Add informative error message for 'Connection refused' errors in MySQL

The Needs Review Queue Bot → tested this issue. It either no longer applies to Drupal core, or fails the Drupal core commit checks. Therefore, this issue status is now "Needs work".

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Made a MR on 10.1.

LGTM!

The patch applies successfully to 10.1.x and works as expected!

Message for invalid "localhost" or empty host option:

Message for incorrect "unix_socket" entry:

Message for general invalid host option:

RTBC!

Although, I am unsure about the unix socket mentioning inside the first screenshot, for the
if (isset($connection_options['host']) && in_array(strtolower($connection_options['host']), ['', 'localhost'], TRUE))
Case. Maybe someone with more insight could have a look.

Adding issue credits

Committed to 10.1.x and 10.0.x, it doesn't apply cleanly to 9.5.x so marking for backport.

Thanks folks

Added a patch for Drupal 9.5.x, and also added reroll diff between MR and the new patch, please review.

There's a fair amount going on here and we're approaching the final bugfix release for 9.5.x, so I think we should leave this fixed in 10.0.x.

Thanks @catch!
Removing "[Needs backport]" from the title so.

Automatically closed - issue fixed for 2 weeks with no activity.