[Bug #20802] Copy encodings at reopen as well

io.c

@@ -8326,6 +8326,7 @@ io_reopen(VALUE io, VALUE nfile)
 
     /* copy rb_io_t structure */
     fptr->mode = orig->mode | (fptr->mode & FMODE_EXTERNAL);
+    fptr->encs = orig->encs;
     fptr->pid = orig->pid;
     fptr->lineno = orig->lineno;
     if (RTEST(orig->pathv)) fptr->pathv = orig->pathv;

test/ruby/test_io.rb

@@ -2655,6 +2655,17 @@ def test_reopen_opt
     }
   end
 
+  def test_reopen_binmode
+    f1 = File.open(__FILE__)
+    f2 = File.open(__FILE__)
+    f1.binmode
+    f1.reopen(f2)
+    assert_not_operator(f1, :binmode?)
+  ensure
+    f2.close
+    f1.close
+  end
+
   def make_tempfile_for_encoding
     t = make_tempfile
     open(t.path, "rb+:utf-8") {|f| f.puts "\u7d05\u7389bar\n"}
@@ -2685,6 +2696,16 @@ def test_reopen_encoding
     }
   end
 
+  def test_reopen_encoding_from_io
+    f1 = File.open(__FILE__, "rb:UTF-16LE")
+    f2 = File.open(__FILE__, "r:UTF-8")
+    f1.reopen(f2)
+    assert_equal(Encoding::UTF_8, f1.external_encoding)
+  ensure
+    f2.close
+    f1.close
+  end
+
   def test_reopen_opt_encoding
     feature7103 = '[ruby-core:47806]'
     make_tempfile_for_encoding {|t|