non_constant_list_element

The values in a const list literal must be constants.

The analyzer produces this diagnostic when an element in a constant list literal isn't a constant value. The list literal can be constant either explicitly (because it's prefixed by the const keyword) or implicitly (because it appears in a constant context).

The following code produces this diagnostic because x isn't a constant, even though it appears in an implicitly constant list literal:

var x = 2;
var y = const <int>[0, 1, x];

If the list needs to be a constant list, then convert the element to be a constant. In the example above, you might add the const keyword to the declaration of x:

const x = 2;
var y = const <int>[0, 1, x];

If the expression can't be made a constant, then the list can't be a constant either, so you must change the code so that the list isn't a constant. In the example above this means removing the const keyword before the list literal:

var x = 2;
var y = <int>[0, 1, x];