sdk_version_as_expression_in_const_context

The use of an as expression in a constant expression 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 as 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 as 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 num n = 3;
const int i = n as int;

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 an as expression, or change the code so that the as expression isn't in a constant context:

num x = 3;
int y = x as int;

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