io.c: read BOM only for reading

* io.c (io_strip_bom): just abandon detecting UTF encoding by BOM
  unless opened for reading.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60884 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 14 insertions, 0 deletions

diff --git a/test/ruby/test_io_m17n.rb b/test/ruby/test_io_m17n.rb
index ccb124a46b..8ba34845fa 100644
--- a/test/ruby/test_io_m17n.rb
+++ b/test/ruby/test_io_m17n.rb
@@ -2168,6 +2168,20 @@ EOT
     assert_nil(enc)
   end
 
+  def test_bom_non_reading
+    with_tmpdir {
+      enc = nil
+      assert_nothing_raised(IOError) {
+        open("test", "w:bom|utf-8") {|f|
+          enc = f.external_encoding
+          f.print("abc")
+        }
+      }
+      assert_equal(Encoding::UTF_8, enc)
+      assert_equal("abc", File.binread("test"))
+    }
+  end
+
   def test_cbuf
     with_tmpdir {
       fn = "tst"