Compat: Replace warning-suppression in _wp_can_use_pcre_u()

This patch replaces the use of the problematic error-suppresssion operator with a specific error-handler to catch and report Unicode PCRE support without raising the related issues of error-suppression: notably conflating errors and failing to prevent completely the logging of the warnings.

In this case, the WPCS rule against using error-suppression was actually helpful in pointing out the risk, but the code was left in place with an “ignore” comment to silence the violation; this patch addresses the risk and removes the need for the comment.

Developed in #9576
Discussed in https://core.trac.wordpress.org/ticket/63865

Follow-up to: [45611].

Props dmsnell.
Fixes #63865.


git-svn-id: https://develop.svn.wordpress.org/trunk@60694 602fd350-edb4-49c9-b593-d223f7449a82

Author: dmsnell

src/wp-includes/compat.php

@@ -48,8 +48,28 @@ function _wp_can_use_pcre_u( $set = null ) {
 	}
 
 	if ( 'reset' === $utf8_pcre ) {
-		// phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged -- intentional error generated to detect PCRE/u support.
-		$utf8_pcre = @preg_match( '/^./u', 'a' );
+		$utf8_pcre = true;
+
+		set_error_handler(
+			function ( $errno, $errstr ) use ( &$utf8_pcre ) {
+				if ( str_starts_with( $errstr, 'preg_match():' ) ) {
+					$utf8_pcre = false;
+					return true;
+				}
+
+				return false;
+			},
+			E_WARNING
+		);
+
+		/*
+		 * Attempt to compile a PCRE pattern with the PCRE_UTF8 flag. For
+		 * systems lacking Unicode support this will trigger a warning
+		 * during compilation, which the error handler will intercept.
+		 */
+		preg_match( '//u', '' );
+
+		restore_error_handler();
 	}
 
 	return $utf8_pcre;