Incorrect type for OpenApi spec

[DjordyKoert]

API Platform version(s) affected: 3.2

Description

According to the OpenApi 3.1 specification type cannot contain a list of types. Instead the oneOf, allOf or anyOf key should be used when describing an union/intersection type on a property.

Instead of doing this #5470 changed the behaviour to generate a list of types (invalid) instead.

3.1:

core/src/Hydra/JsonSchema/SchemaFactory.php

Lines 96 to 103 in c617b18

	switch ($schema->getVersion()) {
	case Schema::VERSION_JSON_SCHEMA:
	$nullableStringDefinition = ['type' => ['string', 'null']];
	break;
	case Schema::VERSION_OPENAPI:
	$nullableStringDefinition = ['type' => 'string', 'nullable' => true];
	break;
	}

3.2:

core/src/Hydra/JsonSchema/SchemaFactory.php

Lines 94 to 104 in 002c8b2

	switch ($schema->getVersion()) {
	// JSON Schema + OpenAPI 3.1
	case Schema::VERSION_OPENAPI:
	case Schema::VERSION_JSON_SCHEMA:
	$nullableStringDefinition = ['type' => ['string', 'null']];
	break;
	// Swagger
	default:
	$nullableStringDefinition = ['type' => 'string'];
	break;
	}

How to reproduce

Using the OpenApiFactory to generate documentation and passing this to swagger-php causes an TypeError to be thrown by PHP because an array (list of types) is given instead of the expected string type.

TypeError: OpenApi\Analysis::getSchemaForSource(): Argument #1 ($fqdn) must be of type string, array given
https://github.com/zircote/swagger-php/blob/595d8b63a589e6ac0835c83a45304c7397dc37d1/src/Analysis.php#L326

Possible Solution

A simple rollback on the highlighted code to the version 3.1 variant should fix this issue.

Additional Context

Related issue: zircote/swagger-php#1464.

PHPUnit failure: nelmio/NelmioApiDocBundle#2141 (comment)