Hooks: Fix pointer over-advance in resort_active_iterations()

[liaisontw]

Retest PR from @mrcasual:

When a callback removes itself during execution and is the only entry at that priority, the internal array pointer is re-positioned by resort_active_iterations().

Before this fix, the pointer ended up at the next priority, but the subsequent next() call in the main apply_filters() loop would then advance it once more, skipping the next priority entirely.

Calling prev() ensures the pointer is balanced so the next() call lands correctly on the intended priority.

Fixes #64653.

Trac ticket: https://core.trac.wordpress.org/ticket/64653

[github-actions]

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[github-actions]

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[liaisontw]

Test code. Put above wp-includes directory.
`<?php
/*
Trac #64653: Optimized minimal reproduction
*/

define( 'ABSPATH', dirname( __FILE__ ) . '/' );
define( 'WPINC', 'wp-includes' );

require_once ABSPATH . WPINC . '/plugin.php';

echo "--- Starting Hook Test ---\n";

$executed_priorities = [];

// Priority 10
add_action( 'test_hook', function () use ( &$executed_priorities ) {
$executed_priorities[] = 10;
echo "Executed: Priority 10\n";
}, 10 );

// Priority 50
function wp_hook_bug_self_removing() {
global $executed_priorities;
$executed_priorities[] = 50;
echo "Executed: Priority 50 (removing itself...)\n";

remove_action( 'test_hook', 'wp_hook_bug_self_removing', 50 );

}
add_action( 'test_hook', 'wp_hook_bug_self_removing', 50 );

// Priority 100
add_action( 'test_hook', function () use ( &$executed_priorities ) {
$executed_priorities[] = 100;
echo "Executed: Priority 100\n";
}, 100 );

do_action( 'test_hook' );

echo "--- Test Completed ---\n";

if ( ! in_array( 100, $executed_priorities ) ) {
echo "❌ BUG REPRODUCED: Priority 100 was skipped!\n";
} else {
echo "✅ TEST PASSED: Priority 100 was executed.\n";
}`

[mrcasual]

@liaisontw, I am not sure I follow the logic behind resubmitting my PR. cc @westonruter.

[Copilot]

Pull request overview

Fixes an iteration-pointer edge case in WP_Hook::resort_active_iterations() where a self-removing callback (and only callback at its priority) could cause the next priority level to be skipped during apply_filters()/do_action() execution.

Changes:

• Adjust resort_active_iterations() to step the internal array pointer back when the current priority was removed, preventing an extra next() advance.
• Add PHPUnit coverage for self-removing callbacks to ensure subsequent priorities still execute.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/wp-includes/class-wp-hook.php	Adjusts iteration pointer handling in resort_active_iterations() to avoid skipping priorities after removal.
tests/phpunit/tests/hooks/doAction.php	Adds regression tests for self-removing callbacks at different priority positions.

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