Autoloader: Load only latest version of autoload files to avoid conflicts.

[superdav42]

Fixes #14389

Changes proposed in this Pull Request:

• Register each autoload file declaration and keep track of versions in the same way we do for classes. Only after all plugins have registered their packages and plugins loaded is fired should we attempt to include the files so that only the latest version is loaded.

Is this a new feature or does it add/remove features to an existing part of Jetpack?

No, just a bug fix should cause no BC breaks.

Testing instructions:

• See issue for plugin to test with.
• Activate both and obverse no errors
• Also try other plugins which use jetpack autoloader to ensure they still fuction.
• Trying as many different composer packages is helpful

Proposed changelog entry for your changes:

• Fix: Conflicts which can occur when jetpack autoloader includes autoload files in the wrong order.

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: March 3, 2020.
Scheduled code freeze: February 25, 2020

Generated by 🚫 dangerJS against 4bf8ca0

[kbrown9]

I left some comments; most of them are just nitpicks.

The README for the autoloader package also needs to be updated.

[kbrown9]

This looks good to me!

I manually tested two scenarios:

Reproduced Issue #14389

1. I installed the two plugins provided in issue Jetpack Autoloader: Conflicts can occur when the autoload files are used #14389.
2. I reproduced the issue caused by the classes being installed from one version of the dependency and files being installed from another version of the dependency.
3. I used the updated Autoloader package from this branch in the plugins.
4. I confirmed that the autoload_files_package.php files were properly generated for each plugin.
5. I confirmed that no errors were generated by the plugins.

Two Plugins using the Jetpack Connection Package

We have a test plugin, Client Example, that uses the Jetpack Connection package. That package autoloads a file, so I tested this branch on a site with the Client Example and Jetpack plugins activated.

1. I manually added the new autoloader package to Client Example.
2. I confirmed that the autoload_files_package.php files were properly generated for both plugins.
3. I added log statements to the autoloaded file (legacy/load-ixr.php), manually adjusted the file versions in the autoload_files_package.php files, and confirmed that the expected versions of the files were installed.

[zinigor]

Looks good and works good, thank you!