Fix URL calculation in clone input box (go-gitea#29470)

Ported the function as-is and added comments so we don't forget about
this in the future.

Fixes: go-gitea#29462

templates/repo/clone_script.tmpl

@@ -24,14 +24,22 @@
 		const btn = isSSH ? sshBtn : httpsBtn;
 		if (!btn) return;
 
-		let link = btn.getAttribute('data-link');
-		if (link.startsWith('http://') || link.startsWith('https://')) {
-			// use current protocol/host as the clone link
-			const url = new URL(link);
-			url.protocol = window.location.protocol;
-			url.host = window.location.host;
-			link = url.toString();
+		// NOTE: Keep this function in sync with the one in the js folder
+		function toOriginUrl(urlStr) {
+			try {
+				if (urlStr.startsWith('http://') || urlStr.startsWith('https://') || urlStr.startsWith('/')) {
+					const {origin, protocol, hostname, port} = window.location;
+					const url = new URL(urlStr, origin);
+					url.protocol = protocol;
+					url.hostname = hostname;
+					url.port = port || (protocol === 'https:' ? '443' : '80');
+					return url.toString();
+				}
+			} catch {}
+			return urlStr;
 		}
+		const link = toOriginUrl(btn.getAttribute('data-link'));
+
 		for (const el of document.getElementsByClassName('js-clone-url')) {
 			el[el.nodeName === 'INPUT' ? 'value' : 'textContent'] = link;
 		}

web_src/js/webcomponents/GiteaOriginUrl.js

@@ -1,7 +1,8 @@
-// Convert an absolute or relative URL to an absolute URL with the current origin
+// Convert an absolute or relative URL to an absolute URL with the current origin. It only
+// processes absolute HTTP/HTTPS URLs or relative URLs like '/xxx' or '//host/xxx'.
+// NOTE: Keep this function in sync with clone_script.tmpl
 export function toOriginUrl(urlStr) {
   try {
-    // only process absolute HTTP/HTTPS URL or relative URLs ('/xxx' or '//host/xxx')
     if (urlStr.startsWith('http://') || urlStr.startsWith('https://') || urlStr.startsWith('/')) {
       const {origin, protocol, hostname, port} = window.location;
       const url = new URL(urlStr, origin);