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import_of_legacy_library_into_null_safe

Contents

The library '{0}' is legacy, and shouldn't be imported into a null safe library.

Description

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The analyzer produces this diagnostic when a library that is null safe imports a library that isn't null safe.

Example

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Given a file a.dart that contains the following:

dart
// @dart = 2.9

class A {}

The following code produces this diagnostic because a library that null safe is importing a library that isn't null safe:

dart
import 'a.dart';

A? f() => null;

Common fixes

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If you can migrate the imported library to be null safe, then migrate it and update or remove the migrated library's language version.

If you can't migrate the imported library, then the importing library needs to have a language version that is before 2.12, when null safety was enabled by default.

Unless stated otherwise, the documentation on this site reflects Dart 3.7.3. Page last updated on 2025-05-08. View source or report an issue.