Use C++ exception model in D

[Brad Roberts]

On 4/8/14, 12:56 PM, David Nadlinger wrote:
> 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

Most of the areas where DMD is 'odd' are a case of "I can't figure out the right way, so any way is 
better than no way".  That's particularly true for var args and eh.  I'm confident that pulls that 
fix these issues can and will be accepted.  I'm less confident that someone will volunteer to fix 
it, but it's something I care about.