Add argument choices

docsrc/arguments.rst

@@ -68,3 +68,24 @@ If more than one argument can be consumed, a table is used to store the data.
       pair = {"foo", "bar"},
       optional = "baz"
    }
+
+Setting argument choices
+------------------------
+
+The ``choices`` property can be used to restrict an argument to a set of choices. Its value is an array of string choices.
+
+.. code-block:: lua
+   :linenos:
+
+   parser:argument "direction"
+      :choices {"north", "south", "east", "west"}
+
+.. code-block:: none
+
+   $ lua script.lua foo
+
+.. code-block:: none
+
+   Usage: script.lua [-h] <direction>
+
+   Error: argument 'direction' must be one of 'north', 'south', 'east', 'west'

docsrc/misc.rst

@@ -242,6 +242,7 @@ Property            Type
 ``defmode``         String
 ``show_default``    Boolean
 ``argname``         String or table
+``choices``         Table
 ``action``          Function or string
 ``init``            Any
 ``hidden``          Boolean
@@ -273,6 +274,7 @@ Property            Type
 ``show_default``    Boolean
 ``overwrite``       Booleans
 ``argname``         String or table
+``choices``         Table
 ``action``          Function or string
 ``init``            Any
 ``hidden``          Boolean

docsrc/options.rst

@@ -107,6 +107,11 @@ Just as arguments, options can be configured to take several command line argume
 
 Note that the data passed to ``optional`` option is stored in an array. That is necessary to distinguish whether the option was invoked without an argument or it was not invoked at all.
 
+Setting argument choices
+------------------------
+
+The ``choices`` property can be used to specify a list of choices for an option argument in the same way as for arguments.
+
 Setting number of invocations
 -----------------------------