From: Jacob Fugal <lukfugl@...>
Date: 2005-10-19T02:48:59+09:00
Subject: Re: Strange error: QtRuby and AR (sqlite3)

On 10/18/05, Hans  Fugal <fugalh@gmail.com> wrote:
> I'm developing a recipe app for my wife using ActiveRecord (with
> sqlite3) and QtRuby. It "works" on my iBook, but when I try to test it
> on my Debian sarge box I get the following:
>
> /usr/local/lib/site_ruby/1.8/rubygems.rb:172:in `method_missing':
> unresolved method call (ArgumentError)

Having the luxury of access to Hans' development environment, I
tracked this down. It was a nasty little bugger, and eventually the
fault of QtRuby, but the patch here[1] is against rubygems to help
gems protect itself against other libraries making mistakes like this.

The code in question is from rubygems.rb:

      # Now add the require_paths to the LOAD_PATH
      spec.require_paths.each do |path|
        $:.unshift File.join(spec.full_gem_path, path)
      end

The middle line was throwing the error. Seems really odd for a
method_missing error to show up there, right? $:, File and the gemspec
are all known quantities... or so we thought.

What had happened was that somehow Qt::File had been imported into the
current namespace and occluded ::File from core. When Hans' code tried
to load a gem, the gems code ended up trying to call Qt::File.join,
rather than ::File.join. Qt::File doesn't have a join method, but does
handle missing methods in exactly the manner shown in Hans' error.

The morals of the story?

1) Don't occlude core libraries
2) Use super as the default behavior for method_missing

Regarding 2, if Qt::*'s implementation of method_missing were to
bounce up to super when a suitable replacement could not be found, the
error probably would have looked something like "NoMethodError:
undefined method `join' for Qt::File:Module", rather than the
singularly unhelpful "unresolved method call (ArgumentError)". The
error would have made it abundantly clear what the problem actually
was.

Jacob Fugal

[1] Patch follows:

--- /tmp/rubygems.rb.old        2005-10-18 11:43:11.000000000 -0600
+++ /usr/local/lib/site_ruby/1.8/rubygems.rb    2005-10-18
11:43:32.000000000 -0600
@@ -169,7 +169,7 @@

       # Now add the require_paths to the LOAD_PATH
       spec.require_paths.each do |path|
-       $:.unshift File.join(spec.full_gem_path, path)
+       $:.unshift ::File.join(spec.full_gem_path, path)
       end

       require spec.autorequire if autorequire && spec.autorequire