[wp-trac] [WordPress Trac] #19927: Improve support escaping a shortcode tag

[WordPress Trac]

#19927: Improve support escaping a shortcode tag
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 Reporter:  bobbingwide   |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Shortcodes    |    Version:  3.3.1
 Severity:  normal        |   Keywords:  has-patch needs-testing
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 In do_shortcode_tag there is some code that allows a shortcode to be
 escaped. It is commented with
 // allow [[foo]] syntax for escaping a tag
 This code is fine if do_shortcode() is only invoked once on a particular
 chunk of data.

 But if the code is run more than once then the 'escaped' shortcode once
 again gets selected for processing and the shortcode is expanded.
 e.g. [ [ caption ] ] will be 'escaped' to [ caption ] which then gets
 processed.

 Although this multiple invocation does not normally happen in vanilla
 WordPress, it is very easy to cause it to occur.

 In my case I noticed the problem since I had added the filter for
 'the_content' with a different priority from the WordPress default.
 e.g. add_filter( 'the_content', 'do_shortcode'); I'd missed the '11'.

 Having removed that offending line of code I then discovered that
 Artisteer generated themes call get_the_excerpt() as well as the_excerpt()
 AND I'd added do_shortcode for both these filters.

 The fix is simple. Instead of simply removing the outer square brackets,
 ensure that the first left square bracket is the escaped character [

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Ticket URL: <http://core.trac.wordpress.org/ticket/19927>
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