Now after updating some related tests, I'm concerned that this might break some functional tests out there (after upgrading to 7.3) for example: testing HTML error pages using WebTestCase won't work anymore if these tests are checking for more than just the error message.

Should we consider this a BC break?

Hi,

Thanks, it looks good to me at first glance.
I'll test it on my side to see how it behaves.

testing HTML error pages using WebTestCase won't work anymore if these tests are checking for more than just the error message.

Is there a way to opt-in for this feature (e.g. a dedicated env var)?

testing HTML error pages using WebTestCase won't work anymore if these tests are checking for more than just the error message.

Is there a way to opt-in for this feature (e.g. a dedicated env var)?

This small change restores the previous behavior. We could document this adjustment for situations where you specifically want to test the actual HTML error page:

-    ->alias('error_renderer.default', 'error_handler.error_renderer.default')
+    ->alias('error_renderer.default', 'error_renderer.html')

Most functional/end-to-end tests have a dedicated config file. That could be better than using an env var, since you can enable or disable this behavior case by case.

Or we could add a new framework option to opt-in for this behavior, include a deprecation notice to make it the default in 8.0, and update the recipe file to set it as the default for new projects. What do you think?

Sounds good 👍