io.c: Backport #2267 [ruby-core:26300]; Fix problem with IO so that the file position is correct after a direct write on BSDish platforms like OS X.

test/ruby/test_io.rb: Added a test for the fix.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8_6@28393 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_io.rb

@@ -1,6 +1,33 @@
 require 'test/unit'
+require 'tempfile'
 
 class TestIO < Test::Unit::TestCase
+
+  def make_tempfile
+    t = Tempfile.new("foo")
+    t.binmode
+    t.puts "foo"
+    t.puts "bar"
+    t.puts "baz"
+    t.close
+    t
+  end
+
+  def test_pos
+    t = make_tempfile
+
+    open(t.path, IO::RDWR|IO::CREAT|IO::TRUNC, 0600) do |f|
+      f.write "Hello"
+      assert_equal(5, f.pos)
+    end
+    open(t.path, IO::RDWR|IO::CREAT|IO::TRUNC, 0600) do |f|
+      f.sync = true
+      f.read
+      f.write "Hello"
+      assert_equal(5, f.pos)
+    end
+  end
+
   def test_gets_rs
     r, w = IO.pipe
     w.print "\377xyz"