lock_ref_for_update(): don't re-read non-symbolic references

Before the previous patch, our first read of the reference happened
before the reference was locked, so we couldn't trust its value and had
to read it again. But now that our first read of the reference happens
after acquiring the lock, there is no need to read it a second time. So
move the read_ref_full() call into the (update->type & REF_ISSYMREF)
block.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>

1 files changed, 30 insertions, 18 deletions

diff --git a/refs/files-backend.c b/refs/files-backend.c
index ffc30fd232..7bc18322aa 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3436,33 +3436,45 @@ static int lock_ref_for_update(struct ref_update *update,
 
 	lock = update->lock;
 
-	if (read_ref_full(update->refname,
-			  mustexist ? RESOLVE_REF_READING : 0,
-			  lock->old_oid.hash, NULL)) {
-		if (update->flags & REF_HAVE_OLD) {
-			strbuf_addf(err, "cannot lock ref '%s': can't resolve old value",
-				    update->refname);
+	if (update->type & REF_ISSYMREF) {
+		if (read_ref_full(update->refname,
+				  mustexist ? RESOLVE_REF_READING : 0,
+				  lock->old_oid.hash, NULL)) {
+			if (update->flags & REF_HAVE_OLD) {
+				strbuf_addf(err, "cannot lock ref '%s': can't resolve old value",
+					    update->refname);
+				return TRANSACTION_GENERIC_ERROR;
+			} else {
+				hashclr(lock->old_oid.hash);
+			}
+		}
+		if ((update->flags & REF_HAVE_OLD) &&
+		    hashcmp(lock->old_oid.hash, update->old_sha1)) {
+			strbuf_addf(err, "cannot lock ref '%s': is at %s but expected %s",
+				    update->refname,
+				    sha1_to_hex(lock->old_oid.hash),
+				    sha1_to_hex(update->old_sha1));
 			return TRANSACTION_GENERIC_ERROR;
-		} else {
-			hashclr(lock->old_oid.hash);
 		}
-	}
-	if ((update->flags & REF_HAVE_OLD) &&
-	    hashcmp(lock->old_oid.hash, update->old_sha1)) {
-		strbuf_addf(err, "cannot lock ref '%s': is at %s but expected %s",
-			    update->refname,
-			    sha1_to_hex(lock->old_oid.hash),
-			    sha1_to_hex(update->old_sha1));
-		return TRANSACTION_GENERIC_ERROR;
-	}
 
-	if (update->type & REF_ISSYMREF) {
 		if (!(update->flags & REF_NODEREF)) {
 			ret = split_symref_update(update, referent.buf, transaction,
 						  affected_refnames, err);
 			if (ret)
 				return ret;
 		}
+	} else if ((update->flags & REF_HAVE_OLD) &&
+		   hashcmp(lock->old_oid.hash, update->old_sha1)) {
+		if (is_null_sha1(update->old_sha1))
+			strbuf_addf(err, "cannot lock ref '%s': reference already exists",
+				    update->refname);
+		else
+			strbuf_addf(err, "cannot lock ref '%s': is at %s but expected %s",
+				    update->refname,
+				    sha1_to_hex(lock->old_oid.hash),
+				    sha1_to_hex(update->old_sha1));
+
+		return TRANSACTION_GENERIC_ERROR;
 	}
 
 	if ((update->flags & REF_HAVE_NEW) &&