feature/nuget-in-path: Also search for the NuGet executable in the PATH

src/app/FakeLib/EnvironmentHelper.fs

@@ -52,6 +52,12 @@ let environVarOrNone name =
     if String.IsNullOrEmpty var then None
     else Some var
 
+/// Splits the entries of an environment variable and removes the empty ones.
+let splitEnvironVar name =
+    let var = environVarOrNone name
+    if var = None then [ ]
+    else var.Value.Split([| Path.PathSeparator |]) |> Array.toList
+
 /// Retrieves the application settings variable with the given name
 let appSetting (name : string) = ConfigurationManager.AppSettings.[name]
 

src/app/FakeLib/FileSystemHelper.fs

@@ -97,3 +97,9 @@ let isDirectory path =
 
 /// Detects whether the given path is a file.
 let isFile path = isDirectory path |> not
+
+/// Detects whether the given path does not contains invalid characters.
+let isValidPath (path:string) =
+    Path.GetInvalidPathChars()
+    |> Array.filter (fun char -> path.Contains(char.ToString()))
+    |> Array.isEmpty

src/app/FakeLib/ProcessHelper.fs

@@ -180,6 +180,13 @@ let ExecProcessElevated cmd args timeOut =
         si.FileName <- cmd
         si.UseShellExecute <- true) timeOut
 
+/// Gets the list of valid directories included in the PATH environment variable.
+let pathDirectories =
+    splitEnvironVar "PATH"
+    |> Seq.map (fun value -> value.Trim())
+    |> Seq.filter (fun value -> not <| isNullOrEmpty value)
+    |> Seq.filter isValidPath
+
 /// Sets the environment Settings for the given startInfo.
 /// Existing values will be overriden.
 /// [omit]
@@ -339,8 +346,8 @@ let findFile dirs file =
 /// ## Parameters
 ///  - `exe` - The executable file to locate
 let tryFindFileOnPath (file : string) : string option =
-    Environment.GetEnvironmentVariable("PATH").Split([| Path.PathSeparator |])
-    |> Seq.append ["."]
+    pathDirectories
+    |> Seq.append [ "." ]
     |> fun path -> tryFindFile path file
 
 /// Returns the AppSettings for the key - Splitted on ;

src/app/FakeLib/RestorePackageHelper.fs

@@ -13,6 +13,7 @@ let findNuget defaultPath =
              currentDirectory @@ ".nuget"             
              currentDirectory @@ "packages" @@ "NuGet.Commandline" @@ "tools"
              currentDirectory @@ "packages" @@ "Nuget.Commandline" @@ "tools"]
+            |> Seq.append pathDirectories
 
         let exeNames = ["nuget.exe"; "NuGet.exe"; "Nuget.exe"]