Document highlights: Syntax node is not within syntax tree

[Peter-Juhasz]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

In VS2026 Insider 11206.111, a message bar appears with an error:
"Feature 'Document highlights' is currently unavailable due to an internal error."

StreamJsonRpc.RemoteInvocationException: Syntax node is not within syntax tree
   at StreamJsonRpc.JsonRpc.<InvokeCoreAsync>d__171`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 Microsoft.CodeAnalysis.Remote.BrokeredServiceConnection`1.<TryInvokeAsync>d__20`1.MoveNext()
RPC server exception:
System.ArgumentException: Syntax node is not within syntax tree
      at Microsoft.CodeAnalysis.CSharp.CSharpSemanticModel.CheckSyntaxNode(CSharpSyntaxNode syntax)
      at Microsoft.CodeAnalysis.CSharp.CSharpSemanticModel.GetSymbolInfo(ExpressionSyntax expression, CancellationToken cancellationToken)
      at Microsoft.AspNetCore.Analyzers.RouteEmbeddedLanguage.RoutePatternHighlighter.<>c__DisplayClass2_0.<HighlightSymbol>b__1(IdentifierNameSyntax i)
      at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
      at Microsoft.AspNetCore.Analyzers.RouteEmbeddedLanguage.RoutePatternHighlighter.HighlightSymbol(SemanticModel semanticModel, IMethodSymbol methodSymbol, IList`1 highlightSpans, ISymbol matchingParameter, CancellationToken cancellationToken)
      at Microsoft.AspNetCore.Analyzers.RouteEmbeddedLanguage.RoutePatternHighlighter.GetHighlights(RouteUsageModel routeUsage, SemanticModel semanticModel, Int32 position, CancellationToken cancellationToken)
      at Microsoft.AspNetCore.Analyzers.RouteEmbeddedLanguage.RoutePatternHighlighter.GetDocumentHighlights(SemanticModel semanticModel, SyntaxToken token, Int32 position, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.ExternalAccess.AspNetCore.Internal.EmbeddedLanguages.AspNetCoreEmbeddedLanguageDocumentHighlighter.GetDocumentHighlights(Document document, SemanticModel semanticModel, SyntaxToken token, Int32 position, HighlightingOptions options, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.DocumentHighlighting.AbstractDocumentHighlightsService.TryGetEmbeddedLanguageHighlights(Document document, SemanticModel semanticModel, Int32 position, HighlightingOptions options, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.DocumentHighlighting.AbstractDocumentHighlightsService.GetDocumentHighlightsInCurrentProcessAsync(Document document, Int32 position, IImmutableSet`1 documentsToSearch, HighlightingOptions options, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.DocumentHighlighting.AbstractDocumentHighlightsService.GetDocumentHighlightsAsync(Document document, Int32 position, IImmutableSet`1 documentsToSearch, HighlightingOptions options, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.RemoteDocumentHighlightsService.<>c__DisplayClass2_0.<<GetDocumentHighlightsAsync>b__0>d.MoveNext()
   --- End of stack trace from previous location ---
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.<>c__DisplayClass7_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, Boolean updatePrimaryBranch, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.RunWithSolutionAsync[T](AssetProvider assetProvider, Checksum solutionChecksum, 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)

Expected Behavior

No response

Steps To Reproduce

Move caret to a route parameter in a Minimal API route definition.

public static partial class XEndpoints
{
	public static void MapXEndpoints(this IEndpointRouteBuilder app)
	{
		app.MapPost("/organizations/{organizationId}/y/{yId}/z/{zId}/w/{wId}/load", LoadAsync);
	}
}

Exceptions (if any)

No response

.NET Version

10.0.100

Anything else?

The file is a partial class, endpoints are defined in different files.

[martincostello]

Does it error in a stable release of VS 2026? If not, then this is likely an issue for VS, not ASP.NET Core.

[dotnet-policy-service]

Hi @@Peter-Juhasz. We have added the "Needs: Author Feedback" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.