[ruby-core:29336] Re: [Bug #3112] require "yaml" doesn't use psych as default

On Thu, Apr 08, 2010 at 02:06:55PM +0900, Yui NARUSE wrote:
> Issue #3112 has been updated by Yui NARUSE.
> 
> 
> 
> = Before
> require 'yaml' and you can use YAML by syck.
> 
> = History
> #2340 Removing YAML/Syck.
> http://redmine.ruby-lang.org/issues/show/2340
> 
> After imported psych, it is found that test-all conflicts.
> To avoid this, yamler is introduced.
> By yamler people can switch syck or psych (default is syck).
> 
> = Current
> There is 3 element:
> * lib/yaml.rb
> * ext/syck
> * ext/psych
> 
> = Q&A
> Why psych is bundled:
> * To review psych
> 
> Why psych is not default:
> * it is not confirmed that it can be default in 1.9.2
> * it has some incompatibilities showed following.
> 
> Why syck is still bundled:
> * for machines which libyaml is not installed
> * for Windows
> 
> Incompatibilities are following, can you explain why it can't compatible, Aaron?

Yes!  Many of these methods are exposing implementation specific details
for syck.  For example, the "detect_implicit" method detects whether a
YAML string is an implicit or explicit string.  "try_implicit" which
attempts to use "detect_implicit".  "object_maker" calls allocate on
a class and sets instance variables based on a hash.  These are clearly
methods which should never be exposed as a public API.

Other methods are deprecated because they are simply duplicates.  For
example, YAML.load_documents and YAML.each_document do _exactly_ the same thing.
YAML.each_node and YAML.parse_documents do _exactly_ the same thing.

On top of that, most of these methods are untested, which makes writing
100% compatible software impossible.  All of these methods could
be added to Psych, but it wouldn't be guaranteed that they work the same
way as Syck.

I understood from [ruby-core:28749], that Psych didn't need to have full
compatibility.  The best way I could think to warn users and maintain
compatibility is to default to the old parser and let users choose to
use the new one.

> ext/syck/lib/syck.rb: YAML.generic_parser is deprecated, switch to psych"
> ext/syck/lib/syck.rb: YAML.resolver is deprecated
> ext/syck/lib/syck.rb: YAML.emitter is deprecated
> ext/syck/lib/syck.rb: YAML.each_document is deprecated
> ext/syck/lib/syck.rb: YAML.each_node is deprecated
> ext/syck/lib/syck.rb: YAML.parse_documents is deprecated, use load_stream
> ext/syck/lib/syck.rb: YAML.add_ruby_type is deprecated, use add_domain_ty
> ext/syck/lib/syck.rb: YAML.add_private_type is deprecated, use add_domain
> ext/syck/lib/syck.rb: YAML.detect_implicit is deprecated
> ext/syck/lib/syck.rb: YAML.tagurize is deprecated
> ext/syck/lib/syck.rb: YAML.transfer is deprecated
> ext/syck/lib/syck.rb: YAML.try_implicit is deprecated
> ext/syck/lib/syck.rb: YAML.read_type_class is deprecated
> ext/syck/lib/syck.rb: YAML.object_maker is deprecated
> ext/syck/lib/syck.rb: YAML.quick_emit is deprecated
> ext/syck/lib/syck/basenode.rb: select is deprecated
> ext/syck/lib/syck/basenode.rb: select!() is deprecated
> ext/syck/lib/syck/basenode.rb: search() is deprecated
> ext/syck/lib/syck/basenode.rb: at() is deprecated
> ext/syck/lib/syck/basenode.rb: match_path is deprecated
> ext/syck/lib/syck/basenode.rb: match_segment is deprecated
> ext/syck/lib/syck/basenode.rb: children_with_index is deprecated, use
> ext/syck/lib/syck/encoding.rb: YAML.escape is deprecated
> ext/syck/lib/syck/encoding.rb: YAML.unescape is deprecated
> ext/syck/lib/syck/stream.rb: edit is deprecated
> ext/syck/lib/syck/stringio.rb: yaml/stringio is deprecated
> ext/syck/lib/syck/ypath.rb: YAML::YPath is deprecated

I am happy to add most of these to Psych, *if* Psych is going to be the
default parser.  I do not want to support these methods long term
though.  Please give me a clear direction, and I will make it happen.

-- 
Aaron Patterson
http://tenderlovemaking.com/