Re: [PATCH] revisions(7): clarify that most commands take a single revision range

[Elijah Newren <newren@gmail.com>]

On Wed, May 19, 2021 at 10:03 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Junio C Hamano <gitster@pobox.com> writes:
>
> > Bagas Sanjaya <bagasdotme@gmail.com> writes:
> >
> >> On 18/05/21 18.17, Junio C Hamano wrote:
> >>> ...
> >>> +In other words, writing two "two-dot range notation" next to each
> >>> +other, e.g.
> >>> +
> >>> +    $ git log A..B C..D
> >>> +
> >>> +does *not* specify two revision ranges for most commands.  Instead
> >>> +it will name a single connected set of commits, i.e. those that are
> >>> +reachable from either B or D but are reachable from neither A or C.
> >>> +In a linear history like this:
> >>> +
> >>> +    ---A---B---o---o---C---D
> >>> +
> >>
> >> So "git log A..B C..D" is same as "A..D", right?
> >
> > A..B C..D is equivalent to ^A ^C B D, and in order to be part of the
> > set it represents, a commit must not be reachable from A, must not
> > be reachable from C, and must be reachable from B or D.
> >
> > In the picture, A, B and two o's are all reachable from C, therefore
> > are not part of the set A..B C..D represents.  Neither is C, as it
> > is reachable from C.  That leaves only D in the resulting range.
> >
> > A..D is a set of connected five commits, B o o C D in the above
> > picture.
> >
> > So, no.
> >
> > The confusion we often see goes more like "The set A..B contains B
> > (and nothing else), and C..D contains D (and nothing else), hence
> > 'git log A..B C..D' would show B and D".  But that is not what
> > happens because "git log" (like most other commands) takes just a
> > "range" that is "A..B C..D", which is a set of connected commits
> > each of whose member is reachable from one of the "positive"
> > endpoints (like B and D) and is not reachable from any of the
> > "negative" endpoints (like A and C).
>
> Well, apparently the proposed text may have failed to educate you
> about what a "revision range" is and how it works, so it is not good
> enough, so I'll postpone merging the change down further and see if
> somebody else can come up with a better description.
>
> Thanks.

I think it's helpful and would have answered questions for users that
I've had to manually explain to folks a few times, so while it may not
be optimal, I do think your description is an improvement to the docs.
That said, it can't hurt to see if we can find out what caused Bagas'
confusion and see if we can improve it, but I wouldn't hold it up
indefinitely if no better wording comes along.