From: nobu.nokada@...
Date: 2003-11-29T18:53:07+09:00
Subject: Re: re-raising an exception with the original backtrace

Hi,

At Sat, 29 Nov 2003 08:53:40 +0900,
Joel VanderWerf wrote:
> Ooh, that's nice. I thought 'raise' would just re-raise the _last_ 
> exception, but it's actually sensitive to the dynamic context. The 
> example below would fail in the former case, but since it succeeds, I 
> guess raise looks back down the stack and re-raises the first exception 
> it finds there?

But I found that outer $! was preserved only in rescue clauses,
in 1.6.8 and 1.8.1.

> $ cat exception.rb
> 
>    class MyError < StandardError; end
> 
>    def foo
>      raise MyError
>    end
> 
>    def main
>      foo
>    rescue Exception => e
>      handler(e)
>    end
> 
>    class OtherError < StandardError; end
     def do_something_that_might_use_exceptions(retrying = false)
>      raise OtherError
>    rescue Exception => e
       retry if (retrying ^= true)
>      p e
>      false
>    end
> 
>    def handler(e)
>      ok = do_something_that_might_use_exceptions
>      if ok
>        return true
>      else
>        puts "backtrace:", e.backtrace, "---"
>        raise
>      end
>    end
> 
>    main

$ ruby -v exception.rb
ruby 1.8.1 (2003-11-28) [i686-linux]
#<OtherError: OtherError>
backtrace:
exception.rb:4:in `foo'
exception.rb:8:in `main'
exception.rb:32
---
exception.rb:28:in `handler': unhandled exception
	from exception.rb:10:in `main'
	from exception.rb:32

In other words, only changing $! in rescue clauses has no
effect for outside.

I suspect that rescue blocks should preserve $! value when no
exception raised and $! should not be cleared at retry.


Index: eval.c
===================================================================
RCS file: /cvs/ruby/src/ruby/eval.c,v
retrieving revision 1.598
diff -u -2 -p -r1.598 eval.c
--- eval.c	27 Nov 2003 19:15:29 -0000	1.598
+++ eval.c	29 Nov 2003 09:48:56 -0000
@@ -2857,4 +2857,5 @@ rb_eval(self, n)
 	    PUSH_TAG(PROT_NONE);
 	    if ((state = EXEC_TAG()) == 0) {
+	      retry_entry:
 		result = rb_eval(self, node->nd_head);
 	    }
@@ -2865,9 +2866,8 @@ rb_eval(self, n)
 		else if (state == TAG_RETRY) {
 		    rescuing = state = 0;
-		    e_info = ruby_errinfo = Qnil;
-		    result = rb_eval(self, node->nd_head);
+		    ruby_errinfo = e_info;
+		    goto retry_entry;
 		}
 		else if (state != TAG_RAISE) {
-		    ruby_errinfo = e_info;
 		    result = prot_tag->retval;
 		}
@@ -2883,5 +2883,4 @@ rb_eval(self, n)
 			rescuing = 1;
 			result = rb_eval(self, resq->nd_body);
-			ruby_errinfo = e_info;
 			break;
 		    }
@@ -2893,4 +2892,5 @@ rb_eval(self, n)
 	    }
 	    POP_TAG();
+	    if (state != TAG_RAISE) ruby_errinfo = e_info;
 	    if (state) {
 		if (state == TAG_NEXT) prot_tag->retval = result;


-- 
Nobu Nakada