Use class FileName for the ProjectItem.FileName property.

src/AddIns/BackendBindings/AspNet.Mvc/Test/Helpers/TestableProject.cs

@@ -55,13 +55,13 @@ namespace AspNet.Mvc.Tests.Helpers
 		public FileProjectItem AddFileToProject(string fileName)
 		{
 			var projectItem = new FileProjectItem(this, ItemType.Compile);
-			projectItem.FileName = fileName;
+			projectItem.FileName = FileName.Create(fileName);
 			ProjectService.AddProjectItem(this, projectItem);
 			return projectItem;
 		}
 		
-		public override string OutputAssemblyFullPath {
-			get { return outputAssemblyFullPath; }
+		public override FileName OutputAssemblyFullPath {
+			get { return FileName.Create(outputAssemblyFullPath); }
 		}
 		
 		public void SetOutputAssemblyFullPath(string path)

src/AddIns/BackendBindings/AspNet.Mvc/Test/Src/MvcProjectFileTests.cs

@@ -2,6 +2,7 @@
 // This code is distributed under the GNU LGPL (for details please see \doc\license.txt)
 
 using System;
+using ICSharpCode.Core;
 using AspNet.Mvc.Tests.Helpers;
 using ICSharpCode.AspNet.Mvc;
 using ICSharpCode.SharpDevelop.Project;
@@ -22,7 +23,7 @@ namespace AspNet.Mvc.Tests
 		MvcProjectFile CreateProjectFile(string fullPath)
 		{
 			var projectItem = new FileProjectItem(project, ItemType.Compile);
-			projectItem.FileName = fullPath;
+			projectItem.FileName = FileName.Create(fullPath);
 			file = new MvcProjectFile(projectItem);
 			return file;
 		}

src/AddIns/BackendBindings/CSharpBinding/Project/Src/Refactoring/SearchForIssuesCommand.cs

@@ -98,8 +98,8 @@ namespace CSharpBinding.Refactoring
 			if (project == null)
 				return Enumerable.Empty<FileName>();
 			return from item in project.GetItemsOfType(ItemType.Compile)
-				where item.FileName.EndsWith(".cs", StringComparison.OrdinalIgnoreCase)
-				select FileName.Create(item.FileName);
+				where item.FileName.HasExtension(".cs")
+				select item.FileName;
 		}
 		
 		Task SearchForIssuesAsync(List<FileName> fileNames, IEnumerable<IssueManager.IssueProvider> providers, Action<SearchedFile> callback, IProgressMonitor monitor)

src/AddIns/BackendBindings/CppBinding/CppBinding/Project/CppProject.cs

@@ -51,7 +51,7 @@ namespace ICSharpCode.CppBinding.Project
 //			get { return LanguageProperties.; }
 //		}
 
-		public override string OutputAssemblyFullPath
+		public override FileName OutputAssemblyFullPath
 		{
 			/// <summary>
 			/// For vcxprojs the output assembly location is stored in OutDir property.
@@ -61,19 +61,18 @@ namespace ICSharpCode.CppBinding.Project
 			{
 				string outputPath = GetEvaluatedProperty("OutDir") ?? "";
 				if (!Path.IsPathRooted(outputPath))
-					return FileUtility.NormalizePath(Path.Combine(ParentSolution.Directory, outputPath,
+					return FileName.Create(Path.Combine(ParentSolution.Directory, outputPath,
 					                                    AssemblyName + GetExtension(OutputType)));
 				else
 				{
 					// this will be valid if there is an explicit OutDir property in vcxproj file.
-					if ((GetUnevalatedProperty("OutDir") ?? "").StartsWith("$(SolutionDir)"))
-					{
+					if ((GetUnevalatedProperty("OutDir") ?? "").StartsWith("$(SolutionDir)", StringComparison.OrdinalIgnoreCase)) {
 						// in #D every project is compiled by msbuild separately, this mean that SolutionDir will
 						// be equal to ProjectDir, so it has to be replaced with actual solution directory
 						string evaluatedSolutionDir = GetEvaluatedProperty("SolutionDir") ?? "";
 						outputPath = Path.Combine(ParentSolution.Directory, outputPath.Substring(evaluatedSolutionDir.Length));
 					}
-					return FileUtility.NormalizePath(Path.Combine(outputPath, AssemblyName + GetExtension(OutputType)));
+					return FileName.Create(Path.Combine(outputPath, AssemblyName + GetExtension(OutputType)));
 				}
 			}
 		}

src/AddIns/BackendBindings/CppBinding/CppBinding/Project/ProjectConfigurationProjectItem.cs

@@ -8,6 +8,7 @@
  * Godzina: 18:52
  * 
  */
+using ICSharpCode.Core;
 using ICSharpCode.SharpDevelop.Project;
 
 namespace ICSharpCode.CppBinding.Project
@@ -26,11 +27,11 @@ namespace ICSharpCode.CppBinding.Project
 		/// Returns an empty string as a filename. 
 		/// Project configuration is specific to the whole project, not a specific item.
 		/// </summary>
-		public override string FileName
+		public override FileName FileName
 		{
 			get
 			{
-				return "";
+				return null;
 			}
 		}
 	}

src/AddIns/BackendBindings/WixBinding/Project/Src/Project/WixProject.cs

@@ -8,6 +8,7 @@ using System.ComponentModel;
 using System.Diagnostics;
 using System.IO;
 
+using ICSharpCode.Core;
 using ICSharpCode.SharpDevelop;
 using ICSharpCode.SharpDevelop.Dom;
 using ICSharpCode.SharpDevelop.Project;
@@ -77,13 +78,13 @@ namespace ICSharpCode.WixBinding
 		/// Gets the full path to the installer file that will be generated by
 		/// the Wix compiler and linker.
 		/// </summary>
-		public string GetInstallerFullPath()
+		public FileName GetInstallerFullPath()
 		{
 			string outputPath = GetEvaluatedPropertyOrEmptyString("OutputPath");
 			string outputType = GetEvaluatedPropertyOrEmptyString("OutputType");
 			string outputName = GetEvaluatedPropertyOrEmptyString("OutputName");
 			string fileName = String.Concat(outputName, GetInstallerExtension(outputType));
-			return Path.Combine(Directory, outputPath, fileName);
+			return Directory.CombineDirectory(outputPath).CombineFile(fileName);
 		}
 		
 		string GetEvaluatedPropertyOrEmptyString(string propertyName)
@@ -91,7 +92,7 @@ namespace ICSharpCode.WixBinding
 			return GetEvaluatedProperty(propertyName) ?? String.Empty;
 		}
 		
-		public override string OutputAssemblyFullPath {
+		public override FileName OutputAssemblyFullPath {
 			get { return GetInstallerFullPath(); }
 		}
 		
@@ -108,7 +109,7 @@ namespace ICSharpCode.WixBinding
 		public void AddWixLibrary(string fileName)
 		{
 			WixLibraryProjectItem projectItem = new WixLibraryProjectItem(this);
-			projectItem.FileName = fileName;
+			projectItem.FileName = FileName.Create(fileName);
 			ProjectService.AddProjectItem(this, projectItem);
 		}
 		
@@ -122,7 +123,7 @@ namespace ICSharpCode.WixBinding
 		public void AddWixExtension(string fileName)
 		{
 			WixExtensionProjectItem projectItem = new WixExtensionProjectItem(this);
-			projectItem.FileName = fileName;
+			projectItem.FileName = FileName.Create(fileName);
 			ProjectService.AddProjectItem(this, projectItem);
 		}
 		

src/AddIns/BackendBindings/WixBinding/Test/Project/WixInstallerPathTests.cs

@@ -27,7 +27,7 @@ namespace WixBinding.Tests.Project
 		{
 			WixProject project = WixBindingTestsHelper.CreateEmptyWixProject();
 			
-			Assert.AreEqual(@"C:\Projects\Test\bin\Debug\Test.msi", project.GetInstallerFullPath());
+			Assert.AreEqual(@"C:\Projects\Test\bin\Debug\Test.msi", project.GetInstallerFullPath().ToString());
 		}
 		
 		[Test]
@@ -36,7 +36,7 @@ namespace WixBinding.Tests.Project
 			WixProject project = WixBindingTestsHelper.CreateEmptyWixProject();
 			project.SetProperty("OutputName", "ChangedName");
 			
-			Assert.AreEqual(@"C:\Projects\Test\bin\Debug\ChangedName.msi", project.GetInstallerFullPath());
+			Assert.AreEqual(@"C:\Projects\Test\bin\Debug\ChangedName.msi", project.GetInstallerFullPath().ToString());
 		}
 	}
 }

src/AddIns/BackendBindings/XamlBinding/XamlBinding/XamlSymbolSearch.cs

@@ -38,7 +38,7 @@ namespace ICSharpCode.XamlBinding
 			this.entity = entity;
 			compilation = SD.ParserService.GetCompilation(project);
 			interestingFileNames = new List<FileName>();
-			foreach (var item in project.ParentSolution.Projects.SelectMany(p => p.Items).OfType<FileProjectItem>().Where(i => i.FileName.EndsWith(".xaml", StringComparison.OrdinalIgnoreCase)))
+			foreach (var item in project.ParentSolution.Projects.SelectMany(p => p.Items).OfType<FileProjectItem>().Where(i => i.FileName.HasExtension(".xaml")))
 				interestingFileNames.Add(new FileName(item.FileName));
 			workAmount = interestingFileNames.Count;
 			workAmountInverse = 1.0 / workAmount;

src/AddIns/Misc/PackageManagement/Project/Src/EnvDTE/Project.cs

@@ -175,7 +175,7 @@ namespace ICSharpCode.PackageManagement.EnvDTE
 		internal ProjectItem AddFileProjectItemWithDependentUsingFullPath(string path, string dependentUpon)
 		{
 			FileProjectItem fileProjectItem = CreateFileProjectItemUsingFullPath(path);
-			fileProjectItem.FileName = path;
+			fileProjectItem.FileName = ICSharpCode.Core.FileName.Create(path);
 			fileProjectItem.DependentUpon = dependentUpon;
 			AddProjectItemToMSBuildProject(fileProjectItem);
 			return new ProjectItem(this, fileProjectItem);
@@ -277,7 +277,7 @@ namespace ICSharpCode.PackageManagement.EnvDTE
 		FileProjectItem CreateMSBuildProjectItemForDirectory(string directory)
 		{
 			return new FileProjectItem(MSBuildProject, ItemType.Folder) {
-				FileName = directory
+				FileName = ICSharpCode.Core.FileName.Create(directory)
 			};
 		}
 		

src/AddIns/Misc/PackageManagement/Project/Src/EnvDTE/ProjectItem.cs

@@ -94,7 +94,7 @@ namespace ICSharpCode.PackageManagement.EnvDTE
 			} else if (name == CustomToolPropertyName) {
 				return projectItem.CustomTool;
 			} else if (name == FullPathPropertyName) {
-				return projectItem.FileName;
+				return projectItem.FileName.ToString();
 			}
 			return String.Empty;
 		}

src/AddIns/Misc/PackageManagement/Project/Src/SharpDevelopProjectSystem.cs

@@ -226,7 +226,7 @@ namespace ICSharpCode.PackageManagement
 		{
 			ItemType itemType = project.GetDefaultItemType(path);
 			var fileItem = new FileProjectItem(project, itemType);
-			fileItem.FileName = path;
+			fileItem.FileName = FileName.Create(path);
 			fileItem.CustomTool = projectService.GetDefaultCustomToolForFileName(fileItem);
 			return fileItem;
 		}

src/AddIns/Misc/PackageManagement/Test/Src/EnvDTE/ProjectItemPropertyTests.cs

@@ -139,7 +139,7 @@ namespace PackageManagement.Tests.EnvDTE
 		public void Value_GetFullPath_ReturnsProjectItemFullFileName()
 		{
 			CreateProjectItemProperties();
-			msbuildFileProjectItem.FileName = @"d:\projects\test.cs";
+			msbuildFileProjectItem.FileName = ICSharpCode.Core.FileName.Create(@"d:\projects\test.cs");
 			
 			string path = properties.Item("FullPath").Value as string;
 			

src/AddIns/Misc/PackageManagement/Test/Src/EnvDTE/ProjectItemsTests.cs

@@ -461,7 +461,7 @@ namespace PackageManagement.Tests.EnvDTE
 			var fileItem = msbuildProject.Items.First() as FileProjectItem;
 			
 			Assert.AreEqual(@"tools\test.cs", fileItem.Include);
-			Assert.AreEqual(@"d:\projects\myproject\tools\test.cs", fileItem.FileName);
+			Assert.AreEqual(@"d:\projects\myproject\tools\test.cs", fileItem.FileName.ToString());
 			Assert.AreEqual(ItemType.Page, fileItem.ItemType);
 			Assert.AreEqual(msbuildProject, fileItem.Project);
 		}
@@ -587,7 +587,7 @@ namespace PackageManagement.Tests.EnvDTE
 			
 			Assert.AreEqual(@"tools\a.txt", item.Include);
 			Assert.AreEqual(ItemType.None, item.ItemType);
-			Assert.AreEqual(@"d:\projects\myproject\tools\a.txt", item.FileName);
+			Assert.AreEqual(@"d:\projects\myproject\tools\a.txt", item.FileName.ToString());
 			Assert.AreEqual(1, msbuildProject.Items.Count);
 		}
 		
@@ -638,7 +638,7 @@ namespace PackageManagement.Tests.EnvDTE
 			
 			Assert.AreEqual(@"tools\packages", item.Include);
 			Assert.AreEqual(ItemType.Folder, item.ItemType);
-			Assert.AreEqual(@"d:\projects\myproject\tools\packages", item.FileName);
+			Assert.AreEqual(@"d:\projects\myproject\tools\packages", item.FileName.ToString());
 			Assert.AreEqual(1, msbuildProject.Items.Count);
 		}
 		
@@ -658,7 +658,7 @@ namespace PackageManagement.Tests.EnvDTE
 			
 			Assert.AreEqual(@"tools\packages\a.txt", item.Include);
 			Assert.AreEqual(ItemType.None, item.ItemType);
-			Assert.AreEqual(@"d:\projects\myproject\tools\packages\a.txt", item.FileName);
+			Assert.AreEqual(@"d:\projects\myproject\tools\packages\a.txt", item.FileName.ToString());
 			Assert.AreEqual(1, msbuildProject.Items.Count);
 		}
 		
@@ -809,7 +809,7 @@ namespace PackageManagement.Tests.EnvDTE
 			string linkName = fileItem.GetEvaluatedMetadata("Link");
 			
 			Assert.AreEqual(@"..\anotherproject\test.cs", fileItem.Include);
-			Assert.AreEqual(fileName, fileItem.FileName);
+			Assert.AreEqual(fileName, fileItem.FileName.ToString());
 			Assert.AreEqual(ItemType.Page, fileItem.ItemType);
 			Assert.IsTrue(fileItem.IsLink);
 			Assert.AreEqual("test.cs", linkName);
@@ -853,7 +853,7 @@ namespace PackageManagement.Tests.EnvDTE
 			FileProjectItem fileItem = msbuildProject.FindFile(new FileName(fileName));
 			
 			Assert.AreEqual("MainForm.Designer.cs", fileItem.Include);
-			Assert.AreEqual(fileName, fileItem.FileName);
+			Assert.AreEqual(fileName, fileItem.FileName.ToString());
 			Assert.AreEqual(ItemType.Page, fileItem.ItemType);
 			Assert.AreEqual(msbuildProject, fileItem.Project);
 			Assert.AreEqual("MainForm.cs", fileItem.DependentUpon);

src/AddIns/Misc/PackageManagement/Test/Src/EnvDTE/Reference3Tests.cs

@@ -124,7 +124,7 @@ namespace PackageManagement.Tests.EnvDTE
 		public void Path_SystemXmlReferenceInProjectReferences_ReturnsFullPathToSystemXml()
 		{
 			CreateReference("System.Xml");
-			referenceProjectItem.FileName = @"c:\Program Files\Microsoft\Reference Assemblies\v4\System.Xml.dll";
+			referenceProjectItem.FileName = FileName.Create(@"c:\Program Files\Microsoft\Reference Assemblies\v4\System.Xml.dll");
 			
 			string path = reference.Path;
 			

src/AddIns/Misc/PackageManagement/Test/Src/Helpers/ProjectHelper.cs

@@ -86,7 +86,7 @@ namespace PackageManagement.Tests.Helpers
 		public static void AddFile(MSBuildBasedProject project, string fileName)
 		{
 			var fileProjectItem = new FileProjectItem(project, ItemType.Compile);
-			fileProjectItem.FileName = fileName;
+			fileProjectItem.FileName = FileName.Create(fileName);
 			ProjectService.AddProjectItem(project, fileProjectItem);
 		}
 		

src/AddIns/Misc/PackageManagement/Test/Src/SharpDevelopProjectSystemTests.cs

@@ -476,7 +476,7 @@ namespace PackageManagement.Tests
 			FileProjectItem fileItem = ProjectHelper.GetFile(project, fileName);
 			
 			FileProjectItem expectedFileItem = new FileProjectItem(project, ItemType.Compile);
-			expectedFileItem.FileName = fileName;
+			expectedFileItem.FileName = FileName.Create(fileName);
 			
 			FileProjectItemAssert.AreEqual(expectedFileItem, fileItem);
 		}
@@ -493,7 +493,7 @@ namespace PackageManagement.Tests
 			FileProjectItem fileItem = ProjectHelper.GetFile(project, fileName);
 			
 			FileProjectItem expectedFileItem = new FileProjectItem(project, ItemType.EmbeddedResource);
-			expectedFileItem.FileName = fileName;
+			expectedFileItem.FileName = FileName.Create(fileName);
 			
 			FileProjectItemAssert.AreEqual(expectedFileItem, fileItem);
 		}
@@ -511,7 +511,7 @@ namespace PackageManagement.Tests
 			FileProjectItem fileItem = ProjectHelper.GetFile(project, fileName);
 			
 			FileProjectItem expectedFileItem = new FileProjectItem(project, ItemType.Compile);
-			expectedFileItem.FileName = fileName;
+			expectedFileItem.FileName = FileName.Create(fileName);
 			
 			FileProjectItemAssert.AreEqual(expectedFileItem, fileItem);
 		}
@@ -529,7 +529,7 @@ namespace PackageManagement.Tests
 			FileProjectItem fileItem = ProjectHelper.GetFile(project, fileName);
 			
 			FileProjectItem expectedFileItem = new FileProjectItem(project, ItemType.Compile);
-			expectedFileItem.FileName = fileName;
+			expectedFileItem.FileName = FileName.Create(fileName);
 			
 			FileProjectItemAssert.AreEqual(expectedFileItem, fileItem);
 		}

src/AddIns/Misc/TextTemplating/Test/Helpers/TestableFileProjectItem.cs

@@ -2,13 +2,14 @@
 // This code is distributed under the GNU LGPL (for details please see \doc\license.txt)
 
 using System;
+using ICSharpCode.Core;
 using ICSharpCode.SharpDevelop.Project;
 
 namespace TextTemplating.Tests.Helpers
 {
 	public class TestableFileProjectItem : FileProjectItem
 	{
-		string fileName;
+		FileName fileName;
 		
 		public TestableProject TestableProject;
 		
@@ -21,10 +22,10 @@ namespace TextTemplating.Tests.Helpers
 			: base(project, ItemType.None)
 		{
 			this.TestableProject = project;
-			this.fileName = fileName;
+			this.fileName = FileName.Create(fileName);
 		}
 		
-		public override string FileName {
+		public override FileName FileName {
 			get { return fileName; }
 			set { fileName = value; }
 		}

src/AddIns/Misc/TextTemplating/Test/Src/TextTemplatingAssemblyPathResolverTests.cs

@@ -108,7 +108,7 @@ namespace TextTemplating.Tests
 			CreateResolver();
 			ReferenceProjectItem reference = AddReferenceToProject("Test");
 			string expectedFileName = @"d:\projects\MyProject\lib\Test.dll";
-			reference.FileName = expectedFileName;
+			reference.FileName = FileName.Create(expectedFileName);
 			
 			string result = resolver.ResolvePath("Test");
 			

src/Main/Base/Project/Src/Gui/Dialogs/ReferenceDialog/ServiceReference/ProjectWithServiceReferences.cs

@@ -7,6 +7,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 
+using ICSharpCode.Core;
 using ICSharpCode.SharpDevelop.Project;
 
 namespace ICSharpCode.SharpDevelop.Gui.Dialogs.ReferenceDialog.ServiceReference
@@ -70,7 +71,7 @@ namespace ICSharpCode.SharpDevelop.Gui.Dialogs.ReferenceDialog.ServiceReference
 		void AddServiceReferenceFileToProject(ServiceReferenceFileName fileName)
 		{
 			var projectItem = new FileProjectItem(project, ItemType.Compile);
-			projectItem.FileName = fileName.Path;
+			projectItem.FileName = FileName.Create(fileName.Path);
 			projectItem.DependentUpon = "Reference.svcmap";
 			AddProjectItemToProject(projectItem);
 		}
@@ -169,16 +170,14 @@ namespace ICSharpCode.SharpDevelop.Gui.Dialogs.ReferenceDialog.ServiceReference
 			AddProjectItemToProject(item);
 		}
 		
-		string GetDefaultAppConfigFileName()
+		FileName GetDefaultAppConfigFileName()
 		{
-			return Path.Combine(project.Directory, "app.config");
+			return project.Directory.CombineFile("app.config");
 		}
 		
 		public IEnumerable<ReferenceProjectItem> GetReferences()
 		{
-			foreach (ReferenceProjectItem item in project.GetItemsOfType(ItemType.Reference)) {
-				yield return item;
-			}
+			return project.GetItemsOfType(ItemType.Reference).OfType<ReferenceProjectItem>();
 		}
 	}
 }

src/Main/Base/Project/Src/Gui/Dialogs/ReferenceDialog/ServiceReference/ServiceReferenceMapFileProjectItem.cs

@@ -3,6 +3,7 @@
 
 using System;
 using ICSharpCode.SharpDevelop.Project;
+using ICSharpCode.Core;
 
 namespace ICSharpCode.SharpDevelop.Gui.Dialogs.ReferenceDialog.ServiceReference
 {
@@ -13,7 +14,7 @@ namespace ICSharpCode.SharpDevelop.Gui.Dialogs.ReferenceDialog.ServiceReference
 			string fileName)
 			: base(project, ItemType.None)
 		{
-			this.FileName = fileName;
+			this.FileName = FileName.Create(fileName);
 			AddMetadata();
 		}
 		

src/Main/Base/Project/Src/Gui/Pads/ProjectBrowser/Commands/FolderNodeCommands.cs

@@ -81,7 +81,7 @@ namespace ICSharpCode.SharpDevelop.Project.Commands
 								LoggingService.Debug("Found file " + virtualFullName);
 								FileProjectItem newItem = new FileProjectItem(node.Project, fileItem.ItemType);
 								if (FileUtility.IsBaseDirectory(directoryName, fileItem.FileName)) {
-									newItem.FileName = FileUtility.RenameBaseDirectory(fileItem.FileName, directoryName, copiedFileName);
+									newItem.FileName = FileName.Create(FileUtility.RenameBaseDirectory(fileItem.FileName, directoryName, copiedFileName));
 								} else {
 									newItem.FileName = fileItem.FileName;
 								}

src/Main/Base/Project/Src/Project/AbstractProject.cs

@@ -357,7 +357,7 @@ namespace ICSharpCode.SharpDevelop.Project
 		/// Returns null when the project does not output any assembly.
 		/// </summary>
 		[Browsable(false)]
-		public virtual string OutputAssemblyFullPath {
+		public virtual FileName OutputAssemblyFullPath {
 			get {
 				return null;
 			}
@@ -528,7 +528,7 @@ namespace ICSharpCode.SharpDevelop.Project
 				}
 			}
 			if (!mscorlib) {
-				referenceItems.Add(new ReferenceProjectItem(this, "mscorlib") { FileName = typeof(object).Module.FullyQualifiedName });
+				referenceItems.Add(new ReferenceProjectItem(this, "mscorlib") { FileName = FileName.Create(typeof(object).Module.FullyQualifiedName) });
 			}
 			return referenceItems;
 		}

src/Main/Base/Project/Src/Project/CompilableProject.cs

@@ -111,7 +111,7 @@ namespace ICSharpCode.SharpDevelop.Project
 		/// Gets the path where temporary files are written to during compilation.
 		/// </summary>
 		[Browsable(false)]
-		public string IntermediateOutputFullPath {
+		public DirectoryName IntermediateOutputFullPath {
 			get {
 				string outputPath = GetEvaluatedProperty("IntermediateOutputPath");
 				if (string.IsNullOrEmpty(outputPath)) {
@@ -121,7 +121,7 @@ namespace ICSharpCode.SharpDevelop.Project
 					}
 					outputPath = Path.Combine(outputPath, this.ActiveConfiguration.Configuration);
 				}
-				return Path.Combine(Directory, outputPath);
+				return Directory.CombineDirectory(outputPath);
 			}
 		}
 		
@@ -170,22 +170,22 @@ namespace ICSharpCode.SharpDevelop.Project
 		/// <summary>
 		/// The full path of the assembly generated by the project.
 		/// </summary>
-		public override string OutputAssemblyFullPath {
+		public override FileName OutputAssemblyFullPath {
 			get {
 				string outputPath = GetEvaluatedProperty("OutputPath") ?? "";
-				return FileUtility.NormalizePath(Path.Combine(Path.Combine(Directory, outputPath), AssemblyName + GetExtension(OutputType)));
+				return Directory.CombineDirectory(outputPath).CombineFile(AssemblyName + GetExtension(OutputType));
 			}
 		}
 		
 		/// <summary>
 		/// The full path of the folder where the project's primary output files go.
 		/// </summary>
-		public string OutputFullPath {
+		public DirectoryName OutputFullPath {
 			get {
 				string outputPath = GetEvaluatedProperty("OutputPath");
-				// FileUtility.NormalizePath() cleans up any back references.
+				// CombineDirectory() cleans up any back references.
 				// e.g. C:\windows\system32\..\system becomes C:\windows\system
-				return FileUtility.NormalizePath(Path.Combine(Directory, outputPath));
+				return Directory.CombineDirectory(outputPath);
 			}
 		}
 		

src/Main/Base/Project/Src/Project/CustomTool.cs

@@ -173,7 +173,7 @@ namespace ICSharpCode.SharpDevelop.Project
 			FileProjectItem outputItem = project.FindFile(FileName.Create(outputFileName));
 			if (outputItem == null) {
 				outputItem = new FileProjectItem(project, ItemType.Compile);
-				outputItem.FileName = outputFileName;
+				outputItem.FileName = FileName.Create(outputFileName);
 				outputItem.DependentUpon = Path.GetFileName(baseItem.FileName);
 				outputItem.SetEvaluatedMetadata("AutoGen", "True");
 				ProjectService.AddProjectItem(project, outputItem);

src/Main/Base/Project/Src/Project/IProject.cs

@@ -124,7 +124,7 @@ namespace ICSharpCode.SharpDevelop.Project
 		/// Gets the full path of the output assembly.
 		/// Returns null when the project does not output any assembly.
 		/// </summary>
-		string OutputAssemblyFullPath {
+		FileName OutputAssemblyFullPath {
 			get;
 		}
 		

src/Main/Base/Project/Src/Project/Items/ComReferenceProjectItem.cs

@@ -4,6 +4,7 @@
 using System;
 using System.ComponentModel;
 using System.IO;
+using ICSharpCode.Core;
 
 namespace ICSharpCode.SharpDevelop.Project
 {
@@ -93,12 +94,12 @@ namespace ICSharpCode.SharpDevelop.Project
 		/// <summary>
 		/// Gets the file name of the COM interop assembly.
 		/// </summary>
-		public override string FileName {
+		public override FileName FileName {
 			get {
 				try {
 					if (Project != null && Project.OutputAssemblyFullPath != null) {
-						string outputFolder = Path.GetDirectoryName(Project.OutputAssemblyFullPath);
-						string interopFileName = Path.Combine(outputFolder, String.Concat("Interop.", Include, ".dll"));
+						DirectoryName outputFolder = Project.OutputAssemblyFullPath.GetParentDirectory();
+						FileName interopFileName = outputFolder.CombineFile("Interop." + Include + ".dll");
 						if (File.Exists(interopFileName)) {
 							return interopFileName;
 						}
@@ -111,7 +112,7 @@ namespace ICSharpCode.SharpDevelop.Project
 						// look in obj\Debug:
 						if (Project is CompilableProject) {
 							outputFolder = (Project as CompilableProject).IntermediateOutputFullPath;
-							interopFileName = Path.Combine(outputFolder, String.Concat("Interop.", Include, ".dll"));
+							interopFileName = outputFolder.CombineFile("Interop." + Include + ".dll");
 							if (File.Exists(interopFileName)) {
 								return interopFileName;
 							}
@@ -124,16 +125,16 @@ namespace ICSharpCode.SharpDevelop.Project
 					}
 				}
 				catch (Exception) { }
-				return Include;
+				return FileName.Create(Include);
 			}
 			set {
 			}
 		}
 		
-		static string GetActiveXInteropFileName(string outputFolder, string include)
+		static FileName GetActiveXInteropFileName(DirectoryName outputFolder, string include)
 		{
-			if (include.ToLowerInvariant().StartsWith("ax")) {
-				return Path.Combine(outputFolder, String.Concat("AxInterop.", include.Substring(2), ".dll"));
+			if (include.StartsWith("ax", StringComparison.OrdinalIgnoreCase)) {
+				return outputFolder.CombineFile(String.Concat("AxInterop.", include.Substring(2), ".dll"));
 			}
 			return null;
 		}

src/Main/Base/Project/Src/Project/Items/FileProjectItem.cs

@@ -62,7 +62,7 @@ namespace ICSharpCode.SharpDevelop.Project
 		                   Description = "${res:ICSharpCode.SharpDevelop.Internal.Project.ProjectFile.FileName.Description}")]
 		[Browsable(true)]
 		[ReadOnly(true)]
-		public override string FileName {
+		public override FileName FileName {
 			get { return base.FileName; }
 			set { base.FileName = value; }
 		}

src/Main/Base/Project/Src/Project/Items/ProjectItem.cs

@@ -23,7 +23,7 @@ namespace ICSharpCode.SharpDevelop.Project
 	public abstract class ProjectItem : LocalizedObject, IDisposable, ICloneable
 	{
 		IProject project;
-		volatile string fileNameCache;
+		volatile FileName fileNameCache;
 		bool treatIncludeAsLiteral;
 		
 		// either use: (bound mode)
@@ -414,15 +414,15 @@ namespace ICSharpCode.SharpDevelop.Project
 		/// and the setter throws a NotSupportedException.
 		/// </summary>
 		[Browsable(false)]
-		public virtual string FileName {
+		public virtual FileName FileName {
 			get {
 				if (project == null) {
-					return this.Include;
+					return FileName.Create(this.Include);
 				}
-				string fileName = this.fileNameCache;
+				FileName fileName = this.fileNameCache;
 				if (fileName == null) {
 					lock (SyncRoot) {
-						fileName = FileUtility.NormalizePath(Path.Combine(project.Directory, this.Include));
+						fileName = project.Directory.CombineFile(this.Include);
 						fileNameCache = fileName;
 					}
 				}

src/Main/Base/Project/Src/Project/Items/ReferenceProjectItem.cs

@@ -169,36 +169,38 @@ namespace ICSharpCode.SharpDevelop.Project
 			set { redist = value; }
 		}
 		
-		string fullPath;
+		FileName fullPath;
 		
 		[ReadOnly(true)]
 		[Browsable(true)]
-		public override string FileName {
+		public override FileName FileName {
 			get {
 				if (fullPath != null) {
 					return fullPath;
 				}
 				
 				if (Project != null) {
-					string projectDir = Project.Directory;
+					DirectoryName projectDir = Project.Directory;
 					string hintPath = HintPath;
 					try {
 						if (hintPath != null && hintPath.Length > 0) {
-							return FileUtility.NormalizePath(Path.Combine(projectDir, hintPath));
+							return projectDir.CombineFile(hintPath);
 						}
-						string name = FileUtility.NormalizePath(Path.Combine(projectDir, Include));
+						FileName name = projectDir.CombineFile(Include);
 						if (File.Exists(name)) {
 							return name;
 						}
-						if (File.Exists(name + ".dll")) {
-							return name + ".dll";
+						name = projectDir.CombineFile(Include + ".dll");
+						if (File.Exists(name)) {
+							return name;
 						}
-						if (File.Exists(name + ".exe")) {
-							return name + ".exe";
+						name = projectDir.CombineFile(Include + ".exe");
+						if (File.Exists(name)) {
+							return name;
 						}
 					} catch {} // ignore errors when path is invalid
 				}
-				return Include;
+				return FileName.Create(Include);
 			}
 			set {
 				fullPath = value;

src/Main/Base/Project/Src/Project/WebReferenceUrl.cs

@@ -100,10 +100,10 @@ namespace ICSharpCode.SharpDevelop.Project
 			}
 		}
 		
-		public override string FileName {
+		public override FileName FileName {
 			get {
 				if (Project != null && RelPath != null) {
-					return Path.Combine(Project.Directory, RelPath.Trim('\\'));
+					return FileName.Create(Path.Combine(Project.Directory, RelPath.Trim('\\')));
 				}
 				return null;
 			}

src/Main/Base/Test/ServiceReferences/ServiceReferenceGeneratorTests.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.ServiceModel.Description;
+using ICSharpCode.Core;
 using ICSharpCode.SharpDevelop.Gui.Dialogs.ReferenceDialog.ServiceReference;
 using ICSharpCode.SharpDevelop.Project;
 using NUnit.Framework;
@@ -130,7 +131,7 @@ namespace ICSharpCode.SharpDevelop.Tests.ServiceReferences
 			IProject dummyProject = MockRepository.GenerateStub<IProject>();
 			dummyProject.Stub(p => p.SyncRoot).Return(new object());
 			var projectItem = new ReferenceProjectItem(dummyProject, reference);
-			projectItem.FileName = fileName;
+			projectItem.FileName = FileName.Create(fileName);
 			projectReferences.Add(projectItem);
 			return projectItem;
 		}

src/Main/Core/Project/Src/Services/FileUtility/DirectoryName.cs

@@ -64,6 +64,26 @@ namespace ICSharpCode.Core
 			return FileName.Create(Path.Combine(normalizedPath, relativePath));
 		}
 		
+		/// <summary>
+		/// Combines this directory name with a relative path.
+		/// </summary>
+		public FileName CombineFile(string relativeFileName)
+		{
+			if (relativeFileName == null)
+				return null;
+			return FileName.Create(Path.Combine(normalizedPath, relativeFileName));
+		}
+		
+		/// <summary>
+		/// Combines this directory name with a relative path.
+		/// </summary>
+		public DirectoryName CombineDirectory(string relativeDirectoryName)
+		{
+			if (relativeDirectoryName == null)
+				return null;
+			return DirectoryName.Create(Path.Combine(normalizedPath, relativeDirectoryName));
+		}
+		
 		/// <summary>
 		/// Converts the specified absolute path into a relative path (relative to <c>this</c>).
 		/// </summary>

src/Main/SharpDevelop/Project/Build/MSBuildEngine/MSBuildEngine.cs

@@ -172,7 +172,7 @@ namespace ICSharpCode.SharpDevelop.Project
 				//LoggingService.Debug("Got information about " + assembly.OriginalInclude + "; fullpath=" + assembly.FullPath);
 				foreach (var referenceItem in assembly.ReferenceItems) {
 					referenceItem.AssemblyName = assembly.AssemblyName;
-					referenceItem.FileName = assembly.FullPath;
+					referenceItem.FileName = FileName.Create(assembly.FullPath);
 					referenceItem.Redist = assembly.Redist;
 					referenceItem.DefaultCopyLocalValue = assembly.CopyLocal;
 					handledReferenceItems.Add(referenceItem);
@@ -181,7 +181,7 @@ namespace ICSharpCode.SharpDevelop.Project
 				if (firstItem != null) {
 					resolvedAssemblies.Add(firstItem);
 				} else {
-					resolvedAssemblies.Add(new ReferenceProjectItem(baseProject, assembly.OriginalInclude) { FileName = assembly.FullPath });
+					resolvedAssemblies.Add(new ReferenceProjectItem(baseProject, assembly.OriginalInclude) { FileName = FileName.Create(assembly.FullPath) });
 				}
 			}
 			// Add any assemblies that weren't resolved yet. This is important - for example, this adds back project references.

src/Main/SharpDevelop/Project/Solution.cs

@@ -355,7 +355,7 @@ namespace ICSharpCode.SharpDevelop.Project
 					foreach (ProjectItem item in project.Items) {
 						if (FileUtility.IsBaseDirectory(oldName, item.FileName)) {
 							SD.GetRequiredService<IProjectServiceRaiseEvents>().RaiseProjectItemRemoved(new ProjectItemEventArgs(project, item));
-							item.FileName = FileUtility.RenameBaseDirectory(item.FileName, oldName, newName);
+							item.FileName = FileName.Create(FileUtility.RenameBaseDirectory(item.FileName, oldName, newName));
 							SD.GetRequiredService<IProjectServiceRaiseEvents>().RaiseProjectItemAdded(new ProjectItemEventArgs(project, item));
 						}
 					}