Added helper to support plain robocopy and mirroring.

src/app/FakeLib/FakeLib.fsproj

@@ -98,7 +98,7 @@
     <Compile Include="DynamicsNavHelper.fs" />
     <Compile Include="DynamicsNavFile.fs" />
     <Compile Include="SCPHelper.fs" />
-    <Compile Include="XCopyHelper.fs" />
+    <Compile Include="RoboCopyHelper.fs" />
     <Compile Include="XpkgHelper.fs" />
     <Compile Include="VersionHelper.fs" />
     <Compile Include="MSBuild\ProjectSystem.fs" />
@@ -163,6 +163,7 @@
     <None Include="app.config" />
     <Compile Include="RaygunHelper.fs" />
     <Compile Include="SquirrelHelper.fs" />
+    <Compile Include="XCopyHelper.fs" />
   </ItemGroup>
   <ItemGroup>
     <Reference Include="ICSharpCode.SharpZipLib">

src/app/FakeLib/RoboCopyHelper.fs

@@ -0,0 +1,54 @@
+/// Contains a task to use [robocopy](https://en.wikipedia.org/wiki/Robocopy) on Windows.
+module Fake.RoboCopyHelper
+
+type RoboCopyOptions = { Mirror: bool }
+
+/// Executes a RoboCopy command with options
+/// ## Parameters
+///  - `source` - The source directory
+///  - `destination` - The target directory
+///  - `options` - The options to pass to robocopy
+let private roboCopyWithOptions (source:string) (destination:string) (options:RoboCopyOptions) =
+    let args =
+          "/D /c robocopy " +
+            (source.TrimEnd('\\') |> FullName |> toParam) +
+            (destination.TrimEnd('\\') |> FullName |> toParam) +
+            if options.Mirror then " /MIR /IT"
+            else " /IT"
+
+    let exitcode = ExecProcess (fun info ->
+       info.FileName <- "CMD.exe"
+       info.Arguments <- args) System.TimeSpan.MaxValue
+
+    // Exit codes from https://support.microsoft.com/en-us/kb/954404
+    let exitCodeWithMessage = 
+        match exitcode with
+        | 0 -> (exitcode, "No files were copied. No failure was encountered. No files were mismatched. The files already exist in the destination directory; therefore, the copy operation was skipped.")
+        | 1 -> (exitcode, "All files were copied successfully.")
+        | 2 -> (exitcode, "There are some additional files in the destination directory that are not present in the source directory. No files were copied.")
+        | 3 -> (exitcode, "Some files were copied. Additional files were present. No failure was encountered.")
+        | 4 -> (exitcode, "Some Mismatched files or directories were detected. Examine the output log. Housekeeping might be required.")
+        | 5 -> (exitcode, "Some files were copied. Some files were mismatched. No failure was encountered.")
+        | 6 -> (exitcode, "Additional files and mismatched files exist. No files were copied and no failures were encountered. This means that the files already exist in the destination directory. ")
+        | 7 -> (exitcode, "Files were copied, a file mismatch was present, and additional files were present.")
+        | 8 -> (exitcode, "Several files did not copy.")
+        | _ -> (exitcode, "UNKNOWN ERROR")
+
+    match exitCodeWithMessage with
+    | (exitcode, message) when exitcode < 2 -> tracefn "Succeeded in RoboCopy From: %s To: %s \n%s\n" source destination message |> ignore
+    | (exitcode, message) when exitcode < 8 -> traceImportant <| sprintf "Important notice in RoboCopy From: %s To: %s \n%s\n" source destination message |> ignore
+    | (_, _) -> failwithf "Error during RoboCopy From: %s To: %s" source destination
+
+/// Executes a RoboCopy command
+/// ## Parameters
+///  - `source` - The source directory
+///  - `destination` - The target directory
+let RoboCopy (source:string) (destination:string) =
+   roboCopyWithOptions source destination { Mirror = false }
+
+/// Executes a RoboCopy mirror command (potentially destructive)
+/// ## Parameters
+///  - `source` - The source directory
+///  - `destination` - The target directory
+let RoboCopyMirror (source:string) (destination:string) =
+    roboCopyWithOptions source destination { Mirror = true }