BASE: Remove bad casts between incompatible Plugin types

Previously, a C-style cast was used to convert a
Common::Array<Plugin *>, populated with pointers to StaticPlugin
and DynamicPlugin instances, to a
Common::Array<PluginSubclass<T> *>, but PluginSubclass<T> is a
*sibling* class to StaticPlugin/DynamicPlugin, so this cast was
invalid and the results undefined. The methods for retrieving
subclasses of plugins can't be easily changed to just generate an
array of temporary wrapper objects that expose an identical API
which dereferences to the preferred PluginObject subclass because
pointers to these objects are retained by other parts of ScummVM,
so the wrappers would needed to be persisted or they would need to
just re-expose the underlying Plugin object again. This indicated
that a way to solve this problem is to have the callers receive
Plugin objects and get the PluginObject from the Plugin by
explicitly stating their desired type, in a similar manner to
std::get(std::variant), so that the pattern used by this patch to
solve the problem.

Closes gh-1051.

8 files changed, 44 insertions, 45 deletions

diff --git a/gui/EventRecorder.cpp b/gui/EventRecorder.cpp
index f1b486d394..39811513e3 100644
--- a/gui/EventRecorder.cpp
+++ b/gui/EventRecorder.cpp
@@ -598,8 +598,7 @@ void EventRecorder::setFileHeader() {
 		return;
 	}
 	TimeDate t;
-	const EnginePlugin *plugin = 0;
-	GameDescriptor desc = EngineMan.findGame(ConfMan.getActiveDomainName(), &plugin);
+	GameDescriptor desc = EngineMan.findGame(ConfMan.getActiveDomainName());
 	g_system->getTimeAndDate(t);
 	if (_author.empty()) {
 		setAuthor("Unknown Author");
@@ -619,19 +618,19 @@ SDL_Surface *EventRecorder::getSurface(int width, int height) {
 
 bool EventRecorder::switchMode() {
 	const Common::String gameId = ConfMan.get("gameid");
-	const EnginePlugin *plugin = 0;
+	const Plugin *plugin = nullptr;
 	EngineMan.findGame(gameId, &plugin);
-	bool metaInfoSupport = (*plugin)->hasFeature(MetaEngine::kSavesSupportMetaInfo);
+	bool metaInfoSupport = plugin->get<MetaEngine>().hasFeature(MetaEngine::kSavesSupportMetaInfo);
 	bool featuresSupport = metaInfoSupport &&
 						  g_engine->canSaveGameStateCurrently() &&
-						  (*plugin)->hasFeature(MetaEngine::kSupportsListSaves) &&
-						  (*plugin)->hasFeature(MetaEngine::kSupportsDeleteSave);
+						  plugin->get<MetaEngine>().hasFeature(MetaEngine::kSupportsListSaves) &&
+						  plugin->get<MetaEngine>().hasFeature(MetaEngine::kSupportsDeleteSave);
 	if (!featuresSupport) {
 		return false;
 	}
 
 	int emptySlot = 1;
-	SaveStateList saveList = (*plugin)->listSaves(gameId.c_str());
+	SaveStateList saveList = plugin->get<MetaEngine>().listSaves(gameId.c_str());
 	for (SaveStateList::const_iterator x = saveList.begin(); x != saveList.end(); ++x) {
 		int saveSlot = x->getSaveSlot();
 		if (saveSlot == 0) {
@@ -667,9 +666,9 @@ bool EventRecorder::checkForContinueGame() {
 void EventRecorder::deleteTemporarySave() {
 	if (_temporarySlot == -1) return;
 	const Common::String gameId = ConfMan.get("gameid");
-	const EnginePlugin *plugin = 0;
+	const Plugin *plugin = 0;
 	EngineMan.findGame(gameId, &plugin);
-	 (*plugin)->removeSaveState(gameId.c_str(), _temporarySlot);
+	 plugin->get<MetaEngine>().removeSaveState(gameId.c_str(), _temporarySlot);
 	_temporarySlot = -1;
 }
 
diff --git a/gui/about.cpp b/gui/about.cpp
index bde5db310a..25912557f9 100644
--- a/gui/about.cpp
+++ b/gui/about.cpp
@@ -110,16 +110,16 @@ AboutDialog::AboutDialog()
 	engines += _("Available engines:");
 	addLine(engines.c_str());
 
-	const EnginePlugin::List &plugins = EngineMan.getPlugins();
-	EnginePlugin::List::const_iterator iter = plugins.begin();
+	const PluginList &plugins = EngineMan.getPlugins();
+	PluginList::const_iterator iter = plugins.begin();
 	for (; iter != plugins.end(); ++iter) {
 		Common::String str;
 		str = "C0";
-		str += (**iter).getName();
+		str += (*iter)->getName();
 		addLine(str.c_str());
 
 		str = "C2";
-		str += (**iter)->getOriginalCopyright();
+		str += (*iter)->get<MetaEngine>().getOriginalCopyright();
 		addLine(str.c_str());
 
 		//addLine("");
diff --git a/gui/editgamedialog.cpp b/gui/editgamedialog.cpp
index 94c74b40c0..348ba5cb91 100644
--- a/gui/editgamedialog.cpp
+++ b/gui/editgamedialog.cpp
@@ -97,7 +97,7 @@ protected:
 EditGameDialog::EditGameDialog(const String &domain, const String &desc)
 	: OptionsDialog(domain, "GameOptions") {
 	// Retrieve all game specific options.
-	const EnginePlugin *plugin = 0;
+	const Plugin *plugin = nullptr;
 	// To allow for game domains without a gameid.
 	// TODO: Is it intentional that this is still supported?
 	String gameId(ConfMan.get("gameid", domain));
@@ -107,7 +107,7 @@ EditGameDialog::EditGameDialog(const String &domain, const String &desc)
 	// implementation.
 	EngineMan.findGame(gameId, &plugin);
 	if (plugin) {
-		_engineOptions = (*plugin)->getExtraGuiOptions(domain);
+		_engineOptions = plugin->get<MetaEngine>().getExtraGuiOptions(domain);
 	} else {
 		warning("Plugin for target \"%s\" not found! Game specific settings might be missing", domain.c_str());
 	}
diff --git a/gui/launcher.cpp b/gui/launcher.cpp
index 3ed1236a91..fd75674300 100644
--- a/gui/launcher.cpp
+++ b/gui/launcher.cpp
@@ -504,7 +504,7 @@ void LauncherDialog::loadGame(int item) {
 	if (gameId.empty())
 		gameId = _domains[item];
 
-	const EnginePlugin *plugin = 0;
+	const Plugin *plugin = nullptr;
 
 	EngineMan.findGame(gameId, &plugin);
 
@@ -512,8 +512,9 @@ void LauncherDialog::loadGame(int item) {
 	target.toLowercase();
 
 	if (plugin) {
-		if ((*plugin)->hasFeature(MetaEngine::kSupportsListSaves) &&
-			(*plugin)->hasFeature(MetaEngine::kSupportsLoadingDuringStartup)) {
+		const MetaEngine &metaEngine = plugin->get<MetaEngine>();
+		if (metaEngine.hasFeature(MetaEngine::kSupportsListSaves) &&
+			metaEngine.hasFeature(MetaEngine::kSupportsLoadingDuringStartup)) {
 			int slot = _loadDialog->runModalWithPluginAndTarget(plugin, target);
 			if (slot >= 0) {
 				ConfMan.setActiveDomain(_domains[item]);
diff --git a/gui/options.cpp b/gui/options.cpp
index 82eb252cf1..f1ca21a90d 100644
--- a/gui/options.cpp
+++ b/gui/options.cpp
@@ -1040,9 +1040,9 @@ void OptionsDialog::addAudioControls(GuiObject *boss, const Common::String &pref
 	const Common::String allFlags = MidiDriver::musicType2GUIO((uint32)-1);
 	bool hasMidiDefined = (strpbrk(_guioptions.c_str(), allFlags.c_str()) != NULL);
 
-	const MusicPlugin::List p = MusicMan.getPlugins();
-	for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end(); ++m) {
-		MusicDevices i = (**m)->getDevices();
+	const PluginList p = MusicMan.getPlugins();
+	for (PluginList::const_iterator m = p.begin(); m != p.end(); ++m) {
+		MusicDevices i = (*m)->get<MusicPluginObject>().getDevices();
 		for (MusicDevices::iterator d = i.begin(); d != i.end(); ++d) {
 			Common::String deviceGuiOption = MidiDriver::musicType2GUIO(d->getMusicType());
 
@@ -1078,19 +1078,19 @@ void OptionsDialog::addMIDIControls(GuiObject *boss, const Common::String &prefi
 	_gmDevicePopUp = new PopUpWidget(boss, prefix + "auPrefGmPopup");
 
 	// Populate
-	const MusicPlugin::List p = MusicMan.getPlugins();
+	const PluginList p = MusicMan.getPlugins();
 	// Make sure the null device is the first one in the list to avoid undesired
 	// auto detection for users who don't have a saved setting yet.
-	for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end(); ++m) {
-		MusicDevices i = (**m)->getDevices();
+	for (PluginList::const_iterator m = p.begin(); m != p.end(); ++m) {
+		MusicDevices i = (*m)->get<MusicPluginObject>().getDevices();
 		for (MusicDevices::iterator d = i.begin(); d != i.end(); ++d) {
 			if (d->getMusicDriverId() == "null")
 				_gmDevicePopUp->appendEntry(_("Don't use General MIDI music"), d->getHandle());
 		}
 	}
 	// Now we add the other devices.
-	for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end(); ++m) {
-		MusicDevices i = (**m)->getDevices();
+	for (PluginList::const_iterator m = p.begin(); m != p.end(); ++m) {
+		MusicDevices i = (*m)->get<MusicPluginObject>().getDevices();
 		for (MusicDevices::iterator d = i.begin(); d != i.end(); ++d) {
 			if (d->getMusicType() >= MT_GM) {
 				if (d->getMusicType() != MT_MT32)
@@ -1141,19 +1141,19 @@ void OptionsDialog::addMT32Controls(GuiObject *boss, const Common::String &prefi
 	// GS Extensions setting
 	_enableGSCheckbox = new CheckboxWidget(boss, prefix + "mcGSCheckbox", _("Roland GS Device (enable MT-32 mappings)"), _("Check if you want to enable patch mappings to emulate an MT-32 on a Roland GS device"));
 
-	const MusicPlugin::List p = MusicMan.getPlugins();
+	const PluginList p = MusicMan.getPlugins();
 	// Make sure the null device is the first one in the list to avoid undesired
 	// auto detection for users who don't have a saved setting yet.
-	for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end(); ++m) {
-		MusicDevices i = (**m)->getDevices();
+	for (PluginList::const_iterator m = p.begin(); m != p.end(); ++m) {
+		MusicDevices i = (*m)->get<MusicPluginObject>().getDevices();
 		for (MusicDevices::iterator d = i.begin(); d != i.end(); ++d) {
 			if (d->getMusicDriverId() == "null")
 				_mt32DevicePopUp->appendEntry(_("Don't use Roland MT-32 music"), d->getHandle());
 		}
 	}
 	// Now we add the other devices.
-	for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end(); ++m) {
-		MusicDevices i = (**m)->getDevices();
+	for (PluginList::const_iterator m = p.begin(); m != p.end(); ++m) {
+		MusicDevices i = (*m)->get<MusicPluginObject>().getDevices();
 		for (MusicDevices::iterator d = i.begin(); d != i.end(); ++d) {
 			if (d->getMusicType() >= MT_GM)
 				_mt32DevicePopUp->appendEntry(d->getCompleteName(), d->getHandle());
@@ -1265,10 +1265,10 @@ bool OptionsDialog::loadMusicDeviceSetting(PopUpWidget *popup, Common::String se
 
 	if (_domain != Common::ConfigManager::kApplicationDomain || ConfMan.hasKey(setting, _domain) || preferredType) {
 		const Common::String drv = ConfMan.get(setting, (_domain != Common::ConfigManager::kApplicationDomain && !ConfMan.hasKey(setting, _domain)) ? Common::ConfigManager::kApplicationDomain : _domain);
-		const MusicPlugin::List p = MusicMan.getPlugins();
+		const PluginList p = MusicMan.getPlugins();
 
-		for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end(); ++m) {
-			MusicDevices i = (**m)->getDevices();
+		for (PluginList::const_iterator m = p.begin(); m != p.end(); ++m) {
+			MusicDevices i = (*m)->get<MusicPluginObject>().getDevices();
 			for (MusicDevices::iterator d = i.begin(); d != i.end(); ++d) {
 				if (setting.empty() ? (preferredType == d->getMusicType()) : (drv == d->getCompleteId())) {
 					popup->setSelectedTag(d->getHandle());
@@ -1285,10 +1285,10 @@ void OptionsDialog::saveMusicDeviceSetting(PopUpWidget *popup, Common::String se
 	if (!popup || !_enableAudioSettings)
 		return;
 
-	const MusicPlugin::List p = MusicMan.getPlugins();
+	const PluginList p = MusicMan.getPlugins();
 	bool found = false;
-	for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end() && !found; ++m) {
-		MusicDevices i = (**m)->getDevices();
+	for (PluginList::const_iterator m = p.begin(); m != p.end() && !found; ++m) {
+		MusicDevices i = (*m)->get<MusicPluginObject>().getDevices();
 		for (MusicDevices::iterator d = i.begin(); d != i.end(); ++d) {
 			if (d->getHandle() == popup->getSelectedTag()) {
 				ConfMan.set(setting, d->getCompleteId(), _domain);
diff --git a/gui/recorderdialog.cpp b/gui/recorderdialog.cpp
index c08b3e149a..7e8e12bcf8 100644
--- a/gui/recorderdialog.cpp
+++ b/gui/recorderdialog.cpp
@@ -167,8 +167,7 @@ void RecorderDialog::handleCommand(CommandSender *sender, uint32 cmd, uint32 dat
 	case kRecordCmd: {
 		TimeDate t;
 		Common::String gameId = ConfMan.get("gameid", _target);
-		const EnginePlugin *plugin = 0;
-		GameDescriptor desc = EngineMan.findGame(gameId, &plugin);
+		GameDescriptor desc = EngineMan.findGame(gameId);
 		g_system->getTimeAndDate(t);
 		EditRecordDialog editDlg(_("Unknown Author"), Common::String::format("%.2d.%.2d.%.4d ", t.tm_mday, t.tm_mon, 1900 + t.tm_year) + desc.description(), "");
 		if (editDlg.runModal() != kOKCmd) {
diff --git a/gui/saveload.cpp b/gui/saveload.cpp
index ba17dacc48..a893f3c0db 100644
--- a/gui/saveload.cpp
+++ b/gui/saveload.cpp
@@ -76,14 +76,14 @@ Common::String SaveLoadChooser::createDefaultSaveDescription(const int slot) con
 int SaveLoadChooser::runModalWithCurrentTarget() {
 	const Common::String gameId = ConfMan.get("gameid");
 
-	const EnginePlugin *plugin = 0;
+	const Plugin *plugin = 0;
 	EngineMan.findGame(gameId, &plugin);
 
 	return runModalWithPluginAndTarget(plugin, ConfMan.getActiveDomainName());
 }
 
-int SaveLoadChooser::runModalWithPluginAndTarget(const EnginePlugin *plugin, const String &target) {
-	selectChooser(**plugin);
+int SaveLoadChooser::runModalWithPluginAndTarget(const Plugin *plugin, const String &target) {
+	selectChooser(plugin->get<MetaEngine>());
 	if (!_impl)
 		return -1;
 
@@ -98,10 +98,10 @@ int SaveLoadChooser::runModalWithPluginAndTarget(const EnginePlugin *plugin, con
 
 	int ret;
 	do {
-		ret = _impl->run(target, &(**plugin));
+		ret = _impl->run(target, &plugin->get<MetaEngine>());
 #ifndef DISABLE_SAVELOADCHOOSER_GRID
 		if (ret == kSwitchSaveLoadDialog) {
-			selectChooser(**plugin);
+			selectChooser(plugin->get<MetaEngine>());
 		}
 #endif // !DISABLE_SAVELOADCHOOSER_GRID
 	} while (ret < -1);
diff --git a/gui/saveload.h b/gui/saveload.h
index 01a78c4924..be0bc4206f 100644
--- a/gui/saveload.h
+++ b/gui/saveload.h
@@ -51,7 +51,7 @@ public:
 	 * @return The selcted save slot. -1 in case none is selected.
 	 */
 	int runModalWithCurrentTarget();
-	int runModalWithPluginAndTarget(const EnginePlugin *plugin, const String &target);
+	int runModalWithPluginAndTarget(const Plugin *plugin, const String &target);
 
 	const Common::String &getResultString() const;