TyperChecker2 fix which ended up as UnionType Table Indexer Support

Analysis/src/TypeChecker2.cpp

@@ -3015,6 +3015,60 @@ PropertyType TypeChecker2::hasIndexTypeFromType(
             if (isPrim(indexType, PrimitiveType::String))
                 return {NormalizationResult::True, {tt->indexer->indexResultType}};
             // If the indexer looks like { [any] : _} - the prop lookup should be allowed!
+            else if (auto indexTy = get<UnionType>(indexType))
+            {
+                // If the Indexer is a UnionType
+                // TODO: This is looping everytime, on every request, through everything?
+                // That doesn't sound good. But I am not sure if the other parts do that as well.
+                auto visitOption = [&](TypeId& option, const std::string& prop) -> PropertyType
+                {
+                    if (auto tySingleton = get<SingletonType>(option))
+                        if (auto ty = get<StringSingleton>(tySingleton))
+                            if (ty->value == prop)
+                                return {NormalizationResult::True, {tt->indexer->indexResultType}};
+
+                    // If all fails
+                    return {NormalizationResult::False, {}};
+                };
+
+                auto visitUnionOptions = [&](UnionType unionTy, const std::string& prop) -> PropertyType
+                {
+                    for (TypeId option : unionTy.options)
+                    {
+                        option = follow(option);
+
+                        // No recurse
+                        if (get<UnionType>(option))
+                            return {NormalizationResult::False, {}};
+
+                        PropertyType result = visitOption(option, prop);
+                        if (result.present == NormalizationResult::False)
+                            continue; // Continue searching if it failed
+
+                        // Otherwise return
+                        return result;
+                    }
+
+                    // If all fails
+                    return {NormalizationResult::False, {}};
+                };
+
+                for (TypeId option : indexTy->options)
+                {
+                    option = follow(option);
+
+                    if (auto unionTy = get<UnionType>(option))
+                    {
+                        PropertyType result = visitUnionOptions(*unionTy, prop);
+                        if (result.present == NormalizationResult::False)
+                            continue; // Continue searching if it failed
+                        else
+                            return result; // Otherwise return
+                    }
+
+                    return visitOption(option, prop);
+                }
+            }
             else if (get<AnyType>(indexType) || get<UnknownType>(indexType))
                 return {NormalizationResult::True, {tt->indexer->indexResultType}};
         }

tests/TypeFunction.test.cpp

@@ -690,6 +690,85 @@ TEST_CASE_FIXTURE(ClassFixture, "vector2_multiply_is_overloaded")
     CHECK("mul<Vector2, string>" == toString(requireType("v4")));
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "union_used_as_table_indexer_assignProp_no_error")
+{
+    if (!FFlag::LuauSolverV2)
+        return;
+
+    CheckResult check1 = check(R"(
+--!strict
+
+type NumberTable = {
+    One: number,
+    Two: number,
+    Three: number
+}
+
+type Indexables = "One" | "Two" | "Three" | typeof(5)
+
+type Test = {
+    TestKey: number,
+    [Indexables | "Four"]: number
+}
+
+local tbl = {} :: Test 
+
+-- This was just used to compare it with index
+-- type TestIndex = index<typeof(tbl), "Three">
+
+tbl["Three"] = 3;
+tbl.Three = 3;
+tbl.Four = 4;
+tbl.TestKey = 5;
+)");
+
+    // It should be possible to do "tbl.Three" without erroring.
+    LUAU_REQUIRE_NO_ERRORS(check1);
+
+    // auto test1 = requireTypeAlias("TestIndex");
+    // auto test2 = requireType("tbl");
+
+    // TODO: This doesn't include the autocomplete fix
+    // That has to be still made.
+    // It is supposed to include the indexes from the UnionType
+    // but it is possible to have more than just that
+    // It's also to note that strings may not be the only indexable things
+    // auto ac = autocomplete('1');
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "keyof_used_as_table_indexer_assignProp_no_error")
+{
+    if (!FFlag::LuauSolverV2)
+        return;
+
+    CheckResult check1 = check(R"(
+--!strict
+
+type NumberTable = {
+    One: number,
+    Two: number,
+    Three: number
+}
+
+type Indexables = keyof<NumberTable>
+
+type Test = {
+    TestKey: number,
+    [Indexables | "Four"]: number
+}
+
+local tbl = {} :: Test 
+
+tbl["Three"] = 3;
+tbl.Three = 3;
+tbl.Four = 4;
+tbl.TestKey = 5;
+)");
+
+    // It should be possible to do "tbl.Three" without erroring.
+    LUAU_REQUIRE_NO_ERRORS(check1);
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "keyof_rfc_example")
 {
     if (!FFlag::LuauSolverV2)