log: add %S option (like --source) to log --format

Make it possible to write for example

        git log --format="%H,%S"

where the %S at the end is a new placeholder that prints out the ref
(tag/branch) for each commit.

Using %d might seem like an alternative but it only shows the ref for the last
commit in the branch.

Signed-off-by: Issac Trotts <issactrotts@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/pretty.h b/pretty.h
index 7359d31..87ca5df 100644
--- a/pretty.h
+++ b/pretty.h
@@ -60,6 +60,7 @@ static inline int cmit_fmt_is_mail(enum cmit_fmt fmt)
 
 struct userformat_want {
 	unsigned notes:1;
+	unsigned source:1;
 };
 
 /* Set the flag "w->notes" if there is placeholder %N in "fmt". */