fix(rename): unload referencing projects before rewriting their .csproj

When a renamed project has dependents, Visual Studio keeps a file handle
on each referencing .csproj (workspace, file watchers, design-time build).
Writing through XmlDocument.Save would frequently fail with
'The process cannot access the file because it is being used by another
process', leaving the rename in a partially applied state.

Each referencing project is now unloaded via IVsSolution4.UnloadProject,
rewritten, and reloaded in a finally block. If the unload cannot be
performed (no GUID, service missing, HRESULT failure), we fall back to
the previous direct-save behavior so this change never regresses.

Author: CalvinAllen

src/CodingWithCalvin.ProjectRenamifier/Commands/RenamifyProjectCommand.cs

@@ -8,6 +8,7 @@
 using CodingWithCalvin.Otel4Vsix;
 using EnvDTE;
 using EnvDTE80;
+using Microsoft.VisualStudio.Shell.Interop;
 
 namespace CodingWithCalvin.ProjectRenamifier
 {
@@ -172,9 +173,11 @@ private void RenameProject(Project project, DTE2 dte)
             var stepIndex = 0;
             var projectRemovedFromSolution = false;
             var projectReaddedToSolution = false;
-            List<string> referencingProjects = null;
+            List<ProjectReferenceService.ReferencingProjectInfo> referencingProjects = null;
             Project parentSolutionFolder = null;
 
+            var vsSolution = ServiceProvider.GetService(typeof(SVsSolution)) as IVsSolution;
+
             try
             {
                 // Step 1: Collect projects that reference this project before removal
@@ -230,7 +233,7 @@ private void RenameProject(Project project, DTE2 dte)
                 // Step 9: Update references in projects that referenced this project
                 ExecuteStep(progressDialog, stepIndex++, () =>
                 {
-                    ProjectReferenceService.UpdateProjectReferences(referencingProjects, oldProjectFilePath, projectFilePath);
+                    ProjectReferenceService.UpdateProjectReferences(vsSolution, referencingProjects, oldProjectFilePath, projectFilePath);
                 });
 
                 // Step 10: Re-add project to solution, preserving solution folder location

src/CodingWithCalvin.ProjectRenamifier/Services/ProjectReferenceService.cs

@@ -2,6 +2,8 @@
 using System.IO;
 using System.Xml;
 using EnvDTE;
+using Microsoft.VisualStudio;
+using Microsoft.VisualStudio.Shell.Interop;
 
 namespace CodingWithCalvin.ProjectRenamifier.Services
 {
@@ -10,17 +12,26 @@ namespace CodingWithCalvin.ProjectRenamifier.Services
     /// </summary>
     internal static class ProjectReferenceService
     {
+        /// <summary>
+        /// Metadata for a project that references the target project being renamed.
+        /// </summary>
+        public sealed class ReferencingProjectInfo
+        {
+            public string FullPath { get; set; }
+            public string UniqueName { get; set; }
+        }
+
         /// <summary>
         /// Finds all projects in the solution that reference the specified project.
         /// </summary>
         /// <param name="solution">The solution to search.</param>
         /// <param name="targetProjectPath">The full path to the project being renamed.</param>
-        /// <returns>A list of project paths that reference the target project.</returns>
-        public static List<string> FindProjectsReferencingTarget(Solution solution, string targetProjectPath)
+        /// <returns>A list of referencing project descriptors (full path + unique name).</returns>
+        public static List<ReferencingProjectInfo> FindProjectsReferencingTarget(Solution solution, string targetProjectPath)
         {
             ThreadHelper.ThrowIfNotOnUIThread();
 
-            var referencingProjects = new List<string>();
+            var referencingProjects = new List<ReferencingProjectInfo>();
             var targetFileName = Path.GetFileName(targetProjectPath);
 
             foreach (Project project in solution.Projects)
@@ -34,7 +45,7 @@ public static List<string> FindProjectsReferencingTarget(Solution solution, stri
         /// <summary>
         /// Recursively searches a project (and solution folders) for references to the target.
         /// </summary>
-        private static void FindReferencesInProject(Project project, string targetProjectPath, string targetFileName, List<string> referencingProjects)
+        private static void FindReferencesInProject(Project project, string targetProjectPath, string targetFileName, List<ReferencingProjectInfo> referencingProjects)
         {
             ThreadHelper.ThrowIfNotOnUIThread();
 
@@ -67,7 +78,11 @@ private static void FindReferencesInProject(Project project, string targetProjec
             {
                 if (ProjectReferencesTarget(project.FullName, targetFileName))
                 {
-                    referencingProjects.Add(project.FullName);
+                    referencingProjects.Add(new ReferencingProjectInfo
+                    {
+                        FullPath = project.FullName,
+                        UniqueName = project.UniqueName,
+                    });
                 }
             }
         }
@@ -118,18 +133,77 @@ private static bool ProjectReferencesTarget(string projectFilePath, string targe
 
         /// <summary>
         /// Updates project references in all projects that referenced the old project path.
+        /// Each referencing project is temporarily unloaded via <see cref="IVsSolution4"/> so Visual Studio
+        /// releases its file handle before we rewrite the .csproj on disk, then reloaded afterwards.
         /// </summary>
-        /// <param name="referencingProjectPaths">Projects that need their references updated.</param>
+        /// <param name="vsSolution">The Visual Studio solution service used to unload and reload projects.</param>
+        /// <param name="referencingProjects">Projects that need their references updated.</param>
         /// <param name="oldProjectPath">The old path to the renamed project.</param>
         /// <param name="newProjectPath">The new path to the renamed project.</param>
-        public static void UpdateProjectReferences(List<string> referencingProjectPaths, string oldProjectPath, string newProjectPath)
+        public static void UpdateProjectReferences(IVsSolution vsSolution, List<ReferencingProjectInfo> referencingProjects, string oldProjectPath, string newProjectPath)
         {
+            ThreadHelper.ThrowIfNotOnUIThread();
+
             var oldFileName = Path.GetFileName(oldProjectPath);
+            var solution4 = vsSolution as IVsSolution4;
+
+            foreach (var info in referencingProjects)
+            {
+                UpdateSingleProjectReference(vsSolution, solution4, info, oldFileName, oldProjectPath, newProjectPath);
+            }
+        }
+
+        private static void UpdateSingleProjectReference(
+            IVsSolution vsSolution,
+            IVsSolution4 solution4,
+            ReferencingProjectInfo info,
+            string oldFileName,
+            string oldProjectPath,
+            string newProjectPath)
+        {
+            ThreadHelper.ThrowIfNotOnUIThread();
+
+            var projectGuid = System.Guid.Empty;
+            var unloaded = false;
+
+            if (solution4 != null && TryGetProjectGuid(vsSolution, info.UniqueName, out projectGuid))
+            {
+                var hr = solution4.UnloadProject(ref projectGuid, (uint)_VSProjectUnloadStatus.UNLOADSTATUS_UnloadedByUser);
+                unloaded = ErrorHandler.Succeeded(hr);
+            }
 
-            foreach (var projectPath in referencingProjectPaths)
+            try
             {
-                UpdateReferencesInProject(projectPath, oldFileName, oldProjectPath, newProjectPath);
+                UpdateReferencesInProject(info.FullPath, oldFileName, oldProjectPath, newProjectPath);
             }
+            finally
+            {
+                if (unloaded)
+                {
+                    solution4.ReloadProject(ref projectGuid);
+                }
+            }
+        }
+
+        private static bool TryGetProjectGuid(IVsSolution vsSolution, string uniqueName, out System.Guid projectGuid)
+        {
+            ThreadHelper.ThrowIfNotOnUIThread();
+
+            projectGuid = System.Guid.Empty;
+
+            if (string.IsNullOrEmpty(uniqueName))
+            {
+                return false;
+            }
+
+            var hr = vsSolution.GetProjectOfUniqueName(uniqueName, out var hierarchy);
+            if (!ErrorHandler.Succeeded(hr) || hierarchy == null)
+            {
+                return false;
+            }
+
+            hr = vsSolution.GetGuidOfProject(hierarchy, out projectGuid);
+            return ErrorHandler.Succeeded(hr) && projectGuid != System.Guid.Empty;
         }
 
         /// <summary>