Check if _deprecated_file function exists in class-phpmailer.php

[TimothyBlynJacobs]

The class-phpmailer.php library is loaded early in the tests bootstrap, before wp-settings.php is loaded. This means that the _deprecated_file function is not available at this point. Core's test bootstrap was updated at the same time to point to the new file location which means it hasn't run into this issue. However, any other bootstraps, like ​wp-phpunit ( which is used by Gutenberg ) likely have not been updated.

This causes errors like:

Fatal error: Uncaught Error: Call to undefined function _deprecated_file() in /var/www/html/wp-includes/class-phpmailer.php:6

We could provide compatibility for those alternate test runners by first checking if the _deprecated_file function exists before calling it.

[TimothyBlynJacobs]

To note, I haven't been able to actually test that fixes the Gutenberg issue since everything is brought in dynamically, testing it is difficult. But I think it should.

[SergeyBiryukov]

Makes sense to me, let's try and see if that fixes the Gutenberg build.

[TimothyBlynJacobs]

In 48034:

External Libraries: Skip deprecated file warning for PHPMailer if the API is not loaded.

In [48033] the "class-phpmailer.php" file was deprecated. In test suites, this file is loaded before WordPress in order to setup a mock PHPMailer instance. This means that for test suites that are still loading that file, they'll experience fatal errors due to the undefined "_deprecated_file" function.

This commit skips issuing the deprecated file warning if the "_deprecated_file" function is not available.

Fixes #50380.

[desrosj]

This was mentioned in the following dev note: ​https://make.wordpress.org/core/2020/07/01/external-library-updates-in-wordpress-5-5-call-for-testing/