[lints] Prevent non src/ imports from src/

[dcharkes]

Often lib/my_package.dart exports a bunch of lib/src/xxx.dart. When working on lib/src/abc.dart, I want to only import other src/xxx.dart files, I don't want the blanket import of the whole package that imports all public classes.

I've created a custom lint for this for the packages I work on, but maybe it would be worth it to have this lint available more generally.

import 'package:analyzer/error/listener.dart';
import 'package:custom_lint_builder/custom_lint_builder.dart';

class DontImportOutsideSrcRule extends DartLintRule {
  DontImportOutsideSrcRule() : super(code: _code);

  static const _code = LintCode(
    name: 'avoid_import_outside_src',
    problemMessage:
        "Avoid importing files outside 'lib/src/' from files within 'lib/src/'.",
    correctionMessage:
        "Files outside 'lib/src/' likely only export definitions from inside 'lib/src/'. "
        'Import the file with the definition directly.',
  );

  @override
  void run(
    CustomLintResolver resolver,
    ErrorReporter reporter,
    CustomLintContext context,
  ) {
    context.registry.addImportDirective((node) {
      final importedUri = node.uri.stringValue;
      if (importedUri == null) {
        return;
      }
      final importingFile = resolver.source.uri;

      if (importedUri.startsWith('package:')) {
        // Package imports are of no interest. Use prefer_relative_imports to
        // prevent package imports of the same package.
        return;
      }
      if (importedUri.startsWith('dart:')) {
        return;
      }
      final importedUriAbsolute = importingFile.resolve(importedUri);
      if (_isInSrcDirectory(importingFile)) {
        if (!_isInSrcDirectory(importedUriAbsolute)) {
          reporter.atNode(node, code);
        }
      }
    });
  }

  bool _isInSrcDirectory(Uri uri) {
    if (uri.toFilePath(windows: false).contains('lib/src/')) {
      return true;
    }
    if (uri.toFilePath(windows: false).contains('lib/')) {
      return false;
    }
    return false;
  }
}

[devoncarew]

This issue should likely be filed against the sdk repo; that tracks creating new lints.

This package (package:lints) is about promoting current lints to our recommended sets for the community.

fwiw, the lint above sounds like it depends on some coding conventions that aren't universal; probably a good use case for the upcoming analyzer plugins work?

[FMorschel]

For visibility @srawlins.

[srawlins]

I love it. Might be a good candidate for an analyzer plugin lint, when those become ready.

[lrhn]

Definitely a lint that's based on some choice of modularization and file structuring.
Not something I'd want to recommend to everybody, because it may not make sense.

Also, the way many packages are written, the top-level libraries are just thin export 'src/packagename.dart'; files that exports a file in src/. Sometimes its a barrel file that exports more than one file, sometimes the barrel file itself is in src/.

This lint wouldn't do any good in the latter case, since you can just import src/mypackage.dart instead of mypackage.dart, and get all the same names imported.

And other package declare their important types and APIs in the top-level library, and only use src/ for utility functions, and those may have to import the top-level libraries.

Those are all valid approaches, not something we'd want to mandate in any direction.

[dcharkes]

I'm happy if I can have custom lints.

@srawlins let's connect offline to see if we can migrate what I wrote can be rewritten in what you're working on.