From: Paul Brannan <pbrannan@...>
Date: 2007-10-23T06:20:36+09:00
Subject: Re: Improving 'syntax error, unexpected $end, expecting kEND'?

On Fri, Oct 19, 2007 at 03:01:55AM +0900, Hugh Sasse wrote:
> I've had a look at this, but can't see how to do it: When I get 
>   syntax error, unexpected $end, expecting kEND
> I know from experience that $end means "end of file" and kEND means
> the lexical token "end".  What I can't figure out from reading

IMO this is a pretty cryptic message.  It gets easier to diagnose the
more you see the message, but I'd rather see a message like:

  Syntax error: unexpected end of file while looking for matching 'end'

> parse.c is how the stack works and how the rules are stored. I think
> knowing if it was expecting the 'end' from a 'class', 'def', 'begin'
> 'while', 'for', 'do', 'if', 'unless' or 'case' would help me narrow
> down where I've failed to have a closing "end".  If there's line
> number information that would be even better.  Indentation has not
> solved this for me.

Indentation may not solve the problem, but it does help.

When all else fails I comment out sections of code until the code
compiles; when that happens, I know the offending code is probably in
the code block I most recently commented out.

I don't think that specifying which element was missing the end
necessarily helps track down the problem.  Consider:

  class Foo
  def foo
  while true
  end
  return 42
  end
  1+2

With your proposed change I might expect to see something like:

  Syntax error: unexpected end of file; expecting matching 'end' for 'class Foo'

but blindly putting an 'end' after bar() might be wrong; the user might
have meant either:

  class Foo
    def foo
      while true
      end
      return 42
    end
    bar()
  end

or:

  class Foo
    def foo
      while true
      end
      return 42
    end
  end
  bar()

but it's impossible to know without probing the user's brain (though
analyzing indentation could possibly help).

Paul