Re: [RFC/PATCH 4/5] completion: get rid of compgen

["SZEDER Gábor" <szeder@ira.uka.de>]

On Sat, Nov 17, 2012 at 12:42:38PM +0100, Felipe Contreras wrote:
> On Sat, Nov 17, 2012 at 12:00 PM, SZEDER Gábor <szeder@ira.uka.de> wrote:
> > On Sat, Nov 17, 2012 at 02:38:17AM +0100, Felipe Contreras wrote:
> >> The functionality we use is very simple, plus, this fixes a known
> >> breakage 'complete tree filename with metacharacters'.
> >>
> >> Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
> >> ---
> >>  contrib/completion/git-completion.bash | 6 +++++-
> >>  1 file changed, 5 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
> >> index 975ae13..ad3e1fe 100644
> >> --- a/contrib/completion/git-completion.bash
> >> +++ b/contrib/completion/git-completion.bash
> >> @@ -227,7 +227,11 @@ fi
> >>
> >>  __gitcompadd ()
> >>  {
> >> -     COMPREPLY=($(compgen -W "$1" -P "$2" -S "$4" -- "$3"))
> >> +     for x in $1; do
> >> +             if [[ "$x" = "$3"* ]]; then
> >> +                     COMPREPLY+=("$2$x$4")
> >> +             fi
> >> +     done
> >
> > The whole point of creating __gitcomp_nl() back then was to fill
> > COMPREPLY without iterating through all words in the wordlist, making
> > completion faster for large number of words, e.g. a lot of refs, or
> > later a lot of symbols for 'git grep' in a larger project.
> >
> > The loop here kills that optimization.
> 
> So your solution is to move the loop to awk? I fail to see how that
> could bring more optimization, specially since it includes an extra
> fork now.

This patch didn't aim for more optimization, but it was definitely a
goal not to waste what we gained by creating __gitcomp_nl() in
a31e6262 (completion: optimize refs completion, 2011-10-15).  However,
as it turns out the new version with awk is actually faster than
current master with compgen:

  Before:

    $ refs="$(for i in {0..9999} ; do echo branch$i ; done)"
    $ time __gitcomp_nl "$refs"

    real    0m0.242s
    user    0m0.220s
    sys     0m0.028s

  After:

    $ time __gitcomp_nl "$refs"

    real    0m0.109s
    user    0m0.096s
    sys     0m0.012s