System.InvalidOperationException: Unexpected value 'UnboundLambda' of type 'Microsoft.CodeAnalysis.CSharp.BoundKind'

[TessenR]

Version Used:

Branch C# 8.0: Nullable reference type (29 Oct 2018)
https://github.com/dotnet/csharplang/blob/master/proposals/nullable-reference-types.md
Latest commit 2f8fef by AlekseyTs:
Compare Nullable modifiers while comparing type symbols by default. (#30770)

Steps to Reproduce:

Compile the following code:

#nullable enable
class C
{
    static void Main()
    {
        System.Action a = null!;
        a = () => { }!;
    }
}

https://sharplab.io/#v2:EYLgZgpghgLgrgJwgZwLQDk4BstWFiAJQkiQDsBjCAFQE8AHFAGgBMQBqAHwGIztd8EAAQQyeAgFgAUAAEATEIDC0gN7ShGoTICMANi0AWIQFkoASzIAKAJTrNaqZqdbtAOh0KoQgLxC+OAEIAbjtnIS9fGx8APiEVIQBfYNDE6QSgA=

Actual Behavior:

System.InvalidOperationException: Unexpected value 'UnboundLambda' of type 'Microsoft.CodeAnalysis.CSharp.BoundKind' at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpressionCore(BoundExpression expression, Boolean used) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 323 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpression(BoundExpression expression, Boolean used) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 59 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitConversionExpression(BoundConversion conversion, Boolean used) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitConversion.cs:line 40 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpressionCore(BoundExpression expression, Boolean used) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 115 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpression(BoundExpression expression, Boolean used) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 59 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitAssignmentValue(BoundAssignmentOperator assignmentOperator) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 2447 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitAssignmentExpression(BoundAssignmentOperator assignmentOperator, UseKind useKind) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 2052 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpressionCore(BoundExpression expression, Boolean used) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 91 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpressionCoreWithStackGuard(BoundExpression expression, Boolean used) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 75 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpression(BoundExpression expression, Boolean used) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 63 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitStatement(BoundStatement statement) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 42 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitStatementAndCountInstructions(BoundStatement statement) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 103 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitSequencePointStatement(BoundSequencePoint node) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\CodeGenerator.cs:line 353 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitStatement(BoundStatement statement) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 34 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitStatements(ImmutableArray`1 statements) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 648 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitBlock(BoundBlock block) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 615 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitStatement(BoundStatement statement) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 26 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitStatementList(BoundStatementList list) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 109 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitStatement(BoundStatement statement) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 46 at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.GenerateImpl() in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\CodeGenerator.cs:line 258 at Microsoft.CodeAnalysis.CSharp.MethodCompiler.GenerateMethodBody(PEModuleBuilder moduleBuilder, MethodSymbol method, Int32 methodOrdinal, BoundStatement block, ImmutableArray`1 lambdaDebugInfo, ImmutableArray`1 closureDebugInfo, StateMachineTypeSymbol stateMachineTypeOpt, VariableSlotAllocator variableSlotAllocatorOpt, DiagnosticBag diagnostics, DebugDocumentProvider debugDocumentProvider, ImportChain importChainOpt, Boolean emittingPdb, Boolean emitTestCoverageData, ImmutableArray`1 dynamicAnalysisSpans) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 1428 at Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileMethod(MethodSymbol methodSymbol, Int32 methodOrdinal, ProcessedFieldInitializers& processedInitializers, SynthesizedSubmissionFields previousSubmissionFields, TypeCompilationState compilationState) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 1196 at Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileNamedType(NamedTypeSymbol containingType) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 498 at Microsoft.CodeAnalysis.CSharp.MethodCompiler.<>c__DisplayClass21_0.<CompileNamedTypeAsTask>b__0() in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 388 at Roslyn.Utilities.UICultureUtilities.<>c__DisplayClass5_0.<WithCurrentUICulture>b__0() in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\Core\Portable\InternalUtilities\UICultureUtilities.cs:line 136 at System.Threading.Tasks.Task.InnerInvoke() at System.Threading.Tasks.Task.Execute() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.CodeAnalysis.CSharp.MethodCompiler.WaitForWorkers() in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 303 at Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileMethodBodies(CSharpCompilation compilation, PEModuleBuilder moduleBeingBuiltOpt, Boolean emittingPdb, Boolean emitTestCoverageData, Boolean hasDeclarationErrors, DiagnosticBag diagnostics, Predicate`1 filterOpt, CancellationToken cancellationToken) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 144 at Microsoft.CodeAnalysis.CSharp.CSharpCompilation.CompileMethods(CommonPEModuleBuilder moduleBuilder, Boolean emittingPdb, Boolean emitMetadataOnly, Boolean emitTestCoverageData, DiagnosticBag diagnostics, Predicate`1 filterOpt, CancellationToken cancellationToken) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\Compilation\CSharpCompilation.cs:line 2626 at Microsoft.CodeAnalysis.Compilation.Emit(Stream peStream, Stream metadataPEStream, Stream pdbStream, Stream xmlDocumentationStream, Stream win32Resources, IEnumerable`1 manifestResources, EmitOptions options, IMethodSymbol debugEntryPoint, Stream sourceLinkStream, IEnumerable`1 embeddedTexts, CompilationTestData testData, CancellationToken cancellationToken) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\Core\Portable\Compilation\Compilation.cs:line 2387 at Microsoft.CodeAnalysis.Compilation.Emit(Stream peStream, Stream pdbStream, Stream xmlDocumentationStream, Stream win32Resources, IEnumerable`1 manifestResources, EmitOptions options, IMethodSymbol debugEntryPoint, Stream sourceLinkStream, IEnumerable`1 embeddedTexts, Stream metadataPEStream, CancellationToken cancellationToken) in D:\$TC\work\142fd509662c8cdc\!roslyn\sources\dotnet\src\Compilers\Core\Portable\Compilation\Compilation.cs:line 2335 at SharpLab.Server.Compilation.Compiler.<TryCompileToStreamAsync>d__1.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) at SharpLab.Server.MirrorSharp.SlowUpdate.<ProcessAsync>d__7.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at MirrorSharp.Internal.Handlers.SlowUpdateHandler.<ExecuteAsync>d__4.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) at MirrorSharp.Internal.Connection.<ReceiveAndProcessInternalAsync>d__13.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at MirrorSharp.Internal.Connection.<ReceiveAndProcessAsync>d__12.MoveNext()

[jcouv]

Thanks @TessenR
There is a class of similar bugs around !. It should behave transparently, just like parentheses. I'm working on a general solution that should solve the entire class of bugs.

[jcouv]

Was fixed by #32850 (represents suppression as flag in bound tree)