Re: [PATCH] name-rev: prefer shorter names over following merges

> From: Elijah Newren <newren@gmail.com>
>
> name-rev has a MERGE_TRAVERSAL_WEIGHT to say that traversing a second or
> later parent of a merge should be 65535 times more expensive than a
> first-parent traversal, as per ac076c29ae8d (name-rev: Fix non-shortest
> description, 2007-08-27).  The point of this weight is to prefer names
> like
>
>     v2.32.0~1471^2
>
> over names like
>
>     v2.32.0~43^2~15^2~11^2~20^2~31^2
>
> which are two equally valid names in git.git for the same commit.  Note
> that the first follows 1472 parent traversals compared to a mere 125 for
> the second.  Weighting all traversals equally would clearly prefer the
> second name since it has fewer parent traversals, but humans aren't
> going to be traversing commits and they tend to have an easier time
> digesting names with fewer segments.  The fact that the former only has
> two segments (~1471, ^2) makes it much simpler than the latter which has
> six segments (~43, ^2, ~15, etc.).  Since name-rev is meant to "find
> symbolic names suitable for human digestion", we prefer fewer segments.
>
> However, the particular rule implemented in name-rev would actually
> prefer
>
>     v2.33.0-rc0~11^2~1
>
> over
>
>     v2.33.0-rc0~20^2
>
> because both have precisely one second parent traversal, and it gives
> the tie breaker to shortest number of total parent traversals.  Fewer
> segments is more important for human consumption than number of hops, so
> we'd rather see the latter which has one fewer segment.
>
> Include the generation in is_better_name() and use a new
> effective_distance() calculation so that we prefer fewer segments in
> the printed name over fewer total parent traversals performed to get the
> answer.