[compiler is broken] dart2js failed when using object pattern that checks for == null, != null and _ wildcard

[hambergerpls]

- Dart 3.1.1 (stable) (Tue Sep 5 12:20:14 2023 +0000) on "linux_x64"
- on linux / Linux 5.15.90.1-microsoft-standard-WSL2 #1 SMP Fri Jan 27 02:56:13 UTC 2023
- locale is en_US.UTF-8

flutter build web --release

Target dart2js failed: ProcessException: Process exited abnormally:
.dart_tool/flutter_build/87e9c14443d6c4520b47d6deb58aa331/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 (3.1.1), and

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

The compiler crashed: Crash when compiling:
Bad state: No element

#0      List.last (dart:core-patch/growable_array.dart:348:5)
#1      LateLowering._addToCurrentScope (package:compiler/src/kernel/transformations/late_lowering.dart:212:28)
#2      LateLowering._initializedVariableCell (package:compiler/src/kernel/transformations/late_lowering.dart:262:12)
#3      LateLowering._variableCell (package:compiler/src/kernel/transformations/late_lowering.dart:221:11)
#4      LateLowering.transformVariableDeclaration (package:compiler/src/kernel/transformations/late_lowering.dart:275:12)
#5      _Lowering.visitVariableDeclaration (package:compiler/src/kernel/transformations/lowering.dart:73:26)
#6      VariableDeclaration.accept (package:kernel/ast.dart:10709:43)
#7      Transformer.transform (package:kernel/visitor.dart:1774:17)
#8      Transformer.transformList (package:kernel/visitor.dart:1791:18)
#9      Block.transformChildren (package:kernel/ast.dart:9185:7)
#10     Transformer.defaultTreeNode (package:kernel/visitor.dart:1808:10)
#11     TreeVisitor.defaultStatement (package:kernel/visitor.dart:415:41)
#12     TreeVisitor.visitBlock (package:kernel/visitor.dart:420:31)
#13     Block.accept (package:kernel/ast.dart:9173:43)
#14     Transformer.transform (package:kernel/visitor.dart:1774:17)
#15     BlockExpression.transformChildren (package:kernel/ast.dart:8788:14)
#16     Transformer.defaultTreeNode (package:kernel/visitor.dart:1808:10)
#17     TreeVisitor.defaultExpression (package:kernel/visitor.dart:223:43)
#18     TreeVisitor.visitBlockExpression (package:kernel/visitor.dart:350:51)
#19     BlockExpression.accept (package:kernel/ast.dart:8774:44)
#20     Transformer.transform (package:kernel/visitor.dart:1774:17)
#21     Transformer.transformList (package:kernel/visitor.dart:1791:18)
#22     Arguments.transformChildren (package:kernel/ast.dart:5425:7)
#23     Transformer.defaultTreeNode (package:kernel/visitor.dart:1808:10)
#24     TreeVisitor.visitArguments (package:kernel/visitor.dart:510:39)
#25     Arguments.accept (package:kernel/ast.dart:5410:38)
#26     Transformer.transform (package:kernel/visitor.dart:1774:17)
#27     SuperInitializer.transformChildren (package:kernel/ast.dart:3556:19)
#28     Transformer.defaultTreeNode (package:kernel/visitor.dart:1808:10)
#29     TreeVisitor.defaultInitializer (package:kernel/visitor.dart:486:45)
#30     TreeVisitor.visitSuperInitializer (package:kernel/visitor.dart:493:53)
#31     SuperInitializer.accept (package:kernel/ast.dart:3542:45)
#32     Transformer.transform (package:kernel/visitor.dart:1774:17)
#33     Transformer.transformList (package:kernel/visitor.dart:1791:18)
#34     Constructor.transformChildren (package:kernel/ast.dart:2768:7)
#35     Transformer.defaultTreeNode (package:kernel/visitor.dart:1808:10)
#36     TreeVisitor.defaultMember (package:kernel/visitor.dart:471:35)
#37     _Lowering.defaultMember (package:compiler/src/kernel/transformations/lowering.dart:44:18)
#38     TreeVisitor.visitConstructor (package:kernel/visitor.dart:473:43)
#39     Constructor.accept (package:kernel/ast.dart:2747:40)
#40     Transformer.transform (package:kernel/visitor.dart:1774:17)
#41     Transformer.transformList (package:kernel/visitor.dart:1791:18)
#42     Class.transformChildren (package:kernel/ast.dart:1475:7)
#43     Transformer.defaultTreeNode (package:kernel/visitor.dart:1808:10)
#44     TreeVisitor.visitClass (package:kernel/visitor.dart:480:31)
#45     Class.accept (package:kernel/ast.dart:1422:38)
#46     Transformer.transform (package:kernel/visitor.dart:1774:17)
#47     Transformer.transformList (package:kernel/visitor.dart:1791:18)
#48     Library.transformChildren (package:kernel/ast.dart:601:7)
#49     _Lowering.visitLibrary (package:compiler/src/kernel/transformations/lowering.dart:49:10)
#50     List.forEach (dart:core-patch/growable_array.dart:416:8)
#51     transformLibraries (package:compiler/src/kernel/transformations/lowering.dart:22:13)
#52     Dart2jsTarget.performModularTransformationsOnLibraries (package:compiler/src/kernel/dart2js_target.dart:179:14)
#53     KernelTarget.runBuildTransformations (package:front_end/src/fasta/kernel/kernel_target.dart:1571:19)
#54     KernelTarget.buildComponent.<anonymous closure> (package:front_end/src/fasta/kernel/kernel_target.dart:637:7)
<asynchronous suspension>
#55     withCrashReporting (package:front_end/src/fasta/crash.dart:133:12)
<asynchronous suspension>
#56     KernelTarget.buildComponent (package:front_end/src/fasta/kernel/kernel_target.dart:588:12)
<asynchronous suspension>
#57     _buildInternal (package:front_end/src/kernel_generator_impl.dart:210:19)
<asynchronous suspension>
#58     withCrashReporting (package:front_end/src/fasta/crash.dart:133:12)
<asynchronous suspension>
#59     compile.<anonymous closure> (package:front_end/src/api_unstable/dart2js.dart:198:37)
<asynchronous suspension>
#60     compile (package:front_end/src/api_unstable/dart2js.dart:196:36)
<asynchronous suspension>
#61     _loadFromSource (package:compiler/src/phase/load_kernel.dart:304:29)
<asynchronous suspension>
#62     run (package:compiler/src/phase/load_kernel.dart:417:36)
<asynchronous suspension>
#63     Compiler.loadKernel (package:compiler/src/compiler.dart:388:9)
<asynchronous suspension>
#64     Compiler.produceKernel (package:compiler/src/compiler.dart:395:36)
<asynchronous suspension>
#65     Compiler.runSequentialPhases (package:compiler/src/compiler.dart:711:20)
<asynchronous suspension>
#66     Compiler.runInternal.<anonymous closure> (package:compiler/src/compiler.dart:311:7)
<asynchronous suspension>
#67     Compiler.runInternal (package:compiler/src/compiler.dart:310:5)
<asynchronous suspension>
#68     Compiler.run.<anonymous closure> (package:compiler/src/compiler.dart:231:11)
<asynchronous suspension>
#69     main (package:compiler/src/dart2js.dart:1241:3)
<asynchronous suspension>
  Command: /home/danial/flutter/bin/cache/dart-sdk/bin/dart --disable-dart-dev /home/danial/flutter/bin/cache/dart-sdk/bin/snapshots/dart2js.dart.snapshot
  --platform-binaries=/home/danial/flutter/bin/cache/flutter_web_sdk/kernel --invoker=flutter_tool -Ddart.vm.product=true -DFLUTTER_WEB_AUTO_DETECT=true
  -DFLUTTER_WEB_CANVASKIT_URL=https://www.gstatic.com/flutter-canvaskit/b8d35810e91ab8fc39ba5e7a41bff6f697e8e3a8/ --native-null-assertions --no-source-maps -o
  /home/danial/moi-systems/test_project/.dart_tool/flutter_build/87e9c14443d6c4520b47d6deb58aa331/app.dill --packages=.dart_tool/package_config.json --cfe-only
  /home/danial/moi-systems/test_project/.dart_tool/flutter_build/87e9c14443d6c4520b47d6deb58aa331/main.dart
#0      RunResult.throwException (package:flutter_tools/src/base/process.dart:125:5)
#1      _DefaultProcessUtils.run (package:flutter_tools/src/base/process.dart:278:19)
<asynchronous suspension>
#2      Dart2JSTarget.build (package:flutter_tools/src/build_system/targets/web.dart:189:5)
<asynchronous suspension>
#3      _BuildInstance._invokeInternal (package:flutter_tools/src/build_system/build_system.dart:853:9)
<asynchronous suspension>
#4      Future.wait.<anonymous closure> (dart:async/future.dart:525:21)
<asynchronous suspension>
#5      _BuildInstance.invokeTarget (package:flutter_tools/src/build_system/build_system.dart:791:32)
<asynchronous suspension>
#6      Future.wait.<anonymous closure> (dart:async/future.dart:525:21)
<asynchronous suspension>
#7      _BuildInstance.invokeTarget (package:flutter_tools/src/build_system/build_system.dart:791:32)
<asynchronous suspension>
#8      FlutterBuildSystem.build (package:flutter_tools/src/build_system/build_system.dart:620:16)
<asynchronous suspension>
#9      WebBuilder.buildWeb (package:flutter_tools/src/web/compile.dart:89:34)
<asynchronous suspension>
#10     BuildWebCommand.runCommand (package:flutter_tools/src/commands/build_web.dart:198:5)
<asynchronous suspension>
#11     FlutterCommand.run.<anonymous closure> (package:flutter_tools/src/runner/flutter_command.dart:1297:27)
<asynchronous suspension>
#12     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:150:19)
<asynchronous suspension>
#13     CommandRunner.runCommand (package:args/command_runner.dart:212:13)
<asynchronous suspension>
#14     FlutterCommandRunner.runCommand.<anonymous closure> (package:flutter_tools/src/runner/flutter_command_runner.dart:339:9)
<asynchronous suspension>
#15     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:150:19)
<asynchronous suspension>
#16     FlutterCommandRunner.runCommand (package:flutter_tools/src/runner/flutter_command_runner.dart:285:5)
<asynchronous suspension>
#17     run.<anonymous closure>.<anonymous closure> (package:flutter_tools/runner.dart:115:9)
<asynchronous suspension>
#18     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:150:19)
<asynchronous suspension>
#19     main (package:flutter_tools/executable.dart:90:3)
<asynchronous suspension>

Compiling lib/main.dart for the Web...                              8.4s
Exception: Failed to compile application for the Web.

The following code crashes when trying to compile with flutter build web but works when running flutter run -d web-server

class Foo<T> {
  Foo(this.value);
  T? value;
}

class Bar extends Foo {
  Bar(Baz baz)
      : super(switch (baz) {
          Baz(someString: == null) => 'someString is empty',
          Baz(someString: != null) => 'someString is something',
          _ => 'someString is something else',
        });
}

class Baz {
  Baz();
  String? someString;
}

dart2js can compile when the switch statement contains either == null or != null.

// can compile
class Bar extends Foo {
  Bar(Baz baz)
      : super(switch (baz) {
          Baz(someString: == null) => 'someString is empty',
          _ => 'someString is something else',
        });
}

// can compile
class Bar extends Foo {
  Bar(Baz baz)
      : super(switch (baz) {
          Baz(someString: != null) => 'someString is something',
          _ => 'someString is empty',
        });
}

[sigmundch]

Thanks so much for the error report and the detailed repro instructions.

We recently saw an issue with using pattern destructuring within initializers (see #53358), so I wonder if this and that issue are caused by the same bug. The fix for that other issue was approved to be cherry-picked (see #53449) and will be part of the next stable release (3.1.2).

[sigmundch]

Just did a quick check in the master channel and the crash is still there, so this doesn't appear to be the same issue.

[sigmundch]

My mistake - I checked using dartpad's notion of the master channel, but that's behind the current tip-of-tree. After checking locally I can confirm that it was indeed fixed by the same fix as the other issue. That is, using Dart 3.1.1 I can reproduce the crash, but downloading and running Dart 3.1.2 the crash goes away 🎉

It seems 3.1.2 was just released, so please give it a try and let us know if it doesn't work on your end. Thanks again!

[parlough]

As a note, Flutter 3.13.4 (or later) should have the fix as well.

dartpad's notion of the master channet, but that's behind the current tip-of-tree

Sorry about that! Working on getting it updated - dart-lang/dart-pad#2651

[hambergerpls]

Good to hear! Thank you!

UPDATE: Can confirm that it works now 🎉