Re: Advice on edits to git-rebase man page

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 5, 2015, 18:58 UTC
Message-ID: <xmqqa90smbhu.fsf@gitster.dls.corp.google.com>
In-Reply-To: <vpqa90s4oz2.fsf@anie.imag.fr>

Matthieu Moy <Matthieu.Moy@grenoble-inp.fr> writes:

>   NAME
>        git-rebase - Forward-port local commits to the updated upstream head
>
> => Quite technical already.

Very much true, and I would say the description is "technically correct" in the sense that "it is not wrong per-se". There are a few points that this fails to state and some that this overspecifies.

 - Rebase is about changing the base of an existing branch, but the
   description does not even mention the word "branch" [*1*].

 - There is nothing "forward" about it.  I often see myself applying
   (tentatively) incoming patches on top of whatever commit I happen
   to have checked out, review it and then rebasing it to apply to
   older maintenance track if the topic is about fixing an old bug.

 - There is no point stressing "local" commits; all the operations
   you do to munge commits are local.

Perhaps something like this instead?

    git-rebase - Rebuild a branch on top of a different commit

Show 6 quoted lines

>   DESCRIPTION
>        If <branch> is specified, git rebase will perform an automatic
>        git checkout <branch> before doing anything else. Otherwise it
>        remains on the current branch.
>
> => Ouch, do we really want to start a documentation like this?

No. We should say what the command does and what the command is for in more general terms first and then describe how arguments can be used to affect it.

> So, the DESCRIPTION part can definitely be improved IMHO. Your notation
> <graft-point>, <exclude-from> and <include-from> may be an improvement
> already.

<graft-point>, <exclude-from> and <include-from> aren't technically wrong per-se, but I do not think bulk-replacing the words currently used in the manual page with these is an improvement at all, unless the mental picture the explanation draws is also updated to match these new words.

reBASE is about changing the base of the affected branch, and the mental picture the current documentation draws is "there is a plant, from which you cut a branch, scion. Then you graft the scion onto understock". It calls the original tree (that the branch being transplanted is part of) the "old-base", and the understock (that the scion is going to be grafted onto) the "new-base". The word "graft" in "graft point" may better convey that we are doing a transplanting than the current wording, but the word "point" makes it unclear to the readers if it refers to the "point" where the scion was cut from or where it is going to transplanted to, I am afraid.

Also <exclude-from> and <include-from> is probably too operational, and describing the command with only these two words would miss the point that the command is about transplanting a branch. It is true that in order to transplant a branch, you first need to figure out the set of commits whose effects are to be replayed, you would need <exclude-from>..<include-from> range computation, but it is an lower-level implemention detail.

> Some concrete examples may help too, like "I started developing against
> origin/foo, on local branch bar, and now want to rebase my work on top
> of origin/boz".

Very much so, but I wonder if it would be better to just refer to examples in the tutorial (and if we do not have good examples there, we should add some).

[Footnote]

 *1* Yes, "git rebase $newbase $commit^0" form can be used to
     transplant a part of history leading to the $commit that does
     not sit at the tip of a branch (nor repoint a branch to point
     at the result at the end) as if $commit^0 were at the tip of
     some branch, but the key word here is "as if".  The user is
     allowed to use the command pretending something that is not a
     branch is a branch, but what it tells us is that the command
     *is* about a branch.