Bail out early from `esc_url()` if the URL becomes empty after stripping out disallowed characters.

Fixes #28015
Props jesin for the unit test


git-svn-id: https://develop.svn.wordpress.org/trunk@33923 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/formatting.php

@@ -3277,6 +3277,11 @@ function esc_url( $url, $protocols = null, $_context = 'display' ) {
 
 	$url = str_replace( ' ', '%20', $url );
 	$url = preg_replace('|[^a-z0-9-~+_.?#=!&;,/:%@$\|*\'()\\x80-\\xff]|i', '', $url);
+
+	if ( '' === $url ) {
+		return $url;
+	}
+
 	if ( 0 !== stripos( $url, 'mailto:' ) ) {
 		$strip = array('%0d', '%0a', '%0D', '%0A');
 		$url = _deep_replace($strip, $url);

tests/phpunit/tests/formatting/EscUrl.php

@@ -171,5 +171,11 @@ EOT;
 		$this->assertEquals( 'mailto:?body=Hi%20there,%20I%20thought%20you%20might%20want%20to%20sign%20up%20for%20this%20newsletter', $email_link );
 	}
 
+	/**
+	 * @ticket 28015
+	 */
+	function test_invalid_charaters() {
+		$this->assertEmpty( esc_url_raw('"^[]<>{}`') );
+	}
 
 }