27 files declare their use of ResponseInterface in Zircon Profile 8

Client.php in vendor/fabpot/goutte/Goutte/Client.php

Client.php in vendor/guzzlehttp/guzzle/src/Client.php

ClientInterface.php in vendor/guzzlehttp/guzzle/src/ClientInterface.php

CookieJar.php in vendor/guzzlehttp/guzzle/src/Cookie/CookieJar.php

CookieJarInterface.php in vendor/guzzlehttp/guzzle/src/Cookie/CookieJarInterface.php

DefaultFetcher.php in core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php

Contains \Drupal\aggregator\Plugin\aggregator\fetcher\DefaultFetcher.

EasyHandle.php in vendor/guzzlehttp/guzzle/src/Handler/EasyHandle.php

EmitterInterface.php in vendor/zendframework/zend-diactoros/src/Response/EmitterInterface.php

functions.php in vendor/guzzlehttp/psr7/src/functions.php

HttpFoundationFactory.php in vendor/symfony/psr-http-message-bridge/Factory/HttpFoundationFactory.php

HttpFoundationFactoryInterface.php in vendor/symfony/psr-http-message-bridge/HttpFoundationFactoryInterface.php

HttpMessageFactoryInterface.php in vendor/symfony/psr-http-message-bridge/HttpMessageFactoryInterface.php

locale.batch.inc in core/modules/locale/locale.batch.inc

Batch process to check the availability of remote or local po files.

MessageFormatter.php in vendor/guzzlehttp/guzzle/src/MessageFormatter.php

Middleware.php in vendor/guzzlehttp/guzzle/src/Middleware.php

MockHandler.php in vendor/guzzlehttp/guzzle/src/Handler/MockHandler.php

PsrResponseSubscriber.php in core/lib/Drupal/Core/EventSubscriber/PsrResponseSubscriber.php

Contains \Drupal\Core\EventSubscriber\PsrResponseSubscriber.

RedirectMiddleware.php in vendor/guzzlehttp/guzzle/src/RedirectMiddleware.php

RequestException.php in vendor/guzzlehttp/guzzle/src/Exception/RequestException.php

Response.php in vendor/zendframework/zend-diactoros/src/Response.php

Response.php in vendor/guzzlehttp/psr7/src/Response.php

Response.php in vendor/symfony/psr-http-message-bridge/Tests/Fixtures/Response.php

SapiEmitter.php in vendor/zendframework/zend-diactoros/src/Response/SapiEmitter.php

Serializer.php in vendor/zendframework/zend-diactoros/src/Response/Serializer.php

Server.php in vendor/zendframework/zend-diactoros/src/Server.php

StreamHandler.php in vendor/guzzlehttp/guzzle/src/Handler/StreamHandler.php

TransferStats.php in vendor/guzzlehttp/guzzle/src/TransferStats.php