argument_must_be_a_constant

Argument '{0}' must be a constant.

The analyzer produces this diagnostic when an invocation of either Pointer.asFunction or DynamicLibrary.lookupFunction has an isLeaf argument whose value isn't a constant expression.

The analyzer also produces this diagnostic when an invocation of either Pointer.fromFunction or NativeCallable.isolateLocal has an exceptionalReturn argument whose value isn't a constant expression.

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

The following code produces this diagnostic because the value of the isLeaf argument is a parameter, and hence isn't a constant:

import 'dart:ffi';
​
int Function(int) fromPointer(
    Pointer<NativeFunction<Int8 Function(Int8)>> p, bool isLeaf) {
  return p.asFunction(isLeaf: isLeaf);
}

If there's a suitable constant that can be used, then replace the argument with a constant:

import 'dart:ffi';
​
const isLeaf = false;
​
int Function(int) fromPointer(Pointer<NativeFunction<Int8 Function(Int8)>> p) {
  return p.asFunction(isLeaf: isLeaf);
}

If there isn't a suitable constant, then replace the argument with a boolean literal:

import 'dart:ffi';
​
int Function(int) fromPointer(Pointer<NativeFunction<Int8 Function(Int8)>> p) {
  return p.asFunction(isLeaf: true);
}