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 +1,38 @@
+[<AutoOpen>]
+/// 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 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 result = ExecProcess (fun info ->
+       info.FileName <- "CMD.exe"
+       info.Arguments <- args) System.TimeSpan.MaxValue
+
+    if result <> 0 then 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 }