On Mon, Feb 12, 2018 at 1:00 PM, Stephen Rothwell [off-list ref] wrote:

Linus, this happens a bit after the merge window, so I am wondering
about the rational of not doing a fast forward merge when merging a
signed tag (I forget the reasoning).

The reasoning is to avoid losing the signature from the tag (when
merging a signed tag, the signature gets inserted into the merge
commit itself - use "git log --show-signature" to see them).

So when I merge a signed tag, I do *not* want to fast-forward to the
top commit, because then I'd lose the signature from the tag. Thus the
"merging signed tags are non-fast-forward by default" reasoning.

But, yes, that reasoning is really only valid for proper merges of new
features, not for back-merges.

The problem, of course, is that since git is distributed, git doesn't
know who is "upstream" and who is "downstream", so there's no
_technical_ difference between merging a development tree, and a
development tree doing a back-merge of the upstream tree.

Maybe it was a mistake to make signed tag merges non-fast-forward,
since they cause these kinds of issues with people who use "pull" to
update their otherwise unmodified trees.

I can always teach myself to just use --no-ff, since I end up doing
things like verifying at the signatures anyway.

Junio, comments?

               Linus