[PATCH 8/8] refs: support symrefs in 'reference-transaction' hook

[Karthik Nayak <karthik.188@gmail.com>]

From: Karthik Nayak <karthik.188@gmail.com>

The 'reference-transaction' hook runs whenever a reference update is
made to the system. In the previous commit, we added support for the
`update-symref` command in `git-update-ref`. While it allowed us to now
create symbolic refs via `git-update-ref`, it didn't activate the
'reference-transaction' hook.

Let's activate the hook for symbolic reference updates too. This takes
the form `<symref-target> SP <ref-name> LF`, which deviates from the
form for regular updates since this only contains two fields.

While this seems to be backward incompatible, it is okay, since the only
way the `reference-transaction` hook outputs this syntax is when
`git-update-ref` is used with `update-symref` command. The command was
only introduced in the previous commit and hence only users of this
command will face this incompatibility.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 Documentation/githooks.txt       | 13 +++++++++++--
 refs.c                           | 17 +++++++++--------
 t/t1416-ref-transaction-hooks.sh | 27 +++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 10 deletions(-)

diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index 37f91d5b50..ae9f02974d 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -485,8 +485,7 @@ reference-transaction
 
 This hook is invoked by any Git command that performs reference
 updates. It executes whenever a reference transaction is prepared,
-committed or aborted and may thus get called multiple times. The hook
-does not cover symbolic references (but that may change in the future).
+committed or aborted and may thus get called multiple times.
 
 The hook takes exactly one argument, which is the current state the
 given reference transaction is in:
@@ -513,6 +512,16 @@ to be created anew, `<old-value>` is the all-zeroes object name. To
 distinguish these cases, you can inspect the current value of
 `<ref-name>` via `git rev-parse`.
 
+For each symbolic reference update that was added to the transaction,
+the hook receives on standard input a line of the format:
+
+  <symref-target> SP <ref-name> LF
+
+where `<symref-target>` is the target of the symbolic reference update
+passed into the reference transaction, `<ref-name>` is the full name of
+the ref being updated. To distinguish from the regular updates, we can
+note that there are only two fields.
+
 The exit status of the hook is ignored for any state except for the
 "prepared" state. In the "prepared" state, a non-zero exit status will
 cause the transaction to be aborted. The hook will not be called with
diff --git a/refs.c b/refs.c
index 706dcd6deb..d0929c5684 100644
--- a/refs.c
+++ b/refs.c
@@ -2342,16 +2342,17 @@ static int run_transaction_hook(struct ref_transaction *transaction,
 
 	for (i = 0; i < transaction->nr; i++) {
 		struct ref_update *update = transaction->updates[i];
+		strbuf_reset(&buf);
 
-		// Reference transaction does not support symbolic updates.
 		if (update->flags & REF_UPDATE_SYMREF)
-			continue;
-
-		strbuf_reset(&buf);
-		strbuf_addf(&buf, "%s %s %s\n",
-			    oid_to_hex(&update->old_oid),
-			    oid_to_hex(&update->new_oid),
-			    update->refname);
+			strbuf_addf(&buf, "%s %s\n",
+				    update->symref_target,
+				    update->refname);
+		else
+			strbuf_addf(&buf, "%s %s %s\n",
+				    oid_to_hex(&update->old_oid),
+				    oid_to_hex(&update->new_oid),
+				    update->refname);
 
 		if (write_in_full(proc.in, buf.buf, buf.len) < 0) {
 			if (errno != EPIPE) {
diff --git a/t/t1416-ref-transaction-hooks.sh b/t/t1416-ref-transaction-hooks.sh
index 2092488090..fac5d5fc6d 100755
--- a/t/t1416-ref-transaction-hooks.sh
+++ b/t/t1416-ref-transaction-hooks.sh
@@ -83,6 +83,33 @@ test_expect_success 'hook gets all queued updates in committed state' '
 	test_cmp expect actual
 '
 
+test_expect_success 'hook gets all queued symref updates' '
+	test_when_finished "rm actual" &&
+	test_hook reference-transaction <<-\EOF &&
+		echo "$*" >>actual
+		while read -r line
+		do
+			printf "%s\n" "$line"
+		done >>actual
+	EOF
+	cat >expect <<-EOF &&
+		prepared
+		refs/heads/test TESTSYMREF
+		refs/heads/test refs/heads/symref
+		committed
+		refs/heads/test TESTSYMREF
+		refs/heads/test refs/heads/symref
+	EOF
+	git update-ref --no-deref --stdin <<-EOF &&
+		start
+		update-symref TESTSYMREF refs/heads/test
+		update-symref refs/heads/symref refs/heads/test
+		prepare
+		commit
+	EOF
+	test_cmp expect actual
+'
+
 test_expect_success 'hook gets all queued updates in aborted state' '
 	test_when_finished "rm actual" &&
 	git reset --hard PRE &&
-- 
2.43.GIT