Merge branch 'ps/reflog-migrate-fixes'

"git refs migrate" to migrate the reflog entries from a refs
backend to another had a handful of bugs squashed.

* ps/reflog-migrate-fixes:
  refs: fix invalid old object IDs when migrating reflogs
  refs: stop unsetting REF_HAVE_OLD for log-only updates
  refs/files: detect race when generating reflog entry for HEAD
  refs: fix identity for migrated reflogs
  ident: fix type of string length parameter
  builtin/reflog: implement subcommand to write new entries
  refs: export `ref_transaction_update_reflog()`
  builtin/reflog: improve grouping of subcommands
  Documentation/git-reflog: convert to use synopsis type

diff --cc builtin/reflog.c
index 1db26aa65f2fdd55a9fd62cd86d7e306b03ddb94,a1b4e02204178f3ccdfc4eb733be7b2627e34c20..c8f6b93d60b1e811c2f3a0ce6dd40088ca127f52
--- 1/builtin/reflog.c
--- 2/builtin/reflog.c
+++ b/builtin/reflog.c
@@@ -3,6 -3,8 +3,8 @@@
  #include "builtin.h"
  #include "config.h"
  #include "gettext.h"
 -#include "object-store.h"
+ #include "hex.h"
++#include "odb.h"
  #include "revision.h"
  #include "reachable.h"
  #include "wildmatch.h"
@@@ -395,6 -403,59 +406,59 @@@ static int cmd_reflog_drop(int argc, co
        return ret;
  }
  
 -      if (!is_null_oid(&old_oid) && !has_object(the_repository, &old_oid, 0))
+ 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(&new_oid) && !has_object(the_repository, &new_oid, 0))
++      if (!is_null_oid(&old_oid) && !odb_has_object(repo->objects, &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) && !odb_has_object(repo->objects, &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"
   */

diff --cc ident.c
Simple merge

diff --cc refs.c
Simple merge

diff --cc refs.h
Simple merge

diff --cc refs/files-backend.c
Simple merge

diff --cc refs/refs-internal.h
Simple merge

diff --cc refs/reftable-backend.c
Simple merge

diff --cc t/meson.build
Simple merge