Add minimum arity lookup to parameter

lib/tty/option/parameter.rb

@@ -39,10 +39,6 @@ def check_settings!(settings)
         end
       end
 
-      def default_arity
-        1
-      end
-
       def arity(value = (not_set = true))
         if not_set
           @settings.fetch(:arity) { default_arity }
@@ -51,6 +47,17 @@ def arity(value = (not_set = true))
         end
       end
 
+      def default_arity
+        1
+      end
+
+      # Determine minimum boundary for arity parameter
+      #
+      # @api private
+      def min_arity
+        arity < 0 ? arity.abs - 1 : arity
+      end
+
       # Check if multiple occurrences are allowed
       #
       # @return [Boolean]

spec/unit/parameter/argument_spec.rb

@@ -17,6 +17,7 @@
     it "defaults to 1" do
       arg = described_class.new(:foo)
       expect(arg.arity).to eq(1)
+      expect(arg.min_arity).to eq(1)
       expect(arg.multiple?).to eq(false)
     end
 
@@ -37,12 +38,21 @@
     it "accepts * as zero or more arity" do
       arg = described_class.new(:foo, arity: "*")
       expect(arg.arity).to eq(-1)
+      expect(arg.min_arity).to eq(0)
       expect(arg.multiple?).to eq(true)
     end
 
     it "accepts :any as zero or more arity" do
       arg = described_class.new(:foo, arity: :any)
       expect(arg.arity).to eq(-1)
+      expect(arg.min_arity).to eq(0)
+      expect(arg.multiple?).to eq(true)
+    end
+
+    it "accepts one or more arity" do
+      arg = described_class.new(:foo, arity: -2)
+      expect(arg.arity).to eq(-2)
+      expect(arg.min_arity).to eq(1)
       expect(arg.multiple?).to eq(true)
     end
   end