Fetching Multiple Branches

Here was my question:

If I run git fetch, that would imply that running git diff origin/main main should have a meaningful difference, correct? Put differently, I'd have a response for this command.

Not necessarily. git fetch updates your remote-tracking refs with the remote state it finds, but it does not guarantee the remote differs from your local branch.

There are three common scenarios after you run git fetch:

1. The remote-tracking ref is ahead of the local ref#

Your remote repository has commits your local branch does not have (likely another engineer pushed to that repository), meaning local main is behind origin/main.

2. The local and remote-tracking refs are in sync#

Your remote-tracking ref and local branch point to snapshots with the same contents, so git diff origin/main main produces no patch output.

3. You have local commits you haven't pushed#

In this scenario, main is ahead of origin/main, meaning the diff can be non-empty even though git fetch downloaded no new commits. The difference arises from your unpushed work, not from the fetch.

The key thing to realize is that git fetch doesn't necessarily make a visible difference. It refreshes remote-tracking refs such as origin/main to reflect what the remote advertised at fetch time. Those refs can be stale until the next operation that contacts the remote.

And another thing...

git diff compares the snapshots the refs resolve to, not whether their commit hashes differ. Two different commits with identical file contents can therefore produce an empty diff.

If you care about which commits exist on only one side, rather than just file content, try:

git log --oneline --left-right main...origin/main