Navigation block: block_core_navigation_get_inner_blocks_from_unstable_location() calls deprecated function and lacks null-coalescing guard #77442

Description

Three related bugs exist in packages/block-library/src/navigation/index.php:

1. block_core_navigation_get_inner_blocks_from_unstable_location() (added 6.5.0) calls block_core_navigation_parse_blocks_from_menu_items() which was deprecated in 6.3.0. This triggers a _deprecated_function() notice on every page render when the Navigation block uses the __unstableLocation attribute (classic menu location fallback) and WP_DEBUG is enabled.
2. The deprecated function's docblock references a non-existent replacement: WP_Navigation_Fallback::parse_blocks_from_menu_items(). That method does not exist. The actual replacement is WP_Classic_To_Block_Menu_Converter::to_blocks().
3. Missing null-coalescing fallback: Line 1088 accesses $menu_items_by_parent_id[0] directly without ?? array(). The equivalent call inside the already-deprecated block_core_navigation_get_classic_menu_fallback_blocks() (line 1726) correctly guards this access. If all menu items carry a non-zero parent ID, the 0 key is absent and PHP 8.x raises an undefined array key notice.

Step-by-step reproduction instructions

1. Enable WP_DEBUG and WP_DEBUG_LOG in wp-config.php.
2. Create a Navigation block that uses a classic menu via the __unstableLocation attribute (a theme location fallback menu).
3. Load any front-end page that renders the Navigation block.
4. Check the debug log.

Expected: No deprecation notices.
Actual: _deprecated_function notice for block_core_navigation_parse_blocks_from_menu_items fires on every request.

Screenshots, screen recording, code snippet

`// packages/block-library/src/navigation/index.php

// Line 1088 — calls deprecated function, missing ?? array() guard:
function block_core_navigation_get_inner_blocks_from_unstable_location( $attributes ) {
$menu_items = block_core_navigation_get_menu_items_at_location( $attributes['__unstableLocation'] );
if ( empty( $menu_items ) ) {
return new WP_Block_List( array(), $attributes );
}
$menu_items_by_parent_id = block_core_navigation_sort_menu_items_by_parent_id( $menu_items );
$parsed_blocks = block_core_navigation_parse_blocks_from_menu_items( $menu_items_by_parent_id[0], $menu_items_by_parent_id ); // ← deprecated call + missing ?? array()
return new WP_Block_List( $parsed_blocks, $attributes );
}

// Line 1591 — incorrect @deprecated docblock:
// @deprecated 6.3.0 Use WP_Navigation_Fallback::parse_blocks_from_menu_items() instead.
// WP_Navigation_Fallback has no such method. The actual replacement is:
// WP_Classic_To_Block_Menu_Converter::to_blocks()

// Line 1726 — correct guard used in the already-deprecated sibling function:
$inner_blocks = block_core_navigation_parse_blocks_from_menu_items(
$menu_items_by_parent_id[0] ?? array(), // ← correct pattern
$menu_items_by_parent_id
);`

Proposed fix:
function block_core_navigation_get_inner_blocks_from_unstable_location( $attributes ) { $menu_items = block_core_navigation_get_menu_items_at_location( $attributes['__unstableLocation'] ); if ( empty( $menu_items ) ) { return new WP_Block_List( array(), $attributes ); } $menu_items_by_parent_id = block_core_navigation_sort_menu_items_by_parent_id( $menu_items ); $parsed_blocks = WP_Classic_To_Block_Menu_Converter::to_blocks( $menu_items_by_parent_id[0] ?? array(), $menu_items_by_parent_id ); return new WP_Block_List( $parsed_blocks, $attributes ); }

Also correct the @deprecated docblock at line 1591:
`- * @deprecated 6.3.0 Use WP_Navigation_Fallback::parse_blocks_from_menu_items() instead.

• • @deprecated 6.3.0 Use WP_Classic_To_Block_Menu_Converter::to_blocks() instead.`

Note: WP_Classic_To_Block_Menu_Converter::to_blocks() and ::group_by_parent_id() are currently private — they may need to be made public, or a new public static wrapper added.

Environment info

• WordPress version: N/A (bug is in Gutenberg source, confirmed in trunk)
• Gutenberg version: trunk (confirmed in packages/block-library/src/navigation/index.php)
• Affects any site using a Navigation block with the __unstableLocation attribute
• PHP 8.x required to surface the undefined array key notice (Issue 3)

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure