sdk_version_is_expression_in_const_context

The use of an is expression in a constant context wasn't supported until version 2.3.2, but this code is required to be able to run on earlier versions.

The analyzer produces this diagnostic when an is expression inside a constant context is found in code that has an SDK constraint whose lower bound is less than 2.3.2. Using an is expression in a constant context wasn't supported in earlier versions, so this code won't be able to run against earlier versions of the SDK.

Here's an example of a pubspec that defines an SDK constraint with a lower bound of less than 2.3.2:

environment:
  sdk: '>=2.1.0 <2.4.0'

In the package that has that pubspec, code like the following produces this diagnostic:

const Object x = 4;
const y = x is int ? 0 : 1;

If you don't need to support older versions of the SDK, then you can increase the SDK constraint to allow the expression to be used:

environment:
  sdk: '>=2.3.2 <2.4.0'

If you need to support older versions of the SDK, then either rewrite the code to not use the is operator, or, if that isn't possible, change the code so that the is expression isn't in a constant context:

const Object x = 4;
var y = x is int ? 0 : 1;