src/dawn/native/Serializable.h

// Copyright 2022 The Dawn & Tint Authors
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this
//    list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice,
//    this list of conditions and the following disclaimer in the documentation
//    and/or other materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its
//    contributors may be used to endorse or promote products derived from
//    this software without specific prior written permission.
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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#ifndef SRC_DAWN_NATIVE_SERIALIZABLE_H_
#define SRC_DAWN_NATIVE_SERIALIZABLE_H_

#include <utility>

#include "dawn/native/VisitableMembers.h"
#include "dawn/native/stream/BlobSource.h"
#include "dawn/native/stream/ByteVectorSink.h"
#include "dawn/native/stream/Stream.h"

namespace dawn::native {

// Base CRTP for implementing StreamIn/StreamOut/FromBlob/ToBlob for Derived,
// assuming Derived has VisitAll methods provided by DAWN_VISITABLE_MEMBERS.
template <typename Derived>
class Serializable {
  public:
    friend void StreamIn(stream::Sink* s, const Derived& in) {
        in.VisitAll([&](const auto&... members) { StreamIn(s, members...); });
    }

    friend MaybeError StreamOut(stream::Source* s, Derived* out) {
        return out->VisitAll([&](auto&... members) { return StreamOut(s, &members...); });
    }

    static ResultOrError<Derived> FromBlob(Blob blob) {
        stream::BlobSource source(std::move(blob));
        Derived out;
        DAWN_TRY(StreamOut(&source, &out));
        return out;
    }

    Blob ToBlob() const {
        stream::ByteVectorSink sink;
        StreamIn(&sink, static_cast<const Derived&>(*this));
        return CreateBlob(std::move(sink));
    }
};

// UnsafeUnserializedValue holds a value of type T that does nothing when StreamIn to a sink, calls
// default constructor when StreamOut from a source, and always compares as equal between objects of
// the same type UnsafeUnserializedValue<T>. This is used for members in DAWN_SERIALIZABLE or
// DAWN_MAKE_CACHE_REQUEST to prevent a member to get streamed into cache key, or enable having
// unserializabled fields that get computed by cache missed function and returned together with
// cached fields.
template <typename T>
class UnsafeUnserializedValue {
  public:
    UnsafeUnserializedValue() = default;
    explicit UnsafeUnserializedValue(T&& value) : mValue(std::forward<T>(value)) {}
    explicit UnsafeUnserializedValue(const T& value) : mValue(value) {}
    UnsafeUnserializedValue(const UnsafeUnserializedValue<T>& other)
        : mValue(other.UnsafeGetValue()) {}
    UnsafeUnserializedValue<T>& operator=(UnsafeUnserializedValue<T>&& other) {
        mValue = std::move(other.UnsafeGetValue());
        return *this;
    }

    constexpr const T& UnsafeGetValue() const { return mValue; }
    constexpr T& UnsafeGetValue() { return mValue; }

    friend constexpr void StreamIn(stream::Sink*, const UnsafeUnserializedValue<T>&) {}
    friend MaybeError StreamOut(stream::Source*, UnsafeUnserializedValue<T>* out) {
        // Call default constructor to initialize the value.
        out->mValue = T();
        return {};
    }
    // Enabling DAWN_SERIALIZABLE classes with UnsafeUnserializedOptional member to use default
    // equality operator. Equality comparison always returns true for the same type.
    bool operator==(const UnsafeUnserializedValue<T>& other) const { return true; }

  protected:
    T mValue;
};

// Template deduction guide for UnsafeUnserializedValue to enable deducting type of
// UnsafeUnserializedValue(T{}) to UnsafeUnserializedValue<T>.
template <typename T>
UnsafeUnserializedValue(T&& value) -> UnsafeUnserializedValue<std::decay_t<T>>;
}  // namespace dawn::native

// Helper macro to define a struct or class along with VisitAll methods to call
// a functor on all members. Derives from Visitable which provides
// implementations of StreamIn/StreamOut/FromBlob/ToBlob, and provides a default equality
// comparison. Example usage:
//   #define MEMBERS(X) \
//       X(int, a)              \
//       X(float, b)            \
//       X(Foo, foo)            \
//       X(Bar, bar)
//   DAWN_SERIALIZABLE(struct, MyStruct, MEMBERS) {
//      void SomeAdditionalMethod();
//   };
//   #undef MEMBERS
#define DAWN_SERIALIZABLE(qualifier, Name, MEMBERS)                     \
    struct Name##__Contents {                                           \
        DAWN_VISITABLE_MEMBERS(MEMBERS)                                 \
        bool operator==(const Name##__Contents& other) const = default; \
    };                                                                  \
    qualifier Name : Name##__Contents, public ::dawn::native::Serializable<Name>

#endif  // SRC_DAWN_NATIVE_SERIALIZABLE_H_