[wp-hackers] Plugin conflicts with latest version of Jetpack

[Otto]

Ian, the bug is actually in your plugin, and how you're using shortcodes.

In http://plugins.svn.wordpress.org/basic-google-maps-placemarks/trunk/core.php
you have a function called mapShortcodeCalled() which says it is
supposed to "Checks the current posts to see if they contain the map
shortcode."

However, what it's actually doing is to set up the post data and then
call get_the_content(). This would be fine if you wanted to get the
resulting HTML output, because what you're actually doing with that
call is to have it process the shortcodes.

Instead, you should examine the post->post_content directly to
determine if the shortcode is contained in it. Although honestly, I'm
not sure why you'd go to all that trouble. You can enqueue things like
scripts and such in shortcode functions directly now, they'll get
included in the footer instead of the header, so you don't need to
pre-process the content to determine that sort of thing.

But basically, shortcodes and filters need to have a specific
behaviorism that you're not really adhering to very well, and that is
this: No side effects. A filter should filter some input in a certain
way, and do it every time, because it can be called more than once. A
shortcode is really just a special case of filter, it should take the
shortcode as input and return the resulting HTML to be put into the
post. By making filters or shortcodes have dependencies outside of
their inputs, then you introduce strange cases like this.

Jetpack is doing it right here. They want to get the_content, so they
run it through the the_content filter. This is not unusual or
unexpected. What is unexpected is the way your plugin behaves oddly
when some other piece of code is filtering something with the_content
filter. Your plugin is making assumptions about the ordering of
filters and when the_content runs that are not always true, basically.
Moreso since any theme can call the_content any number of times, and
in any place.

-Otto


On Tue, Jan 1, 2013 at 4:42 PM, Ian Dunn <ian at iandunn.name> wrote:
> I just spent a couple hours tracking down a problem that was reported with
> one of my plugins, and it turns out that the latest version of Jetpack is
> causing problems with a lot of different plugins. I've seen reports of at
> least half a dozen different ones, so I thought I'd pass these links along
> in case it might save anyone else some time:
>
> http://wordpress.org/support/topic/jetpack-204-breaks-nextgen-galleries
> http://wordpress.org/support/topic/jetpack-204-upgrade-breaks-several-plugins
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