non_native_function_type_argument_to_pointer

Can't invoke 'asFunction' because the function signature '{0}' for the pointer isn't a valid C function signature.

The analyzer produces this diagnostic when the method asFunction is invoked on a pointer to a native function, but the signature of the native function isn't a valid C function signature.

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

The following code produces this diagnostic because function signature associated with the pointer p (FNative) isn't a valid C function signature:

import 'dart:ffi';

typedef FNative = int Function(int);
typedef F = int Function(int);

class C {
  void f(Pointer<NativeFunction<FNative>> p) {
    p.asFunction<F>();
  }
}

Make the NativeFunction signature a valid C signature:

import 'dart:ffi';

typedef FNative = Int8 Function(Int8);
typedef F = int Function(int);

class C {
  void f(Pointer<NativeFunction<FNative>> p) {
    p.asFunction<F>();
  }
}