From 29a5198055450451bf7f9e65c08f4ca9157c45ff Mon Sep 17 00:00:00 2001
From: karl-police <karl-police2001@bluewin.ch>
Date: Thu, 20 Feb 2025 21:32:47 +0100
Subject: [PATCH] Fix the order of the arguments being inputted into
 result.append in print() from the Type Function Runtime (#1676)

---

Co-authored-by: vegorov-rbx <75688451+vegorov-rbx@users.noreply.github.com>
---
 Analysis/src/TypeFunctionRuntime.cpp |  8 +++++++-
 tests/TypeFunction.user.test.cpp     | 21 +++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/Analysis/src/TypeFunctionRuntime.cpp b/Analysis/src/TypeFunctionRuntime.cpp
index 79c4f6a1..e36a53c0 100644
--- a/Analysis/src/TypeFunctionRuntime.cpp
+++ b/Analysis/src/TypeFunctionRuntime.cpp
@@ -15,6 +15,7 @@
 
 LUAU_DYNAMIC_FASTINT(LuauTypeFunctionSerdeIterationLimit)
 LUAU_FASTFLAGVARIABLE(LuauUserTypeFunTypeofReturnsType)
+LUAU_FASTFLAGVARIABLE(LuauTypeFunPrintFix)
 
 namespace Luau
 {
@@ -1610,7 +1611,12 @@ static int print(lua_State* L)
         size_t l = 0;
         const char* s = luaL_tolstring(L, i, &l); // convert to string using __tostring et al
         if (i > 1)
-            result.append('\t', 1);
+        {
+            if (FFlag::LuauTypeFunPrintFix)
+                result.append(1, '\t');
+            else
+                result.append('\t', 1);
+        }
         result.append(s, l);
         lua_pop(L, 1);
     }
diff --git a/tests/TypeFunction.user.test.cpp b/tests/TypeFunction.user.test.cpp
index 2cd586c9..1d54e1b7 100644
--- a/tests/TypeFunction.user.test.cpp
+++ b/tests/TypeFunction.user.test.cpp
@@ -10,6 +10,7 @@ using namespace Luau;
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(DebugLuauEqSatSimplification)
 LUAU_FASTFLAG(LuauUserTypeFunTypeofReturnsType)
+LUAU_FASTFLAG(LuauTypeFunPrintFix)
 
 TEST_SUITE_BEGIN("UserDefinedTypeFunctionTests");
 
@@ -1885,4 +1886,24 @@ local _:test<number>
     CHECK(toString(result.errors[0]) == R"(type)");
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_print_tab_char_fix")
+{
+    ScopedFastFlag sffs[] = {{FFlag::LuauSolverV2, true}, {FFlag::LuauTypeFunPrintFix, true}};
+
+    CheckResult result = check(R"(
+        type function test(t)
+            print(1,2)
+
+            return t
+        end
+
+        local _:test<number>
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    // It should be \t and not \x1
+    CHECK_EQ("1\t2", toString(result.errors[0]));
+}
+
 TEST_SUITE_END();