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improve stringification of metatable types #2545

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687b943
initial change
nnullcolumn Jul 12, 2026
ea90963
remove space
nnullcolumn Jul 12, 2026
15d847a
update tests
nnullcolumn Jul 12, 2026
8ae628f
i'm so fucking stupid lol
nnullcolumn Jul 12, 2026
2d9ce84
run clang-format
nnullcolumn Jul 14, 2026
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8 changes: 4 additions & 4 deletions Analysis/src/ToString.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -861,12 +861,12 @@ struct TypeStringifier
return;
}

state.emit("{ @metatable ");
stringify(mtv.metatable);
state.emit("setmetatable<");
stringify(mtv.table);
state.emit(",");
state.newline();
stringify(mtv.table);
state.emit(" }");
stringify(mtv.metatable);
state.emit(">");
}

void operator()(TypeId ty, const ExternType& etv)
Expand Down
2 changes: 1 addition & 1 deletion tests/Normalize.test.cpp
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Expand Up @@ -844,7 +844,7 @@ TEST_CASE_FIXTURE(NormalizeFixture, "narrow_union_of_extern_types_with_intersect

TEST_CASE_FIXTURE(NormalizeFixture, "intersection_of_metatables_where_the_metatable_is_top_or_bottom")
{
CHECK("{ @metatable *error-type*, { } }" == toString(normal("Mt<{}, any> & Mt<{}, err>")));
CHECK("setmetatable<{ }, *error-type*>" == toString(normal("Mt<{}, any> & Mt<{}, err>")));
}

TEST_CASE_FIXTURE(NormalizeFixture, "recurring_intersection")
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6 changes: 3 additions & 3 deletions tests/ToString.test.cpp
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Expand Up @@ -145,7 +145,7 @@ TEST_CASE_FIXTURE(Fixture, "metatable")
Type table{TypeVariant(TableType())};
Type metatable{TypeVariant(TableType())};
Type mtv{TypeVariant(MetatableType{&table, &metatable})};
CHECK_EQ("{ @metatable {| |}, {| |} }", toString(&mtv));
CHECK_EQ("setmetatable<{| |}, {| |}>", toString(&mtv));
}

TEST_CASE_FIXTURE(Fixture, "named_metatable")
Expand Down Expand Up @@ -204,15 +204,15 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "exhaustive_toString_of_cyclic_table")
CHECK(
"t2 where "
"t1 = { __index: t1, __mul: ((t2, number) -> t2) & ((t2, t2) -> t2), new: () -> t2 } ; "
"t2 = { @metatable t1, { x: number, y: number, z: number } }" == a
"t2 = setmetatable<{ x: number, y: number, z: number }, t1>" == a
);
}
else
{
CHECK_EQ(
"t2 where "
"t1 = {| __index: t1, __mul: ((t2, number) -> t2) & ((t2, t2) -> t2), new: () -> t2 |} ; "
"t2 = { @metatable t1, { x: number, y: number, z: number } }",
"t2 = setmetatable<{ x: number, y: number, z: number }, t1>",
a
);
}
Expand Down
8 changes: 4 additions & 4 deletions tests/TypeFunction.test.cpp
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Expand Up @@ -1428,7 +1428,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_type_function_assigns_correct_m
LUAU_REQUIRE_NO_ERRORS(result);

TypeId id = requireTypeAlias("Identity");
CHECK_EQ(toString(id, {true}), "{ @metatable { __index: { } }, { } }");
CHECK_EQ(toString(id, {true}), "setmetatable<{ }, { __index: { } }>");
const MetatableType* mt = get<MetatableType>(id);
REQUIRE(mt);
CHECK_EQ(toString(mt->metatable), "{ __index: { } }");
Expand All @@ -1447,15 +1447,15 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_type_function_assigns_correct_m
LUAU_REQUIRE_NO_ERRORS(result);

TypeId id = requireTypeAlias("Identity");
CHECK_EQ(toString(id, {true}), "{ @metatable { __index: { } }, { } }");
CHECK_EQ(toString(id, {true}), "setmetatable<{ }, { __index: { } }>");
const MetatableType* mt = get<MetatableType>(id);
REQUIRE(mt);
CHECK_EQ(toString(mt->metatable), "{ __index: { } }");

TypeId foobar = requireTypeAlias("FooBar");
const MetatableType* mt2 = get<MetatableType>(foobar);
REQUIRE(mt2);
CHECK_EQ(toString(mt2->metatable, {true}), "{ @metatable { __index: { } }, { } }");
CHECK_EQ(toString(mt2->metatable, {true}), "setmetatable<{ }, { __index: { } }>");
}

TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_type_function_errors_on_metatable_with_metatable_metamethod")
Expand All @@ -1471,7 +1471,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_type_function_errors_on_metatab
LUAU_REQUIRE_ERROR_COUNT(1, result);

TypeId id = requireTypeAlias("Identity");
CHECK_EQ(toString(id, {true}), "{ @metatable { __metatable: \"blocked\" }, { } }");
CHECK_EQ(toString(id, {true}), "setmetatable<{ }, { __metatable: \"blocked\" }>");
const MetatableType* mt = get<MetatableType>(id);
REQUIRE(mt);
CHECK_EQ(toString(mt->metatable), "{ __metatable: \"blocked\" }");
Expand Down
6 changes: 3 additions & 3 deletions tests/TypeFunction.user.test.cpp
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Expand Up @@ -915,7 +915,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_check_mutability")
LUAU_REQUIRE_ERROR_COUNT(1, result);
TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
REQUIRE(tm);
CHECK(toString(tm->givenType) == "{ @metatable {boolean}, { } }");
CHECK(toString(tm->givenType) == "setmetatable<{ }, {boolean}>");
}

TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_copy_works")
Expand Down Expand Up @@ -947,7 +947,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_copy_works")
LUAU_REQUIRE_ERROR_COUNT(1, result);
TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
REQUIRE(tm);
CHECK(toString(tm->givenType) == "{ @metatable { [number]: boolean, string: number }, { } }");
CHECK(toString(tm->givenType) == "setmetatable<{ }, { [number]: boolean, string: number }>");
}

TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_simple_cyclic_serialization_works")
Expand Down Expand Up @@ -1486,7 +1486,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "metatable_serialization")
)");

LUAU_REQUIRE_ERROR_COUNT(1, result);
CHECK(toString(result.errors[0]) == R"(Expected this to be 'number', but got '{ @metatable { ma: boolean }, { a: number } }')");
CHECK(toString(result.errors[0]) == R"(Expected this to be 'number', but got 'setmetatable<{ a: number }, { ma: boolean }>')");
}

TEST_CASE_FIXTURE(BuiltinsFixture, "nonstrict_mode")
Expand Down
4 changes: 2 additions & 2 deletions tests/TypeInfer.builtins.test.cpp
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Expand Up @@ -387,9 +387,9 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_on_union_of_tables")

LUAU_REQUIRE_NO_ERRORS(result);
if (!FFlag::DebugLuauForceOldSolver)
CHECK("{ @metatable { }, A } | { @metatable { }, B }" == toString(requireTypeAlias("X")));
CHECK("setmetatable<A, { }> | setmetatable<B, { }>" == toString(requireTypeAlias("X")));
else
CHECK("{ @metatable {| |}, A } | { @metatable {| |}, B }" == toString(requireTypeAlias("X")));
CHECK("setmetatable<A, {| |}> | setmetatable<B, { }>" == toString(requireTypeAlias("X")));
}

TEST_CASE_FIXTURE(BuiltinsFixture, "table_insert_correctly_infers_type_of_array_2_args_overload")
Expand Down
10 changes: 5 additions & 5 deletions tests/TypeInfer.oop.test.cpp
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Expand Up @@ -396,9 +396,9 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "augmenting_an_unsealed_table_with_a_metatabl
)");

if (!FFlag::DebugLuauForceOldSolver)
CHECK("{ @metatable { number: number }, { method: (unknown) -> string } }" == toString(requireType("B"), {true}));
CHECK("setmetatable<{ method: (unknown) -> string }, { number: number }>" == toString(requireType("B"), {true}));
else
CHECK("{ @metatable {| number: number |}, {| method: <a>(a) -> string |} }" == toString(requireType("B"), {true}));
CHECK("setmetatable<{| method: <a>(a) -> string |}, {| number: number |}>" == toString(requireType("B"), {true}));
}

TEST_CASE_FIXTURE(BuiltinsFixture, "react_style_oo")
Expand Down Expand Up @@ -597,7 +597,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "cross_module_metatable")

TypeId clsType = clsBinding->typeId;

CHECK("{ @metatable cls, tbl }" == toString(clsType));
CHECK("setmetatable<tbl, cls>" == toString(clsType));
}

// https://luau.org/typecheck#adding-types-for-faux-object-oriented-programs
Expand Down Expand Up @@ -760,7 +760,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "metatable_field_disallows_invalid_upcast")
auto err = get<TypeMismatch>(results.errors[0]);
REQUIRE(err);
CHECK_EQ("{ const: number }", toString(err->wantedType));
CHECK_EQ("{ @metatable t1, { } } where t1 = { __index: t1, const: number }", toString(err->givenType, {/* exhaustive */ true}));
CHECK_EQ("setmetatable<{ }, t1> where t1 = { __index: t1, const: number }", toString(err->givenType, {/* exhaustive */ true}));
}

TEST_CASE_FIXTURE(BuiltinsFixture, "metatable_field_precedence_for_subtyping")
Expand All @@ -783,7 +783,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "metatable_field_precedence_for_subtyping")
auto err = get<TypeMismatch>(results.errors[0]);
REQUIRE(err);
CHECK_EQ("{ read foo: string }", toString(err->wantedType, {/* exhaustive */ true}));
CHECK_EQ("{ @metatable { __index: { bar: boolean, foo: string } }, { foo: number } }", toString(err->givenType, {/* exhaustive */ true}));
CHECK_EQ("setmetatable<{ foo: number }, { __index: { bar: boolean, foo: string } }>", toString(err->givenType, {/* exhaustive */ true}));
}

TEST_CASE_FIXTURE(BuiltinsFixture, "assign_to_prop_of_intersection_of_metatables")
Expand Down
2 changes: 1 addition & 1 deletion tests/TypeInfer.provisional.test.cpp
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Expand Up @@ -1374,7 +1374,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "function_indexer_satisfies_reading_property"
LUAU_REQUIRE_ERROR_COUNT(1, result);
auto err = get<TypeMismatch>(result.errors[0]);
REQUIRE(err);
CHECK_EQ("{ @metatable { __index: (unknown, string) -> number }, { } }", toString(err->givenType, {/* exhaustive */ true}));
CHECK_EQ("setmetatable<{ }, { __index: (unknown, string) -> number }>", toString(err->givenType, {/* exhaustive */ true}));
CHECK_EQ("{ read X: number }", toString(err->wantedType));
}

Expand Down
14 changes: 7 additions & 7 deletions tests/TypeInfer.tables.test.cpp
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Expand Up @@ -2658,7 +2658,7 @@ b()

LUAU_REQUIRE_ERROR_COUNT(1, result);

CHECK_EQ(toString(result.errors[0]), R"(Cannot call a value of type t1 where t1 = { @metatable {| __call: t1 |}, {| |} })");
CHECK_EQ(toString(result.errors[0]), R"(Cannot call a value of type t1 where t1 = setmetatable<{| |}, {| __call: t1 |}>)");
}

TEST_CASE_FIXTURE(Fixture, "table_subtyping_shouldn't_add_optional_properties_to_sealed_tables")
Expand Down Expand Up @@ -3911,7 +3911,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_has_a_side_effect")
)");

LUAU_REQUIRE_NO_ERRORS(result);
CHECK(toString(requireType("foo")) == "{ @metatable mt, foo }");
CHECK(toString(requireType("foo")) == "setmetatable<foo, mt>");
}

TEST_CASE_FIXTURE(BuiltinsFixture, "tables_should_be_fully_populated")
Expand Down Expand Up @@ -5255,9 +5255,9 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "subtyping_with_a_metatable_table_path")
CHECK("Type function instance setmetatable<unknown, unknown> is uninhabited" == toString(result.errors.at(2)));

CHECK(
"Expected this to be 'setmetatable<unknown, unknown>', but got '{ @metatable { }, { } & { } }'; \n"
"the 1st entry in the type pack is `{ @metatable { }, { } & { } }` and in the 1st entry in the type packreduces to "
"`never`, and `{ @metatable { }, { } & { } }` is not a subtype of `never`" == toString(result.errors.at(3))
"Expected this to be 'setmetatable<unknown, unknown>', but got 'setmetatable<{ } & { }, { }>'; \n"
"the 1st entry in the type pack is `setmetatable<{ } & { }, { }>` and in the 1st entry in the type packreduces to "
"`never`, and `setmetatable<{ } & { }, { }>` is not a subtype of `never`" == toString(result.errors.at(3))
);
}

Expand All @@ -5281,8 +5281,8 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "metatable_union_type")
)");
LUAU_REQUIRE_ERROR_COUNT(1, result);
CHECK_EQ(
"Cannot add indexer to table '{ @metatable t1, (nil & ~(false?)) | { } } where t1 = { new: <a>(a) -> { @metatable t1, (a & ~(false?)) | { "
"} } }'",
"Cannot add indexer to table 'setmetatable<(nil & ~(false?)) | { }, t1> where t1 = { new: <a>(a) -> setmetatable<(a & ~(false?)) | { }, "
"t1> }'",
toString(result.errors[0])
);
}
Expand Down
2 changes: 1 addition & 1 deletion tests/TypeInfer.test.cpp
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Expand Up @@ -1886,7 +1886,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "getmetatable_infer_any_param")
if (!FFlag::DebugLuauForceOldSolver)
CHECK_EQ("(unknown) -> any", toString(requireType("check")));
else
CHECK_EQ("({ @metatable any, {+ +} }) -> any", toString(requireType("check")));
CHECK_EQ("(setmetatable<{+ +}, any>) -> any", toString(requireType("check")));
}

TEST_CASE_FIXTURE(BuiltinsFixture, "fuzzer_pack_check_missing_follow")
Expand Down
2 changes: 1 addition & 1 deletion tests/TypeInfer.typestates.test.cpp
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Expand Up @@ -880,7 +880,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_depends_on_sub_expression")

auto err = get<TypeMismatch>(result.errors[0]);
REQUIRE(err);
CHECK_EQ("{ @metatable { bar: number }, { foo: number } }", toString(err->wantedType, { /* exhaustive */ true}));
CHECK_EQ("setmetatable<{ foo: number }, { bar: number }>", toString(err->wantedType, {/* exhaustive */ true}));
CHECK_EQ("{ foo: number }", toString(err->givenType, { /* exhaustive */ true}));
}

Expand Down
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