graph.c: mark root commit differentlymf/graph-show-root

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

Signed-off-by: Milton Soares Filho <milton.soares.filho@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/revision.c b/revision.c
index 0173e0148b..2734454ef1 100644
--- a/revision.c
+++ b/revision.c
@@ -3066,9 +3066,12 @@ char *get_revision_mark(const struct rev_info *revs, const struct commit *commit
 			return "<";
 		else
 			return ">";
-	} else if (revs->graph)
-		return "*";
-	else if (revs->cherry_mark)
+	} else if (revs->graph) {
+		if (commit->parents == NULL)
+			return "x"; /* diverges root-commits in subsequent series */
+		else
+			return "*";
+	} else if (revs->cherry_mark)
 		return "+";
 	return "";
 }