WP_Error objects returned by REST API validation callbacks aren't formatted correctly

[bradyvercher]

Here's an example response with two missing parameters. The software_id validation callback returns a WP_Error instance, while the software_version is required, but doesn't have a validation callback defined.

{  
   "code":"rest_invalid_param",
   "message":"Invalid parameter(s): software_id (Invalid software identifier.), Invalid parameter.",
   "data":{  
      "status":400,
      "params":{  
         "0":"software_id (Invalid software identifier.)",
         "software_version":"Invalid parameter."
      }
   }
}

[bradyvercher]

Here's how the same response is formatted with the attached patch applied:

{  
   "code":"rest_invalid_param",
   "message":"Invalid parameter(s): Invalid software identifier., Invalid parameter.",
   "data":{  
      "status":400,
      "params":{  
         "software_id":"Invalid software identifier.",
         "software_version":"Invalid parameter."
      }
   }
}

[swissspidy]

There are couple of tests for the has_valid_params() method already. It would be good to have a test for this as well.

[joehoyle]

In 35890:

REST API: Improve formatting of failed validation errors.

If a validation_callback returns a WP_Error it should give the same response format as if it returned false. This makes programmatically reading the validation errors better.

Props bradyvercher for initial patch.
Fixes #35028.

[joehoyle]

I updated the response format to be:

{  
   "code":"rest_invalid_param",
   "message":"Invalid parameter(s): software_id, software_version",
   "data":{  
      "status":400,
      "params":{  
         "software_id":"Invalid software identifier.",
         "software_version":"Invalid parameter."
      }
   }
}

This makes it a bit more readable too. Also, added unit tests for returning a WP_Error from the validate callback. Thanks bradyvercher!

[bradyvercher]

Very cool. Thanks for the improvements!