Use C++ exception model in D

[David Nadlinger]

On Tuesday, 8 April 2014 at 18:55:35 UTC, Brad Roberts wrote:
> I think, for a mixed language application, that the important 
> part is proper object lifetime management more than being able 
> to catch exceptions from different languages.  When unwinding a 
> c++ exception that has stack frames intermixed with D, 
> destructors need to be executed appropriately, and vice versa.

I haven't actually tried to do this, but in theory, this should 
be the easy part with libunwind. You just ignore foreign 
exceptions during the search phase (i.e. not catch them), and 
during the unwind phase, your own personality function is called 
again for cleanup regardless of the handler the stack actually 
unwinds to.

> This is also an important part of having abi compatibility 
> between D compilers, something which we don't have today but 
> really must have eventually.. hopefully not years away.

This really depends on somebody familiar with the DMD backend 
committing to going through with it. I think both on the GDC and 
LDC sides, there is agreement that we need to work on a common 
ABI. However, the whole thing would be somewhat of a futile 
effort without DMD on board as well.

On x86_64, ABI compatibility is not an unreasonable goal at all 
(and a very important one, in my opinion). There are some areas 
that will need a lot of careful spec'ing and likely entail 
changes in all three compilers, such as the construction of 
nested scopes. However, in some cases, e.g. exception unwinding, 
or proper variadic arguments, it's definitely the case that GDC 
and LDC would be easy to align, whereas DMD would have to give up 
its own bespoke solution. Does DMD still do things like magically 
accessing the scope of the parent function in in/out contract 
calls?

David