Suppress certain patterns from WP debug log lines

wp-config-suppress-debug.php

<?php
/** Suppress certain patterns from WP debug log lines
 *
 * Here, $suppress_patterns is an array of arrays. Each inner array contains first the error
 * level to match and then string parts that should be found (in order) from the log line.
 *
 * You can place this in wp-config.php after `define('WP_DEBUG_LOG', true );`
 */

// Utility function to check if all parts appear in order and non-overlapping in a message
function message_contains_parts_in_order(string $message, array $parts): bool {
    $pos = 0;
    foreach ($parts as $part) {
        $found = strpos($message, $part, $pos);
        if ($found === false) {
            return false;
        }
        $pos = $found + strlen($part);
    }
    return true;
}

// Custom error handler to suppress specific structured messages by error level and content
function custom_error_handler($errno, $errstr, $errfile, $errline) {
    $suppress_patterns = [
        [E_USER_NOTICE, 'Function ', ' was called '],       // English
        [E_USER_NOTICE, 'Funktiota ', ' kutsuttiin '],      // Finnish
        // You can add patterns for other error levels as well:
        // [E_USER_WARNING, 'Deprecated'], 
    ];

    foreach ($suppress_patterns as $pattern) {
        $pattern_errno = array_shift($pattern); // Take first item as the expected errno
        if ($errno === $pattern_errno && message_contains_parts_in_order($errstr, $pattern)) {
            return true; // Suppress a matching message
        }
    }

    return false; // Allow other messages
}

// Register early in wp-config.php
set_error_handler('custom_error_handler');