How to properly turn off REVISIONS and AUTOSAVE for whole site and optionally for a custom post type only

Is there a hook/function combination that can be added to my theme’s functions.php to properly disable REVISIONS and AUTOSAVE for the entire wordpress installation? What about if just for a certain custom post type? Searching online gives various hacks from deregistering scripts to tampering with core files. What’s the acceptable/correct way to do this?

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This should be placed in your wp-config.php (and no where else):

define( 'AUTOSAVE_INTERVAL', 60*60*60*24*365 ); // autosave 1x per year
define( 'EMPTY_TRASH_DAYS',  0 ); // zero days
define( 'WP_POST_REVISIONS', false ); // no revisions

I’m also looking for how to disable autosave. But here’s what I was told in a Trac ticket:

If you really need this feature you should manage the sequential IDs yourself in a custom field and then implement custom URL routing. It shouldn’t be too hard to pull that off.

Placing the defines in wp-config.php is fine until you turn WP_DEBUG on when you will get ‘already defined’ PHP notices in the debug.log every couple of minutes. Others claim placing these defines above the ABSPATH define will help.

However, I can categorically confirm the best place to put your defines is in a plugin, because the activated plugins are loaded before the WP default defines.

The default defines are protected with if exists tests, hence your plugin loaded defines will take precedence and will not cause a clash nor the repetitive PHP notices in the debug log.