Re: MI and anonymous unions

[Jim Ingham <jingham at apple dot com>]

On Nov 15, 2006, at 9:27 AM, Vladimir Prus wrote:

> On Wednesday 15 November 2006 20:20, Jim Ingham wrote:
> > Support for anonymous unions & structures is another of the "things  
> > we
> > fixed but haven't submitted back"...  We do pretty much what Vladimir
> > suggests, though I use #anon#N for the varobj name: the choice  
> > doesn't
> > much matter.  We still return a blank expression (since that's really
> > what the  There's one other tricky bit 'caused by the fact that you
> > might have more than one anonymous union or structure inside a
> > structure.  This wouldn't be a problem, but the varobj code tends to
> > look up structure elements by name, which obviously won't work here.
> > So you have to convert all the code that looks up structure elements
> > to use the index rather than the name.
>
> Ah, I see. So this is not as easy change as I though.

Yeah, I looked at the patch against our sources, and it is not hard,  
but it is annoyingly large.  Mostly just a matter of having to push  
stuff through interfaces where it wasn't intended to go.  I did it in  
two steps, because I didn't think about this complexity at first.  So  
I did the trivial bit with just adding the anon.  Then the major patch  
you can fetch from the Apple CVS with:

cvs -q diff -p -r 1.83 -r 1.84 varobj.c

> > Another of the things we do in our varobj code for C++ is that we  
> > look
> > up the dynamic type of objects (the same mechanism that "set print
> > object on" uses, and the value & children we return are based on the
> > dynamic type.  As soon as you do that, you really do need a "give me
> > the expression that can recreate this varobj" for child varobj's.
> > Otherwise the MI client needs to get all these dynamic casts right to
> > get down to the proper child, which is a bit of a pain.
>
> Good point.
>
> > But it's a generally useful command.  We called it "var-info-path-
> > expression" and given a varobj, it returns the expression that if
> > evaluated would result in the same value.  Xcode uses this for "show
> > in separate window" actions in the debugger variable view.  You can
> > also use the to eliminate the "." for the anonymous structures or
> > unions - though of course the MI client could do this too...
>
> In fact, I've posted a patch that ports -var-info-path-expression to  
> mainline
> some time ago and we talked briefly with Daniel some time ago.
>
> I'll see if I can revive that patch.

Thanks...

I just noticed that that code doesn't actually handle the anonymous  
structure case properly.  You have to check if the structure name is  
anonymous and not emit an extra ".".  Grrr...  I haven't fixed it yet.

Jim