[D-runtime] win32 regression in exception handling

[Jonathan M Davis]

On Wednesday 26 January 2011 04:35:13 Don Clugston wrote:
> On 26 January 2011 12:21, Jonathan M Davis <jmdavisProg at gmx.com> wrote:
> > On Wednesday 26 January 2011 03:02:55 Don Clugston wrote:
> >> On 26 January 2011 11:17, Jonathan M Davis <jmdavisProg at gmx.com> wrote:
> >> > On Wednesday 26 January 2011 01:58:50 Don Clugston wrote:
> >> >> On 26 January 2011 10:32, Jonathan M Davis <jmdavisProg at gmx.com> wrote:
> >> >> > How else would an error be thrown?
> >> >> 
> >> >> In many cases, it's thrown by hardware. The exception object is
> >> >> created long after the throw occurred.
> >> >> There are also 'foreign' exceptions, which are thrown by (say) C++.
> >> >> 
> >> >> (I suspect that Linux DMD can't handle any of those -- but Windows
> >> >> DMD can).
> >> > 
> >> > So, what exactly about that makes it a problem that the file and line
> >> > number have default arguments? If it gives the arguments (like it
> >> > pretty much has to be doing),
> >> 
> >> No, it doesn't give the arguments. It has no way of knowing what they
> >> are (in fact, they may not even exist at all).
> >> 
> >> then it doesn't use the defaults, so they don't cause any problems
> >> 
> >> > there. And is it only file and line number which cause problems if
> >> > they have defaults, or is it everything (e.g. Throwable next)?
> >> 
> >> It's only file and line number that are a problem. next will just be
> >> null. The thing which you're maybe not understanding is that in these
> >> cases, the exception object is created when it is caught, not when it
> >> is thrown.
> > 
> > Well, I certainly I have no clue about what is really going on then, and
> > it would probably take a fair bit of discussion and/or research for me
> > to understand. Obviously, there's stuff going on here that's at a far
> > lower level than I'm used to dealing with.
> 
> Yeah, it's a bit hairy. It took me a few weeks to work out what's going on.
> There's all kinds of weird stuff, where you make function calls that
> never return, because the stack disappears...
> In the end, the whole thing is an elaborate illusion that gives you a
> really nice model to program against.
> Fortunately, all of the weirdness is confined to a very small number
> of functions.
> 
> > Regardless, is it all Throwables that have the problem, or is it just
> > Throwable, Exception, and or Error? Throwable and Error really shouldn't
> > be a problem, since programmers wouldn't normally be creating those (at
> > most, they'd be creating objects derived from them), but you definitely
> > lose something if Exception has the problem as well. And you
> > _definitely_ lose something if _all_ Throwables have the problem. In any
> > case, I need to know which ones are a problem if I'm going to fix them.
> 
> It is only Throwable, and Error. Not anything derived from them.
> (Really, I think both of those should eventually become abstract
> classes anyway. Not right now, because compiler changes are required).

Well, that shouldn't be much of a problem then. I really would have expected 
them to be abstract anyway. I'll check in a fix shortly.

- Jonathan M Davis