slngen does not include legacy project types that do not define TargetFramework about slngen

[jeffkl]

The code above is slightly different than you think. SlnGen uses an MSBuild API called "Static Graph" which loads all projects and then loads each project again per target framework. This means if you have:

<PropertyGroup>
  <TargetFramework>net46;netcoreapp3.1</TargetFramework>
</PropertyGroup>

Static graph will load the project 3 times. The code above is ignoring the "inner" projects since they are not needed for solution file generation.

So something else is causing your project to be left out of the solution. This is the code that determines if a project should be in a solution:

slngen/src/Microsoft.VisualStudio.SlnGen/SlnProject.cs

Lines 345 to 358 in b72a477

	/// <summary>
	/// Checks whether a project should be included in the solution or not.
	/// </summary>
	/// <param name="project">The project.</param>
	/// <returns><code>true</code> if it should be included, false otherwise.</returns>
	internal static bool ShouldIncludeInSolution(Project project)
	{
	return
	!project.GetPropertyValue(MSBuildPropertyNames.IncludeInSolutionFile).Equals(bool.FalseString, StringComparison.OrdinalIgnoreCase) // Filter out projects that explicitly should not be included
	&&
	!project.GetPropertyValue(MSBuildPropertyNames.IsTraversal).Equals(bool.TrueString, StringComparison.OrdinalIgnoreCase) // Filter out traversal projects by looking for an IsTraversal property
	&&
	!project.GetPropertyValue(MSBuildPropertyNames.IsTraversalProject).Equals(bool.TrueString, StringComparison.OrdinalIgnoreCase); // Filter out traversal projects by looking for an IsTraversal property
	}

Does any of that logic exclude your project?

[jeffkl]

Closing due to inactivity, feel free to reopen if my suggestion above didn't resolve the issue