[PATCH] Modify git-rev-list to linearise the commit history in merge order.

This patch linearises the GIT commit history graph into merge order
which is defined by invariants specified in Documentation/git-rev-list.txt.

The linearisation produced by this patch is superior in an objective sense
to that produced by the existing git-rev-list implementation in that
the linearisation produced is guaranteed to have the minimum number of
discontinuities, where a discontinuity is defined as an adjacent pair of
commits in the output list which are not related in a direct child-parent
relationship.

With this patch a graph like this:

	a4 ---
	| \   \
	|  b4 |
	|/ |  |
	a3 |  |
	|  |  |
	a2 |  |
	|  |  c3
	|  |  |
	|  |  c2
	|  b3 |
	|  | /|
	|  b2 |
	|  |  c1
	|  | /
	|  b1
	a1 |
	|  |
	a0 |
	| /
	root

Sorts like this:

	= a4
	| c3
	| c2
	| c1
	^ b4
	| b3
	| b2
	| b1
	^ a3
	| a2
	| a1
	| a0
	= root

Instead of this:

	= a4
	| c3
	^ b4
	| a3
	^ c2
	^ b3
	^ a2
	^ b2
	^ c1
	^ a1
	^ b1
	^ a0
	= root

A test script, t/t6000-rev-list.sh, includes a test which demonstrates
that the linearisation produced by --merge-order has less discontinuities
than the linearisation produced by git-rev-list without the --merge-order
flag specified. To see this, do the following:

	cd t
	./t6000-rev-list.sh
	cd trash
	cat actual-default-order
	cat actual-merge-order

The existing behaviour of git-rev-list is preserved, by default. To obtain
the modified behaviour, specify --merge-order or --merge-order --show-breaks
on the command line.

This version of the patch has been tested on the git repository and also on the linux-2.6
repository and has reasonable performance on both - ~50-100% slower than the original algorithm.

This version of the patch has incorporated a functional equivalent of the Linus' output limiting
algorithm into the merge-order algorithm itself. This operates per the notes associated
with Linus' commit 337cb3fb8da45f10fe9a0c3cf571600f55ead2ce.

This version has incorporated Linus' feedback regarding proposed changes to rev-list.c.
(see: [PATCH] Factor out filtering in rev-list.c)

This version has improved the way sort_first_epoch marks commits as uninteresting.

For more details about this change, refer to Documentation/git-rev-list.txt
and http://blackcubes.dyndns.org/epoch/.

Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/commit.h b/commit.h
index 85736a89f9..51d95764ab 100644
--- a/commit.h
+++ b/commit.h
@@ -42,6 +42,7 @@ enum cmit_fmt {
 
 extern unsigned long pretty_print_commit(enum cmit_fmt fmt, const char *msg, unsigned long len, char *buf, unsigned long space);
 
+void insert_by_date(struct commit_list **list, struct commit *item);
 
 /** Removes the first commit from a list sorted by date, and adds all
  * of its parents.
@@ -49,4 +50,7 @@ extern unsigned long pretty_print_commit(enum cmit_fmt fmt, const char *msg, uns
 struct commit *pop_most_recent_commit(struct commit_list **list, 
 				      unsigned int mark);
 
+struct commit *pop_commit(struct commit_list **stack);
+
+int count_parents(struct commit * commit);
 #endif /* COMMIT_H */