diff --git a/Documentation/RelNotes/2.50.0.adoc b/Documentation/RelNotes/2.50.0.adoc
index 07759cf98b3cca..6794031f996034 100644
--- a/Documentation/RelNotes/2.50.0.adoc
+++ b/Documentation/RelNotes/2.50.0.adoc
@@ -53,6 +53,15 @@ UI, Workflows & Features
 
  * The build procedure installs bash (but not zsh) completion script.
 
+ * send-email has been updated to work better with Outlook's smtp server.
+
+ * "git diff --minimal" used to give non-minimal output when its
+   optimization kicked in, which has been disabled.
+
+ * "git index-pack --fix-thin" used to abort to prevent a cycle in
+   delta chains from forming in a corner case even when there is no
+   such cycle.
+
 
 Performance, Internal Implementation, Development Support etc.
 --------------------------------------------------------------
@@ -134,6 +143,8 @@ Performance, Internal Implementation, Development Support etc.
 
  * Add an equivalent to "make hdr-check" target to meson based builds.
 
+ * Further code clean-up in the object-store layer.
+
 
 Fixes since v2.49
 -----------------
@@ -261,6 +272,10 @@ Fixes since v2.49
    now detected and the command errors out.
    (merge 974f0d4664 ps/mv-contradiction-fix later to maint).
 
+ * Further refinement on CI messages when an optional external
+   software is unavailable (e.g. due to third-party service outage).
+   (merge 956acbefbd jc/ci-skip-unavailable-external-software later to maint).
+
  * Other code cleanup, docfix, build fix, etc.
    (merge 227c4f33a0 ja/doc-block-delimiter-markup-fix later to maint).
    (merge 2bfd3b3685 ab/decorate-code-cleanup later to maint).
diff --git a/Documentation/git-send-email.adoc b/Documentation/git-send-email.adoc
index 7f223db42dd313..92389036fa368c 100644
--- a/Documentation/git-send-email.adoc
+++ b/Documentation/git-send-email.adoc
@@ -115,6 +115,19 @@ illustration below where `[PATCH v2 0/3]` is in reply to `[PATCH 0/2]`:
 Only necessary if --compose is also set.  If --compose
 is not set, this will be prompted for.
 
+--[no-]outlook-id-fix::
+	Microsoft Outlook SMTP servers discard the Message-ID sent via email and
+	assign a new random Message-ID, thus breaking threads.
++
+With `--outlook-id-fix`, 'git send-email' uses a mechanism specific to
+Outlook servers to learn the Message-ID the server assigned to fix the
+threading. Use it only when you know that the server reports the
+rewritten Message-ID the same way as Outlook servers do.
++
+Without this option specified, the fix is done by default when talking
+to 'smtp.office365.com' or 'smtp-mail.outlook.com'. Use
+`--no-outlook-id-fix` to disable even when talking to these two servers.
+
 --subject=<string>::
 	Specify the initial subject of the email thread.
 	Only necessary if --compose is also set.  If --compose
diff --git a/Makefile b/Makefile
index 8a7f1c76543fa6..de73c6ddcd1e30 100644
--- a/Makefile
+++ b/Makefile
@@ -819,6 +819,7 @@ TEST_BUILTINS_OBJS += test-mergesort.o
 TEST_BUILTINS_OBJS += test-mktemp.o
 TEST_BUILTINS_OBJS += test-name-hash.o
 TEST_BUILTINS_OBJS += test-online-cpus.o
+TEST_BUILTINS_OBJS += test-pack-deltas.o
 TEST_BUILTINS_OBJS += test-pack-mtimes.o
 TEST_BUILTINS_OBJS += test-parse-options.o
 TEST_BUILTINS_OBJS += test-parse-pathspec-file.o
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 0e3f10a946700e..3914a2a3f61c61 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -169,7 +169,8 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 		goto cleanup;
 
 	case 'e':
-		ret = !repo_has_object_file(the_repository, &oid);
+		ret = !has_object(the_repository, &oid,
+				  HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR);
 		goto cleanup;
 
 	case 'w':
diff --git a/builtin/clone.c b/builtin/clone.c
index b6f378c438257e..91b9cd0d164198 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -504,9 +504,7 @@ static void write_followtags(const struct ref *refs, const char *msg)
 			continue;
 		if (ends_with(ref->name, "^{}"))
 			continue;
-		if (!repo_has_object_file_with_flags(the_repository, &ref->old_oid,
-						     OBJECT_INFO_QUICK |
-						     OBJECT_INFO_SKIP_FETCH_OBJECT))
+		if (!has_object(the_repository, &ref->old_oid, 0))
 			continue;
 		refs_update_ref(get_main_ref_store(the_repository), msg,
 				ref->name, &ref->old_oid, NULL, 0,
diff --git a/builtin/count-objects.c b/builtin/count-objects.c
index 0bb5360b2f262c..a88c0c9c09af64 100644
--- a/builtin/count-objects.c
+++ b/builtin/count-objects.c
@@ -12,7 +12,7 @@
 #include "parse-options.h"
 #include "quote.h"
 #include "packfile.h"
-#include "object-store.h"
+#include "object-file.h"
 
 static unsigned long garbage;
 static off_t size_garbage;
diff --git a/builtin/fast-import.c b/builtin/fast-import.c
index c1e198f4e34df9..b2839c5f439b7b 100644
--- a/builtin/fast-import.c
+++ b/builtin/fast-import.c
@@ -811,7 +811,8 @@ static char *keep_pack(const char *curr_index_name)
 	int keep_fd;
 
 	odb_pack_name(pack_data->repo, &name, pack_data->hash, "keep");
-	keep_fd = odb_pack_keep(name.buf);
+	keep_fd = safe_create_file_with_leading_directories(pack_data->repo,
+							    name.buf);
 	if (keep_fd < 0)
 		die_errno("cannot create keep file");
 	write_or_die(keep_fd, keep_msg, strlen(keep_msg));
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 5279997c960721..cda6eaf1fd6edc 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -337,7 +337,6 @@ static void find_non_local_tags(const struct ref *refs,
 	struct string_list_item *remote_ref_item;
 	const struct ref *ref;
 	struct refname_hash_entry *item = NULL;
-	const int quick_flags = OBJECT_INFO_QUICK | OBJECT_INFO_SKIP_FETCH_OBJECT;
 
 	refname_hash_init(&existing_refs);
 	refname_hash_init(&remote_refs);
@@ -367,9 +366,9 @@ static void find_non_local_tags(const struct ref *refs,
 		 */
 		if (ends_with(ref->name, "^{}")) {
 			if (item &&
-			    !repo_has_object_file_with_flags(the_repository, &ref->old_oid, quick_flags) &&
+			    !has_object(the_repository, &ref->old_oid, 0) &&
 			    !oidset_contains(&fetch_oids, &ref->old_oid) &&
-			    !repo_has_object_file_with_flags(the_repository, &item->oid, quick_flags) &&
+			    !has_object(the_repository, &item->oid, 0) &&
 			    !oidset_contains(&fetch_oids, &item->oid))
 				clear_item(item);
 			item = NULL;
@@ -383,7 +382,7 @@ static void find_non_local_tags(const struct ref *refs,
 		 * fetch.
 		 */
 		if (item &&
-		    !repo_has_object_file_with_flags(the_repository, &item->oid, quick_flags) &&
+		    !has_object(the_repository, &item->oid, 0) &&
 		    !oidset_contains(&fetch_oids, &item->oid))
 			clear_item(item);
 
@@ -404,7 +403,7 @@ static void find_non_local_tags(const struct ref *refs,
 	 * checked to see if it needs fetching.
 	 */
 	if (item &&
-	    !repo_has_object_file_with_flags(the_repository, &item->oid, quick_flags) &&
+	    !has_object(the_repository, &item->oid, 0) &&
 	    !oidset_contains(&fetch_oids, &item->oid))
 		clear_item(item);
 
@@ -911,7 +910,8 @@ static int update_local_ref(struct ref *ref,
 	struct commit *current = NULL, *updated;
 	int fast_forward = 0;
 
-	if (!repo_has_object_file(the_repository, &ref->new_oid))
+	if (!has_object(the_repository, &ref->new_oid,
+			HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 		die(_("object %s not found"), oid_to_hex(&ref->new_oid));
 
 	if (oideq(&ref->old_oid, &ref->new_oid)) {
@@ -1330,8 +1330,7 @@ static int check_exist_and_connected(struct ref *ref_map)
 	 * we need all direct targets to exist.
 	 */
 	for (r = rm; r; r = r->next) {
-		if (!repo_has_object_file_with_flags(the_repository, &r->old_oid,
-						     OBJECT_INFO_SKIP_FETCH_OBJECT))
+		if (!has_object(the_repository, &r->old_oid, HAS_OBJECT_RECHECK_PACKED))
 			return -1;
 	}
 
diff --git a/builtin/gc.c b/builtin/gc.c
index e690453d4f80f6..78a2751aa8a6ce 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -28,7 +28,7 @@
 #include "commit.h"
 #include "commit-graph.h"
 #include "packfile.h"
-#include "object-store.h"
+#include "object-file.h"
 #include "pack.h"
 #include "pack-objects.h"
 #include "path.h"
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 60a8ee05dbc982..bb7925bd29f0aa 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -892,9 +892,8 @@ static void sha1_object(const void *data, struct object_entry *obj_entry,
 
 	if (startup_info->have_repository) {
 		read_lock();
-		collision_test_needed =
-			repo_has_object_file_with_flags(the_repository, oid,
-							OBJECT_INFO_QUICK);
+		collision_test_needed = has_object(the_repository, oid,
+						   HAS_OBJECT_FETCH_PROMISOR);
 		read_unlock();
 	}
 
@@ -1109,8 +1108,8 @@ static void *threaded_second_pass(void *data)
 		set_thread_data(data);
 	for (;;) {
 		struct base_data *parent = NULL;
-		struct object_entry *child_obj;
-		struct base_data *child;
+		struct object_entry *child_obj = NULL;
+		struct base_data *child = NULL;
 
 		counter_lock();
 		display_progress(progress, nr_resolved_deltas);
@@ -1137,15 +1136,18 @@ static void *threaded_second_pass(void *data)
 			parent = list_first_entry(&work_head, struct base_data,
 						  list);
 
-			if (parent->ref_first <= parent->ref_last) {
+			while (parent->ref_first <= parent->ref_last) {
 				int offset = ref_deltas[parent->ref_first++].obj_no;
 				child_obj = objects + offset;
-				if (child_obj->real_type != OBJ_REF_DELTA)
-					die("REF_DELTA at offset %"PRIuMAX" already resolved (duplicate base %s?)",
-					    (uintmax_t) child_obj->idx.offset,
-					    oid_to_hex(&parent->obj->idx.oid));
+				if (child_obj->real_type != OBJ_REF_DELTA) {
+					child_obj = NULL;
+					continue;
+				}
 				child_obj->real_type = parent->obj->real_type;
-			} else {
+				break;
+			}
+
+			if (!child_obj && parent->ofs_first <= parent->ofs_last) {
 				child_obj = objects +
 					ofs_deltas[parent->ofs_first++].obj_no;
 				assert(child_obj->real_type == OBJ_OFS_DELTA);
@@ -1178,29 +1180,32 @@ static void *threaded_second_pass(void *data)
 		}
 		work_unlock();
 
-		if (parent) {
-			child = resolve_delta(child_obj, parent);
-			if (!child->children_remaining)
-				FREE_AND_NULL(child->data);
-		} else {
-			child = make_base(child_obj, NULL);
-			if (child->children_remaining) {
-				/*
-				 * Since this child has its own delta children,
-				 * we will need this data in the future.
-				 * Inflate now so that future iterations will
-				 * have access to this object's data while
-				 * outside the work mutex.
-				 */
-				child->data = get_data_from_pack(child_obj);
-				child->size = child_obj->size;
+		if (child_obj) {
+			if (parent) {
+				child = resolve_delta(child_obj, parent);
+				if (!child->children_remaining)
+					FREE_AND_NULL(child->data);
+			} else{
+				child = make_base(child_obj, NULL);
+				if (child->children_remaining) {
+					/*
+					 * Since this child has its own delta children,
+					 * we will need this data in the future.
+					 * Inflate now so that future iterations will
+					 * have access to this object's data while
+					 * outside the work mutex.
+					 */
+					child->data = get_data_from_pack(child_obj);
+					child->size = child_obj->size;
+				}
 			}
 		}
 
 		work_lock();
 		if (parent)
 			parent->retain_data--;
-		if (child->data) {
+
+		if (child && child->data) {
 			/*
 			 * This child has its own children, so add it to
 			 * work_head.
@@ -1209,7 +1214,7 @@ static void *threaded_second_pass(void *data)
 			base_cache_used += child->size;
 			prune_base_data(NULL);
 			free_base_data(child);
-		} else {
+		} else if (child) {
 			/*
 			 * This child does not have its own children. It may be
 			 * the last descendant of its ancestors; free those
@@ -1565,7 +1570,7 @@ static void write_special_file(const char *suffix, const char *msg,
 	else
 		filename = odb_pack_name(the_repository, &name_buf, hash, suffix);
 
-	fd = odb_pack_keep(filename);
+	fd = safe_create_file_with_leading_directories(the_repository, filename);
 	if (fd < 0) {
 		if (errno != EEXIST)
 			die_errno(_("cannot write %s file '%s'"),
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index be314879e82908..c92e57ba188a19 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1506,7 +1506,9 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 		}
 	}
 
-	if (!is_null_oid(new_oid) && !repo_has_object_file(the_repository, new_oid)) {
+	if (!is_null_oid(new_oid) &&
+	    !has_object(the_repository, new_oid,
+			HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR)) {
 		error("unpack should have generated %s, "
 		      "but I can't find it!", oid_to_hex(new_oid));
 		ret = "bad pack";
diff --git a/builtin/remote.c b/builtin/remote.c
index b4baa34e665a8f..0d6755bcb71e3d 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -454,7 +454,8 @@ static int get_push_ref_states(const struct ref *remote_refs,
 			info->status = PUSH_STATUS_UPTODATE;
 		else if (is_null_oid(&ref->old_oid))
 			info->status = PUSH_STATUS_CREATE;
-		else if (repo_has_object_file(the_repository, &ref->old_oid) &&
+		else if (has_object(the_repository, &ref->old_oid,
+				    HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR) &&
 			 ref_newer(&ref->new_oid, &ref->old_oid))
 			info->status = PUSH_STATUS_FASTFORWARD;
 		else
diff --git a/builtin/show-ref.c b/builtin/show-ref.c
index f81209f23c3386..623a52a45f85cf 100644
--- a/builtin/show-ref.c
+++ b/builtin/show-ref.c
@@ -35,7 +35,8 @@ static void show_one(const struct show_one_options *opts,
 	const char *hex;
 	struct object_id peeled;
 
-	if (!repo_has_object_file(the_repository, oid))
+	if (!has_object(the_repository, oid,
+			HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 		die("git show-ref: bad ref %s (%s)", refname,
 		    oid_to_hex(oid));
 
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index 661be789f1340c..e905d5f4e1964b 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -449,7 +449,8 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
 		delta_data = get_data(delta_size);
 		if (!delta_data)
 			return;
-		if (repo_has_object_file(the_repository, &base_oid))
+		if (has_object(the_repository, &base_oid,
+			       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 			; /* Ok we have this one */
 		else if (resolve_against_held(nr, &base_oid,
 					      delta_data, delta_size))
diff --git a/bulk-checkin.c b/bulk-checkin.c
index c31c31b18d8a0b..678e2ecc2c29da 100644
--- a/bulk-checkin.c
+++ b/bulk-checkin.c
@@ -130,7 +130,8 @@ static void flush_batch_fsync(void)
 static int already_written(struct bulk_checkin_packfile *state, struct object_id *oid)
 {
 	/* The object may already exist in the repository */
-	if (repo_has_object_file(the_repository, oid))
+	if (has_object(the_repository, oid,
+		       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 		return 1;
 
 	/* Might want to keep the list sorted */
diff --git a/cache-tree.c b/cache-tree.c
index c0e1e9ee1d4af0..fa3858e2829aa8 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -238,7 +238,9 @@ int cache_tree_fully_valid(struct cache_tree *it)
 	int i;
 	if (!it)
 		return 0;
-	if (it->entry_count < 0 || !repo_has_object_file(the_repository, &it->oid))
+	if (it->entry_count < 0 ||
+	    has_object(the_repository, &it->oid,
+		       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 		return 0;
 	for (i = 0; i < it->subtree_nr; i++) {
 		if (!cache_tree_fully_valid(it->down[i]->cache_tree))
@@ -289,7 +291,9 @@ static int update_one(struct cache_tree *it,
 		}
 	}
 
-	if (0 <= it->entry_count && repo_has_object_file(the_repository, &it->oid))
+	if (0 <= it->entry_count &&
+	    has_object(the_repository, &it->oid,
+		       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 		return it->entry_count;
 
 	/*
@@ -395,7 +399,8 @@ static int update_one(struct cache_tree *it,
 		ce_missing_ok = mode == S_IFGITLINK || missing_ok ||
 			!must_check_existence(ce);
 		if (is_null_oid(oid) ||
-		    (!ce_missing_ok && !repo_has_object_file(the_repository, oid))) {
+		    (!ce_missing_ok && !has_object(the_repository, oid,
+						   HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))) {
 			strbuf_release(&buffer);
 			if (expected_missing)
 				return -1;
@@ -443,7 +448,7 @@ static int update_one(struct cache_tree *it,
 		struct object_id oid;
 		hash_object_file(the_hash_algo, buffer.buf, buffer.len,
 				 OBJ_TREE, &oid);
-		if (repo_has_object_file_with_flags(the_repository, &oid, OBJECT_INFO_SKIP_FETCH_OBJECT))
+		if (has_object(the_repository, &oid, HAS_OBJECT_RECHECK_PACKED))
 			oidcpy(&it->oid, &oid);
 		else
 			to_invalidate = 1;
diff --git a/ci/install-dependencies.sh b/ci/install-dependencies.sh
index da19dada2cecb6..d061a4729339e0 100755
--- a/ci/install-dependencies.sh
+++ b/ci/install-dependencies.sh
@@ -9,7 +9,7 @@ begin_group "Install dependencies"
 
 P4WHENCE=https://cdist2.perforce.com/perforce/r23.2
 LFSWHENCE=https://github.com/github/git-lfs/releases/download/v$LINUX_GIT_LFS_VERSION
-JGITWHENCE=https://repo.eclipse.org/content/groups/releases//org/eclipse/jgit/org.eclipse.jgit.pgm/6.8.0.202311291450-r/org.eclipse.jgit.pgm-6.8.0.202311291450-r.sh
+JGITWHENCE=https://repo1.maven.org/maven2/org/eclipse/jgit/org.eclipse.jgit.pgm/6.8.0.202311291450-r/org.eclipse.jgit.pgm-6.8.0.202311291450-r.sh
 
 # Make sudo a no-op and execute the command directly when running as root.
 # While using sudo would be fine on most platforms when we are root already,
@@ -71,7 +71,6 @@ ubuntu-*|i386/ubuntu-*|debian-*)
 		chmod a+x "$CUSTOM_PATH/p4d" "$CUSTOM_PATH/p4" || {
 			rm -f "$CUSTOM_PATH/p4"
 			rm -f "$CUSTOM_PATH/p4d"
-			echo >&2 "P4 download (optional) failed"
 		}
 
 		wget --quiet \
@@ -79,16 +78,12 @@ ubuntu-*|i386/ubuntu-*|debian-*)
 		tar -xzf "git-lfs-linux-amd64-$LINUX_GIT_LFS_VERSION.tar.gz" \
 			-C "$CUSTOM_PATH" --strip-components=1 \
 			"git-lfs-$LINUX_GIT_LFS_VERSION/git-lfs" &&
-		rm "git-lfs-linux-amd64-$LINUX_GIT_LFS_VERSION.tar.gz" || {
-			rm -f "$CUSTOM_PATH/git-lfs"
-			echo >&2 "LFS download (optional) failed"
-		}
+		rm "git-lfs-linux-amd64-$LINUX_GIT_LFS_VERSION.tar.gz" ||
+		rm -f "$CUSTOM_PATH/git-lfs"
 
 		wget --quiet "$JGITWHENCE" --output-document="$CUSTOM_PATH/jgit" &&
-		chmod a+x "$CUSTOM_PATH/jgit" || {
-			rm -f "$CUSTOM_PATH/jgit"
-			echo >&2 "JGit download (optional) failed"
-		}
+		chmod a+x "$CUSTOM_PATH/jgit" ||
+		rm -f "$CUSTOM_PATH/jgit"
 		;;
 	esac
 	;;
@@ -151,7 +146,7 @@ then
 	echo "$(tput setaf 6)Perforce Client Version$(tput sgr0)"
 	p4 -V
 else
-	echo >&2 "WARNING: perforce wasn't installed, see above for clues why"
+	echo >&2 "::warning:: perforce wasn't installed, see above for clues why"
 fi
 
 if type git-lfs >/dev/null 2>&1
@@ -159,7 +154,7 @@ then
 	echo "$(tput setaf 6)Git-LFS Version$(tput sgr0)"
 	git-lfs version
 else
-	echo >&2 "WARNING: git-lfs wasn't installed, see above for clues why"
+	echo >&2 "::warning:: git-lfs wasn't installed, see above for clues why"
 fi
 
 if type jgit >/dev/null 2>&1
@@ -167,7 +162,7 @@ then
 	echo "$(tput setaf 6)JGit Version$(tput sgr0)"
 	jgit version
 else
-	echo >&2 "WARNING: JGit wasn't installed, see above for clues why"
+	echo >&2 "::warning:: JGit wasn't installed, see above for clues why"
 fi
 
 end_group "Install dependencies"
diff --git a/convert.c b/convert.c
index 8783e17941ff70..b5f7cf6306c3c3 100644
--- a/convert.c
+++ b/convert.c
@@ -8,7 +8,7 @@
 #include "copy.h"
 #include "gettext.h"
 #include "hex.h"
-#include "object-store.h"
+#include "object-file.h"
 #include "attr.h"
 #include "run-command.h"
 #include "quote.h"
diff --git a/diffcore-rename.c b/diffcore-rename.c
index 179731462b53fd..7723bc3334e084 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -8,7 +8,7 @@
 #include "git-compat-util.h"
 #include "diff.h"
 #include "diffcore.h"
-#include "object-store.h"
+#include "object-file.h"
 #include "hashmap.h"
 #include "mem-pool.h"
 #include "oid-array.h"
diff --git a/dir.c b/dir.c
index 5c4675b4ac40e8..e11342e13660fb 100644
--- a/dir.c
+++ b/dir.c
@@ -17,7 +17,7 @@
 #include "environment.h"
 #include "gettext.h"
 #include "name-hash.h"
-#include "object-store.h"
+#include "object-file.h"
 #include "path.h"
 #include "refs.h"
 #include "repository.h"
diff --git a/fetch-pack.c b/fetch-pack.c
index 210dc30d50f6d6..fa4231fee74c9f 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -769,9 +769,7 @@ static void mark_complete_and_common_ref(struct fetch_negotiator *negotiator,
 		if (!commit) {
 			struct object *o;
 
-			if (!repo_has_object_file_with_flags(the_repository, &ref->old_oid,
-							     OBJECT_INFO_QUICK |
-							     OBJECT_INFO_SKIP_FETCH_OBJECT))
+			if (!has_object(the_repository, &ref->old_oid, 0))
 				continue;
 			o = parse_object(the_repository, &ref->old_oid);
 			if (!o || o->type != OBJ_COMMIT)
@@ -1985,7 +1983,8 @@ static void update_shallow(struct fetch_pack_args *args,
 		struct oid_array extra = OID_ARRAY_INIT;
 		struct object_id *oid = si->shallow->oid;
 		for (i = 0; i < si->shallow->nr; i++)
-			if (repo_has_object_file(the_repository, &oid[i]))
+			if (has_object(the_repository, &oid[i],
+				       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 				oid_array_append(&extra, &oid[i]);
 		if (extra.nr) {
 			setup_alternate_shallow(&shallow_lock,
diff --git a/git-send-email.perl b/git-send-email.perl
index 1f613fa979df45..4215f8f7e951e3 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -41,6 +41,8 @@ sub usage {
     --subject               <str>  * Email "Subject:"
     --reply-to              <str>  * Email "Reply-To:"
     --in-reply-to           <str>  * Email "In-Reply-To:"
+    --[no-]outlook-id-fix          * The SMTP host is an Outlook server that munges the
+                                     Message-ID. Retrieve it from the server.
     --[no-]xmailer                 * Add "X-Mailer:" header (default).
     --[no-]annotate                * Review each patch that will be sent in an editor.
     --compose                      * Open an editor for introduction.
@@ -68,7 +70,7 @@ sub usage {
     --smtp-auth             <str>  * Space-separated list of allowed AUTH mechanisms, or
                                      "none" to disable authentication.
                                      This setting forces to use one of the listed mechanisms.
-    --no-smtp-auth                   Disable SMTP authentication. Shorthand for
+    --no-smtp-auth                 * Disable SMTP authentication. Shorthand for
                                      `--smtp-auth=none`
     --smtp-debug            <0|1>  * Disable, enable Net::SMTP debug.
 
@@ -290,6 +292,7 @@ sub do_edit {
 my $mailmap = 0;
 my $target_xfer_encoding = 'auto';
 my $forbid_sendmail_variables = 1;
+my $outlook_id_fix = 'auto';
 
 my %config_bool_settings = (
     "thread" => \$thread,
@@ -305,6 +308,7 @@ sub do_edit {
     "xmailer" => \$use_xmailer,
     "forbidsendmailvariables" => \$forbid_sendmail_variables,
     "mailmap" => \$mailmap,
+    "outlookidfix" => \$outlook_id_fix,
 );
 
 my %config_settings = (
@@ -551,6 +555,7 @@ sub config_regexp {
 		    "relogin-delay=i" => \$relogin_delay,
 		    "git-completion-helper" => \$git_completion_helper,
 		    "v=s" => \$reroll_count,
+		    "outlook-id-fix!" => \$outlook_id_fix,
 );
 $rc = GetOptions(%options);
 
@@ -1574,6 +1579,16 @@ sub gen_header {
 	return ($recipients_ref, $to, $date, $gitversion, $cc, $ccline, $header);
 }
 
+sub is_outlook {
+	my ($host) = @_;
+	if ($outlook_id_fix eq 'auto') {
+		$outlook_id_fix =
+			($host eq 'smtp.office365.com' ||
+			 $host eq 'smtp-mail.outlook.com') ? 1 : 0;
+	}
+	return $outlook_id_fix;
+}
+
 # Prepares the email, then asks the user what to do.
 #
 # If the user chooses to send the email, it's sent and 1 is returned.
@@ -1737,6 +1752,22 @@ sub send_message {
 			$smtp->datasend("$line") or die $smtp->message;
 		}
 		$smtp->dataend() or die $smtp->message;
+
+		# Outlook discards the Message-ID header we set while sending the email
+		# and generates a new random Message-ID. So in order to avoid breaking
+		# threads, we simply retrieve the Message-ID from the server response
+		# and assign it to the $message_id variable, which will then be
+		# assigned to $in_reply_to by the caller when the next message is sent
+		# as a response to this message.
+		if (is_outlook($smtp_server)) {
+			if ($smtp->message =~ /<([^>]+)>/) {
+				$message_id = "<$1>";
+				printf __("Outlook reassigned Message-ID to: %s\n"), $message_id;
+			} else {
+				warn __("Warning: Could not retrieve Message-ID from server response.\n");
+			}
+		}
+
 		$smtp->code =~ /250|200/ or die sprintf(__("Failed to send %s\n"), $subject).$smtp->message;
 	}
 	if ($quiet) {
diff --git a/http-push.c b/http-push.c
index 32e37565f4e08f..f9e67cabd4bee8 100644
--- a/http-push.c
+++ b/http-push.c
@@ -1446,7 +1446,9 @@ static void one_remote_ref(const char *refname)
 	 * Fetch a copy of the object if it doesn't exist locally - it
 	 * may be required for updating server info later.
 	 */
-	if (repo->can_update_info_refs && !repo_has_object_file(the_repository, &ref->old_oid)) {
+	if (repo->can_update_info_refs &&
+	    !has_object(the_repository, &ref->old_oid,
+			HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR)) {
 		obj = lookup_unknown_object(the_repository, &ref->old_oid);
 		fprintf(stderr,	"  fetch %s for %s\n",
 			oid_to_hex(&ref->old_oid), refname);
@@ -1651,14 +1653,14 @@ static int delete_remote_branch(const char *pattern, int force)
 			return error("Remote HEAD symrefs too deep");
 		if (is_null_oid(&head_oid))
 			return error("Unable to resolve remote HEAD");
-		if (!repo_has_object_file(the_repository, &head_oid))
+		if (!has_object(the_repository, &head_oid, HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 			return error("Remote HEAD resolves to object %s\nwhich does not exist locally, perhaps you need to fetch?", oid_to_hex(&head_oid));
 
 		/* Remote branch must resolve to a known object */
 		if (is_null_oid(&remote_ref->old_oid))
 			return error("Unable to resolve remote branch %s",
 				     remote_ref->name);
-		if (!repo_has_object_file(the_repository, &remote_ref->old_oid))
+		if (!has_object(the_repository, &remote_ref->old_oid, HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 			return error("Remote branch %s resolves to object %s\nwhich does not exist locally, perhaps you need to fetch?", remote_ref->name, oid_to_hex(&remote_ref->old_oid));
 
 		/* Remote branch must be an ancestor of remote HEAD */
@@ -1879,7 +1881,8 @@ int cmd_main(int argc, const char **argv)
 		if (!force_all &&
 		    !is_null_oid(&ref->old_oid) &&
 		    !ref->force) {
-			if (!repo_has_object_file(the_repository, &ref->old_oid) ||
+			if (!has_object(the_repository, &ref->old_oid,
+					HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR) ||
 			    !ref_newer(&ref->peer_ref->new_oid,
 				       &ref->old_oid)) {
 				/*
diff --git a/http-walker.c b/http-walker.c
index 882cae19c2468c..463f7b119ad4ca 100644
--- a/http-walker.c
+++ b/http-walker.c
@@ -9,6 +9,7 @@
 #include "list.h"
 #include "transport.h"
 #include "packfile.h"
+#include "object-file.h"
 #include "object-store.h"
 
 struct alt_base {
@@ -137,7 +138,8 @@ static int fill_active_slot(void *data UNUSED)
 	list_for_each_safe(pos, tmp, head) {
 		obj_req = list_entry(pos, struct object_request, node);
 		if (obj_req->state == WAITING) {
-			if (repo_has_object_file(the_repository, &obj_req->oid))
+			if (has_object(the_repository, &obj_req->oid,
+				       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 				obj_req->state = COMPLETE;
 			else {
 				start_object_request(obj_req);
@@ -495,7 +497,8 @@ static int fetch_object(struct walker *walker, const struct object_id *oid)
 	if (!obj_req)
 		return error("Couldn't find request for %s in the queue", hex);
 
-	if (repo_has_object_file(the_repository, &obj_req->oid)) {
+	if (has_object(the_repository, &obj_req->oid,
+		       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR)) {
 		if (obj_req->req)
 			abort_http_object_request(&obj_req->req);
 		abort_object_request(obj_req);
@@ -540,7 +543,7 @@ static int fetch_object(struct walker *walker, const struct object_id *oid)
 		ret = error("File %s has bad hash", hex);
 	} else if (req->rename < 0) {
 		struct strbuf buf = STRBUF_INIT;
-		loose_object_path(the_repository, &buf, &req->oid);
+		odb_loose_path(the_repository->objects->odb, &buf, &req->oid);
 		ret = error("unable to write sha1 filename %s", buf.buf);
 		strbuf_release(&buf);
 	}
diff --git a/http.c b/http.c
index 0c41138042562f..3c029cf8947df7 100644
--- a/http.c
+++ b/http.c
@@ -2662,7 +2662,7 @@ struct http_object_request *new_http_object_request(const char *base_url,
 	oidcpy(&freq->oid, oid);
 	freq->localfile = -1;
 
-	loose_object_path(the_repository, &filename, oid);
+	odb_loose_path(the_repository->objects->odb, &filename, oid);
 	strbuf_addf(&freq->tmpfile, "%s.temp", filename.buf);
 
 	strbuf_addf(&prevfile, "%s.prev", filename.buf);
@@ -2814,7 +2814,7 @@ int finish_http_object_request(struct http_object_request *freq)
 		unlink_or_warn(freq->tmpfile.buf);
 		return -1;
 	}
-	loose_object_path(the_repository, &filename, &freq->oid);
+	odb_loose_path(the_repository->objects->odb, &filename, &freq->oid);
 	freq->rename = finalize_object_file(freq->tmpfile.buf, filename.buf);
 	strbuf_release(&filename);
 
diff --git a/list-objects.c b/list-objects.c
index 1e5512e1318a2c..597114281f6596 100644
--- a/list-objects.c
+++ b/list-objects.c
@@ -74,7 +74,8 @@ static void process_blob(struct traversal_context *ctx,
 	 * of missing objects.
 	 */
 	if (ctx->revs->exclude_promisor_objects &&
-	    !repo_has_object_file(the_repository, &obj->oid) &&
+	    !has_object(the_repository, &obj->oid,
+			HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR) &&
 	    is_promisor_object(ctx->revs->repo, &obj->oid))
 		return;
 
diff --git a/log-tree.c b/log-tree.c
index a4d4ab59ca0714..1d05dc1c7010d5 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -9,7 +9,7 @@
 #include "environment.h"
 #include "hex.h"
 #include "object-name.h"
-#include "object-store.h"
+#include "object-file.h"
 #include "repository.h"
 #include "tmp-objdir.h"
 #include "commit.h"
diff --git a/meson.build b/meson.build
index 270ce933d0f5d6..148ae668eb017d 100644
--- a/meson.build
+++ b/meson.build
@@ -243,7 +243,11 @@ shell = find_program('sh', dirs: program_path, native: true)
 tar = find_program('tar', dirs: program_path, native: true)
 time = find_program('time', dirs: program_path, required: get_option('benchmarks'))
 
-target_shell = find_program('sh', dirs: program_path, native: false)
+# Detect the target shell that is used by Git at runtime. Note that we prefer
+# "/bin/sh" over a PATH-based lookup, which provides a working shell on most
+# supported systems. This path is also the default shell path used by our
+# Makefile. This lookup can be overridden via `program_path`.
+target_shell = find_program('sh', dirs: program_path + [ '/bin' ], native: false)
 
 # Sanity-check that programs required for the build exist.
 foreach tool : ['cat', 'cut', 'grep', 'sort', 'tr', 'uname']
@@ -2174,3 +2178,9 @@ summary({
   'sha256': sha256_backend,
   'zlib': zlib_backend,
 }, section: 'Backends')
+
+summary({
+  'perl': target_perl,
+  'python': target_python,
+  'shell': target_shell,
+}, section: 'Runtime executable paths')
diff --git a/notes.c b/notes.c
index d9645c4b5dc603..0a128f1de98050 100644
--- a/notes.c
+++ b/notes.c
@@ -794,7 +794,8 @@ static int prune_notes_helper(const struct object_id *object_oid,
 	struct note_delete_list **l = (struct note_delete_list **) cb_data;
 	struct note_delete_list *n;
 
-	if (repo_has_object_file(the_repository, object_oid))
+	if (has_object(the_repository, object_oid,
+		       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 		return 0; /* nothing to do for this note */
 
 	/* failed to find object => prune this note */
diff --git a/object-file.c b/object-file.c
index 9cc3a24a40da1a..dc56a4766df4d1 100644
--- a/object-file.c
+++ b/object-file.c
@@ -932,7 +932,7 @@ static int write_loose_object(const struct object_id *oid, char *hdr,
 	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
 		prepare_loose_object_bulk_checkin();
 
-	loose_object_path(the_repository, &filename, oid);
+	odb_loose_path(the_repository->objects->odb, &filename, oid);
 
 	fd = start_loose_object_common(&tmp_file, filename.buf, flags,
 				       &stream, compressed, sizeof(compressed),
@@ -1079,7 +1079,7 @@ int stream_loose_object(struct input_stream *in_stream, size_t len,
 		goto cleanup;
 	}
 
-	loose_object_path(the_repository, &filename, oid);
+	odb_loose_path(the_repository->objects->odb, &filename, oid);
 
 	/* We finally know the object path, and create the missing dir. */
 	dirlen = directory_size(filename.buf);
diff --git a/object-file.h b/object-file.h
index c002fbe23451b3..a85b2e5b494c8f 100644
--- a/object-file.h
+++ b/object-file.h
@@ -3,6 +3,7 @@
 
 #include "git-zlib.h"
 #include "object.h"
+#include "object-store.h"
 
 struct index_state;
 
@@ -25,6 +26,20 @@ int index_path(struct index_state *istate, struct object_id *oid, const char *pa
 
 struct object_directory;
 
+/*
+ * Populate and return the loose object cache array corresponding to the
+ * given object ID.
+ */
+struct oidtree *odb_loose_cache(struct object_directory *odb,
+				const struct object_id *oid);
+
+/* Empty the loose object cache for the specified object directory. */
+void odb_clear_loose_cache(struct object_directory *odb);
+
+/*
+ * Put in `buf` the name of the file in the local object database that
+ * would be used to store a loose object with the specified oid.
+ */
 const char *odb_loose_path(struct object_directory *odb,
 			   struct strbuf *buf,
 			   const struct object_id *oid);
@@ -38,6 +53,68 @@ int has_loose_object_nonlocal(const struct object_id *);
 
 int has_loose_object(const struct object_id *);
 
+void *map_loose_object(struct repository *r, const struct object_id *oid,
+		       unsigned long *size);
+
+/*
+ * Iterate over the files in the loose-object parts of the object
+ * directory "path", triggering the following callbacks:
+ *
+ *  - loose_object is called for each loose object we find.
+ *
+ *  - loose_cruft is called for any files that do not appear to be
+ *    loose objects. Note that we only look in the loose object
+ *    directories "objects/[0-9a-f]{2}/", so we will not report
+ *    "objects/foobar" as cruft.
+ *
+ *  - loose_subdir is called for each top-level hashed subdirectory
+ *    of the object directory (e.g., "$OBJDIR/f0"). It is called
+ *    after the objects in the directory are processed.
+ *
+ * Any callback that is NULL will be ignored. Callbacks returning non-zero
+ * will end the iteration.
+ *
+ * In the "buf" variant, "path" is a strbuf which will also be used as a
+ * scratch buffer, but restored to its original contents before
+ * the function returns.
+ */
+typedef int each_loose_object_fn(const struct object_id *oid,
+				 const char *path,
+				 void *data);
+typedef int each_loose_cruft_fn(const char *basename,
+				const char *path,
+				void *data);
+typedef int each_loose_subdir_fn(unsigned int nr,
+				 const char *path,
+				 void *data);
+int for_each_file_in_obj_subdir(unsigned int subdir_nr,
+				struct strbuf *path,
+				each_loose_object_fn obj_cb,
+				each_loose_cruft_fn cruft_cb,
+				each_loose_subdir_fn subdir_cb,
+				void *data);
+int for_each_loose_file_in_objdir(const char *path,
+				  each_loose_object_fn obj_cb,
+				  each_loose_cruft_fn cruft_cb,
+				  each_loose_subdir_fn subdir_cb,
+				  void *data);
+int for_each_loose_file_in_objdir_buf(struct strbuf *path,
+				      each_loose_object_fn obj_cb,
+				      each_loose_cruft_fn cruft_cb,
+				      each_loose_subdir_fn subdir_cb,
+				      void *data);
+
+/*
+ * Iterate over all accessible loose objects without respect to
+ * reachability. By default, this includes both local and alternate objects.
+ * The order in which objects are visited is unspecified.
+ *
+ * Any flags specific to packs are ignored.
+ */
+int for_each_loose_object(each_loose_object_fn, void *,
+			  enum for_each_object_flags flags);
+
+
 /**
  * format_object_header() is a thin wrapper around s xsnprintf() that
  * writes the initial "<type> <obj-len>" part of the loose object
@@ -154,6 +231,10 @@ int finalize_object_file(const char *tmpfile, const char *filename);
 int finalize_object_file_flags(const char *tmpfile, const char *filename,
 			       enum finalize_object_file_flags flags);
 
+void hash_object_file(const struct git_hash_algo *algo, const void *buf,
+		      unsigned long len, enum object_type type,
+		      struct object_id *oid);
+
 /* Helper to check and "touch" a file */
 int check_and_freshen_file(const char *fn, int freshen);
 
diff --git a/object-name.c b/object-name.c
index 2c751a5352a75d..9288b2dd2453a0 100644
--- a/object-name.c
+++ b/object-name.c
@@ -19,7 +19,7 @@
 #include "oidtree.h"
 #include "packfile.h"
 #include "pretty.h"
-#include "object-store.h"
+#include "object-file.h"
 #include "read-cache-ll.h"
 #include "repo-settings.h"
 #include "repository.h"
diff --git a/object-store.c b/object-store.c
index 6ab50d25d3eb4f..2f51d0e3b037e3 100644
--- a/object-store.c
+++ b/object-store.c
@@ -83,25 +83,6 @@ int odb_mkstemp(struct strbuf *temp_filename, const char *pattern)
 	return xmkstemp_mode(temp_filename->buf, mode);
 }
 
-int odb_pack_keep(const char *name)
-{
-	int fd;
-
-	fd = open(name, O_RDWR|O_CREAT|O_EXCL, 0600);
-	if (0 <= fd)
-		return fd;
-
-	/* slow path */
-	safe_create_leading_directories_const(the_repository, name);
-	return open(name, O_RDWR|O_CREAT|O_EXCL, 0600);
-}
-
-const char *loose_object_path(struct repository *r, struct strbuf *buf,
-			      const struct object_id *oid)
-{
-	return odb_loose_path(r->objects->odb, buf, oid);
-}
-
 /*
  * Return non-zero iff the path is usable as an alternate object database.
  */
@@ -866,7 +847,7 @@ int pretend_object_file(struct repository *repo,
 	char *co_buf;
 
 	hash_object_file(repo->hash_algo, buf, len, type, oid);
-	if (repo_has_object_file_with_flags(repo, oid, OBJECT_INFO_QUICK | OBJECT_INFO_SKIP_FETCH_OBJECT) ||
+	if (has_object(repo, oid, 0) ||
 	    find_cached_object(repo->objects, oid))
 		return 0;
 
@@ -956,27 +937,16 @@ void *read_object_with_reference(struct repository *r,
 int has_object(struct repository *r, const struct object_id *oid,
 	       unsigned flags)
 {
-	int quick = !(flags & HAS_OBJECT_RECHECK_PACKED);
-	unsigned object_info_flags = OBJECT_INFO_SKIP_FETCH_OBJECT |
-		(quick ? OBJECT_INFO_QUICK : 0);
-
-	if (!startup_info->have_repository)
-		return 0;
-	return oid_object_info_extended(r, oid, NULL, object_info_flags) >= 0;
-}
+	unsigned object_info_flags = 0;
 
-int repo_has_object_file_with_flags(struct repository *r,
-				    const struct object_id *oid, int flags)
-{
 	if (!startup_info->have_repository)
 		return 0;
-	return oid_object_info_extended(r, oid, NULL, flags) >= 0;
-}
+	if (!(flags & HAS_OBJECT_RECHECK_PACKED))
+		object_info_flags |= OBJECT_INFO_QUICK;
+	if (!(flags & HAS_OBJECT_FETCH_PROMISOR))
+		object_info_flags |= OBJECT_INFO_SKIP_FETCH_OBJECT;
 
-int repo_has_object_file(struct repository *r,
-			 const struct object_id *oid)
-{
-	return repo_has_object_file_with_flags(r, oid, 0);
+	return oid_object_info_extended(r, oid, NULL, object_info_flags) >= 0;
 }
 
 void assert_oid_type(const struct object_id *oid, enum object_type expect)
diff --git a/object-store.h b/object-store.h
index 46961dc954257b..c2fe5a19605040 100644
--- a/object-store.h
+++ b/object-store.h
@@ -82,75 +82,8 @@ struct object_directory *set_temporary_primary_odb(const char *dir, int will_des
  */
 void restore_primary_odb(struct object_directory *restore_odb, const char *old_path);
 
-/*
- * Populate and return the loose object cache array corresponding to the
- * given object ID.
- */
-struct oidtree *odb_loose_cache(struct object_directory *odb,
-				  const struct object_id *oid);
-
-/* Empty the loose object cache for the specified object directory. */
-void odb_clear_loose_cache(struct object_directory *odb);
-
-struct packed_git {
-	struct hashmap_entry packmap_ent;
-	struct packed_git *next;
-	struct list_head mru;
-	struct pack_window *windows;
-	off_t pack_size;
-	const void *index_data;
-	size_t index_size;
-	uint32_t num_objects;
-	size_t crc_offset;
-	struct oidset bad_objects;
-	int index_version;
-	time_t mtime;
-	int pack_fd;
-	int index;              /* for builtin/pack-objects.c */
-	unsigned pack_local:1,
-		 pack_keep:1,
-		 pack_keep_in_core:1,
-		 freshened:1,
-		 do_not_close:1,
-		 pack_promisor:1,
-		 multi_pack_index:1,
-		 is_cruft:1;
-	unsigned char hash[GIT_MAX_RAWSZ];
-	struct revindex_entry *revindex;
-	const uint32_t *revindex_data;
-	const uint32_t *revindex_map;
-	size_t revindex_size;
-	/*
-	 * mtimes_map points at the beginning of the memory mapped region of
-	 * this pack's corresponding .mtimes file, and mtimes_size is the size
-	 * of that .mtimes file
-	 */
-	const uint32_t *mtimes_map;
-	size_t mtimes_size;
-
-	/* repo denotes the repository this packfile belongs to */
-	struct repository *repo;
-
-	/* something like ".git/objects/pack/xxxxx.pack" */
-	char pack_name[FLEX_ARRAY]; /* more */
-};
-
+struct packed_git;
 struct multi_pack_index;
-
-static inline int pack_map_entry_cmp(const void *cmp_data UNUSED,
-				     const struct hashmap_entry *entry,
-				     const struct hashmap_entry *entry2,
-				     const void *keydata)
-{
-	const char *key = keydata;
-	const struct packed_git *pg1, *pg2;
-
-	pg1 = container_of(entry, const struct packed_git, packmap_ent);
-	pg2 = container_of(entry2, const struct packed_git, packmap_ent);
-
-	return strcmp(pg1->pack_name, key ? key : pg2->pack_name);
-}
-
 struct cached_object_entry;
 
 struct raw_object_store {
@@ -246,23 +179,6 @@ void raw_object_store_clear(struct raw_object_store *o);
  */
 int odb_mkstemp(struct strbuf *temp_filename, const char *pattern);
 
-/*
- * Create a pack .keep file named "name" (which should generally be the output
- * of odb_pack_name). Returns a file descriptor opened for writing, or -1 on
- * error.
- */
-int odb_pack_keep(const char *name);
-
-/*
- * Put in `buf` the name of the file in the local object database that
- * would be used to store a loose object with the specified oid.
- */
-const char *loose_object_path(struct repository *r, struct strbuf *buf,
-			      const struct object_id *oid);
-
-void *map_loose_object(struct repository *r, const struct object_id *oid,
-		       unsigned long *size);
-
 void *repo_read_object_file(struct repository *r,
 			    const struct object_id *oid,
 			    enum object_type *type,
@@ -271,10 +187,6 @@ void *repo_read_object_file(struct repository *r,
 /* Read and unpack an object file into memory, write memory to an object file */
 int oid_object_info(struct repository *r, const struct object_id *, unsigned long *);
 
-void hash_object_file(const struct git_hash_algo *algo, const void *buf,
-		      unsigned long len, enum object_type type,
-		      struct object_id *oid);
-
 /*
  * Add an object file to the in-memory object store, without writing it
  * to disk.
@@ -350,33 +262,20 @@ int oid_object_info_extended(struct repository *r,
 			     const struct object_id *,
 			     struct object_info *, unsigned flags);
 
-/* Retry packed storage after checking packed and loose storage */
-#define HAS_OBJECT_RECHECK_PACKED 1
+enum {
+	/* Retry packed storage after checking packed and loose storage */
+	HAS_OBJECT_RECHECK_PACKED = (1 << 0),
+	/* Allow fetching the object in case the repository has a promisor remote. */
+	HAS_OBJECT_FETCH_PROMISOR = (1 << 1),
+};
 
 /*
  * Returns 1 if the object exists. This function will not lazily fetch objects
- * in a partial clone.
+ * in a partial clone by default.
  */
 int has_object(struct repository *r, const struct object_id *oid,
 	       unsigned flags);
 
-/*
- * These macros and functions are deprecated. If checking existence for an
- * object that is likely to be missing and/or whose absence is relatively
- * inconsequential (or is consequential but the caller is prepared to handle
- * it), use has_object(), which has better defaults (no lazy fetch in a partial
- * clone and no rechecking of packed storage). In the unlikely event that a
- * caller needs to assert existence of an object that it fully expects to
- * exist, and wants to trigger a lazy fetch in a partial clone, use
- * oid_object_info_extended() with a NULL struct object_info.
- *
- * These functions can be removed once all callers have migrated to
- * has_object() and/or oid_object_info_extended().
- */
-int repo_has_object_file(struct repository *r, const struct object_id *oid);
-int repo_has_object_file_with_flags(struct repository *r,
-				    const struct object_id *oid, int flags);
-
 void assert_oid_type(const struct object_id *oid, enum object_type expect);
 
 /*
@@ -411,56 +310,7 @@ static inline void obj_read_unlock(void)
 	if(obj_read_use_lock)
 		pthread_mutex_unlock(&obj_read_mutex);
 }
-
-/*
- * Iterate over the files in the loose-object parts of the object
- * directory "path", triggering the following callbacks:
- *
- *  - loose_object is called for each loose object we find.
- *
- *  - loose_cruft is called for any files that do not appear to be
- *    loose objects. Note that we only look in the loose object
- *    directories "objects/[0-9a-f]{2}/", so we will not report
- *    "objects/foobar" as cruft.
- *
- *  - loose_subdir is called for each top-level hashed subdirectory
- *    of the object directory (e.g., "$OBJDIR/f0"). It is called
- *    after the objects in the directory are processed.
- *
- * Any callback that is NULL will be ignored. Callbacks returning non-zero
- * will end the iteration.
- *
- * In the "buf" variant, "path" is a strbuf which will also be used as a
- * scratch buffer, but restored to its original contents before
- * the function returns.
- */
-typedef int each_loose_object_fn(const struct object_id *oid,
-				 const char *path,
-				 void *data);
-typedef int each_loose_cruft_fn(const char *basename,
-				const char *path,
-				void *data);
-typedef int each_loose_subdir_fn(unsigned int nr,
-				 const char *path,
-				 void *data);
-int for_each_file_in_obj_subdir(unsigned int subdir_nr,
-				struct strbuf *path,
-				each_loose_object_fn obj_cb,
-				each_loose_cruft_fn cruft_cb,
-				each_loose_subdir_fn subdir_cb,
-				void *data);
-int for_each_loose_file_in_objdir(const char *path,
-				  each_loose_object_fn obj_cb,
-				  each_loose_cruft_fn cruft_cb,
-				  each_loose_subdir_fn subdir_cb,
-				  void *data);
-int for_each_loose_file_in_objdir_buf(struct strbuf *path,
-				      each_loose_object_fn obj_cb,
-				      each_loose_cruft_fn cruft_cb,
-				      each_loose_subdir_fn subdir_cb,
-				      void *data);
-
-/* Flags for for_each_*_object() below. */
+/* Flags for for_each_*_object(). */
 enum for_each_object_flags {
 	/* Iterate only over local objects, not alternates. */
 	FOR_EACH_OBJECT_LOCAL_ONLY = (1<<0),
@@ -480,33 +330,6 @@ enum for_each_object_flags {
 	FOR_EACH_OBJECT_SKIP_ON_DISK_KEPT_PACKS = (1<<4),
 };
 
-/*
- * Iterate over all accessible loose objects without respect to
- * reachability. By default, this includes both local and alternate objects.
- * The order in which objects are visited is unspecified.
- *
- * Any flags specific to packs are ignored.
- */
-int for_each_loose_object(each_loose_object_fn, void *,
-			  enum for_each_object_flags flags);
-
-/*
- * Iterate over all accessible packed objects without respect to reachability.
- * By default, this includes both local and alternate packs.
- *
- * Note that some objects may appear twice if they are found in multiple packs.
- * Each pack is visited in an unspecified order. By default, objects within a
- * pack are visited in pack-idx order (i.e., sorted by oid).
- */
-typedef int each_packed_object_fn(const struct object_id *oid,
-				  struct packed_git *pack,
-				  uint32_t pos,
-				  void *data);
-int for_each_object_in_pack(struct packed_git *p,
-			    each_packed_object_fn, void *data,
-			    enum for_each_object_flags flags);
-int for_each_packed_object(struct repository *repo, each_packed_object_fn cb,
-			   void *data, enum for_each_object_flags flags);
 
 void *read_object_with_reference(struct repository *r,
 				 const struct object_id *oid,
diff --git a/pack-objects.h b/pack-objects.h
index d1c4ae7f9b6189..475a2d67ce30eb 100644
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -4,6 +4,7 @@
 #include "object-store.h"
 #include "thread-utils.h"
 #include "pack.h"
+#include "packfile.h"
 
 struct repository;
 
diff --git a/packfile.h b/packfile.h
index 25097213d06d61..3a3c77cf05a63d 100644
--- a/packfile.h
+++ b/packfile.h
@@ -1,13 +1,71 @@
 #ifndef PACKFILE_H
 #define PACKFILE_H
 
+#include "list.h"
 #include "object.h"
+#include "object-store.h"
 #include "oidset.h"
 
 /* in object-store.h */
-struct packed_git;
 struct object_info;
 
+struct packed_git {
+	struct hashmap_entry packmap_ent;
+	struct packed_git *next;
+	struct list_head mru;
+	struct pack_window *windows;
+	off_t pack_size;
+	const void *index_data;
+	size_t index_size;
+	uint32_t num_objects;
+	size_t crc_offset;
+	struct oidset bad_objects;
+	int index_version;
+	time_t mtime;
+	int pack_fd;
+	int index;              /* for builtin/pack-objects.c */
+	unsigned pack_local:1,
+		 pack_keep:1,
+		 pack_keep_in_core:1,
+		 freshened:1,
+		 do_not_close:1,
+		 pack_promisor:1,
+		 multi_pack_index:1,
+		 is_cruft:1;
+	unsigned char hash[GIT_MAX_RAWSZ];
+	struct revindex_entry *revindex;
+	const uint32_t *revindex_data;
+	const uint32_t *revindex_map;
+	size_t revindex_size;
+	/*
+	 * mtimes_map points at the beginning of the memory mapped region of
+	 * this pack's corresponding .mtimes file, and mtimes_size is the size
+	 * of that .mtimes file
+	 */
+	const uint32_t *mtimes_map;
+	size_t mtimes_size;
+
+	/* repo denotes the repository this packfile belongs to */
+	struct repository *repo;
+
+	/* something like ".git/objects/pack/xxxxx.pack" */
+	char pack_name[FLEX_ARRAY]; /* more */
+};
+
+static inline int pack_map_entry_cmp(const void *cmp_data UNUSED,
+				     const struct hashmap_entry *entry,
+				     const struct hashmap_entry *entry2,
+				     const void *keydata)
+{
+	const char *key = keydata;
+	const struct packed_git *pg1, *pg2;
+
+	pg1 = container_of(entry, const struct packed_git, packmap_ent);
+	pg2 = container_of(entry2, const struct packed_git, packmap_ent);
+
+	return strcmp(pg1->pack_name, key ? key : pg2->pack_name);
+}
+
 struct pack_window {
 	struct pack_window *next;
 	unsigned char *base;
@@ -60,6 +118,24 @@ void for_each_file_in_pack_dir(const char *objdir,
 			       each_file_in_pack_dir_fn fn,
 			       void *data);
 
+/*
+ * Iterate over all accessible packed objects without respect to reachability.
+ * By default, this includes both local and alternate packs.
+ *
+ * Note that some objects may appear twice if they are found in multiple packs.
+ * Each pack is visited in an unspecified order. By default, objects within a
+ * pack are visited in pack-idx order (i.e., sorted by oid).
+ */
+typedef int each_packed_object_fn(const struct object_id *oid,
+				  struct packed_git *pack,
+				  uint32_t pos,
+				  void *data);
+int for_each_object_in_pack(struct packed_git *p,
+			    each_packed_object_fn, void *data,
+			    enum for_each_object_flags flags);
+int for_each_packed_object(struct repository *repo, each_packed_object_fn cb,
+			   void *data, enum for_each_object_flags flags);
+
 /* A hook to report invalid files in pack directory */
 #define PACKDIR_FILE_PACK 1
 #define PACKDIR_FILE_IDX 2
diff --git a/path.c b/path.c
index 4505bb78e8b470..3b598b2847ff03 100644
--- a/path.c
+++ b/path.c
@@ -1011,6 +1011,20 @@ enum scld_error safe_create_leading_directories_const(struct repository *repo,
 	return result;
 }
 
+int safe_create_file_with_leading_directories(struct repository *repo,
+					      const char *path)
+{
+	int fd;
+
+	fd = open(path, O_RDWR|O_CREAT|O_EXCL, 0600);
+	if (0 <= fd)
+		return fd;
+
+	/* slow path */
+	safe_create_leading_directories_const(repo, path);
+	return open(path, O_RDWR|O_CREAT|O_EXCL, 0600);
+}
+
 static int have_same_root(const char *path1, const char *path2)
 {
 	int is_abs1, is_abs2;
diff --git a/path.h b/path.h
index fd1a194b060135..e67348f25397cc 100644
--- a/path.h
+++ b/path.h
@@ -266,6 +266,13 @@ enum scld_error safe_create_leading_directories_const(struct repository *repo,
 						      const char *path);
 enum scld_error safe_create_leading_directories_no_share(char *path);
 
+/*
+ * Create a file, potentially creating its leading directories in case they
+ * don't exist. Returns the return value of the open(3p) call.
+ */
+int safe_create_file_with_leading_directories(struct repository *repo,
+					      const char *path);
+
 # ifdef USE_THE_REPOSITORY_VARIABLE
 #  include "strbuf.h"
 #  include "repository.h"
diff --git a/prune-packed.c b/prune-packed.c
index c1d95a519d7479..92fb4fbb0ed3d1 100644
--- a/prune-packed.c
+++ b/prune-packed.c
@@ -2,7 +2,7 @@
 
 #include "git-compat-util.h"
 #include "gettext.h"
-#include "object-store.h"
+#include "object-file.h"
 #include "packfile.h"
 #include "progress.h"
 #include "prune-packed.h"
diff --git a/reachable.c b/reachable.c
index e5f56f40181d88..9dc748f0b9a0f7 100644
--- a/reachable.c
+++ b/reachable.c
@@ -14,7 +14,7 @@
 #include "list-objects.h"
 #include "packfile.h"
 #include "worktree.h"
-#include "object-store.h"
+#include "object-file.h"
 #include "pack-bitmap.h"
 #include "pack-mtimes.h"
 #include "config.h"
diff --git a/reflog.c b/reflog.c
index 12f7a02e3408db..15d81ebea978d3 100644
--- a/reflog.c
+++ b/reflog.c
@@ -152,7 +152,8 @@ static int tree_is_complete(const struct object_id *oid)
 	init_tree_desc(&desc, &tree->object.oid, tree->buffer, tree->size);
 	complete = 1;
 	while (tree_entry(&desc, &entry)) {
-		if (!repo_has_object_file(the_repository, &entry.oid) ||
+		if (!has_object(the_repository, &entry.oid,
+				HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR) ||
 		    (S_ISDIR(entry.mode) && !tree_is_complete(&entry.oid))) {
 			tree->object.flags |= INCOMPLETE;
 			complete = 0;
diff --git a/refs.c b/refs.c
index 6559db378909e4..dce5c49ca2ba65 100644
--- a/refs.c
+++ b/refs.c
@@ -376,7 +376,7 @@ int ref_resolves_to_object(const char *refname,
 {
 	if (flags & REF_ISBROKEN)
 		return 0;
-	if (!repo_has_object_file(repo, oid)) {
+	if (!has_object(repo, oid, HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR)) {
 		error(_("%s does not point to a valid object!"), refname);
 		return 0;
 	}
diff --git a/remote.c b/remote.c
index 9fa3614e7a3374..4099183cacdc8a 100644
--- a/remote.c
+++ b/remote.c
@@ -1702,7 +1702,7 @@ void set_ref_status_for_push(struct ref *remote_refs, int send_mirror,
 		if (!reject_reason && !ref->deletion && !is_null_oid(&ref->old_oid)) {
 			if (starts_with(ref->name, "refs/tags/"))
 				reject_reason = REF_STATUS_REJECT_ALREADY_EXISTS;
-			else if (!repo_has_object_file_with_flags(the_repository, &ref->old_oid, OBJECT_INFO_SKIP_FETCH_OBJECT))
+			else if (!has_object(the_repository, &ref->old_oid, HAS_OBJECT_RECHECK_PACKED))
 				reject_reason = REF_STATUS_REJECT_FETCH_FIRST;
 			else if (!lookup_commit_reference_gently(the_repository, &ref->old_oid, 1) ||
 				 !lookup_commit_reference_gently(the_repository, &ref->new_oid, 1))
diff --git a/send-pack.c b/send-pack.c
index 5005689cb55a48..86592ce526db95 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -45,10 +45,7 @@ int option_parse_push_signed(const struct option *opt,
 static void feed_object(struct repository *r,
 			const struct object_id *oid, FILE *fh, int negative)
 {
-	if (negative &&
-	    !repo_has_object_file_with_flags(r, oid,
-					     OBJECT_INFO_SKIP_FETCH_OBJECT |
-					     OBJECT_INFO_QUICK))
+	if (negative && !has_object(r, oid, 0))
 		return;
 
 	if (negative)
diff --git a/shallow.c b/shallow.c
index 2f82ebd6e3f5e5..faeeeb45f986e1 100644
--- a/shallow.c
+++ b/shallow.c
@@ -310,7 +310,8 @@ static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
 	if (graft->nr_parent != -1)
 		return 0;
 	if (data->flags & QUICK) {
-		if (!repo_has_object_file(the_repository, &graft->oid))
+		if (!has_object(the_repository, &graft->oid,
+				HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 			return 0;
 	} else if (data->flags & SEEN_ONLY) {
 		struct commit *c = lookup_commit(the_repository, &graft->oid);
@@ -476,7 +477,8 @@ void prepare_shallow_info(struct shallow_info *info, struct oid_array *sa)
 	ALLOC_ARRAY(info->ours, sa->nr);
 	ALLOC_ARRAY(info->theirs, sa->nr);
 	for (size_t i = 0; i < sa->nr; i++) {
-		if (repo_has_object_file(the_repository, sa->oid + i)) {
+		if (has_object(the_repository, sa->oid + i,
+			       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR)) {
 			struct commit_graft *graft;
 			graft = lookup_commit_graft(the_repository,
 						    &sa->oid[i]);
@@ -513,7 +515,8 @@ void remove_nonexistent_theirs_shallow(struct shallow_info *info)
 	for (i = dst = 0; i < info->nr_theirs; i++) {
 		if (i != dst)
 			info->theirs[dst] = info->theirs[i];
-		if (repo_has_object_file(the_repository, oid + info->theirs[i]))
+		if (has_object(the_repository, oid + info->theirs[i],
+			       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
 			dst++;
 	}
 	info->nr_theirs = dst;
diff --git a/t/helper/meson.build b/t/helper/meson.build
index d2cabaa2bcfcc9..d4e8b26df8d6de 100644
--- a/t/helper/meson.build
+++ b/t/helper/meson.build
@@ -36,6 +36,7 @@ test_tool_sources = [
   'test-mktemp.c',
   'test-name-hash.c',
   'test-online-cpus.c',
+  'test-pack-deltas.c',
   'test-pack-mtimes.c',
   'test-parse-options.c',
   'test-parse-pathspec-file.c',
diff --git a/t/helper/test-pack-deltas.c b/t/helper/test-pack-deltas.c
new file mode 100644
index 00000000000000..4caa024b1ebe73
--- /dev/null
+++ b/t/helper/test-pack-deltas.c
@@ -0,0 +1,148 @@
+#define USE_THE_REPOSITORY_VARIABLE
+
+#include "test-tool.h"
+#include "git-compat-util.h"
+#include "delta.h"
+#include "git-zlib.h"
+#include "hash.h"
+#include "hex.h"
+#include "pack.h"
+#include "pack-objects.h"
+#include "parse-options.h"
+#include "setup.h"
+#include "strbuf.h"
+#include "string-list.h"
+
+static const char *usage_str[] = {
+	"test-tool pack-deltas --num-objects <num-objects>",
+	NULL
+};
+
+static unsigned long do_compress(void **pptr, unsigned long size)
+{
+	git_zstream stream;
+	void *in, *out;
+	unsigned long maxsize;
+
+	git_deflate_init(&stream, 1);
+	maxsize = git_deflate_bound(&stream, size);
+
+	in = *pptr;
+	out = xmalloc(maxsize);
+	*pptr = out;
+
+	stream.next_in = in;
+	stream.avail_in = size;
+	stream.next_out = out;
+	stream.avail_out = maxsize;
+	while (git_deflate(&stream, Z_FINISH) == Z_OK)
+		; /* nothing */
+	git_deflate_end(&stream);
+
+	free(in);
+	return stream.total_out;
+}
+
+static void write_ref_delta(struct hashfile *f,
+			    struct object_id *oid,
+			    struct object_id *base)
+{
+	unsigned char header[MAX_PACK_OBJECT_HEADER];
+	unsigned long size, base_size, delta_size, compressed_size, hdrlen;
+	enum object_type type;
+	void *base_buf, *delta_buf;
+	void *buf = repo_read_object_file(the_repository,
+					  oid, &type,
+					  &size);
+
+	if (!buf)
+		die("unable to read %s", oid_to_hex(oid));
+
+	base_buf = repo_read_object_file(the_repository,
+					 base, &type,
+					 &base_size);
+
+	if (!base_buf)
+		die("unable to read %s", oid_to_hex(base));
+
+	delta_buf = diff_delta(base_buf, base_size,
+			       buf, size, &delta_size, 0);
+
+	compressed_size = do_compress(&delta_buf, delta_size);
+
+	hdrlen = encode_in_pack_object_header(header, sizeof(header),
+					      OBJ_REF_DELTA, delta_size);
+	hashwrite(f, header, hdrlen);
+	hashwrite(f, base->hash, the_repository->hash_algo->rawsz);
+	hashwrite(f, delta_buf, compressed_size);
+
+	free(buf);
+	free(base_buf);
+	free(delta_buf);
+}
+
+int cmd__pack_deltas(int argc, const char **argv)
+{
+	int num_objects = -1;
+	struct hashfile *f;
+	struct strbuf line = STRBUF_INIT;
+	struct option options[] = {
+		OPT_INTEGER('n', "num-objects", &num_objects, N_("the number of objects to write")),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, NULL,
+			     options, usage_str, 0);
+
+	if (argc || num_objects < 0)
+		usage_with_options(usage_str, options);
+
+	setup_git_directory();
+
+	f = hashfd(the_repository->hash_algo, 1, "<stdout>");
+	write_pack_header(f, num_objects);
+
+	/* Read each line from stdin into 'line' */
+	while (strbuf_getline_lf(&line, stdin) != EOF) {
+		const char *type_str, *content_oid_str, *base_oid_str = NULL;
+		struct object_id content_oid, base_oid;
+		struct string_list items = STRING_LIST_INIT_NODUP;
+		/*
+		 * Tokenize into two or three parts:
+		 * 1. REF_DELTA, OFS_DELTA, or FULL.
+		 * 2. The object ID for the content object.
+		 * 3. The object ID for the base object (optional).
+		 */
+		if (string_list_split_in_place(&items, line.buf, " ", 3) < 0)
+			die("invalid input format: %s", line.buf);
+
+		if (items.nr < 2)
+			die("invalid input format: %s", line.buf);
+
+		type_str = items.items[0].string;
+		content_oid_str = items.items[1].string;
+
+		if (get_oid_hex(content_oid_str, &content_oid))
+			die("invalid object: %s", content_oid_str);
+		if (items.nr >= 3) {
+			base_oid_str = items.items[2].string;
+			if (get_oid_hex(base_oid_str, &base_oid))
+				die("invalid object: %s", base_oid_str);
+		}
+		string_list_clear(&items, 0);
+
+		if (!strcmp(type_str, "REF_DELTA"))
+			write_ref_delta(f, &content_oid, &base_oid);
+		else if (!strcmp(type_str, "OFS_DELTA"))
+			die("OFS_DELTA not implemented");
+		else if (!strcmp(type_str, "FULL"))
+			die("FULL not implemented");
+		else
+			die("unknown pack type: %s", type_str);
+	}
+
+	finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK,
+			  CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
+	strbuf_release(&line);
+	return 0;
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 50dc4dac4ed625..74812ed86d385a 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -46,6 +46,7 @@ static struct test_cmd cmds[] = {
 	{ "mktemp", cmd__mktemp },
 	{ "name-hash", cmd__name_hash },
 	{ "online-cpus", cmd__online_cpus },
+	{ "pack-deltas", cmd__pack_deltas },
 	{ "pack-mtimes", cmd__pack_mtimes },
 	{ "parse-options", cmd__parse_options },
 	{ "parse-options-flags", cmd__parse_options_flags },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index 6d62a5b53d9596..2571a3ccfe8991 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -39,6 +39,7 @@ int cmd__mergesort(int argc, const char **argv);
 int cmd__mktemp(int argc, const char **argv);
 int cmd__name_hash(int argc, const char **argv);
 int cmd__online_cpus(int argc, const char **argv);
+int cmd__pack_deltas(int argc, const char **argv);
 int cmd__pack_mtimes(int argc, const char **argv);
 int cmd__parse_options(int argc, const char **argv);
 int cmd__parse_options_flags(int argc, const char **argv);
diff --git a/t/meson.build b/t/meson.build
index b09c0becb8dd12..00543f720aca02 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -501,6 +501,7 @@ integration_tests = [
   't4068-diff-symmetric-merge-base.sh',
   't4069-remerge-diff.sh',
   't4070-diff-pairs.sh',
+  't4071-diff-minimal.sh',
   't4100-apply-stat.sh',
   't4101-apply-nonl.sh',
   't4102-apply-rename.sh',
diff --git a/t/t4071-diff-minimal.sh b/t/t4071-diff-minimal.sh
new file mode 100755
index 00000000000000..4c484dadfb0ada
--- /dev/null
+++ b/t/t4071-diff-minimal.sh
@@ -0,0 +1,14 @@
+#!/bin/sh
+
+test_description='minimal diff algorithm'
+
+. ./test-lib.sh
+
+test_expect_success 'minimal diff should not mark changes between changed lines' '
+	test_write_lines x x x x >pre &&
+	test_write_lines x x x A B C D x E F G >post &&
+	test_expect_code 1 git diff --no-index --minimal pre post >diff &&
+	test_grep ! ^[+-]x diff 
+'
+
+test_done
diff --git a/t/t5309-pack-delta-cycles.sh b/t/t5309-pack-delta-cycles.sh
index 60fc710bacb20e..6b03675d91b5e1 100755
--- a/t/t5309-pack-delta-cycles.sh
+++ b/t/t5309-pack-delta-cycles.sh
@@ -60,7 +60,10 @@ test_expect_success 'index-pack detects REF_DELTA cycles' '
 test_expect_success 'failover to an object in another pack' '
 	clear_packs &&
 	git index-pack --stdin <ab.pack &&
-	test_must_fail git index-pack --stdin --fix-thin <cycle.pack
+
+	# This cycle does not fail since the existence of A & B in
+	# the repo allows us to resolve the cycle.
+	git index-pack --stdin --fix-thin <cycle.pack
 '
 
 test_expect_success 'failover to a duplicate object in the same pack' '
@@ -72,7 +75,34 @@ test_expect_success 'failover to a duplicate object in the same pack' '
 		pack_obj $A
 	} >recoverable.pack &&
 	pack_trailer recoverable.pack &&
-	test_must_fail git index-pack --fix-thin --stdin <recoverable.pack
+
+	# This cycle does not fail since the existence of a full copy
+	# of A in the pack allows us to resolve the cycle.
+	git index-pack --fix-thin --stdin <recoverable.pack
+'
+
+test_expect_success 'index-pack works with thin pack A->B->C with B on disk' '
+	git init server &&
+	(
+		cd server &&
+		test_commit_bulk 4
+	) &&
+
+	A=$(git -C server rev-parse HEAD^{tree}) &&
+	B=$(git -C server rev-parse HEAD~1^{tree}) &&
+	C=$(git -C server rev-parse HEAD~2^{tree}) &&
+	git -C server reset --hard HEAD~1 &&
+
+	test-tool -C server pack-deltas --num-objects=2 >thin.pack <<-EOF &&
+	REF_DELTA $A $B
+	REF_DELTA $B $C
+	EOF
+
+	git clone "file://$(pwd)/server" client &&
+	(
+		cd client &&
+		git index-pack --fix-thin --stdin <../thin.pack
+	)
 '
 
 test_done
diff --git a/upload-pack.c b/upload-pack.c
index 30e4630f3a1cb3..956da5b061a0e5 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -509,8 +509,7 @@ static int got_oid(struct upload_pack_data *data,
 {
 	if (get_oid_hex(hex, oid))
 		die("git upload-pack: expected SHA1 object, got '%s'", hex);
-	if (!repo_has_object_file_with_flags(the_repository, oid,
-					     OBJECT_INFO_QUICK | OBJECT_INFO_SKIP_FETCH_OBJECT))
+	if (!has_object(the_repository, oid, 0))
 		return -1;
 	return do_got_oid(data, oid);
 }
diff --git a/walker.c b/walker.c
index 4fedc19f346e66..b470d43e54d486 100644
--- a/walker.c
+++ b/walker.c
@@ -150,7 +150,8 @@ static int process(struct walker *walker, struct object *obj)
 		return 0;
 	obj->flags |= SEEN;
 
-	if (repo_has_object_file(the_repository, &obj->oid)) {
+	if (has_object(the_repository, &obj->oid,
+		       HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR)) {
 		/* We already have it, so we should scan it now. */
 		obj->flags |= TO_SCAN;
 	}
diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
index c84549f6c5089e..e1d4017b2ddeac 100644
--- a/xdiff/xprepare.c
+++ b/xdiff/xprepare.c
@@ -368,6 +368,7 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xd
 	xrecord_t **recs;
 	xdlclass_t *rcrec;
 	char *dis, *dis1, *dis2;
+	int need_min = !!(cf->flags & XDF_NEED_MINIMAL);
 
 	if (!XDL_CALLOC_ARRAY(dis, xdf1->nrec + xdf2->nrec + 2))
 		return -1;
@@ -379,7 +380,7 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xd
 	for (i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart]; i <= xdf1->dend; i++, recs++) {
 		rcrec = cf->rcrecs[(*recs)->ha];
 		nm = rcrec ? rcrec->len2 : 0;
-		dis1[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+		dis1[i] = (nm == 0) ? 0: (nm >= mlim && !need_min) ? 2: 1;
 	}
 
 	if ((mlim = xdl_bogosqrt(xdf2->nrec)) > XDL_MAX_EQLIMIT)
@@ -387,7 +388,7 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xd
 	for (i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart]; i <= xdf2->dend; i++, recs++) {
 		rcrec = cf->rcrecs[(*recs)->ha];
 		nm = rcrec ? rcrec->len1 : 0;
-		dis2[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+		dis2[i] = (nm == 0) ? 0: (nm >= mlim && !need_min) ? 2: 1;
 	}
 
 	for (nreff = 0, i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart];