add IRB::FileInputMethod.open to ensure closing associated File

* tweak some methods not to raise exception after `#close`
* use it in `IRB::IrbLoader#{source_file,load_file}

lib/irb/ext/loader.rb

@@ -50,16 +50,18 @@ def search_file_from_ruby_path(fn) # :nodoc:
     # See Irb#suspend_input_method for more information.
     def source_file(path)
       irb.suspend_name(path, File.basename(path)) do
-        irb.suspend_input_method(FileInputMethod.new(path)) do
-          |back_io|
-          irb.signal_status(:IN_LOAD) do
-            if back_io.kind_of?(FileInputMethod)
-              irb.eval_input
-            else
-              begin
+        FileInputMethod.open(path) do |io|
+          irb.suspend_input_method(io) do
+            |back_io|
+            irb.signal_status(:IN_LOAD) do
+              if back_io.kind_of?(FileInputMethod)
                 irb.eval_input
-              rescue LoadAbort
-                print "load abort!!\n"
+              else
+                begin
+                  irb.eval_input
+                rescue LoadAbort
+                  print "load abort!!\n"
+                end
               end
             end
           end
@@ -79,16 +81,18 @@ def load_file(path, priv = nil)
           ws = WorkSpace.new
         end
         irb.suspend_workspace(ws) do
-          irb.suspend_input_method(FileInputMethod.new(path)) do
-            |back_io|
-            irb.signal_status(:IN_LOAD) do
-              if back_io.kind_of?(FileInputMethod)
-                irb.eval_input
-              else
-                begin
+          FileInputMethod.open(path) do |io|
+            irb.suspend_input_method(io) do
+              |back_io|
+              irb.signal_status(:IN_LOAD) do
+                if back_io.kind_of?(FileInputMethod)
                   irb.eval_input
-                rescue LoadAbort
-                  print "load abort!!\n"
+                else
+                  begin
+                    irb.eval_input
+                  rescue LoadAbort
+                    print "load abort!!\n"
+                  end
                 end
               end
             end

lib/irb/input-method.rb

@@ -124,10 +124,22 @@ def inspect
 
   # Use a File for IO with irb, see InputMethod
   class FileInputMethod < InputMethod
+    class << self
+      def open(file, &block)
+        begin
+          io = new(file)
+          block.call(io)
+        ensure
+          io&.close
+        end
+      end
+    end
+
     # Creates a new input method object
     def initialize(file)
       super
       @io = IRB::MagicFile.open(file)
+      @external_encoding = @io.external_encoding
     end
     # The file name of this input method, usually given during initialization.
     attr_reader :file_name
@@ -137,7 +149,7 @@ def initialize(file)
     #
     # See IO#eof? for more information.
     def eof?
-      @io.eof?
+      @io.closed? || @io.eof?
     end
 
     # Reads the next line from this input method.
@@ -150,13 +162,17 @@ def gets
 
     # The external encoding for standard input.
     def encoding
-      @io.external_encoding
+      @external_encoding
     end
 
     # For debug message
     def inspect
       'FileInputMethod'
     end
+
+    def close
+      @io.close
+    end
   end
 
   begin