Re: [PATCH] Tweak the handling of $HISTSIZE edge cases [PR gdb/16999]

[Patrick Palka <patrick at parcs dot ath dot cx>]

On Thu, May 21, 2015 at 8:41 PM, Pedro Alves <palves@redhat.com> wrote:
> On 05/22/2015 01:26 AM, Patrick Palka wrote:
>> On Thu, May 21, 2015 at 7:33 PM, Pedro Alves <palves@redhat.com> wrote:
>
>>> If I'm reading correctly, this treats HISTSIZE=" " as "disable history".
>>> Is that intended?
>>
>> It's not really intended.  The motivation was to make sure that an
>> obvious typo in HISTSIZE (e.g. HISTSIZE="1000-") will not truncate the
>> history size, but HISTSIZE=" " is not really a typo.  But IMO adding a
>> more intelligent typo heuristic (one to replace *endptr != '\0') is
>> not worth it -- it's just a history file after all.
>
> I haven't gone back to recheck what bash does, but, I can see
> that happening in scripts, like:
>
>   if whatever; then
>      mysize=1000
>   fi
>   HISTSIZE="$mysize " HISTFILESIZE="$mysize"
>
> and then mysize ends up unset.

bash would treat HISTSIZE=" " as non-numeric and thus do nothing.
This patch on the other hand treats non-numeric values as if they are
typos and thus sets the history size to unlimited to avoid truncation.
But now I'm starting to question whether this is a good idea...
sigh...

>
>>
>> But that reminds me that the strings " 10" and "10 " should not be
>> considered non-numeric.  That could easily be achieved via a couple of
>> calls to isspace().
>
> Exactly, I was thinking of those too, but I didn't want to call
> out what the behavior should be.  :-)
>
>>
>>>
>>> Also, a nit: I find it a bit odd to see strlen to check empty string
>>> in one case, and != '\0' in another, instead of:
>>>
>>>       if (*tmpenv == '\0'
>>>           || var < 0
>>>           || *endptr != '\0')
>>>
>>>> +     history_size_setshow_var = -1;
>>>> +      else
>>>> +     history_size_setshow_var = var;
>>>>      }
>>>>    /* If the init file hasn't set a size yet, pick the default.  */
>>>>    else if (history_size_setshow_var == -2)
>>
>> Well semantically endptr is less of a string and more of a pointer to
>> a char within a string -- at least that's how I view it.  But I will
>> change the first condition to check for '\0'.
>
> Ah.  Good point.  I'm fine either way then.
>
>>
>> On a related note, I wonder whether it is a good idea for GDB to look
>> at HISTSIZE at all.  As the buildbots and you have shown, some distros
>> export HISTSIZE by default and by doing so it renders useless GDB's
>> internal "history size" setting (as far as .gdbinit is concerned).  I
>> think people expect HISTSIZE to only affect shells, not e.g. readline
>> applications.  (Otherwise, I would expect the readline library to
>> already extract the default history size from HISTSIZE or from another
>> environment variable, something it currently has no support for.)  So
>> I wonder whether it would be better to stop reading HISTSIZE, to
>> instead read GDBHISTSIZE or something.
>
> Yeah, I'm inclined to agree.

I will make a small patch series that does this then (which will
include this patch).

>
> Thanks,
> Pedro Alves
>