Subject: Re: git fetch --dry-run can modify the repo

From: Jeff King <[email-masked]>
Date: Tue, 10 Feb 2026 02:50:17 -0500

On Mon, Feb 09, 2026 at 09:33:33PM -0800, Tyler Breisacher wrote:

> Interesting bug we came across -- or at least I think it's a bug. In
> any git repo that is not a shallow clone:
> 
> $ cat .git/shallow # "No such file or directory"
> $ git fetch --depth=1 --dry-run
> $ cat .git/shallow # Prints a git sha
> 
> I would think no command should make any changes to the local repo if
> --dry-run is passed.

Here's a related thread with some more discussion:

  https://lore.kernel.org/git/[email-masked]/

This is intended-ish, as --dry-run does still transfer objects, but just
avoids updating any refs. And if we have shallow'd objects, we have to
mark them as such (otherwise they appear corrupted).

There's some discussion in the thread above about whether a truly "dry"
fetch would be a good idea. But short of that, probably the
documentation could stand to be updated.

-Peff