Description

In API Platform 4.4 / 5.0, defining a QueryParameter with allowed values from a PHP backed enum requires manually duplicating its values in the OpenAPI schema.

For example:

enum FooEnum: string
{
    case A = 'a';
    case B = 'b';
    case C = 'c';
}

Currently, the values must be explicitly listed:

new QueryParameter(
    schema: [
        'type' => 'string',
        'enum' => ['a', 'b', 'c'],
    ],
)

This duplicates the enum definition and requires updating the schema whenever enum cases change.

PHP does not allow calling FooEnum::cases() directly in attribute arguments.

Proposed solution

Allow referencing a PHP backed enum class directly in a QueryParameter schema.

For example:

new QueryParameter(
    schema: [
        'type' => 'string',
        'enumClass' => FooEnum::class,
    ],
)

Alternatively, a dedicated enumClass option on QueryParameter could be introduced.

The syntax is illustrative; the goal is to avoid manually duplicating enum values.

Expected behavior

API Platform should automatically:

• Extract backed enum values using FooEnum::cases().
• Include these values in the generated OpenAPI schema.
• Validate incoming parameter values against the enum.

Generated OpenAPI schema:

type: string
enum:
  - a
  - b
  - c

Automatic conversion to PHP enum instances is not required as part of this feature.

Additional context

API Platform already supports PHP backed enums in resource properties and OpenAPI schema generation.

It would be useful to provide equivalent support for explicitly declared query parameters, keeping the enum as the single source of truth.