Fix segfault in REAPER due to new vendor extension

This `effVendorSpecific` call would pass a non-zero non-pointer value to
the pointer argument, which would then of course result in segfaults.

CHANGELOG.md

@@ -17,6 +17,12 @@ Versioning](https://semver.org/spec/v2.0.0.html).
   yabridge now includes a small workaround to make sure that the affected code
   never gets compiled.
 
+### Fixed
+
+- Added a workaround for **REAPER** using a new vendor-specific VST2.4 extension
+  that passes a non-pointer value to a pointer parameter. This would cause
+  segfaults with some plugins.
+
 ## [3.0.0] - 2021-02-14
 
 ### Added

src/common/communication/vst2.cpp

@@ -16,21 +16,27 @@
 
 #include "vst2.h"
 
-EventPayload DefaultDataConverter::read(const int /*opcode*/,
-                                        const int /*index*/,
+EventPayload DefaultDataConverter::read(const int opcode,
+                                        const int index,
                                         const intptr_t /*value*/,
                                         const void* data) const {
+    // HACK: REAPER has recently started using `effVendorSpecific` with a
+    //       non-pointer `data` argument, so we need to explicitly handle this
+    if (opcode == effVendorSpecific && index == effSetSpeakerArrangement) {
+        return static_cast<native_size_t>(reinterpret_cast<size_t>(data));
+    }
+
     if (!data) {
         return nullptr;
     }
 
-    // This is a simple fallback that will work in almost every case.
-    // Because some plugins don't zero out their string buffers when sending
-    // host callbacks, we will explicitely list all callbacks that expect a
-    // string in `DispatchDataConverter` adn `HostCallbackDataConverter`.
-    const char* c_string = static_cast<const char*>(data);
-    if (c_string[0] != 0) {
-        return std::string(c_string);
+    // This is a simple fallback that will work in almost every case. Because
+    // some plugins don't zero out their string buffers when sending host
+    // callbacks, we will explicitely list all callbacks that expect a string in
+    // `DispatchDataConverter` and `HostCallbackDataConverter`.
+    const char* str = static_cast<const char*>(data);
+    if (str[0] != 0) {
+        return std::string(str);
     } else {
         return WantsString{};
     }

src/common/logging/vst2.cpp

@@ -156,6 +156,9 @@ std::optional<std::string> opcode_to_string(bool is_dispatch, int opcode) {
             case effGetSpeakerArrangement:
                 return "effGetSpeakerArrangement";
                 break;
+            case effVendorSpecific:
+                return "effVendorSpecific";
+                break;
             case effGetTailSize:
                 return "effGetTailSize";
                 break;

src/common/vst24.h

@@ -47,6 +47,14 @@
 [[maybe_unused]] constexpr int effSetSpeakerArrangement = 42;
 [[maybe_unused]] constexpr int effGetSpeakerArrangement = 69;
 
+/**
+ * Used by REAPER for some VST2.4 extensions. Most of the arguments passed to
+ * this will be able to be handled automatically by our `DefaultDataConverter`.
+ * We need one special case because for when they're now using the `data`
+ * argument with a non-pointer value. Found on the same list as above.
+ */
+[[maybe_unused]] constexpr int effVendorSpecific = 50;
+
 /**
  * Used by hosts to query the length of reverb tails (equivalent to
  * `IAudioProcessor::getTailSamples`). Found on the same list as above.