name-rev: stop including taggerdate in naming of commits
PATCH 1/1 name-rev: stop including taggerdate in naming of commits
From: Elijah Newren <[email protected]>
Commit 7550424804 ("name-rev: include taggerdate in considering the best name", 2016-04-22) introduced the idea of using taggerdate in the criteria for selecting the best name. At the time, a certain commit in linux.git -- namely, aed06b9cfcab -- was being named by name-rev as
v4.6-rc1~9^2~792
which, while correct, felt very suboptimal. Some investigation found
that tweaking the MERGE_TRAVERSAL_WEIGHT to lower it could give
alternate answers such as
v3.13-rc7~9^2~14^2~42
or
v3.13~5^2~4^2~2^2~1^2~42
A manual solution involving looking at tagger dates came up with
v3.13-rc1~65^2^2~42which was then implemented in name-rev.
It turns out that this taggerdate heuristic isn't needed due to a subsequent change to fix the naming logic in 3656f84278 ("name-rev:
prefer shorter names over following merges", 2021-12-04). Simply removing the taggerdate heuristic from the calculation nowadays still causes us to get the optimal answer on that particular commit of interest in linux.git, namely:
v3.13-rc1~65^2^2~42
Further, the taggerdate heuristic is causing bugs of its own. I was pointed to a case in a private repository where name-rev reports a name of the form
v2022.10.02~86
when users expected to see one of the form
v2022.10.01~2(I've modified the names and numbers a bit from the real testcase.) As you can probably guess, v2022.10.01 was created after v2022.10.02 (by a few hours), even though it pointed to an older commit. While the condition is unusual even in the repository in question, it is not the only problematic set of tags in that repository. The taggerdate logic was a workaround that is no longer needed, and is now causing suboptimal results in other cases.
As such, remove the taggerdate in the comparison. However, note that "taggerdate" is actually also used to store commit dates since ef1e74065c ("name-rev: favor describing with tags and use committer date to tiebreak", 2017-03-29), where it is used as a fallback tiebreaker when distances are equal. We do not want to remove that fallback tiebreaker, we are only removing the use of actual taggerdates as a primary criteria overridding effective distance calculations.
---
name-rev: stop including taggerdate in naming of commits
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1468%2Fnewren%2Ffix-name-rev-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1468/newren/fix-name-rev-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1468
builtin/name-rev.c | 4 +--- t/t6120-describe.sh | 6 ++++++ 2 files changed, 7 insertions(+), 3 deletions(-)
builtin/name-rev.c +1 -3
@@ -113,9 +113,7 @@ static int is_better_name(struct rev_name *name,* based on the older tag, even if it is farther away. */ if (from_tag && name->from_tag) -return (name->taggerdate > taggerdate || - (name->taggerdate == taggerdate && - name_distance > new_distance)); +return name_distance > new_distance;/* * We know that at least one of them is a non-tag at this point.
t/t6120-describe.sh +6 -0
@@ -657,4 +657,10 @@ test_expect_success 'setup: describe commits with disjoint bases 2' ' check_describe -C disjoint2 "B-3-gHASH" HEAD +test_expect_success 'setup misleading taggerdates' ' + GIT_COMMITTER_DATE="2006-12-12 12:31" git tag -a -m "another tag" newer-tag-older-commit unique-file~1 +' + +check_describe newer-tag-older-commit~1 --contains unique-file~2 + test_done
base-commit: 221222b278e713054e65cbbbcb2b1ac85483ea89
Signature · 1 line
gitgitgadget
PATCH v2 1/1 name-rev: fix names by dropping taggerdate workaround
From: Elijah Newren <[email protected]>
Commit 7550424804 ("name-rev: include taggerdate in considering the best name", 2016-04-22) introduced the idea of using taggerdate in the criteria for selecting the best name. At the time, a certain commit in linux.git -- namely, aed06b9cfcab -- was being named by name-rev as
v4.6-rc1~9^2~792
which, while correct, was very suboptimal. Some investigation found
that tweaking the MERGE_TRAVERSAL_WEIGHT to lower it could give
alternate answers such as
v3.13-rc7~9^2~14^2~42
or
v3.13~5^2~4^2~2^2~1^2~42
A manual solution involving looking at tagger dates came up with
v3.13-rc1~65^2^2~42which is much nicer. That workaround was then implemented in name-rev.
Unfortunately, the taggerdate heuristic is causing bugs. I was pointed to a case in a private repository where name-rev reports a name of the form
v2022.10.02~86
when users expected to see one of the form
v2022.10.01~2(I've modified the names and numbers a bit from the real testcase.) As you can probably guess, v2022.10.01 was created after v2022.10.02 (by a few hours), even though it pointed to an older commit. While the condition is unusual even in the repository in question, it is not the only problematic set of tags in that repository. The taggerdate logic is causing problems.
Further, it turns out that this taggerdate heuristic isn't even helping anymore. Due to the fix to naming logic in 3656f84278 ("name-rev:
prefer shorter names over following merges", 2021-12-04), we get improved names without the taggerdate heuristic. For the original commit of interest in linux.git, a modern git without the taggerdate heuristic still provides the same optimal answer of interest, namely:
v3.13-rc1~65^2^2~42
So, the taggerdate is no longer providing benefit, and it is causing problems. Simply get rid of it.
However, note that "taggerdate" as a variable is used to store things besides a taggerdate these days. Ever since commit ef1e74065c ("name-rev: favor describing with tags and use committer date to tiebreak", 2017-03-29), this has been used to store committer dates and there it is used as a fallback tiebreaker (as opposed to a primary criteria overriding effective distance calculations). We do not want to remove that fallback tiebreaker, so not all instances of "taggerdate" are removed in this change.
---
name-rev: fix names by dropping taggerdate workaround
Changes since v1: Slight tweaks to the commit message
v1 was never picked up or commented on, so this is mostly just a resubmission, with a rewording to make it clear this is a bugfix.
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1468%2Fnewren%2Ffix-name-rev-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1468/newren/fix-name-rev-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1468
Range-diff vs v1:
1: 78bbfb3286b ! 1: 206726fc954 name-rev: stop including taggerdate in naming of commits
@@ Metadata
Author: Elijah Newren <[email protected]>
## Commit message ##
- name-rev: stop including taggerdate in naming of commits
+ name-rev: fix names by dropping taggerdate workaround
Commit 7550424804 ("name-rev: include taggerdate in considering the best name", 2016-04-22) introduced the idea of using taggerdate in the criteria for selecting the best name. At the time, a certain commit in linux.git -- namely, aed06b9cfcab -- was being named by name-rev as
v4.6-rc1~9^2~792
- which, while correct, felt very suboptimal. Some investigation found
+ which, while correct, was very suboptimal. Some investigation found
that tweaking the MERGE_TRAVERSAL_WEIGHT to lower it could give alternate answers such as
v3.13-rc7~9^2~14^2~42
@@ Commit message
v3.13~5^2~4^2~2^2~1^2~42
A manual solution involving looking at tagger dates came up with
v3.13-rc1~65^2^2~42
- which was then implemented in name-rev.
+ which is much nicer. That workaround was then implemented in name-rev.
- It turns out that this taggerdate heuristic isn't needed due to a
- subsequent change to fix the naming logic in 3656f84278 ("name-rev:
- prefer shorter names over following merges", 2021-12-04). Simply
- removing the taggerdate heuristic from the calculation nowadays
- still causes us to get the optimal answer on that particular commit
- of interest in linux.git, namely:
- v3.13-rc1~65^2^2~42
-
- Further, the taggerdate heuristic is causing bugs of its own. I was
- pointed to a case in a private repository where name-rev reports a name
- of the form
+ Unfortunately, the taggerdate heuristic is causing bugs. I was pointed
+ to a case in a private repository where name-rev reports a name of the
+ form
v2022.10.02~86
when users expected to see one of the form
v2022.10.01~2
@@ Commit message
few hours), even though it pointed to an older commit. While the condition is unusual even in the repository in question, it is not the only problematic set of tags in that repository. The taggerdate logic
- was a workaround that is no longer needed, and is now causing suboptimal
- results in other cases.
+ is causing problems.
+
+ Further, it turns out that this taggerdate heuristic isn't even helping
+ anymore. Due to the fix to naming logic in 3656f84278 ("name-rev:
+ prefer shorter names over following merges", 2021-12-04), we get
+ improved names without the taggerdate heuristic. For the original
+ commit of interest in linux.git, a modern git without the taggerdate
+ heuristic still provides the same optimal answer of interest, namely:
+ v3.13-rc1~65^2^2~42
+
+ So, the taggerdate is no longer providing benefit, and it is causing
+ problems. Simply get rid of it.
- As such, remove the taggerdate in the comparison. However, note that
- "taggerdate" is actually also used to store commit dates since
- ef1e74065c ("name-rev: favor describing with tags and use committer date
- to tiebreak", 2017-03-29), where it is used as a fallback tiebreaker
- when distances are equal. We do not want to remove that fallback
- tiebreaker, we are only removing the use of actual taggerdates as a
- primary criteria overridding effective distance calculations.
+ However, note that "taggerdate" as a variable is used to store things
+ besides a taggerdate these days. Ever since commit ef1e74065c
+ ("name-rev: favor describing with tags and use committer date to
+ tiebreak", 2017-03-29), this has been used to store committer dates and
+ there it is used as a fallback tiebreaker (as opposed to a primary
+ criteria overriding effective distance calculations). We do not want to
+ remove that fallback tiebreaker, so not all instances of "taggerdate"
+ are removed in this change.
builtin/name-rev.c | 4 +--- t/t6120-describe.sh | 6 ++++++ 2 files changed, 7 insertions(+), 3 deletions(-)
builtin/name-rev.c +1 -3
@@ -113,9 +113,7 @@ static int is_better_name(struct rev_name *name,* based on the older tag, even if it is farther away. */ if (from_tag && name->from_tag) -return (name->taggerdate > taggerdate || - (name->taggerdate == taggerdate && - name_distance > new_distance)); +return name_distance > new_distance;/* * We know that at least one of them is a non-tag at this point.
t/t6120-describe.sh +6 -0
@@ -657,4 +657,10 @@ test_expect_success 'setup: describe commits with disjoint bases 2' ' check_describe -C disjoint2 "B-3-gHASH" HEAD +test_expect_success 'setup misleading taggerdates' ' + GIT_COMMITTER_DATE="2006-12-12 12:31" git tag -a -m "another tag" newer-tag-older-commit unique-file~1 +' + +check_describe newer-tag-older-commit~1 --contains unique-file~2 + test_done
base-commit: 221222b278e713054e65cbbbcb2b1ac85483ea89
Signature · 1 line
gitgitgadget
Re: [PATCH v2] name-rev: fix names by dropping taggerdate workaround
Are there any cases where a taggerdate heuristic would be useful now? I'm having a hard time coming up with an example of such, so this change looks very reasonable to me. Even if there existed such a case, I would imagine it would be better solved using other heuristics rather than checking the taggerdate since that was a very loose heuristic to begin with.
builtin/name-rev.c static int is_better_name(struct rev_name *name, · line 116
Quoted 12 lines
builtin/name-rev.c +1
-3@@ -113,9 +113,7 @@ static int is_better_name(struct rev_name *name,* based on the older tag, even if it is farther away. */ if (from_tag && name->from_tag) -return (name->taggerdate > taggerdate || - (name->taggerdate == taggerdate && - name_distance > new_distance)); +return name_distance > new_distance;
Comment above this block should be updated to match the new logic.
-Calvin
Re: [PATCH v2] name-rev: fix names by dropping taggerdate workaround
Quoted 7 lines · Calvin Wan
Are there any cases where a taggerdate heuristic would be useful now? I'm having a hard time coming up with an example of such, so this change looks very reasonable to me. Even if there existed such a case, I would imagine it would be better solved using other heuristics rather than checking the taggerdate since that was a very loose heuristic to begin with.
I'm currently only aware of cases where the heuristic hurts and none where it helps. I know it historically helped, but that was just a workaround to the algorithm being suboptimal. Since the algorithm has been fixed, I think the workaround can be shelved.
Quoted 6 lines
Quoted 6 lines
builtin/name-rev.c +0
-0@@ -113,9 +113,7 @@ static int is_better_name(struct rev_name *name,* based on the older tag, even if it is farther away.
Quoted 8 lines
builtin/name-rev.c static int is_better_name(struct rev_name *name, · line 116
Quoted 6 lines
builtin/name-rev.c +1
-3*/ if (from_tag && name->from_tag) -return (name->taggerdate > taggerdate || - (name->taggerdate == taggerdate && - name_distance > new_distance)); +return name_distance > new_distance;Comment above this block should be updated to match the new logic.
Good catch; will fix.
PATCH v3 1/1 name-rev: fix names by dropping taggerdate workaround
In reply to Elijah Newren via GitGitGadgetFrom: Elijah Newren <[email protected]>
Commit 7550424804 ("name-rev: include taggerdate in considering the best name", 2016-04-22) introduced the idea of using taggerdate in the criteria for selecting the best name. At the time, a certain commit in linux.git -- namely, aed06b9cfcab -- was being named by name-rev as
v4.6-rc1~9^2~792
which, while correct, was very suboptimal. Some investigation found
that tweaking the MERGE_TRAVERSAL_WEIGHT to lower it could give
alternate answers such as
v3.13-rc7~9^2~14^2~42
or
v3.13~5^2~4^2~2^2~1^2~42
A manual solution involving looking at tagger dates came up with
v3.13-rc1~65^2^2~42which is much nicer. That workaround was then implemented in name-rev.
Unfortunately, the taggerdate heuristic is causing bugs. I was pointed to a case in a private repository where name-rev reports a name of the form
v2022.10.02~86
when users expected to see one of the form
v2022.10.01~2(I've modified the names and numbers a bit from the real testcase.) As you can probably guess, v2022.10.01 was created after v2022.10.02 (by a few hours), even though it pointed to an older commit. While the condition is unusual even in the repository in question, it is not the only problematic set of tags in that repository. The taggerdate logic is causing problems.
Further, it turns out that this taggerdate heuristic isn't even helping anymore. Due to the fix to naming logic in 3656f84278 ("name-rev:
prefer shorter names over following merges", 2021-12-04), we get improved names without the taggerdate heuristic. For the original commit of interest in linux.git, a modern git without the taggerdate heuristic still provides the same optimal answer of interest, namely:
v3.13-rc1~65^2^2~42
So, the taggerdate is no longer providing benefit, and it is causing problems. Simply get rid of it.
However, note that "taggerdate" as a variable is used to store things besides a taggerdate these days. Ever since commit ef1e74065c ("name-rev: favor describing with tags and use committer date to tiebreak", 2017-03-29), this has been used to store committer dates and there it is used as a fallback tiebreaker (as opposed to a primary criteria overriding effective distance calculations). We do not want to remove that fallback tiebreaker, so not all instances of "taggerdate" are removed in this change.
---
name-rev: fix names by dropping taggerdate workaround
Changes since v2: Fixed nearby comments based on code changes
Changes since v1: Slight tweaks to the commit message
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1468%2Fnewren%2Ffix-name-rev-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1468/newren/fix-name-rev-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/1468
Range-diff vs v2:
1: 206726fc954 ! 1: ff57b1583b1 name-rev: fix names by dropping taggerdate workaround
@@ Commit message
## builtin/name-rev.c ##
@@ builtin/name-rev.c: static int is_better_name(struct rev_name *name,
- * based on the older tag, even if it is farther away.
- */
+ 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.
+- */
++ /* If both are tags, we prefer the nearer one. */
if (from_tag && name->from_tag)
- return (name->taggerdate > taggerdate ||
- (name->taggerdate == taggerdate &&
- name_distance > new_distance));
+ return name_distance > new_distance;
- /*
- * We know that at least one of them is a non-tag at this point.
+- /*
+- * We know that at least one of them is a non-tag at this point.
+- * favor a tag over a non-tag.
+- */
++ /* Favor a tag over a non-tag. */
+ if (name->from_tag != from_tag)
+ return from_tag;
+
## t/t6120-describe.sh ##
@@ t/t6120-describe.sh: test_expect_success 'setup: describe commits with disjoint bases 2' '
builtin/name-rev.c | 14 +++----------- t/t6120-describe.sh | 6 ++++++ 2 files changed, 9 insertions(+), 11 deletions(-)
builtin/name-rev.c +3 -11
@@ -108,19 +108,11 @@ static int is_better_name(struct rev_name *name,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. -*/ +/* If both are tags, we prefer the nearer one. */ if (from_tag && name->from_tag) -return (name->taggerdate > taggerdate || - (name->taggerdate == taggerdate && - name_distance > new_distance)); +return name_distance > new_distance; -/* -* We know that at least one of them is a non-tag at this point. -* favor a tag over a non-tag. -*/ +/* Favor a tag over a non-tag. */ if (name->from_tag != from_tag)return from_tag;
t/t6120-describe.sh +6 -0
@@ -657,4 +657,10 @@ test_expect_success 'setup: describe commits with disjoint bases 2' ' check_describe -C disjoint2 "B-3-gHASH" HEAD +test_expect_success 'setup misleading taggerdates' ' + GIT_COMMITTER_DATE="2006-12-12 12:31" git tag -a -m "another tag" newer-tag-older-commit unique-file~1 +' + +check_describe newer-tag-older-commit~1 --contains unique-file~2 + test_done
base-commit: 221222b278e713054e65cbbbcb2b1ac85483ea89
Signature · 1 line
gitgitgadget
Re: [PATCH v3] name-rev: fix names by dropping taggerdate workaround
builtin/name-rev.c static int is_better_name(struct rev_name *name, · line 113
Quoted 10 lines · Elijah Newren via GitGitGadget
builtin/name-rev.c +2
-7-/* -* When comparing names based on tags, prefer names -* based on the older tag, even if it is farther away. -*/ +/* If both are tags, we prefer the nearer one. */ if (from_tag && name->from_tag) -return (name->taggerdate > taggerdate || - (name->taggerdate == taggerdate && - name_distance > new_distance)); +return name_distance > new_distance;
OK.
builtin/name-rev.c static int is_better_name(struct rev_name *name, · line 117
Quoted 7 lines
builtin/name-rev.c +1
-4-/* -* We know that at least one of them is a non-tag at this point. -* favor a tag over a non-tag. -*/ +/* Favor a tag over a non-tag. */ if (name->from_tag != from_tag)return from_tag;
The removed sentence is not something whose validity has changed due to the code change. We still know at this point one of from_tag or name->from_tag is false, thanks to the previous check, whose condition did not change (only what is returned when the condition holds changed). But it may be obvious to readers, so, ... OK.