update-ref: support symrefs in the verify command

In the previous commits, we added the required base for adding symref
support to the transaction commands provided by 'git-update-ref(1)'.
Using them, extend the 'verify' command to support symrefs.

The 'verify' command allows users to verify if a provided symbolic
reference `<ref>` contains the provided `<old-oid>` without changing the
`<ref>`. Now we alternatively allow users to provide a
`ref:<old-target>` instead to verify if a symref targets the provided
target. Since we're checking for symbolic refs, this will only work with
the 'no-deref' mode. This is because any dereferenced symbolic ref will
point to an object and not a ref.

Add and use `null_new_value`, a helper function which is used to check
if there is a new_value in a reference update. The new value could
either be a symref target `new_target` or a OID `new_oid`. We also add
tests to test the command in both the regular stdin mode and also with
the '-z' flag.

We also disable the reference-transaction hook for symref-updates which
will be tackled in its own commit.

Add required tests for symref support in 'verify' while also adding
reflog checks for the pre-existing 'verify' tests.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 20 insertions, 1 deletions

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index e6122837c0a..754f413ea45 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -935,7 +935,26 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 		 * individual refs. But the error messages match what the files
 		 * backend returns, which keeps our tests happy.
 		 */
-		if (u->flags & REF_HAVE_OLD && !oideq(&current_oid, &u->old_oid)) {
+		if ((u->flags & REF_HAVE_OLD) && u->old_target) {
+			if (strcmp(referent.buf, u->old_target)) {
+				if (!strcmp(u->old_target, ""))
+					strbuf_addf(err, "verifying symref target: '%s': "
+						    "provided target is empty",
+						    original_update_refname(u));
+				else if (!strcmp(referent.buf, ""))
+					strbuf_addf(err, "verifying symref target: '%s': "
+						    "reference is missing but expected %s",
+						    original_update_refname(u),
+						    u->old_target);
+				else
+					strbuf_addf(err, "verifying symref target: '%s': "
+						    "is at %s but expected %s",
+						    original_update_refname(u),
+						    referent.buf, u->old_target);
+				ret = -1;
+				goto done;
+			}
+		} else if (u->flags & REF_HAVE_OLD && !oideq(&current_oid, &u->old_oid)) {
 			if (is_null_oid(&u->old_oid))
 				strbuf_addf(err, _("cannot lock ref '%s': "
 					    "reference already exists"),