From: "Brian Schröder" <ruby.brian@...>
Date: 2005-04-29T21:04:09+09:00
Subject: Re: Compressing or modifying exception backtraces

On 29/04/05, Greg Millam <ruby-talk@lethalcode.net> wrote:
> In PageTemplate, a project of mine with Brian Wisti, we provide a
> framework of sorts that has a large number of layers between the call to
> PageTemplate.output, and a point where the user's own code is later called.
> 
> If an error exists in the user's code, it looks somewhat like this:
> 
> /home/walker/public_html/deafcode/rbsource/user_instance.rb:3:in
> `fullname': undefined local variable or method `last_nam' for
> #<User:0xb7b92e38> (NameError)
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/parser.rb:86:in `send'
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/parser.rb:86:in `get'
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/parser.rb:78:in `each'
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/parser.rb:78:in `get'
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/commands.rb:248:in `output'
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/commands.rb:145:in `output'
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/commands.rb:145:in `map'
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/commands.rb:145:in `output'
>      ... 13 levels...
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/commands.rb:145:in `output'
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/commands.rb:187:in `output'
>    from /home/walker/public_html/deafcode/rbsource/site.rb:90:in `output'
> from index.cgi:23
> 
> About 23 levels of output of PageTemplate alone.
> 
> What I'd like is to shorten that to one:
> 
> /home/walker/public_html/deafcode/rbsource/user_instance.rb:3:in
> `fullname': undefined local variable or method `last_nam' for
> #<User:0xb7b92e38> (NameError)
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/commands.rb:187:in `output'
>    from /home/walker/public_html/deafcode/rbsource/site.rb:90:in `output'
> from index.cgi:23
> 
> Is there any safe way to do this?
> 
> Alternately, I'd also like to potentially generate output like this:
> 
> /home/walker/public_html/deafcode/rbsource/user_instance.rb:3:in
> `fullname': undefined local variable or method `last_nam' for
> #<User:0xb7b92e38> (NameError)
>    from Template:user_profile.html in "Value: user.fullname"
>    from Template:user_profile.html in "If: user"
>    from Template:main_page.html in "Include user_profile.html"
>    from Template:main_page.html in "Loop users: user"
>    from /usr/lib/ruby/site_ruby/1.8/PageTemplate/commands.rb:187:in `output'
>    from /home/walker/public_html/deafcode/rbsource/site.rb:90:in `output'
> from index.cgi:23
> 
> Considerably more useful for the developer using PT.
> 
> Is it possible to modify the backtrace like this?
> 
> Thanks,
> 
> - Greg
> 
> 

You could expand on this theme:

#!/usr/bin/ruby 

def recurse(i)
  raise "No more recursion please" if i == 0
  recurse_a(i-1)
end

def recurse_a(i)
  recurse(i)
end

begin
  recurse(1000)
rescue => e
  puts e.inspect
  puts e.backtrace[0], '...', e.backtrace[-2..-1]
end

regards,

Brian

-- 
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