Merge branch 'ps/refname-avail-check-optim' into kn/non-transactional-batch-updates

* ps/refname-avail-check-optim: (43 commits)
  refs: reuse iterators when determining refname availability
  refs/iterator: implement seeking for files iterators
  refs/iterator: implement seeking for packed-ref iterators
  refs/iterator: implement seeking for ref-cache iterators
  refs/iterator: implement seeking for reftable iterators
  refs/iterator: implement seeking for merged iterators
  refs/iterator: provide infrastructure to re-seek iterators
  refs/iterator: separate lifecycle from iteration
  refs: stop re-verifying common prefixes for availability
  refs/files: batch refname availability checks for initial transactions
  refs/files: batch refname availability checks for normal transactions
  refs/reftable: batch refname availability checks
  refs: introduce function to batch refname availability checks
  builtin/update-ref: skip ambiguity checks when parsing object IDs
  object-name: allow skipping ambiguity checks in `get_oid()` family
  object-name: introduce `repo_get_oid_with_flags()`
  Git 2.49-rc0
  The fourteenth batch
  mailmap: fix check-mailmap with full mailmap line
  The thirteenth batch
  ...

63 files changed, 764 insertions, 448 deletions

diff --git a/Documentation/Makefile b/Documentation/Makefile
index a734c6d624..c9a7cf662f 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -1,3 +1,6 @@
+# The default target of this Makefile is...
+all::
+
 # Import tree-wide shared Makefile behavior and libraries
 include ../shared.mak
 
@@ -238,7 +241,7 @@ DEFAULT_EDITOR_SQ = $(subst ','\'',$(DEFAULT_EDITOR))
 ASCIIDOC_EXTRA += -a 'git-default-editor=$(DEFAULT_EDITOR_SQ)'
 endif
 
-all: html man
+all:: html man
 
 html: $(DOC_HTML)
 
diff --git a/Documentation/RelNotes/2.49.0.adoc b/Documentation/RelNotes/2.49.0.adoc
index 64323ec4a9..2e9aa0d69f 100644
--- a/Documentation/RelNotes/2.49.0.adoc
+++ b/Documentation/RelNotes/2.49.0.adoc
@@ -33,6 +33,11 @@ UI, Workflows & Features
  * "git rev-list --missing=" learned to accept "print-info" that gives
    known details expected of the missing objects, like path and type.
 
+ * Comes with an updated "gitk".
+
+ * The documentation of "git commit" and "git rebase" now refer to
+   commit titles as such, not "subject".
+
 
 Performance, Internal Implementation, Development Support etc.
 --------------------------------------------------------------
@@ -202,6 +207,25 @@ Fixes since v2.48
  * A thunderbird helper script lost its bashism.
    (merge 59d26bd961 bc/contrib-thunderbird-patch-inline-fix later to maint).
 
+ * The -G/-S options to the "diff" family of commands caused us to hit
+   a BUG() when they get no values; they have been corrected.
+   (merge a620046b29 bc/diff-reject-empty-arg-to-pickaxe later to maint).
+
+ * "git merge-tree --stdin" has been improved (including a workaround
+   for a deadlock).
+   (merge 6a9ae81015 pw/merge-tree-stdin-deadlock-fix later to maint).
+
+ * Correct the default target in Documentation/Makefile, and
+   future-proof all Makefiles from similar breakages by declaring the
+   default target (which happens to be "all") upfront.
+   (merge 5309c1e9fb ad/set-default-target-in-makefiles later to maint).
+
+ * "git check-mailmap" used to segfault when queried without human
+   readable name.
+   (merge bb60c52131 jk/check-mailmap-wo-name-fix later to maint).
+
+ * Support for renaming of symbolic links on Windows has been improved.
+
  * Other code cleanup, docfix, build fix, etc.
    (merge ddb5287894 jk/t7407-use-test-grep later to maint).
    (merge 21e1b44865 aj/difftool-config-doc-fix later to maint).
@@ -217,3 +241,6 @@ Fixes since v2.48
    (merge 087740d65a ps/leakfixes-0129 later to maint).
    (merge 6bba6f604b jp/doc-trailer-config later to maint).
    (merge f1cc562b77 lo/t7603-path-is-file-update later to maint).
+   (merge 45761988ac en/doc-renormalize later to maint).
+   (merge 832f56f06a jc/doc-boolean-synonyms later to maint).
+   (merge 3eeed876a9 ac/doc-http-ssl-type-config later to maint).
diff --git a/Documentation/config/http.adoc b/Documentation/config/http.adoc
index a14371b5c9..22a8803dea 100644
--- a/Documentation/config/http.adoc
+++ b/Documentation/config/http.adoc
@@ -216,6 +216,21 @@ http.sslBackend::
 	This option is ignored if cURL lacks support for choosing the SSL
 	backend at runtime.
 
+http.sslCertType::
+	Type of client certificate used when fetching or pushing over HTTPS.
+	"PEM", "DER" are supported when using openssl or gnutls backends. "P12"
+	is supported on "openssl", "schannel", "securetransport", and gnutls 8.11+.
+	See also libcurl `CURLOPT_SSLCERTTYPE`. Can be overridden by the
+	`GIT_SSL_CERT_TYPE` environment variable.
+
+http.sslKeyType::
+	Type of client private key used when fetching or pushing over HTTPS. (e.g.
+	"PEM", "DER", or "ENG"). Only applicable when using "openssl" backend. "DER"
+	is not supported with openssl. Particularly useful when set to "ENG" for
+	authenticating with PKCS#11 tokens, with a PKCS#11 URL in sslCert option.
+	See also libcurl `CURLOPT_SSLKEYTYPE`. Can be overridden by the
+	`GIT_SSL_KEY_TYPE` environment variable.
+
 http.schannelCheckRevoke::
 	Used to enforce or disable certificate revocation checks in cURL
 	when http.sslBackend is set to "schannel". Defaults to `true` if
diff --git a/Documentation/config/merge.adoc b/Documentation/config/merge.adoc
index 857de5b40b..d2d0f21a71 100644
--- a/Documentation/config/merge.adoc
+++ b/Documentation/config/merge.adoc
@@ -69,7 +69,8 @@ merge.renormalize::
 	Tell Git that canonical representation of files in the
 	repository has changed over time (e.g. earlier commits record
 	text files with CRLF line endings, but recent ones use LF line
-	endings).  In such a repository, Git can convert the data
+	endings).  In such a repository, for each file where a
+	three-way content merge is needed, Git can convert the data
 	recorded in commits to a canonical form before performing a
 	merge to reduce unnecessary conflicts.  For more information,
 	see section "Merging branches with differing checkin/checkout
diff --git a/Documentation/git-commit.adoc b/Documentation/git-commit.adoc
index dfb78169cb..dc219025f1 100644
--- a/Documentation/git-commit.adoc
+++ b/Documentation/git-commit.adoc
@@ -98,8 +98,8 @@ OPTIONS
 	replaces the log message of _<commit>_ with its own log message
 	but makes no changes to the content of _<commit>_.
 +
-The commit created by plain `--fixup=<commit>` has a subject
-composed of "fixup!" followed by the subject line from _<commit>_,
+The commit created by plain `--fixup=<commit>` has a title
+composed of "fixup!" followed by the title of _<commit>_,
 and is recognized specially by `git rebase --autosquash`. The `-m`
 option may be used to supplement the log message of the created
 commit, but the additional commentary will be thrown away once the
@@ -107,7 +107,7 @@ commit, but the additional commentary will be thrown away once the
 `git rebase --autosquash`.
 +
 The commit created by `--fixup=amend:<commit>` is similar but its
-subject is instead prefixed with "amend!". The log message of
+title is instead prefixed with "amend!". The log message of
 _<commit>_ is copied into the log message of the "amend!" commit and
 opened in an editor so it can be refined. When `git rebase
 --autosquash` squashes the "amend!" commit into _<commit>_, the
@@ -128,7 +128,7 @@ See linkgit:git-rebase[1] for details.
 
 `--squash=<commit>`::
 	Construct a commit message for use with `git rebase --autosquash`.
-	The commit message subject line is taken from the specified
+	The commit message title is taken from the specified
 	commit with a prefix of "squash! ".  Can be used with additional
 	commit message options (`-m`/`-c`/`-C`/`-F`). See
 	linkgit:git-rebase[1] for details.
diff --git a/Documentation/git-config.adoc b/Documentation/git-config.adoc
index 888f8ba54b..936e0c5130 100644
--- a/Documentation/git-config.adoc
+++ b/Documentation/git-config.adoc
@@ -213,7 +213,9 @@ See also <<FILES>>.
 +
 Valid `<type>`'s include:
 +
-- 'bool': canonicalize values as either "true" or "false".
+- 'bool': canonicalize values `true`, `yes`,`on`, and positive
+  numbers as "true", and values `false`, `no`, `off` and `0` as
+  "false".
 - 'int': canonicalize values as simple decimal numbers. An optional suffix of
   'k', 'm', or 'g' will cause the value to be multiplied by 1024, 1048576, or
   1073741824 upon input.
diff --git a/Documentation/git-merge-tree.adoc b/Documentation/git-merge-tree.adoc
index 0b6a8a19b1..cf0578f9b5 100644
--- a/Documentation/git-merge-tree.adoc
+++ b/Documentation/git-merge-tree.adoc
@@ -40,11 +40,17 @@ After the merge completes, a new toplevel tree object is created.  See
 OPTIONS
 -------
 
+--stdin::
+	Read the commits to merge from the standard input rather than
+	the command-line. See <<INPUT,INPUT FORMAT>> below for more
+	information.  Implies `-z`.
+
 -z::
 	Do not quote filenames in the <Conflicted file info> section,
 	and end each filename with a NUL character rather than
 	newline.  Also begin the messages section with a NUL character
-	instead of a newline.  See <<OUTPUT>> below for more information.
+	instead of a newline.  See <<OUTPUT,OUTPUT>> below for more
+	information.
 
 --name-only::
 	In the Conflicted file info section, instead of writing a list
@@ -116,8 +122,6 @@ This is an integer status followed by a NUL character.  The integer status is:
 
      0: merge had conflicts
      1: merge was clean
-     <0: something prevented the merge from running (e.g. access to repository
-	 objects denied by filesystem)
 
 [[OIDTLT]]
 OID of toplevel tree
@@ -235,6 +239,7 @@ with linkgit:git-merge[1]:
   * any messages that would have been printed to stdout (the
     <<IM,Informational messages>>)
 
+[[INPUT]]
 INPUT FORMAT
 ------------
 'git merge-tree --stdin' input format is fully text based. Each line
diff --git a/Documentation/git-rebase.adoc b/Documentation/git-rebase.adoc
index 133fe8c5e6..153cb69a4f 100644
--- a/Documentation/git-rebase.adoc
+++ b/Documentation/git-rebase.adoc
@@ -599,11 +599,11 @@ See also INCOMPATIBLE OPTIONS below.
 --no-autosquash::
 	Automatically squash commits with specially formatted messages into
 	previous commits being rebased.  If a commit message starts with
-	"squash! ", "fixup! " or "amend! ", the remainder of the subject line
+	"squash! ", "fixup! " or "amend! ", the remainder of the title
 	is taken as a commit specifier, which matches a previous commit if it
-	matches the subject line or the hash of that commit.  If no commit
+	matches the title or the hash of that commit.  If no commit
 	matches fully, matches of the specifier with the start of commit
-	subjects are considered.
+	titles are considered.
 +
 In the rebase todo list, the actions of squash, fixup and amend commits are
 changed from `pick` to `squash`, `fixup` or `fixup -C`, respectively, and they
@@ -613,7 +613,7 @@ be used to review and edit the todo list before proceeding.
 The recommended way to create commits with squash markers is by using the
 `--squash`, `--fixup`, `--fixup=amend:` or `--fixup=reword:` options of
 linkgit:git-commit[1], which take the target commit as an argument and
-automatically fill in the subject line of the new commit from that.
+automatically fill in the title of the new commit from that.
 +
 Setting configuration variable `rebase.autoSquash` to true enables
 auto-squashing by default for interactive rebase.  The `--no-autosquash`
diff --git a/Documentation/git.adoc b/Documentation/git.adoc
index a9c1183318..743b7b00e4 100644
--- a/Documentation/git.adoc
+++ b/Documentation/git.adoc
@@ -472,8 +472,9 @@ Environment Variables
 ---------------------
 Various Git commands pay attention to environment variables and change
 their behavior.  The environment variables marked as "Boolean" take
-their values the same way as Boolean valued configuration variables, e.g.
-"true", "yes", "on" and positive numbers are taken as "yes".
+their values the same way as Boolean valued configuration variables, i.e.,
+"true", "yes", "on" and positive numbers are taken as "yes", while "false",
+"no", "off", and "0" are taken as "no".
 
 Here are the variables:
 
diff --git a/Documentation/gitattributes.adoc b/Documentation/gitattributes.adoc
index 5d12b78549..7eaca89972 100644
--- a/Documentation/gitattributes.adoc
+++ b/Documentation/gitattributes.adoc
@@ -701,8 +701,8 @@ where the attribute is not in place would normally cause merge
 conflicts.
 
 To prevent these unnecessary merge conflicts, Git can be told to run a
-virtual check-out and check-in of all three stages of a file when
-resolving a three-way merge by setting the `merge.renormalize`
+virtual check-out and check-in of all three stages of each file that
+needs a three-way content merge, by setting the `merge.renormalize`
 configuration variable.  This prevents changes caused by check-in
 conversion from causing spurious merge conflicts when a converted file
 is merged with an unconverted file.
diff --git a/Documentation/merge-strategies.adoc b/Documentation/merge-strategies.adoc
index 5fc54ec060..a5dc95a378 100644
--- a/Documentation/merge-strategies.adoc
+++ b/Documentation/merge-strategies.adoc
@@ -56,7 +56,7 @@ ignore-cr-at-eol;;
 
 renormalize;;
 	This runs a virtual check-out and check-in of all three stages
-	of a file when resolving a three-way merge.  This option is
+	of any file which needs a three-way merge.  This option is
 	meant to be used when merging branches with different clean
 	filters or end-of-line normalization rules.  See "Merging
 	branches with differing checkin/checkout attributes" in
diff --git a/Documentation/pretty-formats.adoc b/Documentation/pretty-formats.adoc
index 8ee940b6a4..07475de8c3 100644
--- a/Documentation/pretty-formats.adoc
+++ b/Documentation/pretty-formats.adoc
@@ -339,10 +339,10 @@ insert an empty string unless we are traversing reflog entries (e.g., by
 decoration format if `--decorate` was not already provided on the command
 line.
 
-The boolean options accept an optional value `[=<bool-value>]`. The values
-`true`, `false`, `on`, `off` etc. are all accepted. See the "boolean"
-sub-section in "EXAMPLES" in linkgit:git-config[1]. If a boolean
-option is given with no value, it's enabled.
+The boolean options accept an optional value `[=<bool-value>]`. The
+values taken by `--type=bool` git-config[1], like `yes` and `off`,
+are all accepted.  Giving a boolean option without `=<value>` is
+equivalent to giving it with `=true`.
 
 If you add a `+` (plus sign) after '%' of a placeholder, a line-feed
 is inserted immediately before the expansion if and only if the
diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN
index 56b45333c1..67fa0401cf 100755
--- a/GIT-VERSION-GEN
+++ b/GIT-VERSION-GEN
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-DEF_VER=v2.48.GIT
+DEF_VER=v2.49.0-rc0
 
 LF='
 '
diff --git a/Makefile b/Makefile
index bcf5ed3f85..6d45093089 100644
--- a/Makefile
+++ b/Makefile
@@ -1704,16 +1704,16 @@ IMAP_SEND_LDFLAGS += $(OPENSSL_LINK) $(OPENSSL_LIBSSL) $(LIB_4_CRYPTO)
 
 ifdef ZLIB_NG
 	BASIC_CFLAGS += -DHAVE_ZLIB_NG
-	ifdef ZLIB_NG_PATH
+        ifdef ZLIB_NG_PATH
 		BASIC_CFLAGS += -I$(ZLIB_NG_PATH)/include
 		EXTLIBS += $(call libpath_template,$(ZLIB_NG_PATH)/$(lib))
-	endif
+        endif
 	EXTLIBS += -lz-ng
 else
-	ifdef ZLIB_PATH
+        ifdef ZLIB_PATH
 		BASIC_CFLAGS += -I$(ZLIB_PATH)/include
 		EXTLIBS += $(call libpath_template,$(ZLIB_PATH)/$(lib))
-	endif
+        endif
 	EXTLIBS += -lz
 endif
 
diff --git a/builtin/check-mailmap.c b/builtin/check-mailmap.c
index df00b5ee13..be2cebe121 100644
--- a/builtin/check-mailmap.c
+++ b/builtin/check-mailmap.c
@@ -35,7 +35,7 @@ static void check_mailmap(struct string_list *mailmap, const char *contact)
 		mail = ident.mail_begin;
 		maillen = ident.mail_end - ident.mail_begin;
 	} else {
-		name = NULL;
+		name = "";
 		namelen = 0;
 		mail = contact;
 		maillen = strlen(contact);
diff --git a/builtin/clone.c b/builtin/clone.c
index f9a2ecbe9c..add9d8600c 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -342,6 +342,8 @@ static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
 		strbuf_setlen(src, src_len);
 		die(_("failed to iterate over '%s'"), src->buf);
 	}
+
+	dir_iterator_free(iter);
 }
 
 static void clone_local(const char *src_repo, const char *dest_repo)
diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index 9a6c8b4e4c..3ec7127b3a 100644
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -18,6 +18,7 @@
 #include "tree.h"
 #include "config.h"
 #include "strvec.h"
+#include "write-or-die.h"
 
 static int line_termination = '\n';
 
@@ -575,7 +576,7 @@ int cmd_merge_tree(int argc,
 	};
 
 	/* Init merge options */
-	init_ui_merge_options(&o.merge_options, the_repository);
+	init_basic_merge_options(&o.merge_options, the_repository);
 
 	/* Parse arguments */
 	original_argc = argc - 1; /* ignoring argv[0] */
@@ -600,7 +601,6 @@ int cmd_merge_tree(int argc,
 		line_termination = '\0';
 		while (strbuf_getline_lf(&buf, stdin) != EOF) {
 			struct strbuf **split;
-			int result;
 			const char *input_merge_base = NULL;
 
 			split = strbuf_split(&buf, ' ');
@@ -617,15 +617,14 @@ int cmd_merge_tree(int argc,
 			if (input_merge_base && split[2] && split[3] && !split[4]) {
 				strbuf_rtrim(split[2]);
 				strbuf_rtrim(split[3]);
-				result = real_merge(&o, input_merge_base, split[2]->buf, split[3]->buf, prefix);
+				real_merge(&o, input_merge_base, split[2]->buf, split[3]->buf, prefix);
 			} else if (!input_merge_base && !split[2]) {
-				result = real_merge(&o, NULL, split[0]->buf, split[1]->buf, prefix);
+				real_merge(&o, NULL, split[0]->buf, split[1]->buf, prefix);
 			} else {
 				die(_("malformed input line: '%s'."), buf.buf);
 			}
+			maybe_flush_or_die(stdout, "stdout");
 
-			if (result < 0)
-				die(_("merging cannot continue; got unclean result of %d"), result);
 			strbuf_list_free(split);
 		}
 		strbuf_release(&buf);
diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 4d35bdc4b4..1d541e13ad 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -179,7 +179,8 @@ static int parse_next_oid(const char **next, const char *end,
 		(*next)++;
 		*next = parse_arg(*next, &arg);
 		if (arg.len) {
-			if (repo_get_oid(the_repository, arg.buf, oid))
+			if (repo_get_oid_with_flags(the_repository, arg.buf, oid,
+						    GET_OID_SKIP_AMBIGUITY_CHECK))
 				goto invalid;
 		} else {
 			/* Without -z, an empty value means all zeros: */
@@ -197,7 +198,8 @@ static int parse_next_oid(const char **next, const char *end,
 		*next += arg.len;
 
 		if (arg.len) {
-			if (repo_get_oid(the_repository, arg.buf, oid))
+			if (repo_get_oid_with_flags(the_repository, arg.buf, oid,
+						    GET_OID_SKIP_AMBIGUITY_CHECK))
 				goto invalid;
 		} else if (flags & PARSE_SHA1_ALLOW_EMPTY) {
 			/* With -z, treat an empty value as all zeros: */
@@ -299,7 +301,8 @@ static void parse_cmd_symref_update(struct ref_transaction *transaction,
 			die("symref-update %s: expected old value", refname);
 
 		if (!strcmp(old_arg, "oid")) {
-			if (repo_get_oid(the_repository, old_target, &old_oid))
+			if (repo_get_oid_with_flags(the_repository, old_target, &old_oid,
+						    GET_OID_SKIP_AMBIGUITY_CHECK))
 				die("symref-update %s: invalid oid: %s", refname, old_target);
 
 			have_old_oid = 1;
@@ -772,7 +775,8 @@ int cmd_update_ref(int argc,
 		refname = argv[0];
 		value = argv[1];
 		oldval = argv[2];
-		if (repo_get_oid(the_repository, value, &oid))
+		if (repo_get_oid_with_flags(the_repository, value, &oid,
+					    GET_OID_SKIP_AMBIGUITY_CHECK))
 			die("%s: not a valid SHA1", value);
 	}
 
@@ -783,7 +787,8 @@ int cmd_update_ref(int argc,
 			 * must not already exist:
 			 */
 			oidclr(&oldoid, the_repository->hash_algo);
-		else if (repo_get_oid(the_repository, oldval, &oldoid))
+		else if (repo_get_oid_with_flags(the_repository, oldval, &oldoid,
+						 GET_OID_SKIP_AMBIGUITY_CHECK))
 			die("%s: not a valid old SHA1", oldval);
 	}
 
diff --git a/builtin/update-server-info.c b/builtin/update-server-info.c
index 47a3f0bdd9..d7467290a8 100644
--- a/builtin/update-server-info.c
+++ b/builtin/update-server-info.c
@@ -1,4 +1,3 @@
-#define USE_THE_REPOSITORY_VARIABLE
 #include "builtin.h"
 #include "config.h"
 #include "gettext.h"
@@ -13,7 +12,7 @@ static const char * const update_server_info_usage[] = {
 int cmd_update_server_info(int argc,
 			   const char **argv,
 			   const char *prefix,
-			   struct repository *repo UNUSED)
+			   struct repository *repo)
 {
 	int force = 0;
 	struct option options[] = {
@@ -21,11 +20,12 @@ int cmd_update_server_info(int argc,
 		OPT_END()
 	};
 
-	git_config(git_default_config, NULL);
+	if (repo)
+		repo_config(repo, git_default_config, NULL);
 	argc = parse_options(argc, argv, prefix, options,
 			     update_server_info_usage, 0);
 	if (argc > 0)
 		usage_with_options(update_server_info_usage, options);
 
-	return !!update_server_info(the_repository, force);
+	return !!update_server_info(repo, force);
 }
diff --git a/compat/mingw.c b/compat/mingw.c
index 1d5b211b54..f524c54d06 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -2278,7 +2278,9 @@ repeat:
 
 		old_handle = CreateFileW(wpold, DELETE,
 					 FILE_SHARE_WRITE | FILE_SHARE_READ | FILE_SHARE_DELETE,
-					 NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+					 NULL, OPEN_EXISTING,
+					 FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT,
+					 NULL);
 		if (old_handle == INVALID_HANDLE_VALUE) {
 			errno = err_win_to_posix(GetLastError());
 			return -1;
diff --git a/contrib/credential/libsecret/Makefile b/contrib/credential/libsecret/Makefile
index 3e67552cc5..97ce9c92fb 100644
--- a/contrib/credential/libsecret/Makefile
+++ b/contrib/credential/libsecret/Makefile
@@ -1,3 +1,6 @@
+# The default target of this Makefile is...
+all::
+
 MAIN:=git-credential-libsecret
 all:: $(MAIN)
 
diff --git a/contrib/credential/osxkeychain/Makefile b/contrib/credential/osxkeychain/Makefile
index 238f5f8c36..0948297e20 100644
--- a/contrib/credential/osxkeychain/Makefile
+++ b/contrib/credential/osxkeychain/Makefile
@@ -1,3 +1,4 @@
+# The default target of this Makefile is...
 all:: git-credential-osxkeychain
 
 CC = gcc
diff --git a/contrib/credential/wincred/Makefile b/contrib/credential/wincred/Makefile
index 6e992c0866..5b795fc9fe 100644
--- a/contrib/credential/wincred/Makefile
+++ b/contrib/credential/wincred/Makefile
@@ -1,4 +1,5 @@
-all: git-credential-wincred.exe
+# The default target of this Makefile is...
+all:: git-credential-wincred.exe
 
 -include ../../../config.mak.autogen
 -include ../../../config.mak
diff --git a/contrib/diff-highlight/Makefile b/contrib/diff-highlight/Makefile
index f2be7cc924..33c2ccc9f7 100644
--- a/contrib/diff-highlight/Makefile
+++ b/contrib/diff-highlight/Makefile
@@ -1,4 +1,5 @@
-all: diff-highlight
+# The default target of this Makefile is...
+all:: diff-highlight
 
 PERL_PATH = /usr/bin/perl
 -include ../../config.mak
diff --git a/contrib/diff-highlight/t/Makefile b/contrib/diff-highlight/t/Makefile
index 5ff5275496..2a98541477 100644
--- a/contrib/diff-highlight/t/Makefile
+++ b/contrib/diff-highlight/t/Makefile
@@ -1,3 +1,6 @@
+# The default target of this Makefile is...
+all::
+
 -include ../../../config.mak.autogen
 -include ../../../config.mak
 
@@ -6,7 +9,7 @@ SHELL_PATH ?= $(SHELL)
 SHELL_PATH_SQ = $(subst ','\'',$(SHELL_PATH))
 T = $(wildcard t[0-9][0-9][0-9][0-9]-*.sh)
 
-all: test
+all:: test
 test: $(T)
 
 .PHONY: help clean all test $(T)
diff --git a/contrib/mw-to-git/Makefile b/contrib/mw-to-git/Makefile
index 4e603512a3..497ac434d6 100644
--- a/contrib/mw-to-git/Makefile
+++ b/contrib/mw-to-git/Makefile
@@ -12,6 +12,9 @@
 #
 #   make install
 
+# The default target of this Makefile is...
+all::
+
 GIT_MEDIAWIKI_PM=Git/Mediawiki.pm
 SCRIPT_PERL=git-remote-mediawiki.perl
 SCRIPT_PERL+=git-mw.perl
@@ -27,7 +30,7 @@ INSTLIBDIR=$(shell $(MAKE) -C $(GIT_ROOT_DIR)/ \
 DESTDIR_SQ = $(subst ','\'',$(DESTDIR))
 INSTLIBDIR_SQ = $(subst ','\'',$(INSTLIBDIR))
 
-all: build
+all:: build
 
 test: all
 	$(MAKE) -C t
diff --git a/contrib/mw-to-git/t/Makefile b/contrib/mw-to-git/t/Makefile
index f422203fa0..6c9f377caa 100644
--- a/contrib/mw-to-git/t/Makefile
+++ b/contrib/mw-to-git/t/Makefile
@@ -8,7 +8,8 @@
 #
 ## Test git-remote-mediawiki
 
-all: test
+# The default target of this Makefile is...
+all:: test
 
 -include ../../../config.mak.autogen
 -include ../../../config.mak
diff --git a/contrib/persistent-https/Makefile b/contrib/persistent-https/Makefile
index 52b84ba3d4..691737e76b 100644
--- a/contrib/persistent-https/Makefile
+++ b/contrib/persistent-https/Makefile
@@ -12,10 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# The default target of this Makefile is...
+all::
+
 BUILD_LABEL=$(shell cut -d" " -f3 ../../GIT-VERSION-FILE)
 TAR_OUT=$(shell go env GOOS)_$(shell go env GOARCH).tar.gz
 
-all: git-remote-persistent-https git-remote-persistent-https--proxy \
+all:: git-remote-persistent-https git-remote-persistent-https--proxy \
 	git-remote-persistent-http
 
 git-remote-persistent-https--proxy: git-remote-persistent-https
diff --git a/contrib/subtree/t/Makefile b/contrib/subtree/t/Makefile
index 093399c788..2a85f5ee84 100644
--- a/contrib/subtree/t/Makefile
+++ b/contrib/subtree/t/Makefile
@@ -3,6 +3,9 @@
 # Copyright (c) 2005 Junio C Hamano
 #
 
+# The default target of this Makefile is...
+all::
+
 -include ../../../config.mak.autogen
 -include ../../../config.mak
 
@@ -31,7 +34,7 @@ TSVN = $(sort $(wildcard t91[0-9][0-9]-*.sh))
 TGITWEB = $(sort $(wildcard t95[0-9][0-9]-*.sh))
 THELPERS = $(sort $(filter-out $(T),$(wildcard *.sh)))
 
-all: $(DEFAULT_TEST_TARGET)
+all:: $(DEFAULT_TEST_TARGET)
 
 test: pre-clean $(TEST_LINT)
 	$(MAKE) aggregate-results-and-cleanup
diff --git a/diff.c b/diff.c
index 019fb893a7..c89c15d98e 100644
--- a/diff.c
+++ b/diff.c
@@ -5493,6 +5493,8 @@ static int diff_opt_pickaxe_regex(const struct option *opt,
 	BUG_ON_OPT_NEG(unset);
 	options->pickaxe = arg;
 	options->pickaxe_opts |= DIFF_PICKAXE_KIND_G;
+	if (arg && !*arg)
+		return error(_("-G requires a non-empty argument"));
 	return 0;
 }
 
@@ -5504,6 +5506,8 @@ static int diff_opt_pickaxe_string(const struct option *opt,
 	BUG_ON_OPT_NEG(unset);
 	options->pickaxe = arg;
 	options->pickaxe_opts |= DIFF_PICKAXE_KIND_S;
+	if (arg && !*arg)
+		return error(_("-S requires a non-empty argument"));
 	return 0;
 }
 
diff --git a/dir-iterator.c b/dir-iterator.c
index de619846f2..857e1d9bda 100644
--- a/dir-iterator.c
+++ b/dir-iterator.c
@@ -193,9 +193,9 @@ int dir_iterator_advance(struct dir_iterator *dir_iterator)
 
 	if (S_ISDIR(iter->base.st.st_mode) && push_level(iter)) {
 		if (errno != ENOENT && iter->flags & DIR_ITERATOR_PEDANTIC)
-			goto error_out;
+			return ITER_ERROR;
 		if (iter->levels_nr == 0)
-			goto error_out;
+			return ITER_ERROR;
 	}
 
 	/* Loop until we find an entry that we can give back to the caller. */
@@ -211,11 +211,11 @@ int dir_iterator_advance(struct dir_iterator *dir_iterator)
 			int ret = next_directory_entry(level->dir, iter->base.path.buf, &de);
 			if (ret < 0) {
 				if (iter->flags & DIR_ITERATOR_PEDANTIC)
-					goto error_out;
+					return ITER_ERROR;
 				continue;
 			} else if (ret > 0) {
 				if (pop_level(iter) == 0)
-					return dir_iterator_abort(dir_iterator);
+					return ITER_DONE;
 				continue;
 			}
 
@@ -223,7 +223,7 @@ int dir_iterator_advance(struct dir_iterator *dir_iterator)
 		} else {
 			if (level->entries_idx >= level->entries.nr) {
 				if (pop_level(iter) == 0)
-					return dir_iterator_abort(dir_iterator);
+					return ITER_DONE;
 				continue;
 			}
 
@@ -232,22 +232,21 @@ int dir_iterator_advance(struct dir_iterator *dir_iterator)
 
 		if (prepare_next_entry_data(iter, name)) {
 			if (errno != ENOENT && iter->flags & DIR_ITERATOR_PEDANTIC)
-				goto error_out;
+				return ITER_ERROR;
 			continue;
 		}
 
 		return ITER_OK;
 	}
-
-error_out:
-	dir_iterator_abort(dir_iterator);
-	return ITER_ERROR;
 }
 
-int dir_iterator_abort(struct dir_iterator *dir_iterator)
+void dir_iterator_free(struct dir_iterator *dir_iterator)
 {
 	struct dir_iterator_int *iter = (struct dir_iterator_int *)dir_iterator;
 
+	if (!iter)
+		return;
+
 	for (; iter->levels_nr; iter->levels_nr--) {
 		struct dir_iterator_level *level =
 			&iter->levels[iter->levels_nr - 1];
@@ -266,7 +265,6 @@ int dir_iterator_abort(struct dir_iterator *dir_iterator)
 	free(iter->levels);
 	strbuf_release(&iter->base.path);
 	free(iter);
-	return ITER_DONE;
 }
 
 struct dir_iterator *dir_iterator_begin(const char *path, unsigned int flags)
@@ -301,7 +299,7 @@ struct dir_iterator *dir_iterator_begin(const char *path, unsigned int flags)
 	return dir_iterator;
 
 error_out:
-	dir_iterator_abort(dir_iterator);
+	dir_iterator_free(dir_iterator);
 	errno = saved_errno;
 	return NULL;
 }
diff --git a/dir-iterator.h b/dir-iterator.h
index 6d438809b6..ccd6a19734 100644
--- a/dir-iterator.h
+++ b/dir-iterator.h
@@ -28,7 +28,7 @@
  *
  *     while ((ok = dir_iterator_advance(iter)) == ITER_OK) {
  *             if (want_to_stop_iteration()) {
- *                     ok = dir_iterator_abort(iter);
+ *                     ok = ITER_DONE;
  *                     break;
  *             }
  *
@@ -39,6 +39,7 @@
  *
  *     if (ok != ITER_DONE)
  *             handle_error();
+ *     dir_iterator_free(iter);
  *
  * Callers are allowed to modify iter->path while they are working,
  * but they must restore it to its original contents before calling
@@ -107,11 +108,7 @@ struct dir_iterator *dir_iterator_begin(const char *path, unsigned int flags);
  */
 int dir_iterator_advance(struct dir_iterator *iterator);
 
-/*
- * End the iteration before it has been exhausted. Free the
- * dir_iterator and any associated resources and return ITER_DONE. On
- * error, free the dir_iterator and return ITER_ERROR.
- */
-int dir_iterator_abort(struct dir_iterator *iterator);
+/* Free the dir_iterator and any associated resources. */
+void dir_iterator_free(struct dir_iterator *iterator);
 
 #endif
diff --git a/git-gui/Makefile b/git-gui/Makefile
index 667c39ed56..6c5a12bc32 100644
--- a/git-gui/Makefile
+++ b/git-gui/Makefile
@@ -1,3 +1,4 @@
+# The default target of this Makefile is...
 all::
 
 # Define V=1 to have a more verbose compile.
diff --git a/git-gui/po/glossary/Makefile b/git-gui/po/glossary/Makefile
index 749aa2e7ec..e656b0d2b0 100644
--- a/git-gui/po/glossary/Makefile
+++ b/git-gui/po/glossary/Makefile
@@ -1,3 +1,6 @@
+# The default target of this Makefile is...
+update-po::
+
 PO_TEMPLATE = git-gui-glossary.pot
 
 ALL_POFILES = $(wildcard *.po)
diff --git a/hash.h b/hash.h
index 4367acfec5..5e3c462dc5 100644
--- a/hash.h
+++ b/hash.h
@@ -193,17 +193,18 @@ struct object_id {
 	int algo;	/* XXX requires 4-byte alignment */
 };
 
-#define GET_OID_QUIETLY           01
-#define GET_OID_COMMIT            02
-#define GET_OID_COMMITTISH        04
-#define GET_OID_TREE             010
-#define GET_OID_TREEISH          020
-#define GET_OID_BLOB             040
-#define GET_OID_FOLLOW_SYMLINKS 0100
-#define GET_OID_RECORD_PATH     0200
-#define GET_OID_ONLY_TO_DIE    04000
-#define GET_OID_REQUIRE_PATH  010000
-#define GET_OID_HASH_ANY      020000
+#define GET_OID_QUIETLY                  01
+#define GET_OID_COMMIT                   02
+#define GET_OID_COMMITTISH               04
+#define GET_OID_TREE                    010
+#define GET_OID_TREEISH                 020
+#define GET_OID_BLOB                    040
+#define GET_OID_FOLLOW_SYMLINKS        0100
+#define GET_OID_RECORD_PATH            0200
+#define GET_OID_ONLY_TO_DIE           04000
+#define GET_OID_REQUIRE_PATH         010000
+#define GET_OID_HASH_ANY             020000
+#define GET_OID_SKIP_AMBIGUITY_CHECK 040000
 
 #define GET_OID_DISAMBIGUATORS \
 	(GET_OID_COMMIT | GET_OID_COMMITTISH | \
diff --git a/iterator.h b/iterator.h
index 0f6900e43a..6b77dcc262 100644
--- a/iterator.h
+++ b/iterator.h
@@ -12,7 +12,7 @@
 #define ITER_OK 0
 
 /*
- * The iterator is exhausted and has been freed.
+ * The iterator is exhausted.
  */
 #define ITER_DONE -1
 
diff --git a/meson.build b/meson.build
index bf95576f83..021a182135 100644
--- a/meson.build
+++ b/meson.build
@@ -778,7 +778,22 @@ endif
 
 # Note that we only set NO_PERL if the Perl features were disabled by the user.
 # It may not be set when we have found Perl, but only use it to run tests.
-perl = find_program('perl', version: '>=5.8.1', dirs: program_path, required: perl_required)
+#
+# At the time of writing, executing `perl --version` results in a string
+# similar to the following output:
+#
+#     This is perl 5, version 40, subversion 0 (v5.40.0) built for x86_64-linux-thread-multi
+#
+# Meson picks up the "40" as version number instead of using "v5.40.0"
+# due to the regular expression it uses. This got fixed in Meson 1.7.0,
+# but meanwhile we have to either use `-V:version` instead of `--version`,
+# which we can do starting with Meson 1.5.0 and newer, or we have to
+# match against the minor version.
+if meson.version().version_compare('>=1.5.0')
+  perl = find_program('perl', dirs: program_path, required: perl_required, version: '>=5.26.0', version_argument: '-V:version')
+else
+  perl = find_program('perl', dirs: program_path, required: perl_required, version: '>=26')
+endif
 perl_features_enabled = perl.found() and get_option('perl').allowed()
 if perl_features_enabled
   build_options_config.set('NO_PERL', '')
diff --git a/object-name.c b/object-name.c
index 945d5bdef2..85444dbb15 100644
--- a/object-name.c
+++ b/object-name.c
@@ -961,7 +961,9 @@ static int get_oid_basic(struct repository *r, const char *str, int len,
 	int fatal = !(flags & GET_OID_QUIETLY);
 
 	if (len == r->hash_algo->hexsz && !get_oid_hex(str, oid)) {
-		if (repo_settings_get_warn_ambiguous_refs(r) && warn_on_object_refname_ambiguity) {
+		if (!(flags & GET_OID_SKIP_AMBIGUITY_CHECK) &&
+		    repo_settings_get_warn_ambiguous_refs(r) &&
+		    warn_on_object_refname_ambiguity) {
 			refs_found = repo_dwim_ref(r, str, len, &tmp_oid, &real_ref, 0);
 			if (refs_found > 0) {
 				warning(warn_msg, len, str);
@@ -1794,18 +1796,20 @@ void object_context_release(struct object_context *ctx)
 	strbuf_release(&ctx->symlink_path);
 }
 
-/*
- * This is like "get_oid_basic()", except it allows "object ID expressions",
- * notably "xyz^" for "parent of xyz"
- */
-int repo_get_oid(struct repository *r, const char *name, struct object_id *oid)
+int repo_get_oid_with_flags(struct repository *r, const char *name,
+			    struct object_id *oid, unsigned flags)
 {
 	struct object_context unused;
-	int ret = get_oid_with_context(r, name, 0, oid, &unused);
+	int ret = get_oid_with_context(r, name, flags, oid, &unused);
 	object_context_release(&unused);
 	return ret;
 }
 
+int repo_get_oid(struct repository *r, const char *name, struct object_id *oid)
+{
+	return repo_get_oid_with_flags(r, name, oid, 0);
+}
+
 /*
  * This returns a non-zero value if the string (built using printf
  * format and the given arguments) is not a valid object.
diff --git a/object-name.h b/object-name.h
index 8dba4a47a4..cda4934cd5 100644
--- a/object-name.h
+++ b/object-name.h
@@ -51,6 +51,12 @@ void strbuf_repo_add_unique_abbrev(struct strbuf *sb, struct repository *repo,
 void strbuf_add_unique_abbrev(struct strbuf *sb, const struct object_id *oid,
 			      int abbrev_len);
 
+/*
+ * This is like "get_oid_basic()", except it allows "object ID expressions",
+ * notably "xyz^" for "parent of xyz". Accepts GET_OID_* flags.
+ */
+int repo_get_oid_with_flags(struct repository *r, const char *str,
+			    struct object_id *oid, unsigned flags);
 int repo_get_oid(struct repository *r, const char *str, struct object_id *oid);
 __attribute__((format (printf, 2, 3)))
 int get_oidf(struct object_id *oid, const char *fmt, ...);
diff --git a/refs.c b/refs.c
index e1a6a2d189..79d5a8b8d4 100644
--- a/refs.c
+++ b/refs.c
@@ -2475,19 +2475,18 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	return ret;
 }
 
-int refs_verify_refname_available(struct ref_store *refs,
-				  const char *refname,
-				  const struct string_list *extras,
-				  const struct string_list *skip,
-				  unsigned int initial_transaction,
-				  struct strbuf *err)
+int refs_verify_refnames_available(struct ref_store *refs,
+				   const struct string_list *refnames,
+				   const struct string_list *extras,
+				   const struct string_list *skip,
+				   unsigned int initial_transaction,
+				   struct strbuf *err)
 {
-	const char *slash;
-	const char *extra_refname;
 	struct strbuf dirname = STRBUF_INIT;
 	struct strbuf referent = STRBUF_INIT;
-	struct object_id oid;
-	unsigned int type;
+	struct string_list_item *item;
+	struct ref_iterator *iter = NULL;
+	struct strset dirnames;
 	int ret = -1;
 
 	/*
@@ -2497,86 +2496,130 @@ int refs_verify_refname_available(struct ref_store *refs,
 
 	assert(err);
 
-	strbuf_grow(&dirname, strlen(refname) + 1);
-	for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
-		/*
-		 * Just saying "Is a directory" when we e.g. can't
-		 * lock some multi-level ref isn't very informative,
-		 * the user won't be told *what* is a directory, so
-		 * let's not use strerror() below.
-		 */
-		int ignore_errno;
-		/* Expand dirname to the new prefix, not including the trailing slash: */
-		strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);
+	strset_init(&dirnames);
+
+	for_each_string_list_item(item, refnames) {
+		const char *refname = item->string;
+		const char *extra_refname;
+		struct object_id oid;
+		unsigned int type;
+		const char *slash;
+
+		strbuf_reset(&dirname);
+
+		for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
+			/*
+			 * Just saying "Is a directory" when we e.g. can't
+			 * lock some multi-level ref isn't very informative,
+			 * the user won't be told *what* is a directory, so
+			 * let's not use strerror() below.
+			 */
+			int ignore_errno;
+
+			/* Expand dirname to the new prefix, not including the trailing slash: */
+			strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);
+
+			/*
+			 * We are still at a leading dir of the refname (e.g.,
+			 * "refs/foo"; if there is a reference with that name,
+			 * it is a conflict, *unless* it is in skip.
+			 */
+			if (skip && string_list_has_string(skip, dirname.buf))
+				continue;
+
+			/*
+			 * If we've already seen the directory we don't need to
+			 * process it again. Skip it to avoid checking checking
+			 * common prefixes like "refs/heads/" repeatedly.
+			 */
+			if (!strset_add(&dirnames, dirname.buf))
+				continue;
+
+			if (!initial_transaction &&
+			    !refs_read_raw_ref(refs, dirname.buf, &oid, &referent,
+					       &type, &ignore_errno)) {
+				strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
+					    dirname.buf, refname);
+				goto cleanup;
+			}
+
+			if (extras && string_list_has_string(extras, dirname.buf)) {
+				strbuf_addf(err, _("cannot process '%s' and '%s' at the same time"),
+					    refname, dirname.buf);
+				goto cleanup;
+			}
+		}
 
 		/*
-		 * We are still at a leading dir of the refname (e.g.,
-		 * "refs/foo"; if there is a reference with that name,
-		 * it is a conflict, *unless* it is in skip.
+		 * We are at the leaf of our refname (e.g., "refs/foo/bar").
+		 * There is no point in searching for a reference with that
+		 * name, because a refname isn't considered to conflict with
+		 * itself. But we still need to check for references whose
+		 * names are in the "refs/foo/bar/" namespace, because they
+		 * *do* conflict.
 		 */
-		if (skip && string_list_has_string(skip, dirname.buf))
-			continue;
+		strbuf_addstr(&dirname, refname + dirname.len);
+		strbuf_addch(&dirname, '/');
 
-		if (!initial_transaction &&
-		    !refs_read_raw_ref(refs, dirname.buf, &oid, &referent,
-				       &type, &ignore_errno)) {
-			strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
-				    dirname.buf, refname);
-			goto cleanup;
-		}
+		if (!initial_transaction) {
+			int ok;
 
-		if (extras && string_list_has_string(extras, dirname.buf)) {
-			strbuf_addf(err, _("cannot process '%s' and '%s' at the same time"),
-				    refname, dirname.buf);
-			goto cleanup;
-		}
-	}
+			if (!iter) {
+				iter = refs_ref_iterator_begin(refs, dirname.buf, NULL, 0,
+							       DO_FOR_EACH_INCLUDE_BROKEN);
+			} else if (ref_iterator_seek(iter, dirname.buf) < 0) {
+				goto cleanup;
+			}
 
-	/*
-	 * We are at the leaf of our refname (e.g., "refs/foo/bar").
-	 * There is no point in searching for a reference with that
-	 * name, because a refname isn't considered to conflict with
-	 * itself. But we still need to check for references whose
-	 * names are in the "refs/foo/bar/" namespace, because they
-	 * *do* conflict.
-	 */
-	strbuf_addstr(&dirname, refname + dirname.len);
-	strbuf_addch(&dirname, '/');
-
-	if (!initial_transaction) {
-		struct ref_iterator *iter;
-		int ok;
-
-		iter = refs_ref_iterator_begin(refs, dirname.buf, NULL, 0,
-					       DO_FOR_EACH_INCLUDE_BROKEN);
-		while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
-			if (skip &&
-			    string_list_has_string(skip, iter->refname))
-				continue;
+			while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
+				if (skip &&
+				    string_list_has_string(skip, iter->refname))
+					continue;
 
-			strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
-				    iter->refname, refname);
-			ref_iterator_abort(iter);
-			goto cleanup;
+				strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
+					    iter->refname, refname);
+				goto cleanup;
+			}
+
+			if (ok != ITER_DONE)
+				BUG("error while iterating over references");
 		}
 
-		if (ok != ITER_DONE)
-			BUG("error while iterating over references");
+		extra_refname = find_descendant_ref(dirname.buf, extras, skip);
+		if (extra_refname) {
+			strbuf_addf(err, _("cannot process '%s' and '%s' at the same time"),
+				    refname, extra_refname);
+			goto cleanup;
+		}
 	}
 
-	extra_refname = find_descendant_ref(dirname.buf, extras, skip);
-	if (extra_refname)
-		strbuf_addf(err, _("cannot process '%s' and '%s' at the same time"),
-			    refname, extra_refname);
-	else
-		ret = 0;
+	ret = 0;
 
 cleanup:
 	strbuf_release(&referent);
 	strbuf_release(&dirname);
+	strset_clear(&dirnames);
+	ref_iterator_free(iter);
 	return ret;
 }
 
+int refs_verify_refname_available(struct ref_store *refs,
+				  const char *refname,
+				  const struct string_list *extras,
+				  const struct string_list *skip,
+				  unsigned int initial_transaction,
+				  struct strbuf *err)
+{
+	struct string_list_item item = { .string = (char *) refname };
+	struct string_list refnames = {
+		.items = &item,
+		.nr = 1,
+	};
+
+	return refs_verify_refnames_available(refs, &refnames, extras, skip,
+					      initial_transaction, err);
+}
+
 struct do_for_each_reflog_help {
 	each_reflog_fn *fn;
 	void *cb_data;
diff --git a/refs.h b/refs.h
index 09be47afbe..b14ba1f9ff 100644
--- a/refs.h
+++ b/refs.h
@@ -124,6 +124,18 @@ int refs_verify_refname_available(struct ref_store *refs,
 				  unsigned int initial_transaction,
 				  struct strbuf *err);
 
+/*
+ * Same as `refs_verify_refname_available()`, but checking for a list of
+ * refnames instead of only a single item. This is more efficient in the case
+ * where one needs to check multiple refnames.
+ */
+int refs_verify_refnames_available(struct ref_store *refs,
+				   const struct string_list *refnames,
+				   const struct string_list *extras,
+				   const struct string_list *skip,
+				   unsigned int initial_transaction,
+				   struct strbuf *err);
+
 int refs_ref_exists(struct ref_store *refs, const char *refname);
 
 int should_autocreate_reflog(enum log_refs_config log_all_ref_updates,
diff --git a/refs/debug.c b/refs/debug.c
index fbc4df08b4..5390fa9c18 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -169,6 +169,16 @@ static int debug_ref_iterator_advance(struct ref_iterator *ref_iterator)
 	return res;
 }
 
+static int debug_ref_iterator_seek(struct ref_iterator *ref_iterator,
+				   const char *prefix)
+{
+	struct debug_ref_iterator *diter =
+		(struct debug_ref_iterator *)ref_iterator;
+	int res = diter->iter->vtable->seek(diter->iter, prefix);
+	trace_printf_key(&trace_refs, "iterator_seek: %s: %d\n", prefix ? prefix : "", res);
+	return res;
+}
+
 static int debug_ref_iterator_peel(struct ref_iterator *ref_iterator,
 				   struct object_id *peeled)
 {
@@ -179,19 +189,19 @@ static int debug_ref_iterator_peel(struct ref_iterator *ref_iterator,
 	return res;
 }
 
-static int debug_ref_iterator_abort(struct ref_iterator *ref_iterator)
+static void debug_ref_iterator_release(struct ref_iterator *ref_iterator)
 {
 	struct debug_ref_iterator *diter =
 		(struct debug_ref_iterator *)ref_iterator;
-	int res = diter->iter->vtable->abort(diter->iter);
-	trace_printf_key(&trace_refs, "iterator_abort: %d\n", res);
-	return res;
+	diter->iter->vtable->release(diter->iter);
+	trace_printf_key(&trace_refs, "iterator_abort\n");
 }
 
 static struct ref_iterator_vtable debug_ref_iterator_vtable = {
 	.advance = debug_ref_iterator_advance,
+	.seek = debug_ref_iterator_seek,
 	.peel = debug_ref_iterator_peel,
-	.abort = debug_ref_iterator_abort,
+	.release = debug_ref_iterator_release,
 };
 
 static struct ref_iterator *
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 29f08dced4..5f921e85eb 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -678,6 +678,7 @@ static void unlock_ref(struct ref_lock *lock)
  */
 static int lock_raw_ref(struct files_ref_store *refs,
 			const char *refname, int mustexist,
+			struct string_list *refnames_to_check,
 			const struct string_list *extras,
 			struct ref_lock **lock_p,
 			struct strbuf *referent,
@@ -855,16 +856,11 @@ retry:
 		}
 
 		/*
-		 * If the ref did not exist and we are creating it,
-		 * make sure there is no existing packed ref that
-		 * conflicts with refname:
+		 * If the ref did not exist and we are creating it, we have to
+		 * make sure there is no existing packed ref that conflicts
+		 * with refname. This check is deferred so that we can batch it.
 		 */
-		if (refs_verify_refname_available(
-				    refs->packed_ref_store, refname,
-				    extras, NULL, 0, err)) {
-			ret = TRANSACTION_NAME_CONFLICT;
-			goto error_return;
-		}
+		string_list_append(refnames_to_check, refname);
 	}
 
 	ret = 0;
@@ -919,13 +915,17 @@ static int files_ref_iterator_advance(struct ref_iterator *ref_iterator)
 		return ITER_OK;
 	}
 
-	iter->iter0 = NULL;
-	if (ref_iterator_abort(ref_iterator) != ITER_DONE)
-		ok = ITER_ERROR;
-
 	return ok;
 }
 
+static int files_ref_iterator_seek(struct ref_iterator *ref_iterator,
+				   const char *prefix)
+{
+	struct files_ref_iterator *iter =
+		(struct files_ref_iterator *)ref_iterator;
+	return ref_iterator_seek(iter->iter0, prefix);
+}
+
 static int files_ref_iterator_peel(struct ref_iterator *ref_iterator,
 				   struct object_id *peeled)
 {
@@ -935,23 +935,18 @@ static int files_ref_iterator_peel(struct ref_iterator *ref_iterator,
 	return ref_iterator_peel(iter->iter0, peeled);
 }
 
-static int files_ref_iterator_abort(struct ref_iterator *ref_iterator)
+static void files_ref_iterator_release(struct ref_iterator *ref_iterator)
 {
 	struct files_ref_iterator *iter =
 		(struct files_ref_iterator *)ref_iterator;
-	int ok = ITER_DONE;
-
-	if (iter->iter0)
-		ok = ref_iterator_abort(iter->iter0);
-
-	base_ref_iterator_free(ref_iterator);
-	return ok;
+	ref_iterator_free(iter->iter0);
 }
 
 static struct ref_iterator_vtable files_ref_iterator_vtable = {
 	.advance = files_ref_iterator_advance,
+	.seek = files_ref_iterator_seek,
 	.peel = files_ref_iterator_peel,
-	.abort = files_ref_iterator_abort,
+	.release = files_ref_iterator_release,
 };
 
 static struct ref_iterator *files_ref_iterator_begin(
@@ -1382,7 +1377,7 @@ static int should_pack_refs(struct files_ref_store *refs,
 				    iter->flags, opts))
 			refcount++;
 		if (refcount >= limit) {
-			ref_iterator_abort(iter);
+			ref_iterator_free(iter);
 			return 1;
 		}
 	}
@@ -1390,6 +1385,7 @@ static int should_pack_refs(struct files_ref_store *refs,
 	if (ret != ITER_DONE)
 		die("error while iterating over references");
 
+	ref_iterator_free(iter);
 	return 0;
 }
 
@@ -1456,6 +1452,7 @@ static int files_pack_refs(struct ref_store *ref_store,
 	packed_refs_unlock(refs->packed_ref_store);
 
 	prune_refs(refs, &refs_to_prune);
+	ref_iterator_free(iter);
 	strbuf_release(&err);
 	return 0;
 }
@@ -2303,35 +2300,33 @@ static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
 		return ITER_OK;
 	}
 
-	iter->dir_iterator = NULL;
-	if (ref_iterator_abort(ref_iterator) == ITER_ERROR)
-		ok = ITER_ERROR;
 	return ok;
 }
 
+static int files_reflog_iterator_seek(struct ref_iterator *ref_iterator UNUSED,
+				      const char *prefix UNUSED)
+{
+	BUG("ref_iterator_seek() called for reflog_iterator");
+}
+
 static int files_reflog_iterator_peel(struct ref_iterator *ref_iterator UNUSED,
 				      struct object_id *peeled UNUSED)
 {
 	BUG("ref_iterator_peel() called for reflog_iterator");
 }
 
-static int files_reflog_iterator_abort(struct ref_iterator *ref_iterator)
+static void files_reflog_iterator_release(struct ref_iterator *ref_iterator)
 {
 	struct files_reflog_iterator *iter =
 		(struct files_reflog_iterator *)ref_iterator;
-	int ok = ITER_DONE;
-
-	if (iter->dir_iterator)
-		ok = dir_iterator_abort(iter->dir_iterator);
-
-	base_ref_iterator_free(ref_iterator);
-	return ok;
+	dir_iterator_free(iter->dir_iterator);
 }
 
 static struct ref_iterator_vtable files_reflog_iterator_vtable = {
 	.advance = files_reflog_iterator_advance,
+	.seek = files_reflog_iterator_seek,
 	.peel = files_reflog_iterator_peel,
-	.abort = files_reflog_iterator_abort,
+	.release = files_reflog_iterator_release,
 };
 
 static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,
@@ -2569,6 +2564,7 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 			       struct ref_update *update,
 			       struct ref_transaction *transaction,
 			       const char *head_ref,
+			       struct string_list *refnames_to_check,
 			       struct string_list *affected_refnames,
 			       struct strbuf *err)
 {
@@ -2597,7 +2593,7 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 		lock->count++;
 	} else {
 		ret = lock_raw_ref(refs, update->refname, mustexist,
-				   affected_refnames,
+				   refnames_to_check, affected_refnames,
 				   &lock, &referent,
 				   &update->type, err);
 		if (ret) {
@@ -2811,6 +2807,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 	size_t i;
 	int ret = 0;
 	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+	struct string_list refnames_to_check = STRING_LIST_INIT_NODUP;
 	char *head_ref = NULL;
 	int head_type;
 	struct files_transaction_backend_data *backend_data;
@@ -2898,7 +2895,8 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 		struct ref_update *update = transaction->updates[i];
 
 		ret = lock_ref_for_update(refs, update, transaction,
-					  head_ref, &affected_refnames, err);
+					  head_ref, &refnames_to_check,
+					  &affected_refnames, err);
 		if (ret)
 			goto cleanup;
 
@@ -2930,6 +2928,26 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 		}
 	}
 
+	/*
+	 * Verify that none of the loose reference that we're about to write
+	 * conflict with any existing packed references. Ideally, we'd do this
+	 * check after the packed-refs are locked so that the file cannot
+	 * change underneath our feet. But introducing such a lock now would
+	 * probably do more harm than good as users rely on there not being a
+	 * global lock with the "files" backend.
+	 *
+	 * Another alternative would be to do the check after the (optional)
+	 * lock, but that would extend the time we spend in the globally-locked
+	 * state.
+	 *
+	 * So instead, we accept the race for now.
+	 */
+	if (refs_verify_refnames_available(refs->packed_ref_store, &refnames_to_check,
+					   &affected_refnames, NULL, 0, err)) {
+		ret = TRANSACTION_NAME_CONFLICT;
+		goto cleanup;
+	}
+
 	if (packed_transaction) {
 		if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
 			ret = TRANSACTION_GENERIC_ERROR;
@@ -2972,6 +2990,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 cleanup:
 	free(head_ref);
 	string_list_clear(&affected_refnames, 0);
+	string_list_clear(&refnames_to_check, 0);
 
 	if (ret)
 		files_transaction_cleanup(refs, transaction);
@@ -3036,6 +3055,7 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 	size_t i;
 	int ret = 0;
 	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+	struct string_list refnames_to_check = STRING_LIST_INIT_NODUP;
 	struct ref_transaction *packed_transaction = NULL;
 	struct ref_transaction *loose_transaction = NULL;
 
@@ -3085,11 +3105,7 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 		    !is_null_oid(&update->old_oid))
 			BUG("initial ref transaction with old_sha1 set");
 
-		if (refs_verify_refname_available(&refs->base, update->refname,
-						  &affected_refnames, NULL, 1, err)) {
-			ret = TRANSACTION_NAME_CONFLICT;
-			goto cleanup;
-		}
+		string_list_append(&refnames_to_check, update->refname);
 
 		/*
 		 * packed-refs don't support symbolic refs, root refs and reflogs,
@@ -3125,8 +3141,19 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 		}
 	}
 
-	if (packed_refs_lock(refs->packed_ref_store, 0, err) ||
-	    ref_transaction_commit(packed_transaction, err)) {
+	if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
+		ret = TRANSACTION_GENERIC_ERROR;
+		goto cleanup;
+	}
+
+	if (refs_verify_refnames_available(&refs->base, &refnames_to_check,
+					   &affected_refnames, NULL, 1, err)) {
+		packed_refs_unlock(refs->packed_ref_store);
+		ret = TRANSACTION_NAME_CONFLICT;
+		goto cleanup;
+	}
+
+	if (ref_transaction_commit(packed_transaction, err)) {
 		ret = TRANSACTION_GENERIC_ERROR;
 		goto cleanup;
 	}
@@ -3147,6 +3174,7 @@ cleanup:
 		ref_transaction_free(packed_transaction);
 	transaction->state = REF_TRANSACTION_CLOSED;
 	string_list_clear(&affected_refnames, 0);
+	string_list_clear(&refnames_to_check, 0);
 	return ret;
 }
 
@@ -3808,6 +3836,7 @@ static int files_fsck_refs_dir(struct ref_store *ref_store,
 		ret = error(_("failed to iterate over '%s'"), sb.buf);
 
 out:
+	dir_iterator_free(iter);
 	strbuf_release(&sb);
 	strbuf_release(&refname);
 	return ret;
diff --git a/refs/iterator.c b/refs/iterator.c
index d25e568bf0..766d96e795 100644
--- a/refs/iterator.c
+++ b/refs/iterator.c
@@ -15,15 +15,26 @@ int ref_iterator_advance(struct ref_iterator *ref_iterator)
 	return ref_iterator->vtable->advance(ref_iterator);
 }
 
+int ref_iterator_seek(struct ref_iterator *ref_iterator,
+		      const char *prefix)
+{
+	return ref_iterator->vtable->seek(ref_iterator, prefix);
+}
+
 int ref_iterator_peel(struct ref_iterator *ref_iterator,
 		      struct object_id *peeled)
 {
 	return ref_iterator->vtable->peel(ref_iterator, peeled);
 }
 
-int ref_iterator_abort(struct ref_iterator *ref_iterator)
+void ref_iterator_free(struct ref_iterator *ref_iterator)
 {
-	return ref_iterator->vtable->abort(ref_iterator);
+	if (ref_iterator) {
+		ref_iterator->vtable->release(ref_iterator);
+		/* Help make use-after-free bugs fail quickly: */
+		ref_iterator->vtable = NULL;
+		free(ref_iterator);
+	}
 }
 
 void base_ref_iterator_init(struct ref_iterator *iter,
@@ -36,20 +47,19 @@ void base_ref_iterator_init(struct ref_iterator *iter,
 	iter->flags = 0;
 }
 
-void base_ref_iterator_free(struct ref_iterator *iter)
-{
-	/* Help make use-after-free bugs fail quickly: */
-	iter->vtable = NULL;
-	free(iter);
-}
-
 struct empty_ref_iterator {
 	struct ref_iterator base;
 };
 
-static int empty_ref_iterator_advance(struct ref_iterator *ref_iterator)
+static int empty_ref_iterator_advance(struct ref_iterator *ref_iterator UNUSED)
+{
+	return ITER_DONE;
+}
+
+static int empty_ref_iterator_seek(struct ref_iterator *ref_iterator UNUSED,
+				   const char *prefix UNUSED)
 {
-	return ref_iterator_abort(ref_iterator);
+	return 0;
 }
 
 static int empty_ref_iterator_peel(struct ref_iterator *ref_iterator UNUSED,
@@ -58,16 +68,15 @@ static int empty_ref_iterator_peel(struct ref_iterator *ref_iterator UNUSED,
 	BUG("peel called for empty iterator");
 }
 
-static int empty_ref_iterator_abort(struct ref_iterator *ref_iterator)
+static void empty_ref_iterator_release(struct ref_iterator *ref_iterator UNUSED)
 {
-	base_ref_iterator_free(ref_iterator);
-	return ITER_DONE;
 }
 
 static struct ref_iterator_vtable empty_ref_iterator_vtable = {
 	.advance = empty_ref_iterator_advance,
+	.seek = empty_ref_iterator_seek,
 	.peel = empty_ref_iterator_peel,
-	.abort = empty_ref_iterator_abort,
+	.release = empty_ref_iterator_release,
 };
 
 struct ref_iterator *empty_ref_iterator_begin(void)
@@ -87,7 +96,8 @@ int is_empty_ref_iterator(struct ref_iterator *ref_iterator)
 struct merge_ref_iterator {
 	struct ref_iterator base;
 
-	struct ref_iterator *iter0, *iter1;
+	struct ref_iterator *iter0, *iter0_owned;
+	struct ref_iterator *iter1, *iter1_owned;
 
 	ref_iterator_select_fn *select;
 	void *cb_data;
@@ -179,9 +189,8 @@ static int merge_ref_iterator_advance(struct ref_iterator *ref_iterator)
 			iter->select(iter->iter0, iter->iter1, iter->cb_data);
 
 		if (selection == ITER_SELECT_DONE) {
-			return ref_iterator_abort(ref_iterator);
+			return ITER_DONE;
 		} else if (selection == ITER_SELECT_ERROR) {
-			ref_iterator_abort(ref_iterator);
 			return ITER_ERROR;
 		}
 
@@ -211,10 +220,31 @@ static int merge_ref_iterator_advance(struct ref_iterator *ref_iterator)
 	}
 
 error:
-	ref_iterator_abort(ref_iterator);
 	return ITER_ERROR;
 }
 
+static int merge_ref_iterator_seek(struct ref_iterator *ref_iterator,
+				   const char *prefix)
+{
+	struct merge_ref_iterator *iter =
+		(struct merge_ref_iterator *)ref_iterator;
+	int ret;
+
+	iter->current = NULL;
+	iter->iter0 = iter->iter0_owned;
+	iter->iter1 = iter->iter1_owned;
+
+	ret = ref_iterator_seek(iter->iter0, prefix);
+	if (ret < 0)
+		return ret;
+
+	ret = ref_iterator_seek(iter->iter1, prefix);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
 static int merge_ref_iterator_peel(struct ref_iterator *ref_iterator,
 				   struct object_id *peeled)
 {
@@ -227,28 +257,19 @@ static int merge_ref_iterator_peel(struct ref_iterator *ref_iterator,
 	return ref_iterator_peel(*iter->current, peeled);
 }
 
-static int merge_ref_iterator_abort(struct ref_iterator *ref_iterator)
+static void merge_ref_iterator_release(struct ref_iterator *ref_iterator)
 {
 	struct merge_ref_iterator *iter =
 		(struct merge_ref_iterator *)ref_iterator;
-	int ok = ITER_DONE;
-
-	if (iter->iter0) {
-		if (ref_iterator_abort(iter->iter0) != ITER_DONE)
-			ok = ITER_ERROR;
-	}
-	if (iter->iter1) {
-		if (ref_iterator_abort(iter->iter1) != ITER_DONE)
-			ok = ITER_ERROR;
-	}
-	base_ref_iterator_free(ref_iterator);
-	return ok;
+	ref_iterator_free(iter->iter0_owned);
+	ref_iterator_free(iter->iter1_owned);
 }
 
 static struct ref_iterator_vtable merge_ref_iterator_vtable = {
 	.advance = merge_ref_iterator_advance,
+	.seek = merge_ref_iterator_seek,
 	.peel = merge_ref_iterator_peel,
-	.abort = merge_ref_iterator_abort,
+	.release = merge_ref_iterator_release,
 };
 
 struct ref_iterator *merge_ref_iterator_begin(
@@ -267,8 +288,8 @@ struct ref_iterator *merge_ref_iterator_begin(
 	 */
 
 	base_ref_iterator_init(ref_iterator, &merge_ref_iterator_vtable);
-	iter->iter0 = iter0;
-	iter->iter1 = iter1;
+	iter->iter0 = iter->iter0_owned = iter0;
+	iter->iter1 = iter->iter1_owned = iter1;
 	iter->select = select;
 	iter->cb_data = cb_data;
 	iter->current = NULL;
@@ -310,10 +331,10 @@ struct ref_iterator *overlay_ref_iterator_begin(
 	 * them.
 	 */
 	if (is_empty_ref_iterator(front)) {
-		ref_iterator_abort(front);
+		ref_iterator_free(front);
 		return back;
 	} else if (is_empty_ref_iterator(back)) {
-		ref_iterator_abort(back);
+		ref_iterator_free(back);
 		return front;
 	}
 
@@ -350,19 +371,15 @@ static int prefix_ref_iterator_advance(struct ref_iterator *ref_iterator)
 
 	while ((ok = ref_iterator_advance(iter->iter0)) == ITER_OK) {
 		int cmp = compare_prefix(iter->iter0->refname, iter->prefix);
-
 		if (cmp < 0)
 			continue;
-
-		if (cmp > 0) {
-			/*
-			 * As the source iterator is ordered, we
-			 * can stop the iteration as soon as we see a
-			 * refname that comes after the prefix:
-			 */
-			ok = ref_iterator_abort(iter->iter0);
-			break;
-		}
+		/*
+		 * As the source iterator is ordered, we
+		 * can stop the iteration as soon as we see a
+		 * refname that comes after the prefix:
+		 */
+		if (cmp > 0)
+			return ITER_DONE;
 
 		if (iter->trim) {
 			/*
@@ -386,12 +403,19 @@ static int prefix_ref_iterator_advance(struct ref_iterator *ref_iterator)
 		return ITER_OK;
 	}
 
-	iter->iter0 = NULL;
-	if (ref_iterator_abort(ref_iterator) != ITER_DONE)
-		return ITER_ERROR;
 	return ok;
 }
 
+static int prefix_ref_iterator_seek(struct ref_iterator *ref_iterator,
+				    const char *prefix)
+{
+	struct prefix_ref_iterator *iter =
+		(struct prefix_ref_iterator *)ref_iterator;
+	free(iter->prefix);
+	iter->prefix = xstrdup_or_null(prefix);
+	return ref_iterator_seek(iter->iter0, prefix);
+}
+
 static int prefix_ref_iterator_peel(struct ref_iterator *ref_iterator,
 				    struct object_id *peeled)
 {
@@ -401,23 +425,19 @@ static int prefix_ref_iterator_peel(struct ref_iterator *ref_iterator,
 	return ref_iterator_peel(iter->iter0, peeled);
 }
 
-static int prefix_ref_iterator_abort(struct ref_iterator *ref_iterator)
+static void prefix_ref_iterator_release(struct ref_iterator *ref_iterator)
 {
 	struct prefix_ref_iterator *iter =
 		(struct prefix_ref_iterator *)ref_iterator;
-	int ok = ITER_DONE;
-
-	if (iter->iter0)
-		ok = ref_iterator_abort(iter->iter0);
+	ref_iterator_free(iter->iter0);
 	free(iter->prefix);
-	base_ref_iterator_free(ref_iterator);
-	return ok;
 }
 
 static struct ref_iterator_vtable prefix_ref_iterator_vtable = {
 	.advance = prefix_ref_iterator_advance,
+	.seek = prefix_ref_iterator_seek,
 	.peel = prefix_ref_iterator_peel,
-	.abort = prefix_ref_iterator_abort,
+	.release = prefix_ref_iterator_release,
 };
 
 struct ref_iterator *prefix_ref_iterator_begin(struct ref_iterator *iter0,
@@ -453,20 +473,14 @@ int do_for_each_ref_iterator(struct ref_iterator *iter,
 	current_ref_iter = iter;
 	while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
 		retval = fn(iter->refname, iter->referent, iter->oid, iter->flags, cb_data);
-		if (retval) {
-			/*
-			 * If ref_iterator_abort() returns ITER_ERROR,
-			 * we ignore that error in deference to the
-			 * callback function's return value.
-			 */
-			ref_iterator_abort(iter);
+		if (retval)
 			goto out;
-		}
 	}
 
 out:
 	current_ref_iter = old_ref_iter;
 	if (ok == ITER_ERROR)
-		return -1;
+		retval = -1;
+	ref_iterator_free(iter);
 	return retval;
 }
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index a7b6f74b6e..f4c82ba2c7 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -819,6 +819,8 @@ struct packed_ref_iterator {
 
 	struct snapshot *snapshot;
 
+	char *prefix;
+
 	/* The current position in the snapshot's buffer: */
 	const char *pos;
 
@@ -841,11 +843,9 @@ struct packed_ref_iterator {
 };
 
 /*
- * Move the iterator to the next record in the snapshot, without
- * respect for whether the record is actually required by the current
- * iteration. Adjust the fields in `iter` and return `ITER_OK` or
- * `ITER_DONE`. This function does not free the iterator in the case
- * of `ITER_DONE`.
+ * Move the iterator to the next record in the snapshot. Adjust the fields in
+ * `iter` and return `ITER_OK` or `ITER_DONE`. This function does not free the
+ * iterator in the case of `ITER_DONE`.
  */
 static int next_record(struct packed_ref_iterator *iter)
 {
@@ -942,6 +942,9 @@ static int packed_ref_iterator_advance(struct ref_iterator *ref_iterator)
 	int ok;
 
 	while ((ok = next_record(iter)) == ITER_OK) {
+		const char *refname = iter->base.refname;
+		const char *prefix = iter->prefix;
+
 		if (iter->flags & DO_FOR_EACH_PER_WORKTREE_ONLY &&
 		    !is_per_worktree_ref(iter->base.refname))
 			continue;
@@ -951,15 +954,41 @@ static int packed_ref_iterator_advance(struct ref_iterator *ref_iterator)
 					    &iter->oid, iter->flags))
 			continue;
 
+		while (prefix && *prefix) {
+			if (*refname < *prefix)
+				BUG("packed-refs backend yielded reference preceding its prefix");
+			else if (*refname > *prefix)
+				return ITER_DONE;
+			prefix++;
+			refname++;
+		}
+
 		return ITER_OK;
 	}
 
-	if (ref_iterator_abort(ref_iterator) != ITER_DONE)
-		ok = ITER_ERROR;
-
 	return ok;
 }
 
+static int packed_ref_iterator_seek(struct ref_iterator *ref_iterator,
+				    const char *prefix)
+{
+	struct packed_ref_iterator *iter =
+		(struct packed_ref_iterator *)ref_iterator;
+	const char *start;
+
+	if (prefix && *prefix)
+		start = find_reference_location(iter->snapshot, prefix, 0);
+	else
+		start = iter->snapshot->start;
+
+	free(iter->prefix);
+	iter->prefix = xstrdup_or_null(prefix);
+	iter->pos = start;
+	iter->eof = iter->snapshot->eof;
+
+	return 0;
+}
+
 static int packed_ref_iterator_peel(struct ref_iterator *ref_iterator,
 				   struct object_id *peeled)
 {
@@ -976,23 +1005,21 @@ static int packed_ref_iterator_peel(struct ref_iterator *ref_iterator,
 	}
 }
 
-static int packed_ref_iterator_abort(struct ref_iterator *ref_iterator)
+static void packed_ref_iterator_release(struct ref_iterator *ref_iterator)
 {
 	struct packed_ref_iterator *iter =
 		(struct packed_ref_iterator *)ref_iterator;
-	int ok = ITER_DONE;
-
 	strbuf_release(&iter->refname_buf);
 	free(iter->jump);
+	free(iter->prefix);
 	release_snapshot(iter->snapshot);
-	base_ref_iterator_free(ref_iterator);
-	return ok;
 }
 
 static struct ref_iterator_vtable packed_ref_iterator_vtable = {
 	.advance = packed_ref_iterator_advance,
+	.seek = packed_ref_iterator_seek,
 	.peel = packed_ref_iterator_peel,
-	.abort = packed_ref_iterator_abort
+	.release = packed_ref_iterator_release,
 };
 
 static int jump_list_entry_cmp(const void *va, const void *vb)
@@ -1104,7 +1131,6 @@ static struct ref_iterator *packed_ref_iterator_begin(
 {
 	struct packed_ref_store *refs;
 	struct snapshot *snapshot;
-	const char *start;
 	struct packed_ref_iterator *iter;
 	struct ref_iterator *ref_iterator;
 	unsigned int required_flags = REF_STORE_READ;
@@ -1120,14 +1146,6 @@ static struct ref_iterator *packed_ref_iterator_begin(
 	 */
 	snapshot = get_snapshot(refs);
 
-	if (prefix && *prefix)
-		start = find_reference_location(snapshot, prefix, 0);
-	else
-		start = snapshot->start;
-
-	if (start == snapshot->eof)
-		return empty_ref_iterator_begin();
-
 	CALLOC_ARRAY(iter, 1);
 	ref_iterator = &iter->base;
 	base_ref_iterator_init(ref_iterator, &packed_ref_iterator_vtable);
@@ -1137,19 +1155,15 @@ static struct ref_iterator *packed_ref_iterator_begin(
 
 	iter->snapshot = snapshot;
 	acquire_snapshot(snapshot);
-
-	iter->pos = start;
-	iter->eof = snapshot->eof;
 	strbuf_init(&iter->refname_buf, 0);
-
 	iter->base.oid = &iter->oid;
-
 	iter->repo = ref_store->repo;
 	iter->flags = flags;
 
-	if (prefix && *prefix)
-		/* Stop iteration after we've gone *past* prefix: */
-		ref_iterator = prefix_ref_iterator_begin(ref_iterator, prefix, 0);
+	if (packed_ref_iterator_seek(&iter->base, prefix) < 0) {
+		ref_iterator_free(&iter->base);
+		return NULL;
+	}
 
 	return ref_iterator;
 }
@@ -1362,8 +1376,10 @@ static int write_with_updates(struct packed_ref_store *refs,
 	 */
 	iter = packed_ref_iterator_begin(&refs->base, "", NULL,
 					 DO_FOR_EACH_INCLUDE_BROKEN);
-	if ((ok = ref_iterator_advance(iter)) != ITER_OK)
+	if ((ok = ref_iterator_advance(iter)) != ITER_OK) {
+		ref_iterator_free(iter);
 		iter = NULL;
+	}
 
 	i = 0;
 
@@ -1411,8 +1427,10 @@ static int write_with_updates(struct packed_ref_store *refs,
 				 * the iterator over the unneeded
 				 * value.
 				 */
-				if ((ok = ref_iterator_advance(iter)) != ITER_OK)
+				if ((ok = ref_iterator_advance(iter)) != ITER_OK) {
+					ref_iterator_free(iter);
 					iter = NULL;
+				}
 				cmp = +1;
 			} else {
 				/*
@@ -1449,8 +1467,10 @@ static int write_with_updates(struct packed_ref_store *refs,
 					       peel_error ? NULL : &peeled))
 				goto write_error;
 
-			if ((ok = ref_iterator_advance(iter)) != ITER_OK)
+			if ((ok = ref_iterator_advance(iter)) != ITER_OK) {
+				ref_iterator_free(iter);
 				iter = NULL;
+			}
 		} else if (is_null_oid(&update->new_oid)) {
 			/*
 			 * The update wants to delete the reference,
@@ -1499,9 +1519,7 @@ write_error:
 		    get_tempfile_path(refs->tempfile), strerror(errno));
 
 error:
-	if (iter)
-		ref_iterator_abort(iter);
-
+	ref_iterator_free(iter);
 	delete_tempfile(&refs->tempfile);
 	return -1;
 }
diff --git a/refs/ref-cache.c b/refs/ref-cache.c
index 02f09e4df8..c1f1bab1d5 100644
--- a/refs/ref-cache.c
+++ b/refs/ref-cache.c
@@ -362,9 +362,7 @@ struct cache_ref_iterator {
 	struct ref_iterator base;
 
 	/*
-	 * The number of levels currently on the stack. This is always
-	 * at least 1, because when it becomes zero the iteration is
-	 * ended and this struct is freed.
+	 * The number of levels currently on the stack.
 	 */
 	size_t levels_nr;
 
@@ -376,7 +374,7 @@ struct cache_ref_iterator {
 	 * The prefix is matched textually, without regard for path
 	 * component boundaries.
 	 */
-	const char *prefix;
+	char *prefix;
 
 	/*
 	 * A stack of levels. levels[0] is the uppermost level that is
@@ -389,6 +387,9 @@ struct cache_ref_iterator {
 	struct cache_ref_iterator_level *levels;
 
 	struct repository *repo;
+	struct ref_cache *cache;
+
+	int prime_dir;
 };
 
 static int cache_ref_iterator_advance(struct ref_iterator *ref_iterator)
@@ -396,6 +397,9 @@ static int cache_ref_iterator_advance(struct ref_iterator *ref_iterator)
 	struct cache_ref_iterator *iter =
 		(struct cache_ref_iterator *)ref_iterator;
 
+	if (!iter->levels_nr)
+		return ITER_DONE;
+
 	while (1) {
 		struct cache_ref_iterator_level *level =
 			&iter->levels[iter->levels_nr - 1];
@@ -409,7 +413,7 @@ static int cache_ref_iterator_advance(struct ref_iterator *ref_iterator)
 		if (++level->index == level->dir->nr) {
 			/* This level is exhausted; pop up a level */
 			if (--iter->levels_nr == 0)
-				return ref_iterator_abort(ref_iterator);
+				return ITER_DONE;
 
 			continue;
 		}
@@ -444,6 +448,41 @@ static int cache_ref_iterator_advance(struct ref_iterator *ref_iterator)
 	}
 }
 
+static int cache_ref_iterator_seek(struct ref_iterator *ref_iterator,
+				   const char *prefix)
+{
+	struct cache_ref_iterator *iter =
+		(struct cache_ref_iterator *)ref_iterator;
+	struct cache_ref_iterator_level *level;
+	struct ref_dir *dir;
+
+	dir = get_ref_dir(iter->cache->root);
+	if (prefix && *prefix)
+		dir = find_containing_dir(dir, prefix);
+	if (!dir) {
+		iter->levels_nr = 0;
+		return 0;
+	}
+
+	if (iter->prime_dir)
+		prime_ref_dir(dir, prefix);
+	iter->levels_nr = 1;
+	level = &iter->levels[0];
+	level->index = -1;
+	level->dir = dir;
+
+	if (prefix && *prefix) {
+		free(iter->prefix);
+		iter->prefix = xstrdup(prefix);
+		level->prefix_state = PREFIX_WITHIN_DIR;
+	} else {
+		FREE_AND_NULL(iter->prefix);
+		level->prefix_state = PREFIX_CONTAINS_DIR;
+	}
+
+	return 0;
+}
+
 static int cache_ref_iterator_peel(struct ref_iterator *ref_iterator,
 				   struct object_id *peeled)
 {
@@ -452,21 +491,19 @@ static int cache_ref_iterator_peel(struct ref_iterator *ref_iterator,
 	return peel_object(iter->repo, ref_iterator->oid, peeled) ? -1 : 0;
 }
 
-static int cache_ref_iterator_abort(struct ref_iterator *ref_iterator)
+static void cache_ref_iterator_release(struct ref_iterator *ref_iterator)
 {
 	struct cache_ref_iterator *iter =
 		(struct cache_ref_iterator *)ref_iterator;
-
-	free((char *)iter->prefix);
+	free(iter->prefix);
 	free(iter->levels);
-	base_ref_iterator_free(ref_iterator);
-	return ITER_DONE;
 }
 
 static struct ref_iterator_vtable cache_ref_iterator_vtable = {
 	.advance = cache_ref_iterator_advance,
+	.seek = cache_ref_iterator_seek,
 	.peel = cache_ref_iterator_peel,
-	.abort = cache_ref_iterator_abort
+	.release = cache_ref_iterator_release,
 };
 
 struct ref_iterator *cache_ref_iterator_begin(struct ref_cache *cache,
@@ -474,39 +511,22 @@ struct ref_iterator *cache_ref_iterator_begin(struct ref_cache *cache,
 					      struct repository *repo,
 					      int prime_dir)
 {
-	struct ref_dir *dir;
 	struct cache_ref_iterator *iter;
 	struct ref_iterator *ref_iterator;
-	struct cache_ref_iterator_level *level;
-
-	dir = get_ref_dir(cache->root);
-	if (prefix && *prefix)
-		dir = find_containing_dir(dir, prefix);
-	if (!dir)
-		/* There's nothing to iterate over. */
-		return empty_ref_iterator_begin();
-
-	if (prime_dir)
-		prime_ref_dir(dir, prefix);
 
 	CALLOC_ARRAY(iter, 1);
 	ref_iterator = &iter->base;
 	base_ref_iterator_init(ref_iterator, &cache_ref_iterator_vtable);
 	ALLOC_GROW(iter->levels, 10, iter->levels_alloc);
 
-	iter->levels_nr = 1;
-	level = &iter->levels[0];
-	level->index = -1;
-	level->dir = dir;
+	iter->repo = repo;
+	iter->cache = cache;
+	iter->prime_dir = prime_dir;
 
-	if (prefix && *prefix) {
-		iter->prefix = xstrdup(prefix);
-		level->prefix_state = PREFIX_WITHIN_DIR;
-	} else {
-		level->prefix_state = PREFIX_CONTAINS_DIR;
+	if (cache_ref_iterator_seek(&iter->base, prefix) < 0) {
+		ref_iterator_free(&iter->base);
+		return NULL;
 	}
 
-	iter->repo = repo;
-
 	return ref_iterator;
 }
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 8894b43d1d..e5862757a7 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -273,11 +273,11 @@ enum do_for_each_ref_flags {
  * the next reference and returns ITER_OK. The data pointed at by
  * refname and oid belong to the iterator; if you want to retain them
  * after calling ref_iterator_advance() again or calling
- * ref_iterator_abort(), you must make a copy. When the iteration has
+ * ref_iterator_free(), you must make a copy. When the iteration has
  * been exhausted, ref_iterator_advance() releases any resources
  * associated with the iteration, frees the ref_iterator object, and
  * returns ITER_DONE. If you want to abort the iteration early, call
- * ref_iterator_abort(), which also frees the ref_iterator object and
+ * ref_iterator_free(), which also frees the ref_iterator object and
  * any associated resources. If there was an internal error advancing
  * to the next entry, ref_iterator_advance() aborts the iteration,
  * frees the ref_iterator, and returns ITER_ERROR.
@@ -293,7 +293,7 @@ enum do_for_each_ref_flags {
  *
  *     while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
  *             if (want_to_stop_iteration()) {
- *                     ok = ref_iterator_abort(iter);
+ *                     ok = ITER_DONE;
  *                     break;
  *             }
  *
@@ -307,6 +307,7 @@ enum do_for_each_ref_flags {
  *
  *     if (ok != ITER_DONE)
  *             handle_error();
+ *     ref_iterator_free(iter);
  */
 struct ref_iterator {
 	struct ref_iterator_vtable *vtable;
@@ -327,18 +328,30 @@ struct ref_iterator {
 int ref_iterator_advance(struct ref_iterator *ref_iterator);
 
 /*
+ * Seek the iterator to the first reference with the given prefix.
+ * The prefix is matched as a literal string, without regard for path
+ * separators. If prefix is NULL or the empty string, seek the iterator to the
+ * first reference again.
+ *
+ * This function is expected to behave as if a new ref iterator with the same
+ * prefix had been created, but allows reuse of iterators and thus may allow
+ * the backend to optimize. Parameters other than the prefix that have been
+ * passed when creating the iterator will remain unchanged.
+ *
+ * Returns 0 on success, a negative error code otherwise.
+ */
+int ref_iterator_seek(struct ref_iterator *ref_iterator,
+		      const char *prefix);
+
+/*
  * If possible, peel the reference currently being viewed by the
  * iterator. Return 0 on success.
  */
 int ref_iterator_peel(struct ref_iterator *ref_iterator,
 		      struct object_id *peeled);
 
-/*
- * End the iteration before it has been exhausted, freeing the
- * reference iterator and any associated resources and returning
- * ITER_DONE. If the abort itself failed, return ITER_ERROR.
- */
-int ref_iterator_abort(struct ref_iterator *ref_iterator);
+/* Free the reference iterator and any associated resources. */
+void ref_iterator_free(struct ref_iterator *ref_iterator);
 
 /*
  * An iterator over nothing (its first ref_iterator_advance() call
@@ -438,13 +451,6 @@ struct ref_iterator *prefix_ref_iterator_begin(struct ref_iterator *iter0,
 void base_ref_iterator_init(struct ref_iterator *iter,
 			    struct ref_iterator_vtable *vtable);
 
-/*
- * Base class destructor for ref_iterators. Destroy the ref_iterator
- * part of iter and shallow-free the object. This is meant to be
- * called only by the destructors of derived classes.
- */
-void base_ref_iterator_free(struct ref_iterator *iter);
-
 /* Virtual function declarations for ref_iterators: */
 
 /*
@@ -456,6 +462,13 @@ void base_ref_iterator_free(struct ref_iterator *iter);
 typedef int ref_iterator_advance_fn(struct ref_iterator *ref_iterator);
 
 /*
+ * Seek the iterator to the first reference matching the given prefix. Should
+ * behave the same as if a new iterator was created with the same prefix.
+ */
+typedef int ref_iterator_seek_fn(struct ref_iterator *ref_iterator,
+				 const char *prefix);
+
+/*
  * Peels the current ref, returning 0 for success or -1 for failure.
  */
 typedef int ref_iterator_peel_fn(struct ref_iterator *ref_iterator,
@@ -463,15 +476,15 @@ typedef int ref_iterator_peel_fn(struct ref_iterator *ref_iterator,
 
 /*
  * Implementations of this function should free any resources specific
- * to the derived class, then call base_ref_iterator_free() to clean
- * up and free the ref_iterator object.
+ * to the derived class.
  */
-typedef int ref_iterator_abort_fn(struct ref_iterator *ref_iterator);
+typedef void ref_iterator_release_fn(struct ref_iterator *ref_iterator);
 
 struct ref_iterator_vtable {
 	ref_iterator_advance_fn *advance;
+	ref_iterator_seek_fn *seek;
 	ref_iterator_peel_fn *peel;
-	ref_iterator_abort_fn *abort;
+	ref_iterator_release_fn *release;
 };
 
 /*
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 7e90e13f74..c8f86da731 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -547,7 +547,7 @@ struct reftable_ref_iterator {
 	struct reftable_ref_record ref;
 	struct object_id oid;
 
-	const char *prefix;
+	char *prefix;
 	size_t prefix_len;
 	char **exclude_patterns;
 	size_t exclude_patterns_index;
@@ -711,20 +711,27 @@ static int reftable_ref_iterator_advance(struct ref_iterator *ref_iterator)
 		break;
 	}
 
-	if (iter->err > 0) {
-		if (ref_iterator_abort(ref_iterator) != ITER_DONE)
-			return ITER_ERROR;
+	if (iter->err > 0)
 		return ITER_DONE;
-	}
-
-	if (iter->err < 0) {
-		ref_iterator_abort(ref_iterator);
+	if (iter->err < 0)
 		return ITER_ERROR;
-	}
-
 	return ITER_OK;
 }
 
+static int reftable_ref_iterator_seek(struct ref_iterator *ref_iterator,
+				      const char *prefix)
+{
+	struct reftable_ref_iterator *iter =
+		(struct reftable_ref_iterator *)ref_iterator;
+
+	free(iter->prefix);
+	iter->prefix = xstrdup_or_null(prefix);
+	iter->prefix_len = prefix ? strlen(prefix) : 0;
+	iter->err = reftable_iterator_seek_ref(&iter->iter, prefix);
+
+	return iter->err;
+}
+
 static int reftable_ref_iterator_peel(struct ref_iterator *ref_iterator,
 				      struct object_id *peeled)
 {
@@ -740,7 +747,7 @@ static int reftable_ref_iterator_peel(struct ref_iterator *ref_iterator,
 	return -1;
 }
 
-static int reftable_ref_iterator_abort(struct ref_iterator *ref_iterator)
+static void reftable_ref_iterator_release(struct ref_iterator *ref_iterator)
 {
 	struct reftable_ref_iterator *iter =
 		(struct reftable_ref_iterator *)ref_iterator;
@@ -751,14 +758,14 @@ static int reftable_ref_iterator_abort(struct ref_iterator *ref_iterator)
 			free(iter->exclude_patterns[i]);
 		free(iter->exclude_patterns);
 	}
-	free(iter);
-	return ITER_DONE;
+	free(iter->prefix);
 }
 
 static struct ref_iterator_vtable reftable_ref_iterator_vtable = {
 	.advance = reftable_ref_iterator_advance,
+	.seek = reftable_ref_iterator_seek,
 	.peel = reftable_ref_iterator_peel,
-	.abort = reftable_ref_iterator_abort
+	.release = reftable_ref_iterator_release,
 };
 
 static int qsort_strcmp(const void *va, const void *vb)
@@ -815,8 +822,6 @@ static struct reftable_ref_iterator *ref_iterator_for_stack(struct reftable_ref_
 
 	iter = xcalloc(1, sizeof(*iter));
 	base_ref_iterator_init(&iter->base, &reftable_ref_iterator_vtable);
-	iter->prefix = prefix;
-	iter->prefix_len = prefix ? strlen(prefix) : 0;
 	iter->base.oid = &iter->oid;
 	iter->flags = flags;
 	iter->refs = refs;
@@ -830,8 +835,11 @@ static struct reftable_ref_iterator *ref_iterator_for_stack(struct reftable_ref_
 	if (ret)
 		goto done;
 
-	reftable_stack_init_ref_iterator(stack, &iter->iter);
-	ret = reftable_iterator_seek_ref(&iter->iter, prefix);
+	ret = reftable_stack_init_ref_iterator(stack, &iter->iter);
+	if (ret)
+		goto done;
+
+	ret = reftable_ref_iterator_seek(&iter->base, prefix);
 	if (ret)
 		goto done;
 
@@ -1069,6 +1077,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 		reftable_be_downcast(ref_store, REF_STORE_WRITE|REF_STORE_MAIN, "ref_transaction_prepare");
 	struct strbuf referent = STRBUF_INIT, head_referent = STRBUF_INIT;
 	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+	struct string_list refnames_to_check = STRING_LIST_INIT_NODUP;
 	struct reftable_transaction_data *tx_data = NULL;
 	struct reftable_backend *be;
 	struct object_id head_oid;
@@ -1224,12 +1233,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 			 * can output a proper error message instead of failing
 			 * at a later point.
 			 */
-			ret = refs_verify_refname_available(ref_store, u->refname,
-							    &affected_refnames, NULL,
-							    transaction->flags & REF_TRANSACTION_FLAG_INITIAL,
-							    err);
-			if (ret < 0)
-				goto done;
+			string_list_append(&refnames_to_check, u->refname);
 
 			/*
 			 * There is no need to write the reference deletion
@@ -1379,6 +1383,12 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 		}
 	}
 
+	ret = refs_verify_refnames_available(ref_store, &refnames_to_check, &affected_refnames, NULL,
+					     transaction->flags & REF_TRANSACTION_FLAG_INITIAL,
+					     err);
+	if (ret < 0)
+		goto done;
+
 	transaction->backend_data = tx_data;
 	transaction->state = REF_TRANSACTION_PREPARED;
 
@@ -1394,6 +1404,7 @@ done:
 	string_list_clear(&affected_refnames, 0);
 	strbuf_release(&referent);
 	strbuf_release(&head_referent);
+	string_list_clear(&refnames_to_check, 0);
 
 	return ret;
 }
@@ -2017,20 +2028,20 @@ static int reftable_reflog_iterator_advance(struct ref_iterator *ref_iterator)
 		break;
 	}
 
-	if (iter->err > 0) {
-		if (ref_iterator_abort(ref_iterator) != ITER_DONE)
-			return ITER_ERROR;
+	if (iter->err > 0)
 		return ITER_DONE;
-	}
-
-	if (iter->err < 0) {
-		ref_iterator_abort(ref_iterator);
+	if (iter->err < 0)
 		return ITER_ERROR;
-	}
-
 	return ITER_OK;
 }
 
+static int reftable_reflog_iterator_seek(struct ref_iterator *ref_iterator UNUSED,
+					 const char *prefix UNUSED)
+{
+	BUG("reftable reflog iterator cannot be seeked");
+	return -1;
+}
+
 static int reftable_reflog_iterator_peel(struct ref_iterator *ref_iterator UNUSED,
 					 struct object_id *peeled UNUSED)
 {
@@ -2038,21 +2049,20 @@ static int reftable_reflog_iterator_peel(struct ref_iterator *ref_iterator UNUSE
 	return -1;
 }
 
-static int reftable_reflog_iterator_abort(struct ref_iterator *ref_iterator)
+static void reftable_reflog_iterator_release(struct ref_iterator *ref_iterator)
 {
 	struct reftable_reflog_iterator *iter =
 		(struct reftable_reflog_iterator *)ref_iterator;
 	reftable_log_record_release(&iter->log);
 	reftable_iterator_destroy(&iter->iter);
 	strbuf_release(&iter->last_name);
-	free(iter);
-	return ITER_DONE;
 }
 
 static struct ref_iterator_vtable reftable_reflog_iterator_vtable = {
 	.advance = reftable_reflog_iterator_advance,
+	.seek = reftable_reflog_iterator_seek,
 	.peel = reftable_reflog_iterator_peel,
-	.abort = reftable_reflog_iterator_abort
+	.release = reftable_reflog_iterator_release,
 };
 
 static struct reftable_reflog_iterator *reflog_iterator_for_stack(struct reftable_ref_store *refs,
diff --git a/refspec.c b/refspec.c
index 3d6cf4dc92..4cb80b5208 100644
--- a/refspec.c
+++ b/refspec.c
@@ -269,28 +269,28 @@ void refspec_ref_prefixes(const struct refspec *rs,
 	}
 }
 
-int match_name_with_pattern(const char *key, const char *name,
-				   const char *value, char **result)
+int match_refname_with_pattern(const char *pattern, const char *refname,
+				   const char *replacement, char **result)
 {
-	const char *kstar = strchr(key, '*');
+	const char *kstar = strchr(pattern, '*');
 	size_t klen;
 	size_t ksuffixlen;
 	size_t namelen;
 	int ret;
 	if (!kstar)
-		die(_("key '%s' of pattern had no '*'"), key);
-	klen = kstar - key;
+		die(_("pattern '%s' has no '*'"), pattern);
+	klen = kstar - pattern;
 	ksuffixlen = strlen(kstar + 1);
-	namelen = strlen(name);
-	ret = !strncmp(name, key, klen) && namelen >= klen + ksuffixlen &&
-		!memcmp(name + namelen - ksuffixlen, kstar + 1, ksuffixlen);
-	if (ret && value) {
+	namelen = strlen(refname);
+	ret = !strncmp(refname, pattern, klen) && namelen >= klen + ksuffixlen &&
+		!memcmp(refname + namelen - ksuffixlen, kstar + 1, ksuffixlen);
+	if (ret && replacement) {
 		struct strbuf sb = STRBUF_INIT;
-		const char *vstar = strchr(value, '*');
+		const char *vstar = strchr(replacement, '*');
 		if (!vstar)
-			die(_("value '%s' of pattern has no '*'"), value);
-		strbuf_add(&sb, value, vstar - value);
-		strbuf_add(&sb, name + klen, namelen - klen - ksuffixlen);
+			die(_("replacement '%s' has no '*'"), replacement);
+		strbuf_add(&sb, replacement, vstar - replacement);
+		strbuf_add(&sb, refname + klen, namelen - klen - ksuffixlen);
 		strbuf_addstr(&sb, vstar + 1);
 		*result = strbuf_detach(&sb, NULL);
 	}
@@ -301,7 +301,7 @@ static int refspec_match(const struct refspec_item *refspec,
 			 const char *name)
 {
 	if (refspec->pattern)
-		return match_name_with_pattern(refspec->src, name, NULL, NULL);
+		return match_refname_with_pattern(refspec->src, name, NULL, NULL);
 
 	return !strcmp(refspec->src, name);
 }
@@ -352,7 +352,7 @@ static int refspec_find_negative_match(struct refspec *rs, struct refspec_item *
 			const char *key = refspec->dst ? refspec->dst : refspec->src;
 			const char *value = refspec->src;
 
-			if (match_name_with_pattern(key, needle, value, &expn_name))
+			if (match_refname_with_pattern(key, needle, value, &expn_name))
 				string_list_append_nodup(&reversed, expn_name);
 		} else if (refspec->matching) {
 			/* For the special matching refspec, any query should match */
@@ -397,7 +397,7 @@ void refspec_find_all_matches(struct refspec *rs,
 		if (!refspec->dst || refspec->negative)
 			continue;
 		if (refspec->pattern) {
-			if (match_name_with_pattern(key, needle, value, result))
+			if (match_refname_with_pattern(key, needle, value, result))
 				string_list_append_nodup(results, *result);
 		} else if (!strcmp(needle, key)) {
 			string_list_append(results, value);
@@ -426,7 +426,7 @@ int refspec_find_match(struct refspec *rs, struct refspec_item *query)
 		if (!refspec->dst || refspec->negative)
 			continue;
 		if (refspec->pattern) {
-			if (match_name_with_pattern(key, needle, value, result)) {
+			if (match_refname_with_pattern(key, needle, value, result)) {
 				query->force = refspec->force;
 				return 0;
 			}
diff --git a/refspec.h b/refspec.h
index f62f83a7ee..e2b5cc54ef 100644
--- a/refspec.h
+++ b/refspec.h
@@ -75,11 +75,12 @@ void refspec_ref_prefixes(const struct refspec *rs,
 int refname_matches_negative_refspec_item(const char *refname, struct refspec *rs);
 
 /*
- * Checks whether a name matches a pattern and optionally generates a result.
- * Returns 1 if the name matches the pattern, 0 otherwise.
+ * Checks if a refname matches a globbing refspec pattern.
+ * If replacement is provided, computes the corresponding mapped refname.
+ * Returns 1 if refname matches pattern, 0 otherwise.
  */
-int match_name_with_pattern(const char *key, const char *name,
-				   const char *value, char **result);
+int match_refname_with_pattern(const char *pattern, const char *refname,
+				   const char *replacement, char **result);
 
 /*
  * Queries a refspec for a match and updates the query item.
diff --git a/remote.c b/remote.c
index c1cf363cca..c9c1384c1d 100644
--- a/remote.c
+++ b/remote.c
@@ -1322,9 +1322,9 @@ static char *get_ref_match(const struct refspec *rs, const struct ref *ref,
 			const char *dst_side = item->dst ? item->dst : item->src;
 			int match;
 			if (direction == FROM_SRC)
-				match = match_name_with_pattern(item->src, ref->name, dst_side, &name);
+				match = match_refname_with_pattern(item->src, ref->name, dst_side, &name);
 			else
-				match = match_name_with_pattern(dst_side, ref->name, item->src, &name);
+				match = match_refname_with_pattern(dst_side, ref->name, item->src, &name);
 			if (match) {
 				matching_refs = i;
 				break;
@@ -1942,7 +1942,7 @@ static struct ref *get_expanded_map(const struct ref *remote_refs,
 
 		if (strchr(ref->name, '^'))
 			continue; /* a dereference item */
-		if (match_name_with_pattern(refspec->src, ref->name,
+		if (match_refname_with_pattern(refspec->src, ref->name,
 					    refspec->dst, &expn_name) &&
 		    !ignore_symref_update(expn_name, &scratch)) {
 			struct ref *cpy = copy_ref(ref);
diff --git a/t/helper/test-dir-iterator.c b/t/helper/test-dir-iterator.c
index 6b297bd753..8d46e8ba40 100644
--- a/t/helper/test-dir-iterator.c
+++ b/t/helper/test-dir-iterator.c
@@ -53,6 +53,7 @@ int cmd__dir_iterator(int argc, const char **argv)
 		printf("(%s) [%s] %s\n", diter->relative_path, diter->basename,
 		       diter->path.buf);
 	}
+	dir_iterator_free(diter);
 
 	if (iter_status != ITER_DONE) {
 		printf("dir_iterator_advance failure\n");
diff --git a/t/interop/Makefile b/t/interop/Makefile
index 6911c2915a..4ff4ed0616 100644
--- a/t/interop/Makefile
+++ b/t/interop/Makefile
@@ -1,3 +1,6 @@
+# The default target of this Makefile is...
+all::
+
 # Import tree-wide shared Makefile behavior and libraries
 include ../../shared.mak
 
@@ -8,7 +11,7 @@ SHELL_PATH ?= $(SHELL)
 SHELL_PATH_SQ = $(subst ','\'',$(SHELL_PATH))
 T = $(sort $(wildcard i[0-9][0-9][0-9][0-9]-*.sh))
 
-all: $(T)
+all:: $(T)
 
 $(T):
 	@echo "*** $@ ***"; '$(SHELL_PATH_SQ)' $@ $(GIT_TEST_OPTS)
diff --git a/t/perf/Makefile b/t/perf/Makefile
index e4808aebed..9b3090c4ed 100644
--- a/t/perf/Makefile
+++ b/t/perf/Makefile
@@ -1,10 +1,13 @@
+# The default target of this Makefile is...
+all::
+
 # Import tree-wide shared Makefile behavior and libraries
 include ../../shared.mak
 
 -include ../../config.mak
 export GIT_TEST_OPTIONS
 
-all: test-lint perf
+all:: test-lint perf
 
 perf: pre-clean
 	./run
diff --git a/t/t4203-mailmap.sh b/t/t4203-mailmap.sh
index 2421491931..4a6242ff99 100755
--- a/t/t4203-mailmap.sh
+++ b/t/t4203-mailmap.sh
@@ -113,6 +113,18 @@ test_expect_success 'check-mailmap --stdin simple address: no mapping' '
 	test_cmp expect actual
 '
 
+test_expect_success 'check-mailmap name and address: mapping' '
+	test_when_finished "rm .mailmap" &&
+	cat >.mailmap <<-EOF &&
+	Bug Reports <bugs-new@company.xx> Bugs <bugs@company.xx>
+	EOF
+	cat >expect <<-EOF &&
+	<bugs@company.xx>
+	EOF
+	git check-mailmap "bugs@company.xx" >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'No mailmap' '
 	cat >expect <<-EOF &&
 	$GIT_AUTHOR_NAME (1):
diff --git a/t/t4209-log-pickaxe.sh b/t/t4209-log-pickaxe.sh
index a675ace081..0e2f80a268 100755
--- a/t/t4209-log-pickaxe.sh
+++ b/t/t4209-log-pickaxe.sh
@@ -93,6 +93,22 @@ test_expect_success 'usage: --no-pickaxe-regex' '
 	test_cmp expect actual
 '
 
+test_expect_success 'usage: -G and -S with empty argument' '
+	cat >expect <<-\EOF &&
+	error: -S requires a non-empty argument
+	EOF
+
+	test_expect_code 129 git log -S "" 2>actual &&
+	test_cmp expect actual &&
+
+	cat >expect <<-\EOF &&
+	error: -G requires a non-empty argument
+	EOF
+
+	test_expect_code 129 git log -G "" 2>actual &&
+	test_cmp expect actual
+'
+
 test_log	expect_initial	--grep initial
 test_log	expect_nomatch	--grep InItial
 test_log_icase	expect_initial	--grep InItial
diff --git a/templates/Makefile b/templates/Makefile
index bd1e9e30c1..722755338d 100644
--- a/templates/Makefile
+++ b/templates/Makefile
@@ -1,3 +1,6 @@
+# The default target of this Makefile is...
+all::
+
 # Import tree-wide shared Makefile behavior and libraries
 include ../shared.mak
 
@@ -23,7 +26,7 @@ PERL_PATH_SQ = $(subst ','\'',$(PERL_PATH))
 DESTDIR_SQ = $(subst ','\'',$(DESTDIR))
 template_instdir_SQ = $(subst ','\'',$(template_instdir))
 
-all: boilerplates.made custom
+all:: boilerplates.made custom
 
 # Put templates that can be copied straight from the source
 # in a file direc--tory--file in the source.  They will be
diff --git a/xdiff/xdiffi.c b/xdiff/xdiffi.c
index 4685ba6137..8889b8b62a 100644
--- a/xdiff/xdiffi.c
+++ b/xdiff/xdiffi.c
@@ -19,7 +19,6 @@
  *  Davide Libenzi <davidel@xmailserver.org>
  *
  */
-#define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "xinclude.h"
 
@@ -1014,7 +1013,7 @@ static void xdl_mark_ignorable_lines(xdchange_t *xscr, xdfenv_t *xe, long flags)
 
 static int record_matches_regex(xrecord_t *rec, xpparam_t const *xpp) {
 	regmatch_t regmatch;
-	int i;
+	size_t i;
 
 	for (i = 0; i < xpp->ignore_regex_nr; i++)
 		if (!regexec_buf(xpp->ignore_regex[i], rec->ptr, rec->size, 1,
diff --git a/xdiff/xemit.c b/xdiff/xemit.c
index 75f0fe4986..f8e3f25b03 100644
--- a/xdiff/xemit.c
+++ b/xdiff/xemit.c
@@ -54,7 +54,7 @@ xdchange_t *xdl_get_hunk(xdchange_t **xscr, xdemitconf_t const *xecfg)
 	xdchange_t *xch, *xchp, *lxch;
 	long max_common = 2 * xecfg->ctxlen + xecfg->interhunkctxlen;
 	long max_ignorable = xecfg->ctxlen;
-	unsigned long ignored = 0; /* number of ignored blank lines */
+	long ignored = 0; /* number of ignored blank lines */
 
 	/* remove ignorable changes that are too far before other changes */
 	for (xchp = *xscr; xchp && xchp->ignore; xchp = xchp->next) {
diff --git a/xdiff/xhistogram.c b/xdiff/xhistogram.c
index 16a8fe2f3f..040d81e0bc 100644
--- a/xdiff/xhistogram.c
+++ b/xdiff/xhistogram.c
@@ -106,7 +106,7 @@ static int scanA(struct histindex *index, int line1, int count1)
 	unsigned int chain_len;
 	struct record **rec_chain, *rec;
 
-	for (ptr = LINE_END(1); line1 <= ptr; ptr--) {
+	for (ptr = LINE_END(1); (unsigned int)line1 <= ptr; ptr--) {
 		tbl_idx = TABLE_HASH(index, 1, ptr);
 		rec_chain = index->records + tbl_idx;
 		rec = *rec_chain;
@@ -181,14 +181,14 @@ static int try_lcs(struct histindex *index, struct region *lcs, int b_ptr,
 			be = bs;
 			rc = rec->cnt;
 
-			while (line1 < as && line2 < bs
+			while ((unsigned int)line1 < as && (unsigned int)line2 < bs
 				&& CMP(index, 1, as - 1, 2, bs - 1)) {
 				as--;
 				bs--;
 				if (1 < rc)
 					rc = XDL_MIN(rc, CNT(index, as));
 			}
-			while (ae < LINE_END(1) && be < LINE_END(2)
+			while (ae < (unsigned int)LINE_END(1) && be < (unsigned int)LINE_END(2)
 				&& CMP(index, 1, ae + 1, 2, be + 1)) {
 				ae++;
 				be++;
@@ -313,7 +313,7 @@ redo:
 	if (count1 <= 0 && count2 <= 0)
 		return 0;
 
-	if (LINE_END(1) >= MAX_PTR)
+	if ((unsigned int)LINE_END(1) >= MAX_PTR)
 		return -1;
 
 	if (!count1) {
diff --git a/xdiff/xinclude.h b/xdiff/xinclude.h
index 7e56542526..a4285ac0eb 100644
--- a/xdiff/xinclude.h
+++ b/xdiff/xinclude.h
@@ -23,8 +23,6 @@
 #if !defined(XINCLUDE_H)
 #define XINCLUDE_H
 
-#define DISABLE_SIGN_COMPARE_WARNINGS
-
 #include "git-compat-util.h"
 #include "xmacros.h"
 #include "xdiff.h"
diff --git a/xdiff/xpatience.c b/xdiff/xpatience.c
index a2d8955537..82f663004e 100644
--- a/xdiff/xpatience.c
+++ b/xdiff/xpatience.c
@@ -19,6 +19,7 @@
  *  Davide Libenzi <davidel@xmailserver.org>
  *
  */
+
 #include "xinclude.h"
 
 /*
@@ -75,7 +76,7 @@ struct hashmap {
 
 static int is_anchor(xpparam_t const *xpp, const char *line)
 {
-	int i;
+	size_t i;
 	for (i = 0; i < xpp->anchors_nr; i++) {
 		if (!strncmp(line, xpp->anchors[i], strlen(xpp->anchors[i])))
 			return 1;
diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index 9e36f24875..444a108f87 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -375,7 +375,7 @@ static int xdl_format_hunk_hdr(long s1, long c1, long s2, long c2,
 	nb += 3;
 	if (func && funclen) {
 		buf[nb++] = ' ';
-		if (funclen > sizeof(buf) - nb - 1)
+		if ((size_t)funclen > sizeof(buf) - nb - 1)
 			funclen = sizeof(buf) - nb - 1;
 		memcpy(buf + nb, func, funclen);
 		nb += funclen;
@@ -437,7 +437,7 @@ void* xdl_alloc_grow_helper(void *p, long nr, long *alloc, size_t size)
 {
 	void *tmp = NULL;
 	size_t n = ((LONG_MAX - 16) / 2 >= *alloc) ? 2 * *alloc + 16 : LONG_MAX;
-	if (nr > n)
+	if ((size_t)nr > n)
 		n = nr;
 	if (SIZE_MAX / size >= n)
 		tmp = xdl_realloc(p, n * size);