Re: [PATCH v2 2/5] gdb: prevent prefix commands from being hooks

[Simon Marchi via Gdb-patches <gdb-patches@sourceware.org>]

On 2021-01-25 6:26 a.m., Marco Barisione via Gdb-patches wrote:
> Currently it's possible for hooks to be prefix commands:
> 
>   define-prefix hook-run
> 
>   define hook-run
>     echo Will run!\n
>   end
> 
>   define hook-run subcommand
>     echo Subcommand\n
>   end
> 
> Then:
> 
>   (gdb) run
>   Will run!
>   [...]
>   (gdb) hook-run subcommand
>   Subcommand
> 
> This doesn't seem very useful or worse, it can be confusing.  Moreover,
> this creates some obscure corner cases in a later patch adding command
> renaming.
> 
> Because of this, this patch prevents hooks to become prefixes and
> prefixes to become hooks.
> 
> An alternative approach would have been to prevent prefixes starting
> with "hook-" or "hookpost-".  The end result would have been similar
> but not identical as GDB allows commands starting with "hook-" or
> "hookpost-" which are not hooks (for instance, "define
> hook-this-doesnt-exist").  To be more consistent with this use case,
> prefixes for commands which are named like hooks but are not hooks are
> allowed.

Ahhh, changes that touch command handling are always scary stuff, we
need to be really careful not to break existing use cases or paint
ourselves in corners for future use cases.  Probably why nobody dares to
review it.  I'll give it a try, but know that it still scares me :).

One question that pops up is, what if someone ever wants to make a hook
for a prefixed command.  For example, let's say I want to hook "info
inferiors".  I don't think that's possible today, but let's say we want
to make it possible.  How would that work?

This doesn't work:

   (gdb) define hook-info inferiors
    Undefined command: "hook-info".  Try "help".

So... maybe defining "hook-info" as a prefix command would allow it?
Not sure, I didn't really think this through, but I wonder if you
thought about that case.

Simon