builtin/commit.c: extract ignore_non_trailer() helper function

Extract a helper function from prepare_to_commit() to determine
where to place a new Signed-off-by: line, which is essentially the
true "end" of the log message, ignoring the trailing "Conflicts:"
line and everything below it.

The detection _should_ make sure the "Conflicts:" line it finds is
truly the conflict hint block by checking everything that follows is
a HT indented pathname to avoid false positive, but this logic will
be revamped in a later patch to ignore comments and blanks anyway,
so it is left as-is in this step.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -593,6 +593,37 @@ static char *cut_ident_timestamp_part(char *string)
 	return ket;
 }
 
+/*
+ * Inspect sb and determine the true "end" of the log message, in
+ * order to find where to put a new Signed-off-by: line.  Ignored are
+ * trailing "Conflict:" block.
+ *
+ * Returns the number of bytes from the tail to ignore, to be fed as
+ * the second parameter to append_signoff().
+ */
+static int ignore_non_trailer(struct strbuf *sb)
+{
+	int ignore_footer = 0;
+	int i, eol, previous = 0;
+	const char *nl;
+
+	for (i = 0; i < sb->len; i++) {
+		nl = memchr(sb->buf + i, '\n', sb->len - i);
+		if (nl)
+			eol = nl - sb->buf;
+		else
+			eol = sb->len;
+		if (!prefixcmp(sb->buf + previous, "\nConflicts:\n")) {
+			ignore_footer = sb->len - previous;
+			break;
+		}
+		while (i < eol)
+			i++;
+		previous = eol;
+	}
+	return ignore_footer;
+}
+
 static int prepare_to_commit(const char *index_file, const char *prefix,
 			     struct commit *current_head,
 			     struct wt_status *s,
@@ -718,32 +749,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	if (clean_message_contents)
 		stripspace(&sb, 0);
 
-	if (signoff) {
-		/*
-		 * See if we have a Conflicts: block at the end. If yes, count
-		 * its size, so we can ignore it.
-		 */
-		int ignore_footer = 0;
-		int i, eol, previous = 0;
-		const char *nl;
-
-		for (i = 0; i < sb.len; i++) {
-			nl = memchr(sb.buf + i, '\n', sb.len - i);
-			if (nl)
-				eol = nl - sb.buf;
-			else
-				eol = sb.len;
-			if (!prefixcmp(sb.buf + previous, "\nConflicts:\n")) {
-				ignore_footer = sb.len - previous;
-				break;
-			}
-			while (i < eol)
-				i++;
-			previous = eol;
-		}
-
-		append_signoff(&sb, ignore_footer, 0);
-	}
+	if (signoff)
+		append_signoff(&sb, ignore_non_trailer(&sb), 0);
 
 	if (fwrite(sb.buf, 1, sb.len, s->fp) < sb.len)
 		die_errno(_("could not write commit template"));