pretty format %(trailers): add a "key_value_separator"

Add a "key_value_separator" option to the "%(trailers)" pretty format,
to go along with the existing "separator" argument. In combination
these two options make it trivial to produce machine-readable (e.g. \0
and \0\0-delimited) format output.

As elaborated on in a previous commit which added "keyonly" it was
needlessly tedious to extract structured data from "%(trailers)"
before the addition of this "key_value_separator" option. As seen by
the test being added here extracting this data now becomes trivial.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/pretty-formats.txt

@@ -284,6 +284,10 @@ option is given with no value, it's enabled.
    `%(trailers:only,unfold=true)` unfolds and shows all trailer lines.
 ** 'keyonly[=<BOOL>]': only show the key part of the trailer.
 ** 'valueonly[=<BOOL>]': only show the value part of the trailer.
+** 'key_value_separator=<SEP>': specify a separator inserted between
+   trailer lines. When this option is not given each trailer key-value
+   pair is separated by ": ". Otherwise it shares the same semantics
+   as 'separator=<SEP>' above.
 
 NOTE: Some placeholders may depend on other options given to the
 revision traversal engine. For example, the `%g*` reflog options will

pretty.c

@@ -1418,6 +1418,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 		struct process_trailer_options opts = PROCESS_TRAILER_OPTIONS_INIT;
 		struct string_list filter_list = STRING_LIST_INIT_NODUP;
 		struct strbuf sepbuf = STRBUF_INIT;
+		struct strbuf kvsepbuf = STRBUF_INIT;
 		size_t ret = 0;
 
 		opts.no_divider = 1;
@@ -1449,6 +1450,14 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 					strbuf_expand(&sepbuf, fmt, strbuf_expand_literal_cb, NULL);
 					free(fmt);
 					opts.separator = &sepbuf;
+				} else if (match_placeholder_arg_value(arg, "key_value_separator", &arg, &argval, &arglen)) {
+					char *fmt;
+
+					strbuf_reset(&kvsepbuf);
+					fmt = xstrndup(argval, arglen);
+					strbuf_expand(&kvsepbuf, fmt, strbuf_expand_literal_cb, NULL);
+					free(fmt);
+					opts.key_value_separator = &kvsepbuf;
 				} 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, "keyonly", &arg, &opts.key_only) &&

t/t4205-log-pretty-formats.sh

@@ -776,6 +776,39 @@ test_expect_success 'pretty format %(trailers:separator=X,unfold) changes separa
 	test_cmp expect actual
 '
 
+test_expect_success 'pretty format %(trailers:key_value_separator) changes key-value separator' '
+	git log --no-walk --pretty=format:"X%(trailers:key_value_separator=%x00)X" >actual &&
+	(
+		printf "XSigned-off-by\0A U Thor <author@example.com>\n" &&
+		printf "Acked-by\0A U Thor <author@example.com>\n" &&
+		printf "[ v2 updated patch description ]\n" &&
+		printf "Signed-off-by\0A U Thor\n  <author@example.com>\nX"
+	) >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'pretty format %(trailers:key_value_separator,unfold) changes key-value separator' '
+	git log --no-walk --pretty=format:"X%(trailers:key_value_separator=%x00,unfold)X" >actual &&
+	(
+		printf "XSigned-off-by\0A U Thor <author@example.com>\n" &&
+		printf "Acked-by\0A U Thor <author@example.com>\n" &&
+		printf "[ v2 updated patch description ]\n" &&
+		printf "Signed-off-by\0A U Thor <author@example.com>\nX"
+	) >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'pretty format %(trailers:separator,key_value_separator) changes both separators' '
+	git log --no-walk --pretty=format:"%(trailers:separator=%x00,key_value_separator=%x00%x00,unfold)" >actual &&
+	(
+		printf "Signed-off-by\0\0A U Thor <author@example.com>\0" &&
+		printf "Acked-by\0\0A U Thor <author@example.com>\0" &&
+		printf "[ v2 updated patch description ]\0" &&
+		printf "Signed-off-by\0\0A U Thor <author@example.com>"
+	) >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success 'pretty format %(trailers) combining separator/key/keyonly/valueonly' '
 	git commit --allow-empty -F - <<-\EOF &&
 	Important fix

trailer.c

@@ -1132,7 +1132,8 @@ static void format_trailer_info(struct strbuf *out,
 
 	/* If we want the whole block untouched, we can take the fast path. */
 	if (!opts->only_trailers && !opts->unfold && !opts->filter &&
-	    !opts->separator && !opts->key_only && !opts->value_only) {
+	    !opts->separator && !opts->key_only && !opts->value_only &&
+	    !opts->key_value_separator) {
 		strbuf_add(out, info->trailer_start,
 			   info->trailer_end - info->trailer_start);
 		return;
@@ -1155,8 +1156,12 @@ static void format_trailer_info(struct strbuf *out,
 					strbuf_addbuf(out, opts->separator);
 				if (!opts->value_only)
 					strbuf_addbuf(out, &tok);
-				if (!opts->key_only && !opts->value_only)
-					strbuf_addstr(out, ": ");
+				if (!opts->key_only && !opts->value_only) {
+					if (opts->key_value_separator)
+						strbuf_addbuf(out, opts->key_value_separator);
+					else
+						strbuf_addstr(out, ": ");
+				}
 				if (!opts->key_only)
 					strbuf_addbuf(out, &val);
 				if (!opts->separator)

trailer.h

@@ -74,6 +74,7 @@ struct process_trailer_options {
 	int key_only;
 	int value_only;
 	const struct strbuf *separator;
+	const struct strbuf *key_value_separator;
 	int (*filter)(const struct strbuf *, void *);
 	void *filter_data;
 };