non_constant_map_key

The keys in a const map literal must be constant.

The analyzer produces this diagnostic when a key in a constant map literal isn't a constant value.

The following code produces this diagnostic because a isn't a constant:

var a = 'a';
var m = const {a: 0};

If the map needs to be a constant map, then make the key a constant:

const a = 'a';
var m = const {a: 0};

If the map doesn't need to be a constant map, then remove the const keyword:

var a = 'a';
var m = {a: 0};