First fun C++ to C problem

src/main.c

@@ -1,6 +1,52 @@
+#include <assert.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <webgpu/webgpu.h>
 
+WGPUAdapter requestAdapterSync(WGPUInstance instance,
+                               WGPURequestAdapterOptions const *options) {
+  typedef struct {
+    WGPUAdapter adapter;
+    bool requestEnded;
+  } UserData;
+
+  UserData userData = {.adapter = NULL, .requestEnded = false};
+
+  // Callback called by wgpuInstanceRequestAdapter when the request returns
+  // This is a C++ lambda function, but could be any function defined in the
+  // global scope. It must be non-capturing (the brackets [] are empty) so
+  // that it behaves like a regular C function pointer, which is what
+  // wgpuInstanceRequestAdapter expects (WebGPU being a C API). The workaround
+  // is to convey what we want to capture through the pUserData pointer,
+  // provided as the last argument of wgpuInstanceRequestAdapter and received
+  // by the callback as its last argument.
+  auto onAdapterRequestEnded = [](WGPURequestAdapterStatus status,
+                                  WGPUAdapter adapter, char const *message,
+                                  void *pUserData) {
+    UserData &userData = *reinterpret_cast<UserData *>(pUserData);
+    if (status == WGPURequestAdapterStatus_Success) {
+      userData.adapter = adapter;
+    } else {
+      std::cout << "Could not get WebGPU adapter: " << message << std::endl;
+    }
+    userData.requestEnded = true;
+  };
+
+  // Call to the WebGPU request adapter procedure
+  wgpuInstanceRequestAdapter(instance /* equivalent of navigator.gpu */,
+                             options, onAdapterRequestEnded, (void *)&userData);
+
+  // We wait until userData.requestEnded gets true
+  {
+    {Wait for request to end
+    }
+  }
+
+  assert(userData.requestEnded);
+
+  return userData.adapter;
+}
+
 int main() {
   // We create a descriptor
   WGPUInstanceDescriptor desc = {};