native_function_missing_type

The native type of this function couldn't be inferred so it must be specified in the annotation.

The analyzer produces this diagnostic when a @Native-annotated function requires a type hint on the annotation to infer the native function 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 correct bindings and call instructions for the function, an explicit type must be given.

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

The following code produces this diagnostic because the function f() has the return type int, but doesn't have an explicit type parameter on the Native annotation:

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

Add the corresponding type to the annotation. For instance, if f() was declared to return an int32_t in C, the Dart function should be declared as:

import 'dart:ffi';
​
@Native<Int32 Function()>()
external int f();