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<title>[61176] trunk: Script Loader: Guard against exponential recursion during calculation of loading strategy and fetchpriority.</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/61176">61176</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/61176","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>westonruter</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2025-11-07 06:11:24 +0000 (Fri, 07 Nov 2025)</dd>
</dl>
<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>Script Loader: Guard against exponential recursion during calculation of loading strategy and fetchpriority.
This addresses a performance issue in the recursive `WP_Scripts::get_highest_fetchpriority_with_dependents()` and `WP_Scripts::filter_eligible_strategies()` methods for redundant processing of shared dependencies in complex dependency graphs. To fix this, a `$stored_results` param is introduced which is passed by reference; this variable contains a cache of the calculated results for all scripts handles, so that subsequent calls for the same handle can return the cached value instead of re-computing it.
Developed in https://github.com/WordPress/wordpress-develop/pull/10459
Follow-up to <a href="https://core.trac.wordpress.org/changeset/60704">[60704]</a>, <a href="https://core.trac.wordpress.org/changeset/60931">[60931]</a>, <a href="https://core.trac.wordpress.org/changeset/56033">[56033]</a>.
Props ciobanucatalin, b1ink0, westonruter, mukesh27.
See <a href="https://core.trac.wordpress.org/ticket/61734">#61734</a>, <a href="https://core.trac.wordpress.org/ticket/12009">#12009</a>.
Fixes <a href="https://core.trac.wordpress.org/ticket/64194">#64194</a>.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunksrcwpincludesclasswpscriptsphp">trunk/src/wp-includes/class-wp-scripts.php</a></li>
<li><a href="#trunktestsphpunittestsdependenciesscriptsphp">trunk/tests/phpunit/tests/dependencies/scripts.php</a></li>
</ul>
</div>
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<h3>Diff</h3>
<a id="trunksrcwpincludesclasswpscriptsphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-includes/class-wp-scripts.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-includes/class-wp-scripts.php 2025-11-07 04:46:14 UTC (rev 61175)
+++ trunk/src/wp-includes/class-wp-scripts.php 2025-11-07 06:11:24 UTC (rev 61176)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -997,12 +997,17 @@
</span><span class="cx" style="display: block; padding: 0 10px"> *
</span><span class="cx" style="display: block; padding: 0 10px"> * @since 6.3.0
</span><span class="cx" style="display: block; padding: 0 10px"> *
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- * @param string $handle The script handle.
- * @param string[]|null $eligible_strategies Optional. The list of strategies to filter. Default null.
- * @param array<string, true> $checked Optional. An array of already checked script handles, used to avoid recursive loops.
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ * @param string $handle The script handle.
+ * @param string[]|null $eligible_strategies Optional. The list of strategies to filter. Default null.
+ * @param array<string, true> $checked Optional. An array of already checked script handles, used to avoid recursive loops.
+ * @param array<string, string[]> $stored_results Optional. An array of already computed eligible loading strategies by handle, used to increase performance in large dependency lists.
</ins><span class="cx" style="display: block; padding: 0 10px"> * @return string[] A list of eligible loading strategies that could be used.
</span><span class="cx" style="display: block; padding: 0 10px"> */
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- private function filter_eligible_strategies( $handle, $eligible_strategies = null, $checked = array() ) {
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ private function filter_eligible_strategies( $handle, $eligible_strategies = null, $checked = array(), array &$stored_results = array() ) {
+ if ( isset( $stored_results[ $handle ] ) ) {
+ return $stored_results[ $handle ];
+ }
+
</ins><span class="cx" style="display: block; padding: 0 10px"> // If no strategies are being passed, all strategies are eligible.
</span><span class="cx" style="display: block; padding: 0 10px"> if ( null === $eligible_strategies ) {
</span><span class="cx" style="display: block; padding: 0 10px"> $eligible_strategies = $this->delayed_strategies;
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -1053,9 +1058,9 @@
</span><span class="cx" style="display: block; padding: 0 10px"> return array();
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $eligible_strategies = $this->filter_eligible_strategies( $dependent, $eligible_strategies, $checked );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $eligible_strategies = $this->filter_eligible_strategies( $dependent, $eligible_strategies, $checked, $stored_results );
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $stored_results[ $handle ] = $eligible_strategies;
</ins><span class="cx" style="display: block; padding: 0 10px"> return $eligible_strategies;
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -1066,11 +1071,16 @@
</span><span class="cx" style="display: block; padding: 0 10px"> * @see self::filter_eligible_strategies()
</span><span class="cx" style="display: block; padding: 0 10px"> * @see WP_Script_Modules::get_highest_fetchpriority_with_dependents()
</span><span class="cx" style="display: block; padding: 0 10px"> *
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- * @param string $handle Script module ID.
- * @param array<string, true> $checked Optional. An array of already checked script handles, used to avoid recursive loops.
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ * @param string $handle Script module ID.
+ * @param array<string, true> $checked Optional. An array of already checked script handles, used to avoid recursive loops.
+ * @param array<string, string> $stored_results Optional. An array of already computed max priority by handle, used to increase performance in large dependency lists.
</ins><span class="cx" style="display: block; padding: 0 10px"> * @return string|null Highest fetch priority for the script and its dependents.
</span><span class="cx" style="display: block; padding: 0 10px"> */
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- private function get_highest_fetchpriority_with_dependents( string $handle, array $checked = array() ): ?string {
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ private function get_highest_fetchpriority_with_dependents( string $handle, array $checked = array(), array &$stored_results = array() ): ?string {
+ if ( isset( $stored_results[ $handle ] ) ) {
+ return $stored_results[ $handle ];
+ }
+
</ins><span class="cx" style="display: block; padding: 0 10px"> // If there is a recursive dependency, return early.
</span><span class="cx" style="display: block; padding: 0 10px"> if ( isset( $checked[ $handle ] ) ) {
</span><span class="cx" style="display: block; padding: 0 10px"> return null;
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -1099,7 +1109,7 @@
</span><span class="cx" style="display: block; padding: 0 10px"> $highest_priority_index = (int) array_search( $fetchpriority, $priorities, true );
</span><span class="cx" style="display: block; padding: 0 10px"> if ( $highest_priority_index !== $high_priority_index ) {
</span><span class="cx" style="display: block; padding: 0 10px"> foreach ( $this->get_dependents( $handle ) as $dependent_handle ) {
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $dependent_priority = $this->get_highest_fetchpriority_with_dependents( $dependent_handle, $checked );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $dependent_priority = $this->get_highest_fetchpriority_with_dependents( $dependent_handle, $checked, $stored_results );
</ins><span class="cx" style="display: block; padding: 0 10px"> if ( is_string( $dependent_priority ) ) {
</span><span class="cx" style="display: block; padding: 0 10px"> $highest_priority_index = max(
</span><span class="cx" style="display: block; padding: 0 10px"> $highest_priority_index,
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -1111,7 +1121,7 @@
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $stored_results[ $handle ] = $priorities[ $highest_priority_index ]; // @phpstan-ignore parameterByRef.type (We know the index is valid and that this will be a string.)
</ins><span class="cx" style="display: block; padding: 0 10px"> return $priorities[ $highest_priority_index ];
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span></span></pre></div>
<a id="trunktestsphpunittestsdependenciesscriptsphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/tests/phpunit/tests/dependencies/scripts.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/tests/phpunit/tests/dependencies/scripts.php 2025-11-07 04:46:14 UTC (rev 61175)
+++ trunk/tests/phpunit/tests/dependencies/scripts.php 2025-11-07 06:11:24 UTC (rev 61176)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -1436,6 +1436,41 @@
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /**
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ * Tests that `WP_Scripts::get_highest_fetchpriority_with_dependents()` correctly reuses cached results.
+ *
+ * @ticket 64194
+ *
+ * @covers WP_Scripts::get_highest_fetchpriority_with_dependents
+ */
+ public function test_highest_fetchpriority_with_dependents_uses_cached_result() {
+ $wp_scripts = new WP_Scripts();
+ $wp_scripts->add( 'd', 'https://example.com/d.js' );
+ $wp_scripts->add_data( 'd', 'fetchpriority', 'low' );
+
+ /*
+ * Simulate a pre-existing `$stored_results` cache entry for `d`.
+ * If the caching logic works, the function should use this "high" value
+ * instead of recalculating based on the actual (lower) value.
+ */
+ $stored_results = array( 'd' => 'high' );
+
+ // Access the private method using reflection.
+ $method = new ReflectionMethod( WP_Scripts::class, 'get_highest_fetchpriority_with_dependents' );
+ if ( PHP_VERSION_ID < 80100 ) {
+ $method->setAccessible( true );
+ }
+
+ // Pass `$stored_results` BY REFERENCE.
+ $result = $method->invokeArgs( $wp_scripts, array( 'd', array(), &$stored_results ) );
+
+ $this->assertSame(
+ 'high',
+ $result,
+ 'Expected "high" indicates that the cached `$stored_results` entry for D was used instead of recalculating.'
+ );
+ }
+
+ /**
</ins><span class="cx" style="display: block; padding: 0 10px"> * Tests that printing a script without enqueueing has the same output as when it is enqueued.
</span><span class="cx" style="display: block; padding: 0 10px"> *
</span><span class="cx" style="display: block; padding: 0 10px"> * @ticket 61734
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -1535,6 +1570,41 @@
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /**
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ * Tests that `WP_Scripts::filter_eligible_strategies()` correctly reuses cached results.
+ *
+ * @ticket 64194
+ *
+ * @covers WP_Scripts::filter_eligible_strategies
+ */
+ public function test_filter_eligible_strategies_uses_cached_result() {
+ $wp_scripts = new WP_Scripts();
+ $wp_scripts->add( 'd', 'https://example.com/d.js' );
+ $wp_scripts->add_data( 'd', 'strategy', 'defer' );
+
+ /*
+ * Simulate a cached result in `$stored_results` for D.
+ * If caching logic is functioning properly, this cached value
+ * should be returned immediately without recomputing.
+ */
+ $stored_results = array( 'd' => array( 'async' ) );
+
+ // Access the private method via reflection.
+ $method = new ReflectionMethod( WP_Scripts::class, 'filter_eligible_strategies' );
+ if ( PHP_VERSION_ID < 80100 ) {
+ $method->setAccessible( true );
+ }
+
+ // Invoke the method with `$stored_results` passed by reference.
+ $result = $method->invokeArgs( $wp_scripts, array( 'd', null, array(), &$stored_results ) );
+
+ $this->assertSame(
+ array( 'async' ),
+ $result,
+ 'Expected cached `$stored_results` value for D to be reused instead of recomputed.'
+ );
+ }
+
+ /**
</ins><span class="cx" style="display: block; padding: 0 10px"> * Tests that scripts registered for the head do indeed end up there.
</span><span class="cx" style="display: block; padding: 0 10px"> *
</span><span class="cx" style="display: block; padding: 0 10px"> * @ticket 12009
</span></span></pre>
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