extra_annotation_on_struct_field

Fields in a struct class must have exactly one annotation indicating the native type.

The analyzer produces this diagnostic when a field in a subclass of Struct has more than one annotation describing the native type of the field.

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

The following code produces this diagnostic because the field x has two annotations describing the native type of the field:

import 'dart:ffi';

final class C extends Struct {
  @Int32()
  @Int16()
  external int x;
}

Remove all but one of the annotations:

import 'dart:ffi';
final class C extends Struct {
  @Int32()
  external int x;
}