Create Vst3HostContextProxy from YaHostApplication

This is quite a huge refactor, but note everything is consistent (and
we're going to need one or two more of these `Vst3*Proxy` objects).
Right now nothing extends `IHostApplication`, but this way it will be
trivial to add support for more host context interfaces.

src/common/serialization/vst3/host-context/host-application.cpp

@@ -0,0 +1,50 @@
+// yabridge: a Wine VST bridge
+// Copyright (C) 2020  Robbert van der Helm
+//
+// This program 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 3 of the License, or
+// (at your option) any later version.
+//
+// This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#include "host-application.h"
+
+YaHostApplication::ConstructArgs::ConstructArgs() {}
+
+YaHostApplication::ConstructArgs::ConstructArgs(
+    Steinberg::IPtr<Steinberg::FUnknown> object)
+    : supported(false) {
+    if (auto host_application =
+            Steinberg::FUnknownPtr<Steinberg::Vst::IHostApplication>(object)) {
+        supported = true;
+
+        // `IHostApplication::getName`
+        Steinberg::Vst::String128 name_array;
+        if (host_application->getName(name_array) == Steinberg::kResultOk) {
+            name = tchar_pointer_to_u16string(name_array);
+        }
+    }
+}
+
+YaHostApplication::YaHostApplication(const ConstructArgs&& args)
+    : arguments(std::move(args)) {}
+
+tresult PLUGIN_API YaHostApplication::getName(Steinberg::Vst::String128 name) {
+    if (arguments.name) {
+        // Terminate with a null byte. There are no nice functions for copying
+        // UTF-16 strings (because who would use those?).
+        std::copy(arguments.name->begin(), arguments.name->end(), name);
+        name[arguments.name->size()] = 0;
+
+        return Steinberg::kResultOk;
+    } else {
+        return Steinberg::kNotImplemented;
+    }
+}

src/common/serialization/vst3/host-context/host-application.h

@@ -0,0 +1,86 @@
+// yabridge: a Wine VST bridge
+// Copyright (C) 2020  Robbert van der Helm
+//
+// This program 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 3 of the License, or
+// (at your option) any later version.
+//
+// This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include <type_traits>
+
+#include <bitsery/ext/std_optional.h>
+#include <bitsery/traits/string.h>
+#include <pluginterfaces/vst/ivsthostapplication.h>
+
+#include "../../common.h"
+#include "../base.h"
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
+
+/**
+ * Wraps around `IHostApplication` for serialization purposes. This is
+ * instantiated as part of `Vst3HostContextProxy`.
+ */
+class YaHostApplication : public Steinberg::Vst::IHostApplication {
+   public:
+    /**
+     * These are the arguments for creating a `YaHostApplication`.
+     */
+    struct ConstructArgs {
+        ConstructArgs();
+
+        /**
+         * Check whether an existing implementation implements
+         * `IHostApplication` and read arguments from it.
+         */
+        ConstructArgs(Steinberg::IPtr<Steinberg::FUnknown> object);
+
+        /**
+         * Whether the object supported this interface.
+         */
+        bool supported;
+
+        /**
+         * For `IHostApplication::getName`.
+         */
+        std::optional<std::u16string> name;
+
+        template <typename S>
+        void serialize(S& s) {
+            s.value1b(supported);
+            s.ext(name, bitsery::ext::StdOptional{},
+                  [](S& s, std::u16string& name) {
+                      s.text2b(name, std::extent_v<Steinberg::Vst::String128>);
+                  });
+        }
+    };
+
+    /**
+     * Instantiate this instance with arguments read from another interface
+     * implementation.
+     */
+    YaHostApplication(const ConstructArgs&& args);
+
+    inline bool supported() const { return arguments.supported; }
+
+    tresult PLUGIN_API getName(Steinberg::Vst::String128 name) override;
+    virtual tresult PLUGIN_API createInstance(Steinberg::TUID cid,
+                                              Steinberg::TUID _iid,
+                                              void** obj) override = 0;
+
+   protected:
+    ConstructArgs arguments;
+};
+
+#pragma GCC diagnostic pop