NullReferenceException in MethodSymbol.get_ParameterCount()

[vsfeedback]

NullReferenceException in MethodSymbol.get_ParameterCount()

[sharwell]

Feature 'Missing import discovery' is currently unavailable due to an internal error.
StreamJsonRpc.RemoteInvocationException: Object reference not set to an instance of an object.
   at StreamJsonRpc.JsonRpc.<InvokeCoreAsync>d__151`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Threading.Tasks.ValueTask`1.get_Result()
   at Microsoft.CodeAnalysis.Remote.BrokeredServiceConnection`1.<TryInvokeAsync>d__22`1.MoveNext()
RPC server exception:
System.NullReferenceException: Object reference not set to an instance of an object.
      at Microsoft.CodeAnalysis.CSharp.Symbols.MethodSymbol.get_ParameterCount()
      at Microsoft.CodeAnalysis.CSharp.InMethodBinder.LookupSymbolsInSingleBinder(LookupResult result, String name, Int32 arity, ConsList`1 basesBeingResolved, LookupOptions options, Binder originalBinder, Boolean diagnose, CompoundUseSiteInfo`1& useSiteInfo)
      at Microsoft.CodeAnalysis.CSharp.Binder.LookupSymbolsInternal(LookupResult result, String name, Int32 arity, ConsList`1 basesBeingResolved, LookupOptions options, Boolean diagnose, CompoundUseSiteInfo`1& useSiteInfo)
      at Microsoft.CodeAnalysis.CSharp.Binder.BindNonGenericSimpleNamespaceOrTypeOrAliasSymbol(IdentifierNameSyntax node, BindingDiagnosticBag diagnostics, ConsList`1 basesBeingResolved, Boolean suppressUseSiteDiagnostics, NamespaceOrTypeSymbol qualifierOpt)
      at Microsoft.CodeAnalysis.CSharp.Binder.BindNamespaceOrTypeOrAliasSymbol(ExpressionSyntax syntax, BindingDiagnosticBag diagnostics, ConsList`1 basesBeingResolved, Boolean suppressUseSiteDiagnostics)
      at Microsoft.CodeAnalysis.CSharp.Binder.BindTypeOrAlias(ExpressionSyntax syntax, BindingDiagnosticBag diagnostics, ConsList`1 basesBeingResolved, Boolean suppressUseSiteDiagnostics)
      at Microsoft.CodeAnalysis.CSharp.Binder.AnalyzeAnonymousFunction(AnonymousFunctionExpressionSyntax syntax, BindingDiagnosticBag diagnostics)
      at Microsoft.CodeAnalysis.CSharp.Binder.IdentifierUsedAsValueFinder.CheckLambda(AnonymousFunctionExpressionSyntax lambdaSyntax, Binder enclosingBinder)
      at Microsoft.CodeAnalysis.CSharp.Binder.IdentifierUsedAsValueFinder.CheckIdentifiersInNode(CSharpSyntaxNode node, Binder binder)
      at Microsoft.CodeAnalysis.CSharp.Binder.CapturedParametersFinder.<GetCapturedParameters>g__checkParameterReferencesInMethodBody|4_2(CSharpSyntaxNode syntaxNode, Binder bodyBinder, <>c__DisplayClass4_0&)
      at Microsoft.CodeAnalysis.CSharp.Binder.CapturedParametersFinder.GetCapturedParameters(SynthesizedPrimaryConstructor primaryConstructor)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SynthesizedPrimaryConstructor.GetCapturedParameters()
      at Microsoft.CodeAnalysis.CSharp.Symbols.SynthesizedPrimaryConstructor.GetBackingFields()
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceMemberContainerTypeSymbol.AddSynthesizedTypeMembersIfNecessary(MembersAndInitializersBuilder builder, DeclaredMembersAndInitializers declaredMembersAndInitializers, BindingDiagnosticBag diagnostics)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceMemberContainerTypeSymbol.AddSynthesizedMembers(MembersAndInitializersBuilder builder, DeclaredMembersAndInitializers declaredMembersAndInitializers, BindingDiagnosticBag diagnostics)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceMemberContainerTypeSymbol.BuildMembersAndInitializers(BindingDiagnosticBag diagnostics)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceMemberContainerTypeSymbol.GetMembersAndInitializers()
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceMemberContainerTypeSymbol.MakeAllMembers(BindingDiagnosticBag diagnostics)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceMemberContainerTypeSymbol.GetMembersByNameSlow()
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceMemberContainerTypeSymbol.ForceComplete(SourceLocation locationOpt, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.Symbol.ForceCompleteMemberByLocation(SourceLocation locationOpt, Symbol member, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceNamespaceSymbol.ForceComplete(SourceLocation locationOpt, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.Symbol.ForceCompleteMemberByLocation(SourceLocation locationOpt, Symbol member, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceNamespaceSymbol.ForceComplete(SourceLocation locationOpt, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.Symbol.ForceCompleteMemberByLocation(SourceLocation locationOpt, Symbol member, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceNamespaceSymbol.ForceComplete(SourceLocation locationOpt, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceModuleSymbol.ForceComplete(SourceLocation locationOpt, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.Symbols.SourceAssemblySymbol.ForceComplete(SourceLocation locationOpt, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.CSharpCompilation.GetSourceDeclarationDiagnostics(SyntaxTree syntaxTree, Nullable`1 filterSpanWithinTree, Func`4 locationFilterOpt, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.CSharpCompilation.GetDiagnosticsForSyntaxTree(CompilationStage stage, SyntaxTree syntaxTree, Nullable`1 filterSpanWithinTree, Boolean includeEarlierStages, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.CSharp.SyntaxTreeSemanticModel.GetDiagnostics(Nullable`1 span, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.GetUniqueFixesAsyncInCurrentProcessAsync(Document document, TextSpan span, ImmutableArray`1 diagnosticIds, ISymbolSearchService symbolSearchService, AddImportOptions options, ImmutableArray`1 packageSources, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.GetUniqueFixesAsync(Document document, TextSpan span, ImmutableArray`1 diagnosticIds, ISymbolSearchService symbolSearchService, AddImportOptions options, ImmutableArray`1 packageSources, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.RemoteMissingImportDiscoveryService.<>c__DisplayClass4_0.<<GetUniqueFixesAsync>b__0>d.MoveNext()
   --- End of stack trace from previous location ---
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.<>c__DisplayClass9_0`1.<<RunWithSolutionAsync>g__ProcessSolutionAsync|1>d.MoveNext()
   --- End of stack trace from previous location ---
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.RunWithSolutionAsync[T](AssetProvider assetProvider, Checksum solutionChecksum, Int32 workspaceVersion, Boolean updatePrimaryBranch, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.RunWithSolutionAsync[T](AssetProvider assetProvider, Checksum solutionChecksum, Int32 workspaceVersion, Boolean updatePrimaryBranch, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.BrokeredServiceBase.RunWithSolutionAsync[T](Checksum solutionChecksum, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.BrokeredServiceBase.RunServiceImplAsync[T](Func`2 implementation, CancellationToken cancellationToken)

[jaredpar]

The stack doesn't have sufficient information for us to track down this crash. It seems likely that _methodSymbol is null but can't be certain. Think the next step here is to enable nullable checking in this file, add some asserts and see where that leads us.

[cston]

From the stack, this looks similar to #71400 and #72862.

Could the NullReferenceException be the result of re-entrancy calculating MethodSymbol.Parameters, in this case when binding a type from a lambda parameter perhaps?