fix: Handle async stacks correctly (#2744)

* fix: Capture stack traces in APIRouter to preserve async stack

* fix: Handle the stack trace better

* fix: Check if error is an instance of Error (5XX rejects with Result)

* fix: Error.captureStackTrace is not supported in all browsers

src/rest/APIRouter.js

@@ -11,13 +11,27 @@ function buildRoute(manager) {
     get(target, name) {
       if (reflectors.includes(name)) return () => route.join('/');
       if (methods.includes(name)) {
+        // Preserve async stack
+        let stackTrace = null;
+        if (Error.captureStackTrace) {
+          stackTrace = {};
+          Error.captureStackTrace(stackTrace, this.get);
+        }
+
         return options => manager.request(name, route.join('/'), Object.assign({
           versioned: manager.versioned,
           route: route.map((r, i) => {
             if (/\d{16,19}/g.test(r)) return /channels|guilds/.test(route[i - 1]) ? r : ':id';
             return r;
           }).join('/'),
-        }, options));
+        }, options)).catch(error => {
+          if (stackTrace && (error instanceof Error)) {
+            stackTrace.name = error.name;
+            stackTrace.message = error.message;
+            error.stack = stackTrace.stack;
+          }
+          throw error;
+        });
       }
       route.push(name);
       return new Proxy(noop, handler);