Preserve topological ordering after merges

From: Sergey Rudyshin <[email protected]>

* E

|\
| * D
| |\
| |/
|/|

* | C
| * B
|/
* A

commit B is placed between A and C, which is wrong because E stays that D and B comes after C

the only correct solution here is

* E

|\
| * D
| |\
| |/
|/|
| * B

* | C
|/
* A

while it seems that it contradicts to
D stating that C should be between D and B
The new algorithm solves this issue

Here is an example:
* walk to to the root via "first" parents;
* go E -> C -> A;
* print A because it has no parents;
* step back to C;
* print C because it has no other parents;
* then step back to E;
* go D -> B -> A;
* do not print A because A is already printed;
* step back to B;
* print B;
* so on.

This change makes option "--topo-order" obsolete, because there is only one way to order parents of a single commit. "--date-order" and "--author-date-order" are preserved and make sense only for the case when multiple commits are given
to be able to sort those commits.

Signed-off-by Sergey Rudyshin <[email protected]>

---
 Documentation/git-rev-list.txt             |   4 +-
 Documentation/rev-list-options.txt         |  41 +++---
 commit.c                                   | 149 ++++++++++++++-------
 commit.h                                   |   4 +-
 t/t4202-log.sh                             |  15 +--
 t/t4215-log-skewed-merges.sh               |  44 +++---
 t/t6003-rev-list-topo-order.sh             |  54 ++++----
 t/t6012-rev-list-simplify.sh               |   8 +-
 t/t6016-rev-list-graph-simplify-history.sh |  41 +++---
 t/t6600-test-reach.sh                      |   6 +-
 10 files changed, 214 insertions(+), 152 deletions(-)

Documentation/git-rev-list.txt +2 -2

index 025c911436..ad1fda7a54 100644
@@ -3,7 +3,7 @@ git-rev-list(1)
 
 NAME
 ----
-git-rev-list - Lists commit objects in reverse chronological order
+git-rev-list - Lists commit objects in reverse topological order
 
 
 SYNOPSIS

@@ -17,7 +17,7 @@ DESCRIPTION
 List commits that are reachable by following the `parent` links from the
 given commit(s), but exclude commits that are reachable from the one(s)
 given with a '{caret}' in front of them.  The output is given in reverse
-chronological order by default.
+topological order by default.
 
 You can think of this as a set operation.  Commits given on the command
 line form a set of commits that are reachable from any of them, and then

Documentation/rev-list-options.txt +22 -19

index bfd02ade99..7ab2f451ae 100644
@@ -643,39 +643,42 @@ ifndef::git-shortlog[]
 Commit Ordering
 ~~~~~~~~~~~~~~~
 
-By default, the commits are shown in reverse chronological order.
+By default, the commits are shown in reverse topological order.
++
+Meaning that no parents are shown before all of its children and
+merges do not change the previous order.
++
+E.g., if commit M0 produces topologically ordered list of
+commits L0 then commit M1 created by merging any commit into M0
+produces list L1 which starts with L0
++
+In case if multiple commits are given via the command line
+the following parameters determine the order among them:
 
 --date-order::
-	Show no parents before all of its children are shown, but
-	otherwise show commits in the commit timestamp order.
+	show commits in the commit timestamp order.
 
 --author-date-order::
-	Show no parents before all of its children are shown, but
-	otherwise show commits in the author timestamp order.
+	show commits in the author timestamp order.
 
 --topo-order::
-	Show no parents before all of its children are shown, and
-	avoid showing commits on multiple lines of history
-	intermixed.
+	show commits in the commit timestamp order.
+	this is deprecated and will be
+	removed in the future.
 +
 For example, in a commit history like this:
 +
 ----------------------------------------------------------------
-
-    ---1----2----4----7
-	\	       \
-	 3----5----6----8---
-
+   1----2-----------5
+    \    \         /
+     -----\---3---4---6
+           \     /
+            ----
 ----------------------------------------------------------------
 +
 where the numbers denote the order of commit timestamps, `git
 rev-list` and friends with `--date-order` show the commits in the
-timestamp order: 8 7 6 5 4 3 2 1.
-+
-With `--topo-order`, they would show 8 6 5 3 7 4 2 1 (or 8 7 4 2 6 5
-3 1); some older commits are shown before newer ones in order to
-avoid showing the commits from two parallel development track mixed
-together.
+following order: 1 2 3 4 5 6.
 
 --reverse::
 	Output the commits chosen to be shown (see Commit Limiting

commit.c +104 -45

index 434ec030d6..01e9d07db9 100644
@@ -738,6 +738,12 @@ int compare_commits_by_author_date(const void *a_, const void *b_,
 	return 0;
 }
 
+static int compare_commits_by_author_date_rev(const void *a_, const void *b_,
+				   void *cb_data)
+{
+	return compare_commits_by_author_date(b_, a_, cb_data);
+}
+
 int compare_commits_by_gen_then_commit_date(const void *a_, const void *b_, void *unused)
 {
 	const struct commit *a = a_, *b = b_;

@@ -767,36 +773,83 @@ int compare_commits_by_commit_date(const void *a_, const void *b_, void *unused)
 	return 0;
 }
 
+static int compare_commits_by_commit_date_rev(const void *a_, const void *b_, void *unused)
+{
+	return compare_commits_by_commit_date (b_, a_, unused);
+}
+
+struct maze {
+	struct commit *ret;
+	struct commit *out;
+};
+
+define_commit_slab(maze_slab, struct maze *);
+
+/*
+ * returns the next commit while exploring the maze
+ * current commit has the information:
+ * 	- what was the last commit we went for (OUT)
+ * 	- from which commit we came in (RET)
+ * trying to find a parent next to OUT
+ * if it does not exists returns RET
+ * otherwise returns the found parent
+ */
+static struct commit *get_next(struct commit *commit, struct maze *mz, struct indegree_slab *indegree)
+{
+	struct commit_list *parents = commit->parents;
+	struct commit *next = NULL;
+	int found = 0;
+
+	while (parents) {
+		struct commit *parent = parents->item;
+
+		if (*indegree_slab_at(indegree, parent)) {
+
+			if (!mz->out || found) {
+				next = parent;
+				break;
+			} else if  (mz->out == parent) {
+				found = 1;
+			}
+		}
+		parents = parents->next;
+	}
+
+	if (!next) next = mz->ret;
+
+	return next;
+}
+
 /*
  * Performs an in-place topological sort on the list supplied.
  */
 void sort_in_topological_order(struct commit_list **list, enum rev_sort_order sort_order)
 {
 	struct commit_list *next, *orig = *list;
-	struct commit_list **pptr;
+	struct commit_list **pptr = list;
 	struct indegree_slab indegree;
-	struct prio_queue queue;
+	struct prio_queue queue_tips;
 	struct commit *commit;
 	struct author_date_slab author_date;
+	struct maze_slab maze;
+	struct maze *mz;
 
 	if (!orig)
 		return;
 	*list = NULL;
 
 	init_indegree_slab(&indegree);
-	memset(&queue, '\0', sizeof(queue));
+	init_maze_slab(&maze);
+	memset(&queue_tips, '\0', sizeof(queue_tips));
 
 	switch (sort_order) {
-	default: /* REV_SORT_IN_GRAPH_ORDER */
-		queue.compare = NULL;
-		break;
-	case REV_SORT_BY_COMMIT_DATE:
-		queue.compare = compare_commits_by_commit_date;
+	default:
+		queue_tips.compare = compare_commits_by_commit_date_rev;
 		break;
 	case REV_SORT_BY_AUTHOR_DATE:
 		init_author_date_slab(&author_date);
-		queue.compare = compare_commits_by_author_date;
-		queue.cb_data = &author_date;
+		queue_tips.compare = compare_commits_by_author_date_rev;
+		queue_tips.cb_data = &author_date;
 		break;
 	}
 

@@ -804,9 +857,10 @@ void sort_in_topological_order(struct commit_list **list, enum rev_sort_order so
 	for (next = orig; next; next = next->next) {
 		struct commit *commit = next->item;
 		*(indegree_slab_at(&indegree, commit)) = 1;
-		/* also record the author dates, if needed */
-		if (sort_order == REV_SORT_BY_AUTHOR_DATE)
-			record_author_date(&author_date, commit);
+		mz = xmalloc(sizeof(struct maze));
+		mz->ret = NULL;
+		mz->out = NULL;
+		*(maze_slab_at(&maze, commit)) = mz;
 	}
 
 	/* update the indegree */

@@ -832,51 +886,56 @@ void sort_in_topological_order(struct commit_list **list, enum rev_sort_order so
 	for (next = orig; next; next = next->next) {
 		struct commit *commit = next->item;
 
-		if (*(indegree_slab_at(&indegree, commit)) == 1)
-			prio_queue_put(&queue, commit);
+		if (*(indegree_slab_at(&indegree, commit)) == 1) {
+			/* also record the author dates, if needed */
+			if (sort_order == REV_SORT_BY_AUTHOR_DATE)
+				record_author_date(&author_date, commit);
+			prio_queue_put(&queue_tips, commit);
+		}
 	}
 
-	/*
-	 * This is unfortunate; the initial tips need to be shown
-	 * in the order given from the revision traversal machinery.
-	 */
-	if (sort_order == REV_SORT_IN_GRAPH_ORDER)
-		prio_queue_reverse(&queue);
-
 	/* We no longer need the commit list */
 	free_commit_list(orig);
 
 	pptr = list;
 	*list = NULL;
-	while ((commit = prio_queue_get(&queue)) != NULL) {
-		struct commit_list *parents;
-
-		for (parents = commit->parents; parents ; parents = parents->next) {
-			struct commit *parent = parents->item;
-			int *pi = indegree_slab_at(&indegree, parent);
 
-			if (!*pi)
+	while ((commit = prio_queue_get(&queue_tips)) != NULL) {
+		struct commit *prev_commit = NULL;
+		while (commit) {
+			mz = *(maze_slab_at(&maze, commit));
+			if (!prev_commit) {
+				/* either a new tip or
+				 * after entering an already visited commit
+				 */
+			}
+			else if (!mz->out) {
+				/* happens only once for every commit
+				 * note that for tips RET is set to NULL
+				 */
+				mz->ret = prev_commit;
+			}
+			else if (prev_commit != mz->out) {
+				/* entered an already visited commit
+				 * step back
+				 */
+				commit = prev_commit;
+				prev_commit = NULL;
 				continue;
-
-			/*
-			 * parents are only enqueued for emission
-			 * when all their children have been emitted thereby
-			 * guaranteeing topological order.
-			 */
-			if (--(*pi) == 1)
-				prio_queue_put(&queue, parent);
+			}
+			mz->out = get_next(commit, mz, &indegree);
+			if (mz->out == mz->ret) {
+				/* upon leaving a commit emit it */
+				*pptr = commit_list_insert(commit, pptr);
+			}
+			prev_commit = commit;
+			commit = mz->out;
 		}
-		/*
-		 * all children of commit have already been
-		 * emitted. we can emit it now.
-		 */
-		*(indegree_slab_at(&indegree, commit)) = 0;
-
-		pptr = &commit_list_insert(commit, pptr)->next;
 	}
 
 	clear_indegree_slab(&indegree);
-	clear_prio_queue(&queue);
+	clear_maze_slab(&maze);
+	clear_prio_queue(&queue_tips);
 	if (sort_order == REV_SORT_BY_AUTHOR_DATE)
 		clear_author_date_slab(&author_date);
 }

commit.h +1 -3

index 221cdaa34b..1fe3cc240e 100644
@@ -209,7 +209,7 @@ struct commit *pop_commit(struct commit_list **stack);
 void clear_commit_marks(struct commit *commit, unsigned int mark);
 void clear_commit_marks_many(int nr, struct commit **commit, unsigned int mark);
 
-
+/* TODO get rid of rev_sort_order in a favour of positional parameters */
 enum rev_sort_order {
 	REV_SORT_IN_GRAPH_ORDER = 0,
 	REV_SORT_BY_COMMIT_DATE,

@@ -222,8 +222,6 @@ enum rev_sort_order {
  *   invariant of resulting list is:
  *      a reachable from b => ord(b) < ord(a)
  *   sort_order further specifies:
- *   REV_SORT_IN_GRAPH_ORDER: try to show a commit on a single-parent
- *                            chain together.
  *   REV_SORT_BY_COMMIT_DATE: show eligible commits in committer-date order.
  */
 void sort_in_topological_order(struct commit_list **, enum rev_sort_order);

t/t4202-log.sh +7 -8

index 2c9489484a..46f04b36a3 100755
@@ -635,17 +635,16 @@ test_expect_success 'set up more tangled history' '
 cat > expect <<\EOF
 *   Merge tag 'reach'
 |\
-| \
+| * reach
+| |
 |  \
 *-. \   Merge tags 'octopus-a' and 'octopus-b'
 |\ \ \
-* | | | seventh
 | | * | octopus-b
-| |/ /
-|/| |
-| * | octopus-a
-|/ /
-| * reach
+| | |/
+| * / octopus-a
+| |/
+* / seventh
 |/
 *   Merge branch 'tangle'
 |\

@@ -673,7 +672,7 @@ cat > expect <<\EOF
 * initial
 EOF
 
-test_expect_success 'log --graph with merge' '
+test_expect_success 'log --graph with merge tag reach' '
 	git log --graph --date-order --pretty=tformat:%s |
 		sed "s/ *\$//" >actual &&
 	test_cmp expect actual

t/t4215-log-skewed-merges.sh +22 -22

index 18709a723e..91630c0cae 100755
@@ -5,7 +5,7 @@ test_description='git log --graph of skewed merges'
 . ./test-lib.sh
 
 check_graph () {
-	cat >expect &&
+	sed "s/ *$//" >expect &&
 	git log --graph --pretty=tformat:%s "$@" >actual.raw &&
 	sed "s/ *$//" actual.raw >actual &&
 	test_cmp expect actual

@@ -185,20 +185,21 @@ test_expect_success 'log --graph with right-skewed merge following a left-skewed
 
 	check_graph --date-order <<-\EOF
 	*   4_H
-	|\
+	|\
 	| *   4_G
-	| |\
+	| |\
+	| | * 4_C
 	| * | 4_F
-	|/| |
+	|/| |
 	| * |   4_E
-	| |\ \
-	| | * | 4_D
-	| |/ /
-	|/| |
-	| | * 4_C
-	| |/
+	| |\ \
+	| | |/
+	| |/|
+	| | * 4_D
+	| |/
+	|/|
 	| * 4_B
-	|/
+	|/
 	* 4_A
 	EOF
 '

@@ -221,21 +222,20 @@ test_expect_success 'log --graph with octopus merge with column joining its penu
 
 	check_graph <<-\EOF
 	*   5_H
-	|\
+	|\
 	| *-.   5_G
-	| |\ \
+	| |\ \
 	| | | * 5_F
 	| | * |   5_E
-	| |/|\ \
-	| |_|/ /
-	|/| | /
-	| | |/
-	* | | 5_D
+	| |/|\ \
+	| |_|/ /
+	|/| | /
+	| | |/
 	| | * 5_C
-	| |/
-	|/|
-	| * 5_B
-	|/
+	| * | 5_B
+	| |/
+	* / 5_D
+	|/
 	* 5_A
 	EOF
 '

t/t6003-rev-list-topo-order.sh +27 -27

index 24d1836f41..19cb79bc29 100755
@@ -87,12 +87,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 l1

@@ -105,15 +105,15 @@ l5
 l4
 l3
 a4
-b4
-a3
-a2
 c3
 c2
+c1
+b4
 b3
 b2
-c1
 b1
+a3
+a2
 a1
 a0
 l2

@@ -127,12 +127,12 @@ l5
 l4
 l3
 a4
-b4
 c3
 c2
+c1
+b4
 b3
 b2
-c1
 b1
 a3
 a2

@@ -205,12 +205,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 EOF

@@ -224,12 +224,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 EOF

@@ -237,10 +237,10 @@ EOF
 test_output_expect_success 'prune near topo' 'git rev-list --topo-order a4 ^c3' <<EOF
 a4
 b4
+b3
 a3
 a2
 a1
-b3
 EOF
 
 test_output_expect_success "head has no parent" 'git rev-list --topo-order  root' <<EOF

@@ -297,8 +297,8 @@ c3
 c2
 c1
 b4
-a3
-a2
+b3
+b2
 EOF
 
 test_output_expect_success "max-count 10 - non topo order" 'git rev-list --max-count=10 l5' <<EOF

@@ -376,12 +376,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 l1

@@ -399,12 +399,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 l1

@@ -428,12 +428,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 l1

t/t6012-rev-list-simplify.sh +4 -4

index a10f0df02b..9f687b6b22 100755
@@ -122,16 +122,16 @@ check_result () {
 
 check_result 'L K J I H F E D C G B A' --full-history --topo-order
 check_result 'L K I H G F E D C B J A' --full-history
-check_result 'L K I H G F E D C B J A' --full-history --date-order
-check_result 'L K I H G F E D B C J A' --full-history --author-date-order
+check_result 'L K J I H F E D C G B A' --full-history --date-order
+check_result 'L K J I H F E D C G B A' --full-history --author-date-order
 check_result 'K I H E C B A' --full-history -- file
 check_result 'K I H E C B A' --full-history --topo-order -- file
 check_result 'K I H E C B A' --full-history --date-order -- file
-check_result 'K I H E B C A' --full-history --author-date-order -- file
+check_result 'K I H E C B A' --full-history --author-date-order -- file
 check_result 'I E C B A' --simplify-merges -- file
 check_result 'I E C B A' --simplify-merges --topo-order -- file
 check_result 'I E C B A' --simplify-merges --date-order -- file
-check_result 'I E B C A' --simplify-merges --author-date-order -- file
+check_result 'I E C B A' --simplify-merges --author-date-order -- file
 check_result 'I B A' -- file
 check_result 'I B A' --topo-order -- file
 check_result 'I B A' --date-order -- file

t/t6016-rev-list-graph-simplify-history.sh +21 -20

index f5e6e92f5b..5750c6f0fd 100755
@@ -235,27 +235,28 @@ test_expect_success '--graph ^C3' '
 # I don't think the ordering of the boundary commits is really
 # that important, but this test depends on it.  If the ordering ever changes
 # in the code, we'll need to update this test.
-test_expect_success '--graph --boundary ^C3' '
+test_expect_success '--graph --boundary --all ^C3' '
 	rm -f expected &&
-	echo "* $A7" >> expected &&
-	echo "*   $A6" >> expected &&
-	echo "|\\  " >> expected &&
-	echo "| * $C4" >> expected &&
-	echo "* | $A5" >> expected &&
-	echo "| |     " >> expected &&
-	echo "|  \\    " >> expected &&
-	echo "*-. \\   $A4" >> expected &&
-	echo "|\\ \\ \\  " >> expected &&
-	echo "| * | | $B2" >> expected &&
-	echo "| * | | $B1" >> expected &&
-	echo "* | | | $A3" >> expected &&
-	echo "o | | | $A2" >> expected &&
-	echo "|/ / /  " >> expected &&
-	echo "o / / $A1" >> expected &&
-	echo " / /  " >> expected &&
-	echo "| o $C3" >> expected &&
-	echo "|/  " >> expected &&
-	echo "o $C2" >> expected &&
+	cat >> expected <<-TESTDATA &&
+	* $A7
+	*   $A6
+	|\
+	| * $C4
+	* | $A5
+	| |
+	|  \
+	*-. \   $A4
+	|\ \ \
+	| * | | $B2
+	| * | | $B1
+	* | | | $A3
+	| | | o $C3
+	| | |/
+	| | o $C2
+	o | $A2
+	|/
+	o $A1
+	TESTDATA
 	git rev-list --graph --boundary --all ^C3 > actual &&
 	test_cmp expected actual
 	'

t/t6600-test-reach.sh +4 -3

index b24d850036..a6d389c4fd 100755
@@ -339,6 +339,8 @@ test_expect_success 'rev-list: ancestry-path topo-order' '
 	run_three_modes git rev-list --topo-order --ancestry-path commit-3-3..commit-6-6
 '
 
+# TODO get rid of the "sort" below
+# if commitGraph is enabled then sort_in_topological_order is not envoked
 test_expect_success 'rev-list: symmetric difference topo-order' '
 	git rev-parse \
 		commit-6-6 commit-5-6 commit-4-6 \

@@ -349,8 +351,8 @@ test_expect_success 'rev-list: symmetric difference topo-order' '
 		commit-6-1 commit-5-1 commit-4-1 \
 		commit-3-8 commit-2-8 commit-1-8 \
 		commit-3-7 commit-2-7 commit-1-7 \
-	>expect &&
-	run_three_modes git rev-list --topo-order commit-3-8...commit-6-6
+	| sort >expect &&
+	run_three_modes git rev-list --topo-order commit-3-8...commit-6-6 | sort
 '
 
 test_expect_success 'get_reachable_subset:all' '
--

gitgitgadget

This modifies the algoritm of topopological ordering. The problem with the current algoritm is that it displays the graph below as following

* E

|\
| * D
| |\
| |/
|/|

* | C
| * B
|/
* A

commit B is placed between A and C, which is wrong because E stays that D and B comes after C

the only correct solution here is

* E

|\
| * D
| |\
| |/
|/|
| * B

* | C
|/
* A

while it seems that it contradicts to D staiting that C shoud be between D and B The new algorithm solves this issue

Here is an example: walk to to the root via "first" parents go E -> C -> A print A because it has no parents step back to C print C because it has no other parents then step back to E go D -> B -> A do not print A becase A is already printed step back to B print B so on

This change makes option "--topo-order" obsolete, because for a single commit there is only one way to order parents. "--date-order" and "--author-date-order" are preserved and make sence only for the case when multiple commits are given to be able to sort those commits.

Sergey Rudyshin (1):
Preserve topological ordering after merges This modifies the algorithm
of topopological ordering. The problem with the current algoritm is that it displays the graph below as follows

 Documentation/git-rev-list.txt             |   4 +-
 Documentation/rev-list-options.txt         |  41 +++---
 commit.c                                   | 149 ++++++++++++++-------
 commit.h                                   |   4 +-
 t/t4202-log.sh                             |  15 +--
 t/t4215-log-skewed-merges.sh               |  44 +++---
 t/t6003-rev-list-topo-order.sh             |  54 ++++----
 t/t6012-rev-list-simplify.sh               |   8 +-
 t/t6016-rev-list-graph-simplify-history.sh |  41 +++---
 t/t6600-test-reach.sh                      |   6 +-
 10 files changed, 214 insertions(+), 152 deletions(-)

base-commit: 8679ef24ed64018bb62170c43ce73e0261c0600a
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-514%2FSergeyRudyshin%2Ftopo_order_fix-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-514/SergeyRudyshin/topo_order_fix-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/514
--
gitgitgadget

From: Sergey Rudyshin <[email protected]>

* E

|\
| * D
| |\
| |/
|/|

* | C
| * B
|/
* A

commit B is placed between A and C, which is wrong because E stays that D and B comes after C

the only correct solution here is

* E

|\
| * D
| |\
| |/
|/|
| * B

* | C
|/
* A

while it seems that it contradicts to
D stating that C should be between D and B
The new algorithm solves this issue

This change makes option "--topo-order" obsolete, because there is only one way to order parents of a single commit. "--date-order" and "--author-date-order" are preserved and make sense only for the case when multiple commits are given
to be able to sort those commits.

void sort_in_topological_order(struct commit_list **list, enum rev_sort_order sort_order)

Hi Sergey,

please note that the commit message's first line should not be longer than 76 characters per line, and it should be followed by an empty line. I think that you forgot the empty line, looking at
https://github.com/gitgitgadget/git/pull/514/commits/542a02020c8578d0e004cb9c929bced8719b902a

Hi Sergey,

please note that the commit message's first line should not be longer than 76 characters per line, and it should be followed by an empty line. I think that you forgot the empty line, looking at
https://github.com/gitgitgadget/git/pull/514/commits/542a02020c8578d0e004cb9c929bced8719b902a

Ciao,
Johannes

Quoted 768 lines · Sergey Rudyshin via GitGitGadget

From: Sergey Rudyshin <[email protected]>

* E

|\
| * D
| |\
| |/
|/|

* | C
| * B
|/
* A

commit B is placed between A and C, which is wrong because E stays that D and B comes after C

the only correct solution here is

* E

|\
| * D
| |\
| |/
|/|
| * B

* | C
|/
* A

while it seems that it contradicts to
D stating that C should be between D and B
The new algorithm solves this issue

Here is an example:
* walk to to the root via "first" parents;
* go E -> C -> A;
* print A because it has no parents;
* step back to C;
* print C because it has no other parents;
* then step back to E;
* go D -> B -> A;
* do not print A because A is already printed;
* step back to B;
* print B;
* so on.

This change makes option "--topo-order" obsolete, because there is only one way to order parents of a single commit. "--date-order" and "--author-date-order" are preserved and make sense only for the case when multiple commits are given
to be able to sort those commits.

Signed-off-by Sergey Rudyshin <[email protected]>

---
 Documentation/git-rev-list.txt             |   4 +-
 Documentation/rev-list-options.txt         |  41 +++---
 commit.c                                   | 149 ++++++++++++++-------
 commit.h                                   |   4 +-
 t/t4202-log.sh                             |  15 +--
 t/t4215-log-skewed-merges.sh               |  44 +++---
 t/t6003-rev-list-topo-order.sh             |  54 ++++----
 t/t6012-rev-list-simplify.sh               |   8 +-
 t/t6016-rev-list-graph-simplify-history.sh |  41 +++---
 t/t6600-test-reach.sh                      |   6 +-
 10 files changed, 214 insertions(+), 152 deletions(-)

Documentation/git-rev-list.txt +2 -2

index 025c911436..ad1fda7a54 100644
@@ -3,7 +3,7 @@ git-rev-list(1)
 
 NAME
 ----
-git-rev-list - Lists commit objects in reverse chronological order
+git-rev-list - Lists commit objects in reverse topological order
 
 
 SYNOPSIS

@@ -17,7 +17,7 @@ DESCRIPTION
 List commits that are reachable by following the `parent` links from the
 given commit(s), but exclude commits that are reachable from the one(s)
 given with a '{caret}' in front of them.  The output is given in reverse
-chronological order by default.
+topological order by default.
 
 You can think of this as a set operation.  Commits given on the command
 line form a set of commits that are reachable from any of them, and then

Documentation/rev-list-options.txt +22 -19

index bfd02ade99..7ab2f451ae 100644
@@ -643,39 +643,42 @@ ifndef::git-shortlog[]
 Commit Ordering
 ~~~~~~~~~~~~~~~
 
-By default, the commits are shown in reverse chronological order.
+By default, the commits are shown in reverse topological order.
++
+Meaning that no parents are shown before all of its children and
+merges do not change the previous order.
++
+E.g., if commit M0 produces topologically ordered list of
+commits L0 then commit M1 created by merging any commit into M0
+produces list L1 which starts with L0
++
+In case if multiple commits are given via the command line
+the following parameters determine the order among them:
 
 --date-order::
-     Show no parents before all of its children are shown, but
-     otherwise show commits in the commit timestamp order.
+     show commits in the commit timestamp order.
 
 --author-date-order::
-     Show no parents before all of its children are shown, but
-     otherwise show commits in the author timestamp order.
+     show commits in the author timestamp order.
 
 --topo-order::
-     Show no parents before all of its children are shown, and
-     avoid showing commits on multiple lines of history
-     intermixed.
+     show commits in the commit timestamp order.
+     this is deprecated and will be
+     removed in the future.
 +
 For example, in a commit history like this:
 +
 ----------------------------------------------------------------
-
-    ---1----2----4----7
-     \              \
-      3----5----6----8---
-
+   1----2-----------5
+    \    \         /
+     -----\---3---4---6
+           \     /
+            ----
 ----------------------------------------------------------------
 +
 where the numbers denote the order of commit timestamps, `git
 rev-list` and friends with `--date-order` show the commits in the
-timestamp order: 8 7 6 5 4 3 2 1.
-+
-With `--topo-order`, they would show 8 6 5 3 7 4 2 1 (or 8 7 4 2 6 5
-3 1); some older commits are shown before newer ones in order to
-avoid showing the commits from two parallel development track mixed
-together.
+following order: 1 2 3 4 5 6.
 
 --reverse::
      Output the commits chosen to be shown (see Commit Limiting

commit.c +104 -45

index 434ec030d6..01e9d07db9 100644
@@ -738,6 +738,12 @@ int compare_commits_by_author_date(const void *a_, const void *b_,
      return 0;
 }
 
+static int compare_commits_by_author_date_rev(const void *a_, const void *b_,
+                                void *cb_data)
+{
+     return compare_commits_by_author_date(b_, a_, cb_data);
+}
+
 int compare_commits_by_gen_then_commit_date(const void *a_, const void *b_, void *unused)
 {
      const struct commit *a = a_, *b = b_;

@@ -767,36 +773,83 @@ int compare_commits_by_commit_date(const void *a_, const void *b_, void *unused)
      return 0;
 }
 
+static int compare_commits_by_commit_date_rev(const void *a_, const void *b_, void *unused)
+{
+     return compare_commits_by_commit_date (b_, a_, unused);
+}
+
+struct maze {
+     struct commit *ret;
+     struct commit *out;
+};
+
+define_commit_slab(maze_slab, struct maze *);
+
+/*
+ * returns the next commit while exploring the maze
+ * current commit has the information:
+ *   - what was the last commit we went for (OUT)
+ *   - from which commit we came in (RET)
+ * trying to find a parent next to OUT
+ * if it does not exists returns RET
+ * otherwise returns the found parent
+ */
+static struct commit *get_next(struct commit *commit, struct maze *mz, struct indegree_slab *indegree)
+{
+     struct commit_list *parents = commit->parents;
+     struct commit *next = NULL;
+     int found = 0;
+
+     while (parents) {
+             struct commit *parent = parents->item;
+
+             if (*indegree_slab_at(indegree, parent)) {
+
+                     if (!mz->out || found) {
+                             next = parent;
+                             break;
+                     } else if  (mz->out == parent) {
+                             found = 1;
+                     }
+             }
+             parents = parents->next;
+     }
+
+     if (!next) next = mz->ret;
+
+     return next;
+}
+
 /*
  * Performs an in-place topological sort on the list supplied.
  */
 void sort_in_topological_order(struct commit_list **list, enum rev_sort_order sort_order)
 {
      struct commit_list *next, *orig = *list;
-     struct commit_list **pptr;
+     struct commit_list **pptr = list;
      struct indegree_slab indegree;
-     struct prio_queue queue;
+     struct prio_queue queue_tips;
      struct commit *commit;
      struct author_date_slab author_date;
+     struct maze_slab maze;
+     struct maze *mz;
 
      if (!orig)
              return;
      *list = NULL;
 
      init_indegree_slab(&indegree);
-     memset(&queue, '\0', sizeof(queue));
+     init_maze_slab(&maze);
+     memset(&queue_tips, '\0', sizeof(queue_tips));
 
      switch (sort_order) {
-     default: /* REV_SORT_IN_GRAPH_ORDER */
-             queue.compare = NULL;
-             break;
-     case REV_SORT_BY_COMMIT_DATE:
-             queue.compare = compare_commits_by_commit_date;
+     default:
+             queue_tips.compare = compare_commits_by_commit_date_rev;
              break;
      case REV_SORT_BY_AUTHOR_DATE:
              init_author_date_slab(&author_date);
-             queue.compare = compare_commits_by_author_date;
-             queue.cb_data = &author_date;
+             queue_tips.compare = compare_commits_by_author_date_rev;
+             queue_tips.cb_data = &author_date;
              break;
      }
 

@@ -804,9 +857,10 @@ void sort_in_topological_order(struct commit_list **list, enum rev_sort_order so
      for (next = orig; next; next = next->next) {
              struct commit *commit = next->item;
              *(indegree_slab_at(&indegree, commit)) = 1;
-             /* also record the author dates, if needed */
-             if (sort_order == REV_SORT_BY_AUTHOR_DATE)
-                     record_author_date(&author_date, commit);
+             mz = xmalloc(sizeof(struct maze));
+             mz->ret = NULL;
+             mz->out = NULL;
+             *(maze_slab_at(&maze, commit)) = mz;
      }
 
      /* update the indegree */

@@ -832,51 +886,56 @@ void sort_in_topological_order(struct commit_list **list, enum rev_sort_order so
      for (next = orig; next; next = next->next) {
              struct commit *commit = next->item;
 
-             if (*(indegree_slab_at(&indegree, commit)) == 1)
-                     prio_queue_put(&queue, commit);
+             if (*(indegree_slab_at(&indegree, commit)) == 1) {
+                     /* also record the author dates, if needed */
+                     if (sort_order == REV_SORT_BY_AUTHOR_DATE)
+                             record_author_date(&author_date, commit);
+                     prio_queue_put(&queue_tips, commit);
+             }
      }
 
-     /*
-      * This is unfortunate; the initial tips need to be shown
-      * in the order given from the revision traversal machinery.
-      */
-     if (sort_order == REV_SORT_IN_GRAPH_ORDER)
-             prio_queue_reverse(&queue);
-
      /* We no longer need the commit list */
      free_commit_list(orig);
 
      pptr = list;
      *list = NULL;
-     while ((commit = prio_queue_get(&queue)) != NULL) {
-             struct commit_list *parents;
-
-             for (parents = commit->parents; parents ; parents = parents->next) {
-                     struct commit *parent = parents->item;
-                     int *pi = indegree_slab_at(&indegree, parent);
 
-                     if (!*pi)
+     while ((commit = prio_queue_get(&queue_tips)) != NULL) {
+             struct commit *prev_commit = NULL;
+             while (commit) {
+                     mz = *(maze_slab_at(&maze, commit));
+                     if (!prev_commit) {
+                             /* either a new tip or
+                              * after entering an already visited commit
+                              */
+                     }
+                     else if (!mz->out) {
+                             /* happens only once for every commit
+                              * note that for tips RET is set to NULL
+                              */
+                             mz->ret = prev_commit;
+                     }
+                     else if (prev_commit != mz->out) {
+                             /* entered an already visited commit
+                              * step back
+                              */
+                             commit = prev_commit;
+                             prev_commit = NULL;
                              continue;
-
-                     /*
-                      * parents are only enqueued for emission
-                      * when all their children have been emitted thereby
-                      * guaranteeing topological order.
-                      */
-                     if (--(*pi) == 1)
-                             prio_queue_put(&queue, parent);
+                     }
+                     mz->out = get_next(commit, mz, &indegree);
+                     if (mz->out == mz->ret) {
+                             /* upon leaving a commit emit it */
+                             *pptr = commit_list_insert(commit, pptr);
+                     }
+                     prev_commit = commit;
+                     commit = mz->out;
              }
-             /*
-              * all children of commit have already been
-              * emitted. we can emit it now.
-              */
-             *(indegree_slab_at(&indegree, commit)) = 0;
-
-             pptr = &commit_list_insert(commit, pptr)->next;
      }
 
      clear_indegree_slab(&indegree);
-     clear_prio_queue(&queue);
+     clear_maze_slab(&maze);
+     clear_prio_queue(&queue_tips);
      if (sort_order == REV_SORT_BY_AUTHOR_DATE)
              clear_author_date_slab(&author_date);
 }

commit.h +1 -3

index 221cdaa34b..1fe3cc240e 100644
@@ -209,7 +209,7 @@ struct commit *pop_commit(struct commit_list **stack);
 void clear_commit_marks(struct commit *commit, unsigned int mark);
 void clear_commit_marks_many(int nr, struct commit **commit, unsigned int mark);
 
-
+/* TODO get rid of rev_sort_order in a favour of positional parameters */
 enum rev_sort_order {
      REV_SORT_IN_GRAPH_ORDER = 0,
      REV_SORT_BY_COMMIT_DATE,

@@ -222,8 +222,6 @@ enum rev_sort_order {
  *   invariant of resulting list is:
  *      a reachable from b => ord(b) < ord(a)
  *   sort_order further specifies:
- *   REV_SORT_IN_GRAPH_ORDER: try to show a commit on a single-parent
- *                            chain together.
  *   REV_SORT_BY_COMMIT_DATE: show eligible commits in committer-date order.
  */
 void sort_in_topological_order(struct commit_list **, enum rev_sort_order);

t/t4202-log.sh +7 -8

index 2c9489484a..46f04b36a3 100755
@@ -635,17 +635,16 @@ test_expect_success 'set up more tangled history' '
 cat > expect <<\EOF
 *   Merge tag 'reach'
 |\
-| \
+| * reach
+| |
 |  \
 *-. \   Merge tags 'octopus-a' and 'octopus-b'
 |\ \ \
-* | | | seventh
 | | * | octopus-b
-| |/ /
-|/| |
-| * | octopus-a
-|/ /
-| * reach
+| | |/
+| * / octopus-a
+| |/
+* / seventh
 |/
 *   Merge branch 'tangle'
 |\

@@ -673,7 +672,7 @@ cat > expect <<\EOF
 * initial
 EOF
 
-test_expect_success 'log --graph with merge' '
+test_expect_success 'log --graph with merge tag reach' '
      git log --graph --date-order --pretty=tformat:%s |
              sed "s/ *\$//" >actual &&
      test_cmp expect actual

t/t4215-log-skewed-merges.sh +22 -22

index 18709a723e..91630c0cae 100755
@@ -5,7 +5,7 @@ test_description='git log --graph of skewed merges'
 . ./test-lib.sh
 
 check_graph () {
-     cat >expect &&
+     sed "s/ *$//" >expect &&
      git log --graph --pretty=tformat:%s "$@" >actual.raw &&
      sed "s/ *$//" actual.raw >actual &&
      test_cmp expect actual

@@ -185,20 +185,21 @@ test_expect_success 'log --graph with right-skewed merge following a left-skewed
 
      check_graph --date-order <<-\EOF
      *   4_H
-     |\
+     |\
      | *   4_G
-     | |\
+     | |\
+     | | * 4_C
      | * | 4_F
-     |/| |
+     |/| |
      | * |   4_E
-     | |\ \
-     | | * | 4_D
-     | |/ /
-     |/| |
-     | | * 4_C
-     | |/
+     | |\ \
+     | | |/
+     | |/|
+     | | * 4_D
+     | |/
+     |/|
      | * 4_B
-     |/
+     |/
      * 4_A
      EOF
 '

@@ -221,21 +222,20 @@ test_expect_success 'log --graph with octopus merge with column joining its penu
 
      check_graph <<-\EOF
      *   5_H
-     |\
+     |\
      | *-.   5_G
-     | |\ \
+     | |\ \
      | | | * 5_F
      | | * |   5_E
-     | |/|\ \
-     | |_|/ /
-     |/| | /
-     | | |/
-     * | | 5_D
+     | |/|\ \
+     | |_|/ /
+     |/| | /
+     | | |/
      | | * 5_C
-     | |/
-     |/|
-     | * 5_B
-     |/
+     | * | 5_B
+     | |/
+     * / 5_D
+     |/
      * 5_A
      EOF
 '

t/t6003-rev-list-topo-order.sh +27 -27

index 24d1836f41..19cb79bc29 100755
@@ -87,12 +87,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 l1

@@ -105,15 +105,15 @@ l5
 l4
 l3
 a4
-b4
-a3
-a2
 c3
 c2
+c1
+b4
 b3
 b2
-c1
 b1
+a3
+a2
 a1
 a0
 l2

@@ -127,12 +127,12 @@ l5
 l4
 l3
 a4
-b4
 c3
 c2
+c1
+b4
 b3
 b2
-c1
 b1
 a3
 a2

@@ -205,12 +205,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 EOF

@@ -224,12 +224,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 EOF

@@ -237,10 +237,10 @@ EOF
 test_output_expect_success 'prune near topo' 'git rev-list --topo-order a4 ^c3' <<EOF
 a4
 b4
+b3
 a3
 a2
 a1
-b3
 EOF
 
 test_output_expect_success "head has no parent" 'git rev-list --topo-order  root' <<EOF

@@ -297,8 +297,8 @@ c3
 c2
 c1
 b4
-a3
-a2
+b3
+b2
 EOF
 
 test_output_expect_success "max-count 10 - non topo order" 'git rev-list --max-count=10 l5' <<EOF

@@ -376,12 +376,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 l1

@@ -399,12 +399,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 l1

@@ -428,12 +428,12 @@ c3
 c2
 c1
 b4
-a3
-a2
-a1
 b3
 b2
 b1
+a3
+a2
+a1
 a0
 l2
 l1

t/t6012-rev-list-simplify.sh +4 -4

index a10f0df02b..9f687b6b22 100755
@@ -122,16 +122,16 @@ check_result () {
 
 check_result 'L K J I H F E D C G B A' --full-history --topo-order
 check_result 'L K I H G F E D C B J A' --full-history
-check_result 'L K I H G F E D C B J A' --full-history --date-order
-check_result 'L K I H G F E D B C J A' --full-history --author-date-order
+check_result 'L K J I H F E D C G B A' --full-history --date-order
+check_result 'L K J I H F E D C G B A' --full-history --author-date-order
 check_result 'K I H E C B A' --full-history -- file
 check_result 'K I H E C B A' --full-history --topo-order -- file
 check_result 'K I H E C B A' --full-history --date-order -- file
-check_result 'K I H E B C A' --full-history --author-date-order -- file
+check_result 'K I H E C B A' --full-history --author-date-order -- file
 check_result 'I E C B A' --simplify-merges -- file
 check_result 'I E C B A' --simplify-merges --topo-order -- file
 check_result 'I E C B A' --simplify-merges --date-order -- file
-check_result 'I E B C A' --simplify-merges --author-date-order -- file
+check_result 'I E C B A' --simplify-merges --author-date-order -- file
 check_result 'I B A' -- file
 check_result 'I B A' --topo-order -- file
 check_result 'I B A' --date-order -- file

t/t6016-rev-list-graph-simplify-history.sh +21 -20

index f5e6e92f5b..5750c6f0fd 100755
@@ -235,27 +235,28 @@ test_expect_success '--graph ^C3' '
 # I don't think the ordering of the boundary commits is really
 # that important, but this test depends on it.  If the ordering ever changes
 # in the code, we'll need to update this test.
-test_expect_success '--graph --boundary ^C3' '
+test_expect_success '--graph --boundary --all ^C3' '
      rm -f expected &&
-     echo "* $A7" >> expected &&
-     echo "*   $A6" >> expected &&
-     echo "|\\  " >> expected &&
-     echo "| * $C4" >> expected &&
-     echo "* | $A5" >> expected &&
-     echo "| |     " >> expected &&
-     echo "|  \\    " >> expected &&
-     echo "*-. \\   $A4" >> expected &&
-     echo "|\\ \\ \\  " >> expected &&
-     echo "| * | | $B2" >> expected &&
-     echo "| * | | $B1" >> expected &&
-     echo "* | | | $A3" >> expected &&
-     echo "o | | | $A2" >> expected &&
-     echo "|/ / /  " >> expected &&
-     echo "o / / $A1" >> expected &&
-     echo " / /  " >> expected &&
-     echo "| o $C3" >> expected &&
-     echo "|/  " >> expected &&
-     echo "o $C2" >> expected &&
+     cat >> expected <<-TESTDATA &&
+     * $A7
+     *   $A6
+     |\
+     | * $C4
+     * | $A5
+     | |
+     |  \
+     *-. \   $A4
+     |\ \ \
+     | * | | $B2
+     | * | | $B1
+     * | | | $A3
+     | | | o $C3
+     | | |/
+     | | o $C2
+     o | $A2
+     |/
+     o $A1
+     TESTDATA
      git rev-list --graph --boundary --all ^C3 > actual &&
      test_cmp expected actual
      '

t/t6600-test-reach.sh +4 -3

index b24d850036..a6d389c4fd 100755
@@ -339,6 +339,8 @@ test_expect_success 'rev-list: ancestry-path topo-order' '
      run_three_modes git rev-list --topo-order --ancestry-path commit-3-3..commit-6-6
 '
 
+# TODO get rid of the "sort" below
+# if commitGraph is enabled then sort_in_topological_order is not envoked
 test_expect_success 'rev-list: symmetric difference topo-order' '
      git rev-parse \
              commit-6-6 commit-5-6 commit-4-6 \

@@ -349,8 +351,8 @@ test_expect_success 'rev-list: symmetric difference topo-order' '
              commit-6-1 commit-5-1 commit-4-1 \
              commit-3-8 commit-2-8 commit-1-8 \
              commit-3-7 commit-2-7 commit-1-7 \
-     >expect &&
-     run_three_modes git rev-list --topo-order commit-3-8...commit-6-6
+     | sort >expect &&
+     run_three_modes git rev-list --topo-order commit-3-8...commit-6-6 | sort
 '
 
 test_expect_success 'get_reachable_subset:all' '
--

gitgitgadget

Hi Sergey,

Quoted 38 lines · Sergey Rudyshin via GitGitGadget

This modifies the algoritm of topopological ordering. The problem with the current algoritm is that it displays the graph below as following

* E

|\
| * D
| |\
| |/
|/|

* | C
| * B
|/
* A

commit B is placed between A and C, which is wrong because E stays that D and B comes after C

the only correct solution here is

* E

|\
| * D
| |\
| |/
|/|
| * B

* | C
|/
* A

while it seems that it contradicts to D staiting that C shoud be between D and B The new algorithm solves this issue

Here is an example: walk to to the root via "first" parents go E -> C -> A print A because it has no parents step back to C print C because it has no other parents then step back to E go D -> B -> A do not print A becase A is already printed step back to B print B so on

Quoted 4 lines

This change makes option "--topo-order" obsolete, because for a single commit there is only one way to order parents. "--date-order" and "--author-date-order" are preserved and make sence only for the case when multiple commits are given to be able to sort those commits.

I have to admit that I am not a fan of this change, as I find that there are legitimate use cases where I want to order the commits by commit topology, and other use cases where I want to order them by date.

Maybe other reviewers agree with your reasoning, though, in that case you still will need to address the test failures in t4202, t4215 and t6012:
https://dev.azure.com/gitgitgadget/git/_build/results?buildId=25867&view=ms.vss-test-web.build-test-results-tab

Ciao,
Johannes

let me explain in more detail why I thought it would make sense to stop using "--topo-order".
in case if a user specifies a single commit, like this
git rev-list E
with a new algorithm the options "--date-order", "--author-date-order", "--topo-order" do not change the ordering. Because there is only one way to sort any git graph with a single tip.

in case if a user specifies multiple tips, like this
git rev-list --topo-order C B ^A
current version of git displays commits ordered by commit timestamp which does not seem like a topological ordering.

so I decided to change the documentation so that "--topo-order" and "--date-order" be the same. And since "--topo-order" does not add anything new decided to deprecate it.

Regarding the failed test
I'll try to find the reason but what puzzles me is why those tests (t4202, t4215 and t6012) succeeded on all other platforms (linux32, osx-clang, windows, ...) and only failed on linux-gcc. In my machine those tests do not fail either (gcc (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609)

Quoted 25 lines · Sergey Rudyshin via GitGitGadget

From: Sergey Rudyshin <[email protected]>

* E

|\
| * D
| |\
| |/
|/|

* | C
| * B
|/
* A

commit B is placed between A and C, which is wrong because E stays that D and B comes after C

the only correct solution here is

* E

|\
| * D
| |\
| |/
|/|
| * B

Quoted 7 lines

* | C
|/
* A

while it seems that it contradicts to
D stating that C should be between D and B
The new algorithm solves this issue

This ordering concern makes sense _somewhat_, because D is the second parent of D and that wants to say "Show everything in C..D before showing C". The issues is that since C is the second parent of D, the topo-ordering says "Show everything in B..C before showing things reachable from B". It is unfortunate that these constraints collide.

Quoted 1 line

Perhaps your description could do a better job clarifying this

issue and how your algorithm change fixes the problem.

However, I'm not sure we even want to make the change, as this is still a valid topological order (parents appear after children). When we have an ambiguous pair (like B and C) the order can differ. The --topo-order option tries to group commits by when they were introduced, and that's the reason for presenting the commits reachable from the later parents before presenting the commits from earlier parents.

The only documentation we have is from [1]:

"Show no parents before all of its children are shown, and avoid showing commits on multiple lines of history intermixed."

The first part of the sentence is still true, and the second part is ambiguous of how to do that.

[1] https://git-scm.com/docs/git-log#Documentation/git-log.txt---topo-order

Quoted 5 lines

This change makes option "--topo-order" obsolete, because there is only one way to order parents of a single commit. "--date-order" and "--author-date-order" are preserved and make sense only for the case when multiple commits are given
to be able to sort those commits.

This part of the change needs to be removed. The default sort does not preserve topological orderings (like --date-order does), and so is much faster to output, especially without a commit-graph file.

Quoted 1 line

void sort_in_topological_order(struct commit_list **list, enum rev_sort_order sort_order)

Since you are only editing this code, and not the incremental topo-order code, your test changes will likely break when run with GIT_TEST_COMMIT_GRAPH=1. When the commit-graph exists and generation numbers are calculated, we use a different algorithm for topo-order.

I've been meaning to clean up this "duplicated" logic by deleting this method in favor of the incremental algorithm in all cases. It needs some perf testing to make sure that refactor doesn't have too large of a perf hit in the case of no commit-graph.

Quoted 5 lines

/* update the indegree */

commit.c +0 -0

@@ -832,51 +886,56 @@ void sort_in_topological_order(struct commit_list **list, enum rev_sort_order so
  	for (next = orig; next; next = next->next) {
  		struct commit *commit = next->item;
 

commit.c void sort_in_topological_order(struct commit_list **list, enum rev_sort_order so · line 894

Quoted 8 lines

commit.c +6 -2

-		if (*(indegree_slab_at(&indegree, commit)) == 1)
-			prio_queue_put(&queue, commit);
+		if (*(indegree_slab_at(&indegree, commit)) == 1) {
+			/* also record the author dates, if needed */
+			if (sort_order == REV_SORT_BY_AUTHOR_DATE)
+				record_author_date(&author_date, commit);
+			prio_queue_put(&queue_tips, commit);
+		}

Your code change looks rather large for what I expected to be a much simpler change. Likely the only thing we need is to avoid adding to the priority queue if we already have the commit in the queue (maybe using a hashset storing the commits that we've added to the queue). I believe the reason C appears before B in your example is that it was added to the queue a second time, and the queue behaves like a stack in the topo-order case.

Thanks,
-Stolee

Quoted 4 lines · Sergey Rudyshin

let me explain in more detail why I thought it would make sense to stop using "--topo-order".
in case if a user specifies a single commit, like this
git rev-list E
with a new algorithm the options "--date-order", "--author-date-order", "--topo-order" do not change the ordering. Because there is only one way to sort any git graph with a single tip.

This is false, unless your history is always linear (no merge commits).

Quoted 5 lines

in case if a user specifies multiple tips, like this
git rev-list --topo-order C B ^A
current version of git displays commits ordered by commit timestamp which does not seem like a topological ordering.

Are you talking about which of C and B are shown first? They are shown in an order based on your input. If C and B are independent (neither can reach the other), then they will swap order if you write "git rev-list --topo-order B C ^A".

Quoted 1 line

so I decided to change the documentation so that "--topo-order" and "--date-order" be the same. And since "--topo-order" does not add anything new decided to deprecate it.

Based on this sentence, it is clear that you do not understand the difference between --topo-order and --date-order. Please take time to examine the output difference for the Git repo with the following commands:

	git log --oneline --graph --topo-order
	git log --oneline --graph --date-order

Quoted 3 lines

Regarding the failed test
I'll try to find the reason but what puzzles me is why those tests (t4202, t4215 and t6012) succeeded on all other platforms (linux32, osx-clang, windows, ...) and only failed on linux-gcc. In my machine those tests do not fail either (gcc (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609)

Try running the tests with GIT_TEST_COMMIT_GRAPH=1.

-Stolee