Function to remove Compile elems missing files

As well as keeping project files in sync, I also need to be able to remove compile nodes from a project, where the Include attribute points to a file that is missing.  This is useful when I have two projects including the same files, and I delete a bunch of them from the 'master' project I happen to be working on.

This PR adds two functions.  RemoveCompileNodesWithMissingFiles is intended for build script use and removeCompileNodesWithMissingFiles exists for testing purposes, because unlike the former, it does not write to the file system.  I noticed this convention elsewhere in FAKE, but I'm not sure if it is considered idiomatic.  Let me know.

src/app/FakeLib/MSBuild/ProjectSystem.fs

@@ -2,6 +2,7 @@
 module Fake.MSBuild.ProjectSystem
 
 open Fake
+open System
 open System.Collections.Generic
 open System.Xml
 open System.Xml.Linq
@@ -159,4 +160,24 @@ let CompareProjectsTo templateProject projects =
         |> toLines
 
     if isNotNullOrEmpty errors then
-        failwith errors
+        failwith errors
+
+let removeCompileNodesWithMissingFiles includeExistsF (project:ProjectFile) =
+    let projectDir = IO.Path.GetDirectoryName(project.ProjectFileName)
+    let missingFiles =
+        seq { for filePath in project.Files do
+                // We have to normalize the path, because csproj can have win style directory separator char on Mono too
+                // Xbuild handles them, so we do too http://www.mono-project.com/archived/porting_msbuild_projects_to_xbuild/#paths 
+                let includePath = Globbing.normalizePath (IO.Path.Combine([|projectDir; filePath|]))
+                if not (includeExistsF(includePath)) then yield filePath }
+    missingFiles
+    |> Seq.fold (fun (project:ProjectFile) file -> project.RemoveFile(file)) project
+
+/// Removes projects Compile nodes that have Include attributes pointing to files missing from the file system.  Saves updated projects.
+let RemoveCompileNodesWithMissingFiles project =
+    let newProject = removeCompileNodesWithMissingFiles System.IO.File.Exists (ProjectFile.FromFile project)
+    newProject.Save()
+
+
+
+

src/test/Test.FAKECore/ProjectSystemSpecs.cs

@@ -1,4 +1,7 @@
-using Fake.MSBuild;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using Fake.MSBuild;
 using Machine.Specifications;
 
 namespace Test.FAKECore
@@ -76,4 +79,29 @@ public class when_removing_duplicate_files
             _project.FindDuplicateFiles().ShouldContain("Git\\CommitMessage.fs");
 
     }
+
+    public class when_removing_compile_nodes_with_missing_files
+    {
+        const string ProjectFilePath = @"ProjectTestFiles/CSharpApp.csproj";
+        private static ProjectSystem.ProjectFile _project;
+
+        private Because of = () =>
+        {
+            Func<string, bool> fileExists = s =>
+            {
+                // We have to use Path.Combine here to work x-plat.
+                var pathsToRemove = new List<string>() {Path.Combine("ProjectTestFiles", "Class1.cs"), Path.Combine("ProjectTestFiles", "Folder", "FolderFile2.cs")};
+                return !pathsToRemove.Exists(pathToRemove => s.Equals(pathToRemove, StringComparison.InvariantCulture));
+            };
+            var projectFile = ProjectSystem.ProjectFile.FromFile(ProjectFilePath);
+            _project = ProjectSystem.removeCompileNodesWithMissingFiles(fileExists.Convert(), projectFile);
+        };
+
+        It should_delete_missing_files_in_csharpapp = () =>
+        {
+            _project.Files.ShouldNotContain(new []{"Class1.cs", @"Folder\FolderFile2.cs"});
+            // We DON'T have to use Path.Combine here, because the CsProj paths are same on both plats for our test proj.
+            _project.Files.ShouldContain(new [] {@"Folder\FolderFile1.cs", @"Program.cs", @"Properties\AssemblyInfo.cs"});
+        };
+    }
 }

src/test/Test.FAKECore/ProjectTestFiles/CSharpApp.csproj

@@ -0,0 +1,62 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+  <PropertyGroup>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <ProjectGuid>{5C1A3730-057D-4C82-AF8B-32135611CB4B}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+    <AppDesignerFolder>Properties</AppDesignerFolder>
+    <RootNamespace>ConsoleApplication2</RootNamespace>
+    <AssemblyName>ConsoleApplication2</AssemblyName>
+    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <FileAlignment>512</FileAlignment>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+    <PlatformTarget>AnyCPU</PlatformTarget>
+    <DebugSymbols>true</DebugSymbols>
+    <DebugType>full</DebugType>
+    <Optimize>false</Optimize>
+    <OutputPath>bin\Debug\</OutputPath>
+    <DefineConstants>DEBUG;TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+    <PlatformTarget>AnyCPU</PlatformTarget>
+    <DebugType>pdbonly</DebugType>
+    <Optimize>true</Optimize>
+    <OutputPath>bin\Release\</OutputPath>
+    <DefineConstants>TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <ItemGroup>
+    <Reference Include="System" />
+    <Reference Include="System.Core" />
+    <Reference Include="System.Xml.Linq" />
+    <Reference Include="System.Data.DataSetExtensions" />
+    <Reference Include="Microsoft.CSharp" />
+    <Reference Include="System.Data" />
+    <Reference Include="System.Net.Http" />
+    <Reference Include="System.Xml" />
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="Class1.cs" />
+    <Compile Include="Folder\FolderFile1.cs" />
+    <Compile Include="Folder\FolderFile2.cs" />
+    <Compile Include="Program.cs" />
+    <Compile Include="Properties\AssemblyInfo.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="App.config" />
+  </ItemGroup>
+  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
+       Other similar extension points exist, see Microsoft.Common.targets.
+  <Target Name="BeforeBuild">
+  </Target>
+  <Target Name="AfterBuild">
+  </Target>
+  -->
+</Project>

src/test/Test.FAKECore/Test.FAKECore.csproj

@@ -203,6 +203,9 @@
     <Content Include="NAVFiles\Table_4.txt">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </Content>
+    <None Include="ProjectTestFiles\CSharpApp.csproj">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
     <Content Include="SideBySideSpecification\Project1.txt">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </Content>