Make IO#set_encoding with binary external encoding use nil internal encoding

This was already the behavior when a single `'external:internal'`
encoding specifier string was passed.  This makes the behavior
consistent for the case where separate external and internal
encoding specifiers are provided.

While here, fix the IO#set_encoding method documentation to
state that either the first or second argument can be a string
with an encoding name, and describe the behavior when the
external encoding is binary.

Fixes [Bug #18899]

1 files changed, 72 insertions, 0 deletions

diff --git a/test/ruby/test_io_m17n.rb b/test/ruby/test_io_m17n.rb
index 9c14087eba..267975d4ac 100644
--- a/test/ruby/test_io_m17n.rb
+++ b/test/ruby/test_io_m17n.rb
@@ -1158,6 +1158,78 @@ EOT
     end
   end
 
+  def test_set_encoding_argument_parsing
+    File.open(File::NULL) do |f|
+      f.set_encoding('binary')
+      assert_equal(Encoding::ASCII_8BIT, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding(Encoding.find('binary'))
+      assert_equal(Encoding::ASCII_8BIT, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding('binary:utf-8')
+      assert_equal(nil, f.internal_encoding)
+      assert_equal(Encoding::ASCII_8BIT, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding('binary', 'utf-8')
+      assert_equal(nil, f.internal_encoding)
+      assert_equal(Encoding::ASCII_8BIT, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding(Encoding.find('binary'), Encoding.find('utf-8'))
+      assert_equal(nil, f.internal_encoding)
+      assert_equal(Encoding::ASCII_8BIT, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding('binary', Encoding.find('utf-8'))
+      assert_equal(nil, f.internal_encoding)
+      assert_equal(Encoding::ASCII_8BIT, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding(Encoding.find('binary'), 'utf-8')
+      assert_equal(nil, f.internal_encoding)
+      assert_equal(Encoding::ASCII_8BIT, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding('iso-8859-1:utf-8')
+      assert_equal(Encoding::UTF_8, f.internal_encoding)
+      assert_equal(Encoding::ISO_8859_1, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding('iso-8859-1', 'utf-8')
+      assert_equal(Encoding::UTF_8, f.internal_encoding)
+      assert_equal(Encoding::ISO_8859_1, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding(Encoding.find('iso-8859-1'), Encoding.find('utf-8'))
+      assert_equal(Encoding::UTF_8, f.internal_encoding)
+      assert_equal(Encoding::ISO_8859_1, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding('iso-8859-1', Encoding.find('utf-8'))
+      assert_equal(Encoding::UTF_8, f.internal_encoding)
+      assert_equal(Encoding::ISO_8859_1, f.external_encoding)
+    end
+
+    File.open(File::NULL) do |f|
+      f.set_encoding(Encoding.find('iso-8859-1'), 'utf-8')
+      assert_equal(Encoding::UTF_8, f.internal_encoding)
+      assert_equal(Encoding::ISO_8859_1, f.external_encoding)
+    end
+  end
+
   def test_textmode_twice
     assert_raise(ArgumentError) {
       open(__FILE__, "rt", textmode: true) {|f|