[wp-hackers] register_uninstall_hook VS uninstall.php

[Jacob Santos]

"The plugin should not run arbitrary code outside of functions, when
registering the uninstall hook. In order to run using the hook, the plugin
will have to be included, which means that any code laying outside of a
function will be run during the uninstall process. The plugin should not
hinder the uninstall process."

*Explanation*:

I'm not sure what the confusion is of this and from what Dion stated. I'm
basically going to restate what he had said earlier. However a little
history.

*History*:

When the hook is used, the plugin is deactivated. In fact, in 2.7 and I will
assume in later versions, the plugin has to be deactivated to be
uninstalled. Therefore, if you are running code outside of functions, then
this will run when the plugin is uninstalled. Most of the time, the code
won't affect anything and should be "safe" however, during the development
of the solution, a lot of compromise and elitism went into the patch.

Really, I had no idea nor I believe anyone else had the best way to do it.
The hook seemed like it would be "best" and the file based alternative was
added later to satisfy some base concerns either I had or other people or
both. It has been a long time since that patch was applied and I'm not going
to read through what other people and I wrote. Not all of which is on that
ticket [1].

*Back to Explanation*:

Simply, the point of the statement is to let you know that you should
*never* run code outside of functions and class methods. During that time, I
noticed that a few plugins were including code that was run in the "global"
scope and thus was causing problems when the "global" scoped switched to
"function" or local scope. Since the uninstall hook is function / local
scope, any "global" scope code will need to be defined as thus:

10. global $my_global_variable;
20. if( conditional() ) {
30.     $my_global_variable = 'womething';
40. } else {
50.    $my_global_variable = 'widget';
60. }

function uninstallhook() {
   global $my_global_variable;
}

The problem is that unless 10 is in the code, the uninstallhook won't
function properly and it was a fear that people would incorrect assume that
the fault was WordPress when it was in fact the crappy [2], poorly coded
plugin's fault.

*Conclusion*:

So basically the comment, and I guess it was a little vague, is just to say
that if you do the above that it is up to you to ensure that your code works
when in function / local scope when the uninstall hook is called. The second
point is that you shouldn't be running anything other than the uninstall
hook anyway. If everything is in functions, then this will be fine since
only the uninstall hook function and its helpers will run.

The second point also includes security. Basically, your code is being
deleted and the reason for the uninstall process in the first place. To
allow for you clean up any tables, metadata, files, etc that you created
during the plugins run and activation. That is it. It does not allow for any
special cases and if that is what you are asking, like, "Well, I want a
screen where they are asked if they want to keep their data." Then guess
want, that has already been debated and while it can be brought up again for
a future patch it was decided that it just wasn't going to happen by the
powers that be. I, alas, do not know if that is already possible since it
has been a year since I looked at any improvements.

I do think that the uninstall.php is the best method for uninstalling, since
it gives you full access to the WordPress library (admin + core) and is, in
my opinion, cleaner when writing than using a function which will most often
be mixed in with a lot of other misc functions. Please note that the define
is only defined for the file (unless this was corrected, I'm going off the
original implementation) and not for the hook, so it should only be checked
for the file in uninstall.php and not the uninstall hook.


[1] I don't know WTF that ticket is, it appears some "improvements" / fixes
that require additional fixes went into a relatively simple process. It
isn't the ticket I'm references earlier and hopefully won't be confused with
the initial uninstall patch and ticket. I'm unsure why two functions are
even required during the uninstall hook process. The primary hook should be
calling other functions that run processes for uninstalling instead of
cycling through a series of functions. This seems like a bug with the
plugin's code than a bug in WordPress codebase, unless it allows it, then it
should only allow one function regardless.

[2] I'm not sure, but I mean the other more obscene curse word, but I'm not
sure if that is "cool" so I'm going to play it safe... well, safer than just
not including it.