[wp-trac] [WordPress Trac] #41488: Customize: uncaught JS error with namespaced nav menu fallbacks

[WordPress Trac]

#41488: Customize: uncaught JS error with namespaced nav menu fallbacks
--------------------------+-----------------------------
 Reporter:  dlh           |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Customize     |    Version:
 Severity:  normal        |   Keywords:  has-patch
  Focuses:                |
--------------------------+-----------------------------
 A `wp_nav_menu()` call with a namespaced `fallback_cb` can generate a
 JavaScript error if the backslash creates invalid JSON. For example:

 {{{#!php
 wp_nav_menu( [
         'fallback_cb' => '\WordPress\my_callback,
         'theme_location' => 'menu-1',
         'menu_id' => 'primary-menu',
 ] );
 }}}

 throws an error at
 https://github.com/WordPress/WordPress/blob/82d0a53e77f0eb6a8de60b67a2b5266c4f042741
 /wp-includes/js/customize-preview-nav-menus.js#L113.

 If the fallback happens to generate escape characters, like
 `\birdpress\bird_callback`, then the error doesn't occur, but the value of
 `navMenuArgs.fallback_cb` is mangled.

 The attached patch takes a conservative approach by checking for a `\`
 before determining a nav menu supports partial refresh.

 I also tested what happens if the backslashes are padded to `\\\\` in
 `$exported_args`. It fixed the issue as far as I could tell, but the
 potential for side-effects seems greater.

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Ticket URL: <https://core.trac.wordpress.org/ticket/41488>
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