JSInterface_GUIProxy.h

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/* Copyright (C) 2023 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef INCLUDED_JSI_GUIPROXY
#define INCLUDED_JSI_GUIPROXY
 
#include "gui/ObjectBases/IGUIObject.h"
#include "scriptinterface/ScriptExtraHeaders.h"
 
#include <memory>
#include <utility>
 
class ScriptInterface;
class ScriptRequest;
 
template <typename T>
class JSI_GUIProxy;
 
// See JSI_GuiProxy below
#if GCC_VERSION
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
#elif MSC_VERSION
# pragma warning(push, 1)
# pragma warning(disable: 4265)
#endif
 
/**
 * JS GUI proxies need to store some private data.
 * This class is responsible for deleting that data.
 */
class IGUIProxyObject final
{
    template<typename T>
    friend class JSI_GUIProxy;
    friend std::unique_ptr<IGUIProxyObject> std::make_unique<IGUIProxyObject>();
public:
    JSObject* Get() const
    {
        return m_Object.get();
    }
 
    using PrivateData = IGUIObject*;
 
    template<typename T>
    static T* FromPrivateSlot(JSObject* obj)
    {
        return static_cast<T*>(FromPrivateSlot<IGUIObject>(obj));
    }
protected:
    template<typename T>
    static T* UnsafeFromPrivateSlot(JSObject* obj)
    {
        return static_cast<T*>(static_cast<PrivateData>(js::GetProxyPrivate(obj).toPrivate()));
    }
 
    IGUIProxyObject() = default;
    IGUIProxyObject(const IGUIProxyObject&) = delete;
    IGUIProxyObject(IGUIProxyObject&&) = delete;
 
    JS::PersistentRootedObject m_Object;
    PrivateData m_Ptr;
};
// Declare the IGUIObject* specialization - it's defined in _impl.h
template<> IGUIObject* IGUIProxyObject::FromPrivateSlot<IGUIObject>(JSObject*);
 
/**
 * Proxies need to store some data whose lifetime is tied to an interface.
 * This is the virtual interface of that data.
 */
class GUIProxyProps
{
public:
    virtual ~GUIProxyProps() {};
 
    // @return true if @param name exists in this cache.
    virtual bool has(const std::string& name) const = 0;
    // @return the JSFunction matching @param name. Must call has() first as it can assume existence.
    virtual JSObject* get(const std::string& name) const = 0;
    virtual bool setFunction(const ScriptRequest& rq, const std::string& name, JSFunction* function) = 0;
};
 
/**
 * Handles the js interface with C++ GUI objects.
 * Proxy handlers must live for at least as long as the JS runtime
 * where a proxy object with that handler was created. The reason is that
 * proxy handlers are called during GC, such as on runtime destruction.
 * In practical terms, this means "just keep them static and store no data".
 *
 * GUI Objects only exist in C++ and have no JS-only properties.
 * As such, there is no "target" JS object that this proxy could point to,
 * and thus we should inherit from BaseProxyHandler and not js::Wrapper.
 *
 * Proxies can be used with prototypes and almost treated like regular JS objects.
 * However, the default implementation embarks a lot of code that we don't really need here,
 * since the only fanciness is that we cache JSFunction* properties.
 * As such, these GUI proxies don't have one and instead override get/set directly.
 *
 * To add a new JSI_GUIProxy, you'll need to:
 *  - overload CreateJSObject in your class header.
 *  - change the CGUI::AddObjectTypes method.
 *  - explicitly instantiate the template & CreateJSObject via DECLARE_GUIPROXY.
 *
 */
template<typename GUIObjectType>
class JSI_GUIProxy : public js::BaseProxyHandler
{
    // Need to friend other specializations so CreateFunctions() can call the IGUIObject version in all codepaths.
    template<typename T>
    friend class JSI_GUIProxy;
public:
    // For convenience, this is the single instantiated JSI_GUIProxy.
    static JSI_GUIProxy& Singleton();
 
    // Call this in CGUI::AddObjectTypes.
    static std::pair<const js::BaseProxyHandler*, GUIProxyProps*> CreateData(ScriptInterface& scriptInterface);
 
    // Create the JS object, the proxy, the data and wrap it in a convenient unique_ptr.
    static std::unique_ptr<IGUIProxyObject> CreateJSObject(const ScriptRequest& rq, GUIObjectType* ptr, GUIProxyProps* data);
protected:
    // @param family can't be nullptr because that's used for some DOM object and it crashes.
    JSI_GUIProxy() : BaseProxyHandler(this, false, false) {};
 
    // Note: SM provides no virtual destructor for baseProxyHandler.
    // This also enforces making proxy handlers dataless static variables.
    ~JSI_GUIProxy() {};
 
    static GUIObjectType* FromPrivateSlot(const ScriptRequest&, JS::CallArgs& args);
 
    // The default implementations need to know the type of the GUIProxyProps for this proxy type.
    // This is done by specializing this struct's alias type.
    struct PropCache;
 
    // Specialize this to define the custom properties of this type.
    static void CreateFunctions(const ScriptRequest& rq, GUIProxyProps* cache);
 
    // Convenience helper for the above.
    template<auto callable>
    static void CreateFunction(const ScriptRequest& rq, GUIProxyProps* cache, const std::string& name);
 
    // This handles returning custom properties. Specialize this if needed.
    bool PropGetter(JS::HandleObject proxy, const std::string& propName, JS::MutableHandleValue vp) const;
protected:
    // BaseProxyHandler interface below
 
    // Handler for `object.x`
    virtual bool get(JSContext* cx, JS::HandleObject proxy, JS::HandleValue receiver, JS::HandleId id, JS::MutableHandleValue vp) const override final;
    // Handler for `object.x = y;`
    virtual bool set(JSContext* cx, JS::HandleObject proxy, JS::HandleId id, JS::HandleValue vp,
                     JS::HandleValue receiver, JS::ObjectOpResult& result) const final;
    // Handler for `delete object.x;`
    virtual bool delete_(JSContext* cx, JS::HandleObject proxy, JS::HandleId id, JS::ObjectOpResult& result) const override final;
 
    // The following methods are not provided by BaseProxyHandler.
    // We provide defaults that do nothing (some raise JS exceptions).
 
    // The JS code will see undefined when querying a property descriptor.
    virtual bool getOwnPropertyDescriptor(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), JS::HandleId UNUSED(id),
                                          JS::MutableHandle<mozilla::Maybe<JS::PropertyDescriptor>> UNUSED(desc)) const override
    {
        return true;
    }
    // Throw an exception is JS code attempts defining a property.
    virtual bool defineProperty(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), JS::HandleId UNUSED(id),
                                JS::Handle<JS::PropertyDescriptor> UNUSED(desc), JS::ObjectOpResult& UNUSED(result)) const override
    {
        return false;
    }
    // No accessible properties.
    virtual bool ownPropertyKeys(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), JS::MutableHandleIdVector UNUSED(props)) const override
    {
        return true;
    }
    // Nothing to enumerate.
    virtual bool enumerate(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), JS::MutableHandleIdVector UNUSED(props)) const override
    {
        return true;
    }
    // Throw an exception is JS attempts to query the prototype.
    virtual bool getPrototypeIfOrdinary(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), bool* UNUSED(isOrdinary), JS::MutableHandleObject UNUSED(protop)) const override
    {
        return false;
    }
    // Throw an exception - no prototype to set.
    virtual bool setImmutablePrototype(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), bool* UNUSED(succeeded)) const override
    {
        return false;
    }
    // We are not extensible.
    virtual bool preventExtensions(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), JS::ObjectOpResult& UNUSED(result)) const override
    {
        return true;
    }
    virtual bool isExtensible(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), bool* extensible) const override
    {
        *extensible = false;
        return true;
    }
};
 
#if GCC_VERSION
# pragma GCC diagnostic pop
#elif MSC_VERSION
# pragma warning(pop)
#endif
 
 
#endif // INCLUDED_JSI_GUIPROXY