Import token evaluation crash

[TheMaverickProgrammer]

• Dart version and tooling diagnostic info (dart info)

If providing this information as part of reporting a bug, please review the information
below to ensure it only contains things you're comfortable posting publicly.

#### General info

- Dart 3.5.2 (stable) (Wed Aug 28 10:01:20 2024 +0000) on "windows_x64"
- on windows / "Windows 10 Home" 10.0 (Build 22631)
- locale is en-US

#### Project info

- sdk constraint: '>=3.4.0 <4.0.0'
- dependencies: appwrite, auto_size_text, badges, beamer, carousel_slider, croppy, cupertino_icons, device_info_plus, dropdown_button2, file_picker, flutter, flutter_animate, flutter_bloc, flutter_blue_plus, flutter_cache_manager, flutter_quill, flutter_svg, flutter_xlider, get_it, gradient_borders, image_size_getter, intl, marquee, octo_image, onboarding_overlay, open_file, path_provider, pdf, permission_handler, photo_view, printing, provider, regexpattern, responsive_framework, result_dart, shared_preferences, sliver_tools, smooth_page_indicator, sticky_headers, super_banners, url_launcher, uuid, vector_math, video_player, visibility_detector, web, webview_flutter, webview_flutter_web
- dev_dependencies: flutter_launcher_icons, flutter_lints, flutter_test, test
- elided dependencies: 7

#### Process info

| Memory | CPU | Elapsed time | Command line |
| -----: | --: | -----------: | ------------ |
|  40 MB |  -- |              | dart.exe     |
| 724 MB |  -- |              | dart.exe     |
|  49 MB |  -- |              | dart.exe     |
|  19 MB |  -- |              | dart.exe     |
|  95 MB |  -- |              | dart.exe     |

• Whether you are using Windows, macOS, or Linux (if applicable)
  Tested on Windows

• Whether you are using Chrome, Safari, Firefox, Edge (if applicable)
  On Android

---

While compiling stub code, our team had repeatable crashes during compilation for android. Only after one of us deleted pubspec lock file and re-ran flutter pub get, changed Kotlin to version 2.0.21 from 1.7.10 it was able to compile. Here was the following compilation errors:

Unhandled exception:
Null check operator used on a null value
#0      TextualOutlineListener.endShow (package:front_end/src/util/textual_outline.dart:877)
#1      ForwardingListener.endShow (package:_fe_analyzer_shared/src/parser/forwarding_listener.dart:1185)
#2      ImportRecoveryListener.endShow (package:_fe_analyzer_shared/src/parser/recovery_listeners.dart:67)
#3      Parser.parseShow (package:_fe_analyzer_shared/src/parser/parser_impl.dart:1177)
#4      Parser.parseCombinatorStar (package:_fe_analyzer_shared/src/parser/parser_impl.dart:1142)
#5      Parser.parseImportRecovery (package:_fe_analyzer_shared/src/parser/parser_impl.dart:1016)
#6      Parser.parseImport (package:_fe_analyzer_shared/src/parser/parser_impl.dart:932)
#7      Parser.parseTopLevelKeywordDeclaration (package:_fe_analyzer_shared/src/parser/parser_impl.dart:731)
#8      Parser.parseTopLevelDeclarationImpl (package:_fe_analyzer_shared/src/parser/parser_impl.dart:532)
#9      Parser.parseUnit (package:_fe_analyzer_shared/src/parser/parser_impl.dart:412)
#10     textualOutline (package:front_end/src/util/textual_outline.dart:458)
#11     IncrementalCompiler._initializeExperimentalInvalidation (package:front_end/src/base/incremental_compiler.dart:1248)
#12     IncrementalCompiler.computeDelta.<anonymous closure> (package:front_end/src/base/incremental_compiler.dart:306)
<asynchronous suspension>
#13     CompilerContext.clear (package:front_end/src/base/compiler_context.dart:128)
<asynchronous suspension>
#14     IncrementalCompiler.compile (package:vm/incremental_compiler.dart:77)
<asynchronous suspension>
#15     FrontendCompiler.compile (package:frontend_server/frontend_server.dart:636)
<asynchronous suspension>
#16     listenAndCompile.<anonymous closure> (package:frontend_server/frontend_server.dart:1385)
<asynchronous suspension>
2
the Dart compiler exited unexpectedly.

While the line number is different to upstream, I can see that the null-assert operator is being used without any safety checks, so it must be expected to not fail here - yet it does.

https://github.com/dart-lang/sdk/blob/main/pkg/front_end/lib/src/util/textual_outline.dart#L874

---

Our code. We were experimenting with making our first cross-platform library. So the code is bare minimal.

stub.dart

import 'dart:typed_data';

import 'package:project/common/utility/platform_file_utils_impl/base.dart';
import 'package:project/constants/enums.dart';

class PlatformFileUtilities extends BaseFileUtilities {
  @override
  void downloadFile(Uint8List bytes, String filename) {}

  @override
  Future<Uint8List> loadLocalFileAsBytes(String path) async {
    return Uint8List.fromList([]);
  }

  @override
  void openFile(Uint8List bytes, MimeType mimeType) {}
}

mobile.dart

import 'dart:typed_data';
import 'package:project/constants/all.dart' as k;
import 'package:project/common/utility/platform_file_utils_impl/base.dart';

class PlatformFileUtilities implements BaseFileUtilities {
  @override
  void downloadFile(Uint8List bytes, String filename) {}

  @override
  Future<Uint8List> loadLocalFileAsBytes(String path) async {
    return Uint8List.fromList([]);
  }

  @override
  void openFile(Uint8List bytes, k.MimeType mimeType) {
    // TODO: implement openFile
  }
}

web.dart

import 'dart:typed_data';
import 'package:project/constants/all.dart' as k;
import 'package:project/common/utility/platform_file_utils_impl/base.dart';
import 'dart:convert' show base64Encode;
import 'package:web/web.dart' as web;
import 'dart:js_interop';

@JS("Blob")
extension type Blob._(JSObject _) implements JSObject {
  external factory Blob(JSArray<JSArrayBuffer> blobParts, JSObject? options);

  factory Blob.fromBytes(List<int> bytes, k.MimeType fileType) {
    final data = Uint8List.fromList(bytes).buffer.toJS;
    return Blob([data].toJS, web.BlobPropertyBag(type: fileType.name));
  }

  external JSArrayBuffer? get blobParts;
  external JSObject? get options;
}

class PlatformFileUtilities implements BaseFileUtilities {
  @override
  void downloadFile(Uint8List bytes, String filename) {
    /// downloads file
    final web.HTMLAnchorElement anchor =
        web.document.createElement('a') as web.HTMLAnchorElement
          ..href = "data:application/octet-stream;base64,${base64Encode(bytes)}"
          ..style.display = 'none'
          ..download = filename;

    /// not quite certain what this actually does
    web.document.body!.appendChild(anchor);
    // simulates a click to download the file
    // (as we arent displaying a download prompt we need to do this)
    anchor.click();

    /// supposed to clean up
    web.document.body!.removeChild(anchor);
  }

  @override
  Future<Uint8List> loadLocalFileAsBytes(String path) {
    // TODO: implement loadFileAsBytes
    throw UnimplementedError();
  }

  @override
  void openFile(Uint8List bytes, k.MimeType mimeType) {
    /// creates a blob from our bytes and formats it so that it will display as a pdf
    /// Note: the extension names are very particular and I assume they are html/web specific
    final Blob blob = Blob.fromBytes(bytes, k.MimeType.pdf);

    // Generate URL object from blob
    final url = web.URL.createObjectURL(blob);

    // opens a window using our blobs url in a new tab
    web.window.open(
      url,
      '_blank',
    );
    web.URL.revokeObjectURL(url);
  }
}

platform_file_utils.dart

export 'package:project/common/utility/platform_file_utils_impl/stub.dart'
    if (dart.library.io) 'package:project/common/utility/platform_file_utils_impl/mobile.dart'
    if (dart.library.js_interop) 'package:project/common/utility/platform_file_utils_impl/web.dart';

enums.dart

This file is commonly exported by package:project/constants/all.dart in our project as k.

enum MimeType {
  jpeg(name: 'image/jpeg'),
  pdf(name: 'application/pdf');

  final String name;

  const MimeType({required this.name});
}

Finally in main, just include and use it like so:

import 'package:project/common/utility/platform_file_utils.dart';

int main() {
    final PlatformFileUtilities fileUtils = PlatformFileUtilities();
    final Uint8List bytes = Uint8List.fromList([]);
    final fileName = "test.pdf";
    fileUtils.downloadFile(bytes, fileName);
}

[dart-github-bot]

Summary: The user is experiencing a crash during compilation on Android when using a custom library that exports different implementations based on platform. The crash occurs during import token evaluation and is related to a null check operator being used on a potentially null value. The user was able to resolve the issue by deleting the pubspec.lock file, running flutter pub get, and upgrading the Kotlin version.