Merge pull request #478 in G/truffleruby from gh-1473 to master

* commit 'a51357e335bb6f362f2adeac5f5d49d11095af18':
  `StringIO#set_encoding` should not attempt to change the encoding the underlying String if that String is frozen.

Author: nirvdrum

CHANGELOG.md

@@ -9,11 +9,12 @@ New features:
 Bug fixes:
 
 * Adding missing support for the `close_others` option to `exec` and `spawn`.
-* Allow signal `0` to be used with `Process.kill`.
 * FFI::Pointer now does the correct range checks for signed and unsigned values.
 * Allow signal `0` to be used with `Process.kill` (#1474).
 * `IO#dup` now properly sets the new `IO` instance to be close-on-exec.
 * `IO#reopen` now properly resets the receiver to be close-on-exec.
+* `StringIO#set_encoding` no longer raises an exception if the underlying
+  `String` is frozen (#1473).
 
 Changes:
 

lib/truffle/stringio.rb

@@ -120,7 +120,8 @@ def check_writable
   def set_encoding(external, internal=nil, options=nil)
     encoding = external || Encoding.default_external
     @__data__.encoding = encoding
-    @__data__.string.force_encoding(encoding)
+    @__data__.string.force_encoding(encoding) if @writable
+
     self
   end
 

spec/ruby/library/stringio/set_encoding_spec.rb

@@ -2,9 +2,19 @@
 require_relative '../../spec_helper'
 
 describe "StringIO#set_encoding" do
-  it "sets the encoding of the underlying String" do
-    io = StringIO.new
+  it "sets the encoding of the underlying String if the String is not frozen" do
+    str = "".encode(Encoding::US_ASCII)
+
+    io = StringIO.new(str)
     io.set_encoding Encoding::UTF_8
     io.string.encoding.should == Encoding::UTF_8
   end
+
+  it "does not set the encoding of the underlying String if the String is frozen" do
+    str = "".encode(Encoding::US_ASCII).freeze
+
+    io = StringIO.new(str)
+    io.set_encoding Encoding::UTF_8
+    io.string.encoding.should == Encoding::US_ASCII
+  end
 end

spec/tags/library/stringio/external_encoding_tags.txt

@@ -1,2 +1 @@
-fails:StringIO#external_encoding does not set the encoding of its buffer string if the string is frozen
 fails:StringIO#external_encoding changes to match string if string's encoding is changed