Missing exceptional return value for method invocation in `dart:ffi`DRT-W1474

The analyzer produces this diagnostic when an invocation of the method Pointer.fromFunction or NativeCallable.isolateLocal doesn't have a second argument (the exceptional return value) when the type to be returned from the invocation is neither void, Handle, nor Pointer. C interop using dart:ffi For more information about FFI, see C interop using dart:ffi.

Example

The following code produces this diagnostic because the type returned by f is expected to be an 8-bit integer but the call to fromFunction doesn't include an exceptional return argument:

import 'dart:ffi';

int f(int i) => i * 2;

void g() {
  Pointer.fromFunction<Int8 Function(Int8)>(f);
}

Common fixes

Add an exceptional return type:

import 'dart:ffi';

int f(int i) => i * 2;

void g() {
  Pointer.fromFunction<Int8 Function(Int8)>(f, 0);
}