[PATCH] graph.c: visual difference on subsequent series

[Milton Soares Filho <milton.soares.filho@gmail.com>]

For projects with separate history lines and, thus, multiple root-commits, the
linear arrangement of `git log --graph --oneline` does not allow the user to
spot where the sequence ends, giving the impression that it's a contiguous
history. E.g.

History sequence A: a1 -- a2 -- a3 (root-commit)
History sequence B: b1 -- b2 -- b3 (root-commit)

    git log --graph --oneline
    * a1
    * a2
    * a3
    * b1
    * b2
    * b3

In a GUI tool, the root-commit of each series would stand out on the graph.

This modification changes the commit char to a different symbol ('x'), so users
of the command-line graph tool can easily identify root-commits and make sense
of where each series is limited to.

    git log --graph --oneline
    * a1
    * a2
    x a3
    * b1
    * b2
    x b3

UPDATE: dealing with the mark at get_revision_mark() to address Junio C Hamano
concerns and give it a proper priority:

> It is unclear why the update goes to this function. At the first
> glance, I feel that it would be more sensible to add the equivalent
> code to get_revision_mark()---we do not have to worry about what
> else, other than calling get_revision_mark() and adding it to sb,
> would be skipped by the added "return" when we later have to update
> this function and add more code after the existing strbuf_addstr().
>
> The change implemented your way will lose other information when a
> root commit is at the boundary, marked as uninteresting, or on the
> left/right side of traversal (when --left-right is requested).  I
> think these pieces of information your patch seems to be losing are
> a lot more relevant than "have we hit the root?", especially in the
> majority of repositories where there is only one root commit.

Signed-off-by: Milton Soares Filho <milton.soares.filho@gmail.com>
---
 revision.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/revision.c b/revision.c
index 0173e01..ab0447f 100644
--- a/revision.c
+++ b/revision.c
@@ -3066,7 +3066,9 @@ char *get_revision_mark(const struct rev_info *revs, const struct commit *commit
 			return "<";
 		else
 			return ">";
-	} else if (revs->graph)
+	} else if (revs->graph && commit->parents == NULL)
+		return "x"; /* diverges root-commits in subsequent series */
+	else if (revs->graph)
 		return "*";
 	else if (revs->cherry_mark)
 		return "+";
-- 
1.8.1.2