always hook initialize_latest_version()

[rrennick]

See #464

This PR is to address

You need to explicitly require AS main file, and do it BEFORE composer autoload, like this:

require_once __DIR__ . '/vendor/woocommerce/action-scheduler/action-scheduler.php';
require_once __DIR__ . '/vendor/autoload.php';

If a Composer autoloader is already active in the containing plugin then the class_exists( 'ActionScheduler_Versions' ) check returns true. Because that check returns true, initialize_latest_version does not get hooked. Before adding a hook, WP checks whether it has already been hooked so adding a hook multiple times will not cause it to be executed multiple times.

Testing Instructions

• Check out add action scheduler package via composer woocommerce-admin#3557
• npm install
• composer install
• deactivate all plugins except WC & WC Admin
• add an action

add_action( 'init', function() {
	$action_id = as_schedule_single_action( time() + 50, 'function_check' );
} );

• load the dashboard should produce a fatal error
• copy action-scheduler.php from this branch to the woocommerce-admin/external/action-scheduler folder
• dashboard should load
• activate AS in this branch
• there should be no errors in the debug log

[rrennick]

I want to do some more testing with this ti verify it doesn't create the problem I outlined in #464 (comment)

[rrennick]

I used 3 plugins where two had composer autoloading and version bumps as follows

• AS - this branch
• as-test version 3.2.1
• woocommerce-admin version 3.1.2

I added error_log( __FILE__ ) in both the as_schedule_single_action and ActionScheduler_ActionFactory with this test snippet:

add_action( 'init', function() {
	error_log( ActionScheduler_Versions::instance()->latest_version() );
	$action_id = as_schedule_single_action( time() + 50, 'which_one' );
} );

The result was

[18-Feb-2020 17:19:17 UTC] 3.2.1
[18-Feb-2020 17:19:17 UTC] /Users/ronrennick/Sites/ron/wp-content/plugins/as-test/vendor/woocommerce/action-scheduler/functions.php
[18-Feb-2020 17:19:17 UTC] /Users/ronrennick/Sites/ron/wp-content/plugins/woocommerce-admin/external/action-scheduler/classes/ActionScheduler_ActionFactory.php

So, I'll leave this on hold for now pending further investigation.