[wp-trac] [WordPress Trac] #46313: WordPress 5.1 and $themes backward compatibility break-ish

[WordPress Trac]

#46313: WordPress 5.1 and $themes backward compatibility break-ish
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 Reporter:  flexithemes   |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Themes        |    Version:  5.1
 Severity:  critical      |   Keywords:
  Focuses:                |
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 First of all, thank you for maintaining WordPress and making it awesome.

 That said, WordPress 5.1 introduced what I consider a backward
 compatibility break, which has broken all 2,200+ of our WordPress themes.

 The issue is with the $theme variable used in the themes. Seems that
 WordPress will use that variable in the core code from this version
 onward.

 Therefore, this global variable produces null:
 {{{#!php
 <?php
  global $theme;
 }}}

 And when reference through:

 {{{#!php
 <?php
 $theme->hook('meta');
 }}}

 The result is a fatal error message now, when things were working
 perfectly in 5.0 and previous.

 Steps to replicate are simple:
 1. Install any of our [https://flexithemes.com themes] on WordPress 5.1
 2. After activating, check the front end of the site.
 3. You'll see an error message like:
 Fatal error: Call to a member function hook() on null in wp-
 content/themes/Teva/header.php on line 6

 If you want to try that specific theme (i.e. Teva), I've attached it to
 this ticket.

 Expected result: theme working as before

 Server environment: PHP 7, LAMP ... I think it would repeatable on any
 server

 Thoughts for discussion if that's allowed here... should the WordPress
 core namespace its variables?

 Should theme developers be namespacing variables? Beyond this
 [https://make.wordpress.org/themes/2012/03/14/theme-frameworks-and-
 namespacing-guidelines/ old guideline for namespacing], I haven't been
 able to find anything else official.

 The conclusion there was:
 "So, bottom line, TL:DR: forked/derivative stand-alone Themes ARE required
 to re-namespace; Themes that use framework libraries are NOT required to
 re-namespace the framework library code."

 Final miscellaneous note: I set the severity to "critical". I wasn't able
 to find a definition in the
 [https://make.wordpress.org/core/handbook/glossary/ glossary] (or anywhere
 else) for what constitutes "critical", but since it's a fatal error so I
 decided to go with it.

 Thank you for your time!

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/46313>
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