[ruby/irb] Gracefully handle missing command argument

(https://github.com/ruby/irb/pull/473)

* Handle file loading commands' argument error gracefully

Currently, if users don't provide an argument to `source`,
`irb_load`, and `irb_require`, IRB raises `ArgumentError` with full
stacktrace. This is confusing because it looks similar to when IRB has
internal issues. The message also isn't helpful on helping users avoid
the error.

So in this commit, I add a new `CommandArgumentError` for commands to
raise explicitly when users' input doesn't satisfy a command's argument
requirement.

* Gracefully handle `fg` command's argument requirement

lib/irb/cmd/load.rb

@@ -17,24 +17,29 @@ module IRB
   # :stopdoc:
 
   module ExtendCommand
-    class Load < Nop
+    class LoaderCommand < Nop
       include IrbLoader
 
-      category "IRB"
-      description "Load a Ruby file."
-
-      def execute(file_name, priv = nil)
-        return irb_load(file_name, priv)
+      def raise_cmd_argument_error
+        raise CommandArgumentError.new("Please specify the file name.")
       end
     end
 
-    class Require < Nop
-      include IrbLoader
+    class Load < LoaderCommand
+      category "IRB"
+      description "Load a Ruby file."
 
+      def execute(file_name = nil, priv = nil)
+        raise_cmd_argument_error unless file_name
+        irb_load(file_name, priv)
+      end
+    end
+
+    class Require < LoaderCommand
       category "IRB"
       description "Require a Ruby file."
-
-      def execute(file_name)
+      def execute(file_name = nil)
+        raise_cmd_argument_error unless file_name
 
         rex = Regexp.new("#{Regexp.quote(file_name)}(\.o|\.rb)?")
         return false if $".find{|f| f =~ rex}
@@ -62,17 +67,16 @@ module IRB
       end
     end
 
-    class Source < Nop
-      include IrbLoader
-
+    class Source < LoaderCommand
       category "IRB"
       description "Loads a given file in the current session."
 
-      def execute(file_name)
+      def execute(file_name = nil)
+        raise_cmd_argument_error unless file_name
+
         source_file(file_name)
       end
     end
   end
-
   # :startdoc:
 end

lib/irb/cmd/nop.rb

@@ -13,6 +13,8 @@ module IRB
   # :stopdoc:
 
   module ExtendCommand
+    class CommandArgumentError < StandardError; end
+
     class Nop
       class << self
         def category(category = nil)
@@ -30,11 +32,15 @@ module IRB
         def self.execute(conf, *opts, **kwargs, &block)
           command = new(conf)
           command.execute(*opts, **kwargs, &block)
+        rescue CommandArgumentError => e
+          puts e.message
         end
       else
         def self.execute(conf, *opts, &block)
           command = new(conf)
           command.execute(*opts, &block)
+        rescue CommandArgumentError => e
+          puts e.message
         end
       end
 

lib/irb/cmd/subirb.rb

@@ -51,7 +51,8 @@ module IRB
       category "IRB"
       description "Switches to the session of the given number."
 
-      def execute(key)
+      def execute(key = nil)
+        raise CommandArgumentError.new("Please specify the id of target IRB job (listed in the `jobs` command).") unless key
         IRB.JobManager.switch(key)
       end
     end

test/irb/test_cmd.rb

@@ -368,6 +368,14 @@ module TestIRB
       ], out)
     end
 
+    def test_irb_source_without_argument
+      out, err = execute_lines(
+        "irb_source\n",
+      )
+      assert_empty err
+      assert_match(/Please specify the file name./, out)
+    end
+
     def test_help
       out, _ = execute_lines(
         "help 'String#gsub'\n",
@@ -416,6 +424,15 @@ module TestIRB
         ], out)
     end
 
+    def test_irb_load_without_argument
+      out, err = execute_lines(
+        "irb_load\n",
+      )
+
+      assert_empty err
+      assert_match(/Please specify the file name./, out)
+    end
+
     def test_ls
       out, err = execute_lines(
         "class P\n",