Re: [RFAv7 0/3] Allow the user to define default args for aliases

[Simon Marchi <simark@simark.ca>]

On 2020-06-14 12:39 p.m., Philippe Waroquiers via Gdb-patches wrote:
> Allow the user to define default args for user-defined aliases.
> 
> This is version 7 of the patch series.
> Compared to version 6, it implements the prevention of
> defining an alias of an alias having default args, as suggested
> by Simon.

Huh, I just realized it's still possible to get into that situation
because of the "set default-args" command:

(gdb) alias aaa = backtrace
(gdb) alias bbb = aaa -past-main
(gdb) set default-args aaa -full

With the current implementation where default args are resolved at define
time, `bbb` will only have `-past-main` as its default args.  But if we
later implement the feature where default args are resolved at use time,
that behavior will change.

I kind of feel like the bad guy because I keep suggesting to reduce the
scope of the feature but... is there a good use case at the moment for
"set default-args", compared to passing default args when defining the
alias?  A use case where you wouldn't know the default args before
defining the alias?  If not, removing "set default-args" would avoid it,
without loss of functionality.  Then we'd have to see if
"show default-args" makes sense without "set default-args".  It's still
possible to see the default args with "help <alias>".

That would make me feel comfortable enough about the feature to merge
it in time for GDB 10.  It is restricted enough that there's not much
risk of introducing a behavior we'll regret later, while still adding
something that has value, being able to add default args to aliases.

Once we have evaluation of default args at runtime, I think it would
be fine to have "set default-args", if you think it's useful.  Using it
on a command X would implicitly affect all the aliases based on X, which
is what I would expect as a user.

Simon