native_field_missing_type

The native type of this field could not be inferred and must be specified in the annotation.

The analyzer produces this diagnostic when an @Native-annotated field requires a type hint on the annotation to infer the native type.

Dart types like int and double have multiple possible native representations. Since the native type needs to be known at compile time to generate the correct load and stores when accessing the field, an explicit type must be given.

The following code produces this diagnostic because the field f has the type int (for which multiple native representations exist), but no explicit type parameter on the Native annotation:

import 'dart:ffi';
​
@Native()
external int f;

To fix this diagnostic, find out the correct native representation from the native declaration of the field. Then, add the corresponding type to the annotation. For instance, if f was declared as an uint8_t in C, the Dart field should be declared as:

import 'dart:ffi';
​
@Native<Uint8>()
external int f;

For more information about FFI, see C interop using dart:ffi.