[Adebayo120]

Summary

• Fix schema validation for nested empty JSON objects by preserving object context from the surrounding schema when json_decode(..., true) turns {} into an empty PHP array.
• Add a regression test covering a nested object like {"parameters": {}} that previously failed with Expected object, but received array.

Reproduction

use Mcp\Capability\Discovery\SchemaValidator;

$data = json_decode('{"parameters":{}}', true, 512, JSON_THROW_ON_ERROR);
$schema = [
    'type' => 'object',
    'properties' => [
        'parameters' => ['type' => 'object'],
    ],
];

$validator = new SchemaValidator();
var_export($validator->validateAgainstJsonSchema($data, $schema));

Before the fix this returned an error complaining /parameters was an array rather than an object.

Validation

• php vendor/bin/phpunit tests/Unit/Capability/Discovery/SchemaValidatorTest.php
• php vendor/bin/phpstan analyse --no-progress --configuration=phpstan.dist.neon src/Capability/Discovery/SchemaValidator.php tests/Unit/Capability/Discovery/SchemaValidatorTest.php
• php vendor/bin/php-cs-fixer fix --config=.php-cs-fixer.dist.php --dry-run --diff src/Capability/Discovery/SchemaValidator.php tests/Unit/Capability/Discovery/SchemaValidatorTest.php

[Copilot]

🟡 Changes recommended

Schema coercion can incorrectly accept arrays as object-valued tool output while rejecting valid nullable-object and additional-property inputs.

3 open issues

• Preserve JSON types during output validation · New
• Handle nullable object schemas during coercion · New
• Do not use item schemas for object properties · New

What changed in this PR

This PR updates schema-aware data preparation to handle nested empty JSON objects that become empty PHP arrays during associative decoding.

Changes:

• Pass property and array-item schemas through recursive data conversion.
• Convert nested empty arrays to objects when the schema explicitly requires an object.
• Add a regression test for an empty nested parameters object.

File	Description
tests/​Unit/​Capability/​Discovery/​SchemaValidatorTest.php	Adds coverage for nested empty-object validation.
src/​Capability/​Discovery/​SchemaValidator.php	Adds schema-aware recursive conversion and schema lookup helpers.

_{Review effort: Balanced}

[chr-hertel]

Replaced by #678 - thanks @Adebayo120!