Dotted revno "algebra"

[Eric Siegerman]

On Tue, 2010-05-04 at 14:19 +0200, Vincent Ladeuil wrote:
> Well, version numbers for released softwares do some funny stuff too
> here: 1.0 comes before 2.0 but 2.0beta comes before 2.0 no ? So we are
> all using some heuristics that are not usual arithmetic ones here :)

That only works because the "beta" signals that it and the
following stuff are out of band.  Have you ever seen a project
that numbers prereleases leading up to 2.4 as simply 2.4.N?  I
sure haven't!

That said, let me retract the bit about dotted-decimal being a
"straightforward extension of (single-)decimal arithmetic".  It
isn't, as revno (or release) 2.1.10 follows 2.1.9, whereas
in math, (2.10 < 2.9).

A more precise statement of the property I value is that "X.Y" is
equivalent to "X.Y.0".


> Moreover, the middle part in the dotted revno is... nearly opaque if
you
> can't visualize the merge subgraph, so it's not helpful to understand
> this subgraph ordering.

True.  I don't rely on the interior components nearly as much as
on the first and last ones.  To me, they're only there to
disambiguate multiple branches that sprang from the same rev.


> But will answer the question I most often ask when dealing with
revnos:
> *when* was this merged in my mainline (as opposed to when was it
branched
> from my mainline which I'm rarely, if ever, interested in, expect
maybe
> at conflict resolution time, but even there...) ?
> 
> I'd like to understand what you are using the revno branch point for
> (except for the ordering that is) ?

I don't need the revno to tell me where the merge point is; "bzr
log -n0" *shows* me that.  But "log" doesn't indicate where the
branch point was; I determine that by comparing revnos.  (Not
sure why I care about the branch point more than you seem to do,
but, well, I do care about it.)

And qlog is a great visualization tool, but there's that
keyboard/mouse context switch again.  With branch-point
numbering, I can use log to understand a typical feature branch;
I only need to resort to qlog for more complex situations.


>     > Numbering dotted revnos by merge point would greatly reduce the
>     > (valuable) partial-ordering property,
> 
> It will define a different partial ordering, yes [...]

Yeah, in which "X.Y" won't mean "X.Y.0", but more like
"X.Y.infinity".  *Shudder*


> Regarding the final part in the revno, both numberings (from merge
point
> or branch point (not exactly that but good enough)) have pros and
cons,
> there is still room for discussion.

Apparently...  But at least we can now discuss it purely on the
basis of (competing ideas of) usability, since, as you point out
in another post, John's recent work has essentially factored out
the performance issues.

  - Eric