Fix wrong EOF detection for ARGF

GitHub: fix GH-328

We can't use ARGF.eof? to detect EOF of ARGF. Because ARGF.eof?
returns true when an file reached EOF but ARGF may use multiple files.

Reported by Takeshi Nishimatsu. Thanks!!!

Author: kou

lib/csv/parser.rb

@@ -18,6 +18,19 @@ class Parser
     # into your Encoding.
     #
 
+    class << self
+      ARGF_OBJECT_ID = ARGF.object_id
+      # Convenient method to check whether the give input reached EOF
+      # or not.
+      def eof?(input)
+        # We can't use input != ARGF in Ractor. Because ARGF isn't a
+        # shareable object.
+        input.object_id != ARGF_OBJECT_ID and
+          input.respond_to?(:eof) and
+          input.eof?
+      end
+    end
+
     # Raised when encoding is invalid.
     class InvalidEncoding < StandardError
     end
@@ -312,7 +325,7 @@ def read_chunk
             raise InvalidEncoding unless chunk.valid_encoding?
             # trace(__method__, :chunk, chunk)
             @scanner = StringScanner.new(chunk)
-            if input.respond_to?(:eof?) and input.eof?
+            if Parser.eof?(input)
               @inputs.shift
               @last_scanner = @inputs.empty?
             end
@@ -869,10 +882,7 @@ def build_scanner
         string = nil
         if @samples.empty? and @input.is_a?(StringIO)
           string = @input.read
-        elsif @samples.size == 1 and
-              @input != ARGF and
-              @input.respond_to?(:eof?) and
-              @input.eof?
+        elsif @samples.size == 1 and Parser.eof?(@input)
           string = @samples[0]
         end
         if string