From 9a102e2aff99ecaf2ad1e5ca59fc1c893d5e9b7c Mon Sep 17 00:00:00 2001
From: vegorov-rbx <75688451+vegorov-rbx@users.noreply.github.com>
Date: Fri, 20 Dec 2024 11:30:43 -0800
Subject: [PATCH] Fix negation type 'inner' method in user-defined type
 functions (#1582)

Fixes #1580
---
 Analysis/src/TypeFunctionRuntime.cpp | 18 +++++++++++++++---
 tests/TypeFunction.user.test.cpp     | 23 +++++++++++++++++++++++
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/Analysis/src/TypeFunctionRuntime.cpp b/Analysis/src/TypeFunctionRuntime.cpp
index 24c75a510..bb0309fc3 100644
--- a/Analysis/src/TypeFunctionRuntime.cpp
+++ b/Analysis/src/TypeFunctionRuntime.cpp
@@ -14,6 +14,7 @@
 #include <vector>
 
 LUAU_DYNAMIC_FASTINT(LuauTypeFunctionSerdeIterationLimit)
+LUAU_FASTFLAGVARIABLE(LuauUserTypeFunFixInner)
 LUAU_FASTFLAGVARIABLE(LuauUserTypeFunPrintToError)
 LUAU_FASTFLAGVARIABLE(LuauUserTypeFunFixNoReadWrite)
 LUAU_FASTFLAGVARIABLE(LuauUserTypeFunThreadBuffer)
@@ -413,10 +414,21 @@ static int getNegatedValue(lua_State* L)
         luaL_error(L, "type.inner: expected 1 argument, but got %d", argumentCount);
 
     TypeFunctionTypeId self = getTypeUserData(L, 1);
-    if (auto tfnt = get<TypeFunctionNegationType>(self); !tfnt)
-        allocTypeUserData(L, tfnt->type->type);
+    
+    if (FFlag::LuauUserTypeFunFixInner)
+    {
+        if (auto tfnt = get<TypeFunctionNegationType>(self); tfnt)
+            allocTypeUserData(L, tfnt->type->type);
+        else
+            luaL_error(L, "type.inner: cannot call inner method on non-negation type: `%s` type", getTag(L, self).c_str());
+    }
     else
-        luaL_error(L, "type.inner: cannot call inner method on non-negation type: `%s` type", getTag(L, self).c_str());
+    {
+        if (auto tfnt = get<TypeFunctionNegationType>(self); !tfnt)
+            allocTypeUserData(L, tfnt->type->type);
+        else
+            luaL_error(L, "type.inner: cannot call inner method on non-negation type: `%s` type", getTag(L, self).c_str());
+    }
 
     return 1;
 }
diff --git a/tests/TypeFunction.user.test.cpp b/tests/TypeFunction.user.test.cpp
index a5af44fba..281c73c72 100644
--- a/tests/TypeFunction.user.test.cpp
+++ b/tests/TypeFunction.user.test.cpp
@@ -9,6 +9,7 @@ using namespace Luau;
 
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauUserTypeFunFixNoReadWrite)
+LUAU_FASTFLAG(LuauUserTypeFunFixInner)
 LUAU_FASTFLAG(LuauUserTypeFunPrintToError)
 LUAU_FASTFLAG(LuauUserTypeFunExportedAndLocal)
 LUAU_FASTFLAG(LuauUserDefinedTypeFunParseExport)
@@ -475,6 +476,28 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_negation_methods_work")
     CHECK(toString(tpm->givenTp) == "~string");
 }
 
+TEST_CASE_FIXTURE(ClassFixture, "udtf_negation_inner")
+{
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+    ScopedFastFlag luauUserTypeFunFixInner{FFlag::LuauUserTypeFunFixInner, true};
+
+    CheckResult result = check(R"(
+type function pass(t)
+    return types.negationof(t):inner()
+end
+
+type function fail(t)
+    return t:inner()
+end
+
+local function ok(idx: pass<number>): number return idx end
+local function notok(idx: fail<number>): never return idx end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(4, result);
+    CHECK(toString(result.errors[0]) == R"('fail' type function errored at runtime: [string "fail"]:7: type.inner: cannot call inner method on non-negation type: `number` type)");
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_table_serialization_works")
 {
     ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};