Better error message when trying to call non-worklet from UI thread

Common/cpp/SharedItems/Shareables.h

@@ -285,7 +285,14 @@ class ShareableRemoteFunction
         function_(std::move(function)) {}
   jsi::Value toJSValue(jsi::Runtime &rt) override {
     if (runtimeHelper_->isUIRuntime(rt)) {
+#ifdef DEBUG
+      return runtimeHelper_->valueUnpacker->call(
+          rt,
+          ShareableJSRef::newHostObject(rt, shared_from_this()),
+          jsi::String::createFromAscii(rt, "RemoteFunction"));
+#else
       return ShareableJSRef::newHostObject(rt, shared_from_this());
+#endif
     } else {
       return jsi::Value(rt, function_);
     }

src/reanimated2/commonTypes.ts

@@ -96,6 +96,7 @@ export interface NativeEvent<T> {
 export interface ComplexWorkletFunction<A extends any[], R>
   extends WorkletFunction {
   (...args: A): R;
+  __remoteFunction?: (...args: A) => R;
 }
 
 export interface NestedObject<T> {

src/reanimated2/core.ts

@@ -114,7 +114,7 @@ export function getViewProp<T>(viewTag: string, propName: string): Promise<T> {
   });
 }
 
-function valueUnpacker(objectToUnpack: any): any {
+function valueUnpacker(objectToUnpack: any, category?: string): any {
   'worklet';
   let workletsCache = global.__workletsCache;
   let handleCache = global.__handleCache;
@@ -142,6 +142,16 @@ function valueUnpacker(objectToUnpack: any): any {
       handleCache!.set(objectToUnpack, value);
     }
     return value;
+  } else if (category === 'RemoteFunction') {
+    const fun = () => {
+      throw new Error(`Tried to synchronously call a non-worklet function on the UI thread.
+
+Possible solutions are:
+  a) If you want to synchronously execute this method, mark it as a worklet
+  b) If you want to execute this function on the JS thread, wrap it using \`runOnJS\``);
+    };
+    fun.__remoteFunction = objectToUnpack;
+    return fun;
   } else {
     throw new Error('data type not recognized by unpack method');
   }

src/reanimated2/threads.ts

@@ -27,6 +27,13 @@ export function runOnJS<A extends any[], R>(
   fun: ComplexWorkletFunction<A, R>
 ): (...args: A) => void {
   'worklet';
+  if (fun.__remoteFunction) {
+    // in development mode the function provided as `fun` throws an error message
+    // such that when someone accidently calls it directly on the UI runtime, they
+    // see that they should use `runOnJS` instead. To facilitate that we purt the
+    // reference to the original remote function in the `__remoteFunction` property.
+    fun = fun.__remoteFunction;
+  }
   if (!_WORKLET) {
     return fun;
   }