openapi-generator creates a PHP SDK where the OAuth typehints in the `OpenAPI\Client\Api\ApiAppApi::apiAppCreate()` method are not namespaced

ApiAppApi.php

<?php
/**
 * ApiAppApi
 * PHP version 7.3
 *
 * @category Class
 * @package  OpenAPI\Client
 * @author   OpenAPI Generator team
 * @link     https://openapi-generator.tech
 */

/**
 * My API
 *
 * v3 API
 *
 * The version of the OpenAPI document: 3.0.0
 * Contact: [email protected]
 * Generated by: https://openapi-generator.tech
 * OpenAPI Generator version: 5.3.0
 */

/**
 * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
 * https://openapi-generator.tech
 * Do not edit the class manually.
 */

namespace OpenAPI\Client\Api;

use GuzzleHttp\Client;
use GuzzleHttp\ClientInterface;
use GuzzleHttp\Exception\RequestException;
use GuzzleHttp\Exception\ConnectException;
use GuzzleHttp\Psr7\MultipartStream;
use GuzzleHttp\Psr7\Request;
use GuzzleHttp\RequestOptions;
use OpenAPI\Client\ApiException;
use OpenAPI\Client\Configuration;
use OpenAPI\Client\HeaderSelector;
use OpenAPI\Client\ObjectSerializer;

/**
 * ApiAppApi Class Doc Comment
 *
 * @category Class
 * @package  OpenAPI\Client
 * @author   OpenAPI Generator team
 * @link     https://openapi-generator.tech
 */
class ApiAppApi
{
    /**
     * @var ClientInterface
     */
    protected $client;

    /**
     * @var Configuration
     */
    protected $config;

    /**
     * @var HeaderSelector
     */
    protected $headerSelector;

    /**
     * @var int Host index
     */
    protected $hostIndex;

    /**
     * @param ClientInterface $client
     * @param Configuration   $config
     * @param HeaderSelector  $selector
     * @param int             $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
     */
    public function __construct(
        ClientInterface $client = null,
        Configuration $config = null,
        HeaderSelector $selector = null,
        $hostIndex = 0
    ) {
        $this->client = $client ?: new Client();
        $this->config = $config ?: new Configuration();
        $this->headerSelector = $selector ?: new HeaderSelector();
        $this->hostIndex = $hostIndex;
    }

    /**
     * Set the host index
     *
     * @param int $hostIndex Host index (required)
     */
    public function setHostIndex($hostIndex): void
    {
        $this->hostIndex = $hostIndex;
    }

    /**
     * Get the host index
     *
     * @return int Host index
     */
    public function getHostIndex()
    {
        return $this->hostIndex;
    }

    /**
     * @return Configuration
     */
    public function getConfig()
    {
        return $this->config;
    }

    /**
     * Operation apiAppCreate
     *
     * Creates a new API App.
     *
     * @param  string[] $domains The domain names the ApiApp will be associated with. (required)
     * @param  string $name The name you want to assign to the ApiApp. (required)
     * @param  string $callback_url The URL at which the ApiApp should receive event callbacks. (optional)
     * @param  \SplFileObject $custom_logo_file An image file to use as a custom logo in embedded contexts. (Only applies to some API plans) (optional)
     * @param  OAuth $oauth oauth (optional)
     *
     * @throws \OpenAPI\Client\ApiException on non-2xx response
     * @throws \InvalidArgumentException
     * @return mixed
     */
    public function apiAppCreate($domains, $name, $callback_url = null, $custom_logo_file = null, $oauth = null)
    {
        list($response) = $this->apiAppCreateWithHttpInfo($domains, $name, $callback_url, $custom_logo_file, $oauth);
        return $response;
    }

    /**
     * Operation apiAppCreateWithHttpInfo
     *
     * Creates a new API App.
     *
     * @param  string[] $domains The domain names the ApiApp will be associated with. (required)
     * @param  string $name The name you want to assign to the ApiApp. (required)
     * @param  string $callback_url The URL at which the ApiApp should receive event callbacks. (optional)
     * @param  \SplFileObject $custom_logo_file An image file to use as a custom logo in embedded contexts. (Only applies to some API plans) (optional)
     * @param  OAuth $oauth (optional)
     *
     * @throws \OpenAPI\Client\ApiException on non-2xx response
     * @throws \InvalidArgumentException
     * @return array of mixed, HTTP status code, HTTP response headers (array of strings)
     */
    public function apiAppCreateWithHttpInfo($domains, $name, $callback_url = null, $custom_logo_file = null, $oauth = null)
    {
        $request = $this->apiAppCreateRequest($domains, $name, $callback_url, $custom_logo_file, $oauth);

        try {
            $options = $this->createHttpClientOption();
            try {
                $response = $this->client->send($request, $options);
            } catch (RequestException $e) {
                throw new ApiException(
                    "[{$e->getCode()}] {$e->getMessage()}",
                    (int) $e->getCode(),
                    $e->getResponse() ? $e->getResponse()->getHeaders() : null,
                    $e->getResponse() ? (string) $e->getResponse()->getBody() : null
                );
            } catch (ConnectException $e) {
                throw new ApiException(
                    "[{$e->getCode()}] {$e->getMessage()}",
                    (int) $e->getCode(),
                    null,
                    null
                );
            }

            $statusCode = $response->getStatusCode();

            if ($statusCode < 200 || $statusCode > 299) {
                throw new ApiException(
                    sprintf(
                        '[%d] Error connecting to the API (%s)',
                        $statusCode,
                        (string) $request->getUri()
                    ),
                    $statusCode,
                    $response->getHeaders(),
                    (string) $response->getBody()
                );
            }

            switch($statusCode) {
                case 200:
                    if ('mixed' === '\SplFileObject') {
                        $content = $response->getBody(); //stream goes to serializer
                    } else {
                        $content = (string) $response->getBody();
                    }

                    return [
                        ObjectSerializer::deserialize($content, 'mixed', []),
                        $response->getStatusCode(),
                        $response->getHeaders()
                    ];
            }

            $returnType = 'mixed';
            if ($returnType === '\SplFileObject') {
                $content = $response->getBody(); //stream goes to serializer
            } else {
                $content = (string) $response->getBody();
            }

            return [
                ObjectSerializer::deserialize($content, $returnType, []),
                $response->getStatusCode(),
                $response->getHeaders()
            ];

        } catch (ApiException $e) {
            switch ($e->getCode()) {
                case 200:
                    $data = ObjectSerializer::deserialize(
                        $e->getResponseBody(),
                        'mixed',
                        $e->getResponseHeaders()
                    );
                    $e->setResponseObject($data);
                    break;
            }
            throw $e;
        }
    }

    /**
     * Operation apiAppCreateAsync
     *
     * Creates a new API App.
     *
     * @param  string[] $domains The domain names the ApiApp will be associated with. (required)
     * @param  string $name The name you want to assign to the ApiApp. (required)
     * @param  string $callback_url The URL at which the ApiApp should receive event callbacks. (optional)
     * @param  \SplFileObject $custom_logo_file An image file to use as a custom logo in embedded contexts. (Only applies to some API plans) (optional)
     * @param  OAuth $oauth (optional)
     *
     * @throws \InvalidArgumentException
     * @return \GuzzleHttp\Promise\PromiseInterface
     */
    public function apiAppCreateAsync($domains, $name, $callback_url = null, $custom_logo_file = null, $oauth = null)
    {
        return $this->apiAppCreateAsyncWithHttpInfo($domains, $name, $callback_url, $custom_logo_file, $oauth)
            ->then(
                function ($response) {
                    return $response[0];
                }
            );
    }

    /**
     * Operation apiAppCreateAsyncWithHttpInfo
     *
     * Creates a new API App.
     *
     * @param  string[] $domains The domain names the ApiApp will be associated with. (required)
     * @param  string $name The name you want to assign to the ApiApp. (required)
     * @param  string $callback_url The URL at which the ApiApp should receive event callbacks. (optional)
     * @param  \SplFileObject $custom_logo_file An image file to use as a custom logo in embedded contexts. (Only applies to some API plans) (optional)
     * @param  OAuth $oauth (optional)
     *
     * @throws \InvalidArgumentException
     * @return \GuzzleHttp\Promise\PromiseInterface
     */
    public function apiAppCreateAsyncWithHttpInfo($domains, $name, $callback_url = null, $custom_logo_file = null, $oauth = null)
    {
        $returnType = 'mixed';
        $request = $this->apiAppCreateRequest($domains, $name, $callback_url, $custom_logo_file, $oauth);

        return $this->client
            ->sendAsync($request, $this->createHttpClientOption())
            ->then(
                function ($response) use ($returnType) {
                    if ($returnType === '\SplFileObject') {
                        $content = $response->getBody(); //stream goes to serializer
                    } else {
                        $content = (string) $response->getBody();
                    }

                    return [
                        ObjectSerializer::deserialize($content, $returnType, []),
                        $response->getStatusCode(),
                        $response->getHeaders()
                    ];
                },
                function ($exception) {
                    $response = $exception->getResponse();
                    $statusCode = $response->getStatusCode();
                    throw new ApiException(
                        sprintf(
                            '[%d] Error connecting to the API (%s)',
                            $statusCode,
                            $exception->getRequest()->getUri()
                        ),
                        $statusCode,
                        $response->getHeaders(),
                        (string) $response->getBody()
                    );
                }
            );
    }

    /**
     * Create request for operation 'apiAppCreate'
     *
     * @param  string[] $domains The domain names the ApiApp will be associated with. (required)
     * @param  string $name The name you want to assign to the ApiApp. (required)
     * @param  string $callback_url The URL at which the ApiApp should receive event callbacks. (optional)
     * @param  \SplFileObject $custom_logo_file An image file to use as a custom logo in embedded contexts. (Only applies to some API plans) (optional)
     * @param  OAuth $oauth (optional)
     *
     * @throws \InvalidArgumentException
     * @return \GuzzleHttp\Psr7\Request
     */
    public function apiAppCreateRequest($domains, $name, $callback_url = null, $custom_logo_file = null, $oauth = null)
    {
        // verify the required parameter 'domains' is set
        if ($domains === null || (is_array($domains) && count($domains) === 0)) {
            throw new \InvalidArgumentException(
                'Missing the required parameter $domains when calling apiAppCreate'
            );
        }
        if (count($domains) > 2) {
            throw new \InvalidArgumentException('invalid value for "$domains" when calling ApiAppApi.apiAppCreate, number of items must be less than or equal to 2.');
        }
        if (count($domains) < 1) {
            throw new \InvalidArgumentException('invalid value for "$domains" when calling ApiAppApi.apiAppCreate, number of items must be greater than or equal to 1.');
        }

        // verify the required parameter 'name' is set
        if ($name === null || (is_array($name) && count($name) === 0)) {
            throw new \InvalidArgumentException(
                'Missing the required parameter $name when calling apiAppCreate'
            );
        }

        $resourcePath = '/api_app';
        $formParams = [];
        $queryParams = [];
        $headerParams = [];
        $httpBody = '';
        $multipart = false;




        // form params
        if ($callback_url !== null) {
            $formParams['callback_url'] = ObjectSerializer::toFormValue($callback_url);
        }
        // form params
        if ($custom_logo_file !== null) {
            $multipart = true;
            $formParams['custom_logo_file'] = [];
            $paramFiles = is_array($custom_logo_file) ? $custom_logo_file : [$custom_logo_file];
            foreach ($paramFiles as $paramFile) {
                $formParams['custom_logo_file'][] = \GuzzleHttp\Psr7\Utils::tryFopen(
                    ObjectSerializer::toFormValue($paramFile),
                    'rb'
                );
            }
        }
        // form params
        if ($domains !== null) {
            $formParams['domains'] = ObjectSerializer::toFormValue($domains);
        }
        // form params
        if ($name !== null) {
            $formParams['name'] = ObjectSerializer::toFormValue($name);
        }
        // form params
        if ($oauth !== null) {
            $formParams['oauth'] = ObjectSerializer::toFormValue($oauth);
        }

        if ($multipart) {
            $headers = $this->headerSelector->selectHeadersForMultipart(
                ['application/json']
            );
        } else {
            $headers = $this->headerSelector->selectHeaders(
                ['application/json'],
                ['multipart/form-data']
            );
        }

        // for model (json/xml)
        if (count($formParams) > 0) {
            if ($multipart) {
                $multipartContents = [];
                foreach ($formParams as $formParamName => $formParamValue) {
                    $formParamValueItems = is_array($formParamValue) ? $formParamValue : [$formParamValue];
                    foreach ($formParamValueItems as $formParamValueItem) {
                        $multipartContents[] = [
                            'name' => $formParamName,
                            'contents' => $formParamValueItem
                        ];
                    }
                }
                // for HTTP post (form)
                $httpBody = new MultipartStream($multipartContents);

            } elseif ($headers['Content-Type'] === 'application/json') {
                $httpBody = \GuzzleHttp\json_encode($formParams);

            } else {
                // for HTTP post (form)
                $httpBody = \GuzzleHttp\Psr7\Query::build($formParams);
            }
        }


        $defaultHeaders = [];
        if ($this->config->getUserAgent()) {
            $defaultHeaders['User-Agent'] = $this->config->getUserAgent();
        }

        $headers = array_merge(
            $defaultHeaders,
            $headerParams,
            $headers
        );

        $query = \GuzzleHttp\Psr7\Query::build($queryParams);
        return new Request(
            'POST',
            $this->config->getHost() . $resourcePath . ($query ? "?{$query}" : ''),
            $headers,
            $httpBody
        );
    }

    /**
     * Create http client option
     *
     * @throws \RuntimeException on file opening failure
     * @return array of http client options
     */
    protected function createHttpClientOption()
    {
        $options = [];
        if ($this->config->getDebug()) {
            $options[RequestOptions::DEBUG] = fopen($this->config->getDebugFile(), 'a');
            if (!$options[RequestOptions::DEBUG]) {
                throw new \RuntimeException('Failed to open the debug file: ' . $this->config->getDebugFile());
            }
        }

        return $options;
    }
}

openapi.yaml

openapi: 3.0.3
info:
    title: 'My API'
    description: 'v3 API'
    termsOfService: 'https://www.example.com/terms'
    contact:
        email: [email protected]
    license:
        name: MIT
        url: 'https://opensource.org/licenses/MIT'
    version: 3.0.0
servers:
    -
        url: 'https://api.example.com/v3'
paths:
    /api_app:
        post:
            tags:
                - 'Api App'
            summary: 'Creates a new API App.'
            description: 'Creates a new API App.'
            operationId: apiAppCreate
            requestBody:
                content:
                    multipart/form-data:
                        schema:
                            $ref: '#/components/schemas/ApiAppCreateRequest'
            responses:
                '200':
                    description: 'successful operation'
                    content:
                        application/json:
                            schema: {}
components:
    schemas:
        ApiAppCreateRequest:
            required:
                - name
                - domains
            properties:
                callback_url:
                    description: 'The URL at which the ApiApp should receive event callbacks.'
                    type: string
                custom_logo_file:
                    description: 'An image file to use as a custom logo in embedded contexts. (Only applies to some API plans)'
                    type: string
                    format: binary
                domains:
                    description: 'The domain names the ApiApp will be associated with.'
                    type: array
                    items:
                        type: string
                    maxItems: 2
                    minItems: 1
                    example: ["example.com"]
                name:
                    description: 'The name you want to assign to the ApiApp.'
                    type: string
                    example: 'My Production App'
                oauth:
                    allOf:
                        - $ref: '#/components/schemas/OAuth'
                        -
                            properties:
                                callback_url:
                                    example: 'https://example.com/oauth'
                                scopes:
                                    example:
                                        - basic_account_info
                                        - request_signature
            type: object
        OAuth:
            title: OAuth
            type: object
            properties:
                callback_url:
                    nullable: true
                    description: "The callback URL to be used for OAuth flows.\n(Required if oauth[scopes] is provided)"
                    type: string
                scopes:
                    description: "A list of OAuth scopes to be granted to the app.\n(Required if oauth[callback_url] is provided)."
                    type: array
                    items:
                        type: string
tags:
    -
        name: 'Api App'
        description: 'Contains information about an API App'

Specifically this bit:

    /**
     * Operation apiAppCreate
     *
     * Creates a new API App.
     *
     * @param  string[] $domains The domain names the ApiApp will be associated with. (required)
     * @param  string $name The name you want to assign to the ApiApp. (required)
     * @param  string $callback_url The URL at which the ApiApp should receive event callbacks. (optional)
     * @param  \SplFileObject $custom_logo_file An image file to use as a custom logo in embedded contexts. (Only applies to some API plans) (optional)
     * @param  OAuth $oauth oauth (optional)
     *
     * @throws \OpenAPI\Client\ApiException on non-2xx response
     * @throws \InvalidArgumentException
     * @return mixed
     */
    public function apiAppCreate($domains, $name, $callback_url = null, $custom_logo_file = null, $oauth = null)

The OAuth $oauth oauth (optional) should be namespaced. The class itself is correctly generated and is namespaced, but this typehint doesn't use namespacing when referencing it.

Here's command I use:

openapi-generator generate \
  -i "openapi.yaml" \
  --global-property "skipFormModel=false" \
  -g php \
  -o openapi-sdks/