Webapi Swagger schema generation fail in case when Get endpoint has param with Extension Attributes [Case#2]

[swnsma]

After refactoring which was done in 735024a, the issue #24116 is come back.
Original report: tap

Preconditions (*)

1. Magento 2.3.1 & 2.3-develop
2. Created and enabled custom module 'DreamVendor\DreamModule'.

Steps to reproduce (*)

1. Create php interface which will be used for the endpoint. E.g.

namespace DreamVendor\DreamModule\Api;

use Magento\Framework\Api\Search\SearchResultInterface;

/**
 * My Custom Endpoint API.
 */
interface MyCustomEndpointInterface
{
    /**
     * Get some awesome stuff!
     *
     * @param \DreamVendor\DreamModule\Api\Data\SearchRequestInterface $searchRequest
     *
     * @return \Magento\Framework\Api\Search\SearchResultInterface
     */
    public function execute(\DreamVendor\DreamModule\Api\Data\SearchRequestInterface $searchRequest): SearchResultInterface;
}

2. Create SearchRequestInterface. Make it extensible with extension attributes.

namespace DreamVendor\DreamModule\Api\Data;

use Magento\Framework\Api\ExtensibleDataInterface;

/**
 * Search Request Data Object.
 */
interface SearchRequestInterface extends ExtensibleDataInterface
{
    /**
     * Get Extension Attributes.
     *
     * @return \DreamVendor\DreamModule\Api\Data\SearchRequestExtensionInterface|null
     */
    public function getExtensionAttributes(): ?\DreamVendor\DreamModule\Api\Data\SearchRequestExtensionInterface;

    /**
     * Set Extension Attributes.
     *
     * @param \DreamVendor\DreamModule\Api\Data\SearchRequestExtensionInterface|null $extension
     */
    public function setExtensionAttributes(?\DreamVendor\DreamModule\Api\Data\SearchRequestExtensionInterface $extension): void;

3. Declare your endpoint via webapi.xml in etc folder of your module.

<routes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Webapi:etc/webapi.xsd">
    <route url="/V1/my-custom-endpoint" method="GET">
        <service class="DreamVendor\DreamModule\Api\MyCustomEndpointInterface" method="execute"/>
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
</routes>

4. Flush caches.
5. Try to generate schema. Go to your.website.com/swagger/.

Expected result (*)

1. The page has been opened.
2. You can see your new endpoint.

Actual result (*)

1. You can see message like Failed to load API definition. Internal Server Error http://magento2.local/rest/all/schema?services=all
2. Error message Warning: array_merge() expects at least 1 parameter, 0 given in \/var\/www\/html\/app\/code\/Magento\/Webapi\/Model\/Rest\/Swagger\/Generator.php:762

[m2-assistant]

Hi @swnsma. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

• Summary of the issue
• Information on your environment
• Steps to reproduce
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Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

@magento give me 2.3-develop instance - upcoming 2.3.x release

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@swnsma do you confirm that you were able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• yes
• no

---

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[m2-assistant]

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[magento-engcom-team]

✅ Confirmed by @engcom-Charlie
Thank you for verifying the issue. Based on the provided information internal tickets MC-20198 were created

Issue Available: @engcom-Charlie, You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself.