Re: [RFA] PR python/13598 - add before_prompt event

[Matt Rice <ratmice@gmail.com>]

On Fri, Jul 22, 2016 at 3:01 AM, Yao Qi <qiyaoltc@gmail.com> wrote:
> Hi Tom,
>
> On Sat, May 21, 2016 at 6:00 AM, Tom Tromey <tom@tromey.com> wrote:
>> This adds an event that is emitted just before GDB presents a prompt
>> to the user.  This provides Python code a way to react to whatever
>> changes might have been made by the previous command.  For example, in
>> my GUI I use this to track changes to the selected frame and reflect
>> them in the UI.
>
> I read this patch multiple times, but don't know the motivation of adding this
> event.  In PR python/13598, you mentioned you want to get event when
> something is changed.  If so, why don't you add the python event for the changes
> you are interested in?  What is your use case of using python code in GDB?


FWIW, I have long used or more precisely abused the prompt_hook
function for controlling vi by vi --remote to have an editor that
tracks the current file/line which gdb is stopped at, a mechanism for
this which doesn't abuse the actual prompt string formatting functions
by producing some side-effect before returning the prompt string.
such as that proposed by Tom would be nice.

in particular abusing the prompt_hook in this fashion inhibits the
ability to use the python extended-prompt stuff for controlling the
prompt, because the extended-prompt stuff uses the prompt_hook itself!

In particular it's just a nice time to take a snapshot of some
otherwise obtainable property from gdb right before control is handed
back to the user.