ladybird/Userland/Libraries/LibJS/Runtime/Completion.h

/*
 * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
 * Copyright (c) 2021-2022, Linus Groh <linusg@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/FlyString.h>
#include <AK/Optional.h>
#include <AK/Try.h>
#include <AK/Variant.h>
#include <LibJS/Runtime/Value.h>

namespace JS {

// 6.2.3 The Completion Record Specification Type, https://tc39.es/ecma262/#sec-completion-record-specification-type
class [[nodiscard]] Completion {
public:
    enum class Type {
        Empty,
        Normal,
        Break,
        Continue,
        Return,
        Throw,
    };

    ALWAYS_INLINE Completion(Type type, Optional<Value> value, Optional<FlyString> target)
        : m_type(type)
        , m_value(move(value))
        , m_target(move(target))
    {
        VERIFY(type != Type::Empty);
        if (m_value.has_value())
            VERIFY(!m_value->is_empty());
    }

    Completion(ThrowCompletionOr<Value> const&);

    // 5.2.3.1 Implicit Completion Values, https://tc39.es/ecma262/#sec-implicit-completion-values
    // Not `explicit` on purpose.
    ALWAYS_INLINE Completion(Value value)
        : Completion(Type::Normal, value, {})
    {
    }

    ALWAYS_INLINE Completion(Optional<Value> value)
        : Completion(Type::Normal, move(value), {})
    {
    }

    ALWAYS_INLINE Completion()
        : Completion(js_undefined())
    {
    }

    Completion(Completion const&) = default;
    Completion& operator=(Completion const&) = default;
    Completion(Completion&&) = default;
    Completion& operator=(Completion&&) = default;

    [[nodiscard]] Type type() const
    {
        VERIFY(m_type != Type::Empty);
        return m_type;
    }
    [[nodiscard]] Optional<Value>& value() { return m_value; }
    [[nodiscard]] Optional<Value> const& value() const { return m_value; }
    [[nodiscard]] Optional<FlyString>& target() { return m_target; }
    [[nodiscard]] Optional<FlyString> const& target() const { return m_target; }

    // "abrupt completion refers to any completion with a [[Type]] value other than normal"
    [[nodiscard]] bool is_abrupt() const { return m_type != Type::Normal; }

    // These are for compatibility with the TRY() macro in AK.
    [[nodiscard]] bool is_error() const { return m_type == Type::Throw; }
    [[nodiscard]] Optional<Value> release_value() { return move(m_value); }
    Completion release_error()
    {
        VERIFY(is_error());
        VERIFY(m_value.has_value());
        return { m_type, release_value(), move(m_target) };
    }

    // 6.2.3.4 UpdateEmpty ( completionRecord, value ), https://tc39.es/ecma262/#sec-updateempty
    Completion update_empty(Optional<Value> value) const
    {
        // 1. Assert: If completionRecord.[[Type]] is either return or throw, then completionRecord.[[Value]] is not empty.
        if (m_type == Type::Return || m_type == Type::Throw)
            VERIFY(m_value.has_value());

        // 2. If completionRecord.[[Value]] is not empty, return ? completionRecord.
        if (m_value.has_value())
            return *this;

        // 3. Return Completion Record { [[Type]]: completionRecord.[[Type]], [[Value]]: value, [[Target]]: completionRecord.[[Target]] }.
        return { m_type, move(value), m_target };
    }

private:
    class EmptyTag {
    };
    friend AK::Optional<Completion>;

    Completion(EmptyTag)
        : m_type(Type::Empty)
    {
    }

    bool is_empty() const
    {
        return m_type == Type::Empty;
    }

    Type m_type { Type::Normal }; // [[Type]]
    Optional<Value> m_value;      // [[Value]]
    Optional<FlyString> m_target; // [[Target]]
};

}

namespace AK {

template<>
class Optional<JS::Completion> {
    template<typename U>
    friend class Optional;

public:
    using ValueType = JS::Completion;

    Optional()
        : m_value(JS::Completion(JS::Completion::EmptyTag {}))
    {
    }

    Optional(Optional<JS::Completion> const& other)
    {
        if (other.has_value())
            m_value = other.m_value;
    }

    Optional(Optional&& other)
        : m_value(other.m_value)
    {
    }

    template<typename U = JS::Completion>
    explicit(!IsConvertible<U&&, JS::Completion>) Optional(U&& value) requires(!IsSame<RemoveCVReference<U>, Optional<JS::Completion>> && IsConstructible<JS::Completion, U&&>)
        : m_value(forward<U>(value))
    {
    }

    Optional& operator=(Optional const& other)
    {
        if (this != &other) {
            clear();
            m_value = other.m_value;
        }
        return *this;
    }

    Optional& operator=(Optional&& other)
    {
        if (this != &other) {
            clear();
            m_value = other.m_value;
        }
        return *this;
    }

    void clear()
    {
        m_value = JS::Completion(JS::Completion::EmptyTag {});
    }

    [[nodiscard]] bool has_value() const
    {
        return !m_value.is_empty();
    }

    [[nodiscard]] JS::Completion& value() &
    {
        VERIFY(has_value());
        return m_value;
    }

    [[nodiscard]] JS::Completion const& value() const&
    {
        VERIFY(has_value());
        return m_value;
    }

    [[nodiscard]] JS::Completion value() &&
    {
        return release_value();
    }

    [[nodiscard]] JS::Completion release_value()
    {
        VERIFY(has_value());
        JS::Completion released_value = m_value;
        clear();
        return released_value;
    }

    JS::Completion value_or(JS::Completion const& fallback) const&
    {
        if (has_value())
            return value();
        return fallback;
    }

    [[nodiscard]] JS::Completion value_or(JS::Completion&& fallback) &&
    {
        if (has_value())
            return value();
        return fallback;
    }

    JS::Completion const& operator*() const { return value(); }
    JS::Completion& operator*() { return value(); }

    JS::Completion const* operator->() const { return &value(); }
    JS::Completion* operator->() { return &value(); }

private:
    JS::Completion m_value;
};

}

namespace JS {

template<typename ValueType>
class [[nodiscard]] ThrowCompletionOr {
public:
    ThrowCompletionOr() requires(IsSame<ValueType, Empty>)
        : m_value(Empty {})
    {
    }

    // Not `explicit` on purpose so that `return vm.throw_completion<Error>(...);` is possible.
    ThrowCompletionOr(Completion throw_completion)
        : m_throw_completion(move(throw_completion))
    {
        VERIFY(m_throw_completion->is_error());
    }

    // Not `explicit` on purpose so that `return value;` is possible.
    ThrowCompletionOr(ValueType value)
        : m_value(move(value))
    {
        if constexpr (IsSame<ValueType, Value>)
            VERIFY(!m_value->is_empty());
    }

    ThrowCompletionOr(ThrowCompletionOr const&) = default;
    ThrowCompletionOr& operator=(ThrowCompletionOr const&) = default;
    ThrowCompletionOr(ThrowCompletionOr&&) = default;
    ThrowCompletionOr& operator=(ThrowCompletionOr&&) = default;

    // Allows implicit construction of ThrowCompletionOr<T> from a type U if T(U) is a supported constructor.
    // Most commonly: Value from Object* or similar, so we can omit the curly braces from "return { TRY(...) };".
    // Disabled for POD types to avoid weird conversion shenanigans.
    template<typename WrappedValueType>
    ThrowCompletionOr(WrappedValueType value) requires(!IsPOD<ValueType>)
        : m_value(move(value))
    {
    }

    [[nodiscard]] bool is_throw_completion() const { return m_throw_completion.has_value(); }
    Completion const& throw_completion() const { return *m_throw_completion; }

    [[nodiscard]] bool has_value() const requires(!IsSame<ValueType, Empty>) { return m_value.has_value(); }
    [[nodiscard]] ValueType const& value() const requires(!IsSame<ValueType, Empty>) { return *m_value; }

    // These are for compatibility with the TRY() macro in AK.
    [[nodiscard]] bool is_error() const { return m_throw_completion.has_value(); }
    [[nodiscard]] ValueType release_value() { return m_value.release_value(); }
    Completion release_error() { return m_throw_completion.release_value(); }

private:
    Optional<Completion> m_throw_completion;
    Optional<ValueType> m_value;
};

template<>
class ThrowCompletionOr<void> : public ThrowCompletionOr<Empty> {
public:
    using ThrowCompletionOr<Empty>::ThrowCompletionOr;
};

ThrowCompletionOr<Value> await(VM&, Value);

// 6.2.3.2 NormalCompletion ( value ), https://tc39.es/ecma262/#sec-normalcompletion
inline Completion normal_completion(Optional<Value> value)
{
    return { Completion::Type::Normal, move(value), {} };
}

// 6.2.3.3 ThrowCompletion ( value ), https://tc39.es/ecma262/#sec-throwcompletion
Completion throw_completion(Value);

}