implementation_imports

Don't import implementation files from another package.

This rule is available as of Dart 2.0.0.

Rule sets: recommended, flutter

From the the pub package layout doc:

DON'T import implementation files from another package.

The libraries inside lib are publicly visible: other packages are free to import them. But much of a package's code is internal implementation libraries that should only be imported and used by the package itself. Those go inside a subdirectory of lib called src. You can create subdirectories in there if it helps you organize things.

You are free to import libraries that live in lib/src from within other Dart code in the same package (like other libraries in lib, scripts in bin, and tests) but you should never import from another package's lib/src directory. Those files are not part of the package's public API, and they might change in ways that could break your code.

BAD:

// In 'road_runner'
import 'package:acme/src/internals.dart';

To enable the implementation_imports rule, add implementation_imports under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - implementation_imports