[wp-trac] [WordPress Trac] #65287: block_core_navigation_submenu_render_submenu_icon() removed without deprecation, causing fatal errors on sites using the function

[WordPress Trac]

#65287: block_core_navigation_submenu_render_submenu_icon() removed without
deprecation, causing fatal errors on sites using the function
--------------------------+-----------------------------
 Reporter:  ecairol       |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Menus         |    Version:  7.0
 Severity:  normal        |   Keywords:  has-patch
  Focuses:                |
--------------------------+-----------------------------
 Version:      Gutenberg 23.x / WP 7.0


 **Description**

 `block_core_navigation_submenu_render_submenu_icon()` was silently removed
 in Gutenberg PR #74853 (synced to Core via wordpress-develop PR #10865) as
 part of a refactor that consolidated submenu icon rendering into a new
 shared
 function: `block_core_shared_navigation_render_submenu_icon()`.

 The old was deleted with no
 `_deprecated_function()`. Since no backwards-compatible alias
 was provided, this is a breaking change for any theme or plugin that
 previously called the function directly.

 **Steps to Reproduce**

 1. Install or activate a custom theme (or plugin) that calls
    `block_core_navigation_submenu_render_submenu_icon()` as part of a
    `render_block_core/navigation-submenu` filter (a documented and
    reasonable usage pattern for customizing the dropdown chevron icon).
 2. Update to Gutenberg 23.x (or WordPress 7.0 with the synced change).
 3. Load any page on the site.

 **Expected Behavior**

 - The function call either continues to work, OR
 - WordPress triggers a `_deprecated_function()` notice with guidance to
   use `block_core_shared_navigation_render_submenu_icon()` instead, while
   remaining functional until a future major version.

 **Actual Behavior**

 A fatal PHP error is thrown.

 **Proposed Fix**

 Add a deprecated shim in Core.

 In `wp-includes/blocks/navigation-submenu.php` (or wherever the function
 previously lived), add a backwards-compatible wrapper:

 {{{#!php
 <?php
 /**
  * Renders the submenu icon SVG for the Navigation Submenu block.
  *
  * @deprecated Use block_core_shared_navigation_render_submenu_icon()
 instead.
  * @return string SVG markup for the submenu icon.
  */
 function block_core_navigation_submenu_render_submenu_icon() {
     _deprecated_function(
         __FUNCTION__,
         '7.0.0',
         'block_core_shared_navigation_render_submenu_icon()'
     );
     return block_core_shared_navigation_render_submenu_icon();
 }
 }}}

 **References**
 Gutenberg PR (introduced change):
 https://github.com/WordPress/gutenberg/pull/74853
 WP Core sync PR: https://github.com/WordPress/wordpress-develop/pull/10865

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Ticket URL: <https://core.trac.wordpress.org/ticket/65287>
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