find out which git commit a file was taken from

Question

A collaborator that does not use version control has sent me a file with some local modifications. Now he went on vacation. I would like to find out which version his edits were

Answer 1

I'd create a new branch with the colleague's change and then use git merge-base:

git merge-base finds best common ancestor(s) between two commits to use in a three-way merge. One common ancestor is better than another common ancestor if the latter is an ancestor of the former. A common ancestor that does not have any better common ancestor is a best common ancestor, i.e. a merge base. Note that there can be more than one merge base for a pair of commits.