pretty: refactor `format_sanitized_subject()`

The function 'format_sanitized_subject()' is responsible for
sanitized subject line in pretty.c
e.g.
the subject line
the-sanitized-subject-line

It would be a nice enhancement to `subject` atom to have the
same feature. So in the later commits, we plan to add this feature
to ref-filter.

Refactor `format_sanitized_subject()`, so it can be reused in
ref-filter.c for adding new modifier `sanitize` to "subject" atom.

Currently, the loop inside `format_sanitized_subject()` runs
until `\n` is found. But now, we stored the first occurrence
of `\n` in a variable `eol` and passed it in
`format_sanitized_subject()`. And the loop runs upto `eol`.

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Mentored-by: Heba Waly <heba.waly@gmail.com>
Signed-off-by: Hariom Verma <hariom18599@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pretty.c

@@ -839,21 +839,22 @@ static int istitlechar(char c)
 		(c >= '0' && c <= '9') || c == '.' || c == '_';
 }
 
-static void format_sanitized_subject(struct strbuf *sb, const char *msg)
+void format_sanitized_subject(struct strbuf *sb, const char *msg, size_t len)
 {
 	size_t trimlen;
 	size_t start_len = sb->len;
 	int space = 2;
+	int i;
 
-	for (; *msg && *msg != '\n'; msg++) {
-		if (istitlechar(*msg)) {
+	for (i = 0; i < len; i++) {
+		if (istitlechar(msg[i])) {
 			if (space == 1)
 				strbuf_addch(sb, '-');
 			space = 0;
-			strbuf_addch(sb, *msg);
-			if (*msg == '.')
-				while (*(msg+1) == '.')
-					msg++;
+			strbuf_addch(sb, msg[i]);
+			if (msg[i] == '.')
+				while (msg[i+1] == '.')
+					i++;
 		} else
 			space |= 1;
 	}
@@ -1155,7 +1156,7 @@ 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;
+	const char *arg, *eol;
 	size_t res;
 	char **slot;
 
@@ -1405,7 +1406,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 		format_subject(sb, msg + c->subject_off, " ");
 		return 1;
 	case 'f':	/* sanitized subject */
-		format_sanitized_subject(sb, msg + c->subject_off);
+		eol = strchrnul(msg + c->subject_off, '\n');
+		format_sanitized_subject(sb, msg + c->subject_off, eol - (msg + c->subject_off));
 		return 1;
 	case 'b':	/* body */
 		strbuf_addstr(sb, msg + c->body_off);

pretty.h

@@ -139,4 +139,7 @@ const char *format_subject(struct strbuf *sb, const char *msg,
 /* Check if "cmit_fmt" will produce an empty output. */
 int commit_format_is_empty(enum cmit_fmt);
 
+/* Make subject of commit message suitable for filename */
+void format_sanitized_subject(struct strbuf *sb, const char *msg, size_t len);
+
 #endif /* PRETTY_H */