pretty: support normalization options for %(trailers)

The interpret-trailers command recently learned some options
to make its output easier to parse (for a caller whose only
interested in picking out the trailer values). But it's not
very efficient for asking for the trailers of many commits
in a single invocation.

We already have "%(trailers)" to do that, but it doesn't
know about unfolding or omitting non-trailers. Let's plumb
those options through, so you can have the best of both.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/pretty-formats.txt

@@ -201,7 +201,10 @@ endif::git-rev-list[]
 - '%><(<N>)', '%><|(<N>)': similar to '% <(<N>)', '%<|(<N>)'
   respectively, but padding both sides (i.e. the text is centered)
 - %(trailers): display the trailers of the body as interpreted by
-  linkgit:git-interpret-trailers[1]
+  linkgit:git-interpret-trailers[1]. If the `:only` option is given,
+  omit non-trailer lines from the trailer block.  If the `:unfold`
+  option is given, behave as if interpret-trailer's `--unfold` option
+  was given. E.g., `%(trailers:only:unfold)` to do both.
 
 NOTE: Some placeholders may depend on other options given to the
 revision traversal engine. For example, the `%g*` reflog options will

pretty.c

@@ -1044,6 +1044,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 	const struct commit *commit = c->commit;
 	const char *msg = c->message;
 	struct commit_list *p;
+	const char *arg;
 	int ch;
 
 	/* these are independent of the commit */
@@ -1262,10 +1263,18 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 		return 1;
 	}
 
-	if (starts_with(placeholder, "(trailers)")) {
+	if (skip_prefix(placeholder, "(trailers", &arg)) {
 		struct process_trailer_options opts = PROCESS_TRAILER_OPTIONS_INIT;
+		while (*arg == ':') {
+			if (skip_prefix(arg, ":only", &arg))
+				opts.only_trailers = 1;
+			else if (skip_prefix(arg, ":unfold", &arg))
+				opts.unfold = 1;
+		}
+		if (*arg == ')') {
 			format_trailers_from_commit(sb, msg + c->subject_off, &opts);
-		return strlen("(trailers)");
+			return arg - placeholder + 1;
+		}
 	}
 
 	return 0;	/* unknown placeholder */

t/t4205-log-pretty-formats.sh

@@ -543,6 +543,10 @@ Signed-off-by: A U Thor
   <author@example.com>
 EOF
 
+unfold () {
+	perl -0pe 's/\n\s+/ /'
+}
+
 test_expect_success 'set up trailer tests' '
 	echo "Some contents" >trailerfile &&
 	git add trailerfile &&
@@ -565,4 +569,33 @@ test_expect_success 'pretty format %(trailers) shows trailers' '
 	test_cmp expect actual
 '
 
+test_expect_success '%(trailers:only) shows only "key: value" trailers' '
+	git log --no-walk --pretty="%(trailers:only)" >actual &&
+	{
+		grep -v patch.description <trailers &&
+		echo
+	} >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '%(trailers:unfold) unfolds trailers' '
+	git log --no-walk --pretty="%(trailers:unfold)" >actual &&
+	{
+		unfold <trailers &&
+		echo
+	} >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success ':only and :unfold work together' '
+	git log --no-walk --pretty="%(trailers:only:unfold)" >actual &&
+	git log --no-walk --pretty="%(trailers:unfold:only)" >reverse &&
+	test_cmp actual reverse &&
+	{
+		grep -v patch.description <trailers | unfold &&
+		echo
+	} >expect &&
+	test_cmp expect actual
+'
+
 test_done

trailer.c

@@ -1095,8 +1095,36 @@ static void format_trailer_info(struct strbuf *out,
 				const struct trailer_info *info,
 				const struct process_trailer_options *opts)
 {
+	int i;
+
+	/* If we want the whole block untouched, we can take the fast path. */
+	if (!opts->only_trailers && !opts->unfold) {
 		strbuf_add(out, info->trailer_start,
 			   info->trailer_end - info->trailer_start);
+		return;
+	}
+
+	for (i = 0; i < info->trailer_nr; i++) {
+		char *trailer = info->trailers[i];
+		int separator_pos = find_separator(trailer, separators);
+
+		if (separator_pos >= 1) {
+			struct strbuf tok = STRBUF_INIT;
+			struct strbuf val = STRBUF_INIT;
+
+			parse_trailer(&tok, &val, NULL, trailer, separator_pos);
+			if (opts->unfold)
+				unfold_value(&val);
+
+			strbuf_addf(out, "%s: %s\n", tok.buf, val.buf);
+			strbuf_release(&tok);
+			strbuf_release(&val);
+
+		} else if (!opts->only_trailers) {
+			strbuf_addstr(out, trailer);
+		}
+	}
+
 }
 
 void format_trailers_from_commit(struct strbuf *out, const char *msg,