Show choices in help and usage messages

docsrc/arguments.rst

@@ -86,6 +86,6 @@ The ``choices`` property can be used to restrict an argument to a set of choices
 
 .. code-block:: none
 
-   Usage: script.lua [-h] <direction>
+   Usage: script.lua [-h] {north,south,east,west}
 
    Error: argument 'direction' must be one of 'north', 'south', 'east', 'west'

spec/help_spec.lua

@@ -86,6 +86,34 @@ Options:
    --config <config>]], parser:get_help())
    end)
 
+   it("creates correct help message for arguments with choices", function()
+      local parser = Parser "foo"
+      parser:argument "move"
+         :choices {"rock", "paper", "scissors"}
+
+      assert.equal([[
+Usage: foo [-h] {rock,paper,scissors}
+
+Arguments:
+   {rock,paper,scissors}
+
+Options:
+   -h, --help            Show this help message and exit.]], parser:get_help())
+   end)
+
+   it("creates correct help message for options with argument choices", function()
+      local parser = Parser "foo"
+      parser:option "--format"
+         :choices {"short", "medium", "full"}
+
+      assert.equal([[
+Usage: foo [-h] [--format {short,medium,full}]
+
+Options:
+   -h, --help            Show this help message and exit.
+   --format {short,medium,full}]], parser:get_help())
+   end)
+
    it("adds margin for multiline descriptions", function()
       local parser = Parser "foo"
       parser:flag "-v"

spec/usage_spec.lua

@@ -89,6 +89,30 @@ Usage: foo <first> <second-and-third> <second-and-third>
       )
    end)
 
+   it("creates correct usage message for arguments with choices", function()
+      local parser = Parser "foo"
+         :add_help(false)
+      parser:argument "move"
+         :choices {"rock", "paper", "scissors"}
+
+      assert.equal(
+         [=[Usage: foo {rock,paper,scissors}]=],
+         parser:get_usage()
+      )
+   end)
+
+   it("creates correct usage message for options with argument choices", function()
+      local parser = Parser "foo"
+         :add_help(false)
+      parser:option "--format"
+         :choices {"short", "medium", "full"}
+
+      assert.equal(
+         [=[Usage: foo [--format {short,medium,full}]]=],
+         parser:get_usage()
+      )
+   end)
+
    it("creates correct usage message for commands", function()
       local parser = Parser "foo"
          :add_help(false)

src/argparse.lua

@@ -513,17 +513,33 @@ function Argument:_get_argname(narg)
    end
 end
 
+function Argument:_get_choices_list()
+   return "{" .. table.concat(self._choices, ",") .. "}"
+end
+
 function Argument:_get_default_argname()
-   return "<" .. self._name .. ">"
+   if self._choices then
+      return self:_get_choices_list()
+   else
+      return "<" .. self._name .. ">"
+   end
 end
 
 function Option:_get_default_argname()
-   return "<" .. self:_get_default_target() .. ">"
+   if self._choices then
+      return self:_get_choices_list()
+   else
+      return "<" .. self:_get_default_target() .. ">"
+   end
 end
 
 -- Returns labels to be shown in the help message.
 function Argument:_get_label_lines()
-   return {self._name}
+   if self._choices then
+      return {self:_get_choices_list()}
+   else
+      return {self._name}
+   end
 end
 
 function Option:_get_label_lines()