luau/tests/TypeInfer.unknownnever.test.cpp

// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details

#include "Fixture.h"

#include "doctest.h"

using namespace Luau;

LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);

TEST_SUITE_BEGIN("TypeInferUnknownNever");

TEST_CASE_FIXTURE(Fixture, "string_subtype_and_unknown_supertype")
{
    CheckResult result = check(R"(
        local function f(x: string)
            local foo: unknown = x
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "unknown_subtype_and_string_supertype")
{
    CheckResult result = check(R"(
        local function f(x: unknown)
            local foo: string = x
        end
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
}

TEST_CASE_FIXTURE(Fixture, "unknown_is_reflexive")
{
    CheckResult result = check(R"(
        local function f(x: unknown)
            local foo: unknown = x
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "string_subtype_and_never_supertype")
{
    CheckResult result = check(R"(
        local function f(x: string)
            local foo: never = x
        end
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
}

TEST_CASE_FIXTURE(Fixture, "never_subtype_and_string_supertype")
{
    CheckResult result = check(R"(
        local function f(x: never)
            local foo: string = x
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "never_is_reflexive")
{
    CheckResult result = check(R"(
        local function f(x: never)
            local foo: never = x
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "unknown_is_optional_because_it_too_encompasses_nil")
{
    CheckResult result = check(R"(
        local t: {x: unknown} = {}
    )");
}

TEST_CASE_FIXTURE(Fixture, "table_with_prop_of_type_never_is_uninhabitable")
{
    CheckResult result = check(R"(
        local t: {x: never} = {}
    )");

    LUAU_REQUIRE_ERROR_COUNT(1, result);
}

TEST_CASE_FIXTURE(Fixture, "table_with_prop_of_type_never_is_also_reflexive")
{
    CheckResult result = check(R"(
        local t: {x: never} = {x = 5 :: never}
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "array_like_table_of_never_is_inhabitable")
{
    CheckResult result = check(R"(
        local t: {never} = {}
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "type_packs_containing_never_is_itself_uninhabitable")
{
    CheckResult result = check(R"(
        local function f() return "foo", 5 :: never end

        local x, y, z = f()
    )");

    if (FFlag::DebugLuauDeferredConstraintResolution)
    {
        LUAU_REQUIRE_ERROR_COUNT(1, result);
        CHECK_EQ("Function only returns 2 values, but 3 are required here", toString(result.errors[0]));

        CHECK_EQ("string", toString(requireType("x")));
        CHECK_EQ("never", toString(requireType("y")));
        CHECK_EQ("*error-type*", toString(requireType("z")));
    }
    else
    {
        LUAU_REQUIRE_NO_ERRORS(result);

        CHECK_EQ("never", toString(requireType("x")));
        CHECK_EQ("never", toString(requireType("y")));
        CHECK_EQ("never", toString(requireType("z")));
    }
}

TEST_CASE_FIXTURE(Fixture, "type_packs_containing_never_is_itself_uninhabitable2")
{
    CheckResult result = check(R"(
        local function f(): (string, never) return "", 5 :: never end
        local function g(): (never, string) return 5 :: never, "" end

        local x1, x2 = f()
        local y1, y2 = g()
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    if (FFlag::DebugLuauDeferredConstraintResolution)
    {
        CHECK_EQ("string", toString(requireType("x1")));
        CHECK_EQ("never", toString(requireType("x2")));
        CHECK_EQ("never", toString(requireType("y1")));
        CHECK_EQ("string", toString(requireType("y2")));
    }
    else
    {
        CHECK_EQ("never", toString(requireType("x1")));
        CHECK_EQ("never", toString(requireType("x2")));
        CHECK_EQ("never", toString(requireType("y1")));
        CHECK_EQ("never", toString(requireType("y2")));
    }
}

TEST_CASE_FIXTURE(Fixture, "index_on_never")
{
    CheckResult result = check(R"(
        local x: never = 5 :: never
        local z = x.y
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ("never", toString(requireType("z")));
}

TEST_CASE_FIXTURE(Fixture, "call_never")
{
    CheckResult result = check(R"(
        local f: never = 5 :: never
        local x, y, z = f()
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ("never", toString(requireType("x")));
    CHECK_EQ("never", toString(requireType("y")));
    CHECK_EQ("never", toString(requireType("z")));
}

TEST_CASE_FIXTURE(Fixture, "assign_to_local_which_is_never")
{
    CheckResult result = check(R"(
        local t: never
        t = 3
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "assign_to_global_which_is_never")
{
    CheckResult result = check(R"(
        --!nonstrict
        t = 5 :: never
        t = ""
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "assign_to_prop_which_is_never")
{
    CheckResult result = check(R"(
        local t: never
        t.x = 5
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "assign_to_subscript_which_is_never")
{
    CheckResult result = check(R"(
        local t: never
        t[5] = 7
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "for_loop_over_never")
{
    CheckResult result = check(R"(
        for i, v in (5 :: never) do
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "pick_never_from_variadic_type_pack")
{
    CheckResult result = check(R"(
        local function f(...: never)
            local x, y = (...)
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
}

TEST_CASE_FIXTURE(Fixture, "index_on_union_of_tables_for_properties_that_is_never")
{
    CheckResult result = check(R"(
        type Disjoint = {foo: never, bar: unknown, tag: "ok"} | {foo: never, baz: unknown, tag: "err"}
        local disjoint: Disjoint = {foo = 5 :: never, bar = true, tag = "ok"}
        local foo = disjoint.foo
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ("never", toString(requireType("foo")));
}

TEST_CASE_FIXTURE(Fixture, "index_on_union_of_tables_for_properties_that_is_sorta_never")
{
    CheckResult result = check(R"(
        type Disjoint = {foo: string, bar: unknown, tag: "ok"} | {foo: never, baz: unknown, tag: "err"}
        local disjoint: Disjoint = {foo = 5 :: never, bar = true, tag = "ok"}
        local foo = disjoint.foo
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ("string", toString(requireType("foo")));
}

TEST_CASE_FIXTURE(Fixture, "unary_minus_of_never")
{
    CheckResult result = check(R"(
        local x = -(5 :: never)
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ("never", toString(requireType("x")));
}

TEST_CASE_FIXTURE(Fixture, "length_of_never")
{
    CheckResult result = check(R"(
        local x = #({} :: never)
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ("number", toString(requireType("x")));
}

TEST_CASE_FIXTURE(Fixture, "dont_unify_operands_if_one_of_the_operand_is_never_in_any_ordering_operators")
{
    CheckResult result = check(R"(
        local function ord(x: nil, y)
            return x ~= nil and x > y
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);

    CHECK_EQ("<a>(nil, a) -> boolean", toString(requireType("ord")));
}

TEST_CASE_FIXTURE(Fixture, "math_operators_and_never")
{
    CheckResult result = check(R"(
        local function mul(x: nil, y)
            return x ~= nil and x * y -- infers boolean | never, which is normalized into boolean
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
    CHECK_EQ("<a>(nil, a) -> boolean", toString(requireType("mul")));
}

TEST_CASE_FIXTURE(Fixture, "compare_never")
{
    CheckResult result = check(R"(
        local function cmp(x: nil, y: number)
            return x ~= nil and x > y and x < y -- infers boolean | never, which is normalized into boolean
        end
    )");

    LUAU_REQUIRE_NO_ERRORS(result);
    CHECK_EQ("(nil, number) -> boolean", toString(requireType("cmp")));
}

TEST_SUITE_END();