Internal problem: Unimplemented constant evaluation during expression evaluation

[a-siva]

When ExperimentalFlag.constantUpdate2018 is turned on by default using the following patches

https://dart-review.googlesource.com/c/sdk/+/98485
https://dart-review.googlesource.com/c/sdk/+/98563
and setting ExperimentalFlag.constantUpdate2018 to true in https://github.com/dart-lang/sdk/blob/master/pkg/front_end/lib/src/api_prototype/experimental_flags.dart#L29

many service tests fail with the following stack trace

ServerRpcException(org-dartlang-debug:synthetic_debug_expression:1: Internal problem: Unimplemented constant evaluation during expression evaluation.
#0      internalProblem (package:front_end/src/fasta/problems.dart:45:3)
#1      unimplemented (package:front_end/src/fasta/problems.dart:51:10)
#2      KernelTarget.runProcedureTransformations (package:front_end/src/fasta/kernel/kernel_target.dart:794:7)
#3      IncrementalCompiler.compileExpression.<anonymous closure> (package:front_end/src/fasta/incremental_compiler.dart:795:16)
<asynchronous suspension>
#4      CompilerContext.runInContext.<anonymous closure>.<anonymous closure> (package:front_end/src/fasta/compiler_context.dart:122:46)
#5      new Future.sync (dart:async/future.dart:224:31)
#6      CompilerContext.runInContext.<anonymous closure> (package:front_end/src/fasta/compiler_context.dart:122:19)
#7      _rootRun (dart:async/zone.dart:1124:13)
#8      _CustomZone.run (dart:async/zone.dart:1021:19)
#9      _runZoned (dart:async/zone.dart:1516:10)
#10     runZoned (dart:async/zone.dart:1463:12)
#11     CompilerContext.runInContext (package:front_end/src/fasta/compiler_context.dart:121:12)
#12     IncrementalCompiler.compileExpression (package:front_end/src/fasta/incremental_compiler.dart:709:26)
<asynchronous suspension>
#13     IncrementalCompiler.compileExpression (package:vm/incremental_compiler.dart:156:23)
#14     _processExpressionCompilationRequest (file:///usr/local/google/home/asiva/workspace/dart-ws2/sdk/pkg/vm/bin/kernel_service.dart:374:52)
<asynchronous suspension>
#15     _processLoadRequest (file:///usr/local/google/home/asiva/workspace/dart-ws2/sdk/pkg/vm/bin/kernel_service.dart:468:11)
<asynchronous suspension>
#16     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:171:12)
)

[a-siva]

/cc @aam

[kmillikin]

You no longer need to manually update experimental_flags.dart, I've updated https://dart-review.googlesource.com/c/sdk/+/98485 to include it.

If you also patch in https://dart-review.googlesource.com/c/sdk/+/98675 then it will re-enable expression compilation but we will not evaluate constants. This leaves two service test failures:

service/auth_token_test
service/get_source_report_test

@a-siva could you get someone on the VM team to look into these and see if they are just different expectations or indicate a deeper problem? If there is no problem other than missing static checks on constants, then we could consider this a temporary solution. (Unfortunately, it requires keeping the old C++ constant evaluation code.)

A better solution is to perform constant evaluation and serialize a constant pool back to the VM, but this doesn't match the way that things work right now so it will take some time.

[aam]

The test seems to rely on DART_SERVICE_USE_AUTH environment define https://github.com/dart-lang/sdk/blob/master/sdk/lib/vmservice/vmservice.dart#L45, which is not defined during platform.dill build. Switching from const to new seems to fix the problem

diff --git a/sdk/lib/vmservice/vmservice.dart b/sdk/lib/vmservice/vmservice.dart
index 10df9dee92..8524da8f90 100644
--- a/sdk/lib/vmservice/vmservice.dart
+++ b/sdk/lib/vmservice/vmservice.dart
@@ -42,7 +42,7 @@ String _makeAuthToken() {
 final String serviceAuthToken = _makeAuthToken();
 
 // TODO(johnmccutchan): Enable the auth token and drop the origin check.
-final bool useAuthToken = const bool.fromEnvironment('DART_SERVICE_USE_AUTH');
+final bool useAuthToken = new bool.fromEnvironment('DART_SERVICE_USE_AUTH');
 
 // This is for use by the embedder. It is a map from the isolateId to
 // anything implementing IsolateEmbedderData. When an isolate goes away,

[vsmenon]

It looks like @aam landed the above. Does this unblock us from flipping the const flag in the SDK?

[vsmenon]

ping - @kmillikin @askeksa-google - is there work pending here?

[kmillikin]

We need to land CL 98675 to enable expression compilation and then we are passing all the VM service tests with the constant-update-2018.

[a-siva]

I patched in CL 98675 and tried all the VM service tests and they pass with that patch. I think this issue can be closed after the CL lands.