Improper use of a variable variable ($$) in remove_all_filters()

[chrisjean]

In wp-includes/plugin.php's remove_all_filters function are the following lines of code:

if( false !== $priority && isset($$wp_filter[$tag][$priority]) )
    unset($wp_filter[$tag][$priority]);

The $$ is a ​variable variable, which is clearly a typo in this case given the next line. I first found this when the following warning was generated by trying to make use of the priority option of remove_all_actions:

Notice: Array to string conversion in /opt/lampp/htdocs/trunk/wp-includes/plugin.php on line 225

Since this amounts to checking for variables of type $false, $10, or any other given argument, which won't exist, the second argument is currently useless. Thus, until the supplied patch is implemented, it won't be possible to use remove_all_filters or remove_all_actions to remove all hooks of a specific priority.

A sample plugin showing this bug is attached. The sample plugin hooks the same function to the template_redirect action three times with priorities of default, 20, and 30. It then uses the remove_all_actions function (which simply calls remove_all_filters) to remove all template_redirect hooks for priority 10. This should result in the hooked function being called twice, but produces nothing as all the hooks are cleared.

With my supplied patch applied, the hooked function is called twice, echoing "This should render twice." each time. Thus, the expected result is achieved with this patch.

[chrisbliss18]

Example plugin that shows bug

[chrisbliss18]

Bug fix

[hakre]

Thanks for reporting, looks like this is unnoticed since a longer period, westi put that code in back some time.

Reference: r8660

Reviewed, report is valid IMHO.

[chrisbliss18]

Yeah. It's an unfortunate typo that has been there as long as the function has been around.

I did a search through trunk for other $$ typos and didn't see any. Personally, I'd like to see the $$ uses removed. The same functionality can be derived in numerous ways. The main issue with variable variables is that they are difficult to distinguish from a bug and make code clarity very difficult.

[hakre]

Some code cleanups added.

[hakre]

Replying to chrisbliss18:

Yeah. It's an unfortunate typo that has been there as long as the function has been around.

ack.

I did a search through trunk for other $$ typos and didn't see any. Personally, I'd like to see the $$ uses removed. The same functionality can be derived in numerous ways. The main issue with variable variables is that they are difficult to distinguish from a bug and make code clarity very difficult.

true.

[nacin]

(In [13567]) Fix typo in remove_all_filters() that prevented hooks from being removed by priority. fixes #12492, props chrisbliss18.