Performance: avoid over-allocation in wp_is_numeric_array()

When a trace of allocations revealed that `wp_is_numeric_array()`
accounted for a significant fraction of the allocations in a page
render, it was observed that the function eagerly allocates and copies
array keys and then filters them when all it wants to know is whether a
single key in the array meets a condition.

In this patch the `array_filter( array_keys() )` invocation is replaced
with early-aborting iteration to avoid the memory allocation and
copying.

This patch was prepared as part of WCEU 2026 Contributor Day.

Developed in: WordPress#12100
Discussed in: https://core.trac.wordpress.org/ticket/65467

Follow-up to [34927].

Props dmsnell, westonruter, yusufmudagal.
Fixes #65467.


git-svn-id: https://develop.svn.wordpress.org/trunk@62524 602fd350-edb4-49c9-b593-d223f7449a82

Author: dmsnell

src/wp-includes/functions.php

@@ -5290,20 +5290,41 @@ function _wp_to_kebab_case( $input_string ) {
 /**
  * Determines if the variable is a numeric-indexed array.
  *
+ * Note! This answers a different question than {@see array_is_list()} and is
+ *       more flexible to handle situations where some numeric array indices
+ *       have been removed. A numeric-indexed array is only a “list” when the
+ *       array keys form a contiguous range from zero to the highest key.
+ *
+ * Example:
+ *
+ *     true  === wp_is_numeric_array( array( 1, 2, 3, 4 ) );
+ *     false === wp_is_numeric_array( array( 'name' => 'WordPress' ) );
+ *
+ *     // All-numeric keys vs. list.
+ *     $above_two   = array_filter( array( 1, 2, 8, 9 ), fn ( $v ) => $v > 2 );
+ *     $above_two === array( '2' => 8, '3' => 9 );
+ *     true       === wp_is_numeric_array( $above_two );
+ *     false      === array_is_list( $above_two );
+ *
  * @since 4.4.0
  *
  * @param mixed $data Variable to check.
  * @return bool Whether the variable is a list.
+ *
+ * @phpstan-assert-if-true array<int, mixed> $data
  */
-function wp_is_numeric_array( $data ) {
+function wp_is_numeric_array( $data ): bool {
 	if ( ! is_array( $data ) ) {
 		return false;
 	}
 
-	$keys        = array_keys( $data );
-	$string_keys = array_filter( $keys, 'is_string' );
+	foreach ( $data as $key => $value ) {
+		if ( is_string( $key ) ) {
+			return false;
+		}
+	}
 
-	return count( $string_keys ) === 0;
+	return true;
 }
 
 /**

tests/phpunit/tests/functions/wpIsNumericArray.php

@@ -26,43 +26,50 @@ public function test_wp_is_numeric_array( $input, $expected ) {
 	 */
 	public function data_wp_is_numeric_array() {
 		return array(
-			'no index'             => array(
+			'no index'                             => array(
 				'test_array' => array( 'www', 'eee' ),
 				'expected'   => true,
 			),
-			'text index'           => array(
+			'text index'                           => array(
 				'test_array' => array( 'www' => 'eee' ),
 				'expected'   => false,
 			),
-			'numeric index'        => array(
+			'numeric index'                        => array(
 				'test_array' => array( 99 => 'eee' ),
 				'expected'   => true,
 			),
-			'- numeric index'      => array(
+			'filtered list (missing numeric keys)' => array(
+				'test_array' => array_filter(
+					array( 1, 12, 13, 15, 16, 17, 20 ),
+					fn ( $v ) => 0 === $v % 2
+				),
+				'expected'   => true,
+			),
+			'- numeric index'                      => array(
 				'test_array' => array( -11 => 'eee' ),
 				'expected'   => true,
 			),
-			'numeric string index' => array(
+			'numeric string index'                 => array(
 				'test_array' => array( '11' => 'eee' ),
 				'expected'   => true,
 			),
-			'nested number index'  => array(
+			'nested number index'                  => array(
 				'test_array' => array(
 					'next' => array(
 						11 => 'vvv',
 					),
 				),
 				'expected'   => false,
 			),
-			'nested string index'  => array(
+			'nested string index'                  => array(
 				'test_array' => array(
 					'11' => array(
 						'eee' => 'vvv',
 					),
 				),
 				'expected'   => true,
 			),
-			'not an array'         => array(
+			'not an array'                         => array(
 				'test_array' => null,
 				'expected'   => false,
 			),