[web] Invalid argument(s): Type parameter TypeParameter(ConfigValue.T) is not indexed

[dnys1]

Original Issue: flutter/flutter#105840

I have a Flutter app which will not build on Web (release-mode). In all other platforms and in debug mode it builds fine. Further, the issue is not reproducible with dart2js.

The compiler crashed: Invalid argument(s): Type parameter TypeParameter(ConfigValue.T) is not indexed
#0      TypeParameterIndexer.[] (package:kernel/binary/ast_to_binary.dart:2921:8)
#1      BinaryPrinter.visitTypeParameterType (package:kernel/binary/ast_to_binary.dart:2426:38)
#2      TypeParameterType.accept (package:kernel/ast.dart:11890:42)
#3      BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)

Crash Logs

$ flutter build web

💪 Building with sound null safety 💪

Target dart2js failed: Exception: Warning: The 'dart2js' entrypoint script is deprecated, please use 'dart compile js'
instead.
.dart_tool/flutter_build/d0b42d48aad4d4cb905f52ff662e43ea/main.dart:
Internal Error: The compiler crashed when compiling this element.

The compiler is broken.

When compiling the above element, the compiler crashed. It is not
possible to tell if this is caused by a problem in your program or
not. Regardless, the compiler should not crash.

The Dart team would greatly appreciate if you would take a moment to
report this problem at http://dartbug.com/new.

Please include the following information:

* the name and version of your operating system,

* the Dart SDK build number (2.17.1), and

* the entire message you see here (including the full stack trace
  below as well as the source location above).

The compiler crashed: Invalid argument(s): Type parameter TypeParameter(ConfigValue.T) is not indexed
#0      TypeParameterIndexer.[] (package:kernel/binary/ast_to_binary.dart:2921:8)
#1      BinaryPrinter.visitTypeParameterType (package:kernel/binary/ast_to_binary.dart:2426:38)
#2      TypeParameterType.accept (package:kernel/ast.dart:11890:42)
#3      BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#4      BinaryPrinter.visitFunctionType (package:kernel/binary/ast_to_binary.dart:2397:7)
#5      FunctionType.accept (package:kernel/ast.dart:11218:42)
#6      BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#7      BinaryPrinter.writeOptionalNode (package:kernel/binary/ast_to_binary.dart:522:7)
#8      BinaryPrinter.visitConditionalExpression (package:kernel/binary/ast_to_binary.dart:1797:5)
#9      ConditionalExpression.accept (package:kernel/ast.dart:6679:44)
#10     BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#11     BinaryPrinter.visitInstanceCreation.<anonymous closure> (package:kernel/binary/ast_to_binary.dart:1841:7)
#12     _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:614:13)
#13     BinaryPrinter.visitInstanceCreation (package:kernel/binary/ast_to_binary.dart:1839:22)
#14     InstanceCreation.accept (package:kernel/ast.dart:7076:44)
#15     BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#16     BinaryPrinter.visitFileUriExpression (package:kernel/binary/ast_to_binary.dart:1852:5)
#17     FileUriExpression.accept (package:kernel/ast.dart:7194:44)
#18     BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#19     BinaryPrinter.writeConstantTableEntry (package:kernel/binary/ast_to_binary.dart:289:7)
#20     BinaryPrinter.writeConstantTable (package:kernel/binary/ast_to_binary.dart:198:7)
#21     BinaryPrinter.writeComponentFile.<anonymous closure> (package:kernel/binary/ast_to_binary.dart:598:7)
#22     Timeline.timeSync (dart:developer/timeline.dart:157:22)
#23     BinaryPrinter.writeComponentFile (package:kernel/binary/ast_to_binary.dart:577:14)
#24     SerializationTask.serializeComponent.<anonymous closure> (package:compiler/src/serialization/task.dart:119:15)
#25     CompilerTask.measureSubtask (package:compiler/src/common/tasks.dart:181:35)
#26     SerializationTask.serializeComponent (package:compiler/src/serialization/task.dart:110:5)
#27     Compiler.produceKernel (package:compiler/src/compiler.dart:411:33)
<asynchronous suspension>
#28     Compiler.runSequentialPhases (package:compiler/src/compiler.dart:621:33)
<asynchronous suspension>
#29     Compiler.runInternal.<anonymous closure> (package:compiler/src/compiler.dart:305:7)
<asynchronous suspension>
#30     Compiler.runInternal (package:compiler/src/compiler.dart:304:5)
<asynchronous suspension>
#31     main (package:compiler/src/dart2js.dart:1407:3)
<asynchronous suspension>



Compiling lib/main.dart for the Web...                           2,616ms
Exception: Failed to compile application for the Web.

The issue is with a class which looks like the following. This is the smallest reproduction I could find.

Reproduction

T _identity<T extends Object>(String o) => o as T;

class ConfigValue<T extends Object> {
  const ConfigValue._(
    this.value, {
    T Function(String)? parse,
  }) : _parse = parse ?? _identity;

  final String value;
  final T Function(String) _parse;
}

void main() {
  const myValue = ConfigValue<int>._(
    String.fromEnvironment('MY_VALUE'),
    parse: int.parse,
  );
}

Building the above reproduction with dart2js works fine.

dart2js Logs

$ dart --version
Dart SDK version: 2.17.1 (stable) (Tue May 17 17:58:21 2022 +0000) on "macos_x64"

$ dart compile js -o main.dart.js main.dart
Info: Compiling with sound null safety
Compiled 9,540,220 characters Dart to 92,755 characters JavaScript in 0.72 seconds
Dart file main.dart compiled to JavaScript: main.dart.js

The issue appears on master as well:

master Crash Logs

$ flutter build web

💪 Building with sound null safety 💪

Upgrading .gitignore
Compiling lib/main.dart for the Web...                          
Target dart2js failed: Exception: Warning: The 'dart2js' entrypoint script is deprecated, please use 'dart compile js' instead.
.dart_tool/flutter_build/cc613de6d9215dd6f5e75f306d00d5e3/main.dart:
Internal Error: The compiler crashed when compiling this element.

The compiler is broken.

When compiling the above element, the compiler crashed. It is not
possible to tell if this is caused by a problem in your program or
not. Regardless, the compiler should not crash.

The Dart team would greatly appreciate if you would take a moment to
report this problem at http://dartbug.com/new.

Please include the following information:

* the name and version of your operating system,

* the Dart SDK build number (2.18.0-178.0.dev), and

* the entire message you see here (including the full stack trace
  below as well as the source location above).

The compiler crashed: Invalid argument(s): Type parameter TypeParameter(AWSConfigValue.T) is not indexed
#0      TypeParameterIndexer.[] (package:kernel/binary/ast_to_binary.dart:2947:8)
#1      BinaryPrinter.visitTypeParameterType (package:kernel/binary/ast_to_binary.dart:2452:38)
#2      TypeParameterType.accept (package:kernel/ast.dart:12216:42)
#3      BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#4      BinaryPrinter.visitFunctionType (package:kernel/binary/ast_to_binary.dart:2424:7)
#5      FunctionType.accept (package:kernel/ast.dart:11547:42)
#6      BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#7      BinaryPrinter.writeOptionalNode (package:kernel/binary/ast_to_binary.dart:522:7)
#8      BinaryPrinter.visitConditionalExpression (package:kernel/binary/ast_to_binary.dart:1823:5)
#9      ConditionalExpression.accept (package:kernel/ast.dart:6992:44)
#10     BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#11     BinaryPrinter.visitInstanceCreation.<anonymous closure> (package:kernel/binary/ast_to_binary.dart:1867:7)
#12     _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:614:13)
#13     BinaryPrinter.visitInstanceCreation (package:kernel/binary/ast_to_binary.dart:1865:22)
#14     InstanceCreation.accept (package:kernel/ast.dart:7389:44)
#15     BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#16     BinaryPrinter.visitFileUriExpression (package:kernel/binary/ast_to_binary.dart:1878:5)
#17     FileUriExpression.accept (package:kernel/ast.dart:7507:44)
#18     BinaryPrinter.writeNode (package:kernel/binary/ast_to_binary.dart:430:10)
#19     BinaryPrinter.writeConstantTableEntry (package:kernel/binary/ast_to_binary.dart:289:7)
#20     BinaryPrinter.writeConstantTable (package:kernel/binary/ast_to_binary.dart:198:7)
#21     BinaryPrinter.writeComponentFile.<anonymous closure> (package:kernel/binary/ast_to_binary.dart:598:7)
#22     Timeline.timeSync (dart:developer/timeline.dart:160:22)
#23     BinaryPrinter.writeComponentFile (package:kernel/binary/ast_to_binary.dart:577:14)
#24     SerializationTask.serializeComponent.<anonymous closure> (package:compiler/src/serialization/task.dart:124:15)
#25     CompilerTask.measureSubtask (package:compiler/src/common/tasks.dart:181:35)
#26     SerializationTask.serializeComponent (package:compiler/src/serialization/task.dart:115:5)
#27     Compiler.produceKernel (package:compiler/src/compiler.dart:420:35)
<asynchronous suspension>
#28     Compiler.runSequentialPhases (package:compiler/src/compiler.dart:643:33)
<asynchronous suspension>
#29     Compiler.runInternal.<anonymous closure> (package:compiler/src/compiler.dart:309:7)
<asynchronous suspension>
#30     Compiler.runInternal (package:compiler/src/compiler.dart:308:5)
<asynchronous suspension>
#31     main (package:compiler/src/dart2js.dart:1424:3)
<asynchronous suspension>


Compiling lib/main.dart for the Web...                             21.7s
Exception: Failed to compile application for the Web.

[sigmundch]

@dnys1 - thanks for filing the bug and for the very nice, small, and detailed repro! Can you comment on how you normally provide the value the "MY_VALUE" constant? Historically we delayed evaluation of these constants (which is why we call them "unevaluated" constants), but our hope is to eventually move towards evaluating them eagerly at the time the compiler is being invoked. (keeping these unevaluated brings us other challenges we'd like to get rid of).

@johnniwinther - the crash itself appears to be a CFE bug in serializing unevaluated constants.

If you want to see it locally, you can use the example above from @dnys1:

T _identity<T extends Object>(String o) => o as T;

class ConfigValue<T extends Object> {
  const ConfigValue._(
    this.value, {
    T Function(String)? parse,
  }) : _parse = parse ?? _identity;

  final String value;
  final T Function(String) _parse;
}

void main() {
  const myValue = ConfigValue<int>._(
    String.fromEnvironment('MY_VALUE'),
    parse: int.parse,
  );
}

But run dart2js with --cfe-only to force serialization of the unevaluated constants:

dart compile js --cfe-only main.dart

That reproduces the crash reported above.

[dnys1]

Hi @sigmundch - my pleasure and thanks for the quick reply as well!

I would like to enable this option for cases where it's simpler than providing an environment variable (esp. on web). I should have included passing a variable in the examples, but it would be like:

flutter build web --dart-define=MY_VALUE=123

or

dart -DMY_VALUE=123 compile js ...

I believe this aligns with what you mention about compile-time evaluation. A fallback for environment variables is included as well for runtime overrides in the full class this was based on.

https://github.com/aws-amplify/amplify-flutter/blob/next/packages/aws_common/lib/src/config/aws_config_value.dart

[jensjoha]

Fixed with 9e32094.