io.c: BOM with non-UTF

* io.c (io_encname_bom_p): check BOM prefix only, not including
  UTF prefix.
* io.c (parse_mode_enc): warn BOM with non-UTF encoding.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53084 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 63eb4b7d88..fb99c0cd6d 100644
--- a/test/ruby/test_io_m17n.rb
+++ b/test/ruby/test_io_m17n.rb
@@ -2095,6 +2095,20 @@ EOT
     end;
   end
 
+  def test_bom_non_utf
+    enc = nil
+
+    assert_warn(/BOM/) {
+      open(__FILE__, "r:bom|us-ascii") {|f| enc = f.external_encoding}
+    }
+    assert_equal(Encoding::US_ASCII, enc)
+
+    assert_warn(/BOM/) {
+      open(IO::NULL, "w:bom|us-ascii") {|f| enc = f.external_encoding}
+    }
+    assert_equal(Encoding::US_ASCII, enc)
+  end
+
   def test_cbuf
     with_tmpdir {
       fn = "tst"