[wp-trac] [WordPress Trac] #44809: Safeguard `has_errors()` check in extra Customizer validation

[WordPress Trac]

#44809: Safeguard `has_errors()` check in extra Customizer validation
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 Reporter:  flixos90      |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Customize     |    Version:
 Severity:  normal        |   Keywords:  needs-patch
  Focuses:                |
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 The `customize_validate_{$setting_id}` filter is run in both the
 `WP_Customize_Setting` class, but then again in `WP_Customize_Manager`, to
 account for cases where someone might have overridden that method without
 maintaining the filter.

 I ran into an issue earlier causing a fatal error: While the documentation
 for `customize_validate_{$setting->id}` states that the parameter is a
 `WP_Error`, several plugins and themes have been returning true in case of
 success. This is correctly taken care of in `WP_Customize_Setting`, but
 not when the filter is executed again in
 `WP_Customize_Manager::validate_setting_values()`. `has_errors()` is
 called on the filter result, which however (unfortunately) may not always
 be a `WP_Error` object. We should add a `is_wp_error()` check to be safe.

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Ticket URL: <https://core.trac.wordpress.org/ticket/44809>
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