VSIX Manifest fails to resolve asset in SDK-style projects

[rahul7720]

I’m unable to add a project template asset via the source.extension.vsixmanifest designer when using an SDK-style project.

When attempting to add an existing project from the solution as a Microsoft.VisualStudio.ProjectTemplate, the VSIX Manifest Editor throws the following error:

VSIX Manifest Editor

No Extenders could be found for the name
'vsixProjectReferenceContentItemObjectExtender' under the CATID
{2F0FA3B8-C855-4A4E-95A5-CB45C67D6C27}.
Make sure that the Extender Provider for this Extender is correctly registered.

Steps to Reproduce

1. Create a VSIX project using SDK-style (Sdk="Microsoft.NET.Sdk").

2. Add another project to the same solution intended to be used as a Project Template.

3. Open source.extension.vsixmanifest in the designer.

4. Try to add an asset:

   • Type: Microsoft.VisualStudio.ProjectTemplate
   • Source: Project
   • Select the existing project in the solution

Expected Behavior

• The VSIX Manifest Editor should allow adding the project as a ProjectTemplate asset without errors.
• The project should be correctly referenced and included in the VSIX build output.

Actual Behavior

• The VSIX Manifest Editor fails with the “No Extenders could be found”
• The asset cannot be added through the designer UI.

Workaround Attempted

I manually edited source.extension.vsixmanifest and added the asset entry directly:

<Asset
  Type="Microsoft.VisualStudio.ProjectTemplate"
  d:Source="Project"
  d:ProjectName="MyProjectTemplate"
  d:TargetPath="|MyProjectTemplate;TemplateProjectOutputGroup|"
  Path="ProjectTemplates"
  d:VsixSubPath="ProjectTemplates" />

However, this results in a build-time error:

Could not find project MyProjectTemplate referenced from source.extension.vsixmanifest.
Please add a ProjectReference to MyProjectTemplate or correct project name in source.extension.vsixmanifest.

• The project does exist in the solution
• The project name matches
• Adding a ProjectReference does not resolve the issue

Additional Notes

• This same approach works correctly in non–SDK-style VSIX projects.
• The issue appears to be specific to SDK-style VSIX projects and the VSIX Manifest Editor tooling.
• It seems the designer or underlying extender infrastructure does not properly support SDK-style project references for ProjectTemplate assets.

Environment

• Visual Studio: 2026
• VSIX Project Type: SDK-style
• .NET SDK: net472
• OS: Windows

[CalvinAllen]

@rahul7720 Looking into this now!

[CalvinAllen]

@rahul7720 This one is going to be interesting and take some time. While the manifest designer works for the basic stuff using the SDK-style project, its not going to work for project references like that. I've got a couple ideas I'm working through - will keep you updated.

[rahul7720]

@CalvinAllen thanks.
After further investigation, I found that the issue is not limited to project template projects. It also reproduces with standard project references, for example when referencing a class library that implements IWizard.

[CalvinAllen]

@rahul7720 Interesting, that sounds like it may be a different issues though. I’m not familiar with the IWizard interface - any chance you have a very simple repro?

[CalvinAllen]

@rahul7720 Wait, are you talking about a traditional project reference, or the Dependency section of the manifest?

[CalvinAllen]

Root Cause Analysis

After investigation, we've identified two distinct problems with SDK-style VSIX projects:

Problem 1: Designer UI Cannot Enumerate SDK-style Projects

The VSIX Manifest Designer uses legacy DTE extenders (vsixProjectReferenceContentItemObjectExtender) registered under CATIDs for the legacy project system. SDK-style projects use CPS (Common Project System) which has different CATIDs, so the extenders aren't found.

This affects any manifest section that uses "Project" as a source:

Manifest Section	"Project" Source	Designer Works?	Build Works?
Assets (non-template types)	Yes	❌ No	✅ Yes
Assets (ProjectTemplate/ItemTemplate)	Yes	❌ No	❌ No
Dependencies	Yes	❌ No	✅ Yes

Problem 2: Template Build Fails for SDK-style Projects

Even if you manually edit the manifest XML, template assets fail at build time because SDK-style projects don't define the required MSBuild output groups:

Asset Type	Output Group Required	SDK-style Has It?
Assembly, MefComponent, VsPackage, Analyzer, etc.	BuiltProjectOutputGroup	✅ Yes
ProjectTemplate	TemplateProjectOutputGroup	❌ No
ItemTemplate	ItemTemplateOutputGroup	❌ No

Sections NOT Affected

These manifest sections work fine because they don't involve project enumeration:

• Metadata, Installation Targets, Prerequisites
• Dependencies with Manual/Installed/File source
• Assets with File source

---

Solution Plan

We're addressing this with two parallel efforts:

1. VsixSdk Template Support (this repo) - MSBuild-based template inclusion that bypasses the designer's broken project resolution
2. New WPF Manifest Designer (VS-VsixManifestDesigner) - Uses IVsSolution.GetProjectEnum instead of DTE extenders to enumerate all project types

See tracking issues: #21, #22, #23

[rahul7720]

@rahul7720 Interesting, that sounds like it may be a different issues though. I’m not familiar with the IWizard interface - any chance you have a very simple repro?

@CalvinAllen

In a VSIX project, IWizard is an interface provided by Visual Studio’s templating system that allows you to inject custom logic into the project or item creation process. It runs while a template is being created.
E.g: Passing custom values via parameters to the template

The IWizard can be hooked into the Project/Item templates by adding the assembly reference to the Project/Item template:

<WizardExtension>
  <Assembly>MyTemplateWizard, Version=1.0.0.0</Assembly>
  <FullClassName>MyTemplateWizard.ProjectWizard</FullClassName>
</WizardExtension>

In this case, MyTemplateWizard is a class library, which should be added to the project as a project assembly reference in the vsix manifest.
Reference:
https://learn.microsoft.com/en-us/visualstudio/extensibility/how-to-use-wizards-with-project-templates?view=visualstudio

An old repo: https://github.com/tunnelvisionlabs/VsixWizardSample

[rahul7720]

@rahul7720 Wait, are you talking about a traditional project reference, or the Dependency section of the manifest?

I'm talking about adding assembly dependencies as assets in the vsix manifest. Adding an assembly as an asset will automatically add the corresponding project as a project reference to the vsix project as well.

<Assets>
	<Asset Type="Microsoft.VisualStudio.Assembly" d:Source="Project" d:ProjectName="MyTemplateWizard" Path="|MyTemplateWizard|" AssemblyName="|MyTemplateWizard;AssemblyName|" />
</Assets>

[CalvinAllen]

@rahul7720 Alright, thanks, I’m with you now. Working on it!