format-patch: fix rfc2047 address encoding with respect to rfc822 specials

According to RFC 2047 and RFC 822, rfc2047 encoded words and and rfc822
quoted strings do not mix. Since add_rfc2047() no longer leaves RFC 822
specials behind, the quoting is also no longer necessary to create a
standard-conforming mail.

Remove the quoting, when RFC 2047 encoding takes place. This actually
requires to refactor add_rfc2047() a bit, so that the different cases
can be distinguished.

With this patch, my own name gets correctly decoded as Jan H. Schönherr
(without quotes) and not as "Jan H. Schönherr" (with quotes).

Signed-off-by: Jan H. Schönherr <schnhrr@cs.tu-berlin.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pretty.c

@@ -231,7 +231,7 @@ static int is_rfc822_special(char ch)
 	}
 }
 
-static int has_rfc822_specials(const char *s, int len)
+static int needs_rfc822_quoting(const char *s, int len)
 {
 	int i;
 	for (i = 0; i < len; i++)
@@ -329,25 +329,29 @@ static int is_rfc2047_special(char ch, enum rfc2047_type type)
 	return !(isalnum(ch) || ch == '!' || ch == '*' || ch == '+' || ch == '-' || ch == '/');
 }
 
-static void add_rfc2047(struct strbuf *sb, const char *line, int len,
-		       const char *encoding, enum rfc2047_type type)
+static int needs_rfc2047_encoding(const char *line, int len,
+				  enum rfc2047_type type)
 {
-	static const int max_length = 78; /* per rfc2822 */
-	static const int max_encoded_length = 76; /* per rfc2047 */
 	int i;
-	int line_len = last_line_length(sb);
 
 	for (i = 0; i < len; i++) {
 		int ch = line[i];
 		if (non_ascii(ch) || ch == '\n')
-			goto needquote;
+			return 1;
 		if ((i + 1 < len) && (ch == '=' && line[i+1] == '?'))
-			goto needquote;
+			return 1;
 	}
-	strbuf_add_wrapped_bytes(sb, line, len, -line_len, 1, max_length);
-	return;
 
-needquote:
+	return 0;
+}
+
+static void add_rfc2047(struct strbuf *sb, const char *line, int len,
+		       const char *encoding, enum rfc2047_type type)
+{
+	static const int max_encoded_length = 76; /* per rfc2047 */
+	int i;
+	int line_len = last_line_length(sb);
+
 	strbuf_grow(sb, len * 3 + strlen(encoding) + 100);
 	strbuf_addf(sb, "=?%s?q?", encoding);
 	line_len += strlen(encoding) + 5; /* 5 for =??q? */
@@ -383,6 +387,7 @@ void pp_user_info(const struct pretty_print_context *pp,
 		  const char *what, struct strbuf *sb,
 		  const char *line, const char *encoding)
 {
+	int max_length = 78; /* per rfc2822 */
 	char *date;
 	int namelen;
 	unsigned long time;
@@ -406,17 +411,21 @@ void pp_user_info(const struct pretty_print_context *pp,
 			name_tail--;
 		display_name_length = name_tail - line;
 		strbuf_addstr(sb, "From: ");
-		if (!has_rfc822_specials(line, display_name_length)) {
+		if (needs_rfc2047_encoding(line, display_name_length, RFC2047_ADDRESS)) {
 			add_rfc2047(sb, line, display_name_length,
 						encoding, RFC2047_ADDRESS);
-		} else {
+			max_length = 76; /* per rfc2047 */
+		} else if (needs_rfc822_quoting(line, display_name_length)) {
 			struct strbuf quoted = STRBUF_INIT;
 			add_rfc822_quoted(&quoted, line, display_name_length);
-			add_rfc2047(sb, quoted.buf, quoted.len,
-						encoding, RFC2047_ADDRESS);
+			strbuf_add_wrapped_bytes(sb, quoted.buf, quoted.len,
+							-6, 1, max_length);
 			strbuf_release(&quoted);
+		} else {
+			strbuf_add_wrapped_bytes(sb, line, display_name_length,
+							-6, 1, max_length);
 		}
-		if (namelen - display_name_length + last_line_length(sb) > 78) {
+		if (namelen - display_name_length + last_line_length(sb) > max_length) {
 			strbuf_addch(sb, '\n');
 			if (!isspace(name_tail[0]))
 				strbuf_addch(sb, ' ');
@@ -1336,6 +1345,7 @@ void pp_title_line(const struct pretty_print_context *pp,
 		   const char *encoding,
 		   int need_8bit_cte)
 {
+	static const int max_length = 78; /* per rfc2047 */
 	struct strbuf title;
 
 	strbuf_init(&title, 80);
@@ -1345,7 +1355,12 @@ void pp_title_line(const struct pretty_print_context *pp,
 	strbuf_grow(sb, title.len + 1024);
 	if (pp->subject) {
 		strbuf_addstr(sb, pp->subject);
-		add_rfc2047(sb, title.buf, title.len, encoding, RFC2047_SUBJECT);
+		if (needs_rfc2047_encoding(title.buf, title.len, RFC2047_SUBJECT))
+			add_rfc2047(sb, title.buf, title.len,
+						encoding, RFC2047_SUBJECT);
+		else
+			strbuf_add_wrapped_bytes(sb, title.buf, title.len,
+					 -last_line_length(sb), 1, max_length);
 	} else {
 		strbuf_addbuf(sb, &title);
 	}

t/t4014-format-patch.sh

@@ -839,7 +839,7 @@ test_expect_success 'format-patch uses rfc2047-encoded from-headers when necessa
 cat >expect <<'EOF'
 From: =?UTF-8?q?F=C3=B6o=20B=2E=20Bar?= <author@example.com>
 EOF
-test_expect_failure 'rfc2047-encoded from-headers leave no rfc822 specials' '
+test_expect_success 'rfc2047-encoded from-headers leave no rfc822 specials' '
 	check_author "Föo B. Bar"
 '