Error: Couldn't resolve the package 'flag' in 'package:flag/flag.dart'.

[codelovercc]

flutter pub add successfully

 % flutter pub add flag   
Resolving dependencies... 
  build_runner_core 7.2.11 (7.3.0 available)
  built_value 8.8.1 (8.9.0 available)
  custom_lint 0.5.8 (0.6.0 available)
  custom_lint_builder 0.5.8 (0.6.1 available)
  custom_lint_core 0.5.8 (0.6.1 available)
  dio 5.4.0 (5.4.1 available)
+ enum_to_string 2.0.1
  ffi 2.1.0 (2.1.2 available)
+ flag 7.0.0
  flutter_lints 2.0.3 (3.0.1 available)
  flutter_riverpod 2.4.9 (2.4.10 available)
+ flutter_svg 2.0.9
  hotreloader 4.1.0 (4.2.0 available)
  intl 0.18.1 (0.19.0 available)
  js 0.6.7 (0.7.1 available)
  lints 2.1.1 (3.0.0 available)
  matcher 0.12.16 (0.12.16+1 available)
  material_color_utilities 0.5.0 (0.8.0 available)
! meta 1.11.0 (overridden) (1.12.0 available)
  mime 1.0.4 (1.0.5 available)
  path 1.8.3 (1.9.0 available)
+ path_parsing 1.0.1
+ petitparser 6.0.2
  riverpod 2.4.9 (2.5.0 available)
  riverpod_analyzer_utils 0.5.0 (0.5.1 available)
  riverpod_annotation 2.3.3 (2.3.4 available)
  riverpod_generator 2.3.9 (2.3.11 available)
  riverpod_lint 2.3.7 (2.3.9 available)
  test_api 0.6.1 (0.7.0 available)
+ vector_graphics 1.1.10+1
+ vector_graphics_codec 1.1.10+1
+ vector_graphics_compiler 1.1.10+1
  vm_service 13.0.0 (14.0.0 available)
  web 0.3.0 (0.5.0 available)
  web_socket_channel 2.4.0 (2.4.4 available)
+ xml 6.5.0
Changed 9 dependencies!
27 packages have newer versions incompatible with dependency constraints.
Try `flutter pub outdated` for more information.

% flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.16.9, on macOS 12.7.1 21G920 darwin-x64, locale zh-Hans-CN)
[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 14.2)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2023.1)
[✓] VS Code (version 1.85.1)
[✓] Connected device (2 available)

Launching lib/main.dart on macOS in debug mode...
Building macOS application...
Invalid depfile: /path/to/project/.dart_tool/flutter_build/7bf370e92f8c1c63abe3e2ccbd009a91/kernel_snapshot.d
Invalid depfile: /path/to/project/.dart_tool/flutter_build/7bf370e92f8c1c63abe3e2ccbd009a91/kernel_snapshot.d
Error: Couldn't resolve the package 'flag' in 'package:flag/flag.dart'.
../path/to/project/lib/src/widgets/localizations.dart:1:8: Error: Not found: 'package:flag/flag.dart'
import 'package:flag/flag.dart';
       ^
../path/to/project/lib/src/widgets/localizations.dart:57:11: Error: The getter 'Flag' isn't defined for the class 'LocalePicker'.
 - 'LocalePicker' is from 'package:/path/to/project/src/widgets/localizations.dart' ('../path/to/project/lib/src/widgets/localizations.dart').
Try correcting the name to the name of an existing getter, or defining a getter or field named 'Flag'.
          Flag.fromString(current.countryCode!),
          ^^^^
Unhandled exception:
FileSystemException(uri=org-dartlang-untranslatable-uri:package%3Aflag%2Fflag.dart; message=StandardFileSystem only supports file:* and data:* URIs)
#0      StandardFileSystem.entityForUri (package:front_end/src/api_prototype/standard_file_system.dart:34:7)
#1      asFileUri (package:vm/kernel_front_end.dart:732:37)
#2      writeDepfile (package:vm/kernel_front_end.dart:870:21)
<asynchronous suspension>
#3      FrontendCompiler.compile (package:frontend_server/frontend_server.dart:676:9)
<asynchronous suspension>
#4      starter (package:frontend_server/starter.dart:102:12)
<asynchronous suspension>
#5      main (file:///Volumes/Work/s/w/ir/x/w/sdk/pkg/frontend_server/bin/frontend_server_starter.dart:13:14)
<asynchronous suspension>

Target kernel_snapshot failed: Exception

Command PhaseScriptExecution failed with a nonzero exit code
** BUILD FAILED **

Exception: Build process failed