depend_on_referenced_packages

The imported package '{0}' isn't a dependency of the importing package.

The analyzer produces this diagnostic when a package import refers to a package that is not specified in the pubspec.yaml file.

Depending explicitly on packages that you reference ensures they will always exist and allows you to put a dependency constraint on them to guard against breaking changes.

Given a pubspec.yaml file containing the following:

dependencies:
  meta: ^3.0.0

The following code produces this diagnostic because there is no dependency on the package a:

import 'package:a/a.dart';

Whether the dependency should be a regular dependency or dev dependency depends on whether the package is referenced from a public library (one under either lib or bin), or only private libraries, (such as one under test).

If the package is referenced from at least one public library, then add a regular dependency on the package to the pubspec.yaml file under the dependencies field:

dependencies:
  a: ^1.0.0
  meta: ^3.0.0

If the package is referenced only from private libraries, then add a dev dependency on the package to the pubspec.yaml file under the dev_dependencies field:

dependencies:
  meta: ^3.0.0
dev_dependencies:
  a: ^1.0.0