Re: MI -break-info command issues

[Vladimir Prus <ghost@cs.msu.su>]

On Thursday 26 January 2006 23:43, Eli Zaretskii wrote:
> > From:  Vladimir Prus <ghost@cs.msu.su>
> > Date:  Thu, 26 Jan 2006 10:01:43 +0300
> >
> > Eli Zaretskii wrote:
> > >> The extra information doesn't pertain to breakpoint itself, it's gdb
> > >> opinion on formatting and is hardly usefull for machine interface.
> > >> IMO, of course.
> > >
> > > This output is produced by the UI-independent output functions.  So
> > > judging its usefulness from the point of view of a GUI is taking a too
> > > narrow view.  The advantage of ui_out routines is that ....
> >
> > I'm actually talking about MI *protocol*.
>
> What ``protocol''?

Let's replace "protocol" with "formal interface". I was told here that all 
frontends should use MI, because unlike console output, it's a formal 
interface. And I'd expect that "formal" means "designed in detail for 
specific task". That's why I don't understand the reasoning that MI response 
contains certain field just because some internal code works that way. That's 
backward -- if MI is to be formal interface, then MI spec should drive the 
code, not the other way around.

> > I think that usefulness of that
> > should be judged from the point of view of its intended clients -- that
> > are frontends, which nowdays means GUI. If MI is protocol specifically
> > designed for some task, then it should not include some fields just
> > because TUI needs those fields.
>
> You may, of course, unilaterally decide that GDB/MI was (or should be)
> meant for GUIs only, but that's not what it actually is about, as far
> as GDB development is concerned.

Can you name frontend that uses MI and that is not GUI, just as example.

> > > whoever writes
> > > the code defines the layout once, and then each UI gleans whatever it
> > > needs from the results.  The programmer who wrote the code does not
> > > need to bother which UI needs what information.  Yes, that means some
> > > of the info will be redundant or useless for certain types of UI, but
> > > that's by design, and I think the advantages of a single interface far
> > > outweigh the small annoyances of having to read and discard unused
> > > parts of the output.
> >
> > Why can't MI layer weed out unnecessary information?
>
> And we are back to the beginning of this discussion, sigh...

Ok, let's consider another command which does not share any implementation 
with console output: -data-read-memory, implemented entirely in mi-main.c.
The output from that command is:

      (gdb)5-data-read-memory shorts+64 d 2 1 1
      5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
      next-row="0x00001512",prev-row="0x0000150e",
      next-page="0x00001512",prev-page="0x0000150e",memory=[
      {addr="0x00001510",data=["128"]}]
      (gdb)

It includes fields like "next-page", which IMO, are not sufficiently 
documented. At the same time, the code to compute that field is this:

     ui_out_field_core_addr (uiout, "next-page", addr + total_bytes);

What is the point for machine interface to have a field that is not documented 
and that can be trivially computed by the frontend if needed? If you had the 
luxury to design MI from the start, would you include this field?

- Volodya