How can I find the merge commit given a Git commit?

Oftentimes, we know the commit hash of a specific Git commit and want to find the merge commit where the changes from that commit were merged into a branch.

This can be especially useful if your team uses GitHub and you want to find the pull request that introduced a specific change. It's also pretty helpful when you need to understand the context of a commit and how it fits into the project's history or when you're looking for files related to a change.

While there are a few different solutions that might work under different circumstances, after trial and error and a whole lot of Googling, I found a method that works pretty well. Adding the following alias to your Git configuration will allow you to use git find-merge <commit> to find the merge commit for a given commit hash.

[alias]
  find-merge = "!sh -c 'commit=$0 && branch=${1:-HEAD} && (git rev-list $commit..$branch --ancestry-path | cat -n; git rev-list $commit..$branch --first-parent | cat -n) | sort -k2 -s | uniq -f1 -d | sort -n | tail -1 | cut -f2'"

# Syntax: git find-merge <commit>

git find-merge 3050fc0
# c2ec1385b47a4b9024bdde77c0978a34359480ac

Using git rev-list, the command lists all the commits between the given commit and the branch, first following the full ancestry path and then following only the first parent. The output of these two commands is then concatenated, sorted, and filtered to find the merge commit where the two paths converge. Finally, the resulting commit hash is returned.