[PATCH v4 7/7] ref: 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 commits, we added symref support for
various commands in `git-update-ref`. While it allowed us to now
manipulate symbolic refs via `git-update-ref`, it didn't activate the
'reference-transaction' hook.

Let's activate the hook for symbolic reference updates too. There is no
new format described for this and we stick to the existing format of:
    <old-value> SP <new-value> SP <ref-name> LF
but now, <old-value> and <new-value> could also denote references
instead of objects, where the format is similar to that in
'git-update-ref', i.e. 'ref:<ref-target>'.

While this seems to be backward incompatible, it is okay, since the only
way the `reference-transaction` hook has refs in its output is when
`git-update-ref` is used to manipulate symrefs. Also the documentation
for reference-transaction hook always stated that support for symbolic
references may be added in the future.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 Documentation/githooks.txt       | 14 +++++++----
 refs.c                           | 21 ++++++++--------
 t/t1416-ref-transaction-hooks.sh | 41 ++++++++++++++++++++++++++++++++
 3 files changed, 61 insertions(+), 15 deletions(-)

diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index ee9b92c90d..0bf8ca87a6 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -486,7 +486,7 @@ 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).
+also cover symbolic references.
 
 The hook takes exactly one argument, which is the current state the
 given reference transaction is in:
@@ -503,16 +503,20 @@ given reference transaction is in:
 For each reference update that was added to the transaction, the hook
 receives on standard input a line of the format:
 
-  <old-oid> SP <new-oid> SP <ref-name> LF
+  <old-value> SP <new-value> SP <ref-name> LF
 
-where `<old-oid>` is the old object name passed into the reference
-transaction, `<new-oid>` is the new object name to be stored in the
+where `<old-value>` is the old object name passed into the reference
+transaction, `<new-value>` is the new object name to be stored in the
 ref and `<ref-name>` is the full name of the ref. When force updating
 the reference regardless of its current value or when the reference is
-to be created anew, `<old-oid>` is the all-zeroes object name. To
+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 symbolic reference updates the `<old_value>` and `<new-value>`
+fields could denote references instead of objects, denoted via the
+`ref:<ref-target>` format.
+
 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 42cb4126a7..9a510744a7 100644
--- a/refs.c
+++ b/refs.c
@@ -2365,18 +2365,19 @@ 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);
 
-		/*
-		 * Skip reference transaction for symbolic refs.
-		 */
-		if (update->new_target || update->old_target)
-			continue;
+		if (update->flags & REF_HAVE_OLD && update->old_target)
+			strbuf_addf(&buf, "ref:%s ", update->old_target);
+		else
+			strbuf_addf(&buf, "%s ", oid_to_hex(&update->old_oid));
 
-		strbuf_reset(&buf);
-		strbuf_addf(&buf, "%s %s %s\n",
-			    oid_to_hex(&update->old_oid),
-			    oid_to_hex(&update->new_oid),
-			    update->refname);
+		if (update->flags & REF_HAVE_NEW && update->new_target)
+			strbuf_addf(&buf, "ref:%s ", update->new_target);
+		else
+			strbuf_addf(&buf, "%s ", oid_to_hex(&update->new_oid));
+
+		strbuf_addf(&buf, "%s\n", 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..0a7e86062e 100755
--- a/t/t1416-ref-transaction-hooks.sh
+++ b/t/t1416-ref-transaction-hooks.sh
@@ -134,4 +134,45 @@ test_expect_success 'interleaving hook calls succeed' '
 	test_cmp expect target-repo.git/actual
 '
 
+# This test doesn't add a check for symref 'delete' since there is a
+# variation between the ref backends WRT 'delete'. In the files backend,
+# 'delete' also triggers an additional transaction update on the
+# packed-refs backend, which constitutes additional reflog entries.
+test_expect_success 'hook gets all queued symref updates' '
+	test_when_finished "rm actual" &&
+
+	git update-ref refs/heads/branch $POST_OID &&
+	git symbolic-ref refs/heads/symref refs/heads/main &&
+	git symbolic-ref refs/heads/symrefu refs/heads/main &&
+
+	test_hook reference-transaction <<-\EOF &&
+		echo "$*" >>actual
+		while read -r line
+		do
+			printf "%s\n" "$line"
+		done >>actual
+	EOF
+
+	cat >expect <<-EOF &&
+		prepared
+		ref:refs/heads/main $ZERO_OID refs/heads/symref
+		$ZERO_OID ref:refs/heads/main refs/heads/symrefc
+		ref:refs/heads/main ref:refs/heads/branch refs/heads/symrefu
+		committed
+		ref:refs/heads/main $ZERO_OID refs/heads/symref
+		$ZERO_OID ref:refs/heads/main refs/heads/symrefc
+		ref:refs/heads/main ref:refs/heads/branch refs/heads/symrefu
+	EOF
+
+	git update-ref --no-deref --stdin <<-EOF &&
+		start
+		symref-verify refs/heads/symref refs/heads/main
+		symref-create refs/heads/symrefc refs/heads/main
+		symref-update refs/heads/symrefu refs/heads/branch ref refs/heads/main
+		prepare
+		commit
+	EOF
+	test_cmp expect actual
+'
+
 test_done
-- 
2.43.GIT