Civi::url() - Fix inconsistent generation of absolute URLs

CRM/Utils/Url.php

@@ -58,6 +58,25 @@ public static function toRelative(string $value, ?string $currentHostPort = NULL
     return $value;
   }
 
+  /**
+   * Convert to an absolute URL (if relative).
+   *
+   * @param string $value
+   * @param string|null $currentHostPort
+   *   The value of HTTP_HOST. (NULL means "lookup HTTP_HOST")
+   * @return string
+   *   Either the relative version of $value (if on the same HTTP_HOST), or else
+   *   the absolute version.
+   */
+  public static function toAbsolute(string $value, ?string $currentHostPort = NULL): string {
+    if ($value[0] === '/') {
+      $currentHostPort = $currentHostPort ?: $_SERVER['HTTP_HOST'] ?? NULL;
+      $scheme = CRM_Utils_System::isSSL() ? 'https' : 'http';
+      return $scheme . '://' . $currentHostPort . $value;
+    }
+    return $value;
+  }
+
   /**
    * Parse an internal URL. Extract the CiviCRM route.
    *

Civi/Core/Url.php

@@ -684,6 +684,9 @@ public function __toString(): string {
     if ($preferFormat === 'relative') {
       $result = \CRM_Utils_Url::toRelative($result);
     }
+    elseif ($preferFormat === 'absolute') {
+      $result = \CRM_Utils_Url::toAbsolute($result);
+    }
 
     // TODO decide if the current default is good enough for future
     $ssl = $this->getSsl() ?: \CRM_Utils_System::isSSL();