Stop firing WP CRON when it's disabled

[wordpressfan]

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• Made sure you’re on the latest version Yes
• Used the search feature to ensure that the bug hasn’t been reported before Yes

Describe the bug
When the constant DISABLE_WP_CRON is true, we need to stop calling the method spawn_cron here:

wp-rocket/inc/Engine/Optimization/RUCSS/Admin/Subscriber.php

Line 616 in 06381b8

spawn_cron();

This was a suggestion from Kinsta not to fire the CRON because this may cause CPU issues.

To Reproduce
Steps to reproduce the behavior:

1. Add the following line in wp-config.php define( 'DISABLE_WP_CRON', true )
2. Activate RUCSS
3. Wait in WPR settings page for 90 seconds
4. Ajax request will be sent to our backend to fire the CRON

Expected behavior
CRON should not be called at all when this constant is set.

Additional context
Slack convos:

https://wp-media.slack.com/archives/CUT7FLHF1/p1700469134274159
https://wp-media.slack.com/archives/C056ZJMHG0P/p1700248478315299

Acceptance Criteria (for WP Media team use only)

1. When the CRON is disabled, we should run our functions manually to make sure that Used CSS for homepage is generated
2. We should not spawn CRON if it's disabled

[wordpressfan]

Reproduce the issue

Yes

Root cause

As mentioned in the issue, we force the cron to run once the RUCSS option is activated and wait for 90 seconds, this ajax request will be sent to backend to fire the CRON.

Scope a solution

We need to fix this from both sides (the js part and the php part)

JS part:
Here

wp-rocket/inc/Engine/Optimization/RUCSS/Admin/Settings.php

Line 368 in 06381b8

$data['notice_end_time'] = $transient;

We need to add a new key for cron_disabled which has the value as below:

$data['cron_disabled'] = rocket_get_constant( 'DISABLE_WP_CRON', false );

Then in JS here add new condition to check on this new attribute rocket_ajax_data.cron_disabled

PHP Part:
Here we need to add the following check:

if ( rocket_get_constant( 'DISABLE_WP_CRON', false ) ) {
    return;//Bailout and don't fire the CRON.
}

#Effort
[S]

[Miraeld]

Seems good to me :)

[piotrbak]

Changed the Acceptance Criteria here.