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sdk_version_ui_as_code_in_const_context

The if and spread elements weren't supported in constant expressions until version 2.5.0, but this code is required to be able to run on earlier versions.

Description

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The analyzer produces this diagnostic when an if or spread element inside a constant context is found in code that has an SDK constraint whose lower bound is less than 2.5.0. Using an if or spread element inside a constant context wasn't supported in earlier versions, so this code won't be able to run against earlier versions of the SDK.

Example

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Here's an example of a pubspec that defines an SDK constraint with a lower bound of less than 2.5.0:

yaml
environment:
  sdk: '>=2.4.0 <2.6.0'

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

dart
const a = [1, 2];
const b = [...a];

Common fixes

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

yaml
environment:
  sdk: '>=2.5.0 <2.6.0'

If you need to support older versions of the SDK, then rewrite the code to not make use of those elements:

dart
const a = [1, 2];
const b = [1, 2];

If that isn't possible, change the code so that the element isn't in a constant context:

dart
const a = [1, 2];
var b = [...a];