Git Spelunking
Find all commits containing a particular piece of code
git log -S "method_name"
See the diffs alongside the commit messages
git log -S "method_name" -p
Find the commit that first added some code
git log -S "method_name" -p --reverse
Limit the scope of the search
git log -S "some code" -p app/models/user.rb
Search the commit messages themselves
git log --grep "commit message search"