Creating object of class PubSubClient when PUBSUB_EMULATOR_HOST is set produces Class "Grpc\ChannelCredentials" not found when grcp extension is not installed

[botzkobg]

Environment details

• OS: All supported
• PHP version: All supported
• Package name and version: google/cloud-pubsub 2.9.1

Steps to reproduce

1. Configure php without installing grcp extension
2. Try to create an object of class PubSubClient when env var PUBSUB_EMULATOR_HOST is set

Code example

$pubsubClient = new PubSubClient([
            'projectId'         => 'emulator-project',
            'credentialsConfig' => [
                'keyFile' => [
                    "client_id"     => "fake-fake-fake.apps.googleusercontent.com",
                    "client_secret" => "fake-fake-fake",
                    "refresh_token" => "fake-fake-fake",
                    "type"          => "authorized_user",
                ],
            ],
            'transportConfig'   => [
                'rest' => [
                    'httpHandler' => [HttpHandlerFactory::build($client), 'async'],
                ],
            ],
        ]);

Other affected classes

• PublisherClient
• SchemaServiceClient
• SubscriberClient

This was introduced by PR https://github.com/googleapis/google-cloud-php/pull/8043/files#diff-7531da9182e8b27adc9c92152bb021494ed2dde7cfb50433a16d8adbcce60518 and more specifically commit googleapis/google-cloud-php-pubsub@7b2d692

This commit adds a method called setDefaultEmulatorConfig() to all affected classes to set $options['transportConfig']['grpc']['stubOpts']['credentials'] but the code doesn't check if Grpc\ChannelCredentials exits.

Workaround

Source: #7187 (comment)

To resolve the issue before a new version with a fix is released you can create a stub (grpc.php.stub) and load it before creating any of the affected objects:

<?php

/**
 * PubSubClient assumes that if the PUBSUB_EMULATOR_HOST env var is set that the grpc extension is installed :(
 */

declare(strict_types=1);

namespace Grpc;

if (! class_exists('Grpc\ChannelCredentials')) {
    class ChannelCredentials {
        public static function createInsecure(): null
        {
            return null;
        }
    }
}

<?php
require_once 'grpc.php.stub';

$pubsubClient = new PubSubClient([
            'projectId'         => 'emulator-project',
            'credentialsConfig' => [
                'keyFile' => [
                    "client_id"     => "fake-fake-fake.apps.googleusercontent.com",
                    "client_secret" => "fake-fake-fake",
                    "refresh_token" => "fake-fake-fake",
                    "type"          => "authorized_user",
                ],
            ],
            'transportConfig'   => [
                'rest' => [
                    'httpHandler' => [HttpHandlerFactory::build($client), 'async'],
                ],
            ],
        ]);