[wp-trac] [WordPress Trac] #15155: Allow filtering of shortcode attributes

[WordPress Trac]

#15155: Allow filtering of shortcode attributes
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 Reporter:  coffee2code  |       Owner:                 
     Type:  enhancement  |      Status:  new            
 Priority:  normal       |   Milestone:  Awaiting Review
Component:  Shortcodes   |     Version:  3.0.1          
 Severity:  normal       |    Keywords:  has-patch      
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 It would be handy to have the ability to filter the array returned from
 `shortcode_atts()`.  This would allow plugins to take the default
 shortcode attributes, the user supplied attributes, and the merged array
 of those two into account prior to `shortcode_atts()` returning.

 Potential uses:
  * Override the default shortcode attributes (in a fashion)
  * Ignore certain attribute values from the user and instead use the
 defaults
  * Dynamically generate shortcode attribute values
  * Modifying the behavior of a shortcode handler via attributes without
 redefining and rewriting the handler, particularly if the shortcode
 handler doesn't present filters of its own

 This would be particularly useful to modify the behavior of core-supplied
 shortcodes.  For instance, #14390 requests a way of omitting post
 thumbnails from the gallery shortcode.  Using this patch, this could
 easily be done via hooks in a number of ways (i.e. omit post thumbnails if
 the 'exclude' attribute isn't supplied, or always ignore post thumbnails,
 etc).  In fact, these hooks allow for custom exclusion of any number of
 images for any number of custom reasons.

 The patch introduces two filters, "shortcode_atts_$shortcode" and
 "shortcode_atts".  The former allows hooking only the shortcode_atts for a
 specified shortcode, whereas the latter is a more generic hook.

 `shortcode_atts()` really has no context, so I introduced an optional
 argument, `$shortcode`.  If supplied, the new hooks are fired.  I opted
 not to fire them if no `$shortcode` was supplied since the lack of context
 (namely, the name of the shortcode whose attributes are being processed)
 makes the use of the hooks a questionable proposition.  The patch amends
 all existing `shortcode_atts()` calls to include the new argument.  We'd
 want to promote use of the argument going forward, which is why I (perhaps
 overzealously) made use of  `_deprecated_argument()` to alert developers
 not to a deprecated argument, but to an added argument (is there a better
 way? making the argument required would of course break a lot plugins).

 By way of example, here's a patch for #14390 making use of this patch to
 omit the post thumbnail from the gallery shortcode:

 {{{
 add_filter( 'shortcode_atts_gallery',
 'gallery_shortcode_exclude_thumbnail', 10, 3 );

 /**
  * Exclude post thumbnail image from gallery if user doesn't explicitly
 exclude any images
  *
  * @since 3.1
  * @param array $result The shortcode_atts() merging of $defaults and
 $atts
  * @param array $defaults The default attributes defined for the shortcode
  * @param array $atts The attributes supplied by the user within the
 shortcode
  * @return array The potentially modified $result array
  *
  */
 function gallery_shortcode_exclude_thumbnail( $result, $defaults, $atts )
 {
         if ( empty( $atts['exclude'] ) )
                 $result['exclude'] = get_post_thumbnail_id();
         return $result;
 }
 }}}

 Another example would be modifying the `[caption]` shortcode to prepend or
 append text to whatever caption the user provided.

 {{{
 function append_copyright_to_caption( $result, $defaults, $atts ) {
         $copyright = '© 2010 Example, Inc.';
         if ( isset( $result['caption'] )  && ! empty( $result['caption'] )
 )
                 $result['caption'] .= "<br />$copyright";
         else
                 $result['caption'] =  $copyright;
         return $result;
 }
 add_filter( 'shortcode_atts-caption', 'append_copyright_to_caption', 10,
 3);
 }}}

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Ticket URL: <http://core.trac.wordpress.org/ticket/15155>
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