[Core] Avoid showing duplicated files in project tree

There are some cases where, it seems, we don't evaluate conditions as we should,
resulting in duplicated items being added to the project and, thus, also shown
in the project tree (see dotnet/aspnetcore#17088).

Also, by just adding a <None Include="*"/>, duplicated files show also.

So, due to this limitation on the project system, work around it on the project
tree, by checking for duplicates based on the files' paths.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1005277

Author: Rodrigo Moya

main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.Gui.Pads.ProjectPad/FolderNodeBuilder.cs

@@ -81,6 +81,7 @@ void GetFolderContent (Project project, string folder, out List<ProjectFile> fil
 		{
 			string folderPrefix = folder + Path.DirectorySeparatorChar;
 
+			var visitedFiles = new HashSet<FilePath> ();
 			files = new List<ProjectFile> ();
 			folders = new List<string> ();
 
@@ -100,7 +101,8 @@ void GetFolderContent (Project project, string folder, out List<ProjectFile> fil
 						? project.BaseDirectory.Combine (file.ProjectVirtualPath).ParentDirectory
 						: file.FilePath.ParentDirectory;
 
-					if (dir == folder) {
+					if (dir == folder && !visitedFiles.Contains (file.FilePath)) {
+						visitedFiles.Add (file.FilePath);
 						files.Add (file);
 						continue;
 					}

main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.Projects.FileNesting/FileNestingService.cs

@@ -31,6 +31,7 @@
 using System.Linq;
 using System.Runtime.CompilerServices;
 using Mono.Addins;
+using MonoDevelop.Core;
 using MonoDevelop.Projects;
 
 namespace MonoDevelop.Ide.Projects.FileNesting
@@ -166,7 +167,7 @@ public ProjectFileNestingInfo (ProjectFile projectFile)
 			}
 		}
 
-		readonly ConcurrentDictionary<ProjectFile, ProjectFileNestingInfo> projectFiles = new ConcurrentDictionary<ProjectFile, ProjectFileNestingInfo> ();
+		readonly ConcurrentDictionary<FilePath, ProjectFileNestingInfo> projectFiles = new ConcurrentDictionary<FilePath, ProjectFileNestingInfo> ();
 		bool fileNestingEnabled;
 
 		public Project Project { get; }
@@ -195,10 +196,10 @@ void EnsureInitialized ()
 
 		ProjectFileNestingInfo AddFile (ProjectFile projectFile)
 		{
-			var tmp = projectFiles.GetOrAdd (projectFile, new ProjectFileNestingInfo (projectFile));
+			var tmp = projectFiles.GetOrAdd (projectFile.FilePath, new ProjectFileNestingInfo (projectFile));
 			tmp.Parent = FileNestingService.InternalGetParentFile (projectFile);
 			if (tmp.Parent != null) {
-				var parent = projectFiles.GetOrAdd (tmp.Parent, new ProjectFileNestingInfo (tmp.Parent));
+				var parent = projectFiles.GetOrAdd (tmp.Parent.FilePath, new ProjectFileNestingInfo (tmp.Parent));
 				if (parent.Children == null) {
 					parent.Children = new ProjectFileCollection ();
 				}
@@ -207,19 +208,19 @@ ProjectFileNestingInfo AddFile (ProjectFile projectFile)
 				}
 			}
 
-			projectFiles [projectFile] = tmp;
+			projectFiles [projectFile.FilePath] = tmp;
 			return tmp;
 		}
 
 		ProjectFileNestingInfo RemoveFile (ProjectFile projectFile, List<ProjectFile> originalFilesToRemove = null)
 		{
 			bool actuallyRemoveFiles = originalFilesToRemove == null;
 
-			projectFiles.TryRemove (projectFile, out var nestingInfo);
+			projectFiles.TryRemove (projectFile.FilePath, out var nestingInfo);
 
 			// Update parent
 			if (nestingInfo?.Parent != null) {
-				if (projectFiles.TryGetValue (nestingInfo.Parent, out var tmp)) {
+				if (projectFiles.TryGetValue (nestingInfo.Parent.FilePath, out var tmp)) {
 					tmp.Children.Remove (projectFile);
 				}
 			}
@@ -296,7 +297,7 @@ public ProjectFile GetParentForFile (ProjectFile inputFile)
 			if (!fileNestingEnabled)
 				return null;
 
-			return projectFiles.TryGetValue (inputFile, out var nestingInfo) ? nestingInfo.Parent : null;
+			return projectFiles.TryGetValue (inputFile.FilePath, out var nestingInfo) ? nestingInfo.Parent : null;
 		}
 
 		public ProjectFileCollection GetChildrenForFile (ProjectFile inputFile)
@@ -305,7 +306,7 @@ public ProjectFileCollection GetChildrenForFile (ProjectFile inputFile)
 			if (!fileNestingEnabled)
 				return null;
 
-			return projectFiles.TryGetValue (inputFile, out var nestingInfo) ? nestingInfo.Children : null;
+			return projectFiles.TryGetValue (inputFile.FilePath, out var nestingInfo) ? nestingInfo.Children : null;
 		}
 
 		public void Dispose ()