array<string, mixed> only allows string values in the generated schema #8665

The problem

API Platform treats mixed as string when it generates the OpenAPI schema. A property that can hold any value ends up as "strings only".

Example

/** @var array<string, mixed> */
public array $metadata = [];

The data is {"chunk_number": 0}. The number 0 is valid for mixed.

The generated schema says:

"metadata": { "type": "object", "additionalProperties": { "type": ["string", "null"] } }

That only allows strings and null. A client that validates the data against the schema reports it as invalid.

What I expected

mixed means "any value", so the schema should allow any value.

Where it comes from

SchemaPropertyMetadataFactory contains TypeIdentifier::MIXED => ['type' => 'string']. It is also on main.

Version: api-platform/core 4.4.2