bug#72667: 31.0.50; gud-print moves the cursor after execution

bug#72667: 31.0.50; gud-print moves the cursor after execution

[TatriX]

When one runs `gud-print' with `C-x C-a C-p`, point moves to a line that
 is the debugger stopped at instead of staying where it was. I'm not
 sure if it is an intended behaviour. If it is, it would be very nice if
 one could override it, since I find that I want the point to keep it's
 position after I print a value. I can always run `C-x C-a C-l` to jump
 to the currently executing line.

Here's a an illustration. Suppose you have a program `test.c':

```
    int main() {
      int a = 42;
      int b = 13;
      int c = 69;
      return a + b + c;
    }
```

Which you can compile for example like this: `gcc -g -Wall -o test01 test.c'.
Now, if you stop execution at `int b', move the point to `int a' and run
`C-x C-a C-p' the point will jump back to `int b' instead of staying at
`int a'.

Thanks!

----------------------------------------------------------------------------


In GNU Emacs 31.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.43, cairo version 1.18.0) of 2024-07-29 built on twork
Repository revision: e4d22abcab60ead179e7d114faa4c2def559cfbb
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101013
System Description: Arch Linux

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bug#72667: 31.0.50; gud-print moves the cursor after execution

[Eli Zaretskii]

> From: TatriX <tatrics@gmail.com>
> Date: Fri, 16 Aug 2024 13:38:26 +0200
> 
> When one runs `gud-print' with `C-x C-a C-p`, point moves to a line that
>  is the debugger stopped at instead of staying where it was. I'm not
>  sure if it is an intended behaviour. If it is, it would be very nice if
>  one could override it, since I find that I want the point to keep it's
>  position after I print a value. I can always run `C-x C-a C-l` to jump
>  to the currently executing line.
> 
> Here's a an illustration. Suppose you have a program `test.c':
> 
> ```
>     int main() {
>       int a = 42;
>       int b = 13;
>       int c = 69;
>       return a + b + c;
>     }
> ```
> 
> Which you can compile for example like this: `gcc -g -Wall -o test01 test.c'.
> Now, if you stop execution at `int b', move the point to `int a' and run
> `C-x C-a C-p' the point will jump back to `int b' instead of staying at
> `int a'.

I think this is an intentional feature: after each GUD command Emacs
returns point to the current line as indicated by the debugger.  The
intent is to keep the current line always visible on display.  Since
Emacs doesn't really understand the effect of debugger commands, it
must restore point after each such command.

May I ask why you use gud-print and not gud-tooltip-mode?  The latter
will allow you to show values of variables without moving point.

bug#72667: 31.0.50; gud-print moves the cursor after execution

[Eli Zaretskii]

[Please use Reply All to reply, to keep the bug tracker CC'ed.]

> From: TatriX <tatrics@gmail.com>
> Date: Sat, 17 Aug 2024 15:41:54 +0200
> 
> > May I ask why you use gud-print and not gud-tooltip-mode?  The latter
> > will allow you to show values of variables without moving point.
> 
> I do use it sometimes. Most of the time I just switch to *gud* buffer
> and print the values manually, which requires quite some window
> switching.
> 
> I suppose what I would prefer is to be able to run something similar to
> gud-print which would ask me for an expression, defaulting to whatever
> is near the point. Still, moving the point is undesirable since it
> changes what is in focus.
> 
> I tried to change the behavior myself, but couldn't find what actually
> moves the point.

I think it happens in gud-refresh.

bug#72667: 31.0.50; gud-print moves the cursor after execution

[TatriX]

> I think it happens in gud-refresh.

I thought that too, but at least when I edebug-it, debugger doesn't stop
in it.

It looks like it happens during one of the invocations of gud-filter
after gud-call send the data to the gdb.

Point moves when gud-marker-filter which is set to
gud-gdbmi-marker-filter is called.  Which in turns call gdbmi-bnf-output
and it seems that the point moves in gdbmi-bnf-out-of-band-record.

The callstack is quite deep and there are a lot of loops, so I wasn't
able to pin point a specific piece of code that actually moves the point
yet.