Proposed changes to empty command handling in JDB

[Chris Plummer]

On 8/5/21 10:42 AM, Jakob Cornell wrote:
> Hi Alan, thanks for the input.
>
>> The gdb behavior is context dependent and not clear to me that it's 
>> worth trying to add it to jdb.
>
> Could you provide some more detail about the context upon which GDB's 
> behavior depends?  And are you saying that my proposed changes aren't 
> worth adding, or that it's not worth replicating the exact behavior of 
> GDB?  In my opinion a straightforward approximation of GDB's behavior 
> will be more convenient for users than the current behavior.
I believe only "list" and "x" have content dependent behavior. I'm not 
sure of the list of commands that are purposefully not repeated, such as 
"run".
>
>> If it is added then I think Chris is right that is might have to be 
>> disabled by default as it could otherwise break existing 
>> scripts/tests with empty lines. One place for configuration ~/.jdbrc 
>> and it might be that it can only be enabled for interactive sessions.
>
> Okay, so it sounds like rather than using a command line option you're 
> suggesting we create new JDB commands (e.g. `repeat' and `norepeat') 
> to enable/disable the feature, plus a check (`System.console() != 
> null' perhaps?) that honors `repeat' only in an interactive session.  
> This sounds fine to me, although I suspect it becomes a lot more 
> difficult to test this feature when it doesn't work in non-interactive 
> sessions.
>
>> If usability is an issue then maybe it would be better to look at 
>> jshell  (the REPL that has been included since JDK 9). It makes us of 
>> jline so you get better input navigation, history navigation, and tab 
>> completion.  I suspect there is an interesting project there.
>
> Thanks for this tip; line editing is also on my wishlist for JDB, so I 
> would be interested in a jline integration.  However, based on the JBS 
> discussion Chris seems to have sort of the opposite view; that a jline 
> integration likely isn't worth the effort whereas command repetition 
> may be.  I would be interested in both, since I think automatic 
> repetition provides utility beyond line editing, and I would be 
> willing to work on both, but I want to make sure I end up with a 
> change that someone is willing to sponsor and review.
Yes, your last comment is part of what I was getting at when I said this 
is probably not worth the effort. It will take a fair amount of review 
effort, and as I pointed out in my previous email, in general jdb is not 
high priority and we shouldn't be directing much of our time to it.

thanks,

Chris
>
> Jakob