Introduce Thor2, a class with less unexpected defaults

This new class allows having more expected defaults without breaking backward compatibility. Documentation can then recommend using Thor2 for new CLIs which will be more intuitive for users.

lib/thor.rb

@@ -507,3 +507,5 @@ def help(command = nil, subcommand = false)
     end
   end
 end
+
+require "thor/thor2"

lib/thor/base.rb

@@ -138,7 +138,8 @@ def attr_accessor(*) #:nodoc:
       end
 
       # If you want to raise an error for unknown options, call check_unknown_options!
-      # This is disabled by default to allow dynamic invocations.
+      # This is disabled by default in the Thor class to allow dynamic invocations.
+      # This is enabled by default in the Thor2 class
       def check_unknown_options!
         @check_unknown_options = true
       end
@@ -153,7 +154,8 @@ def check_unknown_options?(config) #:nodoc:
 
       # If you want to raise an error when the default value of an option does not match
       # the type call check_default_type!
-      # This is disabled by default for compatibility.
+      # This is disabled by default in the Thor class for compatibility.
+      # This is enabled by default in the Thor2 class
       def check_default_type!
         @check_default_type = true
       end

lib/thor/thor2.rb

@@ -0,0 +1,32 @@
+class Thor
+  class Thor2 < Thor
+    # This is a class to use instead of Thor when declaring your CLI
+    # This alternative works the same way as Thor, but has more common defaults:
+    #  * If there is a failure in the argument parsing and other Thor-side
+    #    things, the exit code will be non-zero
+    #  * Things that look like options but are not valid options will
+    #    will show an error of being unknown option instead of being
+    #    used as arguments.
+    #  * Make sure the default value of options is of the correct type
+    # For backward compatibility reasons, these cannot be made default in
+    # the regular `Thor` class
+    #
+    # This class is available in the top-level as Thor2, so you can do
+    # class MyCli < Thor2
+    #   ...
+    # end
+
+    # Fail on unknown options instead of treating them as argument
+    check_unknown_options!
+
+    # Make sure the default value of options is of the correct type
+    check_default_type!
+
+    # All failures should result in non-zero error code
+    def self.exit_on_failure?
+      true
+    end
+  end
+end
+
+::Thor2 = Thor::Thor2

spec/thor2_spec.rb

@@ -0,0 +1,33 @@
+require "helper"
+
+describe Thor2 do
+  my_script = Class.new(Thor2) do
+    class_option "verbose",   :type => :boolean
+    class_option "mode",      :type => :string
+
+    desc "checked", "a command with checked"
+    def checked(*args)
+      [options, args]
+    end
+  end
+
+  describe "#check_unknown_options!" do
+    it "still accept options and arguments" do
+      expect(my_script.start(%w[checked command --verbose])).to eq [{"verbose" => true}, %w[command]]
+    end
+
+    it "does not accept if non-option that looks like an option is after an argument" do
+      expect(capture(:stderr) do
+        my_script.start(%w[checked command --foo --bar])
+      end.strip).to eq("Unknown switches '--foo, --bar'")
+    end
+  end
+
+  it "checks the default type" do
+    expect do
+      Class.new(Thor2) do
+        option "bar", :type => :numeric, :default => "foo"
+      end
+    end.to raise_error(ArgumentError, "Expected numeric default value for '--bar'; got \"foo\" (string)")
+  end
+end