Re: GDB/MI interactive capability?

[Vladimir Prus <vladimir.prus@gmail.com>]

On 04/29/2015 06:30 PM, Joel Brobecker wrote:
>> I think a bigger problem is that it will make the MI protocol itself stateful.
>> Right now, we have GDB and program state, of course, but each MI command is
>> generally independent of any other one. The above proposal will basically
>> create interdependencies between MI commands.
>
> OK, makes sense.
>
>>> Another idea, which might be easier to implement, would be to use
>>> a two-step approach where the first step is to return an error
>>> that shows the various choices the user can choose, have the IDE
>>> use that to query the user, and then have the IDE resubmit the
>>> expression evaluation, this time with the choice given by the user.
>>
>> That would work just fine, I think. GDB can report the ambiguities it
>> finds, and the frontend can resubmit the expression with appropriate
>> syntax to disambiguate.  I don't know whether there's appropriate
>> syntax for Ada, in C++ a cast to appropriate type is sometimes used to
>> select the right function, e.g.:
>>
>> 	static_cast<void (C::*)(int)>(&C::foo)
>>
>> is the standard example. The downside is that GDB might have to know a
>> bit more about language than now, or a special syntax might have to be
>> introduced.
>
> It wouldn't work in GDB, because overload resolution is extremely
> complex, and not something we want to implement in GDB. Right now,
> we have a primitive resolver, doing the easiest part of the resolution,
> but nothing more.

I don't think the above requires overload resolution, it requires that GDB pick a member
function whose signature exactly matches the cast destination type, which should be quite
possible. I can't really think of an example where ambiguity cannot be resolved by
language expression - except for function templates, but GDB can't do much with them
anyway. But see below.

> So, I think having a way to just pass the answer back to the query
> would be the way to go. And it'd be more general in case we want
> to ask other things that are not related to symbol resolution.

True, passing responses to queries via an option is a more general solution. Also,
it means that frontend does not have to know how to transform expression to disambiguate
things - it can just pass the responses.


-- 
Vladimir Prus
CodeSourcery / Mentor Embedded
http://vladimirprus.com