update-ref: add support for 'symref-delete' command

Add a new command 'symref-delete' to allow deletions of symbolic refs in
a transaction via the '--stdin' mode of the 'git-update-ref' command.
The 'symref-delete' command can, when given an <old-target>, delete the
provided <ref> only when it points to <old-target>.

This command is only compatible with the 'no-deref' mode because we
optionally want to check the 'old_target' of the ref being deleted.
De-referencing a symbolic ref would provide a regular ref and we already
have the 'delete' command for regular refs.

While users can also use 'git symbolic-ref -d' to delete symbolic refs,
the 'symref-delete' command in 'git-update-ref' allows users to do so
within a transaction, which promises atomicity of the operation and can
be batched with other commands.

When no 'old_target' is provided it can also delete regular refs,
similar to how the 'delete' command can delete symrefs when no 'old_oid'
is provided.

Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 32 insertions, 1 deletions

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 6dce1cd663..833ebbdd42 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -293,7 +293,7 @@ static void parse_cmd_delete(struct ref_transaction *transaction,
 
 	if (ref_transaction_delete(transaction, refname,
 				   have_old ? &old_oid : NULL,
-				   update_flags, msg, &err))
+				   NULL, update_flags, msg, &err))
 		die("%s", err.buf);
 
 	update_flags = default_flags;
@@ -301,6 +301,36 @@ static void parse_cmd_delete(struct ref_transaction *transaction,
 	strbuf_release(&err);
 }
 
+
+static void parse_cmd_symref_delete(struct ref_transaction *transaction,
+				    const char *next, const char *end)
+{
+	struct strbuf err = STRBUF_INIT;
+	char *refname, *old_target;
+
+	if (!(update_flags & REF_NO_DEREF))
+		die("symref-delete: cannot operate with deref mode");
+
+	refname = parse_refname(&next);
+	if (!refname)
+		die("symref-delete: missing <ref>");
+
+	old_target = parse_next_refname(&next);
+
+	if (*next != line_termination)
+		die("symref-delete %s: extra input: %s", refname, next);
+
+	if (ref_transaction_delete(transaction, refname, NULL,
+				   old_target, update_flags, msg, &err))
+		die("%s", err.buf);
+
+	update_flags = default_flags;
+	free(refname);
+	free(old_target);
+	strbuf_release(&err);
+}
+
+
 static void parse_cmd_verify(struct ref_transaction *transaction,
 			     const char *next, const char *end)
 {
@@ -443,6 +473,7 @@ static const struct parse_cmd {
 	{ "create",        parse_cmd_create,        2, UPDATE_REFS_OPEN },
 	{ "delete",        parse_cmd_delete,        2, UPDATE_REFS_OPEN },
 	{ "verify",        parse_cmd_verify,        2, UPDATE_REFS_OPEN },
+	{ "symref-delete", parse_cmd_symref_delete, 2, UPDATE_REFS_OPEN },
 	{ "symref-verify", parse_cmd_symref_verify, 2, UPDATE_REFS_OPEN },
 	{ "option",        parse_cmd_option,        1, UPDATE_REFS_OPEN },
 	{ "start",         parse_cmd_start,         0, UPDATE_REFS_STARTED },