SolutionProjectExtensions.cs

using System.Collections.Generic;
using System.Linq;
using EnvDTE;
using EnvDTE80;
using Microsoft.VisualStudio.Shell;

namespace ICSharpCode.CodeConverter.VsExtension;

/// <summary>
/// http://www.wwwlicious.com/2011/03/29/envdte-getting-all-projects-html/#comment-2557459433
/// </summary>
public static class SolutionProjectExtensions
{
    public static IEnumerable<Project> GetAllProjects(this Solution sln)
    {
        ThreadHelper.ThrowIfNotOnUIThread();
        return sln.Projects.Cast<Project>().SelectMany(GetProjects);
    }

    public static IEnumerable<Project> GetProjects(this Project project)
    {
        ThreadHelper.ThrowIfNotOnUIThread();
#pragma warning disable VSTHRD010 // Invoke single-threaded types on Main thread
        if (project.Kind == ProjectKinds.vsProjectKindSolutionFolder) {
            return project.ProjectItems.Cast<ProjectItem>()
                .Select(x => x.SubProject).Where(x => x != null)
                .SelectMany(GetProjects);
        }
#pragma warning restore VSTHRD010 // Invoke single-threaded types on Main thread
        return new[] { project };
    }
}