Possible Solution

I have temporarily fixed it by using the Injector and added the additional condition for it, !$request->getVar('CMSPreview').

Additional Context

Validations

• [X] Check that there isn't already an issue that reports the same bug
• [X] Double check that your reproduction steps work in a fresh installation of silverstripe/installer (with any code examples you've provided)

[tractorcow]

I think that temporary fix is fine as a permanent fix. Do you want to PR the change to add the extra condition?

[pack254]

Yep, sure thing! I will raise a PR for this @tractorcow 👍