Hi Elijah, On Sat, 13 Nov 2021, Elijah Newren via GitGitGadget wrote: > From: Elijah Newren <newren@xxxxxxxxx> > > 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. Thank you. As you most likely figured out, that magic weight was introduced by me, in ac076c29ae8 (name-rev: Fix non-shortest description, 2007-08-27). And indeed the motivation was to keep the name as short as possible. Technically, your solution does not fix the problem fully, as we still do not determine the _shortest possible_ name. Having said that, I think your patch improves the situation dramatically, so: ACK! Thanks, Dscho > > Signed-off-by: Elijah Newren <newren@xxxxxxxxx> > --- > name-rev: prefer shorter names over following merges > > Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1119%2Fnewren%2Fprefer-shorter-names-in-name-rev-v1 > Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1119/newren/prefer-shorter-names-in-name-rev-v1 > Pull-Request: https://github.com/git/git/pull/1119 > > builtin/name-rev.c | 17 +++++++++++++---- > 1 file changed, 13 insertions(+), 4 deletions(-) > > diff --git a/builtin/name-rev.c b/builtin/name-rev.c > index b221d300147..27f60153a6c 100644 > --- a/builtin/name-rev.c > +++ b/builtin/name-rev.c > @@ -44,11 +44,20 @@ static struct rev_name *get_commit_rev_name(const struct commit *commit) > return is_valid_rev_name(name) ? name : NULL; > } > > +static int effective_distance(int distance, int generation) > +{ > + return distance + (generation > 0 ? MERGE_TRAVERSAL_WEIGHT : 0); > +} > + > static int is_better_name(struct rev_name *name, > timestamp_t taggerdate, > + int generation, > int distance, > int from_tag) > { > + int name_distance = effective_distance(name->distance, name->generation); > + int new_distance = effective_distance(distance, generation); > + > /* > * When comparing names based on tags, prefer names > * based on the older tag, even if it is farther away. > @@ -56,7 +65,7 @@ static int is_better_name(struct rev_name *name, > if (from_tag && name->from_tag) > return (name->taggerdate > taggerdate || > (name->taggerdate == taggerdate && > - name->distance > distance)); > + name_distance > new_distance)); > > /* > * We know that at least one of them is a non-tag at this point. > @@ -69,8 +78,8 @@ static int is_better_name(struct rev_name *name, > * We are now looking at two non-tags. Tiebreak to favor > * shorter hops. > */ > - if (name->distance != distance) > - return name->distance > distance; > + if (name_distance != new_distance) > + return name_distance > new_distance; > > /* ... or tiebreak to favor older date */ > if (name->taggerdate != taggerdate) > @@ -88,7 +97,7 @@ static struct rev_name *create_or_update_name(struct commit *commit, > struct rev_name *name = commit_rev_name_at(&rev_names, commit); > > if (is_valid_rev_name(name)) { > - if (!is_better_name(name, taggerdate, distance, from_tag)) > + if (!is_better_name(name, taggerdate, generation, distance, from_tag)) > return NULL; > > /* > > base-commit: 9d530dc0024503ab4218fe6c4395b8a0aa245478 > -- > gitgitgadget >
