CLI: Force thor to exit with a correct exit status

Long-time issues on Thor related to exit status code cause msync to return a inappropriate exit code.

As example: rails/thor#244

features/cli.feature

@@ -4,18 +4,22 @@ Feature: CLI
   Scenario: When passing no arguments to the msync command
     When I run `msync`
     And the output should match /Commands:/
+    Then the exit status should be 1
 
   Scenario: When passing invalid arguments to the msync update command
     When I run `msync update`
     And the output should match /No value provided for required option/
+    Then the exit status should be 1
 
   Scenario: When passing invalid arguments to the msync hook command
     When I run `msync hook`
     And the output should match /Commands:/
+    Then the exit status should be 1
 
-  Scenario: When running the help subcommand
+  Scenario: When running the help command
     When I run `msync help`
     And the output should match /Commands:/
+    Then the exit status should be 0
 
   Scenario: When overriding a setting from the config file on the command line
     Given a basic setup with a puppet module "puppet-test" from "fakenamespace"

lib/modulesync/cli.rb

@@ -1,10 +1,12 @@
 require 'thor'
+
 require 'modulesync'
+require 'modulesync/cli/thor'
 require 'modulesync/constants'
 require 'modulesync/util'
 
 module ModuleSync
-  class CLI
+  module CLI
     def self.defaults
       @defaults ||= Util.symbolize_keys(Util.parse_config(Constants::MODULESYNC_CONF_FILE))
     end

lib/modulesync/cli/thor.rb

@@ -0,0 +1,24 @@
+require 'thor'
+require 'modulesync/cli'
+
+module ModuleSync
+  module CLI
+    # Workaround some, still unfixed, Thor behaviors
+    #
+    # This class extends ::Thor class to
+    # - exit with status code sets to `1` on Thor failure (e.g. missing required option)
+    # - exit with status code sets to `1` when user calls `msync` (or a subcommand) without required arguments
+    class Thor < ::Thor
+      desc '_invalid_command_call', 'Invalid command', hide: true
+      def _invalid_command_call
+        self.class.new.help
+        exit 1
+      end
+      default_task :_invalid_command_call
+
+      def self.exit_on_failure?
+        true
+      end
+    end
+  end
+end