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.

2 files changed, 27 insertions, 30 deletions

diff --git a/audio/mididrv.cpp b/audio/mididrv.cpp
index f053ec8440..2b7463e553 100644
--- a/audio/mididrv.cpp
+++ b/audio/mididrv.cpp
@@ -92,9 +92,9 @@ MusicType MidiDriver::getMusicType(MidiDriver::DeviceHandle handle) {
 		return MT_MT32;
 
 	if (handle) {
-		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++) {
 				if (handle == d->getHandle())
 					return d->getMusicType();
@@ -107,9 +107,9 @@ MusicType MidiDriver::getMusicType(MidiDriver::DeviceHandle handle) {
 
 Common::String MidiDriver::getDeviceString(DeviceHandle handle, DeviceStringType type) {
 	if (handle) {
-		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++) {
 				if (handle == d->getHandle()) {
 					if (type == kDriverName)
@@ -226,7 +226,7 @@ MidiDriver::DeviceHandle MidiDriver::detectDevice(int flags) {
 
 	// If the selected driver did not match the flags setting,
 	// we try to determine a suitable and "optimal" music driver.
-	const MusicPlugin::List p = MusicMan.getPlugins();
+	const PluginList p = MusicMan.getPlugins();
 	// If only MDT_MIDI but not MDT_PREFER_MT32 or MDT_PREFER_GM is set we prefer the other devices (which will always be
 	// detected since they are hard coded and cannot be disabled).
 	bool skipMidi = !(flags & (MDT_PREFER_GM | MDT_PREFER_MT32));
@@ -280,8 +280,8 @@ MidiDriver::DeviceHandle MidiDriver::detectDevice(int flags) {
 				// and there is no preferred MT32 or GM device selected either or if the detected device is unavailable we arrive here.
 				// If MT32 is preferred we try for the first available device with music type 'MT_MT32' (usually the mt32 emulator).
 				if (flags & MDT_PREFER_MT32) {
-					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_MT32) {
 								hdl = d->getHandle();
@@ -295,8 +295,8 @@ MidiDriver::DeviceHandle MidiDriver::detectDevice(int flags) {
 				// Now we default to the first available device with music type 'MT_GM' if not
 				// MT-32 is preferred or if MT-32 is preferred but all other devices have failed.
 				if (!(flags & MDT_PREFER_MT32) || flags == (MDT_PREFER_MT32 | MDT_MIDI)) {
-					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 || d->getMusicType() == MT_GS) {
 								hdl = d->getHandle();
@@ -348,8 +348,8 @@ MidiDriver::DeviceHandle MidiDriver::detectDevice(int flags) {
 			tp = MT_AUTO;
 		}
 
-		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() == tp) {
 					hdl = d->getHandle();
@@ -365,33 +365,35 @@ MidiDriver::DeviceHandle MidiDriver::detectDevice(int flags) {
 
 MidiDriver *MidiDriver::createMidi(MidiDriver::DeviceHandle handle) {
 	MidiDriver *driver = 0;
-	const MusicPlugin::List p = MusicMan.getPlugins();
-	for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end(); m++) {
-		if (getDeviceString(handle, MidiDriver::kDriverId).equals((**m)->getId()))
-			(**m)->createInstance(&driver, handle);
+	const PluginList p = MusicMan.getPlugins();
+	for (PluginList::const_iterator m = p.begin(); m != p.end(); m++) {
+		const MusicPluginObject &musicPlugin = (*m)->get<MusicPluginObject>();
+		if (getDeviceString(handle, MidiDriver::kDriverId).equals(musicPlugin.getId()))
+			musicPlugin.createInstance(&driver, handle);
 	}
 
 	return driver;
 }
 
 bool MidiDriver::checkDevice(MidiDriver::DeviceHandle handle) {
-	const MusicPlugin::List p = MusicMan.getPlugins();
-	for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end(); m++) {
-		if (getDeviceString(handle, MidiDriver::kDriverId).equals((**m)->getId()))
-			return (**m)->checkDevice(handle);
+	const PluginList p = MusicMan.getPlugins();
+	for (PluginList::const_iterator m = p.begin(); m != p.end(); m++) {
+		const MusicPluginObject &musicPlugin = (*m)->get<MusicPluginObject>();
+		if (getDeviceString(handle, MidiDriver::kDriverId).equals(musicPlugin.getId()))
+			return musicPlugin.checkDevice(handle);
 	}
 
 	return false;
 }
 
 MidiDriver::DeviceHandle MidiDriver::getDeviceHandle(const Common::String &identifier) {
-	const MusicPlugin::List p = MusicMan.getPlugins();
+	const PluginList p = MusicMan.getPlugins();
 
 	if (p.begin() == p.end())
 		error("MidiDriver::getDeviceHandle: Music plugins must be loaded prior to calling this method");
 
-	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++) {
 			// The music driver id isn't unique, but it will match
 			// driver's first device. This is useful when selecting
diff --git a/audio/musicplugin.h b/audio/musicplugin.h
index 849d3f92cd..b83e93a445 100644
--- a/audio/musicplugin.h
+++ b/audio/musicplugin.h
@@ -112,11 +112,6 @@ public:
 	virtual Common::Error createInstance(MidiDriver **mididriver, MidiDriver::DeviceHandle = 0) const = 0;
 };
 
-
-// Music plugins
-
-typedef PluginSubclass<MusicPluginObject> MusicPlugin;
-
 /**
  * Singleton class which manages all Music plugins.
  */
@@ -125,7 +120,7 @@ private:
 	friend class Common::Singleton<SingletonBaseType>;
 
 public:
-	const MusicPlugin::List &getPlugins() const;
+	const PluginList &getPlugins() const;
 };
 
 /** Convenience shortcut for accessing the Music manager. */