Add FFlag and move test case

Analysis/src/TypeInfer.cpp

@@ -41,6 +41,7 @@ LUAU_FASTFLAGVARIABLE(LuauTinyControlFlowAnalysis, false)
 LUAU_FASTFLAGVARIABLE(LuauTypecheckClassTypeIndexers, false)
 LUAU_FASTFLAGVARIABLE(LuauAlwaysCommitInferencesOfFunctionCalls, false)
 LUAU_FASTFLAG(LuauParseDeclareClassIndexer)
+LUAU_FASTFLAGVARIABLE(LuauIndexTableIntersectionStringExpr, false)
 
 namespace Luau
 {
@@ -3412,7 +3413,7 @@ TypeId TypeChecker::checkLValueBinding(const ScopePtr& scope, const AstExprIndex
                 return prop->type();
             }
         }
-        else if (get<IntersectionType>(exprType))
+        else if (FFlag::LuauIndexTableIntersectionStringExpr && get<IntersectionType>(exprType))
         {
             Name name = std::string(value->value.data, value->value.size);
 

tests/TypeInfer.intersectionTypes.test.cpp

@@ -880,4 +880,34 @@ TEST_CASE_FIXTURE(Fixture, "less_greedy_unification_with_intersection_types_2")
     CHECK_EQ("({| x: number |} & {| x: string |}) -> never", toString(requireType("f")));
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "index_property_table_intersection_1")
+{
+    CheckResult result = check(R"(
+type Foo = {
+	Bar: string,
+} & { Baz: number }
+
+local x: Foo = { Bar = "1", Baz = 2 }
+local y = x.Bar
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "index_property_table_intersection_2")
+{
+    ScopedFastFlag sff{"LuauIndexTableIntersectionStringExpr", true};
+
+    CheckResult result = check(R"(
+type Foo = {
+	Bar: string,
+} & { Baz: number }
+
+local x: Foo = { Bar = "1", Baz = 2 }
+local y = x["Bar"]
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.tables.test.cpp

@@ -216,7 +216,9 @@ TEST_CASE_FIXTURE(Fixture, "used_dot_instead_of_colon")
         local a = T.method()
     )");
 
-    auto it = std::find_if(result.errors.begin(), result.errors.end(), [](const TypeError& e) {
+    auto it = std::find_if(result.errors.begin(), result.errors.end(),
+        [](const TypeError& e)
+        {
             return nullptr != get<FunctionRequiresSelf>(e);
         });
     REQUIRE(it != result.errors.end());
@@ -261,7 +263,9 @@ TEST_CASE_FIXTURE(Fixture, "used_colon_instead_of_dot")
         local a = T:method()
     )");
 
-    auto it = std::find_if(result.errors.begin(), result.errors.end(), [](const TypeError& e) {
+    auto it = std::find_if(result.errors.begin(), result.errors.end(),
+        [](const TypeError& e)
+        {
             return nullptr != get<FunctionDoesNotTakeSelf>(e);
         });
     REQUIRE(it != result.errors.end());
@@ -3642,34 +3646,51 @@ end
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
-TEST_CASE_FIXTURE(BuiltinsFixture, "index_property_table_intersection_1")
+TEST_CASE_FIXTURE(BuiltinsFixture, "write_common_property_to_table_unions")
 {
 
     CheckResult result = check(R"(
 type Foo = {
-	Bar: string,
+    Enabled: boolean,
-} & { Baz: number }
+    Size: number,
+}
 
-local x: Foo = { Bar = "1", Baz = 2 }
+type Bar = {
-local y = x.Bar
+    Enabled: boolean,
+    Width: number,
+    Height: number,
+}
+
+local x: Foo | Bar = { Enabled = true, Size = 5 }
+
+x.Enabled = false
     )");
 
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
-TEST_CASE_FIXTURE(BuiltinsFixture, "index_property_table_intersection_2")
+TEST_CASE_FIXTURE(BuiltinsFixture, "write_common_property_to_table_unions_2")
 {
 
     CheckResult result = check(R"(
 type Foo = {
-	Bar: string,
+    Enabled: boolean,
-} & { Baz: number }
+    Size: number,
+}
 
-local x: Foo = { Bar = "1", Baz = 2 }
+type Bar = {
-local y = x["Bar"]
+    Enabled: boolean,
+    Width: number,
+    Height: number,
+}
+
+local x: Foo | Bar = { Enabled = true, Size = 5 }
+
+x.Size = 6
     )");
 
-    LUAU_REQUIRE_NO_ERRORS(result);
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ("error", toString(result.errors[0])); // TODO
 }
 
 TEST_SUITE_END();