pretty: add support for "valueonly" option in %(trailers)

With the new "key=" option to %(trailers) it often makes little sense to
show the key, as it by definition already is knows which trailer is
printed there. This new "valueonly" option makes it omit the key when
printing trailers.

E.g.:
 $ git show -s --pretty='%s%n%(trailers:key=Signed-off-by,valueonly)' aaaa88182
will show:
 > upload-pack: fix broken if/else chain in config callback
 > Jeff King <peff@peff.net>
 > Junio C Hamano <gitster@pobox.com>

Signed-off-by: Anders Waldenborg <anders@0x63.nu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/trailer.c b/trailer.c
index d6da555cd7..d0d9e91631 100644
--- a/trailer.c
+++ b/trailer.c
@@ -1150,8 +1150,10 @@ static void format_trailer_info(struct strbuf *out,
 			if (!opts->filter || opts->filter(&tok, opts->filter_data)) {
 				if (opts->unfold)
 					unfold_value(&val);
-
-				strbuf_addf(out, "%s: %s\n", tok.buf, val.buf);
+				if (!opts->value_only)
+					strbuf_addf(out, "%s: ", tok.buf);
+				strbuf_addbuf(out, &val);
+				strbuf_addch(out, '\n');
 			}
 			strbuf_release(&tok);
 			strbuf_release(&val);