object-file: rename variables in check_collision()

Rename variables used in `check_collision()` to clearly identify which
file is the source and which is the destination. This will make the next
step easier to reason about when we start to treat those files different
from one another.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

object-file.c

@@ -1974,56 +1974,56 @@ static void write_object_file_prepare_literally(const struct git_hash_algo *algo
 	hash_object_body(algo, &c, buf, len, oid, hdr, hdrlen);
 }
 
-static int check_collision(const char *filename_a, const char *filename_b)
+static int check_collision(const char *source, const char *dest)
 {
-	char buf_a[4096], buf_b[4096];
-	int fd_a = -1, fd_b = -1;
+	char buf_source[4096], buf_dest[4096];
+	int fd_source = -1, fd_dest = -1;
 	int ret = 0;
 
-	fd_a = open(filename_a, O_RDONLY);
-	if (fd_a < 0) {
+	fd_source = open(source, O_RDONLY);
+	if (fd_source < 0) {
 		if (errno != ENOENT)
-			ret = error_errno(_("unable to open %s"), filename_a);
+			ret = error_errno(_("unable to open %s"), source);
 		goto out;
 	}
 
-	fd_b = open(filename_b, O_RDONLY);
-	if (fd_b < 0) {
+	fd_dest = open(dest, O_RDONLY);
+	if (fd_dest < 0) {
 		if (errno != ENOENT)
-			ret = error_errno(_("unable to open %s"), filename_b);
+			ret = error_errno(_("unable to open %s"), dest);
 		goto out;
 	}
 
 	while (1) {
 		ssize_t sz_a, sz_b;
 
-		sz_a = read_in_full(fd_a, buf_a, sizeof(buf_a));
+		sz_a = read_in_full(fd_source, buf_source, sizeof(buf_source));
 		if (sz_a < 0) {
-			ret = error_errno(_("unable to read %s"), filename_a);
+			ret = error_errno(_("unable to read %s"), source);
 			goto out;
 		}
 
-		sz_b = read_in_full(fd_b, buf_b, sizeof(buf_b));
+		sz_b = read_in_full(fd_dest, buf_dest, sizeof(buf_dest));
 		if (sz_b < 0) {
-			ret = error_errno(_("unable to read %s"), filename_b);
+			ret = error_errno(_("unable to read %s"), dest);
 			goto out;
 		}
 
-		if (sz_a != sz_b || memcmp(buf_a, buf_b, sz_a)) {
+		if (sz_a != sz_b || memcmp(buf_source, buf_dest, sz_a)) {
 			ret = error(_("files '%s' and '%s' differ in contents"),
-				    filename_a, filename_b);
+				    source, dest);
 			goto out;
 		}
 
-		if (sz_a < sizeof(buf_a))
+		if (sz_a < sizeof(buf_source))
 			break;
 	}
 
 out:
-	if (fd_a > -1)
-		close(fd_a);
-	if (fd_b > -1)
-		close(fd_b);
+	if (fd_source > -1)
+		close(fd_source);
+	if (fd_dest > -1)
+		close(fd_dest);
 	return ret;
 }