From 34330d313db2e066a6b2e58a78c081ddf23ce233 Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Tue, 29 Jul 2025 10:55:19 +0200
Subject: [PATCH 01/16] Documentation/git-reflog: convert to use synopsis type

With 974cdca345c (doc: introduce a synopsis typesetting, 2024-09-24) we
have introduced a new synopsis type that simplifies the rules for
typesetting a command's synopsis. Convert the git-reflog(1)
documentation to use it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/git-reflog.adoc | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/Documentation/git-reflog.adoc b/Documentation/git-reflog.adoc
index 412f06b8fec..707a9b39edb 100644
--- a/Documentation/git-reflog.adoc
+++ b/Documentation/git-reflog.adoc
@@ -8,16 +8,16 @@ git-reflog - Manage reflog information
 
 SYNOPSIS
 --------
-[verse]
-'git reflog' [show] [<log-options>] [<ref>]
-'git reflog list'
-'git reflog expire' [--expire=<time>] [--expire-unreachable=<time>]
+[synopsis]
+git reflog [show] [<log-options>] [<ref>]
+git reflog list
+git reflog expire [--expire=<time>] [--expire-unreachable=<time>]
 	[--rewrite] [--updateref] [--stale-fix]
 	[--dry-run | -n] [--verbose] [--all [--single-worktree] | <refs>...]
-'git reflog delete' [--rewrite] [--updateref]
+git reflog delete [--rewrite] [--updateref]
 	[--dry-run | -n] [--verbose] <ref>@{<specifier>}...
-'git reflog drop' [--all [--single-worktree] | <refs>...]
-'git reflog exists' <ref>
+git reflog drop [--all [--single-worktree] | <refs>...]
+git reflog exists <ref>
 
 DESCRIPTION
 -----------
-- 
GitLab


From 7453cd545e16ad52fcf661aeeceea377a3dde23b Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Tue, 29 Jul 2025 10:55:20 +0200
Subject: [PATCH 02/16] builtin/reflog: improve grouping of subcommands

The way subcommands of git-reflog(1) are laid out does not make any
immediate sense. Reorder them such that read-only subcommands precede
writing commands for a bit more structure.

Furthermore, move the "expire" subcommand last. This prepares for a
subsequent change where we are about to introduce a new "write" command
to append reflog entries. Like this, the writing subcommands are ordered
such that those affecting a single reflog come before those spanning
across all reflogs.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/git-reflog.adoc | 61 ++++++++++++++++++-----------------
 builtin/reflog.c              | 38 +++++++++++-----------
 2 files changed, 50 insertions(+), 49 deletions(-)

diff --git a/Documentation/git-reflog.adoc b/Documentation/git-reflog.adoc
index 707a9b39edb..c3801b82fb6 100644
--- a/Documentation/git-reflog.adoc
+++ b/Documentation/git-reflog.adoc
@@ -11,13 +11,13 @@ SYNOPSIS
 [synopsis]
 git reflog [show] [<log-options>] [<ref>]
 git reflog list
-git reflog expire [--expire=<time>] [--expire-unreachable=<time>]
-	[--rewrite] [--updateref] [--stale-fix]
-	[--dry-run | -n] [--verbose] [--all [--single-worktree] | <refs>...]
+git reflog exists <ref>
 git reflog delete [--rewrite] [--updateref]
 	[--dry-run | -n] [--verbose] <ref>@{<specifier>}...
 git reflog drop [--all [--single-worktree] | <refs>...]
-git reflog exists <ref>
+git reflog expire [--expire=<time>] [--expire-unreachable=<time>]
+	[--rewrite] [--updateref] [--stale-fix]
+	[--dry-run | -n] [--verbose] [--all [--single-worktree] | <refs>...]
 
 DESCRIPTION
 -----------
@@ -43,11 +43,9 @@ actions, and in addition the `HEAD` reflog records branch switching.
 
 The "list" subcommand lists all refs which have a corresponding reflog.
 
-The "expire" subcommand prunes older reflog entries. Entries older
-than `expire` time, or entries older than `expire-unreachable` time
-and not reachable from the current tip, are removed from the reflog.
-This is typically not used directly by end users -- instead, see
-linkgit:git-gc[1].
+The "exists" subcommand checks whether a ref has a reflog.  It exits
+with zero status if the reflog exists, and non-zero status if it does
+not.
 
 The "delete" subcommand deletes single entries from the reflog, but
 not the reflog itself. Its argument must be an _exact_ entry (e.g. "`git
@@ -58,9 +56,11 @@ The "drop" subcommand completely removes the reflog for the specified
 references. This is in contrast to "expire" and "delete", both of which
 can be used to delete reflog entries, but not the reflog itself.
 
-The "exists" subcommand checks whether a ref has a reflog.  It exits
-with zero status if the reflog exists, and non-zero status if it does
-not.
+The "expire" subcommand prunes older reflog entries. Entries older
+than `expire` time, or entries older than `expire-unreachable` time
+and not reachable from the current tip, are removed from the reflog.
+This is typically not used directly by end users -- instead, see
+linkgit:git-gc[1].
 
 OPTIONS
 -------
@@ -71,6 +71,25 @@ Options for `show`
 `git reflog show` accepts any of the options accepted by `git log`.
 
 
+Options for `delete`
+~~~~~~~~~~~~~~~~~~~~
+
+`git reflog delete` accepts options `--updateref`, `--rewrite`, `-n`,
+`--dry-run`, and `--verbose`, with the same meanings as when they are
+used with `expire`.
+
+Options for `drop`
+~~~~~~~~~~~~~~~~~~
+
+--all::
+	Drop the reflogs of all references from all worktrees.
+
+--single-worktree::
+	By default when `--all` is specified, reflogs from all working
+	trees are dropped. This option limits the processing to reflogs
+	from the current working tree only.
+
+
 Options for `expire`
 ~~~~~~~~~~~~~~~~~~~~
 
@@ -130,24 +149,6 @@ which didn't protect objects referred to by reflogs.
 	Print extra information on screen.
 
 
-Options for `delete`
-~~~~~~~~~~~~~~~~~~~~
-
-`git reflog delete` accepts options `--updateref`, `--rewrite`, `-n`,
-`--dry-run`, and `--verbose`, with the same meanings as when they are
-used with `expire`.
-
-Options for `drop`
-~~~~~~~~~~~~~~~~~~
-
---all::
-	Drop the reflogs of all references from all worktrees.
-
---single-worktree::
-	By default when `--all` is specified, reflogs from all working
-	trees are dropped. This option limits the processing to reflogs
-	from the current working tree only.
-
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/builtin/reflog.c b/builtin/reflog.c
index 3acaf3e32c2..b00b3f9edc9 100644
--- a/builtin/reflog.c
+++ b/builtin/reflog.c
@@ -17,21 +17,21 @@
 #define BUILTIN_REFLOG_LIST_USAGE \
 	N_("git reflog list")
 
-#define BUILTIN_REFLOG_EXPIRE_USAGE \
-	N_("git reflog expire [--expire=<time>] [--expire-unreachable=<time>]\n" \
-	   "                  [--rewrite] [--updateref] [--stale-fix]\n" \
-	   "                  [--dry-run | -n] [--verbose] [--all [--single-worktree] | <refs>...]")
+#define BUILTIN_REFLOG_EXISTS_USAGE \
+	N_("git reflog exists <ref>")
 
 #define BUILTIN_REFLOG_DELETE_USAGE \
 	N_("git reflog delete [--rewrite] [--updateref]\n" \
 	   "                  [--dry-run | -n] [--verbose] <ref>@{<specifier>}...")
 
-#define BUILTIN_REFLOG_EXISTS_USAGE \
-	N_("git reflog exists <ref>")
-
 #define BUILTIN_REFLOG_DROP_USAGE \
 	N_("git reflog drop [--all [--single-worktree] | <refs>...]")
 
+#define BUILTIN_REFLOG_EXPIRE_USAGE \
+	N_("git reflog expire [--expire=<time>] [--expire-unreachable=<time>]\n" \
+	   "                  [--rewrite] [--updateref] [--stale-fix]\n" \
+	   "                  [--dry-run | -n] [--verbose] [--all [--single-worktree] | <refs>...]")
+
 static const char *const reflog_show_usage[] = {
 	BUILTIN_REFLOG_SHOW_USAGE,
 	NULL,
@@ -42,9 +42,9 @@ static const char *const reflog_list_usage[] = {
 	NULL,
 };
 
-static const char *const reflog_expire_usage[] = {
-	BUILTIN_REFLOG_EXPIRE_USAGE,
-	NULL
+static const char *const reflog_exists_usage[] = {
+	BUILTIN_REFLOG_EXISTS_USAGE,
+	NULL,
 };
 
 static const char *const reflog_delete_usage[] = {
@@ -52,23 +52,23 @@ static const char *const reflog_delete_usage[] = {
 	NULL
 };
 
-static const char *const reflog_exists_usage[] = {
-	BUILTIN_REFLOG_EXISTS_USAGE,
-	NULL,
-};
-
 static const char *const reflog_drop_usage[] = {
 	BUILTIN_REFLOG_DROP_USAGE,
 	NULL,
 };
 
+static const char *const reflog_expire_usage[] = {
+	BUILTIN_REFLOG_EXPIRE_USAGE,
+	NULL
+};
+
 static const char *const reflog_usage[] = {
 	BUILTIN_REFLOG_SHOW_USAGE,
 	BUILTIN_REFLOG_LIST_USAGE,
-	BUILTIN_REFLOG_EXPIRE_USAGE,
+	BUILTIN_REFLOG_EXISTS_USAGE,
 	BUILTIN_REFLOG_DELETE_USAGE,
 	BUILTIN_REFLOG_DROP_USAGE,
-	BUILTIN_REFLOG_EXISTS_USAGE,
+	BUILTIN_REFLOG_EXPIRE_USAGE,
 	NULL
 };
 
@@ -404,10 +404,10 @@ int cmd_reflog(int argc,
 	struct option options[] = {
 		OPT_SUBCOMMAND("show", &fn, cmd_reflog_show),
 		OPT_SUBCOMMAND("list", &fn, cmd_reflog_list),
-		OPT_SUBCOMMAND("expire", &fn, cmd_reflog_expire),
-		OPT_SUBCOMMAND("delete", &fn, cmd_reflog_delete),
 		OPT_SUBCOMMAND("exists", &fn, cmd_reflog_exists),
+		OPT_SUBCOMMAND("delete", &fn, cmd_reflog_delete),
 		OPT_SUBCOMMAND("drop", &fn, cmd_reflog_drop),
+		OPT_SUBCOMMAND("expire", &fn, cmd_reflog_expire),
 		OPT_END()
 	};
 
-- 
GitLab


From ff644892ce13acc4f230d2619ffe43f4ae85b2d6 Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Tue, 29 Jul 2025 10:55:21 +0200
Subject: [PATCH 03/16] refs: export `ref_transaction_update_reflog()`

In a subsequent commit we'll add another user that wants to write reflog
entries. This requires them to call `ref_transaction_update_reflog()`,
but that function is local to "refs.c".

Export the function to prepare for the change. While at it, drop the
`flags` field, as all callers are for now expected to use the same flags
anyway.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 refs.c | 29 +++++++++++------------------
 refs.h | 15 +++++++++++++++
 2 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/refs.c b/refs.c
index dce5c49ca2b..8aa9f7236a3 100644
--- a/refs.c
+++ b/refs.c
@@ -1371,27 +1371,21 @@ int ref_transaction_update(struct ref_transaction *transaction,
 	return 0;
 }
 
-/*
- * Similar to`ref_transaction_update`, but this function is only for adding
- * a reflog update. Supports providing custom committer information. The index
- * field can be utiltized to order updates as desired. When not used, the
- * updates default to being ordered by refname.
- */
-static int ref_transaction_update_reflog(struct ref_transaction *transaction,
-					 const char *refname,
-					 const struct object_id *new_oid,
-					 const struct object_id *old_oid,
-					 const char *committer_info,
-					 unsigned int flags,
-					 const char *msg,
-					 uint64_t index,
-					 struct strbuf *err)
+int ref_transaction_update_reflog(struct ref_transaction *transaction,
+				  const char *refname,
+				  const struct object_id *new_oid,
+				  const struct object_id *old_oid,
+				  const char *committer_info,
+				  const char *msg,
+				  uint64_t index,
+				  struct strbuf *err)
 {
 	struct ref_update *update;
+	unsigned int flags;
 
 	assert(err);
 
-	flags |= REF_LOG_ONLY | REF_FORCE_CREATE_REFLOG | REF_NO_DEREF;
+	flags = REF_HAVE_OLD | REF_HAVE_NEW | REF_LOG_ONLY | REF_FORCE_CREATE_REFLOG | REF_NO_DEREF;
 
 	if (!transaction_refname_valid(refname, new_oid, flags, err))
 		return -1;
@@ -3019,8 +3013,7 @@ static int migrate_one_reflog_entry(struct object_id *old_oid,
 
 	ret = ref_transaction_update_reflog(data->transaction, data->refname,
 					    new_oid, old_oid, data->sb->buf,
-					    REF_HAVE_NEW | REF_HAVE_OLD, msg,
-					    data->index++, data->errbuf);
+					    msg, data->index++, data->errbuf);
 	return ret;
 }
 
diff --git a/refs.h b/refs.h
index 46a6008e07f..253dd8f4d5d 100644
--- a/refs.h
+++ b/refs.h
@@ -795,6 +795,21 @@ int ref_transaction_update(struct ref_transaction *transaction,
 			   unsigned int flags, const char *msg,
 			   struct strbuf *err);
 
+/*
+ * Similar to `ref_transaction_update`, but this function is only for adding
+ * a reflog update. Supports providing custom committer information. The index
+ * field can be utiltized to order updates as desired. When set to zero, the
+ * updates default to being ordered by refname.
+ */
+int ref_transaction_update_reflog(struct ref_transaction *transaction,
+				  const char *refname,
+				  const struct object_id *new_oid,
+				  const struct object_id *old_oid,
+				  const char *committer_info,
+				  const char *msg,
+				  uint64_t index,
+				  struct strbuf *err);
+
 /*
  * Add a reference creation to transaction. new_oid is the value that
  * the reference should have after the update; it must not be
-- 
GitLab


From 823804888e5419b8b9cb5d2f688a13c4faed3474 Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Tue, 29 Jul 2025 10:55:22 +0200
Subject: [PATCH 04/16] builtin/reflog: implement subcommand to write new
 entries

While we provide a couple of subcommands in git-reflog(1) to remove
reflog entries, we don't provide any to write new entries. Obviously
this is not an operation that really would be needed for many use cases
out there, or otherwise people would have complained that such a command
does not exist yet. But the introduction of the "reftable" backend
changes the picture a bit, as it is now basically impossible to manually
append a reflog entry if one wanted to do so due to the binary format.

Plug this gap by introducing a simple "write" subcommand. For now, all
this command does is to append a single new reflog entry with the given
object IDs and message to the reflog. More specifically, it is not yet
possible to:

  - Write multiple reflog entries at once.

  - Insert reflog entries at arbitrary indices.

  - Specify the date of the reflog entry.

  - Insert reflog entries that refer to nonexistent objects.

If required, those features can be added at a future point in time. For
now though, the new command aims to fulfill the most basic use cases
while being as strict as possible when it comes to verifying parameters.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/git-reflog.adoc |   7 ++
 builtin/reflog.c              |  65 ++++++++++++++++++
 t/meson.build                 |   1 +
 t/t1421-reflog-write.sh       | 126 ++++++++++++++++++++++++++++++++++
 4 files changed, 199 insertions(+)
 create mode 100755 t/t1421-reflog-write.sh

diff --git a/Documentation/git-reflog.adoc b/Documentation/git-reflog.adoc
index c3801b82fb6..34232a539a7 100644
--- a/Documentation/git-reflog.adoc
+++ b/Documentation/git-reflog.adoc
@@ -12,6 +12,7 @@ SYNOPSIS
 git reflog [show] [<log-options>] [<ref>]
 git reflog list
 git reflog exists <ref>
+git reflog write <ref> <old-oid> <new-oid> <message>
 git reflog delete [--rewrite] [--updateref]
 	[--dry-run | -n] [--verbose] <ref>@{<specifier>}...
 git reflog drop [--all [--single-worktree] | <refs>...]
@@ -47,6 +48,12 @@ The "exists" subcommand checks whether a ref has a reflog.  It exits
 with zero status if the reflog exists, and non-zero status if it does
 not.
 
+The "write" subcommand writes a single entry to the reflog of a given
+reference. This new entry is appended to the reflog and will thus become
+the most recent entry. The reference name must be fully qualified. Both the old
+and new object IDs must not be abbreviated and must point to existing objects.
+The reflog message gets normalized.
+
 The "delete" subcommand deletes single entries from the reflog, but
 not the reflog itself. Its argument must be an _exact_ entry (e.g. "`git
 reflog delete master@{2}`"). This subcommand is also typically not used
diff --git a/builtin/reflog.c b/builtin/reflog.c
index b00b3f9edc9..a1b4e022041 100644
--- a/builtin/reflog.c
+++ b/builtin/reflog.c
@@ -3,6 +3,8 @@
 #include "builtin.h"
 #include "config.h"
 #include "gettext.h"
+#include "hex.h"
+#include "object-store.h"
 #include "revision.h"
 #include "reachable.h"
 #include "wildmatch.h"
@@ -20,6 +22,9 @@
 #define BUILTIN_REFLOG_EXISTS_USAGE \
 	N_("git reflog exists <ref>")
 
+#define BUILTIN_REFLOG_WRITE_USAGE \
+	N_("git reflog write <ref> <old-oid> <new-oid> <message>")
+
 #define BUILTIN_REFLOG_DELETE_USAGE \
 	N_("git reflog delete [--rewrite] [--updateref]\n" \
 	   "                  [--dry-run | -n] [--verbose] <ref>@{<specifier>}...")
@@ -47,6 +52,11 @@ static const char *const reflog_exists_usage[] = {
 	NULL,
 };
 
+static const char *const reflog_write_usage[] = {
+	BUILTIN_REFLOG_WRITE_USAGE,
+	NULL,
+};
+
 static const char *const reflog_delete_usage[] = {
 	BUILTIN_REFLOG_DELETE_USAGE,
 	NULL
@@ -66,6 +76,7 @@ static const char *const reflog_usage[] = {
 	BUILTIN_REFLOG_SHOW_USAGE,
 	BUILTIN_REFLOG_LIST_USAGE,
 	BUILTIN_REFLOG_EXISTS_USAGE,
+	BUILTIN_REFLOG_WRITE_USAGE,
 	BUILTIN_REFLOG_DELETE_USAGE,
 	BUILTIN_REFLOG_DROP_USAGE,
 	BUILTIN_REFLOG_EXPIRE_USAGE,
@@ -392,6 +403,59 @@ static int cmd_reflog_drop(int argc, const char **argv, const char *prefix,
 	return ret;
 }
 
+static int cmd_reflog_write(int argc, const char **argv, const char *prefix,
+			    struct repository *repo)
+{
+	const struct option options[] = {
+		OPT_END()
+	};
+	struct object_id old_oid, new_oid;
+	struct strbuf err = STRBUF_INIT;
+	struct ref_transaction *tx;
+	const char *ref, *message;
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, reflog_write_usage, 0);
+	if (argc != 4)
+		usage_with_options(reflog_write_usage, options);
+
+	ref = argv[0];
+	if (!is_root_ref(ref) && check_refname_format(ref, 0))
+		die(_("invalid reference name: %s"), ref);
+
+	ret = get_oid_hex_algop(argv[1], &old_oid, repo->hash_algo);
+	if (ret)
+		die(_("invalid old object ID: '%s'"), argv[1]);
+	if (!is_null_oid(&old_oid) && !has_object(the_repository, &old_oid, 0))
+		die(_("old object '%s' does not exist"), argv[1]);
+
+	ret = get_oid_hex_algop(argv[2], &new_oid, repo->hash_algo);
+	if (ret)
+		die(_("invalid new object ID: '%s'"), argv[2]);
+	if (!is_null_oid(&new_oid) && !has_object(the_repository, &new_oid, 0))
+		die(_("new object '%s' does not exist"), argv[2]);
+
+	message = argv[3];
+
+	tx = ref_store_transaction_begin(get_main_ref_store(repo), 0, &err);
+	if (!tx)
+		die(_("cannot start transaction: %s"), err.buf);
+
+	ret = ref_transaction_update_reflog(tx, ref, &new_oid, &old_oid,
+					    git_committer_info(0),
+					    message, 0, &err);
+	if (ret)
+		die(_("cannot queue reflog update: %s"), err.buf);
+
+	ret = ref_transaction_commit(tx, &err);
+	if (ret)
+		die(_("cannot commit reflog update: %s"), err.buf);
+
+	ref_transaction_free(tx);
+	strbuf_release(&err);
+	return 0;
+}
+
 /*
  * main "reflog"
  */
@@ -405,6 +469,7 @@ int cmd_reflog(int argc,
 		OPT_SUBCOMMAND("show", &fn, cmd_reflog_show),
 		OPT_SUBCOMMAND("list", &fn, cmd_reflog_list),
 		OPT_SUBCOMMAND("exists", &fn, cmd_reflog_exists),
+		OPT_SUBCOMMAND("write", &fn, cmd_reflog_write),
 		OPT_SUBCOMMAND("delete", &fn, cmd_reflog_delete),
 		OPT_SUBCOMMAND("drop", &fn, cmd_reflog_drop),
 		OPT_SUBCOMMAND("expire", &fn, cmd_reflog_expire),
diff --git a/t/meson.build b/t/meson.build
index d052fc3e23d..adcdf09e740 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -220,6 +220,7 @@ integration_tests = [
   't1418-reflog-exists.sh',
   't1419-exclude-refs.sh',
   't1420-lost-found.sh',
+  't1421-reflog-write.sh',
   't1430-bad-ref-name.sh',
   't1450-fsck.sh',
   't1451-fsck-buffer.sh',
diff --git a/t/t1421-reflog-write.sh b/t/t1421-reflog-write.sh
new file mode 100755
index 00000000000..6cad64f40ab
--- /dev/null
+++ b/t/t1421-reflog-write.sh
@@ -0,0 +1,126 @@
+#!/bin/sh
+
+test_description='Manually write reflog entries'
+
+. ./test-lib.sh
+
+SIGNATURE="C O Mitter <committer@example.com> 1112911993 -0700"
+
+test_reflog_matches () {
+	repo="$1" &&
+	refname="$2" &&
+	cat >actual &&
+	test-tool -C "$repo" ref-store main for-each-reflog-ent "$refname" >expected &&
+	test_cmp expected actual
+}
+
+test_expect_success 'invalid number of arguments' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		for args in "" "1" "1 2" "1 2 3" "1 2 3 4 5"
+		do
+			test_must_fail git reflog write $args 2>err &&
+			test_grep "usage: git reflog write" err || return 1
+		done
+	)
+'
+
+test_expect_success 'invalid refname' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_must_fail git reflog write "refs/heads/ invalid" $ZERO_OID $ZERO_OID first 2>err &&
+		test_grep "invalid reference name: " err
+	)
+'
+
+test_expect_success 'unqualified refname is rejected' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_must_fail git reflog write unqualified $ZERO_OID $ZERO_OID first 2>err &&
+		test_grep "invalid reference name: " err
+	)
+'
+
+test_expect_success 'nonexistent object IDs' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_must_fail git reflog write refs/heads/something $(test_oid deadbeef) $ZERO_OID old-object-id 2>err &&
+		test_grep "old object .* does not exist" err &&
+		test_must_fail git reflog write refs/heads/something $ZERO_OID $(test_oid deadbeef) new-object-id 2>err &&
+		test_grep "new object .* does not exist" err
+	)
+'
+
+test_expect_success 'abbreviated object IDs' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_must_fail git reflog write refs/heads/something 12345 $ZERO_OID old-object-id 2>err &&
+		test_grep "invalid old object ID" err &&
+		test_must_fail git reflog write refs/heads/something $ZERO_OID 12345 new-object-id 2>err &&
+		test_grep "invalid new object ID" err
+	)
+'
+
+test_expect_success 'reflog message gets normalized' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit initial &&
+		COMMIT_OID=$(git rev-parse HEAD) &&
+		git reflog write HEAD $COMMIT_OID $COMMIT_OID "$(printf "message\nwith\nnewlines")" &&
+		git reflog show -1 --format=%gs HEAD >actual &&
+		echo "message with newlines" >expected &&
+		test_cmp expected actual
+	)
+'
+
+test_expect_success 'simple writes' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit initial &&
+		COMMIT_OID=$(git rev-parse HEAD) &&
+
+		git reflog write refs/heads/something $ZERO_OID $COMMIT_OID first &&
+		test_reflog_matches . refs/heads/something <<-EOF &&
+		$ZERO_OID $COMMIT_OID $SIGNATURE	first
+		EOF
+
+		git reflog write refs/heads/something $COMMIT_OID $COMMIT_OID second &&
+		# Note: the old object ID of the second reflog entry is broken.
+		# This will be fixed in subsequent commits.
+		test_reflog_matches . refs/heads/something <<-EOF
+		$ZERO_OID $COMMIT_OID $SIGNATURE	first
+		$ZERO_OID $COMMIT_OID $SIGNATURE	second
+		EOF
+	)
+'
+
+test_expect_success 'can write to root ref' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit initial &&
+		COMMIT_OID=$(git rev-parse HEAD) &&
+
+		git reflog write ROOT_REF_HEAD $ZERO_OID $COMMIT_OID first &&
+		test_reflog_matches . ROOT_REF_HEAD <<-EOF
+		$ZERO_OID $COMMIT_OID $SIGNATURE	first
+		EOF
+	)
+'
+
+test_done
-- 
GitLab


From f874af8d9914936097170c868c1e4a7a77da5360 Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Tue, 29 Jul 2025 10:55:23 +0200
Subject: [PATCH 05/16] ident: fix type of string length parameter

The last parameter in `split_ident_line()` is the length of the line
passed in by the caller. As such, most callers pass in either the result
of `strlen()`, `struct strbuf::len` or a pointer diff, all of which
are expected to be positive numbers. Regardless of that, the function
accepts a signed integer, which is somewhat confusing.

Fix the function signature to instead accept a `size_t`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 ident.c | 2 +-
 ident.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/ident.c b/ident.c
index 967895d8850..a7a2d132579 100644
--- a/ident.c
+++ b/ident.c
@@ -272,7 +272,7 @@ static void strbuf_addstr_without_crud(struct strbuf *sb, const char *src)
  * can still be NULL if the input line only has the name/email part
  * (e.g. reading from a reflog entry).
  */
-int split_ident_line(struct ident_split *split, const char *line, int len)
+int split_ident_line(struct ident_split *split, const char *line, size_t len)
 {
 	const char *cp;
 	size_t span;
diff --git a/ident.h b/ident.h
index 6a79febba15..3c034038791 100644
--- a/ident.h
+++ b/ident.h
@@ -35,7 +35,7 @@ void reset_ident_date(void);
  * Signals an success with 0, but time part of the result may be NULL
  * if the input lacks timestamp and zone
  */
-int split_ident_line(struct ident_split *, const char *, int);
+int split_ident_line(struct ident_split *, const char *, size_t);
 
 /*
  * Given a commit or tag object buffer and the commit or tag headers, replaces
-- 
GitLab


From cddd1302dea605714b793f030b5ae7aeeaf46b33 Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Tue, 29 Jul 2025 10:55:24 +0200
Subject: [PATCH 06/16] refs: fix identity for migrated reflogs

When migrating reflog entries between different storage formats we must
reconstruct the identity of reflog entries. This is done by passing the
committer passed to the `migrate_one_reflog_entry()` callback function
to `fmt_ident()`.

This results in an invalid identity though: `fmt_ident()` expects the
caller to provide both name and mail of the author, but we pass the full
identity as mail. This leads to an identity like:

    pks <Patrick Steinhardt ps@pks.im>

Fix the bug by splitting the identity line first. This allows us to
extract both the name and mail so that we can pass them to `fmt_ident()`
separately.

This commit does not yet add any tests as there is another bug in the
reflog migration that will be fixed in a subsequent commit. Once that
bug is fixed we'll make the reflog verification in t1450 stricter, and
that will catch both this bug here and the other bug.

Note that we also add two new `name` and `mail` string buffers to the
callback structures and splice them through to the callbacks. This is
done so that we can avoid allocating a new buffer every time we compute
the committer information.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 refs.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/refs.c b/refs.c
index 8aa9f7236a3..a5f9ffaa45d 100644
--- a/refs.c
+++ b/refs.c
@@ -2954,7 +2954,7 @@ struct migration_data {
 	struct ref_store *old_refs;
 	struct ref_transaction *transaction;
 	struct strbuf *errbuf;
-	struct strbuf sb;
+	struct strbuf sb, name, mail;
 };
 
 static int migrate_one_ref(const char *refname, const char *referent UNUSED, const struct object_id *oid,
@@ -2993,7 +2993,7 @@ struct reflog_migration_data {
 	struct ref_store *old_refs;
 	struct ref_transaction *transaction;
 	struct strbuf *errbuf;
-	struct strbuf *sb;
+	struct strbuf *sb, *name, *mail;
 };
 
 static int migrate_one_reflog_entry(struct object_id *old_oid,
@@ -3003,13 +3003,21 @@ static int migrate_one_reflog_entry(struct object_id *old_oid,
 				    const char *msg, void *cb_data)
 {
 	struct reflog_migration_data *data = cb_data;
+	struct ident_split ident;
 	const char *date;
 	int ret;
 
+	if (split_ident_line(&ident, committer, strlen(committer)) < 0)
+		return -1;
+
+	strbuf_reset(data->name);
+	strbuf_add(data->name, ident.name_begin, ident.name_end - ident.name_begin);
+	strbuf_reset(data->mail);
+	strbuf_add(data->mail, ident.mail_begin, ident.mail_end - ident.mail_begin);
+
 	date = show_date(timestamp, tz, DATE_MODE(NORMAL));
 	strbuf_reset(data->sb);
-	/* committer contains name and email */
-	strbuf_addstr(data->sb, fmt_ident("", committer, WANT_BLANK_IDENT, date, 0));
+	strbuf_addstr(data->sb, fmt_ident(data->name->buf, data->mail->buf, WANT_BLANK_IDENT, date, 0));
 
 	ret = ref_transaction_update_reflog(data->transaction, data->refname,
 					    new_oid, old_oid, data->sb->buf,
@@ -3026,6 +3034,8 @@ static int migrate_one_reflog(const char *refname, void *cb_data)
 		.transaction = migration_data->transaction,
 		.errbuf = migration_data->errbuf,
 		.sb = &migration_data->sb,
+		.name = &migration_data->name,
+		.mail = &migration_data->mail,
 	};
 
 	return refs_for_each_reflog_ent(migration_data->old_refs, refname,
@@ -3124,6 +3134,8 @@ int repo_migrate_ref_storage_format(struct repository *repo,
 	struct strbuf new_gitdir = STRBUF_INIT;
 	struct migration_data data = {
 		.sb = STRBUF_INIT,
+		.name = STRBUF_INIT,
+		.mail = STRBUF_INIT,
 	};
 	int did_migrate_refs = 0;
 	int ret;
@@ -3299,6 +3311,8 @@ int repo_migrate_ref_storage_format(struct repository *repo,
 	ref_transaction_free(transaction);
 	strbuf_release(&new_gitdir);
 	strbuf_release(&data.sb);
+	strbuf_release(&data.name);
+	strbuf_release(&data.mail);
 	return ret;
 }
 
-- 
GitLab


From 988cfcf6aabeee00079408bb60cf6ba415524078 Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Tue, 29 Jul 2025 10:55:25 +0200
Subject: [PATCH 07/16] refs/files: detect race when generating reflog entry
 for HEAD

When updating a reference that is being pointed to HEAD we don't only
write a reflog message for that particular reference, but also generate
one for HEAD. This logic is handled by `split_head_update()`, where we:

  1. Verify that the condition actually triggered. This is done by
     reading HEAD at the start of the transaction so that we can then
     check whether a given reference update refers to its target.

  2. Queue a new log-only update for HEAD in case it did.

But the logic is unfortunately not free of races, as we do not lock the
HEAD reference after we have read its target. This can lead to the
following two scenarios:

  - HEAD gets concurrently updated to point to one of the references we
    have already processed. This causes us not writing a reflog message
    even though we should have done so.

  - HEAD gets concurrently updated to point to not point to a reference
    anymore that we have already processed. This causes us to write a
    reflog message even though we should _not_ have done so.

Improve the situation by introducing a new `REF_LOG_VIA_SPLIT` flag that
is specific to the "files" backend. If set, we will double check that
the HEAD reference still points to the reference that we are creating
the reflog entry for after we have locked HEAD. Furthermore, instead of
manually resolving the old object ID of that entry, we now use the same
old state as for the parent update.

Unfortunately, this change only helps with the second race. We cannot
reliably plug the first race without locking the HEAD reference at the
start of the transaction. Locking HEAD unconditionally would effectively
serialize all writes though, and that doesn't seem like an option. Also,
double checking its value at the end of the transaction is not an option
either, as its target may have flip-flopped during the transaction.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 refs/files-backend.c | 40 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/refs/files-backend.c b/refs/files-backend.c
index bf6f89b1d19..ba018b0984a 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -68,6 +68,12 @@
  */
 #define REF_DELETED_RMDIR (1 << 9)
 
+/*
+ * Used to indicate that the reflog-only update has been created via
+ * `split_head_update()`.
+ */
+#define REF_LOG_VIA_SPLIT (1 << 14)
+
 struct ref_lock {
 	char *ref_name;
 	struct lock_file lk;
@@ -2420,9 +2426,10 @@ static enum ref_transaction_error split_head_update(struct ref_update *update,
 
 	new_update = ref_transaction_add_update(
 			transaction, "HEAD",
-			update->flags | REF_LOG_ONLY | REF_NO_DEREF,
+			update->flags | REF_LOG_ONLY | REF_NO_DEREF | REF_LOG_VIA_SPLIT,
 			&update->new_oid, &update->old_oid,
 			NULL, NULL, update->committer_info, update->msg);
+	new_update->parent_update = update;
 
 	/*
 	 * Add "HEAD". This insertion is O(N) in the transaction
@@ -2600,7 +2607,36 @@ static enum ref_transaction_error lock_ref_for_update(struct files_ref_store *re
 
 	update->backend_data = lock;
 
-	if (update->type & REF_ISSYMREF) {
+	if (update->flags & REF_LOG_VIA_SPLIT) {
+		struct ref_lock *parent_lock;
+
+		if (!update->parent_update)
+			BUG("split update without a parent");
+
+		parent_lock = update->parent_update->backend_data;
+
+		/*
+		 * Check that "HEAD" didn't racily change since we have looked
+		 * it up. If it did we must refuse to write the reflog entry.
+		 *
+		 * Note that this does not catch all races: if "HEAD" was
+		 * racily changed to point to one of the refs part of the
+		 * transaction then we would miss writing the split reflog
+		 * entry for "HEAD".
+		 */
+		if (!(update->type & REF_ISSYMREF) ||
+		    strcmp(update->parent_update->refname, referent.buf)) {
+			strbuf_addstr(err, "HEAD has been racily updated");
+			ret = REF_TRANSACTION_ERROR_GENERIC;
+			goto out;
+		}
+
+		if (update->flags & REF_HAVE_OLD) {
+			oidcpy(&lock->old_oid, &update->old_oid);
+		} else {
+			oidcpy(&lock->old_oid, &parent_lock->old_oid);
+		}
+	} else if (update->type & REF_ISSYMREF) {
 		if (update->flags & REF_NO_DEREF) {
 			/*
 			 * We won't be reading the referent as part of
-- 
GitLab


From ec4d8b728aae612ab47e1d3d8e00b06bf5cd70ee Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Tue, 29 Jul 2025 10:55:26 +0200
Subject: [PATCH 08/16] refs: stop unsetting REF_HAVE_OLD for log-only updates

The `REF_HAVE_OLD` flag indicates whether a given ref update has its old
object ID set. If so, the value of that field is used to verify whether
the current state of the reference matches this expected state. It is
thus an important part of mitigating races with a concurrent process
that updates the same set of references.

When writing reflogs though we explicitly unset that flag. This is a
sensible thing to do: the old state of reflog entry updates may not
necessarily match the current on-disk state of its accompanying ref, but
it's only intended to signal what old object ID we want to write into
the new reflog entry. For example when migrating refs we end up writing
many reflog entries for a single reference, and most likely those reflog
entries will have many different old object IDs.

But unsetting this flag also removes a useful signal, namely that the
caller _did_ provide an old object ID for a given reflog entry. This
signal will become useful in a subsequent commit, where we add a new
flag that tells the transaction to use the provided old and new object
IDs to write a reflog entry. The `REF_HAVE_OLD` flag is then used as a
signal to verify that the caller really did provide an old object ID.

Stop unsetting the flag so that we can use it as this described signal
in a subsequent commit. Skip checking the old object ID for log-only
updates so that we don't expect it to match the current on-disk state.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 refs.c                  |  8 +++-----
 refs/files-backend.c    |  9 +++++----
 refs/refs-internal.h    |  3 ++-
 refs/reftable-backend.c | 12 +++---------
 4 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/refs.c b/refs.c
index a5f9ffaa45d..f88928de746 100644
--- a/refs.c
+++ b/refs.c
@@ -1393,11 +1393,6 @@ int ref_transaction_update_reflog(struct ref_transaction *transaction,
 	update = ref_transaction_add_update(transaction, refname, flags,
 					    new_oid, old_oid, NULL, NULL,
 					    committer_info, msg);
-	/*
-	 * While we do set the old_oid value, we unset the flag to skip
-	 * old_oid verification which only makes sense for refs.
-	 */
-	update->flags &= ~REF_HAVE_OLD;
 	update->index = index;
 
 	/*
@@ -3318,6 +3313,9 @@ int repo_migrate_ref_storage_format(struct repository *repo,
 
 int ref_update_expects_existing_old_ref(struct ref_update *update)
 {
+	if (update->flags & REF_LOG_ONLY)
+		return 0;
+
 	return (update->flags & REF_HAVE_OLD) &&
 		(!is_null_oid(&update->old_oid) || update->old_target);
 }
diff --git a/refs/files-backend.c b/refs/files-backend.c
index ba018b0984a..85ab2ef2b94 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2500,7 +2500,6 @@ static enum ref_transaction_error split_symref_update(struct ref_update *update,
 	 * done when new_update is processed.
 	 */
 	update->flags |= REF_LOG_ONLY | REF_NO_DEREF;
-	update->flags &= ~REF_HAVE_OLD;
 
 	return 0;
 }
@@ -2515,8 +2514,9 @@ static enum ref_transaction_error check_old_oid(struct ref_update *update,
 						struct object_id *oid,
 						struct strbuf *err)
 {
-	if (!(update->flags & REF_HAVE_OLD) ||
-		   oideq(oid, &update->old_oid))
+	if (update->flags & REF_LOG_ONLY ||
+	    !(update->flags & REF_HAVE_OLD) ||
+	    oideq(oid, &update->old_oid))
 		return 0;
 
 	if (is_null_oid(&update->old_oid)) {
@@ -3095,7 +3095,8 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 	for (i = 0; i < transaction->nr; i++) {
 		struct ref_update *update = transaction->updates[i];
 
-		if ((update->flags & REF_HAVE_OLD) &&
+		if (!(update->flags & REF_LOG_ONLY) &&
+		    (update->flags & REF_HAVE_OLD) &&
 		    !is_null_oid(&update->old_oid))
 			BUG("initial ref transaction with old_sha1 set");
 
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index f8688708519..95a4dc3902f 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -802,7 +802,8 @@ enum ref_transaction_error ref_update_check_old_target(const char *referent,
 
 /*
  * Check if the ref must exist, this means that the old_oid or
- * old_target is non NULL.
+ * old_target is non NULL. Log-only updates never require the old state to
+ * match.
  */
 int ref_update_expects_existing_old_ref(struct ref_update *update);
 
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 4c3817f4ec1..44af58ac50b 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1180,8 +1180,6 @@ static enum ref_transaction_error prepare_single_update(struct reftable_ref_stor
 	if (ret > 0) {
 		/* The reference does not exist, but we expected it to. */
 		strbuf_addf(err, _("cannot lock ref '%s': "
-
-
 				   "unable to resolve reference '%s'"),
 			    ref_update_original_update_refname(u), u->refname);
 		return REF_TRANSACTION_ERROR_NONEXISTENT_REF;
@@ -1235,13 +1233,8 @@ static enum ref_transaction_error prepare_single_update(struct reftable_ref_stor
 
 			new_update->parent_update = u;
 
-			/*
-			 * Change the symbolic ref update to log only. Also, it
-			 * doesn't need to check its old OID value, as that will be
-			 * done when new_update is processed.
-			 */
+			/* Change the symbolic ref update to log only. */
 			u->flags |= REF_LOG_ONLY | REF_NO_DEREF;
-			u->flags &= ~REF_HAVE_OLD;
 		}
 	}
 
@@ -1265,7 +1258,8 @@ static enum ref_transaction_error prepare_single_update(struct reftable_ref_stor
 		ret = ref_update_check_old_target(referent->buf, u, err);
 		if (ret)
 			return ret;
-	} else if ((u->flags & REF_HAVE_OLD) && !oideq(&current_oid, &u->old_oid)) {
+	} else if ((u->flags & (REF_LOG_ONLY | REF_HAVE_OLD)) == REF_HAVE_OLD &&
+		   !oideq(&current_oid, &u->old_oid)) {
 		if (is_null_oid(&u->old_oid)) {
 			strbuf_addf(err, _("cannot lock ref '%s': "
 					   "reference already exists"),
-- 
GitLab


From f0fde561f0367e902cc909da257af8b3da8796f4 Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Tue, 29 Jul 2025 10:55:27 +0200
Subject: [PATCH 09/16] refs: fix invalid old object IDs when migrating reflogs

When migrating reflog entries between different storage formats we end
up with invalid old object IDs for the migrated entries: instead of
writing the old object ID of the to-be-migrated entry, we end up with
the all-zeroes object ID.

The root cause of this issue is that we don't know to use the old object
ID provided by the caller. Instead, we manually resolve the old object
ID by resolving the current value of its matching reference. But as that
reference does not yet exist in the target ref storage we always end up
resolving it to all-zeroes.

This issue got unnoticed as there is no user-facing command that would
even show the old object ID. While `git log -g` knows to show the new
object ID, we don't have any formatting directive to show the old object
ID.

Fix the bug by introducing a new flag `REF_LOG_USE_PROVIDED_OIDS`. If
set, backends are instructed to use the old and new object IDs provided
by the caller, without doing any manual resolving. Set this flag in
`ref_transaction_update_reflog()`.

Amend our tests in t1460-refs-migrate to use our test tool to read
reflog entries. This test tool prints out both old and new object ID of
each reflog entry, which fixes the test gap. Furthermore it also prints
the full identity used to write the reflog, which provides test coverage
for the previous commit in this patch series that fixed the identity for
migrated reflogs.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 refs.c                  |  3 ++-
 refs.h                  |  9 ++++++++-
 refs/files-backend.c    | 16 +++++++++++++++-
 refs/reftable-backend.c | 14 ++++++++++++++
 t/t1421-reflog-write.sh |  4 +---
 t/t1460-refs-migrate.sh | 22 +++++++++++++++-------
 6 files changed, 55 insertions(+), 13 deletions(-)

diff --git a/refs.c b/refs.c
index f88928de746..946eb48941b 100644
--- a/refs.c
+++ b/refs.c
@@ -1385,7 +1385,8 @@ int ref_transaction_update_reflog(struct ref_transaction *transaction,
 
 	assert(err);
 
-	flags = REF_HAVE_OLD | REF_HAVE_NEW | REF_LOG_ONLY | REF_FORCE_CREATE_REFLOG | REF_NO_DEREF;
+	flags = REF_HAVE_OLD | REF_HAVE_NEW | REF_LOG_ONLY | REF_FORCE_CREATE_REFLOG | REF_NO_DEREF |
+		REF_LOG_USE_PROVIDED_OIDS;
 
 	if (!transaction_refname_valid(refname, new_oid, flags, err))
 		return -1;
diff --git a/refs.h b/refs.h
index 253dd8f4d5d..090b4fdff4f 100644
--- a/refs.h
+++ b/refs.h
@@ -760,13 +760,20 @@ struct ref_transaction *ref_store_transaction_begin(struct ref_store *refs,
  */
 #define REF_SKIP_CREATE_REFLOG (1 << 12)
 
+/*
+ * When writing a REF_LOG_ONLY record, use the old and new object IDs provided
+ * in the update instead of resolving the old object ID. The caller must also
+ * set both REF_HAVE_OLD and REF_HAVE_NEW.
+ */
+#define REF_LOG_USE_PROVIDED_OIDS (1 << 13)
+
 /*
  * Bitmask of all of the flags that are allowed to be passed in to
  * ref_transaction_update() and friends:
  */
 #define REF_TRANSACTION_UPDATE_ALLOWED_FLAGS                                  \
 	(REF_NO_DEREF | REF_FORCE_CREATE_REFLOG | REF_SKIP_OID_VERIFICATION | \
-	 REF_SKIP_REFNAME_VERIFICATION | REF_SKIP_CREATE_REFLOG)
+	 REF_SKIP_REFNAME_VERIFICATION | REF_SKIP_CREATE_REFLOG | REF_LOG_USE_PROVIDED_OIDS)
 
 /*
  * Add a reference update to transaction. `new_oid` is the value that
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 85ab2ef2b94..905555365b8 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3010,6 +3010,20 @@ static int parse_and_write_reflog(struct files_ref_store *refs,
 				  struct ref_lock *lock,
 				  struct strbuf *err)
 {
+	struct object_id *old_oid = &lock->old_oid;
+
+	if (update->flags & REF_LOG_USE_PROVIDED_OIDS) {
+		if (!(update->flags & REF_HAVE_OLD) ||
+		    !(update->flags & REF_HAVE_NEW) ||
+		    !(update->flags & REF_LOG_ONLY)) {
+			strbuf_addf(err, _("trying to write reflog for '%s'"
+					   "with incomplete values"), update->refname);
+			return REF_TRANSACTION_ERROR_GENERIC;
+		}
+
+		old_oid = &update->old_oid;
+	}
+
 	if (update->new_target) {
 		/*
 		 * We want to get the resolved OID for the target, to ensure
@@ -3027,7 +3041,7 @@ static int parse_and_write_reflog(struct files_ref_store *refs,
 		}
 	}
 
-	if (files_log_ref_write(refs, lock->ref_name, &lock->old_oid,
+	if (files_log_ref_write(refs, lock->ref_name, old_oid,
 				&update->new_oid, update->committer_info,
 				update->msg, update->flags, err)) {
 		char *old_msg = strbuf_detach(err, NULL);
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 44af58ac50b..99fafd75ebe 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1096,6 +1096,20 @@ static enum ref_transaction_error prepare_single_update(struct reftable_ref_stor
 	if (ret)
 		return REF_TRANSACTION_ERROR_GENERIC;
 
+	if (u->flags & REF_LOG_USE_PROVIDED_OIDS) {
+		if (!(u->flags & REF_HAVE_OLD) ||
+		    !(u->flags & REF_HAVE_NEW) ||
+		    !(u->flags & REF_LOG_ONLY)) {
+			strbuf_addf(err, _("trying to write reflog for '%s'"
+					   "with incomplete values"), u->refname);
+			return REF_TRANSACTION_ERROR_GENERIC;
+		}
+
+		if (queue_transaction_update(refs, tx_data, u, &u->old_oid, err))
+			return REF_TRANSACTION_ERROR_GENERIC;
+		return 0;
+	}
+
 	/* Verify that the new object ID is valid. */
 	if ((u->flags & REF_HAVE_NEW) && !is_null_oid(&u->new_oid) &&
 	    !(u->flags & REF_SKIP_OID_VERIFICATION) &&
diff --git a/t/t1421-reflog-write.sh b/t/t1421-reflog-write.sh
index 6cad64f40ab..d4e41838f8f 100755
--- a/t/t1421-reflog-write.sh
+++ b/t/t1421-reflog-write.sh
@@ -99,11 +99,9 @@ test_expect_success 'simple writes' '
 		EOF
 
 		git reflog write refs/heads/something $COMMIT_OID $COMMIT_OID second &&
-		# Note: the old object ID of the second reflog entry is broken.
-		# This will be fixed in subsequent commits.
 		test_reflog_matches . refs/heads/something <<-EOF
 		$ZERO_OID $COMMIT_OID $SIGNATURE	first
-		$ZERO_OID $COMMIT_OID $SIGNATURE	second
+		$COMMIT_OID $COMMIT_OID $SIGNATURE	second
 		EOF
 	)
 '
diff --git a/t/t1460-refs-migrate.sh b/t/t1460-refs-migrate.sh
index 2ab97e1b7df..0e1116a319d 100755
--- a/t/t1460-refs-migrate.sh
+++ b/t/t1460-refs-migrate.sh
@@ -7,6 +7,17 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
 
+print_all_reflog_entries () {
+	repo=$1 &&
+	test-tool -C "$repo" ref-store main for-each-reflog >reflogs &&
+	while read reflog
+	do
+		echo "REFLOG: $reflog" &&
+		test-tool -C "$repo" ref-store main for-each-reflog-ent "$reflog" ||
+		return 1
+	done <reflogs
+}
+
 # Migrate the provided repository from one format to the other and
 # verify that the references and logs are migrated over correctly.
 # Usage: test_migration <repo> <format> [<skip_reflog_verify> [<options...>]]
@@ -28,8 +39,7 @@ test_migration () {
 		--format='%(refname) %(objectname) %(symref)' >expect &&
 	if ! $skip_reflog_verify
 	then
-	   git -C "$repo" reflog --all >expect_logs &&
-	   git -C "$repo" reflog list >expect_log_list
+		print_all_reflog_entries "$repo" >expect_logs
 	fi &&
 
 	git -C "$repo" refs migrate --ref-format="$format" "$@" &&
@@ -39,10 +49,8 @@ test_migration () {
 	test_cmp expect actual &&
 	if ! $skip_reflog_verify
 	then
-		git -C "$repo" reflog --all >actual_logs &&
-		git -C "$repo" reflog list >actual_log_list &&
-		test_cmp expect_logs actual_logs &&
-		test_cmp expect_log_list actual_log_list
+		print_all_reflog_entries "$repo" >actual_logs &&
+		test_cmp expect_logs actual_logs
 	fi &&
 
 	git -C "$repo" rev-parse --show-ref-format >actual &&
@@ -273,7 +281,7 @@ test_expect_success 'multiple reftable blocks with multiple entries' '
 	test_commit -C repo second &&
 	printf "update refs/heads/ref-%d HEAD\n" $(test_seq 3000) >stdin &&
 	git -C repo update-ref --stdin <stdin &&
-	test_migration repo reftable
+	test_migration repo reftable true
 '
 
 test_expect_success 'migrating from files format deletes backend files' '
-- 
GitLab


From b8de34c96d6b890ee37cf97db70ab6236451746a Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Fri, 25 Jul 2025 11:35:21 +0200
Subject: [PATCH 10/16] builtin/remote: rework how remote refs get renamed
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Hi,

this patch series is the result from the discussion at [1]. On the one
hand this series fixes the reported bug where dangling symrefs are not
renamed via `git remote rename`.

On the other hand this series reworks the logic used to rename remotes
so that we use two transactions instead of one transaction per ref. This
fixes quadratic runtime behaviour, where renaming 10k refs takes ~4
minutes, 100k takes hours. This results in a significant speedup with
both the "files" backend (benchmarked with a smaller number of refs to
retain sanity):

    Benchmark 1: rename remote (refformat = files, revision = HEAD~)
      Time (mean ± σ):     238.770 s ± 13.857 s    [User: 91.473 s, System: 143.793 s]
      Range (min … max):   204.863 s … 247.699 s    10 runs

    Benchmark 2: rename remote (refformat = files, revision = HEAD)
      Time (mean ± σ):      2.103 s ±  0.036 s    [User: 0.360 s, System: 1.313 s]
      Range (min … max):    2.011 s …  2.141 s    10 runs

    Summary
      rename remote (refformat = files, revision = HEAD) ran
      113.53 ± 6.87 times faster than rename remote (refformat = files, revision = HEAD~)

For the "reftable" backend we see a significant speedup, as well, but
not as extreme as with the "files" backend:

    Benchmark 1: rename remote (refformat = reftable, revision = HEAD~)
      Time (mean ± σ):      8.604 s ±  0.539 s    [User: 4.985 s, System: 2.368 s]
      Range (min … max):    7.880 s …  9.556 s    10 runs

    Benchmark 2: rename remote (refformat = reftable, revision = HEAD)
      Time (mean ± σ):      1.177 s ±  0.103 s    [User: 0.446 s, System: 0.270 s]
      Range (min … max):    1.023 s …  1.410 s    10 runs

    Summary
      rename remote (refformat = reftable, revision = HEAD) ran
        7.31 ± 0.79 times faster than rename remote (refformat = reftable, revision = HEAD~)

But in any case, it's one more case where the "reftable" backend
outperforms the "files" backend.

The series is built on top of e4ef0485fd7 (The fourteenth batch,
2025-07-24) with ps/reflog-migrate-fixes at f0fde561f0 (refs: fix
invalid old object IDs when migrating reflogs, 2025-07-29) merged into
it.

I'd normally have withheld sending until that series was merged to
"next", but given that I promised to send something on Friday already I
decided to just get it out. In any case, if that causes problems I'm
happy to wait a bit before this series here gets merged into "seen".

Changes in v2:
  - Insert another commit to fix sign-comparison warnings.
  - Some code formatting fixes.
  - Drop the infrastructure to reuse buffers. It didn't really help much
    with performance anyway.
  - I'm now using a single transaction to rename references so that we
    have proper atomicity. Conflicts are detected early before any
    changes are performed in the repository and an advice is printed
    indicating what has happened.
  - Link to v1: https://lore.kernel.org/r/20250728-pks-remote-rename-improvements-v1-0-f654f2b5c5ae@pks.im

Changes in v3:
  - Adujst the base of this topic to use f0fde561f0 (refs: fix invalid
    old object IDs when migrating reflogs, 2025-07-29).
  - Link to v2: https://lore.kernel.org/r/20250731-pks-remote-rename-improvements-v2-0-dda6f083674d@pks.im

Thanks!

Patrick

[1]: <CANrWfmQWa=RJnm7d3C7ogRX6Tth2eeuGwvwrNmzS2gr+eP0OpA@mail.gmail.com>

To: git@vger.kernel.org
Cc: Junio C Hamano <gitster@pobox.com>
Cc: Jeff King <peff@peff.net>
Cc: Han Jiang <jhcarl0814@gmail.com>
Cc: Justin Tobler <jltobler@gmail.com>
Cc: Karthik Nayak <karthik.188@gmail.com>

--- b4-submit-tracking ---
# This section is used internally by b4 prep for tracking purposes.
{
  "series": {
    "revision": 3,
    "change-id": "20250725-pks-remote-rename-improvements-85ce262146e0",
    "prefixes": [],
    "history": {
      "v1": [
        "20250728-pks-remote-rename-improvements-v1-0-f654f2b5c5ae@pks.im"
      ],
      "v2": [
        "20250731-pks-remote-rename-improvements-v2-0-dda6f083674d@pks.im"
      ]
    }
  }
}
-- 
GitLab


From 8067efae4a9ab79d0fe50a035cc315fbae81300f Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Fri, 25 Jul 2025 08:34:26 +0200
Subject: [PATCH 11/16] refs: pass refname when invoking reflog entry callback

With `refs_for_each_reflog_ent()` callers can iterate through all the
reflog entries for a given reference. The callback that is being invoked
for each such entry does not receive the name of the reference that we
are currently iterating through. This isn't really a limiting factor, as
callers can simply pass the name via the callback data.

But this layout sometimes does make for a bit of an awkward calling
pattern. One example: when iterating through all reflogs, and for each
reflog we iterate through all refnames, we have to do some extra book
keeping to track which reference name we are currently yielding reflog
entries for.

Change the signature of the callback function so that the reference name
of the reflog gets passed through to it. Adapt callers accordingly and
start using the new parameter in trivial cases. The next commit will
refactor the reference migration logic to make use of this parameter so
that we can simplify its logic a bit.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/fsck.c            |  9 ++++-----
 builtin/gc.c              |  3 ++-
 builtin/stash.c           |  6 ++++--
 commit.c                  |  3 ++-
 object-name.c             |  3 ++-
 reflog-walk.c             |  7 ++++---
 reflog.c                  |  3 ++-
 reflog.h                  |  3 ++-
 refs.c                    | 20 +++++++++-----------
 refs.h                    | 11 +++++++----
 refs/debug.c              |  5 +++--
 refs/files-backend.c      | 15 +++++++++------
 refs/reftable-backend.c   |  2 +-
 remote.c                  |  6 ++++--
 revision.c                |  3 ++-
 t/helper/test-ref-store.c |  3 ++-
 wt-status.c               |  6 ++++--
 17 files changed, 63 insertions(+), 45 deletions(-)

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 0084cf7400b..67eb5e4fa0f 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -502,13 +502,12 @@ static void fsck_handle_reflog_oid(const char *refname, struct object_id *oid,
 	}
 }
 
-static int fsck_handle_reflog_ent(struct object_id *ooid, struct object_id *noid,
+static int fsck_handle_reflog_ent(const char *refname,
+				  struct object_id *ooid, struct object_id *noid,
 				  const char *email UNUSED,
 				  timestamp_t timestamp, int tz UNUSED,
-				  const char *message UNUSED, void *cb_data)
+				  const char *message UNUSED, void *cb_data UNUSED)
 {
-	const char *refname = cb_data;
-
 	if (verbose)
 		fprintf_ln(stderr, _("Checking reflog %s->%s"),
 			   oid_to_hex(ooid), oid_to_hex(noid));
@@ -525,7 +524,7 @@ static int fsck_handle_reflog(const char *logname, void *cb_data)
 	strbuf_worktree_ref(cb_data, &refname, logname);
 	refs_for_each_reflog_ent(get_main_ref_store(the_repository),
 				 refname.buf, fsck_handle_reflog_ent,
-				 refname.buf);
+				 NULL);
 	strbuf_release(&refname);
 	return 0;
 }
diff --git a/builtin/gc.c b/builtin/gc.c
index fab8f4dd4f7..9ae87065d35 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -312,7 +312,8 @@ struct count_reflog_entries_data {
 	size_t limit;
 };
 
-static int count_reflog_entries(struct object_id *old_oid, struct object_id *new_oid,
+static int count_reflog_entries(const char *refname UNUSED,
+				struct object_id *old_oid, struct object_id *new_oid,
 				const char *committer, timestamp_t timestamp,
 				int tz, const char *msg, void *cb_data)
 {
diff --git a/builtin/stash.c b/builtin/stash.c
index e2f95cc2ebc..a1ed67661e3 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -738,7 +738,8 @@ static int apply_stash(int argc, const char **argv, const char *prefix,
 	return ret;
 }
 
-static int reject_reflog_ent(struct object_id *ooid UNUSED,
+static int reject_reflog_ent(const char *refname UNUSED,
+			     struct object_id *ooid UNUSED,
 			     struct object_id *noid UNUSED,
 			     const char *email UNUSED,
 			     timestamp_t timestamp UNUSED,
@@ -2173,7 +2174,8 @@ struct stash_entry_data {
 	size_t count;
 };
 
-static int collect_stash_entries(struct object_id *old_oid UNUSED,
+static int collect_stash_entries(const char *refname UNUSED,
+				 struct object_id *old_oid UNUSED,
 				 struct object_id *new_oid,
 				 const char *committer UNUSED,
 				 timestamp_t timestamp UNUSED,
diff --git a/commit.c b/commit.c
index 15115125c36..7ebd05f3527 100644
--- a/commit.c
+++ b/commit.c
@@ -1031,7 +1031,8 @@ static void add_one_commit(struct object_id *oid, struct rev_collect *revs)
 	commit->object.flags |= TMP_MARK;
 }
 
-static int collect_one_reflog_ent(struct object_id *ooid, struct object_id *noid,
+static int collect_one_reflog_ent(const char *refname UNUSED,
+				  struct object_id *ooid, struct object_id *noid,
 				  const char *ident UNUSED,
 				  timestamp_t timestamp UNUSED, int tz UNUSED,
 				  const char *message UNUSED, void *cbdata)
diff --git a/object-name.c b/object-name.c
index ddafe7f9b13..9ec192c3731 100644
--- a/object-name.c
+++ b/object-name.c
@@ -1516,7 +1516,8 @@ struct grab_nth_branch_switch_cbdata {
 	struct strbuf *sb;
 };
 
-static int grab_nth_branch_switch(struct object_id *ooid UNUSED,
+static int grab_nth_branch_switch(const char *refname UNUSED,
+				  struct object_id *ooid UNUSED,
 				  struct object_id *noid UNUSED,
 				  const char *email UNUSED,
 				  timestamp_t timestamp UNUSED,
diff --git a/reflog-walk.c b/reflog-walk.c
index c7070b13b00..4f1ce047498 100644
--- a/reflog-walk.c
+++ b/reflog-walk.c
@@ -22,9 +22,10 @@ struct complete_reflogs {
 	int nr, alloc;
 };
 
-static int read_one_reflog(struct object_id *ooid, struct object_id *noid,
-		const char *email, timestamp_t timestamp, int tz,
-		const char *message, void *cb_data)
+static int read_one_reflog(const char *refname UNUSED,
+			   struct object_id *ooid, struct object_id *noid,
+			   const char *email, timestamp_t timestamp, int tz,
+			   const char *message, void *cb_data)
 {
 	struct complete_reflogs *array = cb_data;
 	struct reflog_info *item;
diff --git a/reflog.c b/reflog.c
index 39c205fd26e..2264b3bd605 100644
--- a/reflog.c
+++ b/reflog.c
@@ -492,7 +492,8 @@ void reflog_expiry_cleanup(void *cb_data)
 	free_commit_list(cb->mark_list);
 }
 
-int count_reflog_ent(struct object_id *ooid UNUSED,
+int count_reflog_ent(const char *refname UNUSED,
+		     struct object_id *ooid UNUSED,
 		     struct object_id *noid UNUSED,
 		     const char *email UNUSED,
 		     timestamp_t timestamp, int tz UNUSED,
diff --git a/reflog.h b/reflog.h
index 63bb56280f4..44b306c08ae 100644
--- a/reflog.h
+++ b/reflog.h
@@ -63,7 +63,8 @@ void reflog_expiry_prepare(const char *refname, const struct object_id *oid,
 int should_expire_reflog_ent(struct object_id *ooid, struct object_id *noid,
 			     const char *email, timestamp_t timestamp, int tz,
 			     const char *message, void *cb_data);
-int count_reflog_ent(struct object_id *ooid, struct object_id *noid,
+int count_reflog_ent(const char *refname,
+		     struct object_id *ooid, struct object_id *noid,
 		     const char *email, timestamp_t timestamp, int tz,
 		     const char *message, void *cb_data);
 int should_expire_reflog_ent_verbose(struct object_id *ooid,
diff --git a/refs.c b/refs.c
index 4bd80287054..6ed0cd6ddca 100644
--- a/refs.c
+++ b/refs.c
@@ -1022,7 +1022,6 @@ int is_branch(const char *refname)
 }
 
 struct read_ref_at_cb {
-	const char *refname;
 	timestamp_t at_time;
 	int cnt;
 	int reccnt;
@@ -1052,7 +1051,8 @@ static void set_read_ref_cutoffs(struct read_ref_at_cb *cb,
 		*cb->cutoff_cnt = cb->reccnt;
 }
 
-static int read_ref_at_ent(struct object_id *ooid, struct object_id *noid,
+static int read_ref_at_ent(const char *refname,
+			   struct object_id *ooid, struct object_id *noid,
 			   const char *email UNUSED,
 			   timestamp_t timestamp, int tz,
 			   const char *message, void *cb_data)
@@ -1072,14 +1072,13 @@ static int read_ref_at_ent(struct object_id *ooid, struct object_id *noid,
 			oidcpy(cb->oid, noid);
 			if (!oideq(&cb->ooid, noid))
 				warning(_("log for ref %s has gap after %s"),
-					cb->refname, show_date(cb->date, cb->tz, DATE_MODE(RFC2822)));
+					refname, show_date(cb->date, cb->tz, DATE_MODE(RFC2822)));
 		}
 		else if (cb->date == cb->at_time)
 			oidcpy(cb->oid, noid);
 		else if (!oideq(noid, cb->oid))
 			warning(_("log for ref %s unexpectedly ended on %s"),
-				cb->refname, show_date(cb->date, cb->tz,
-						       DATE_MODE(RFC2822)));
+				refname, show_date(cb->date, cb->tz, DATE_MODE(RFC2822)));
 		cb->reccnt++;
 		oidcpy(&cb->ooid, ooid);
 		oidcpy(&cb->noid, noid);
@@ -1094,7 +1093,8 @@ static int read_ref_at_ent(struct object_id *ooid, struct object_id *noid,
 	return 0;
 }
 
-static int read_ref_at_ent_oldest(struct object_id *ooid, struct object_id *noid,
+static int read_ref_at_ent_oldest(const char *refname UNUSED,
+				  struct object_id *ooid, struct object_id *noid,
 				  const char *email UNUSED,
 				  timestamp_t timestamp, int tz,
 				  const char *message, void *cb_data)
@@ -1117,7 +1117,6 @@ int read_ref_at(struct ref_store *refs, const char *refname,
 	struct read_ref_at_cb cb;
 
 	memset(&cb, 0, sizeof(cb));
-	cb.refname = refname;
 	cb.at_time = at_time;
 	cb.cnt = cnt;
 	cb.msg = msg;
@@ -2976,14 +2975,14 @@ static int migrate_one_ref(const char *refname, const char *referent UNUSED, con
 
 struct reflog_migration_data {
 	uint64_t index;
-	const char *refname;
 	struct ref_store *old_refs;
 	struct ref_transaction *transaction;
 	struct strbuf *errbuf;
 	struct strbuf *sb, *name, *mail;
 };
 
-static int migrate_one_reflog_entry(struct object_id *old_oid,
+static int migrate_one_reflog_entry(const char *refname,
+				    struct object_id *old_oid,
 				    struct object_id *new_oid,
 				    const char *committer,
 				    timestamp_t timestamp, int tz,
@@ -3006,7 +3005,7 @@ static int migrate_one_reflog_entry(struct object_id *old_oid,
 	strbuf_reset(data->sb);
 	strbuf_addstr(data->sb, fmt_ident(data->name->buf, data->mail->buf, WANT_BLANK_IDENT, date, 0));
 
-	ret = ref_transaction_update_reflog(data->transaction, data->refname,
+	ret = ref_transaction_update_reflog(data->transaction, refname,
 					    new_oid, old_oid, data->sb->buf,
 					    msg, data->index++, data->errbuf);
 	return ret;
@@ -3016,7 +3015,6 @@ static int migrate_one_reflog(const char *refname, void *cb_data)
 {
 	struct migration_data *migration_data = cb_data;
 	struct reflog_migration_data data = {
-		.refname = refname,
 		.old_refs = migration_data->old_refs,
 		.transaction = migration_data->transaction,
 		.errbuf = migration_data->errbuf,
diff --git a/refs.h b/refs.h
index 99b58d0b73c..0bf50ce25cc 100644
--- a/refs.h
+++ b/refs.h
@@ -558,10 +558,13 @@ int refs_delete_reflog(struct ref_store *refs, const char *refname);
  * The cb_data is a caller-supplied pointer given to the iterator
  * functions.
  */
-typedef int each_reflog_ent_fn(
-		struct object_id *old_oid, struct object_id *new_oid,
-		const char *committer, timestamp_t timestamp,
-		int tz, const char *msg, void *cb_data);
+typedef int each_reflog_ent_fn(const char *refname,
+			       struct object_id *old_oid,
+			       struct object_id *new_oid,
+			       const char *committer,
+			       timestamp_t timestamp,
+			       int tz, const char *msg,
+			       void *cb_data);
 
 /* Iterate over reflog entries in the log for `refname`. */
 
diff --git a/refs/debug.c b/refs/debug.c
index 485e3079d7a..5e113db307a 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -276,7 +276,8 @@ struct debug_reflog {
 	void *cb_data;
 };
 
-static int debug_print_reflog_ent(struct object_id *old_oid,
+static int debug_print_reflog_ent(const char *refname,
+				  struct object_id *old_oid,
 				  struct object_id *new_oid,
 				  const char *committer, timestamp_t timestamp,
 				  int tz, const char *msg, void *cb_data)
@@ -291,7 +292,7 @@ static int debug_print_reflog_ent(struct object_id *old_oid,
 	if (new_oid)
 		oid_to_hex_r(n, new_oid);
 
-	ret = dbg->fn(old_oid, new_oid, committer, timestamp, tz, msg,
+	ret = dbg->fn(refname, old_oid, new_oid, committer, timestamp, tz, msg,
 		      dbg->cb_data);
 	trace_printf_key(&trace_refs,
 			 "reflog_ent %s (ret %d): %s -> %s, %s %ld \"%.*s\"\n",
diff --git a/refs/files-backend.c b/refs/files-backend.c
index f53895cf4bd..dff52a583a9 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2115,7 +2115,9 @@ static int files_delete_reflog(struct ref_store *ref_store,
 	return ret;
 }
 
-static int show_one_reflog_ent(struct files_ref_store *refs, struct strbuf *sb,
+static int show_one_reflog_ent(struct files_ref_store *refs,
+			       const char *refname,
+			       struct strbuf *sb,
 			       each_reflog_ent_fn fn, void *cb_data)
 {
 	struct object_id ooid, noid;
@@ -2142,7 +2144,7 @@ static int show_one_reflog_ent(struct files_ref_store *refs, struct strbuf *sb,
 		message += 6;
 	else
 		message += 7;
-	return fn(&ooid, &noid, p, timestamp, tz, message, cb_data);
+	return fn(refname, &ooid, &noid, p, timestamp, tz, message, cb_data);
 }
 
 static char *find_beginning_of_line(char *bob, char *scan)
@@ -2226,7 +2228,7 @@ static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
 				strbuf_splice(&sb, 0, 0, bp + 1, endp - (bp + 1));
 				scanp = bp;
 				endp = bp + 1;
-				ret = show_one_reflog_ent(refs, &sb, fn, cb_data);
+				ret = show_one_reflog_ent(refs, refname, &sb, fn, cb_data);
 				strbuf_reset(&sb);
 				if (ret)
 					break;
@@ -2238,7 +2240,7 @@ static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
 				 * Process it, and we can end the loop.
 				 */
 				strbuf_splice(&sb, 0, 0, buf, endp - buf);
-				ret = show_one_reflog_ent(refs, &sb, fn, cb_data);
+				ret = show_one_reflog_ent(refs, refname, &sb, fn, cb_data);
 				strbuf_reset(&sb);
 				break;
 			}
@@ -2288,7 +2290,7 @@ static int files_for_each_reflog_ent(struct ref_store *ref_store,
 		return -1;
 
 	while (!ret && !strbuf_getwholeline(&sb, logfp, '\n'))
-		ret = show_one_reflog_ent(refs, &sb, fn, cb_data);
+		ret = show_one_reflog_ent(refs, refname, &sb, fn, cb_data);
 	fclose(logfp);
 	strbuf_release(&sb);
 	return ret;
@@ -3359,7 +3361,8 @@ struct expire_reflog_cb {
 		     dry_run:1;
 };
 
-static int expire_reflog_ent(struct object_id *ooid, struct object_id *noid,
+static int expire_reflog_ent(const char *refname UNUSED,
+			     struct object_id *ooid, struct object_id *noid,
 			     const char *email, timestamp_t timestamp, int tz,
 			     const char *message, void *cb_data)
 {
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 99fafd75ebe..25a1d516184 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -2148,7 +2148,7 @@ static int yield_log_record(struct reftable_ref_store *refs,
 
 	full_committer = fmt_ident(log->value.update.name, log->value.update.email,
 				   WANT_COMMITTER_IDENT, NULL, IDENT_NO_DATE);
-	return fn(&old_oid, &new_oid, full_committer,
+	return fn(log->refname, &old_oid, &new_oid, full_committer,
 		  log->value.update.time, log->value.update.tz_offset,
 		  log->value.update.message, cb_data);
 }
diff --git a/remote.c b/remote.c
index e965f022f12..db9eea4fa45 100644
--- a/remote.c
+++ b/remote.c
@@ -2578,7 +2578,8 @@ struct check_and_collect_until_cb_data {
 };
 
 /* Get the timestamp of the latest entry. */
-static int peek_reflog(struct object_id *o_oid UNUSED,
+static int peek_reflog(const char *refname UNUSED,
+		       struct object_id *o_oid UNUSED,
 		       struct object_id *n_oid UNUSED,
 		       const char *ident UNUSED,
 		       timestamp_t timestamp, int tz UNUSED,
@@ -2589,7 +2590,8 @@ static int peek_reflog(struct object_id *o_oid UNUSED,
 	return 1;
 }
 
-static int check_and_collect_until(struct object_id *o_oid UNUSED,
+static int check_and_collect_until(const char *refname UNUSED,
+				   struct object_id *o_oid UNUSED,
 				   struct object_id *n_oid,
 				   const char *ident UNUSED,
 				   timestamp_t timestamp, int tz UNUSED,
diff --git a/revision.c b/revision.c
index 212ca0de276..0fc1a167a10 100644
--- a/revision.c
+++ b/revision.c
@@ -1699,7 +1699,8 @@ static void handle_one_reflog_commit(struct object_id *oid, void *cb_data)
 	}
 }
 
-static int handle_one_reflog_ent(struct object_id *ooid, struct object_id *noid,
+static int handle_one_reflog_ent(const char *refname UNUSED,
+				 struct object_id *ooid, struct object_id *noid,
 				 const char *email UNUSED,
 				 timestamp_t timestamp UNUSED,
 				 int tz UNUSED,
diff --git a/t/helper/test-ref-store.c b/t/helper/test-ref-store.c
index 8d9a271845c..b2380d57ba3 100644
--- a/t/helper/test-ref-store.c
+++ b/t/helper/test-ref-store.c
@@ -215,7 +215,8 @@ static int cmd_for_each_reflog(struct ref_store *refs,
 	return refs_for_each_reflog(refs, each_reflog, NULL);
 }
 
-static int each_reflog_ent(struct object_id *old_oid, struct object_id *new_oid,
+static int each_reflog_ent(const char *refname UNUSED,
+			   struct object_id *old_oid, struct object_id *new_oid,
 			   const char *committer, timestamp_t timestamp,
 			   int tz, const char *msg, void *cb_data UNUSED)
 {
diff --git a/wt-status.c b/wt-status.c
index 454601afa15..71bd17b610a 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -972,7 +972,8 @@ static void wt_longstatus_print_changed(struct wt_status *s)
 	wt_longstatus_print_trailer(s);
 }
 
-static int stash_count_refs(struct object_id *ooid UNUSED,
+static int stash_count_refs(const char *refname UNUSED,
+			    struct object_id *ooid UNUSED,
 			    struct object_id *noid UNUSED,
 			    const char *email UNUSED,
 			    timestamp_t timestamp UNUSED, int tz UNUSED,
@@ -1664,7 +1665,8 @@ struct grab_1st_switch_cbdata {
 	struct object_id noid;
 };
 
-static int grab_1st_switch(struct object_id *ooid UNUSED,
+static int grab_1st_switch(const char *refname UNUSED,
+			   struct object_id *ooid UNUSED,
 			   struct object_id *noid,
 			   const char *email UNUSED,
 			   timestamp_t timestamp UNUSED, int tz UNUSED,
-- 
GitLab


From fa015c07a879ad37e556e46dd921d0272f5230cf Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Fri, 25 Jul 2025 08:53:29 +0200
Subject: [PATCH 12/16] refs: simplify logic when migrating reflog entries

When migrating reflog entries between two storage formats we have to do
so via two callback-driven functions:

  - `migrate_one_reflog()` gets invoked via `refs_for_each_reflog()` to
    first list all available reflogs.

  - `migrate_one_reflog_entry()` gets invoked via
    `refs_for_each_reflog_ent()` in `migrate_one_reflog()`.

Before the preceding commit we didn't have the refname available in
`migrate_one_reflog_entry()`, which made it necessary to have a separate
structure that we pass to the second callback so that we can propagate
the refname. Now that `refs_for_each_reflog_ent()` knows to pass the
refname to the callback though that indirection isn't necessary anymore.

There's one catch though: we do have an update index that is also stored
in the entry-specific callback data. This update index is required so
that we can tell the ref backend in which order it should persist the
reflog entries to disk.

But that purpose can be trivially achieved by just converting it into a
global counter that is used for all reflog entries, regardless of which
reference they are for. The ordering will remain the same as both the
update index and the refname is considered when sorting the entries.

Move the index into `struct migration_data` and drop the now-unused
`struct reflog_migration_data` to simplify the code a bit.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 refs.c | 36 ++++++++++--------------------------
 1 file changed, 10 insertions(+), 26 deletions(-)

diff --git a/refs.c b/refs.c
index 6ed0cd6ddca..04c9ace7932 100644
--- a/refs.c
+++ b/refs.c
@@ -2941,6 +2941,7 @@ struct migration_data {
 	struct ref_transaction *transaction;
 	struct strbuf *errbuf;
 	struct strbuf sb, name, mail;
+	uint64_t index;
 };
 
 static int migrate_one_ref(const char *refname, const char *referent UNUSED, const struct object_id *oid,
@@ -2973,14 +2974,6 @@ static int migrate_one_ref(const char *refname, const char *referent UNUSED, con
 	return ret;
 }
 
-struct reflog_migration_data {
-	uint64_t index;
-	struct ref_store *old_refs;
-	struct ref_transaction *transaction;
-	struct strbuf *errbuf;
-	struct strbuf *sb, *name, *mail;
-};
-
 static int migrate_one_reflog_entry(const char *refname,
 				    struct object_id *old_oid,
 				    struct object_id *new_oid,
@@ -2988,7 +2981,7 @@ static int migrate_one_reflog_entry(const char *refname,
 				    timestamp_t timestamp, int tz,
 				    const char *msg, void *cb_data)
 {
-	struct reflog_migration_data *data = cb_data;
+	struct migration_data *data = cb_data;
 	struct ident_split ident;
 	const char *date;
 	int ret;
@@ -2996,17 +2989,17 @@ static int migrate_one_reflog_entry(const char *refname,
 	if (split_ident_line(&ident, committer, strlen(committer)) < 0)
 		return -1;
 
-	strbuf_reset(data->name);
-	strbuf_add(data->name, ident.name_begin, ident.name_end - ident.name_begin);
-	strbuf_reset(data->mail);
-	strbuf_add(data->mail, ident.mail_begin, ident.mail_end - ident.mail_begin);
+	strbuf_reset(&data->name);
+	strbuf_add(&data->name, ident.name_begin, ident.name_end - ident.name_begin);
+	strbuf_reset(&data->mail);
+	strbuf_add(&data->mail, ident.mail_begin, ident.mail_end - ident.mail_begin);
 
 	date = show_date(timestamp, tz, DATE_MODE(NORMAL));
-	strbuf_reset(data->sb);
-	strbuf_addstr(data->sb, fmt_ident(data->name->buf, data->mail->buf, WANT_BLANK_IDENT, date, 0));
+	strbuf_reset(&data->sb);
+	strbuf_addstr(&data->sb, fmt_ident(data->name.buf, data->mail.buf, WANT_BLANK_IDENT, date, 0));
 
 	ret = ref_transaction_update_reflog(data->transaction, refname,
-					    new_oid, old_oid, data->sb->buf,
+					    new_oid, old_oid, data->sb.buf,
 					    msg, data->index++, data->errbuf);
 	return ret;
 }
@@ -3014,17 +3007,8 @@ static int migrate_one_reflog_entry(const char *refname,
 static int migrate_one_reflog(const char *refname, void *cb_data)
 {
 	struct migration_data *migration_data = cb_data;
-	struct reflog_migration_data data = {
-		.old_refs = migration_data->old_refs,
-		.transaction = migration_data->transaction,
-		.errbuf = migration_data->errbuf,
-		.sb = &migration_data->sb,
-		.name = &migration_data->name,
-		.mail = &migration_data->mail,
-	};
-
 	return refs_for_each_reflog_ent(migration_data->old_refs, refname,
-					migrate_one_reflog_entry, &data);
+					migrate_one_reflog_entry, migration_data);
 }
 
 static int move_files(const char *from_path, const char *to_path, struct strbuf *errbuf)
-- 
GitLab


From 7f53a38434618b60dd29738726494e33a9b295db Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Thu, 31 Jul 2025 10:49:06 +0200
Subject: [PATCH 13/16] builtin/remote: fix sign comparison warnings

Fix -Wsign-comparison warnings. All of the warnings we have are about
mismatches in signedness for loop counters. These are trivially fixable
by using the correct integer type.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/remote.c | 54 +++++++++++++++++++++---------------------------
 1 file changed, 23 insertions(+), 31 deletions(-)

diff --git a/builtin/remote.c b/builtin/remote.c
index 5dd6cbbaeed..f63c5eb8881 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -1,5 +1,4 @@
 #define USE_THE_REPOSITORY_VARIABLE
-#define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "builtin.h"
 #include "config.h"
@@ -182,7 +181,6 @@ static int add(int argc, const char **argv, const char *prefix,
 	struct remote *remote;
 	struct strbuf buf = STRBUF_INIT, buf2 = STRBUF_INIT;
 	const char *name, *url;
-	int i;
 	int result = 0;
 
 	struct option options[] = {
@@ -233,7 +231,7 @@ static int add(int argc, const char **argv, const char *prefix,
 		strbuf_addf(&buf, "remote.%s.fetch", name);
 		if (track.nr == 0)
 			string_list_append(&track, "*");
-		for (i = 0; i < track.nr; i++) {
+		for (size_t i = 0; i < track.nr; i++) {
 			add_branch(buf.buf, track.items[i].string,
 				   name, mirror, &buf2);
 		}
@@ -647,18 +645,17 @@ static int read_remote_branches(const char *refname, const char *referent UNUSED
 static int migrate_file(struct remote *remote)
 {
 	struct strbuf buf = STRBUF_INIT;
-	int i;
 
 	strbuf_addf(&buf, "remote.%s.url", remote->name);
-	for (i = 0; i < remote->url.nr; i++)
+	for (size_t i = 0; i < remote->url.nr; i++)
 		git_config_set_multivar(buf.buf, remote->url.v[i], "^$", 0);
 	strbuf_reset(&buf);
 	strbuf_addf(&buf, "remote.%s.push", remote->name);
-	for (i = 0; i < remote->push.nr; i++)
+	for (int i = 0; i < remote->push.nr; i++)
 		git_config_set_multivar(buf.buf, remote->push.items[i].raw, "^$", 0);
 	strbuf_reset(&buf);
 	strbuf_addf(&buf, "remote.%s.fetch", remote->name);
-	for (i = 0; i < remote->fetch.nr; i++)
+	for (int i = 0; i < remote->fetch.nr; i++)
 		git_config_set_multivar(buf.buf, remote->fetch.items[i].raw, "^$", 0);
 #ifndef WITH_BREAKING_CHANGES
 	if (remote->origin == REMOTE_REMOTES)
@@ -744,7 +741,7 @@ static int mv(int argc, const char **argv, const char *prefix,
 		old_remote_context = STRBUF_INIT;
 	struct string_list remote_branches = STRING_LIST_INIT_DUP;
 	struct rename_info rename;
-	int i, refs_renamed_nr = 0, refspec_updated = 0;
+	int refs_renamed_nr = 0, refspec_updated = 0;
 	struct progress *progress = NULL;
 	int result = 0;
 
@@ -790,7 +787,7 @@ static int mv(int argc, const char **argv, const char *prefix,
 		strbuf_addf(&buf, "remote.%s.fetch", rename.new_name);
 		git_config_set_multivar(buf.buf, NULL, NULL, CONFIG_FLAGS_MULTI_REPLACE);
 		strbuf_addf(&old_remote_context, ":refs/remotes/%s/", rename.old_name);
-		for (i = 0; i < oldremote->fetch.nr; i++) {
+		for (int i = 0; i < oldremote->fetch.nr; i++) {
 			char *ptr;
 
 			strbuf_reset(&buf2);
@@ -813,7 +810,7 @@ static int mv(int argc, const char **argv, const char *prefix,
 	}
 
 	read_branches();
-	for (i = 0; i < branch_list.nr; i++) {
+	for (size_t i = 0; i < branch_list.nr; i++) {
 		struct string_list_item *item = branch_list.items + i;
 		struct branch_info *info = item->util;
 		if (info->remote_name && !strcmp(info->remote_name, rename.old_name)) {
@@ -846,7 +843,7 @@ static int mv(int argc, const char **argv, const char *prefix,
 					  _("Renaming remote references"),
 					  rename.remote_branches->nr + rename.symrefs_nr);
 	}
-	for (i = 0; i < remote_branches.nr; i++) {
+	for (size_t i = 0; i < remote_branches.nr; i++) {
 		struct string_list_item *item = remote_branches.items + i;
 		struct strbuf referent = STRBUF_INIT;
 
@@ -859,7 +856,7 @@ static int mv(int argc, const char **argv, const char *prefix,
 		strbuf_release(&referent);
 		display_progress(progress, ++refs_renamed_nr);
 	}
-	for (i = 0; i < remote_branches.nr; i++) {
+	for (size_t i = 0; i < remote_branches.nr; i++) {
 		struct string_list_item *item = remote_branches.items + i;
 
 		if (item->util)
@@ -875,7 +872,7 @@ static int mv(int argc, const char **argv, const char *prefix,
 			die(_("renaming '%s' failed"), item->string);
 		display_progress(progress, ++refs_renamed_nr);
 	}
-	for (i = 0; i < remote_branches.nr; i++) {
+	for (size_t i = 0; i < remote_branches.nr; i++) {
 		struct string_list_item *item = remote_branches.items + i;
 
 		if (!item->util)
@@ -920,7 +917,7 @@ static int rm(int argc, const char **argv, const char *prefix,
 	struct string_list branches = STRING_LIST_INIT_DUP;
 	struct string_list skipped = STRING_LIST_INIT_DUP;
 	struct branches_for_remote cb_data;
-	int i, result;
+	int result;
 
 	memset(&cb_data, 0, sizeof(cb_data));
 	cb_data.branches = &branches;
@@ -942,7 +939,7 @@ static int rm(int argc, const char **argv, const char *prefix,
 	for_each_remote(add_known_remote, &known_remotes);
 
 	read_branches();
-	for (i = 0; i < branch_list.nr; i++) {
+	for (size_t i = 0; i < branch_list.nr; i++) {
 		struct string_list_item *item = branch_list.items + i;
 		struct branch_info *info = item->util;
 		if (info->remote_name && !strcmp(info->remote_name, remote->name)) {
@@ -988,7 +985,7 @@ static int rm(int argc, const char **argv, const char *prefix,
 			      "Note: Some branches outside the refs/remotes/ hierarchy were not removed;\n"
 			      "to delete them, use:",
 			      skipped.nr));
-		for (i = 0; i < skipped.nr; i++)
+		for (size_t i = 0; i < skipped.nr; i++)
 			fprintf(stderr, "  git branch -d %s\n",
 				skipped.items[i].string);
 	}
@@ -1166,7 +1163,6 @@ static int show_local_info_item(struct string_list_item *item, void *cb_data)
 	struct branch_info *branch_info = item->util;
 	struct string_list *merge = &branch_info->merge;
 	int width = show_info->width + 4;
-	int i;
 
 	if (branch_info->rebase >= REBASE_TRUE && branch_info->merge.nr > 1) {
 		error(_("invalid branch.%s.merge; cannot rebase onto > 1 branch"),
@@ -1192,7 +1188,7 @@ static int show_local_info_item(struct string_list_item *item, void *cb_data)
 	} else {
 		printf_ln(_("merges with remote %s"), merge->items[0].string);
 	}
-	for (i = 1; i < merge->nr; i++)
+	for (size_t i = 1; i < merge->nr; i++)
 		printf(_("%-*s    and with remote %s\n"), width, "",
 		       merge->items[i].string);
 
@@ -1277,7 +1273,6 @@ static int get_one_entry(struct remote *remote, void *priv)
 	struct string_list *list = priv;
 	struct strbuf remote_info_buf = STRBUF_INIT;
 	struct strvec *url;
-	int i;
 
 	if (remote->url.nr > 0) {
 		struct strbuf promisor_config = STRBUF_INIT;
@@ -1294,8 +1289,7 @@ static int get_one_entry(struct remote *remote, void *priv)
 	} else
 		string_list_append(list, remote->name)->util = NULL;
 	url = push_url_of_remote(remote);
-	for (i = 0; i < url->nr; i++)
-	{
+	for (size_t i = 0; i < url->nr; i++) {
 		strbuf_addf(&remote_info_buf, "%s (push)", url->v[i]);
 		string_list_append(list, remote->name)->util =
 				strbuf_detach(&remote_info_buf, NULL);
@@ -1312,10 +1306,8 @@ static int show_all(void)
 	result = for_each_remote(get_one_entry, &list);
 
 	if (!result) {
-		int i;
-
 		string_list_sort(&list);
-		for (i = 0; i < list.nr; i++) {
+		for (size_t i = 0; i < list.nr; i++) {
 			struct string_list_item *item = list.items + i;
 			if (verbose)
 				printf("%s\t%s\n", item->string,
@@ -1352,7 +1344,7 @@ static int show(int argc, const char **argv, const char *prefix,
 		query_flag = (GET_REF_STATES | GET_HEAD_NAMES | GET_PUSH_REF_STATES);
 
 	for (; argc; argc--, argv++) {
-		int i;
+		size_t i;
 		struct strvec *url;
 
 		get_remote_ref_states(*argv, &info.states, query_flag);
@@ -1458,7 +1450,7 @@ static void report_set_head_auto(const char *remote, const char *head_name,
 static int set_head(int argc, const char **argv, const char *prefix,
 		    struct repository *repo UNUSED)
 {
-	int i, opt_a = 0, opt_d = 0, result = 0, was_detached;
+	int opt_a = 0, opt_d = 0, result = 0, was_detached;
 	struct strbuf b_head = STRBUF_INIT, b_remote_head = STRBUF_INIT,
 		b_local_head = STRBUF_INIT;
 	char *head_name = NULL;
@@ -1489,7 +1481,7 @@ static int set_head(int argc, const char **argv, const char *prefix,
 		else if (states.heads.nr > 1) {
 			result |= error(_("Multiple remote HEAD branches. "
 					  "Please choose one explicitly with:"));
-			for (i = 0; i < states.heads.nr; i++)
+			for (size_t i = 0; i < states.heads.nr; i++)
 				fprintf(stderr, "  git remote set-head %s %s\n",
 					argv[0], states.heads.items[i].string);
 		} else
@@ -1714,7 +1706,7 @@ static int set_branches(int argc, const char **argv, const char *prefix,
 static int get_url(int argc, const char **argv, const char *prefix,
 		   struct repository *repo UNUSED)
 {
-	int i, push_mode = 0, all_mode = 0;
+	int push_mode = 0, all_mode = 0;
 	const char *remotename = NULL;
 	struct remote *remote;
 	struct strvec *url;
@@ -1742,7 +1734,7 @@ static int get_url(int argc, const char **argv, const char *prefix,
 	url = push_mode ? push_url_of_remote(remote) : &remote->url;
 
 	if (all_mode) {
-		for (i = 0; i < url->nr; i++)
+		for (size_t i = 0; i < url->nr; i++)
 			printf_ln("%s", url->v[i]);
 	} else {
 		printf_ln("%s", url->v[0]);
@@ -1754,7 +1746,7 @@ static int get_url(int argc, const char **argv, const char *prefix,
 static int set_url(int argc, const char **argv, const char *prefix,
 		   struct repository *repo UNUSED)
 {
-	int i, push_mode = 0, add_mode = 0, delete_mode = 0;
+	int push_mode = 0, add_mode = 0, delete_mode = 0;
 	int matches = 0, negative_matches = 0;
 	const char *remotename = NULL;
 	const char *newurl = NULL;
@@ -1818,7 +1810,7 @@ static int set_url(int argc, const char **argv, const char *prefix,
 	if (regcomp(&old_regex, oldurl, REG_EXTENDED))
 		die(_("Invalid old URL pattern: %s"), oldurl);
 
-	for (i = 0; i < urlset->nr; i++)
+	for (size_t i = 0; i < urlset->nr; i++)
 		if (!regexec(&old_regex, urlset->v[i], 0, NULL, 0))
 			matches++;
 		else
-- 
GitLab


From c6eb60305ac3f15ad0d3328e4b20f9e10a78e74f Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Thu, 31 Jul 2025 13:43:59 +0200
Subject: [PATCH 14/16] builtin/remote: determine whether refs need renaming
 early on

When renaming a remote we may have to also rename remote refs in case
the refspec changes. Pull out this computation into a separate loop.
While that seems nonsensical right now, it'll help us in a subsequent
commit where we will prepare the reference transaction before we rewrite
the configuration.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/remote.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/builtin/remote.c b/builtin/remote.c
index f63c5eb8881..34ddcaf5f6f 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -741,7 +741,7 @@ static int mv(int argc, const char **argv, const char *prefix,
 		old_remote_context = STRBUF_INIT;
 	struct string_list remote_branches = STRING_LIST_INIT_DUP;
 	struct rename_info rename;
-	int refs_renamed_nr = 0, refspec_updated = 0;
+	int refs_renamed_nr = 0, refspecs_need_update = 0;
 	struct progress *progress = NULL;
 	int result = 0;
 
@@ -782,11 +782,16 @@ static int mv(int argc, const char **argv, const char *prefix,
 		goto out;
 	}
 
+	strbuf_addf(&old_remote_context, ":refs/remotes/%s/", rename.old_name);
+
+	for (int i = 0; i < oldremote->fetch.nr && !refspecs_need_update; i++)
+		refspecs_need_update = !!strstr(oldremote->fetch.items[i].raw,
+						old_remote_context.buf);
+
 	if (oldremote->fetch.nr) {
 		strbuf_reset(&buf);
 		strbuf_addf(&buf, "remote.%s.fetch", rename.new_name);
 		git_config_set_multivar(buf.buf, NULL, NULL, CONFIG_FLAGS_MULTI_REPLACE);
-		strbuf_addf(&old_remote_context, ":refs/remotes/%s/", rename.old_name);
 		for (int i = 0; i < oldremote->fetch.nr; i++) {
 			char *ptr;
 
@@ -794,7 +799,6 @@ static int mv(int argc, const char **argv, const char *prefix,
 			strbuf_addstr(&buf2, oldremote->fetch.items[i].raw);
 			ptr = strstr(buf2.buf, old_remote_context.buf);
 			if (ptr) {
-				refspec_updated = 1;
 				strbuf_splice(&buf2,
 					      ptr-buf2.buf + strlen(":refs/remotes/"),
 					      strlen(rename.old_name), rename.new_name,
@@ -825,7 +829,7 @@ static int mv(int argc, const char **argv, const char *prefix,
 		}
 	}
 
-	if (!refspec_updated)
+	if (!refspecs_need_update)
 		goto out;
 
 	/*
-- 
GitLab


From c20aa7061416fa45b9d0a9c63a4d6df499eb3ce2 Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Thu, 31 Jul 2025 13:46:18 +0200
Subject: [PATCH 15/16] builtin/remote: rework how remote refs get renamed
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

It was recently reported [1] that renaming a remote that has dangling
symrefs is broken. This issue can be trivially reproduced:

    $ git init repo
    Initialized empty Git repository in /tmp/repo/.git/
    $ cd repo/
    $ git remote add origin /dev/null
    $ git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/master
    $ git remote rename origin renamed
    $ git symbolic-ref refs/remotes/origin/HEAD
    refs/remotes/origin/master
    $ git symbolic-ref refs/remotes/renamed/HEAD
    fatal: ref refs/remotes/renamed/HEAD is not a symbolic ref

As one can see, the "HEAD" reference did not get renamed but stays in
the same place. There are two issues here:

  - We use `refs_resolve_ref_unsafe()` to resolve references, but we
    don't pass the `RESOLVE_REF_NO_RECURSE` flag. Consequently, if the
    reference does not resolve, the function will fail and we thus
    ignore this branch.

  - We use `refs_for_each_ref()` to iterate through the old remote's
    references, but that function ignores broken references.

Both of these issues are easy to fix. But having a closer look at the
logic that renames remote references surfaces that it leaves a lot to be
desired overall.

The problem is that we're using O(|refs| + |symrefs| * 2) many reference
transactions to perform the renames. We first delete all symrefs, then
individually rename every direct reference and finally we recreate the
symrefs. On the one hand this isn't even remotely an atomic operation,
so if we hit any error we'll already have deleted all references.

But more importantly it is also extremely inefficient. The number of
transactions for symrefs doesn't really bother us too much, as there
should generally only be a single symref anyway ("HEAD"). But the
renames are very expensive:

  - For the "reftable" backend we perform auto-compaction after every
    single rename, which does add up.

  - For the "files" backend we potentially have to rewrite the
    "packed-refs" file on every single rename in case they are packed.
    The consequence here is quadratic runtime performance. Renaming a
    100k references takes hours to complete.

Refactor the code to use a single transaction to perform all the
reference updates atomically, which speeds up the transaction quite
significantly:

    Benchmark 1: rename remote (refformat = files, revision = HEAD~)
      Time (mean ± σ):     238.770 s ± 13.857 s    [User: 91.473 s, System: 143.793 s]
      Range (min … max):   204.863 s … 247.699 s    10 runs

    Benchmark 2: rename remote (refformat = files, revision = HEAD)
      Time (mean ± σ):      2.103 s ±  0.036 s    [User: 0.360 s, System: 1.313 s]
      Range (min … max):    2.011 s …  2.141 s    10 runs

    Summary
      rename remote (refformat = files, revision = HEAD) ran
      113.53 ± 6.87 times faster than rename remote (refformat = files, revision = HEAD~)

For the "reftable" backend we see a significant speedup, as well, but
given that we don't have quadratic runtime behaviour there it's way less
extreme:

    Benchmark 1: rename remote (refformat = reftable, revision = HEAD~)
      Time (mean ± σ):      8.604 s ±  0.539 s    [User: 4.985 s, System: 2.368 s]
      Range (min … max):    7.880 s …  9.556 s    10 runs

    Benchmark 2: rename remote (refformat = reftable, revision = HEAD)
      Time (mean ± σ):      1.177 s ±  0.103 s    [User: 0.446 s, System: 0.270 s]
      Range (min … max):    1.023 s …  1.410 s    10 runs

    Summary
      rename remote (refformat = reftable, revision = HEAD) ran
        7.31 ± 0.79 times faster than rename remote (refformat = reftable, revision = HEAD~)

There is one issue though with using atomic transactions: when nesting a
remote into itself it can happen that renamed references conflict with
the old referencse. For example, when we have a reference
"refs/remotes/origin/foo" and we rename "origin" to "origin/foo", then
we'll end up with an F/D conflict when we try to create the renamed
reference "refs/remotes/origin/foo/foo".

This situation is overall quite unlikely to happen: people tend to not
use nested remotes, and if they do they must at the same time also have
a conflicting refname. But the end result would be that the old remote
references stay intact whereas all the other parts of the repository
have been adjusted for the new remote name.

Address this by queueing and preparing the reference update before we
touch any other part of the repository. Like this we can make sure that
the reference update will go through before rewriting the configuration.
Otherwise, if the transaction fails to prepare we can gracefully abort
the whole operation without any changes having been performed in the
repository yet. Furthermore, we can detect the conflict and print some
helpful advice for how the user can resolve this situation. So overall,
the tradeoff is that:

  - Reference transactions are now all-or-nothing. This is a significant
    improvement over the previous state where we may have ended up with
    partially-renamed references.

  - Rewriting references is now significantly faster.

  - We only rewrite the configuration in case we know that all
    references can be updated.

  - But we may refuse to rename a remote in case references conflict.

Overall this seems like an acceptable tradeoff.

While at it, fix the handling of symbolic/broken references by using
`refs_for_each_rawref()`. Add tests that cover both this reported issue
and tests that exercise nesting of remotes.

One thing to note: with this change we cannot provide a proper progress
monitor anymore as we queue the references into the transactions as we
iterate through them. Consequently, as we don't know yet how many refs
there are in total, we cannot report how many percent of the operation
is done anymore. But that's a small price to pay considering that you
now shouldn't need the progress monitor in most situations at all
anymore.

[1]: <CANrWfmQWa=RJnm7d3C7ogRX6Tth2eeuGwvwrNmzS2gr+eP0OpA@mail.gmail.com>

Reported-by: Han Jiang <jhcarl0814@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/remote.c  | 296 ++++++++++++++++++++++++++++++----------------
 t/t5505-remote.sh |  73 ++++++++++++
 2 files changed, 270 insertions(+), 99 deletions(-)

diff --git a/builtin/remote.c b/builtin/remote.c
index 34ddcaf5f6f..db481f39bc9 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -1,8 +1,11 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "config.h"
+#include "date.h"
 #include "gettext.h"
+#include "ident.h"
 #include "parse-options.h"
 #include "path.h"
 #include "transport.h"
@@ -610,36 +613,161 @@ static int add_branch_for_removal(const char *refname,
 struct rename_info {
 	const char *old_name;
 	const char *new_name;
-	struct string_list *remote_branches;
-	uint32_t symrefs_nr;
+	struct ref_transaction *transaction;
+	struct progress *progress;
+	struct strbuf *err;
+	uint32_t progress_nr;
+	uint64_t index;
 };
 
-static int read_remote_branches(const char *refname, const char *referent UNUSED,
-				const struct object_id *oid UNUSED,
-				int flags UNUSED, void *cb_data)
+static void compute_renamed_ref(struct rename_info *rename,
+				const char *refname,
+				struct strbuf *out)
+{
+	strbuf_reset(out);
+	strbuf_addstr(out, refname);
+	strbuf_splice(out, strlen("refs/remotes/"), strlen(rename->old_name),
+		      rename->new_name, strlen(rename->new_name));
+}
+
+static int rename_one_reflog_entry(const char *old_refname,
+				   struct object_id *old_oid,
+				   struct object_id *new_oid,
+				   const char *committer,
+				   timestamp_t timestamp, int tz,
+				   const char *msg, void *cb_data)
 {
 	struct rename_info *rename = cb_data;
-	struct strbuf buf = STRBUF_INIT;
-	struct string_list_item *item;
-	int flag;
-	const char *symref;
-
-	strbuf_addf(&buf, "refs/remotes/%s/", rename->old_name);
-	if (starts_with(refname, buf.buf)) {
-		item = string_list_append(rename->remote_branches, refname);
-		symref = refs_resolve_ref_unsafe(get_main_ref_store(the_repository),
-						 refname, RESOLVE_REF_READING,
-						 NULL, &flag);
-		if (symref && (flag & REF_ISSYMREF)) {
-			item->util = xstrdup(symref);
-			rename->symrefs_nr++;
-		} else {
-			item->util = NULL;
-		}
+	struct strbuf new_refname = STRBUF_INIT;
+	struct strbuf identity = STRBUF_INIT;
+	struct strbuf name = STRBUF_INIT;
+	struct strbuf mail = STRBUF_INIT;
+	struct ident_split ident;
+	const char *date;
+	int error;
+
+	compute_renamed_ref(rename, old_refname, &new_refname);
+
+	if (split_ident_line(&ident, committer, strlen(committer)) < 0) {
+		error = -1;
+		goto out;
 	}
-	strbuf_release(&buf);
 
-	return 0;
+	strbuf_add(&name, ident.name_begin, ident.name_end - ident.name_begin);
+	strbuf_add(&mail, ident.mail_begin, ident.mail_end - ident.mail_begin);
+
+	date = show_date(timestamp, tz, DATE_MODE(NORMAL));
+	strbuf_addstr(&identity, fmt_ident(name.buf, mail.buf,
+					  WANT_BLANK_IDENT, date, 0));
+
+	error = ref_transaction_update_reflog(rename->transaction, new_refname.buf,
+					      new_oid, old_oid, identity.buf, msg,
+					      rename->index++, rename->err);
+
+out:
+	strbuf_release(&new_refname);
+	strbuf_release(&identity);
+	strbuf_release(&name);
+	strbuf_release(&mail);
+	return error;
+}
+
+static int rename_one_reflog(const char *old_refname,
+			     const struct object_id *old_oid,
+			     struct rename_info *rename)
+{
+	struct strbuf new_refname = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
+	int error;
+
+	if (!refs_reflog_exists(get_main_ref_store(the_repository), old_refname))
+		return 0;
+
+	error = refs_for_each_reflog_ent(get_main_ref_store(the_repository),
+					 old_refname, rename_one_reflog_entry, rename);
+	if (error < 0)
+		goto out;
+
+	compute_renamed_ref(rename, old_refname, &new_refname);
+
+	/*
+	 * Manually write the reflog entry for the now-renamed ref. We cannot
+	 * rely on `rename_one_ref()` to do this for us as that would screw
+	 * over order in which reflog entries are being written.
+	 *
+	 * Furthermore, we only append the entry in case the reference
+	 * resolves. Missing references shouldn't have reflogs anyway.
+	 */
+	strbuf_addf(&message, "remote: renamed %s to %s", old_refname,
+		    new_refname.buf);
+
+	error = ref_transaction_update_reflog(rename->transaction, new_refname.buf,
+					      old_oid, old_oid, git_committer_info(0),
+					      message.buf, rename->index++, rename->err);
+	if (error < 0)
+		return error;
+
+out:
+	strbuf_release(&new_refname);
+	strbuf_release(&message);
+	return error;
+}
+
+static int rename_one_ref(const char *old_refname, const char *referent,
+			  const struct object_id *oid,
+			  int flags, void *cb_data)
+{
+	struct strbuf new_referent = STRBUF_INIT;
+	struct strbuf new_refname = STRBUF_INIT;
+	struct rename_info *rename = cb_data;
+	const char *ptr = old_refname;
+	int error;
+
+	if (!skip_prefix(ptr, "refs/remotes/", &ptr) ||
+	    !skip_prefix(ptr, rename->old_name, &ptr) ||
+	    !skip_prefix(ptr, "/", &ptr)) {
+		error = 0;
+		goto out;
+	}
+
+	compute_renamed_ref(rename, old_refname, &new_refname);
+
+	if (flags & REF_ISSYMREF) {
+		/*
+		 * Stupidly enough `referent` is not pointing to the immediate
+		 * target of a symref, but it's the recursively resolved value.
+		 * So symrefs pointing to symrefs would be misresolved, and
+		 * unborn symrefs don't have any value for the `referent` at all.
+		 */
+		referent = refs_resolve_ref_unsafe(get_main_ref_store(the_repository),
+						   old_refname, RESOLVE_REF_NO_RECURSE,
+						   NULL, NULL);
+		compute_renamed_ref(rename, referent, &new_referent);
+		oid = NULL;
+	}
+
+	error = ref_transaction_delete(rename->transaction, old_refname,
+				       oid, referent, REF_NO_DEREF, NULL, rename->err);
+	if (error < 0)
+		goto out;
+
+	error = ref_transaction_update(rename->transaction, new_refname.buf, oid, null_oid(the_hash_algo),
+				       (flags & REF_ISSYMREF) ? new_referent.buf : NULL, NULL,
+				       REF_SKIP_CREATE_REFLOG | REF_NO_DEREF | REF_SKIP_OID_VERIFICATION,
+				       NULL, rename->err);
+	if (error < 0)
+		goto out;
+
+	error = rename_one_reflog(old_refname, oid, rename);
+	if (error < 0)
+		goto out;
+
+	display_progress(rename->progress, ++rename->progress_nr);
+
+out:
+	strbuf_release(&new_referent);
+	strbuf_release(&new_refname);
+	return error;
 }
 
 static int migrate_file(struct remote *remote)
@@ -727,6 +855,14 @@ static void handle_push_default(const char* old_name, const char* new_name)
 	strbuf_release(&push_default.origin);
 }
 
+static const char conflicting_remote_refs_advice[] = N_(
+	"The remote you are trying to rename has conflicting references in the\n"
+	"new target refspec. This is most likely caused by you trying to nest\n"
+	"a remote into itself, e.g. by renaming 'parent' into 'parent/child'\n"
+	"or by unnesting a remote, e.g. the other way round.\n"
+	"\n"
+	"If that is the case, you can address this by first renaming the\n"
+	"remote to a different name.\n");
 
 static int mv(int argc, const char **argv, const char *prefix,
 	      struct repository *repo UNUSED)
@@ -738,11 +874,11 @@ static int mv(int argc, const char **argv, const char *prefix,
 	};
 	struct remote *oldremote, *newremote;
 	struct strbuf buf = STRBUF_INIT, buf2 = STRBUF_INIT, buf3 = STRBUF_INIT,
-		old_remote_context = STRBUF_INIT;
-	struct string_list remote_branches = STRING_LIST_INIT_DUP;
-	struct rename_info rename;
-	int refs_renamed_nr = 0, refspecs_need_update = 0;
-	struct progress *progress = NULL;
+		old_remote_context = STRBUF_INIT, err = STRBUF_INIT;
+	struct rename_info rename = {
+		.err = &err,
+	};
+	int refspecs_need_update = 0;
 	int result = 0;
 
 	argc = parse_options(argc, argv, prefix, options,
@@ -753,8 +889,6 @@ static int mv(int argc, const char **argv, const char *prefix,
 
 	rename.old_name = argv[0];
 	rename.new_name = argv[1];
-	rename.remote_branches = &remote_branches;
-	rename.symrefs_nr = 0;
 
 	oldremote = remote_get(rename.old_name);
 	if (!remote_is_configured(oldremote, 1)) {
@@ -788,6 +922,30 @@ static int mv(int argc, const char **argv, const char *prefix,
 		refspecs_need_update = !!strstr(oldremote->fetch.items[i].raw,
 						old_remote_context.buf);
 
+	if (refspecs_need_update) {
+		rename.transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),
+							       0, &err);
+		if (!rename.transaction)
+			goto out;
+
+		if (show_progress)
+			rename.progress = start_delayed_progress(the_repository,
+								 _("Renaming remote references"), 0);
+
+		result = refs_for_each_rawref(get_main_ref_store(the_repository),
+				rename_one_ref, &rename);
+		if (result < 0)
+			die(_("queueing remote ref renames failed: %s"), rename.err->buf);
+
+		result = ref_transaction_prepare(rename.transaction, &err);
+		if (result < 0) {
+			error("renaming remote references failed: %s", err.buf);
+			if (result == REF_TRANSACTION_ERROR_NAME_CONFLICT)
+				advise(conflicting_remote_refs_advice);
+			die(NULL);
+		}
+	}
+
 	if (oldremote->fetch.nr) {
 		strbuf_reset(&buf);
 		strbuf_addf(&buf, "remote.%s.fetch", rename.new_name);
@@ -829,83 +987,23 @@ static int mv(int argc, const char **argv, const char *prefix,
 		}
 	}
 
-	if (!refspecs_need_update)
-		goto out;
-
-	/*
-	 * First remove symrefs, then rename the rest, finally create
-	 * the new symrefs.
-	 */
-	refs_for_each_ref(get_main_ref_store(the_repository),
-			  read_remote_branches, &rename);
-	if (show_progress) {
-		/*
-		 * Count symrefs twice, since "renaming" them is done by
-		 * deleting and recreating them in two separate passes.
-		 */
-		progress = start_progress(the_repository,
-					  _("Renaming remote references"),
-					  rename.remote_branches->nr + rename.symrefs_nr);
-	}
-	for (size_t i = 0; i < remote_branches.nr; i++) {
-		struct string_list_item *item = remote_branches.items + i;
-		struct strbuf referent = STRBUF_INIT;
-
-		if (refs_read_symbolic_ref(get_main_ref_store(the_repository), item->string,
-					   &referent))
-			continue;
-		if (refs_delete_ref(get_main_ref_store(the_repository), NULL, item->string, NULL, REF_NO_DEREF))
-			die(_("deleting '%s' failed"), item->string);
-
-		strbuf_release(&referent);
-		display_progress(progress, ++refs_renamed_nr);
-	}
-	for (size_t i = 0; i < remote_branches.nr; i++) {
-		struct string_list_item *item = remote_branches.items + i;
+	if (refspecs_need_update) {
+		result = ref_transaction_commit(rename.transaction, &err);
+		if (result < 0)
+			die(_("renaming remote refs failed: %s"), rename.err->buf);
 
-		if (item->util)
-			continue;
-		strbuf_reset(&buf);
-		strbuf_addstr(&buf, item->string);
-		strbuf_splice(&buf, strlen("refs/remotes/"), strlen(rename.old_name),
-				rename.new_name, strlen(rename.new_name));
-		strbuf_reset(&buf2);
-		strbuf_addf(&buf2, "remote: renamed %s to %s",
-				item->string, buf.buf);
-		if (refs_rename_ref(get_main_ref_store(the_repository), item->string, buf.buf, buf2.buf))
-			die(_("renaming '%s' failed"), item->string);
-		display_progress(progress, ++refs_renamed_nr);
-	}
-	for (size_t i = 0; i < remote_branches.nr; i++) {
-		struct string_list_item *item = remote_branches.items + i;
+		stop_progress(&rename.progress);
 
-		if (!item->util)
-			continue;
-		strbuf_reset(&buf);
-		strbuf_addstr(&buf, item->string);
-		strbuf_splice(&buf, strlen("refs/remotes/"), strlen(rename.old_name),
-				rename.new_name, strlen(rename.new_name));
-		strbuf_reset(&buf2);
-		strbuf_addstr(&buf2, item->util);
-		strbuf_splice(&buf2, strlen("refs/remotes/"), strlen(rename.old_name),
-				rename.new_name, strlen(rename.new_name));
-		strbuf_reset(&buf3);
-		strbuf_addf(&buf3, "remote: renamed %s to %s",
-				item->string, buf.buf);
-		if (refs_update_symref(get_main_ref_store(the_repository), buf.buf, buf2.buf, buf3.buf))
-			die(_("creating '%s' failed"), buf.buf);
-		display_progress(progress, ++refs_renamed_nr);
+		handle_push_default(rename.old_name, rename.new_name);
 	}
-	stop_progress(&progress);
-
-	handle_push_default(rename.old_name, rename.new_name);
 
 out:
-	string_list_clear(&remote_branches, 1);
+	ref_transaction_free(rename.transaction);
 	strbuf_release(&old_remote_context);
 	strbuf_release(&buf);
 	strbuf_release(&buf2);
 	strbuf_release(&buf3);
+	strbuf_release(&err);
 	return result;
 }
 
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 2701eef85e9..e592c0bcde9 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -1658,4 +1658,77 @@ test_expect_success 'forbid adding superset of existing remote' '
 	test_grep ".outer. is a superset of existing remote .outer/inner." err
 '
 
+test_expect_success 'rename handles unborn HEAD' '
+	test_when_finished "git remote remove unborn-renamed" &&
+	git remote add unborn url &&
+	git symbolic-ref refs/remotes/unborn/HEAD refs/remotes/unborn/nonexistent &&
+	git remote rename unborn unborn-renamed &&
+	git symbolic-ref refs/remotes/unborn-renamed/HEAD >actual &&
+	echo refs/remotes/unborn-renamed/nonexistent >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'rename can nest a remote into itself' '
+	test_commit parent-commit &&
+	COMMIT_ID=$(git rev-parse HEAD) &&
+	test_when_finished "git remote remove parent || true" &&
+	git remote add parent url &&
+	git update-ref refs/remotes/parent/branch $COMMIT_ID &&
+	test_when_finished "git remote remove parent/child" &&
+	git remote rename parent parent/child &&
+	git for-each-ref refs/remotes/ >actual &&
+	printf "$COMMIT_ID commit\trefs/remotes/parent/child/branch\n" >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'rename can nest a remote into itself with a conflicting branch name' '
+	test_commit parent-conflict &&
+	COMMIT_ID=$(git rev-parse HEAD) &&
+	test_when_finished "git remote remove parent || true" &&
+	git remote add parent url &&
+	git update-ref refs/remotes/parent/child $COMMIT_ID &&
+	test_when_finished "git remote remove parent/child" &&
+	test_must_fail git remote rename parent parent/child 2>err &&
+	test_grep "renaming remote references failed" err &&
+	test_grep "The remote you are trying to rename has conflicting references" err &&
+	git for-each-ref refs/remotes/ >actual &&
+	printf "$COMMIT_ID commit\trefs/remotes/parent/child\n" >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'rename can unnest a remote' '
+	test_commit parent-child-commit &&
+	COMMIT_ID=$(git rev-parse HEAD) &&
+	test_when_finished "git remote remove parent/child || true" &&
+	git remote add parent/child url &&
+	git update-ref refs/remotes/parent/child/branch $COMMIT_ID &&
+	git remote rename parent/child parent &&
+	git for-each-ref refs/remotes/ >actual &&
+	printf "$COMMIT_ID commit\trefs/remotes/parent/branch\n" >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'rename moves around the reflog' '
+	test_commit reflog-old &&
+	COMMIT_ID=$(git rev-parse HEAD) &&
+	test_config core.logAllRefUpdates true &&
+	test_when_finished "git remote remove reflog-old || true" &&
+	git remote add reflog-old url &&
+	git update-ref refs/remotes/reflog-old/branch $COMMIT_ID &&
+	test-tool ref-store main for-each-reflog >actual &&
+	test_grep refs/remotes/reflog-old/branch actual &&
+	test-tool ref-store main for-each-reflog-ent refs/remotes/reflog-old/branch >reflog-entries-old &&
+	test_line_count = 1 reflog-entries-old &&
+	git remote rename reflog-old reflog-new &&
+	test-tool ref-store main for-each-reflog >actual &&
+	test_grep ! refs/remotes/reflog-old actual &&
+	test_grep refs/remotes/reflog-new/branch actual &&
+	test-tool ref-store main for-each-reflog-ent refs/remotes/reflog-new/branch >reflog-entries-new &&
+	cat >expect <<-EOF &&
+	$(cat reflog-entries-old)
+	$COMMIT_ID $COMMIT_ID $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> 1112912173 -0700	remote: renamed refs/remotes/reflog-old/branch to refs/remotes/reflog-new/branch
+	EOF
+	test_cmp expect reflog-entries-new
+'
+
 test_done
-- 
GitLab


From ffdf63b787342fedf933fa27b75d4b28532fdcac Mon Sep 17 00:00:00 2001
From: Patrick Steinhardt <ps@pks.im>
Date: Thu, 31 Jul 2025 14:02:04 +0200
Subject: [PATCH 16/16] builtin/remote: only iterate through refs that are to
 be renamed
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

When renaming a remote we also need to rename all references
accordingly. But while we only need to rename references that are
contained in the "refs/remotes/$OLDNAME/" namespace, we end up using
`refs_for_each_rawref()` that iterates through _all_ references. We know
to exit early in the callback in case we see an irrelevant reference,
but ultimately this is still a waste of compute as we knowingly iterate
through references that we won't ever care about.

Improve this by using `refs_for_each_rawref_in()`, which knows to only
iterate through (potentially broken) references in a given prefix.

The following benchmark renames a remote with a single reference in a
repository that has 100k unrelated references. This shows a sizeable
improvement with the "files" backend:

    Benchmark 1: rename remote (refformat = files, revision = HEAD~)
      Time (mean ± σ):      42.6 ms ±   0.9 ms    [User: 29.1 ms, System: 8.4 ms]
      Range (min … max):    40.1 ms …  43.3 ms    10 runs

    Benchmark 2: rename remote (refformat = files, revision = HEAD)
      Time (mean ± σ):      31.7 ms ±   4.0 ms    [User: 19.6 ms, System: 6.9 ms]
      Range (min … max):    27.1 ms …  36.0 ms    10 runs

    Summary
      rename remote (refformat = files, revision = HEAD) ran
        1.35 ± 0.17 times faster than rename remote (refformat = files, revision = HEAD~)

The "reftable" backend shows roughly the same absolute improvement, but
given that it's already significantly faster than the "files" backend
this translates to a much larger relative improvement:

    Benchmark 1: rename remote (refformat = reftable, revision = HEAD~)
      Time (mean ± σ):      18.2 ms ±   0.5 ms    [User: 12.7 ms, System: 3.0 ms]
      Range (min … max):    17.3 ms …  21.4 ms    110 runs

    Benchmark 2: rename remote (refformat = reftable, revision = HEAD)
      Time (mean ± σ):       8.8 ms ±   0.5 ms    [User: 3.8 ms, System: 2.9 ms]
      Range (min … max):     7.5 ms …   9.9 ms    167 runs

    Summary
      rename remote (refformat = reftable, revision = HEAD) ran
        2.07 ± 0.12 times faster than rename remote (refformat = reftable, revision = HEAD~)

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 builtin/remote.c | 13 ++++---------
 refs.c           |  8 +++++++-
 refs.h           |  2 ++
 3 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/builtin/remote.c b/builtin/remote.c
index db481f39bc9..60e67f1b74c 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -720,16 +720,8 @@ static int rename_one_ref(const char *old_refname, const char *referent,
 	struct strbuf new_referent = STRBUF_INIT;
 	struct strbuf new_refname = STRBUF_INIT;
 	struct rename_info *rename = cb_data;
-	const char *ptr = old_refname;
 	int error;
 
-	if (!skip_prefix(ptr, "refs/remotes/", &ptr) ||
-	    !skip_prefix(ptr, rename->old_name, &ptr) ||
-	    !skip_prefix(ptr, "/", &ptr)) {
-		error = 0;
-		goto out;
-	}
-
 	compute_renamed_ref(rename, old_refname, &new_refname);
 
 	if (flags & REF_ISSYMREF) {
@@ -932,7 +924,10 @@ static int mv(int argc, const char **argv, const char *prefix,
 			rename.progress = start_delayed_progress(the_repository,
 								 _("Renaming remote references"), 0);
 
-		result = refs_for_each_rawref(get_main_ref_store(the_repository),
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "refs/remotes/%s/", rename.old_name);
+
+		result = refs_for_each_rawref_in(get_main_ref_store(the_repository), buf.buf,
 				rename_one_ref, &rename);
 		if (result < 0)
 			die(_("queueing remote ref renames failed: %s"), rename.err->buf);
diff --git a/refs.c b/refs.c
index 04c9ace7932..7e2f02dddf8 100644
--- a/refs.c
+++ b/refs.c
@@ -1839,7 +1839,13 @@ int refs_for_each_namespaced_ref(struct ref_store *refs,
 
 int refs_for_each_rawref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
 {
-	return do_for_each_ref(refs, "", NULL, fn, 0,
+	return refs_for_each_rawref_in(refs, "", fn, cb_data);
+}
+
+int refs_for_each_rawref_in(struct ref_store *refs, const char *prefix,
+			    each_ref_fn fn, void *cb_data)
+{
+	return do_for_each_ref(refs, prefix, NULL, fn, 0,
 			       DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
 }
 
diff --git a/refs.h b/refs.h
index 0bf50ce25cc..19fb1d924ad 100644
--- a/refs.h
+++ b/refs.h
@@ -428,6 +428,8 @@ int refs_for_each_namespaced_ref(struct ref_store *refs,
 
 /* can be used to learn about broken ref and symref */
 int refs_for_each_rawref(struct ref_store *refs, each_ref_fn fn, void *cb_data);
+int refs_for_each_rawref_in(struct ref_store *refs, const char *prefix,
+			    each_ref_fn fn, void *cb_data);
 
 /*
  * Iterates over all refs including root refs, i.e. pseudorefs and HEAD.
-- 
GitLab