Re: Interrupting globs (Re: Something rotten in tar completion)

[Mikael Magnusson <mikachu@gmail.com>]

On Sat, Dec 6, 2014 at 1:36 AM, Mikael Magnusson <mikachu@gmail.com> wrote:
> On Fri, Dec 5, 2014 at 11:07 PM, Peter Stephenson
> <p.w.stephenson@ntlworld.com> wrote:
>> On Fri, 5 Dec 2014 20:34:17 +0000
>> Peter Stephenson <p.w.stephenson@ntlworld.com> wrote:
>>> On the other problem I came up with, that eval is resetting errflag even
>>> if you've interrupted: how about the following?  Add a bit to errflag to
>>> signify that the user interrupted the shell rather than that some
>>> internal error (e.g. syntax) occurred.  Only reset this new bit in a few
>>> key places: the main command loop when executing, the top of ZLE when
>>> editing being the obvious places.  Convert other "errflag = 0"
>>> assignments case by case so that they just remove bit 0; then eval can
>>> continue to do its job of acting as a sandbox but without screwing up
>>> the behaviour of interrupts.  I think doing that is fairly mechanical
>>> and it achieves what's needed without compromising anything else.
>>
>> Here's my first go; it does seem to do what I want, and as a by-product
>> fixes all the little race conditions we've always had that meant you
>> couldn't interrupt chunks of code that were executed in any kind of
>> sandbox because the condition got reset afterwards.  I think a few of
>> these have been annoying me over the years.
>>
>> The general strategy is to use the bit ERRFLAG_ERROR for internal
>> failures and ERRFLAG_INT for user interrupts.  There are only two
>> cases of the latter: on an untrapped SIGINT, the obvious case, and also
>> on a trapped SIGINT or SIGQUIT where we've been told to behave as if the
>> trap didn't trap the error condition.  That's straightforward for
>> SIGINT, less so for SIGQUIT but I took my cue from the fact that Bart
>> thought it worthwhile trapping SIGQUIT as an interactive "no, I really
>> mean abort" in completion, which implies that if we trap it we want it
>> to work at least as well as SIGINT.
>>
>> Correspondingly, most of the time only the ERRFLAG_ERROR bit gets
>> reset.  ERRFLAG_INT gets reset only in the following cases:
>>
>> - in the main command loop.  This is what causes the shell not to exit but
>> instead go back to the main command loop when you ^C a command.
>>
>> - at the start of zleread, so we can read the next thing to do whatever
>> just happened.  I'm not sure this is particularly useful since
>> in this case you'd typically expect the previous condition to have
>> occurred and it could mean e.g. you ignore an interrupt that
>> occurred just before a "vared".
>>
>> - when we just finished completion.  This is needed so that the cases
>> that got this whole business kicked off behave as now (but more
>> reliably) --- a ^C gets you back to the command line, but the command
>> line is not trashed as it would be if you ^Ced outside completion (try
>> it if you're confused).  There's a race here, but it's no worse than it
>> ever was.
>>
>> To ensure ERRFLAG_INT doesn't get reset unnecessarily there are a number
>> of cases where restoring errflag to a previously saved value keeps the
>> ERRFLAG_INT bit if it got set in the meanwhile.  I hope the rationale
>> here is obvious --- the ERRFLAG_ERROR is an internal state that needs
>> resetting, the ERRFLAG_INT an asynchronous condition where the user
>> doesn't care what the internal state is.
>>
>> By the way, looking at the patch below you might wonder if it wouldn't
>> be more efficient to add a separate flag for interrupt error conditions
>> to test.  It wouldn't --- there are many more cases where errflag is
>> tested than when it is set, not affected by the patch below.
>>
>> I suspect we'll just have to try this out and see how it works.
>
> This seems to work well for me in the cases you talked about, but I
> quickly noticed one surprising problem. I have some stuff in my
> chpwd() hook to show git branches and stuff, and these used to be
> interruptible by ctrl-c (the commands are very fast with hot cache,
> but can be somewhat painful with cold cache, like 5-10 seconds delay).
> With the patch, I cannot interrupt them (sometimes?).
>
> chpwd () {
>     stty -echo >&/dev/null
>     test -f .tdldb && tdll -1 >&2
>     test -d .git && {
>         git branch
>         test -d .git/svn && {
>             echo -n r
>             git svn find-rev master
>         }
>         git name-rev HEAD
>         git describe --tags HEAD 2> /dev/null
>     } >&2
>     if [[ "$_NONOCDLS" = 1 ]]
>     then
>         ls $LS_OPTIONS >&2
>     fi
> }

Ah, I think I understand what's happening now. Prior to the patch,
pressing ctrl-c would abort out of chpwd() completely, but now it just
aborts whichever single command is running. Since I have three git
commands in there, I now need to press ctrl-c three times to get back
to the prompt quickly. (I would like it to only require one).

-- 
Mikael Magnusson