Merge branch 'kn/non-transactional-batch-updates'

Updating multiple references have only been possible in all-or-none
fashion with transactions, but it can be more efficient to batch
multiple updates even when some of them are allowed to fail in a
best-effort manner.  A new "best effort batches of updates" mode
has been introduced.

* kn/non-transactional-batch-updates:
  update-ref: add --batch-updates flag for stdin mode
  refs: support rejection in batch updates during F/D checks
  refs: implement batch reference update support
  refs: introduce enum-based transaction error types
  refs/reftable: extract code from the transaction preparation
  refs/files: remove duplicate duplicates check
  refs: move duplicate refname update check to generic layer
  refs/files: remove redundant check in split_symref_update()

refs.h

@@ -16,6 +16,23 @@ struct worktree;
 enum ref_storage_format ref_storage_format_by_name(const char *name);
 const char *ref_storage_format_to_name(enum ref_storage_format ref_storage_format);
 
+enum ref_transaction_error {
+	/* Default error code */
+	REF_TRANSACTION_ERROR_GENERIC = -1,
+	/* Ref name conflict like A vs A/B */
+	REF_TRANSACTION_ERROR_NAME_CONFLICT = -2,
+	/* Ref to be created already exists */
+	REF_TRANSACTION_ERROR_CREATE_EXISTS = -3,
+	/* ref expected but doesn't exist */
+	REF_TRANSACTION_ERROR_NONEXISTENT_REF = -4,
+	/* Provided old_oid or old_target of reference doesn't match actual */
+	REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE = -5,
+	/* Provided new_oid or new_target is invalid */
+	REF_TRANSACTION_ERROR_INVALID_NEW_VALUE = -6,
+	/* Expected ref to be symref, but is a regular ref */
+	REF_TRANSACTION_ERROR_EXPECTED_SYMREF = -7,
+};
+
 /*
  * Resolve a reference, recursively following symbolic references.
  *
@@ -117,24 +134,12 @@ int refs_read_symbolic_ref(struct ref_store *ref_store, const char *refname,
  *
  * extras and skip must be sorted.
  */
-int refs_verify_refname_available(struct ref_store *refs,
-				  const char *refname,
-				  const struct string_list *extras,
-				  const struct string_list *skip,
-				  unsigned int initial_transaction,
-				  struct strbuf *err);
-
-/*
- * Same as `refs_verify_refname_available()`, but checking for a list of
- * refnames instead of only a single item. This is more efficient in the case
- * where one needs to check multiple refnames.
- */
-int refs_verify_refnames_available(struct ref_store *refs,
-				   const struct string_list *refnames,
-				   const struct string_list *extras,
-				   const struct string_list *skip,
-				   unsigned int initial_transaction,
-				   struct strbuf *err);
+enum ref_transaction_error refs_verify_refname_available(struct ref_store *refs,
+						 const char *refname,
+						 const struct string_list *extras,
+						 const struct string_list *skip,
+						 unsigned int initial_transaction,
+						 struct strbuf *err);
 
 int refs_ref_exists(struct ref_store *refs, const char *refname);
 
@@ -650,6 +655,13 @@ enum ref_transaction_flag {
 	 * either be absent or null_oid.
 	 */
 	REF_TRANSACTION_FLAG_INITIAL = (1 << 0),
+
+	/*
+	 * The transaction mechanism by default fails all updates if any conflict
+	 * is detected. This flag allows transactions to partially apply updates
+	 * while rejecting updates which do not match the expected state.
+	 */
+	REF_TRANSACTION_ALLOW_FAILURE = (1 << 1),
 };
 
 /*
@@ -830,13 +842,6 @@ int ref_transaction_verify(struct ref_transaction *transaction,
 			   unsigned int flags,
 			   struct strbuf *err);
 
-/* Naming conflict (for example, the ref names A and A/B conflict). */
-#define TRANSACTION_NAME_CONFLICT -1
-/* When only creation was requested, but the ref already exists. */
-#define TRANSACTION_CREATE_EXISTS -2
-/* All other errors. */
-#define TRANSACTION_GENERIC_ERROR -3
-
 /*
  * Perform the preparatory stages of committing `transaction`. Acquire
  * any needed locks, check preconditions, etc.; basically, do as much
@@ -887,6 +892,21 @@ void ref_transaction_for_each_queued_update(struct ref_transaction *transaction,
 					    ref_transaction_for_each_queued_update_fn cb,
 					    void *cb_data);
 
+/*
+ * Execute the given callback function for each of the reference updates which
+ * have been rejected in the given transaction.
+ */
+typedef void ref_transaction_for_each_rejected_update_fn(const char *refname,
+							 const struct object_id *old_oid,
+							 const struct object_id *new_oid,
+							 const char *old_target,
+							 const char *new_target,
+							 enum ref_transaction_error err,
+							 void *cb_data);
+void ref_transaction_for_each_rejected_update(struct ref_transaction *transaction,
+					      ref_transaction_for_each_rejected_update_fn cb,
+					      void *cb_data);
+
 /*
  * Free `*transaction` and all associated data.
  */