[PATCH v4 5/7] pretty: add support for "valueonly" option in %(trailers)

[Anders Waldenborg <anders@0x63.nu>]

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>
---
 Documentation/pretty-formats.txt | 2 ++
 pretty.c                         | 3 ++-
 t/t4205-log-pretty-formats.sh    | 6 ++++++
 trailer.c                        | 6 ++++--
 trailer.h                        | 1 +
 5 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/Documentation/pretty-formats.txt b/Documentation/pretty-formats.txt
index d6add831c0..a920dd15b1 100644
--- a/Documentation/pretty-formats.txt
+++ b/Documentation/pretty-formats.txt
@@ -243,6 +243,8 @@ endif::git-rev-list[]
    option was given. In same way as to for `only` it can be followed
    by an equal sign and explicit value. E.g.,
    `%(trailers:only,unfold=true)` unfolds and shows all trailer lines.
+** 'valueonly[=val]': skip over the key part of the trailer line and only
+   show the value part. Also this optionally allows explicit value.
 
 NOTE: Some placeholders may depend on other options given to the
 revision traversal engine. For example, the `%g*` reflog options will
diff --git a/pretty.c b/pretty.c
index 541a553ccc..c508357606 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1383,7 +1383,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 					opts.filter_data = &filter_list;
 					opts.only_trailers = 1;
 				} else if (!match_placeholder_bool_arg(arg, "only", &arg, &opts.only_trailers) &&
-					   !match_placeholder_bool_arg(arg, "unfold", &arg, &opts.unfold))
+					   !match_placeholder_bool_arg(arg, "unfold", &arg, &opts.unfold) &&
+					   !match_placeholder_bool_arg(arg, "valueonly", &arg, &opts.value_only))
 					break;
 			}
 		}
diff --git a/t/t4205-log-pretty-formats.sh b/t/t4205-log-pretty-formats.sh
index 54239290cf..22336c5485 100755
--- a/t/t4205-log-pretty-formats.sh
+++ b/t/t4205-log-pretty-formats.sh
@@ -667,6 +667,12 @@ test_expect_success 'pretty format %(trailers:key=foo,only=no) also includes non
 	test_cmp expect actual
 '
 
+test_expect_success '%(trailers:key=foo,valueonly) shows only value' '
+	git log --no-walk --pretty="format:%(trailers:key=Acked-by,valueonly)" >actual &&
+	echo "A U Thor <author@example.com>" >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success 'trailer parsing not fooled by --- line' '
 	git commit --allow-empty -F - <<-\EOF &&
 	this is the subject
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);
diff --git a/trailer.h b/trailer.h
index 5255b676de..06d417fe93 100644
--- a/trailer.h
+++ b/trailer.h
@@ -72,6 +72,7 @@ struct process_trailer_options {
 	int only_input;
 	int unfold;
 	int no_divider;
+	int value_only;
 	int (*filter)(const struct strbuf *, void *);
 	void *filter_data;
 };
-- 
2.17.1