TIL: Use the --root flag in place of HEAD~N for editing the initial commit message

Context

I opted to edit a commit message but ran into trouble when using HEAD~N.

Nerd Activities

I was writing some benchmark tests this evening in Node.js, Python, and Rust. I wanted my commit messages to be more uniform (despite this being deployed absolutely nowhere), so I opted to rebase:

> git log --oneline
4d30acc (HEAD -> master) Rust test
c749165 Python test
397c1a6 Benchmark test for JavaScript
(END)

My first instinct is to reach for git rebase, but I uncovered a fundamental flaw in my understanding of N in HEAD~N.

> git rebase -i HEAD~3
fatal: invalid upstream 'HEAD~3'

I wound up running git rebase -i HEAD~1 and git rebase -i HEAD~2 just to make sure I wasn't losing it. As it turns out, HEAD~N means “go back N commits from the current tip.” Since there were only 3 commits, this triggered the error above.

Solution

I ultimately discovered the --root flag which allowed me to access the first commit message. My commit history now reads much cleaner:

> git log --oneline
4d30acc (HEAD -> master) Rust test
c749165 Python test
397c1a6 Node.js test
(END)