Rails - Dec 2008 - [Bug] !nil returns false for partial instance variable in specific conditions.

Hi,
If we call a partial with a name such that there also exists a
instance variable with the same name (ex: @identity) in the controller
then passing :object => nil to render() and calling (!
identity).inspect in ''_identity.html.erb'' prints false while
identity.inspect prints nil.

Here is a more specific description -

Let there be a controller named Check.

class CheckController < ApplicationController
  def index
    @identity = nil
  end
end

views/check/index.html.erb contains -
<%= render :partial => ''identity'', :object => nil
%>

views/check/_identity.html.erb contains -
<pre>
  identity is <%= identity.inspect %>
  !identity is <%= (!identity).inspect %>
</pre>


calling localhost:3000/check/ prints -
  identity is nil
  !identity is false

NOTE:
1. There must be a controller instance variable with the same name as
of partial.
2. I have been able to trace the problem down to between line 31 and
42 of file
http://github.com/rails/rails/tree/dc0411fad78bfc92fe92dc88bbad726eb4d1a883/actionpack/lib/action_view/renderable_partial.rb

I''m using -
Rails 2.2.2
Ruby 1.8.6 (2007-09-14 patchlevel 111) [i386-mswin32]
RubyGems 1.3.1
Windows XP Home Ed. SP3

I''ve also uploaded a sample app folder at
http://code.google.com/p/googol/source/browse/?r=95#svn/lab/learning/ruby-bug-on-!nil/app/controllers

- thanks

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On Dec 7, 5:35 am, Vikrant
<nas...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi,
> If we call a partial with a name such that there also exists a
> instance variable with the same name (ex: @identity) in the controller
> then passing :object => nil to render() and calling (!
> identity).inspect in ''_identity.html.erb'' prints false
while
> identity.inspect prints nil.
>
The key here is
http://github.com/rails/rails/commit/acbf2b74aa3001fb6064bba96cd0033495774357

What is being deprecated is render :partial => ''foo''
automatically
taking the value of @foo.
The way that this is done is that the foo object in your partial is
actually a tiny proxy object. If you try and do anything with that
object it will just pass it on to the real object (and print a small
deprecation notice - you should see these in your logs).
Ruby being ruby, ==, inspect, class etc... can all be passed on to the
target objects - they are just method calls after all.
That is not true of ! though, which just flips nil/false to true and
everything else to false and so you get the behaviour you demonstrate.


Fred
> Here is a more specific description -
>
> Let there be a controller named Check.
>
> class CheckController < ApplicationController
>   def index
>     @identity = nil
>   end
> end
>
> views/check/index.html.erb contains -
> <%= render :partial => ''identity'', :object =>
nil %>
>
> views/check/_identity.html.erb contains -
> <pre>
>   identity is <%= identity.inspect %>
>   !identity is <%= (!identity).inspect %>
> </pre>
>
> calling localhost:3000/check/ prints -
>   identity is nil
>   !identity is false
>
> NOTE:
> 1. There must be a controller instance variable with the same name as
> of partial.
> 2. I have been able to trace the problem down to between line 31 and
> 42 of
filehttp://github.com/rails/rails/tree/dc0411fad78bfc92fe92dc88bbad726eb4...
>
> I''m using -
> Rails 2.2.2
> Ruby 1.8.6 (2007-09-14 patchlevel 111) [i386-mswin32]
> RubyGems 1.3.1
> Windows XP Home Ed. SP3
>
> I''ve also uploaded a sample app folder
athttp://code.google.com/p/googol/source/browse/?r=95#svn/lab/learning/...
>
> - thanks
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Yes, that might be the "reason" (though not technically strong enough
to understand that proxy thing), but still I find it as a bug. It just
breaks the common assumptions (assumption is perhaps wrong word, it
breaks just how it must work). nil is after all "not true" (and so is
!
nil).
It took me 4+ hours to figure out what went wrong and where (I''m not
complaining though).

On Dec 7, 3:13 pm, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On Dec 7, 5:35 am, Vikrant
<nas...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > Hi,
> > If we call a partial with a name such that there also exists a
> > instance variable with the same name (ex: @identity) in the controller
> > then passing :object => nil to render() and calling (!
> > identity).inspect in ''_identity.html.erb'' prints
false while
> > identity.inspect prints nil.
>
> The key here
ishttp://github.com/rails/rails/commit/acbf2b74aa3001fb6064bba96cd00334...
>
> What is being deprecated is render :partial => ''foo''
automatically
> taking the value of @foo.
> The way that this is done is that the foo object in your partial is
> actually a tiny proxy object. If you try and do anything with that
> object it will just pass it on to the real object (and print a small
> deprecation notice - you should see these in your logs).
> Ruby being ruby, ==, inspect, class etc... can all be passed on to the
> target objects - they are just method calls after all.
> That is not true of ! though, which just flips nil/false to true and
> everything else to false and so you get the behaviour you demonstrate.
>
> Fred
>
> > Here is a more specific description -
>
> > Let there be a controller named Check.
>
> > class CheckController < ApplicationController
> >   def index
> >     @identity = nil
> >   end
> > end
>
> > views/check/index.html.erb contains -
> > <%= render :partial => ''identity'', :object
=> nil %>
>
> > views/check/_identity.html.erb contains -
> > <pre>
> >   identity is <%= identity.inspect %>
> >   !identity is <%= (!identity).inspect %>
> > </pre>
>
> > calling localhost:3000/check/ prints -
> >   identity is nil
> >   !identity is false
>
> > NOTE:
> > 1. There must be a controller instance variable with the same name as
> > of partial.
> > 2. I have been able to trace the problem down to between line 31 and
> > 42 of
filehttp://github.com/rails/rails/tree/dc0411fad78bfc92fe92dc88bbad726eb4...
>
> > I''m using -
> > Rails 2.2.2
> > Ruby 1.8.6 (2007-09-14 patchlevel 111) [i386-mswin32]
> > RubyGems 1.3.1
> > Windows XP Home Ed. SP3
>
> > I''ve also uploaded a sample app folder
athttp://code.google.com/p/googol/source/browse/?r=95#svn/lab/learning/...
>
> > - thanks
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On 7 Dec 2008, at 17:19, Vikrant wrote:
>
> Yes, that might be the "reason" (though not technically strong
enough
> to understand that proxy thing), but still I find it as a bug. It just
> breaks the common assumptions (assumption is perhaps wrong word, it
> breaks just how it must work). nil is after all "not true" (and
so
> is !
> nil).
Short version is that the thing that looks like nil isn''t actually nil
What it''s trying to tell you is that having @identity magically  
assigned to identity in partials called identity is deprecated

Fred

>
> It took me 4+ hours to figure out what went wrong and where (I''m
not
> complaining though).

>
>
> On Dec 7, 3:13 pm, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> wrote:
>> On Dec 7, 5:35 am, Vikrant
<nas...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>
>>> Hi,
>>> If we call a partial with a name such that there also exists a
>>> instance variable with the same name (ex: @identity) in the  
>>> controller
>>> then passing :object => nil to render() and calling (!
>>> identity).inspect in ''_identity.html.erb'' prints
false while
>>> identity.inspect prints nil.
>>
>> The key here
ishttp://github.com/rails/rails/commit/acbf2b74aa3001fb6064bba96cd00334
>> ...
>>
>> What is being deprecated is render :partial =>
''foo'' automatically
>> taking the value of @foo.
>> The way that this is done is that the foo object in your partial is
>> actually a tiny proxy object. If you try and do anything with that
>> object it will just pass it on to the real object (and print a small
>> deprecation notice - you should see these in your logs).
>> Ruby being ruby, ==, inspect, class etc... can all be passed on to  
>> the
>> target objects - they are just method calls after all.
>> That is not true of ! though, which just flips nil/false to true and
>> everything else to false and so you get the behaviour you  
>> demonstrate.
>>
>> Fred
>>
>>> Here is a more specific description -
>>
>>> Let there be a controller named Check.
>>
>>> class CheckController < ApplicationController
>>>   def index
>>>     @identity = nil
>>>   end
>>> end
>>
>>> views/check/index.html.erb contains -
>>> <%= render :partial => ''identity'', :object
=> nil %>
>>
>>> views/check/_identity.html.erb contains -
>>> <pre>
>>>   identity is <%= identity.inspect %>
>>>   !identity is <%= (!identity).inspect %>
>>> </pre>
>>
>>> calling localhost:3000/check/ prints -
>>>   identity is nil
>>>   !identity is false
>>
>>> NOTE:
>>> 1. There must be a controller instance variable with the same name
>>> as
>>> of partial.
>>> 2. I have been able to trace the problem down to between line 31
and
>>> 42 of
filehttp://github.com/rails/rails/tree/dc0411fad78bfc92fe92dc88bbad726eb4
>>> ...
>>
>>> I''m using -
>>> Rails 2.2.2
>>> Ruby 1.8.6 (2007-09-14 patchlevel 111) [i386-mswin32]
>>> RubyGems 1.3.1
>>> Windows XP Home Ed. SP3
>>
>>> I''ve also uploaded a sample app folder
athttp://code.google.com/p/googol/source/browse/?r=95#svn/
>>> lab/learning/...
>>
>>> - thanks
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