[wp-trac] [WordPress Trac] #54013: wp_restore_group_inner_container() causes duplicate inner container on content that already has an inner container

[WordPress Trac]

#54013: wp_restore_group_inner_container() causes duplicate inner container on
content that already has an inner container
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 Reporter:  davecpage     |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  General       |    Version:  5.8
 Severity:  normal        |   Keywords:
  Focuses:                |
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 I have a site that was originally authored in WP 5.7, when the group block
 added into the content an inner container div. The theme CSS relies upon
 this container to set an overall width from the parent.

 When the site was upgraded to 5.8 we noticed that there were width issues
 on groups, and the reason why was due to a duplicate inner container. When
 attempting to edit the page in the editor the content was "fixed". We
 realised it was because the group block now removes the inner container
 from the HTML, with the function `wp_restore_group_inner_container()`
 restoring it if required.

 The problem appears to be that the function will often "restore" the inner
 container even if it's already there. I eventually tracked it down to the
 initial regex used to detect if it's there. The regex appears to be more
 complex than required. The capturing of groups is unused for example. At
 the most simplest level, just changing the regex so that quantifiers are
 ungreedy causes it to no longer fail in a double adding way.

 It was difficult to test on my local environment, but more consistant on
 our staging. I think because of the number of steps that the regex goes
 through. I can imagine different hosts having different limits for
 performance.

 Simple PHP showing the modified regex on the same content
 https://3v4l.org/1s7cT

 Originally added as https://github.com/WordPress/gutenberg/issues/34199

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Ticket URL: <https://core.trac.wordpress.org/ticket/54013>
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