From: "Junio C Hamano" <>
Sent: Wednesday, July 03, 2013 7:08 PM
[catching up on old emails]
Ed Hutchins <> writes:

I'm not trying to change the way git does things (which works
well), I'm asking for some extra information to be added to the
so that analysis of the ancestry graph can be tied to the branch
that the original author was working from. Currently if you have a
rebase-branch/ff-merge-to-master workflow, the graph of commits looks
like a single user produced all of the code. It would be very useful
both forensic and display purposes to categorize those commits by
original topics, but that history is lost in such a workflow.

I am not following that "a single user" part. As long as these
topics are done by different people, the authorship remains
separate, no matter what the shape of the graph is.

It all depends on what you show on the graph other than a circle and
connecting lines, but I presume at least you would show the subject
line. The graph would clearly show which groups of commits tackle
what problems in your history, even if you excessively linearlized
it by rebasing. You need subjects / commit log messages that are
better than "bugfix", of course, for it to work, though.

Arguing that branch names are local and thus meaningless misses
the point: branches are *names* which were meaningful to the
author at the time the branch was being worked on.

That is not necessarily true.

Most of my commits start their life on a single branch that is named
after a very broad theme (or even on a detached HEAD) that ends up
touching different parts of the system and then later split into
separate topic branches that are named after more detailed single
issues. The name of the branch that happened to have been used to
create them have almost no meaning after I am done with multiple and
independent (but related in the larger scheme of things) topics.

It is not just misleading but is actively wrong to recording the
name of the original branch in commits and carrying them forward via
rebase. If you want a record of what a group of commits were about,
the right time to do so is when you merge.

While the general arguments are true that in the main one shouldn't
embed whatever random branch name was used into the commit messages,
there are some workflows and some production (corporate) environments
where adding a relevant branch name is suitable for that environment.

If the existing branch name is poor then the user should do a rebase to
transfer it to a better branch name, and then the 'git filter-branch'
command would be the obvious method to add a "Developed-on: <branch>"
final 'signoff line'.

The 'git filter-branch' man page already includes an example for adding
an acked by, which can easily be modified.

If you need to add Acked-by lines to, say, the last 10 commits (none of
which is a merge), use this command:

git filter-branch --msg-filter '
       cat &&
       echo "Acked-by: Bugs Bunny <>"

I'll leave it to Ed to automate it as a script.... (and possibly making sure it's idempotent so only the final branch name is retained, etc.)

Projects that care about the shape of the ancestry graph have an
obvious option of not excessively/unnecessarily linearlizing their
history. We even have the "--no-ff" mode of merge to create an
otherwise unnecessary merge to mark the point where a topic is
merged to the mainline, so that merge log messages can say what
topic was merged (and also you can even have "merge.log").

Cleaning up a messy history created on a topic branch before
presenting to others by lineralizing is one thing. It is a good
practice. Requiring any update to fast-forward on top of the tip of
the project is quite different. It does not make your history any
easier to read. A topic that has been working fine on top of last
week's trunk can have a subtle interaction with the work done by
others on the trunk since it forked, and rebasing it on top of
today's trunk, just before pushing it out on the trunk, risks
breaking the topic in a subtle way without the person who does such
a rebase without noticing, making later bisection harder.

Any option to encourage such an artificially linear history _is_
actively detrimental.

The boss may not always be right, but she is the boss.
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