For consistency we use the Idna package with WhatWgUrl

Author: nyamsprod

src/WhatWg/Url.php

@@ -15,10 +15,11 @@
 
 use Bakame\Aide\Uri\UrlValidationErrorCollector;
 use Exception;
-use League\Uri\UriString;
 use ReflectionClass;
 use Rowbot\Idna\Idna;
+use Rowbot\URL\Component\Host\StringHost;
 use Rowbot\URL\URL as WhatWgURL;
+use Rowbot\URL\URLRecord;
 use SensitiveParameter;
 use Uri\UriComparisonMode;
 
@@ -294,12 +295,19 @@ public function toUnicodeString(): string
             }
 
             $unicodeHost = $this->getUnicodeHost();
-            $this->urlUnicodeString = $this->getAsciiHost() === $unicodeHost
-                ? $this->url->href
-                : UriString::build([
-                ...UriString::parse($this->url->href),
-                ...['host' => $unicodeHost],
-            ]);
+            if (null === $unicodeHost || $this->getAsciiHost() === $unicodeHost) {
+                $this->urlUnicodeString = $this->url->href;
+
+                return $this->urlUnicodeString;
+            }
+
+            //We use the URLRecord to stay fully compliant with the WHATAG specification
+            //We are forced tu use reflection as we can not access the URLRecord directly
+            $refl = new ReflectionClass(WhatWgURL::class);
+            /** @var URLRecord $urlRecord */
+            $urlRecord = $refl->getProperty('url')->getValue($this->url);
+            $urlRecord->host = new StringHost($unicodeHost);
+            $this->urlUnicodeString = $urlRecord->serializeURL();
 
             return $this->urlUnicodeString;
         }