Question

I’ve got a) a working directory without the .git directory and b) a repository. a is some revision in the middle of the history of b.

How can I find out, which revision a matches in b?

I thought of a shellscript doing a diff from the working directory to all revisions and pick the one with the least (hopefully 0) differences.

That would be a bit raw (and I’m not sure how to do it), is there an easier way?

Answer 1

You could write a script to run diff gitdir workdir | wc -c for each commit. Then you could collate the results and say the commit which has the smallest difference (as measured by wc -c) is the closest commit to the bare working dir.

Here is what it might look like in Python:

find_closest_sha1.py:

#!/usr/bin/env python
import subprocess
import shlex
import sys
import os
import operator

gitdir,workdir=map(os.path.realpath,sys.argv[1:3])
os.chdir(gitdir)
proc=subprocess.Popen(shlex.split('git rev-list --all'),stdout=subprocess.PIPE)
shas,err=proc.communicate()
shas=shas.split()
head=shas[0]
data={}
for sha1 in shas:
    subprocess.Popen(shlex.split('git checkout {s}'.format(s=sha1)),
                          stderr=open('/dev/null')).wait()
    proc=subprocess.Popen(shlex.split('diff {g} {w}'.format(g=gitdir,w=workdir)),
                          stdout=subprocess.PIPE)
    out,err=proc.communicate()
    distance=len(out)
    data[sha1]=distance
answer=min(data.items(),key=operator.itemgetter(1))[0]
print('closest match: {s}'.format(s=answer))
subprocess.Popen(shlex.split('git checkout {h}'.format(h=head)),
                 stderr=open('/dev/null')).wait()

Example:

% rsync -a gitdir/ workdir/
% cd workdir
% git checkout HEAD~10
HEAD is now at b9fcebf... fix foo

% cd ..
% /bin/rm -rf workdir/.git
% find_closest_sha1.py gitdir workdir
closest match: b9fcebfb170785c19390ebb4a9076d11350ade79