Re: [PATCH v6 1/7] refs: accept symref values in `ref_transaction_update()`

> From: Karthik Nayak <karthik.188@gmail.com>
> 
> The function `ref_transaction_update()` obtains ref information and
> flags to create a `ref_update` and add them to the transaction at hand.
> 
> To extend symref support in transactions, we need to also accept the
> old and new ref targets and process it. This commit adds the required
> parameters to the function and modifies all call sites.
> 
> The two parameters added are `new_target` and `old_target`. The
> `new_target` is used to denote what the reference should point to when
> the transaction is applied. Some functions allow this parameter to be
> NULL, meaning that the reference is not changed.
> 
> The `old_target` denotes the value the reference must have before the
> update. Some functions allow this parameter to be NULL, meaning that the
> old value of the reference is not checked.
> 
> We also update the internal function `ref_transaction_add_update()`
> similarly to take the two new parameters.

> Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
> ---
>   branch.c                |  2 +-
>   builtin/fast-import.c   |  5 +++--
>   builtin/fetch.c         |  2 +-
>   builtin/receive-pack.c  |  1 +
>   builtin/replace.c       |  2 +-
>   builtin/tag.c           |  1 +
>   builtin/update-ref.c    |  1 +
>   refs.c                  | 22 +++++++++++++++++-----
>   refs.h                  | 18 +++++++++++++++++-
>   refs/files-backend.c    | 12 ++++++------
>   refs/refs-internal.h    | 14 ++++++++++++++
>   refs/reftable-backend.c |  4 ++--
>   sequencer.c             |  9 +++++----
>   walker.c                |  2 +-
>   14 files changed, 71 insertions(+), 24 deletions(-)
> 
> diff --git a/branch.c b/branch.c
> index e4a738fc7b..48af4c3ceb 100644
> --- a/branch.c
> +++ b/branch.c
> @@ -627,7 +627,7 @@ void create_branch(struct repository *r,
>   	if (!transaction ||
>   		ref_transaction_update(transaction, ref.buf,
>   					&oid, forcing ? NULL : null_oid(),
> -					0, msg, &err) ||
> +					NULL, NULL, 0, msg, &err) ||
>   		ref_transaction_commit(transaction, &err))
>   		die("%s", err.buf);
>   	ref_transaction_free(transaction);
> diff --git a/builtin/fast-import.c b/builtin/fast-import.c
> index dc5a9d32dd..297dfb91a1 100644
> --- a/builtin/fast-import.c
> +++ b/builtin/fast-import.c
> @@ -1634,7 +1634,7 @@ static int update_branch(struct branch *b)
>   	transaction = ref_transaction_begin(&err);
>   	if (!transaction ||
>   	    ref_transaction_update(transaction, b->name, &b->oid, &old_oid,
> -				   0, msg, &err) ||
> +				   NULL, NULL, 0, msg, &err) ||
>   	    ref_transaction_commit(transaction, &err)) {
>   		ref_transaction_free(transaction);
>   		error("%s", err.buf);
> @@ -1675,7 +1675,8 @@ static void dump_tags(void)
>   		strbuf_addf(&ref_name, "refs/tags/%s", t->name);
>   
>   		if (ref_transaction_update(transaction, ref_name.buf,
> -					   &t->oid, NULL, 0, msg, &err)) {
> +					   &t->oid, NULL, NULL, NULL,
> +					   0, msg, &err)) {
>   			failure |= error("%s", err.buf);
>   			goto cleanup;
>   		}
> diff --git a/builtin/fetch.c b/builtin/fetch.c
> index 5857d860db..66840b7c5b 100644
> --- a/builtin/fetch.c
> +++ b/builtin/fetch.c
> @@ -668,7 +668,7 @@ static int s_update_ref(const char *action,
>   
>   	ret = ref_transaction_update(transaction, ref->name, &ref->new_oid,
>   				     check_old ? &ref->old_oid : NULL,
> -				     0, msg, &err);
> +				     NULL, NULL, 0, msg, &err);
>   	if (ret) {
>   		ret = STORE_REF_ERROR_OTHER;
>   		goto out;
> diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
> index e8d7df14b6..b150ef39a8 100644
> --- a/builtin/receive-pack.c
> +++ b/builtin/receive-pack.c
> @@ -1595,6 +1595,7 @@ static const char *update(struct command *cmd, struct shallow_info *si)
>   		if (ref_transaction_update(transaction,
>   					   namespaced_name,
>   					   new_oid, old_oid,
> +					   NULL, NULL,
>   					   0, "push",
>   					   &err)) {
>   			rp_error("%s", err.buf);
> diff --git a/builtin/replace.c b/builtin/replace.c
> index da59600ad2..7690687b0e 100644
> --- a/builtin/replace.c
> +++ b/builtin/replace.c
> @@ -201,7 +201,7 @@ static int replace_object_oid(const char *object_ref,
>   	transaction = ref_transaction_begin(&err);
>   	if (!transaction ||
>   	    ref_transaction_update(transaction, ref.buf, repl, &prev,
> -				   0, NULL, &err) ||
> +				   NULL, NULL, 0, NULL, &err) ||
>   	    ref_transaction_commit(transaction, &err))
>   		res = error("%s", err.buf);
>   
> diff --git a/builtin/tag.c b/builtin/tag.c
> index 9a33cb50b4..40a65fdebc 100644
> --- a/builtin/tag.c
> +++ b/builtin/tag.c
> @@ -660,6 +660,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
>   	transaction = ref_transaction_begin(&err);
>   	if (!transaction ||
>   	    ref_transaction_update(transaction, ref.buf, &object, &prev,
> +				   NULL, NULL,
>   				   create_reflog ? REF_FORCE_CREATE_REFLOG : 0,
>   				   reflog_msg.buf, &err) ||
>   	    ref_transaction_commit(transaction, &err)) {
> diff --git a/builtin/update-ref.c b/builtin/update-ref.c
> index e46afbc46d..21fdbf6ac8 100644
> --- a/builtin/update-ref.c
> +++ b/builtin/update-ref.c
> @@ -204,6 +204,7 @@ static void parse_cmd_update(struct ref_transaction *transaction,
>   
>   	if (ref_transaction_update(transaction, refname,
>   				   &new_oid, have_old ? &old_oid : NULL,
> +				   NULL, NULL,
>   				   update_flags | create_reflog_flag,
>   				   msg, &err))
>   		die("%s", err.buf);
> diff --git a/refs.c b/refs.c
> index 55d2e0b2cb..47bc9dd103 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -1228,6 +1228,7 @@ struct ref_update *ref_transaction_add_update(
>   		const char *refname, unsigned int flags,
>   		const struct object_id *new_oid,
>   		const struct object_id *old_oid,
> +		const char *new_target, const char *old_target,
>   		const char *msg)
>   {
>   	struct ref_update *update;
> @@ -1235,6 +1236,11 @@ struct ref_update *ref_transaction_add_update(
>   	if (transaction->state != REF_TRANSACTION_OPEN)
>   		BUG("update called for transaction that is not open");
>   
> +	if (old_oid && !is_null_oid(old_oid) && old_target)
> +		BUG("only one of old_oid and old_target should be non NULL");
> +	if (new_oid && !is_null_oid(new_oid) && new_target)
> +		BUG("only one of new_oid and new_target should be non NULL");
> +
>   	FLEX_ALLOC_STR(update, refname, refname);
>   	ALLOC_GROW(transaction->updates, transaction->nr + 1, transaction->alloc);
>   	transaction->updates[transaction->nr++] = update;
> @@ -1253,6 +1259,8 @@ int ref_transaction_update(struct ref_transaction *transaction,
>   			   const char *refname,
>   			   const struct object_id *new_oid,
>   			   const struct object_id *old_oid,
> +			   const char *new_target,
> +			   const char *old_target,
>   			   unsigned int flags, const char *msg,
>   			   struct strbuf *err)
>   {
> @@ -1280,7 +1288,8 @@ int ref_transaction_update(struct ref_transaction *transaction,
>   	flags |= (new_oid ? REF_HAVE_NEW : 0) | (old_oid ? REF_HAVE_OLD : 0);
>   
>   	ref_transaction_add_update(transaction, refname, flags,
> -				   new_oid, old_oid, msg);
> +				   new_oid, old_oid, new_target,
> +				   old_target, msg);
>   	return 0;
>   }
>   
> @@ -1295,7 +1304,8 @@ int ref_transaction_create(struct ref_transaction *transaction,
>   		return 1;
>   	}
>   	return ref_transaction_update(transaction, refname, new_oid,
> -				      null_oid(), flags, msg, err);
> +				      null_oid(), NULL, NULL, flags,
> +				      msg, err);
>   }
>   
>   int ref_transaction_delete(struct ref_transaction *transaction,
> @@ -1308,7 +1318,8 @@ int ref_transaction_delete(struct ref_transaction *transaction,
>   		BUG("delete called with old_oid set to zeros");
>   	return ref_transaction_update(transaction, refname,
>   				      null_oid(), old_oid,
> -				      flags, msg, err);
> +				      NULL, NULL, flags,
> +				      msg, err);
>   }
>   
>   int ref_transaction_verify(struct ref_transaction *transaction,
> @@ -1321,6 +1332,7 @@ int ref_transaction_verify(struct ref_transaction *transaction,
>   		BUG("verify called with old_oid set to NULL");
>   	return ref_transaction_update(transaction, refname,
>   				      NULL, old_oid,
> +				      NULL, NULL,
>   				      flags, NULL, err);
>   }
>   
> @@ -1335,8 +1347,8 @@ int refs_update_ref(struct ref_store *refs, const char *msg,
>   
>   	t = ref_store_transaction_begin(refs, &err);
>   	if (!t ||
> -	    ref_transaction_update(t, refname, new_oid, old_oid, flags, msg,
> -				   &err) ||
> +	    ref_transaction_update(t, refname, new_oid, old_oid, NULL, NULL,
> +				   flags, msg, &err) ||
>   	    ref_transaction_commit(t, &err)) {
>   		ret = 1;
>   		ref_transaction_free(t);
> diff --git a/refs.h b/refs.h
> index d278775e08..c7851bf587 100644
> --- a/refs.h
> +++ b/refs.h
> @@ -648,6 +648,16 @@ struct ref_transaction *ref_transaction_begin(struct strbuf *err);
>    *         before the update. A copy of this value is made in the
>    *         transaction.
>    *
> + *     new_target -- the target reference that the reference will be
> + *         updated to point to. If the reference is a regular reference,
> + *         it will be converted to a symbolic reference. Cannot be set
> + *         together with `new_oid`. A copy of this value is made in the
> + *         transaction.
> + *
> + *     old_target -- the reference that the reference must be pointing to.
> + *         Canont be set together with `old_oid`. A copy of this value is
> + *         made in the transaction.
> + *
>    *     flags -- flags affecting the update, passed to
>    *         update_ref_lock(). Possible flags: REF_NO_DEREF,
>    *         REF_FORCE_CREATE_REFLOG. See those constants for more
> @@ -713,7 +723,11 @@ struct ref_transaction *ref_transaction_begin(struct strbuf *err);
>    * beforehand. The old value is checked after the lock is taken to
>    * prevent races. If the old value doesn't agree with old_oid, the
>    * whole transaction fails. If old_oid is NULL, then the previous
> - * value is not checked.
> + * value is not checked. If `old_target` is not NULL, treat the reference
> + * as a symbolic ref and validate that its target before the update is
> + * `old_target`. If the `new_target` is not NULL, then the reference
> + * will be updated to a symbolic ref which targets `new_target`.
> + * Together, these allow us to update between regular refs and symrefs.
>    *
>    * See the above comment "Reference transaction updates" for more
>    * information.
> @@ -722,6 +736,8 @@ int ref_transaction_update(struct ref_transaction *transaction,
>   			   const char *refname,
>   			   const struct object_id *new_oid,
>   			   const struct object_id *old_oid,
> +			   const char *new_target,
> +			   const char *old_target,
>   			   unsigned int flags, const char *msg,
>   			   struct strbuf *err);
>   
> diff --git a/refs/files-backend.c b/refs/files-backend.c
> index a098d14ea0..e4d0aa3d41 100644
> --- a/refs/files-backend.c
> +++ b/refs/files-backend.c
> @@ -1198,7 +1198,7 @@ static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
>   	ref_transaction_add_update(
>   			transaction, r->name,
>   			REF_NO_DEREF | REF_HAVE_NEW | REF_HAVE_OLD | REF_IS_PRUNING,
> -			null_oid(), &r->oid, NULL);
> +			null_oid(), &r->oid, NULL, NULL, NULL);
>   	if (ref_transaction_commit(transaction, &err))
>   		goto cleanup;
>   
> @@ -1292,7 +1292,7 @@ static int files_pack_refs(struct ref_store *ref_store,
>   		 * packed-refs transaction:
>   		 */
>   		if (ref_transaction_update(transaction, iter->refname,
> -					   iter->oid, NULL,
> +					   iter->oid, NULL, NULL, NULL,
>   					   REF_NO_DEREF, NULL, &err))
>   			die("failure preparing to create packed reference %s: %s",
>   			    iter->refname, err.buf);
> @@ -2309,7 +2309,7 @@ static int split_head_update(struct ref_update *update,
>   			transaction, "HEAD",
>   			update->flags | REF_LOG_ONLY | REF_NO_DEREF,
>   			&update->new_oid, &update->old_oid,
> -			update->msg);
> +			NULL, NULL, update->msg);
>   
>   	/*
>   	 * Add "HEAD". This insertion is O(N) in the transaction
> @@ -2372,7 +2372,7 @@ static int split_symref_update(struct ref_update *update,
>   	new_update = ref_transaction_add_update(
>   			transaction, referent, new_flags,
>   			&update->new_oid, &update->old_oid,
> -			update->msg);
> +			NULL, NULL, update->msg);
>   
>   	new_update->parent_update = update;
>   
> @@ -2763,7 +2763,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
>   					packed_transaction, update->refname,
>   					REF_HAVE_NEW | REF_NO_DEREF,
>   					&update->new_oid, NULL,
> -					NULL);
> +					NULL, NULL, NULL);
>   		}
>   	}
>   
> @@ -3048,7 +3048,7 @@ static int files_initial_transaction_commit(struct ref_store *ref_store,
>   		ref_transaction_add_update(packed_transaction, update->refname,
>   					   update->flags & ~REF_HAVE_OLD,
>   					   &update->new_oid, &update->old_oid,
> -					   NULL);
> +					   NULL, NULL, NULL);
>   	}
>   
>   	if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
> diff --git a/refs/refs-internal.h b/refs/refs-internal.h
> index 56641aa57a..108f4ec419 100644
> --- a/refs/refs-internal.h
> +++ b/refs/refs-internal.h
> @@ -124,6 +124,19 @@ struct ref_update {
>   	 */
>   	struct object_id old_oid;
>   
> +	/*
> +	 * If set, point the reference to this value. This can also be
> +	 * used to convert regular references to become symbolic refs.
> +	 * Cannot be set together with `new_oid`.
> +	 */
> +	const char *new_target;
> +
> +	/*
> +	 * If set, check that the reference previously pointed to this
> +	 * value. Cannot be set together with `old_oid`.
> +	 */
> +	const char *old_target;
> +
>   	/*
>   	 * One or more of REF_NO_DEREF, REF_FORCE_CREATE_REFLOG,
>   	 * REF_HAVE_NEW, REF_HAVE_OLD, or backend-specific flags.
> @@ -173,6 +186,7 @@ struct ref_update *ref_transaction_add_update(
>   		const char *refname, unsigned int flags,
>   		const struct object_id *new_oid,
>   		const struct object_id *old_oid,
> +		const char *new_target, const char *old_target,
>   		const char *msg);
>   
>   /*
> diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
> index 1cda48c504..6104471199 100644
> --- a/refs/reftable-backend.c
> +++ b/refs/reftable-backend.c
> @@ -829,7 +829,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
>   			new_update = ref_transaction_add_update(
>   					transaction, "HEAD",
>   					u->flags | REF_LOG_ONLY | REF_NO_DEREF,
> -					&u->new_oid, &u->old_oid, u->msg);
> +					&u->new_oid, &u->old_oid, NULL, NULL, u->msg);
>   			string_list_insert(&affected_refnames, new_update->refname);
>   		}
>   
> @@ -908,7 +908,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
>   				 */
>   				new_update = ref_transaction_add_update(
>   						transaction, referent.buf, new_flags,
> -						&u->new_oid, &u->old_oid, u->msg);
> +						&u->new_oid, &u->old_oid, NULL, NULL, u->msg);
>   				new_update->parent_update = u;
>   
>   				/*
> diff --git a/sequencer.c b/sequencer.c
> index 88de4dc20f..61e007d85f 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -665,7 +665,7 @@ static int fast_forward_to(struct repository *r,
>   	if (!transaction ||
>   	    ref_transaction_update(transaction, "HEAD",
>   				   to, unborn && !is_rebase_i(opts) ?
> -				   null_oid() : from,
> +				   null_oid() : from, NULL, NULL,
>   				   0, sb.buf, &err) ||
>   	    ref_transaction_commit(transaction, &err)) {
>   		ref_transaction_free(transaction);
> @@ -1298,7 +1298,7 @@ int update_head_with_reflog(const struct commit *old_head,
>   	if (!transaction ||
>   	    ref_transaction_update(transaction, "HEAD", new_head,
>   				   old_head ? &old_head->object.oid : null_oid(),
> -				   0, sb.buf, err) ||
> +				   NULL, NULL, 0, sb.buf, err) ||
>   	    ref_transaction_commit(transaction, err)) {
>   		ret = -1;
>   	}
> @@ -3832,8 +3832,9 @@ static int do_label(struct repository *r, const char *name, int len)
>   	} else if (repo_get_oid(r, "HEAD", &head_oid)) {
>   		error(_("could not read HEAD"));
>   		ret = -1;
> -	} else if (ref_transaction_update(transaction, ref_name.buf, &head_oid,
> -					  NULL, 0, msg.buf, &err) < 0 ||
> +	} else if (ref_transaction_update(transaction, ref_name.buf,
> +					  &head_oid, NULL, NULL, NULL,
> +					  0, msg.buf, &err) < 0 ||
>   		   ref_transaction_commit(transaction, &err)) {
>   		error("%s", err.buf);
>   		ret = -1;
> diff --git a/walker.c b/walker.c
> index c0fd632d92..1b3df43906 100644
> --- a/walker.c
> +++ b/walker.c
> @@ -324,7 +324,7 @@ int walker_fetch(struct walker *walker, int targets, char **target,
>   		strbuf_reset(&refname);
>   		strbuf_addf(&refname, "refs/%s", write_ref[i]);
>   		if (ref_transaction_update(transaction, refname.buf,
> -					   oids + i, NULL, 0,
> +					   oids + i, NULL, NULL, NULL, 0,
>   					   msg ? msg : "fetch (unknown)",
>   					   &err)) {
>   			error("%s", err.buf);