luau/tests/TypeInfer.typePacks.cpp

// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
#include "Luau/BuiltinDefinitions.h"
#include "Luau/Parser.h"
#include "Luau/TypeInfer.h"
#include "Luau/TypeVar.h"

#include "Fixture.h"

#include "doctest.h"

using namespace Luau;

TEST_SUITE_BEGIN("TypePackTests");

TEST_CASE_FIXTURE(Fixture, "infer_multi_return")
{
    CheckResult result = check(R"(
        function take_two()
            return 2, 2
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    const FunctionTypeVar* takeTwoType = get<FunctionTypeVar>(requireType("take_two"));
    REQUIRE(takeTwoType != nullptr);

    const auto& [returns, tail] = flatten(takeTwoType->retType);

    CHECK_EQ(2, returns.size());
    CHECK_EQ(typeChecker.numberType, returns[0]);
    CHECK_EQ(typeChecker.numberType, returns[1]);

    CHECK(!tail);
}

TEST_CASE_FIXTURE(Fixture, "empty_varargs_should_return_nil_when_not_in_tail_position")
{
    CheckResult result = check(R"(
        local a, b = ..., 1
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "self_and_varargs_should_work")
{
    CheckResult result = check(R"(
        local t = {}
        function t:f(...) end
        t:f(1)
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "last_element_of_return_statement_can_itself_be_a_pack")
{
    CheckResult result = check(R"(
        function take_two()
            return 2, 2
        end

        function take_three()
            return 1, take_two()
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
    dumpErrors(result);

    const FunctionTypeVar* takeOneMoreType = get<FunctionTypeVar>(requireType("take_three"));
    REQUIRE(takeOneMoreType != nullptr);

    const auto& [rets, tail] = flatten(takeOneMoreType->retType);

    REQUIRE_EQ(3, rets.size());
    CHECK_EQ(typeChecker.numberType, rets[0]);
    CHECK_EQ(typeChecker.numberType, rets[1]);
    CHECK_EQ(typeChecker.numberType, rets[2]);

    CHECK(!tail);
}

TEST_CASE_FIXTURE(Fixture, "higher_order_function")
{
    CheckResult result = check(R"(
        function apply(f, g, x)
            return f(g(x))
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    const FunctionTypeVar* applyType = get<FunctionTypeVar>(requireType("apply"));
    REQUIRE(applyType != nullptr);

    std::vector<TypeId> applyArgs = flatten(applyType->argTypes).first;
    REQUIRE_EQ(3, applyArgs.size());

    const FunctionTypeVar* fType = get<FunctionTypeVar>(applyArgs[0]);
    REQUIRE(fType != nullptr);

    const FunctionTypeVar* gType = get<FunctionTypeVar>(applyArgs[1]);
    REQUIRE(gType != nullptr);

    std::vector<TypeId> gArgs = flatten(gType->argTypes).first;
    REQUIRE_EQ(1, gArgs.size());

    // function(function(t1, T2...): (t3, T4...), function(t5): (t1, T2...), t5): (t3, T4...)

    REQUIRE_EQ(*gArgs[0], *applyArgs[2]);
    REQUIRE_EQ(toString(fType->argTypes), toString(gType->retType));
    REQUIRE_EQ(toString(fType->retType), toString(applyType->retType));
}

TEST_CASE_FIXTURE(Fixture, "return_type_should_be_empty_if_nothing_is_returned")
{
    CheckResult result = check(R"(
        function f() end
        function g() return end
    )");
    LUAU_REQUIRE_NO_ERRORS(result);
    const FunctionTypeVar* fTy = get<FunctionTypeVar>(requireType("f"));
    REQUIRE(fTy != nullptr);
    CHECK_EQ(0, size(fTy->retType));
    const FunctionTypeVar* gTy = get<FunctionTypeVar>(requireType("g"));
    REQUIRE(gTy != nullptr);
    CHECK_EQ(0, size(gTy->retType));
}

TEST_CASE_FIXTURE(Fixture, "no_return_size_should_be_zero")
{
    CheckResult result = check(R"(
        function f(a:any) return a end
        function g() return end
        function h() end

        g(h())
        f(g(),h())
    )");
    LUAU_REQUIRE_NO_ERRORS(result);

    const FunctionTypeVar* fTy = get<FunctionTypeVar>(requireType("f"));
    REQUIRE(fTy != nullptr);
    CHECK_EQ(1, size(follow(fTy->retType)));

    const FunctionTypeVar* gTy = get<FunctionTypeVar>(requireType("g"));
    REQUIRE(gTy != nullptr);
    CHECK_EQ(0, size(gTy->retType));

    const FunctionTypeVar* hTy = get<FunctionTypeVar>(requireType("h"));
    REQUIRE(hTy != nullptr);
    CHECK_EQ(0, size(hTy->retType));
}

TEST_CASE_FIXTURE(Fixture, "varargs_inference_through_multiple_scopes")
{
    CheckResult result = check(R"(
        local function f(...)
            do
                local a: string = ...
                local b: number = ...
            end
        end

        f("foo")
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "multiple_varargs_inference_are_not_confused")
{
    CheckResult result = check(R"(
        local function f(...)
            local a: string = ...

            return function(...)
                local b: number = ...
            end
        end

        f("foo", "bar")(1, 2)
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "parenthesized_varargs_returns_any")
{
    CheckResult result = check(R"(
        --!strict
        local value

        local function f(...)
            value = ...
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
    CHECK_EQ("any", toString(requireType("value")));
}

TEST_CASE_FIXTURE(Fixture, "variadic_packs")
{
    TypeArena& arena = typeChecker.globalTypes;

    unfreeze(arena);

    TypePackId listOfNumbers = arena.addTypePack(TypePackVar{VariadicTypePack{typeChecker.numberType}});
    TypePackId listOfStrings = arena.addTypePack(TypePackVar{VariadicTypePack{typeChecker.stringType}});

    // clang-format off
    addGlobalBinding(typeChecker, "foo",
        arena.addType(
            FunctionTypeVar{
                listOfNumbers,
                arena.addTypePack({typeChecker.numberType})
            }
        ),
        "@test"
    );
    addGlobalBinding(typeChecker, "bar", 
        arena.addType(
            FunctionTypeVar{
                arena.addTypePack({{typeChecker.numberType}, listOfStrings}),
                arena.addTypePack({typeChecker.numberType})
            }
        ),
        "@test"
    );
    // clang-format on

    freeze(arena);

    CheckResult result = check(R"(
        --!strict

        foo(1, 2, 3, "foo")
        bar(1, "foo", "bar", 3)
    )");

    LUAU_REQUIRE_ERROR_COUNT(2, result);

    CHECK_EQ(result.errors[0], (TypeError{Location(Position{3, 21}, Position{3, 26}), TypeMismatch{typeChecker.numberType, typeChecker.stringType}}));

    CHECK_EQ(result.errors[1], (TypeError{Location(Position{4, 29}, Position{4, 30}), TypeMismatch{typeChecker.stringType, typeChecker.numberType}}));
}

TEST_CASE_FIXTURE(Fixture, "variadic_pack_syntax")
{
    CheckResult result = check(R"(
        --!strict

        local function foo(...: number)
        end

        foo(1, 2, 3, 4, 5, 6)
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
    CHECK_EQ(toString(requireType("foo")), "(...number) -> ()");
}

// CLI-45791
TEST_CASE_FIXTURE(UnfrozenFixture, "type_pack_hidden_free_tail_infinite_growth")
{
    CheckResult result = check(R"(
--!nonstrict
if _ then
    _[function(l0)end],l0 = _
elseif _ then
    return l0(nil)
elseif 1 / l0(nil) then
elseif _ then
    return #_,l0()
end
    )");

    LUAU_REQUIRE_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "variadic_argument_tail")
{
    CheckResult result = check(R"(
local _ = function():((...any)->(...any),()->())
	return function() end, function() end
end
for y in _() do
end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "type_alias_type_packs")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    CheckResult result = check(R"(
type Packed<T...> = (T...) -> T...
local a: Packed<>
local b: Packed<number>
local c: Packed<string, number>
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    auto tf = lookupType("Packed");
    REQUIRE(tf);
    CHECK_EQ(toString(*tf), "(T...) -> (T...)");
    CHECK_EQ(toString(requireType("a")), "() -> ()");
    CHECK_EQ(toString(requireType("b")), "(number) -> number");
    CHECK_EQ(toString(requireType("c")), "(string, number) -> (string, number)");

    result = check(R"(
-- (U..., T) cannot be parsed right now
type Packed<T, U...> = { f: (a: T, U...) -> (T, U...) }
local a: Packed<number>
local b: Packed<string, number>
local c: Packed<string, number, boolean>
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    tf = lookupType("Packed");
    REQUIRE(tf);
    CHECK_EQ(toString(*tf), "Packed<T, U...>");
    CHECK_EQ(toString(*tf, {true}), "{| f: (T, U...) -> (T, U...) |}");

    auto ttvA = get<TableTypeVar>(requireType("a"));
    REQUIRE(ttvA);
    CHECK_EQ(toString(requireType("a")), "Packed<number>");
    CHECK_EQ(toString(requireType("a"), {true}), "{| f: (number) -> (number) |}");
    REQUIRE(ttvA->instantiatedTypeParams.size() == 1);
    REQUIRE(ttvA->instantiatedTypePackParams.size() == 1);
    CHECK_EQ(toString(ttvA->instantiatedTypeParams[0], {true}), "number");
    CHECK_EQ(toString(ttvA->instantiatedTypePackParams[0], {true}), "");

    auto ttvB = get<TableTypeVar>(requireType("b"));
    REQUIRE(ttvB);
    CHECK_EQ(toString(requireType("b")), "Packed<string, number>");
    CHECK_EQ(toString(requireType("b"), {true}), "{| f: (string, number) -> (string, number) |}");
    REQUIRE(ttvB->instantiatedTypeParams.size() == 1);
    REQUIRE(ttvB->instantiatedTypePackParams.size() == 1);
    CHECK_EQ(toString(ttvB->instantiatedTypeParams[0], {true}), "string");
    CHECK_EQ(toString(ttvB->instantiatedTypePackParams[0], {true}), "number");

    auto ttvC = get<TableTypeVar>(requireType("c"));
    REQUIRE(ttvC);
    CHECK_EQ(toString(requireType("c")), "Packed<string, number, boolean>");
    CHECK_EQ(toString(requireType("c"), {true}), "{| f: (string, number, boolean) -> (string, number, boolean) |}");
    REQUIRE(ttvC->instantiatedTypeParams.size() == 1);
    REQUIRE(ttvC->instantiatedTypePackParams.size() == 1);
    CHECK_EQ(toString(ttvC->instantiatedTypeParams[0], {true}), "string");
    CHECK_EQ(toString(ttvC->instantiatedTypePackParams[0], {true}), "number, boolean");
}

TEST_CASE_FIXTURE(Fixture, "type_alias_type_packs_import")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    fileResolver.source["game/A"] = R"(
export type Packed<T, U...> = { a: T, b: (U...) -> () }
return {}
    )";

    CheckResult aResult = frontend.check("game/A");
    LUAU_REQUIRE_NO_ERRORS(aResult);

    CheckResult bResult = check(R"(
local Import = require(game.A)
local a: Import.Packed<number>
local b: Import.Packed<string, number>
local c: Import.Packed<string, number, boolean>
local d: { a: typeof(c) }
    )");
    LUAU_REQUIRE_NO_ERRORS(bResult);

    auto tf = lookupImportedType("Import", "Packed");
    REQUIRE(tf);
    CHECK_EQ(toString(*tf), "Packed<T, U...>");
    CHECK_EQ(toString(*tf, {true}), "{| a: T, b: (U...) -> () |}");

    CHECK_EQ(toString(requireType("a"), {true}), "{| a: number, b: () -> () |}");
    CHECK_EQ(toString(requireType("b"), {true}), "{| a: string, b: (number) -> () |}");
    CHECK_EQ(toString(requireType("c"), {true}), "{| a: string, b: (number, boolean) -> () |}");
    CHECK_EQ(toString(requireType("d")), "{| a: Packed<string, number, boolean> |}");
}

TEST_CASE_FIXTURE(Fixture, "type_pack_type_parameters")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    fileResolver.source["game/A"] = R"(
export type Packed<T, U...> = { a: T, b: (U...) -> () }
return {}
    )";

    CheckResult cResult = check(R"(
local Import = require(game.A)
type Alias<S, T, R...> = Import.Packed<S, (T, R...)>
local a: Alias<string, number, boolean>

type B<X...> = Import.Packed<string, X...>
type C<X...> = Import.Packed<string, (number, X...)>
    )");
    LUAU_REQUIRE_NO_ERRORS(cResult);

    auto tf = lookupType("Alias");
    REQUIRE(tf);
    CHECK_EQ(toString(*tf), "Alias<S, T, R...>");
    CHECK_EQ(toString(*tf, {true}), "{| a: S, b: (T, R...) -> () |}");

    CHECK_EQ(toString(requireType("a"), {true}), "{| a: string, b: (number, boolean) -> () |}");

    tf = lookupType("B");
    REQUIRE(tf);
    CHECK_EQ(toString(*tf), "B<X...>");
    CHECK_EQ(toString(*tf, {true}), "{| a: string, b: (X...) -> () |}");

    tf = lookupType("C");
    REQUIRE(tf);
    CHECK_EQ(toString(*tf), "C<X...>");
    CHECK_EQ(toString(*tf, {true}), "{| a: string, b: (number, X...) -> () |}");
}

TEST_CASE_FIXTURE(Fixture, "type_alias_type_packs_nested")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    CheckResult result = check(R"(
type Packed1<T...> = (T...) -> (T...)
type Packed2<T...> = (Packed1<T...>, T...) -> (Packed1<T...>, T...)
type Packed3<T...> = (Packed2<T...>, T...) -> (Packed2<T...>, T...)
type Packed4<T...> = (Packed3<T...>, T...) -> (Packed3<T...>, T...)
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    auto tf = lookupType("Packed4");
    REQUIRE(tf);
    CHECK_EQ(toString(*tf),
        "((((T...) -> (T...), T...) -> ((T...) -> (T...), T...), T...) -> (((T...) -> (T...), T...) -> ((T...) -> (T...), T...), T...), T...) -> "
        "((((T...) -> (T...), T...) -> ((T...) -> (T...), T...), T...) -> (((T...) -> (T...), T...) -> ((T...) -> (T...), T...), T...), T...)");
}

TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_variadic")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    CheckResult result = check(R"(
type X<T...> = (T...) -> (string, T...)

type D = X<...number>
type E = X<(number, ...string)>
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ(toString(*lookupType("D")), "(...number) -> (string, ...number)");
    CHECK_EQ(toString(*lookupType("E")), "(number, ...string) -> (string, number, ...string)");
}

TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_multi")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    CheckResult result = check(R"(
type Y<T..., U...> = (T...) -> (U...)
type A<S...> = Y<S..., S...>
type B<S...> = Y<(number, ...string), S...>

type Z<T, U...> = (T) -> (U...)
type E<S...> = Z<number, S...>
type F<S...> = Z<number, (string, S...)>

type W<T, U..., V...> = (T, U...) -> (T, V...)
type H<S..., R...> = W<number, S..., R...>
type I<S..., R...> = W<number, (string, S...), R...>
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ(toString(*lookupType("A")), "(S...) -> (S...)");
    CHECK_EQ(toString(*lookupType("B")), "(number, ...string) -> (S...)");

    CHECK_EQ(toString(*lookupType("E")), "(number) -> (S...)");
    CHECK_EQ(toString(*lookupType("F")), "(number) -> (string, S...)");

    CHECK_EQ(toString(*lookupType("H")), "(number, S...) -> (number, R...)");
    CHECK_EQ(toString(*lookupType("I")), "(number, string, S...) -> (number, R...)");
}

TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_explicit")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    CheckResult result = check(R"(
type X<T...> = (T...) -> (T...)

type A<S...> = X<(S...)>
type B = X<()>
type C = X<(number)>
type D = X<(number, string)>
type E = X<(...number)>
type F = X<(string, ...number)>
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ(toString(*lookupType("A")), "(S...) -> (S...)");
    CHECK_EQ(toString(*lookupType("B")), "() -> ()");
    CHECK_EQ(toString(*lookupType("C")), "(number) -> number");
    CHECK_EQ(toString(*lookupType("D")), "(number, string) -> (number, string)");
    CHECK_EQ(toString(*lookupType("E")), "(...number) -> (...number)");
    CHECK_EQ(toString(*lookupType("F")), "(string, ...number) -> (string, ...number)");
}

TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_explicit_multi")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    CheckResult result = check(R"(
type Y<T..., U...> = (T...) -> (U...)

type A = Y<(number, string), (boolean)>
type B = Y<(), ()>
type C<S...> = Y<...string, (number, S...)>
type D<X...> = Y<X..., (number, string, X...)>
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ(toString(*lookupType("A")), "(number, string) -> boolean");
    CHECK_EQ(toString(*lookupType("B")), "() -> ()");
    CHECK_EQ(toString(*lookupType("C")), "(...string) -> (number, S...)");
    CHECK_EQ(toString(*lookupType("D")), "(X...) -> (number, string, X...)");
}

TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_explicit_multi_tostring")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
    ScopedFastFlag luauInstantiatedTypeParamRecursion("LuauInstantiatedTypeParamRecursion", true); // For correct toString block

    CheckResult result = check(R"(
type Y<T..., U...> = { f: (T...) -> (U...) }

local a: Y<(number, string), (boolean)>
local b: Y<(), ()>
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ(toString(requireType("a")), "Y<(number, string), (boolean)>");
    CHECK_EQ(toString(requireType("b")), "Y<(), ()>");
}

TEST_CASE_FIXTURE(Fixture, "type_alias_backwards_compatible")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    CheckResult result = check(R"(
type X<T> = () -> T
type Y<T, U> = (T) -> U

type A = X<(number)>
type B = Y<(number), (boolean)>
type C = Y<(number), boolean>
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ(toString(*lookupType("A")), "() -> number");
    CHECK_EQ(toString(*lookupType("B")), "(number) -> boolean");
    CHECK_EQ(toString(*lookupType("C")), "(number) -> boolean");
}

TEST_CASE_FIXTURE(Fixture, "type_alias_type_packs_errors")
{
    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);

    CheckResult result = check(R"(
type Packed<T, U, V...> = (T, U) -> (V...)
local b: Packed<number>
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T, U, V...>' expects at least 2 type arguments, but only 1 is specified");

    result = check(R"(
type Packed<T, U> = (T, U) -> ()
type B<X...> = Packed<number, string, X...>
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T, U>' expects 0 type pack arguments, but 1 is specified");

    result = check(R"(
type Packed<T..., U...> = (T...) -> (U...)
type Other<S...> = Packed<S..., string>
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
    CHECK_EQ(toString(result.errors[0]), "Type parameters must come before type pack parameters");

    result = check(R"(
type Packed<T, U> = (T) -> U
type Other<S...> = Packed<number, S...>
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T, U>' expects 2 type arguments, but only 1 is specified");

    result = check(R"(
type Packed<T...> = (T...) -> T...
local a: Packed
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
    CHECK_EQ(toString(result.errors[0]), "Type parameter list is required");

    result = check(R"(
type Packed<T..., U...> = (T...) -> (U...)
type Other = Packed<>
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T..., U...>' expects 2 type pack arguments, but none are specified");

    result = check(R"(
type Packed<T..., U...> = (T...) -> (U...)
type Other = Packed<number, string>
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T..., U...>' expects 2 type pack arguments, but only 1 is specified");
}

TEST_SUITE_END();