Added HelpName

Author: mrboring

README.md

@@ -77,6 +77,7 @@ The new `Input` module contains functions for the underlying System.CommandLine
 * `desc` adds a description to an `Option` or `Argument`
 * `defaultValue` or `def` provides a default value to an `Option` or `Argument`
 * `defFactory` assigns a default value factor to an `Option` or `Argument`
+* `helpName` adds the name used in help output to describe the option or argument.
 * `required` marks an `Option` as required
 * `validate` allows you to return a `Result<unit, string>` for the parsed value
 * `validateFileExists` ensures that the `FileInfo` exists

src/FSharp.SystemCommandLine/Inputs.fs

@@ -100,6 +100,12 @@ module Input =
         |> editOption (fun o -> o.DefaultValueFactory <- defaultValueFactory)
         |> editArgument (fun a -> a.DefaultValueFactory <- defaultValueFactory)
 
+    /// The name used in help output to describe the option or argument.
+    let helpName (helpName: string) (input: ActionInput<'T>) =
+        input
+        |> editOption (fun o -> o.HelpName <- helpName)
+        |> editArgument (fun a -> a.HelpName <- helpName)
+
     /// Marks an option as required.
     let required (input: ActionInput<'T>) = 
         input |> editOption (fun o -> o.Required <- true)