The keys in a const map literal must be constantDRT-W1516
The analyzer produces this diagnostic when a key in a constant map literal isn't a constant value.
Example
The following code produces this diagnostic because a isn't a constant:
var a = 'a';
var m = const {a: 0};
Common fixes
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};