From: Brian Candler <B.Candler@...>
Date: 2004-10-07T22:37:55+09:00
Subject: Re: quality of error messages

On Thu, Oct 07, 2004 at 10:08:59PM +0900, Gavin Sinclair wrote:
> >   class Foo
> >     def m1
> >       if 1 == 2
> >         puts "Bad"
> >     end
> >     raise unless Class === self   # nothing happens
> >   end
> 
> Try
> 
>   puts 'foo'
> 
> then.  If it's in a class, it will print it.  If it's in a method, it
> won't.  Good enough for debugging?

Hmm: puts "OK at #{__LINE__}" if Class === self

Well, this statement won't be executed until the whole file has been
successfully parsed first. So if you take an example like this:

---- 8< ----
#!/usr/local/bin/ruby -w

def checkpoint(x)
  puts "OK(#{x}) at #{caller[0]}"
end

checkpoint(:Foo)
class Foo
  checkpoint(:bar)
  def bar(x)
    if x == 3
      puts "hello"
  end
  checkpoint(:baz)
  def baz(y)
  end
  checkpoint("end of Foo")
end
---- 8< ----
$ ruby ert.rb
ert.rb:18: syntax error

Then you have to keep adding 'end' statements until it parses successfully.
You then get:

OK(Foo) at ert.rb:7
OK(bar) at ert.rb:9

at which point you can cross-reference to each of the checkpoint lines in
the code, until you find which checkpoint(s) are missing from the output.

I guess it's feasible... but it would be much better if it could work the
other way round, and show you were the error was, not where the good lines
were :-)

Cheers,

Brian.