implementation_imports.dart

// Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/visitor.dart';

import '../analyzer.dart';

const _desc = r"Don't import implementation files from another package.";

const _details = r'''
From the the [pub package layout doc](https://dart.dev/tools/pub/package-layout#implementation-files):

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

''';

bool isImplementation(Uri? uri) {
  var segments = uri?.pathSegments ?? const <String>[];
  if (segments.length > 2) {
    if (segments[1] == 'src') {
      return true;
    }
  }
  return false;
}

bool isPackage(Uri? uri) => uri?.scheme == 'package';

bool samePackage(Uri? uri1, Uri? uri2) {
  if (uri1 == null || uri2 == null) {
    return false;
  }
  var segments1 = uri1.pathSegments;
  var segments2 = uri2.pathSegments;
  if (segments1.isEmpty || segments2.isEmpty) {
    return false;
  }
  return segments1.first == segments2.first;
}

class ImplementationImports extends LintRule {
  static const LintCode code = LintCode('implementation_imports',
      "Import of a library in the 'lib/src' directory of another package.",
      correctionMessage:
          'Try importing a public library that exports this library, or '
          'removing the import.');

  ImplementationImports()
      : super(
            name: 'implementation_imports',
            description: _desc,
            details: _details,
            categories: {Category.style});

  @override
  LintCode get lintCode => code;

  @override
  void registerNodeProcessors(
      NodeLintRegistry registry, LinterContext context) {
    var visitor = _Visitor(this);
    registry.addImportDirective(this, visitor);
  }
}

class _Visitor extends SimpleAstVisitor<void> {
  final LintRule rule;

  _Visitor(this.rule);

  @override
  void visitImportDirective(ImportDirective node) {
    var importUri = node.element?.importedLibrary?.source.uri;
    var sourceUri = node.element?.source.uri;

    // Test for 'package:*/src/'.
    if (!isImplementation(importUri)) {
      return;
    }

    // If the source URI is not a `package` URI bail out.
    if (!isPackage(sourceUri)) {
      return;
    }

    if (!samePackage(importUri, sourceUri)) {
      rule.reportLint(node.uri);
    }
  }
}