Re: RFC: MI - Detecting change of string contents with variable objects

[Vladimir Prus <ghost at cs dot msu dot su>]

On Thursday 04 January 2007 23:50, Daniel Jacobowitz wrote:
> On Fri, Jan 05, 2007 at 09:34:53AM +1300, Nick Roberts wrote:
> >  > Otherwise the patch seems fine, if it tests OK, but I'm still a little
> >  > nervous about it.  For example, you'll call val_print on a struct
> >  > or array to see if it's changed.  Depending on things like "set print
> >  > elements", that might not print out the whole string.  This is
> >  > probably a behavior change.  Is it a harmless one?  If it is, then
> >  > should we be sharing the code with c_value_of_variable that avoids
> >  > printing structs, unions, and arrays, and never mark them as changed
> >  > unless their types change?
> > 
> > The function val_print is already used for -var-evaluate-expression.
> 
> Not in the case I was talking about.  -var-evaluate-expression calls
> varobj_get_value, which calls c_value_of_variable, and will return
> "{...}" for a struct.  Won't it?
> 
> > AFAICS "set print elements" has no effect on variable objects,
> > perhaps because val_print is only called on the leaves but I can see
> > that using it might expose MI to the vagaries of CLI.  Currently,
> > however, string changes don't get reported at all, without the user
> > changing configuration values.
> 
> "set print elements" will affect the output of character pointers, but
> that's not really what I'm worried about - you're now going to print
> out most of an array or struct when comparing print_value.
> 
> 1. Can always set print_value to what c_value_of_variable would return?
> 
> 2. Currently I believe we will mark an array varobj as updated in
> -var-update if any of its children change.  

We never mark array varobj as changed, I believe. array varobj is included
in -var-update output only if the type of the array changes, IIRC.

> I'm not sure if we'll do 
> that any more after your patch, e.g. if something beyond the limit of
> "set print elements" changes.  So, do you think any front end relies on
> the parent being marked updated if any of its children are?  Vlad,
> any opinion?

I think the code in question is never executed for structures or arrays -- only
for "changeable" values.

- Volodya