From 519a1cd23ddb2b87810a9e87b1a3a00c8155f371 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Fri, 10 Feb 2023 11:34:20 -0500
Subject: [PATCH] LibJS: Add a fallible ThrowableStringBuilder::appendff

---
 .../LibJS/Runtime/ThrowableStringBuilder.h         | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/Userland/Libraries/LibJS/Runtime/ThrowableStringBuilder.h b/Userland/Libraries/LibJS/Runtime/ThrowableStringBuilder.h
index a5958bf968..463b590f35 100644
--- a/Userland/Libraries/LibJS/Runtime/ThrowableStringBuilder.h
+++ b/Userland/Libraries/LibJS/Runtime/ThrowableStringBuilder.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/Format.h>
 #include <AK/StringBuilder.h>
 #include <AK/StringView.h>
 #include <LibJS/Forward.h>
@@ -25,6 +26,19 @@ public:
     ThrowCompletionOr<void> append_code_point(u32 value);
     ThrowCompletionOr<String> to_string() const;
 
+    template<typename... Parameters>
+    ThrowCompletionOr<void> appendff(CheckedFormatString<Parameters...>&& fmtstr, Parameters const&... parameters)
+    {
+        AK::VariadicFormatParams<AK::AllowDebugOnlyFormatters::No, Parameters...> variadic_format_params { parameters... };
+
+        if (vformat(*this, fmtstr.view(), variadic_format_params).is_error()) {
+            // The size returned here is a bit of an estimate, as we don't know what the final formatted string length would be.
+            return m_vm.throw_completion<InternalError>(ErrorType::NotEnoughMemoryToAllocate, length() + fmtstr.view().length());
+        }
+
+        return {};
+    }
+
     using AK::StringBuilder::is_empty;
     using AK::StringBuilder::string_view;
     using AK::StringBuilder::trim;