Hi drizzd,

On Wed, 4 Apr 2018, Clemens Buchacher wrote:

From the output of ls-files, we remove all but the leftmost path
component and then we eliminate duplicates. We do this in a while loop,
which is a performance bottleneck when the number of iterations is large
(e.g. for 60000 files in linux.git).

$ COMP_WORDS=(git status -- ar) COMP_CWORD=3; time _git

real    0m11.876s
user    0m4.685s
sys     0m6.808s

Replacing the loop with the cut command improves performance
significantly:

$ COMP_WORDS=(git status -- ar) COMP_CWORD=3; time _git

real    0m1.372s
user    0m0.263s
sys     0m0.167s

The measurements were done with Msys2 bash, which is used by Git for
Windows.

Those are nice numbers right there, so I am eager to get this into Git for
Windows as quickly as it stabilizes (i.e. when it hits `next` or so).

I was wondering about one thing, though:

This is a bit different from the `cut -f1 -d/` logic, as it does *not
necessarily* strip a leading slash: for `/abc` the existing code would
return the string unmodified, for `/abc/def` it would return an empty
string!

Now, I think that this peculiar behavior is most likely bogus as `git
ls-files` outputs only relative paths (that I know of). In any case,
reducing paths to an empty string seems fishy.

I looked through the history of that code and tracked it all the way back
to
https://public-inbox.org/git/1357930123-26310-1-git-send-email-manlio.perillo@gmail.com/
(that is the reason why you are Cc:ed, Manlio). Manlio, do you remember
why you put the `?` in front of `?*/*` here? I know, it's been more than
five years...

Out of curiosity, would the numbers change a lot if you replaced the `cut
-f1 -d/` call by a `sed -e 's/^\//' -e 's/\/.*//'` one?

I am not proposing to change the patch, though, because we really do not
need to expect `ls-files` to print lines with leading slashes.

-		*) echo "$file" ;;
-		esac
-	done | sort | uniq
+	cut -f1 -d/ | sort | uniq
 }
 
 # Lists branches from the local repository.

Ciao,
Dscho