pretty: add support for separator option in %(trailers)

By default trailer lines are terminated by linebreaks ('\n'). By
specifying the new 'separator' option they will instead be separated by
user provided string and have separator semantics rather than terminator
semantics. The separator string can contain the literal formatting codes
%n and %xNN allowing it to be things that are otherwise hard to type
such as %x00, or comma and end-parenthesis which would break parsing.

E.g:
 $ git log --pretty='%(trailers:key=Reviewed-by,valueonly,separator=%x00)'

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

Documentation/pretty-formats.txt

@@ -239,6 +239,15 @@ endif::git-rev-list[]
    `false`, `off`, `no` to show the non-trailer lines. If option is
    given without value it is enabled. If given multiple times the last
    value is used.
+** 'separator=<SEP>': specify a separator inserted between trailer
+   lines. When this option is not given each trailer line is
+   terminated with a line feed character. The string SEP may contain
+   the literal formatting codes described above. To use comma as
+   separator one must use `%x2C` as it would otherwise be parsed as
+   next option. If separator option is given multiple times only the
+   last one is used. E.g., `%(trailers:key=Ticket,separator=%x2C )`
+   shows all trailer lines whose key is "Ticket" separated by a comma
+   and a space.
 ** 'unfold[=val]': make it behave as if interpret-trailer's `--unfold`
    option was given. In same way as to for `only` it can be followed
    by an equal sign and explicit value. E.g.,

pretty.c

@@ -1361,6 +1361,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 	if (skip_prefix(placeholder, "(trailers", &arg)) {
 		struct process_trailer_options opts = PROCESS_TRAILER_OPTIONS_INIT;
 		struct string_list filter_list = STRING_LIST_INIT_NODUP;
+		struct strbuf sepbuf = STRBUF_INIT;
 		size_t ret = 0;
 
 		opts.no_divider = 1;
@@ -1384,6 +1385,14 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 					opts.filter = format_trailer_match_cb;
 					opts.filter_data = &filter_list;
 					opts.only_trailers = 1;
+				} else if (match_placeholder_arg_value(arg, "separator", &arg, &argval, &arglen)) {
+					char *fmt;
+
+					strbuf_reset(&sepbuf);
+					fmt = xstrndup(argval, arglen);
+					strbuf_expand(&sepbuf, fmt, strbuf_expand_literal_cb, NULL);
+					free(fmt);
+					opts.separator = &sepbuf;
 				} 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, "valueonly", &arg, &opts.value_only))
@@ -1396,6 +1405,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 		}
 	trailer_out:
 		string_list_clear(&filter_list, 0);
+		strbuf_release(&sepbuf);
 		return ret;
 	}
 

t/t4205-log-pretty-formats.sh

@@ -679,6 +679,42 @@ test_expect_success '%(trailers:key=foo,valueonly) shows only value' '
 	test_cmp expect actual
 '
 
+test_expect_success 'pretty format %(trailers:separator) changes separator' '
+	git log --no-walk --pretty=format:"X%(trailers:separator=%x00,unfold)X" >actual &&
+	printf "XSigned-off-by: A U Thor <author@example.com>\0Acked-by: A U Thor <author@example.com>\0[ v2 updated patch description ]\0Signed-off-by: A U Thor <author@example.com>X" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'pretty format %(trailers) combining separator/key/valueonly' '
+	git commit --allow-empty -F - <<-\EOF &&
+	Important fix
+
+	The fix is explained here
+
+	Closes: #1234
+	EOF
+
+	git commit --allow-empty -F - <<-\EOF &&
+	Another fix
+
+	The fix is explained here
+
+	Closes: #567
+	Closes: #890
+	EOF
+
+	git commit --allow-empty -F - <<-\EOF &&
+	Does not close any tickets
+	EOF
+
+	git log --pretty="%s% (trailers:separator=%x2c%x20,key=Closes,valueonly)" HEAD~3.. >actual &&
+	test_write_lines \
+		"Does not close any tickets" \
+		"Another fix #567, #890" \
+		"Important fix #1234" >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success 'trailer parsing not fooled by --- line' '
 	git commit --allow-empty -F - <<-\EOF &&
 	this is the subject

trailer.c

@@ -1129,10 +1129,11 @@ static void format_trailer_info(struct strbuf *out,
 				const struct trailer_info *info,
 				const struct process_trailer_options *opts)
 {
+	size_t origlen = out->len;
 	size_t i;
 
 	/* If we want the whole block untouched, we can take the fast path. */
-	if (!opts->only_trailers && !opts->unfold && !opts->filter) {
+	if (!opts->only_trailers && !opts->unfold && !opts->filter && !opts->separator) {
 		strbuf_add(out, info->trailer_start,
 			   info->trailer_end - info->trailer_start);
 		return;
@@ -1150,16 +1151,26 @@ static void format_trailer_info(struct strbuf *out,
 			if (!opts->filter || opts->filter(&tok, opts->filter_data)) {
 				if (opts->unfold)
 					unfold_value(&val);
+
+				if (opts->separator && out->len != origlen)
+					strbuf_addbuf(out, opts->separator);
 				if (!opts->value_only)
 					strbuf_addf(out, "%s: ", tok.buf);
 				strbuf_addbuf(out, &val);
-				strbuf_addch(out, '\n');
+				if (!opts->separator)
+					strbuf_addch(out, '\n');
 			}
 			strbuf_release(&tok);
 			strbuf_release(&val);
 
 		} else if (!opts->only_trailers) {
+			if (opts->separator && out->len != origlen) {
+				strbuf_addbuf(out, opts->separator);
+			}
 			strbuf_addstr(out, trailer);
+			if (opts->separator) {
+				strbuf_rtrim(out);
+			}
 		}
 	}
 

trailer.h

@@ -73,6 +73,7 @@ struct process_trailer_options {
 	int unfold;
 	int no_divider;
 	int value_only;
+	const struct strbuf *separator;
 	int (*filter)(const struct strbuf *, void *);
 	void *filter_data;
 };