IDE no longer error squigglies generic type parameter resolution errors in VB code

_This issue has been moved from [a ticket on Developer Community](https://developercommunity.visualstudio.com/t/IDE-no-longer-error-squigglies-generic-t/11048452)._

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[severity:It's more difficult to complete my work] [regression] [worked-in:last before 18.3.0]
If you create a generic type, referring to the generic type using the wrong number of generic arguments causes compiler error, but code editor does not show error squigglies on it, nor is it shown in error list.

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### Original Comments

#### Feedback Bot on 2/23/2026, 09:23 AM:

We have directed your feedback to the appropriate engineering team for further evaluation. The team will review the feedback and notify you about the next steps.

#### YI CHWEEN ONG (Centific Technologies Inc) [MSFT] on 3/6/2026, 01:12 PM:

Thank you for taking the time to log this issue!

Do you still repro this issue now? I can’t repro this issue in VS2026 Professional (18.3.2) with below steps:

1. File > New > Project > Console App (VB) > Next > Framework: .NET 10.0 > Create.


2. Open the file and intentionally reference a generic type with the wrong number of type arguments.
   
   Result: The editor shows error squiggles, and the error also appears in the Error List.

In order to investigate your issue further, could you help to confirm several questions?

1. Could you upgrade your VS to the latest version, then try to create a new simple solution and check if this issue also reproduces?


2. Would it be possible to provide us a sample demo and a repro video that shows the issue occurring?

(The reason we’re asking for additional information is that we’d like to fully understand the issue and try to reproduce it on our side.)

We look forward to hearing from you!

#### TRI-L Data Systems Claudio Friederich on 3/7/2026, 09:36 AM:

Further testing reveals the problem to occur in the following combination of circumstances (I don’t know if there are others).

1. The project is a .NET Framework 4.8 VB project.


2. It references another project in the solution and uses generic types the other project defines


3. In the referencing project, any sort of invalid types are not squigglied, but they still cause the compile to fail (output window shows compile errors). But other types of errors, such as statements outside of methods, are still squigglied.

Attached is a project that demonstrates this. It is based off of my original project with all members stubbed out. Look at CoreServices project SignLights structure. It contains several members that refer to nonexistent types. That structure references generic types defined in the Data project.

#### TRI-L Data Systems Claudio Friederich on 3/7/2026, 09:40 AM:

updating to 18.3.2 had no effect on the problem.

#### YI CHWEEN ONG (Centific Technologies Inc) [MSFT] on 3/11/2026, 01:46 PM:

Thanks for your sharing the detail steps, I can reproduce this issue through your shared steps and this issue has been escalated for further investigation, if there is any process, I will inform you immediately.

Start with the attached .NET Framework 4.8 VB project, especially the CoreServices project's SignLights structure and the generic types defined in the Data project. Reproduce the invalid type references and compare compiler output with editor squiggles and the Error List; done means these errors are surfaced consistently in the editor and Error List.

Written by the indexing model from the issue text.