From 8ef45854f78d4c60a01d059124b8f1082ce0395a Mon Sep 17 00:00:00 2001
From: Kampfkarren <boynedmaster@gmail.com>
Date: Wed, 27 Jul 2022 17:59:21 -0700
Subject: [PATCH] Add FFlag for %*

---
 VM/src/lstrlib.cpp         | 15 +++++++++++++++
 tests/Conformance.test.cpp |  6 +++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/VM/src/lstrlib.cpp b/VM/src/lstrlib.cpp
index 49158f27..20937727 100644
--- a/VM/src/lstrlib.cpp
+++ b/VM/src/lstrlib.cpp
@@ -8,6 +8,9 @@
 #include <string.h>
 #include <stdio.h>
 
+LUAU_FASTFLAG(LuauInterpolatedStringBaseSupport)
+LUAU_FASTFLAGVARIABLE(LuauTostringFormatSpecifier, false);
+
 /* macro to `unsign' a character */
 #define uchar(c) ((unsigned char)(c))
 
@@ -1034,6 +1037,18 @@ static int str_format(lua_State* L)
             }
             case '*':
             {
+                if (!FFlag::LuauTostringFormatSpecifier)
+                {
+                    if (FFlag::LuauInterpolatedStringBaseSupport)
+                    {
+                        luaL_error(L, "interpolated strings are enabled, but the '*' format specifier is not. this is a configuration bug.");
+                        break;
+                    }
+
+                    luaL_error(L, "invalid option '%%*' to 'format'");
+                    break;
+                }
+
                 if (formatItemSize != 1)
                 {
                     luaL_error(L, "'%%*' does not take a form");
diff --git a/tests/Conformance.test.cpp b/tests/Conformance.test.cpp
index 21d1782e..2880c4d7 100644
--- a/tests/Conformance.test.cpp
+++ b/tests/Conformance.test.cpp
@@ -291,12 +291,16 @@ TEST_CASE("Clear")
 
 TEST_CASE("Strings")
 {
+    ScopedFastFlag sff{"LuauTostringFormatSpecifier", true};
+
     runConformance("strings.lua");
 }
 
 TEST_CASE("StringInterp")
 {
-    ScopedFastFlag sff{"LuauInterpolatedStringBaseSupport", true};
+    ScopedFastFlag sffInterpStrings{"LuauInterpolatedStringBaseSupport", true};
+    ScopedFastFlag sffTostringFormat{"LuauTostringFormatSpecifier", true};
+
     runConformance("stringinterp.lua");
 }