log and rev-list: add --graph option

This new option causes a text-based representation of the history to be
printed to the left of the normal output.

Signed-off-by: Adam Simpkins <adam@adamsimpkins.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 18 insertions, 5 deletions

diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt
index 2648a5508..ce6a1017a 100644
--- a/Documentation/rev-list-options.txt
+++ b/Documentation/rev-list-options.txt
@@ -75,6 +75,16 @@ you would get an output line this:
 	-xxxxxxx... 1st on a
 -----------------------------------------------------------------------
 
+--graph::
+
+	Draw a text-based graphical representation of the commit history
+	on the left hand side of the output.  This may cause extra lines
+	to be printed in between commits, in order for the graph history
+	to be drawn properly.
++
+This implies the '--topo-order' option by default, but the
+'--date-order' option may also be specified.
+
 Diff Formatting
 ~~~~~~~~~~~~~~~
 
diff --git a/Documentation/technical/api-history-graph.txt b/Documentation/technical/api-history-graph.txt
index 5f6465fa2..ce1c08ee8 100644
--- a/Documentation/technical/api-history-graph.txt
+++ b/Documentation/technical/api-history-graph.txt
@@ -74,14 +74,17 @@ state.
 Calling sequence
 ----------------
 
-* Create a `struct git_graph` by calling `graph_init()`.
+* Create a `struct git_graph` by calling `graph_init()`.  When using the
+  revision walking API, this is done automatically by `setup_revisions()` if
+  the '--graph' option is supplied.
 
 * Use the revision walking API to walk through a group of contiguous commits.
+  The `get_revision()` function automatically calls `graph_update()` each time
+  it is invoked.
 
-* For each commit traversed, call `graph_update()` to move the graph to the
-  next commit.  Once `graph_update()` has been called, call `graph_next_line()`
-  repeatedly, until `graph_is_commit_finished()` returns non-zero.  Each call
-  to `graph_next_line()` will output a single line of the graph.  The resulting
+* For each commit, call `graph_next_line()` repeatedly, until
+  `graph_is_commit_finished()` returns non-zero.  Each call go
+  `graph_next_line()` will output a single line of the graph.  The resulting
   lines will not contain any newlines.  `graph_next_line()` returns 1 if the
   resulting line contains the current commit, or 0 if this is merely a line
   needed to adjust the graph before or after the current commit.  This return