Subject: [PATCH v4 8/8] update-ref: add --batch-updates flag for stdin mode

From: Karthik Nayak <[email-masked]>
Date: Thu, 20 Mar 2025 12:44:03 +0100

When updating multiple references through stdin, Git's update-ref
command normally aborts the entire transaction if any single update
fails. This atomic behavior prevents partial updates. Introduce a new
batch update system, where the updates the performed together similar
but individual updates are allowed to fail.

Add a new `--batch-updates` flag that allows the transaction to continue
even when individual reference updates fail. This flag can only be used
in `--stdin` mode and builds upon the batch update support added to the
refs subsystem in the previous commits. When enabled, failed updates are
reported in the following format:

  rejected SP (<old-oid> | <old-target>) SP (<new-oid> | <new-target>) SP <rejection-reason> LF

Update the documentation to reflect this change and also tests to cover
different scenarios where an update could be rejected.

Signed-off-by: Karthik Nayak <[email-masked]>
---
 Documentation/git-update-ref.adoc |  14 ++-
 builtin/update-ref.c              |  67 ++++++++++-
 t/t1400-update-ref.sh             | 233 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 306 insertions(+), 8 deletions(-)

diff --git a/Documentation/git-update-ref.adoc b/Documentation/git-update-ref.adoc
index 9e6935d38d..5be2c16776 100644
--- a/Documentation/git-update-ref.adoc
+++ b/Documentation/git-update-ref.adoc
@@ -7,8 +7,10 @@ git-update-ref - Update the object name stored in a ref safely
 
 SYNOPSIS
 --------
-[verse]
-'git update-ref' [-m <reason>] [--no-deref] (-d <ref> [<old-oid>] | [--create-reflog] <ref> <new-oid> [<old-oid>] | --stdin [-z])
+[synopsis]
+git update-ref [-m <reason>] [--no-deref] -d <ref> [<old-oid>]
+	       [-m <reason>] [--no-deref] [--create-reflog] <ref> <new-oid> [<old-oid>]
+               [-m <reason>] [--no-deref] --stdin [-z] [--batch-updates]
 
 DESCRIPTION
 -----------
@@ -57,6 +59,14 @@ performs all modifications together.  Specify commands of the form:
 With `--create-reflog`, update-ref will create a reflog for each ref
 even if one would not ordinarily be created.
 
+With `--batch-updates`, update-ref executes the updates in a batch but allows
+individual updates to fail due to invalid or incorrect user input, applying only
+the successful updates. However, system-related errors—such as I/O failures or
+memory issues—will result in a full failure of all batched updates. Any failed
+updates will be reported in the following format:
+
+	rejected SP (<old-oid> | <old-target>) SP (<new-oid> | <new-target>) SP <rejection-reason> LF
+
 Quote fields containing whitespace as if they were strings in C source
 code; i.e., surrounded by double-quotes and with backslash escapes.
 Use 40 "0" characters or the empty string to specify a zero value.  To
diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 1d541e13ad..97e14b279e 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -5,6 +5,7 @@
 #include "config.h"
 #include "gettext.h"
 #include "hash.h"
+#include "hex.h"
 #include "refs.h"
 #include "object-name.h"
 #include "parse-options.h"
@@ -13,7 +14,7 @@
 static const char * const git_update_ref_usage[] = {
 	N_("git update-ref [<options>] -d <refname> [<old-oid>]"),
 	N_("git update-ref [<options>]    <refname> <new-oid> [<old-oid>]"),
-	N_("git update-ref [<options>] --stdin [-z]"),
+	N_("git update-ref [<options>] --stdin [-z] [--batch-updates]"),
 	NULL
 };
 
@@ -565,6 +566,49 @@ static void parse_cmd_abort(struct ref_transaction *transaction,
 	report_ok("abort");
 }
 
+static void print_rejected_refs(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 UNUSED)
+{
+	struct strbuf sb = STRBUF_INIT;
+	const char *reason = "";
+
+	switch (err) {
+	case REF_TRANSACTION_ERROR_NAME_CONFLICT:
+		reason = "refname conflict";
+		break;
+	case REF_TRANSACTION_ERROR_CREATE_EXISTS:
+		reason = "reference already exists";
+		break;
+	case REF_TRANSACTION_ERROR_NONEXISTENT_REF:
+		reason = "reference does not exist";
+		break;
+	case REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE:
+		reason = "incorrect old value provided";
+		break;
+	case REF_TRANSACTION_ERROR_INVALID_NEW_VALUE:
+		reason = "invalid new value provided";
+		break;
+	case REF_TRANSACTION_ERROR_EXPECTED_SYMREF:
+		reason = "expected symref but found regular ref";
+		break;
+	default:
+		reason = "unkown failure";
+	}
+
+	strbuf_addf(&sb, "rejected %s %s %s %s\n", refname,
+		    new_oid ? oid_to_hex(new_oid) : new_target,
+		    old_oid ? oid_to_hex(old_oid) : old_target,
+		    reason);
+
+	fwrite(sb.buf, sb.len, 1, stdout);
+	strbuf_release(&sb);
+}
+
 static void parse_cmd_commit(struct ref_transaction *transaction,
 			     const char *next, const char *end UNUSED)
 {
@@ -573,6 +617,10 @@ static void parse_cmd_commit(struct ref_transaction *transaction,
 		die("commit: extra input: %s", next);
 	if (ref_transaction_commit(transaction, &error))
 		die("commit: %s", error.buf);
+
+	ref_transaction_for_each_rejected_update(transaction,
+						 print_rejected_refs, NULL);
+
 	report_ok("commit");
 	ref_transaction_free(transaction);
 }
@@ -609,7 +657,7 @@ static const struct parse_cmd {
 	{ "commit",        parse_cmd_commit,        0, UPDATE_REFS_CLOSED },
 };
 
-static void update_refs_stdin(void)
+static void update_refs_stdin(unsigned int flags)
 {
 	struct strbuf input = STRBUF_INIT, err = STRBUF_INIT;
 	enum update_refs_state state = UPDATE_REFS_OPEN;
@@ -617,7 +665,7 @@ static void update_refs_stdin(void)
 	int i, j;
 
 	transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),
-						  0, &err);
+						  flags, &err);
 	if (!transaction)
 		die("%s", err.buf);
 
@@ -685,7 +733,7 @@ static void update_refs_stdin(void)
 			 */
 			state = cmd->state;
 			transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),
-								  0, &err);
+								  flags, &err);
 			if (!transaction)
 				die("%s", err.buf);
 
@@ -701,6 +749,8 @@ static void update_refs_stdin(void)
 		/* Commit by default if no transaction was requested. */
 		if (ref_transaction_commit(transaction, &err))
 			die("%s", err.buf);
+		ref_transaction_for_each_rejected_update(transaction,
+						 print_rejected_refs, NULL);
 		ref_transaction_free(transaction);
 		break;
 	case UPDATE_REFS_STARTED:
@@ -727,6 +777,8 @@ int cmd_update_ref(int argc,
 	struct object_id oid, oldoid;
 	int delete = 0, no_deref = 0, read_stdin = 0, end_null = 0;
 	int create_reflog = 0;
+	unsigned int flags = 0;
+
 	struct option options[] = {
 		OPT_STRING( 'm', NULL, &msg, N_("reason"), N_("reason of the update")),
 		OPT_BOOL('d', NULL, &delete, N_("delete the reference")),
@@ -735,6 +787,8 @@ int cmd_update_ref(int argc,
 		OPT_BOOL('z', NULL, &end_null, N_("stdin has NUL-terminated arguments")),
 		OPT_BOOL( 0 , "stdin", &read_stdin, N_("read updates from stdin")),
 		OPT_BOOL( 0 , "create-reflog", &create_reflog, N_("create a reflog")),
+		OPT_BIT('0', "batch-updates", &flags, N_("batch reference updates"),
+			REF_TRANSACTION_ALLOW_FAILURE),
 		OPT_END(),
 	};
 
@@ -756,9 +810,10 @@ int cmd_update_ref(int argc,
 			usage_with_options(git_update_ref_usage, options);
 		if (end_null)
 			line_termination = '\0';
-		update_refs_stdin();
+		update_refs_stdin(flags);
 		return 0;
-	}
+	} else if (flags & REF_TRANSACTION_ALLOW_FAILURE)
+		die("--batch-updates can only be used with --stdin");
 
 	if (end_null)
 		usage_with_options(git_update_ref_usage, options);
diff --git a/t/t1400-update-ref.sh b/t/t1400-update-ref.sh
index 29045aad43..d29d23cb89 100755
--- a/t/t1400-update-ref.sh
+++ b/t/t1400-update-ref.sh
@@ -2066,6 +2066,239 @@ do
 		grep "$(git rev-parse $a) $(git rev-parse $a)" actual
 	'
 
+	test_expect_success "stdin $type batch-updates" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit commit &&
+			head=$(git rev-parse HEAD) &&
+
+			format_command $type "update refs/heads/ref1" "$head" "$Z" >stdin &&
+			format_command $type "update refs/heads/ref2" "$head" "$Z" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with invalid new_oid" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$(test_oid 001)" "$head" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "invalid new value provided" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with non-commit new_oid" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			head_tree=$(git rev-parse HEAD^{tree}) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$head_tree" "$head" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "invalid new value provided" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with non-existent ref" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$old_head" "$head" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			test_must_fail git rev-parse refs/heads/ref2 &&
+			test_grep -q "reference does not exist" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with dangling symref" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git symbolic-ref refs/heads/ref2 refs/heads/nonexistent &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$old_head" "$head" >>stdin &&
+			git update-ref $type --no-deref --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			test_must_fail git rev-parse refs/heads/ref2 &&
+			test_grep -q "reference does not exist" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with regular ref as symref" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "symref-update refs/heads/ref2" "$old_head" "ref" "refs/heads/nonexistent" >>stdin &&
+			git update-ref $type --no-deref --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "expected symref but found regular ref" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with invalid old_oid" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$old_head" "$Z" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "reference already exists" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with incorrect old oid" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$head" "$old_head" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "incorrect old value provided" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates refname conflict" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref/foo $head &&
+
+			format_command $type "update refs/heads/ref/foo" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref" "$old_head" "" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref/foo >actual &&
+			test_cmp expect actual &&
+			test_grep -q "refname conflict" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates refname conflict new ref" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref/foo $head &&
+
+			format_command $type "update refs/heads/foo" "$old_head" "" >stdin &&
+			format_command $type "update refs/heads/ref" "$old_head" "" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/foo >actual &&
+			test_cmp expect actual &&
+			test_grep -q "refname conflict" stdout
+		)
+	'
 done
 
 test_expect_success 'update-ref should also create reflog for HEAD' '

-- 
2.48.1