content: // Copyright 2017 Google Inc. Use of this source code is governed by an
  // MIT-style license that can be found in the LICENSE file or at
  // https://opensource.org/licenses/MIT.
  
  import 'importer/async.dart';
  import 'importer/no_op.dart';
  import 'importer/result.dart';
  
  export 'importer/async.dart';
  export 'importer/filesystem.dart';
  export 'importer/package.dart';
  export 'importer/result.dart';
  
  /// An interface for importers that resolves URLs in `@import`s to the contents
  /// of Sass files.
  ///
  /// Importers should override [toString] to provide a human-readable description
  /// of the importer. For example, the default filesystem importer returns its
  /// load path.
  ///
  /// This extends [AsyncImporter] to guarantee that [canonicalize] and [load] are
  /// synchronous. It's usable with both the synchronous and asynchronous
  /// `compile()` functions, and as such should be extended in preference to
  /// [AsyncImporter] if possible.
  ///
  /// Subclasses should extend [Importer], not implement it.
  ///
  /// {@category Importer}
  abstract class Importer extends AsyncImporter {
    /// An importer that never imports any stylesheets.
    ///
    /// This is used for stylesheets which don't support relative imports, such as
    /// those created from Dart code with plain strings.
    static final Importer noOp = NoOpImporter();
  
    Uri? canonicalize(Uri url);
  
    ImporterResult? load(Uri url);
  
    DateTime modificationTime(Uri url) => DateTime.now();
  
    bool couldCanonicalize(Uri url, Uri canonicalUrl) => true;
  
    bool isNonCanonicalScheme(String scheme) => false;
  }
  