WP_Feature::get_input_schema() method throws a "Schema exceeds maximum allowed properties (0)"

[tolecar]

I'm using prebuilt release zip wp-feature-api.zip v0.1.6, and I was able to iterate and call features, but when trying to get it's input schema (or json_encode feature), it throws an exception (this one was while trying to get inputs schema from "Query posts" feature):

Schema exceeds maximum allowed properties (0) in C:\xampp\htdocs\wp-astro\wp-content\plugins\wp-feature-api\includes\class-wp-feature-schema-adapter.php:424
Stack trace:
#0 C:\xampp\htdocs\wp-astro\wp-content\plugins\wp-feature-api\includes\class-wp-feature-schema-adapter.php(211): WP_Feature_Schema_Adapter->rule_max_properties('max_properties', Array)
#1 C:\xampp\htdocs\wp-astro\wp-content\plugins\wp-feature-api\includes\class-wp-feature.php(340): WP_Feature_Schema_Adapter->transform()
#2 C:\xampp\htdocs\wp-astro\wp-content\plugins\my-test\my-test.php(46): WP_Feature->get_input_schema()
#3 C:\xampp\htdocs\wp-astro\wp-includes\class-wp-hook.php(324): {closure}('')
#4 C:\xampp\htdocs\wp-astro\wp-includes\class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array)
#5 C:\xampp\htdocs\wp-astro\wp-includes\plugin.php(517): WP_Hook->do_action(Array)
#6 C:\xampp\htdocs\wp-astro\wp-includes\general-template.php(3208): do_action('wp_footer')
#7 C:\xampp\htdocs\wp-astro\wp-content\themes\kadence\foo in C:\xampp\htdocs\wp-astro\wp-content\plugins\wp-feature-api\includes\class-wp-feature-schema-adapter.php on line 424

Environment info :

• OS: Win 10
• PHP: 7.4.33 (Xampp)
• WP: 6.8.1

---

In addition, here is my test plugin

<?php
/*
Plugin Name: My Test Plugin
Description: A simple test plugin using the Feature API.
Version: 1.0
Author: tole
*/

// Register a new feature
add_action('init', function() {
    if (function_exists('register_feature')) {
        register_feature('my_custom_feature', [
            'title' => 'My Custom Feature',
            'description' => 'This is a custom feature for testing purposes.',
        ]);
    }
});

// Use the Feature API to find and execute a feature
add_action('wp', function() {
    if (function_exists('wp_find_feature')) {
        $feature = wp_find_feature('resource-myplugin/site-title');
        
        if ($feature) {
            $title = $feature->call();
            if (!is_wp_error($title)) {
                add_action('wp_footer', function() use ($title) {
                    echo '<p>Site Title Feature: ' . esc_html($title) . '</p>';
                });
            }
        }
    }
});

// Query multiple features
add_action('wp', function() {
    if (function_exists('wp_get_features')) {
        $features = wp_get_features(array(
            'type' => array('resource'),
            'categories' => array('core', 'post')
        ));
        
        foreach ($features as $feature) {
            add_action('wp_footer', function() use ($feature) {
                echo '<p>Feature Name: ' . esc_html($feature->get_name()) . '</p>';
				echo '<p>Feature Schema: ' . esc_html($feature->get_input_schema()) . '</p>';
            });
        }
    }
});