Media, Editor, Menus: Use isset() instead of in_array() over array_keys()

[mukeshpanchal27]

Summary

Nine call sites in core answer the question "does this array have this key?" the expensive way:

in_array( $needle, array_keys( $array ), true )

That is O(n) in time and O(n) in memory — array_keys() allocates a brand new packed array of every key on each call, purely so in_array() can walk it and throw it away. PHP already indexes arrays by key in a hash table, so the same question is answerable in O(1):

isset( $array[ $needle ] )

Changes

7 files, 9 call sites:

File	Array	Notes
wp-includes/media.php	$_wp_additional_image_sizes	image_constrain_size_for_editor() — runs per image, per size, on every editor/media request. Hottest of the nine.
wp-includes/block-editor.php	$image_size_names	Block editor settings assembly.
wp-includes/sitemaps.php	$provider->get_object_subtypes()	get_sitemap_url().
wp-includes/link-template.php	$blogs	get_dashboard_url() — every site a user belongs to, unbounded on large networks.
wp-admin/includes/dashboard.php	get_blogs_of_user()	Quick Draft widget; same unbounded network array.
wp-admin/includes/class-theme-installer-skin.php	$all_themes	Parent-theme validation.
wp-admin/nav-menus.php (×3)	$dbids_to_orders	Inside the menu-item loop, so the linear scan is multiplied by the number of menu items — effectively O(n²) on large menus.

In media.php the accompanying ! empty( $_wp_additional_image_sizes ) && guard is dropped as redundant — isset() on a key of an empty or undefined array is already false:

-	} elseif ( ! empty( $_wp_additional_image_sizes ) && in_array( $size, array_keys( $_wp_additional_image_sizes ), true ) ) {
+	} elseif ( isset( $_wp_additional_image_sizes[ $size ] ) ) {

Measurement

PHP 8.3.2, 200,000 iterations per case, key present at the last position (worst case for in_array) and absent:

Array size	in_array(array_keys()) hit	isset() hit	in_array(array_keys()) miss	isset() miss	Speed-up
5	21.45 ms	7.61 ms	17.39 ms	6.88 ms	2.8×
30	59.07 ms	7.64 ms	41.47 ms	7.81 ms	7.7×
200	226.34 ms	7.23 ms	194.67 ms	6.84 ms	31×

isset() is flat at ~7 ms regardless of array size; the current form grows linearly. The per-call allocation is avoided entirely, which also takes pressure off the GC.

Behaviour notes

Two differences between the old and new expressions, neither of which is a regression at any of these call sites:

1. isset() is false for a null value. Every array here stores arrays, objects, strings or ints as values — never null. (array_key_exists() would be the literal equivalent, but it is measurably slower than isset() and unnecessary here.)
2. Numeric-string keys. PHP casts the integer-like key '2' to int 2 on insertion, so in_array( '2', array_keys( $a ), true ) returns false for a size registered as '2' while isset( $a['2'] ) correctly returns true. The new code is more correct; the old strict comparison was silently failing to match such keys. In nav-menus.php the needle is already explicitly cast with (int), so both forms agree.

Testing instructions

1. vendor/bin/phpcs src/wp-includes/media.php src/wp-includes/block-editor.php src/wp-includes/sitemaps.php src/wp-includes/link-template.php src/wp-admin/includes/dashboard.php src/wp-admin/includes/class-theme-installer-skin.php src/wp-admin/nav-menus.php
2. Confirm image sizes still resolve: insert an image in the editor at a size registered via add_image_size() and check the constrained dimensions are unchanged.
3. On multisite, confirm get_dashboard_url() still returns the site dashboard for a user who belongs to the current site, and the user dashboard for one who does not.
4. Save a nav menu with nested items and confirm parent/child relationships are preserved.

Verification done

• php -l clean on all 7 files.
• vendor/bin/phpcs: 0 errors. The 2 warnings emitted are pre-existing WordPress.DB.PreparedSQL.NotPrepared notices on unrelated lines (link-template.php:2030, media.php:5716).