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`.

But this change isn't sufficient to reuse this function in
ref-filter.c because there exist tags with multiline subject.

It's wise to replace `\n` with ' ', if `format_sanitized_subject()`
encounters `\n` before end of subject line, just like `copy_subject()`.
Because we'll be only using `format_sanitized_subject()` for
"%(subject:sanitize)", instead of `copy_subject()` and
`format_sanitized_subject()` both. So, added the code:
```
if (char == '\n') /* never true if called inside pretty.c */
    char = ' ';
```

Now, it's ready to be reused in ref-filter.c

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

Author: harry-hov

pretty.c

@@ -839,24 +839,29 @@ static int istitlechar(char c)
 		(c >= '0' && c <= '9') || c == '.' || c == '_';
 }
 
-static void format_sanitized_subject(struct strbuf *sb, const char *msg)
+static void format_sanitized_subject(struct strbuf *sb, const char *msg, size_t len)
 {
+	char *r = xmemdupz(msg, 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 (r[i] == '\n')
+			r[i] = ' ';
+		if (istitlechar(r[i])) {
 			if (space == 1)
 				strbuf_addch(sb, '-');
 			space = 0;
-			strbuf_addch(sb, *msg);
-			if (*msg == '.')
-				while (*(msg+1) == '.')
-					msg++;
+			strbuf_addch(sb, r[i]);
+			if (r[i] == '.')
+				while (r[i+1] == '.')
+					i++;
 		} else
 			space |= 1;
 	}
+	free(r);
 
 	/* trim any trailing '.' or '-' characters */
 	trimlen = 0;
@@ -1155,7 +1160,7 @@ 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 +1410,8 @@ 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);