Introduced _futurizeWithError

lib/ui/painting.dart

@@ -1936,18 +1936,15 @@ base class _Image extends NativeFieldWrapperClass1 {
   external int get height;
 
   Future<ByteData?> toByteData({ImageByteFormat format = ImageByteFormat.rawRgba}) {
-    final Completer<ByteData?> completer = Completer<ByteData?>();
-    final String? syncError = _toByteData(format.index, (Uint8List? encoded, String? error) {
-      if (encoded != null) {
-        completer.complete(encoded.buffer.asByteData());
-      } else {
-        completer.completeError(Exception(error ?? 'Unknown exception.'));
-      }
+    return _futurizeWithError((_CallbackWithError<ByteData?> callback) {
+      return _toByteData(format.index, (Uint8List? encoded, String? error) {
+        if (error == null && encoded != null) {
+          callback(encoded.buffer.asByteData(), null);
+        } else {
+          callback(null, error);
+        }
+      });
     });
-    if (syncError != null) {
-      completer.completeError(Exception(syncError));
-    }
-    return completer.future;
   }
 
   /// Returns an error message on failure, null on success.
@@ -6891,12 +6888,19 @@ base class _NativeImageDescriptor extends NativeFieldWrapperClass1 implements Im
 /// Generic callback signature, used by [_futurize].
 typedef _Callback<T> = void Function(T result);
 
+/// Generic callback signature, used by [_futurizeWithError].
+typedef _CallbackWithError<T> = void Function(T result, String? error);
+
 /// Signature for a method that receives a [_Callback].
 ///
 /// Return value should be null on success, and a string error message on
 /// failure.
 typedef _Callbacker<T> = String? Function(_Callback<T?> callback);
 
+/// Signature for a method that receives a [_CallbackWithError].
+/// See also: [_Callbacker]
+typedef _CallbackerWithError<T> = String? Function(_CallbackWithError<T?> callback);
+
 // Converts a method that receives a value-returning callback to a method that
 // returns a Future.
 //
@@ -6948,6 +6952,31 @@ Future<T> _futurize<T>(_Callbacker<T> callbacker) {
   return completer.future;
 }
 
+/// A variant of `_futurize` that can communicate specific errors.
+Future<T> _futurizeWithError<T>(_CallbackerWithError<T> callbacker) {
+  final Completer<T> completer = Completer<T>.sync();
+  // If the callback synchronously throws an error, then synchronously
+  // rethrow that error instead of adding it to the completer. This
+  // prevents the Zone from receiving an uncaught exception.
+  bool isSync = true;
+  final String? error = callbacker((T? t, String? error) {
+    if (t != null) {
+      completer.complete(t);
+    } else {
+      if (isSync) {
+        throw Exception(error ?? 'operation failed');
+      } else {
+        completer.completeError(Exception(error ?? 'operation failed'));
+      }
+    }
+  });
+  isSync = false;
+  if (error != null) {
+    throw Exception(error);
+  }
+  return completer.future;
+}
+
 /// An exception thrown by [Canvas.drawImage] and related methods when drawing
 /// an [Image] created via [Picture.toImageSync] that is in an invalid state.
 ///