Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

The return type in function declaration contains only one type, the doc comments can contain multiple (even not unique)

...
     * @return \OpenAPI\Client\Model\Permission|\OpenAPI\Client\Model\OdataError|\OpenAPI\Client\Model\OdataError
     */
    public function invite(
        string $drive_id,
        string $item_id,
        ?\OpenAPI\Client\Model\DriveItemInvite $drive_item_invite = null,
        string $contentType = self::contentTypes['invite'][0]
    ): \OpenAPI\Client\Model\Permission
....

openapi-generator version

7.1.0

OpenAPI declaration file content or url

https://github.com/owncloud/libre-graph-api/blob/main/api/openapi-spec/v1.0.yaml

Generation Details

docker run --rm -v $PWD:/local openapitools/openapi-generator-cli:v7.1.0 generate --enable-post-process-file -i /local/api/openapi-spec/v1.0.yaml --additional-properties=packageName=libregraph --git-user-id=owncloud --git-repo-id=libre-graph-api-php -g php-nextgen -o /local/out/php-nextgen

Steps to reproduce

• generate PHP-nextgen code from the above specs

Suggest a fix

• ether set the return value to mixed in

  openapi-generator/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java

  Line 183 in 48f454c

  operation.vendorExtensions.putIfAbsent("x-php-return-type", operation.returnType);

• or list all possible return types in the function declaration, but then it must be ensured that no type is repeated