Add ability preserve parameters definitions when subclassing

lib/tty/option.rb

@@ -16,6 +16,17 @@ def self.included(base)
       base.module_eval do
         include Interface
         extend DSL
+        extend Inheritance
+      end
+    end
+
+    module Inheritance
+      # When class is inherited copy over parameter definitions
+      # This allows for definition of global parameters without
+      # affecting child class parameters and vice versa.
+      def inherited(subclass)
+        subclass.instance_variable_set(:@parameters, @parameters.dup)
+        super
       end
     end
 

spec/unit/subclass_spec.rb

@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+RSpec.describe TTY::Option do
+  it "inherits parameters from parent class" do
+    parent_class = command("ParentCmd") do
+      option :foo do
+        long "--foo string"
+      end
+    end
+
+    child_class = command("ChildCmd", parent_class)
+
+    expect(parent_class.parameters.map(&:name))
+      .to eq(child_class.parameters.map(&:name))
+
+    parent_cmd = parent_class.new
+    child_cmd = child_class.new
+
+    child_cmd.parse(%w[--foo b])
+    parent_cmd.parse(%w[--foo a])
+
+    expect(parent_cmd.params[:foo]).to eq("a")
+    expect(parent_cmd.remaining).to eq([])
+    expect(child_cmd.params[:foo]).to eq("b")
+    expect(child_cmd.remaining).to eq([])
+  end
+
+  it "adds new parameters in child class" do
+    parent_class = command("ParentCmd") do
+      option :foo do
+        long "--foo string"
+      end
+    end
+
+    child_class = command("ChildCmd", parent_class) do
+      option :bar do
+        long "--bar string"
+      end
+    end
+
+    parent_cmd = parent_class.new
+    child_cmd = child_class.new
+
+    child_cmd.parse(%w[--foo a --bar b])
+    parent_cmd.parse(%w[--foo a --bar b], check_invalid_params: false)
+
+    expect(parent_class.parameters.map(&:name)).to eq([:foo])
+    expect(parent_cmd.params[:foo]).to eq("a")
+    expect(parent_cmd.params[:bar]).to eq(nil)
+    expect(parent_cmd.remaining).to eq(%w[--bar b])
+
+    expect(child_class.parameters.map(&:name)).to eq([:foo, :bar])
+    expect(child_cmd.params[:foo]).to eq("a")
+    expect(child_cmd.params[:bar]).to eq("b")
+    expect(child_cmd.remaining).to eq([])
+  end
+end