Multi type on args properties returning invalid error message when not validated

[pentatonicfunk]

I was able to reproduce it only on specific case when type being used are null AND integer, AND specify minimum & maximum. But its probably the case too when using exclusiveMinimum or exclusiveMaximum

Test Case

<?php

$request = new WP_REST_Request();
$request->set_attributes(
    array(
        'args' => array(
            'null_or_integer' => array(
                'type'    => array( 'null', 'integer' ),
                'minimum' => 10,
                'maximum' => 20,
            ),
        ),
    )
);

$param    = 'null_or_integer';
$value    = 1;
$is_valid = rest_validate_request_arg( $value, $request, $param );

print_r( $is_valid->get_error_message() );

Expected

null_or_integer must be between 10 (inclusive) and 20.

Actual

null_or_integer is not of type null,integer.
Which isn't true, since value passed was integer.

[TimothyBlynJacobs]

Thanks for the ticket @pentatonicfunk!

Yeah the error message when using multi types isn't very helpful. We should improve it by separately trying to find the best type for the input based on the possible types.

[pentatonicfunk]

This could be tricky to solve since rest_validate_value_from_schema have multiple responsibilities and multiple exits.
I wonder if this can be solved by break it down into smaller functions, also considering this function tend to get bigger once we add more validation args, such as new formats that recently added min/maxLength and pattern.

[TimothyBlynJacobs]

@pentatonicfunk Definitely. I'd like to introduce a class like WP_REST_Schema_Validator. Something that could also support the recommended ​JSON Schema Output Formats.

This gives us better error messages and makes sanitization more usable in different scenarios.
Trac ticket: https://core.trac.wordpress.org/ticket/50300

[TimothyBlynJacobs]

I've done a first pass at what this could look like. Essentially we match based solely on the type instead of validating each schema as a different type.

This changes a couple of sanitization tests, but I think the new output is more desirable.

[TimothyBlynJacobs]

@pentatonicfunk could you take a look at the attached PR and see if it solves your issue?

[pentatonicfunk]

@TimothyBlynJacobs yes it solves my issue

[TimothyBlynJacobs]

In 48306:

REST API: Make multi-typed schemas more robust.

A multi-type schema is a schema where the type keyword is an array of possible types instead of a single type. For instance, [ 'object', 'string' ] would allow objects or string values.

In [46249] basic support for these schemas was introduced. The validator would loop over each schema type trying to find a version that matched. This worked for valid values, but for invalid values it provided unhelpful error messages. The sanitizer also had its utility restricted.

In this commit, the validators and sanitizers will first determine the best type of the passed value and then apply the schema with that set type. In the case that a value could match multiple types, the schema of the first matching type will be used.

To maintain backward compatibility, if unsupported schema types are used, the value will always pass validation. A doing it wrong notice is issued in this case.

Fixes #50300.
Props pentatonicfunk, dlh, TimothyBlynJacobs.