[PATCH] Support long format for log-based submodule diff

[Robert Dailey <rcdailey.lists@gmail.com>]

I am experimenting with a version of submodule diff (using log style)
that prints the commits brought in from merges, while excluding the
merge commits themselves. This is useful in cases where a merge commit's
summary does not fully explain the changes being merged (for example,
for longer-lived branches).

I could have gone through the effort to make this more configurable, but
before doing that level of work I wanted to get some discussion going to
understand first if this is a useful change and second how it should be
configured. For example, we could allow:

$ git diff --submodule=long-log

Or a supplementary option such as:

$ git diff --submodule=log --submodule-log-detail=(long|short)

I'm not sure what makes sense here. I welcome thoughts/discussion and
will provide follow-up patches.

Signed-off-by: Robert Dailey <rcdailey@gmail.com>
---
 submodule.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/submodule.c b/submodule.c
index 2967704317..a0a62ad7bd 100644
--- a/submodule.c
+++ b/submodule.c
@@ -428,7 +428,8 @@ static int prepare_submodule_summary(struct rev_info *rev, const char *path,
 	init_revisions(rev, NULL);
 	setup_revisions(0, NULL, rev, NULL);
 	rev->left_right = 1;
-	rev->first_parent_only = 1;
+	rev->max_parents = 1;
+	rev->first_parent_only = 0;
 	left->object.flags |= SYMMETRIC_LEFT;
 	add_pending_object(rev, &left->object, path);
 	add_pending_object(rev, &right->object, path);
-- 
2.13.1.windows.2