Support Range in enum option

lib/thor/base.rb

@@ -660,7 +660,7 @@ def print_options(shell, options, group_name = nil)
 
           list << item
           list << ["", "# Default: #{option.print_default}"] if option.show_default?
-          list << ["", "# Possible values: #{option.enum.join(', ')}"] if option.enum
+          list << ["", "# Possible values: #{option.enum_to_s}"] if option.enum
         end
 
         shell.say(group_name ? "#{group_name} options:" : "Options:")

lib/thor/parser/argument.rb

@@ -52,11 +52,19 @@ def show_default?
       end
     end
 
+    def enum_to_s
+      if enum.respond_to? :join
+        enum.join(", ")
+      else
+        "#{enum.first}..#{enum.last}"
+      end
+    end
+
   protected
 
     def validate!
       raise ArgumentError, "An argument cannot be required and have default value." if required? && !default.nil?
-      raise ArgumentError, "An argument cannot have an enum other than an array." if @enum && !@enum.is_a?(Array)
+      raise ArgumentError, "An argument cannot have an enum other than an enumerable." if @enum && !@enum.is_a?(Enumerable)
     end
 
     def valid_type?(type)

lib/thor/parser/arguments.rb

@@ -136,7 +136,7 @@ def parse_numeric(name)
       value = $&.index(".") ? shift.to_f : shift.to_i
       if @switches.is_a?(Hash) && switch = @switches[name]
         if switch.enum && !switch.enum.include?(value)
-          raise MalformattedArgumentError, "Expected '#{name}' to be one of #{switch.enum.join(', ')}; got #{value}"
+          raise MalformattedArgumentError, "Expected '#{name}' to be one of #{switch.enum_to_s}; got #{value}"
         end
       end
       value
@@ -154,7 +154,7 @@ def parse_string(name)
         value = shift
         if @switches.is_a?(Hash) && switch = @switches[name]
           if switch.enum && !switch.enum.include?(value)
-            raise MalformattedArgumentError, "Expected '#{name}' to be one of #{switch.enum.join(', ')}; got #{value}"
+            raise MalformattedArgumentError, "Expected '#{name}' to be one of #{switch.enum_to_s}; got #{value}"
           end
         end
         value

spec/parser/argument_spec.rb

@@ -25,10 +25,10 @@ def argument(name, options = {})
       end.to raise_error(ArgumentError, "An argument cannot be required and have default value.")
     end
 
-    it "raises an error if enum isn't an array" do
+    it "raises an error if enum isn't enumerable" do
       expect do
         argument(:command, type: :string, enum: "bar")
-      end.to raise_error(ArgumentError, "An argument cannot have an enum other than an array.")
+      end.to raise_error(ArgumentError, "An argument cannot have an enum other than an enumerable.")
     end
   end
 

spec/parser/options_spec.rb

@@ -529,11 +529,18 @@ def remaining
                                                      "Expected numeric value for '-n'; got \"foo\"")
       end
 
-      it "raises error when value isn't in enum" do
+      it "raises error when value isn't in Array enum" do
         enum = [1, 2]
         create limit: Thor::Option.new("limit", type: :numeric, enum: enum)
         expect { parse("--limit", "3") }.to raise_error(Thor::MalformattedArgumentError,
-                                                        "Expected '--limit' to be one of #{enum.join(', ')}; got 3")
+                                                        "Expected '--limit' to be one of 1, 2; got 3")
+      end
+
+      it "raises error when value isn't in Range enum" do
+        enum = 1..2
+        create limit: Thor::Option.new("limit", type: :numeric, enum: enum)
+        expect { parse("--limit", "3") }.to raise_error(Thor::MalformattedArgumentError,
+                                                        "Expected '--limit' to be one of 1..2; got 3")
       end
 
       it "allows multiple values if repeatable is specified" do