Question

Someone took a version (unknown to me) of Moodle, applied many changes within a directory, and released it (tree here).

How can I determine which commit of the original project was most likely edited to form this tree?

this would allow me to form a branch at the appropriate commit with this patch. Surely it came from either the 1.8 or 1.9 branches, probably from a release tag, but diffing between particular commits doesn’t help me much.

Postmortem Update: knittl’s answer got me as close as I’m going to get. I first added my patch repo as the remote “foreign” (no commits in common, that’s OK), then did diffs in loops with a couple format options. The first used the --shortstat format:

for REV in $(git rev-list v1.9.0^..v1.9.5); do 
    git diff --shortstat "$REV" f7f7ad53c8839b8ea4e7 -- mod/assignment >> ~/rdiffs.txt; 
    echo "$REV" >> ~/rdiffs.txt; 
done;

The second just counted the line changes in a unified diff with no context:

for REV in $(git rev-list v1.9.0^..v1.9.5); do 
    git diff -U0 "$REV" f7f7ad53c8839b8ea4e7 -- mod/assignment | wc -l >> ~/rdiffs2.txt;
    echo "$REV" >> ~/rdiffs2.txt; 
done;

There were thousands of commits to dig through, but this one seems to be the closest match.

Answer 1

you could write a script, which diffs the given tree against a revision range in your repository.

assume we first fetch the changed tree (without history) into our own repository:

git remote add foreign git://…
git fetch foreign

we then output the diffstat (in short form) for each revision we want to match against:

for REV in $(git rev-list 1.8^..1.9); do
   git diff --shortstat foreign/master $REV;
done

look for the commit with the smallest amount of changes (or use some sorting mechanism)