Merge branch 'bc/object-id'

for_each_ref() callback functions were taught to name the objects
not with "unsigned char sha1[20]" but with "struct object_id".

* bc/object-id: (56 commits)
  struct ref_lock: convert old_sha1 member to object_id
  warn_if_dangling_symref(): convert local variable "junk" to object_id
  each_ref_fn_adapter(): remove adapter
  rev_list_insert_ref(): remove unneeded arguments
  rev_list_insert_ref_oid(): new function, taking an object_oid
  mark_complete(): remove unneeded arguments
  mark_complete_oid(): new function, taking an object_oid
  clear_marks(): rewrite to take an object_id argument
  mark_complete(): rewrite to take an object_id argument
  send_ref(): convert local variable "peeled" to object_id
  upload-pack: rewrite functions to take object_id arguments
  find_symref(): convert local variable "unused" to object_id
  find_symref(): rewrite to take an object_id argument
  write_one_ref(): rewrite to take an object_id argument
  write_refs_to_temp_dir(): convert local variable sha1 to object_id
  submodule: rewrite to take an object_id argument
  shallow: rewrite functions to take object_id arguments
  handle_one_ref(): rewrite to take an object_id argument
  add_info_ref(): rewrite to take an object_id argument
  handle_one_reflog(): rewrite to take an object_id argument
  ...

36 files changed, 300 insertions, 255 deletions

diff --git a/Documentation/technical/api-ref-iteration.txt b/Documentation/technical/api-ref-iteration.txt
index 02adfd45d3..37379d8337 100644
--- a/Documentation/technical/api-ref-iteration.txt
+++ b/Documentation/technical/api-ref-iteration.txt
@@ -6,7 +6,7 @@ Iteration of refs is done by using an iterate function which will call a
 callback function for every ref. The callback function has this
 signature:
 
-	int handle_one_ref(const char *refname, const unsigned char *sha1,
+	int handle_one_ref(const char *refname, const struct object_id *oid,
 			   int flags, void *cb_data);
 
 There are different kinds of iterate functions which all take a
diff --git a/bisect.c b/bisect.c
index 10f5e57ef3..03d5cd9454 100644
--- a/bisect.c
+++ b/bisect.c
@@ -400,16 +400,16 @@ struct commit_list *find_bisection(struct commit_list *list,
 	return best;
 }
 
-static int register_ref(const char *refname, const unsigned char *sha1,
+static int register_ref(const char *refname, const struct object_id *oid,
 			int flags, void *cb_data)
 {
 	if (!strcmp(refname, "bad")) {
 		current_bad_oid = xmalloc(sizeof(*current_bad_oid));
-		hashcpy(current_bad_oid->hash, sha1);
+		oidcpy(current_bad_oid, oid);
 	} else if (starts_with(refname, "good-")) {
-		sha1_array_append(&good_revs, sha1);
+		sha1_array_append(&good_revs, oid->hash);
 	} else if (starts_with(refname, "skip-")) {
-		sha1_array_append(&skipped_revs, sha1);
+		sha1_array_append(&skipped_revs, oid->hash);
 	}
 
 	return 0;
diff --git a/builtin/branch.c b/builtin/branch.c
index c70085c35f..b42e5b6dbc 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -326,7 +326,7 @@ static int match_patterns(const char **pattern, const char *refname)
 	return 0;
 }
 
-static int append_ref(const char *refname, const unsigned char *sha1, int flags, void *cb_data)
+static int append_ref(const char *refname, const struct object_id *oid, int flags, void *cb_data)
 {
 	struct append_ref_cb *cb = (struct append_ref_cb *)(cb_data);
 	struct ref_list *ref_list = cb->ref_list;
@@ -363,7 +363,7 @@ static int append_ref(const char *refname, const unsigned char *sha1, int flags,
 
 	commit = NULL;
 	if (ref_list->verbose || ref_list->with_commit || merge_filter != NO_FILTER) {
-		commit = lookup_commit_reference_gently(sha1, 1);
+		commit = lookup_commit_reference_gently(oid->hash, 1);
 		if (!commit) {
 			cb->ret = error(_("branch '%s' does not point at a commit"), refname);
 			return 0;
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 2f92328db4..9b49f0e413 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -702,10 +702,10 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 }
 
 static int add_pending_uninteresting_ref(const char *refname,
-					 const unsigned char *sha1,
+					 const struct object_id *oid,
 					 int flags, void *cb_data)
 {
-	add_pending_sha1(cb_data, refname, sha1, UNINTERESTING);
+	add_pending_sha1(cb_data, refname, oid->hash, UNINTERESTING);
 	return 0;
 }
 
diff --git a/builtin/describe.c b/builtin/describe.c
index e00a75b121..a36c829e57 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -119,10 +119,10 @@ static void add_to_known_names(const char *path,
 	}
 }
 
-static int get_name(const char *path, const unsigned char *sha1, int flag, void *cb_data)
+static int get_name(const char *path, const struct object_id *oid, int flag, void *cb_data)
 {
 	int is_tag = starts_with(path, "refs/tags/");
-	unsigned char peeled[20];
+	struct object_id peeled;
 	int is_annotated, prio;
 
 	/* Reject anything outside refs/tags/ unless --all */
@@ -134,10 +134,10 @@ static int get_name(const char *path, const unsigned char *sha1, int flag, void
 		return 0;
 
 	/* Is it annotated? */
-	if (!peel_ref(path, peeled)) {
-		is_annotated = !!hashcmp(sha1, peeled);
+	if (!peel_ref(path, peeled.hash)) {
+		is_annotated = !!oidcmp(oid, &peeled);
 	} else {
-		hashcpy(peeled, sha1);
+		oidcpy(&peeled, oid);
 		is_annotated = 0;
 	}
 
@@ -154,7 +154,7 @@ static int get_name(const char *path, const unsigned char *sha1, int flag, void
 	else
 		prio = 0;
 
-	add_to_known_names(all ? path + 5 : path + 10, peeled, prio, sha1);
+	add_to_known_names(all ? path + 5 : path + 10, peeled.hash, prio, oid->hash);
 	return 0;
 }
 
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 7910419c93..8d5b2dba2b 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -179,13 +179,15 @@ static void add_merge_config(struct ref **head,
 	}
 }
 
-static int add_existing(const char *refname, const unsigned char *sha1,
+static int add_existing(const char *refname, const struct object_id *oid,
 			int flag, void *cbdata)
 {
 	struct string_list *list = (struct string_list *)cbdata;
 	struct string_list_item *item = string_list_insert(list, refname);
-	item->util = xmalloc(20);
-	hashcpy(item->util, sha1);
+	struct object_id *old_oid = xmalloc(sizeof(*old_oid));
+
+	oidcpy(old_oid, oid);
+	item->util = old_oid;
 	return 0;
 }
 
@@ -913,9 +915,10 @@ static int do_fetch(struct transport *transport,
 			struct string_list_item *peer_item =
 				string_list_lookup(&existing_refs,
 						   rm->peer_ref->name);
-			if (peer_item)
-				hashcpy(rm->peer_ref->old_sha1,
-					peer_item->util);
+			if (peer_item) {
+				struct object_id *old_oid = peer_item->util;
+				hashcpy(rm->peer_ref->old_sha1, old_oid->hash);
+			}
 		}
 	}
 
diff --git a/builtin/for-each-ref.c b/builtin/for-each-ref.c
index 05dd23d2a3..f7e51a7fad 100644
--- a/builtin/for-each-ref.c
+++ b/builtin/for-each-ref.c
@@ -854,7 +854,8 @@ struct grab_ref_cbdata {
  * A call-back given to for_each_ref().  Filter refs and keep them for
  * later object processing.
  */
-static int grab_single_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int grab_single_ref(const char *refname, const struct object_id *oid,
+			   int flag, void *cb_data)
 {
 	struct grab_ref_cbdata *cb = cb_data;
 	struct refinfo *ref;
@@ -892,7 +893,7 @@ static int grab_single_ref(const char *refname, const unsigned char *sha1, int f
 	 */
 	ref = xcalloc(1, sizeof(*ref));
 	ref->refname = xstrdup(refname);
-	hashcpy(ref->objectname, sha1);
+	hashcpy(ref->objectname, oid->hash);
 	ref->flag = flag;
 
 	cnt = cb->grab_cnt;
diff --git a/builtin/fsck.c b/builtin/fsck.c
index 4783896fd6..4e8e2ee5b7 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -25,7 +25,7 @@ static int include_reflogs = 1;
 static int check_full = 1;
 static int check_strict;
 static int keep_cache_objects;
-static unsigned char head_sha1[20];
+static struct object_id head_oid;
 static const char *head_points_at;
 static int errors_found;
 static int write_lost_and_found;
@@ -476,19 +476,21 @@ static int fsck_handle_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
 	return 0;
 }
 
-static int fsck_handle_reflog(const char *logname, const unsigned char *sha1, int flag, void *cb_data)
+static int fsck_handle_reflog(const char *logname, const struct object_id *oid,
+			      int flag, void *cb_data)
 {
 	for_each_reflog_ent(logname, fsck_handle_reflog_ent, NULL);
 	return 0;
 }
 
-static int fsck_handle_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int fsck_handle_ref(const char *refname, const struct object_id *oid,
+			   int flag, void *cb_data)
 {
 	struct object *obj;
 
-	obj = parse_object(sha1);
+	obj = parse_object(oid->hash);
 	if (!obj) {
-		error("%s: invalid sha1 pointer %s", refname, sha1_to_hex(sha1));
+		error("%s: invalid sha1 pointer %s", refname, oid_to_hex(oid));
 		errors_found |= ERROR_REACHABLE;
 		/* We'll continue with the rest despite the error.. */
 		return 0;
@@ -504,8 +506,8 @@ static int fsck_handle_ref(const char *refname, const unsigned char *sha1, int f
 
 static void get_default_heads(void)
 {
-	if (head_points_at && !is_null_sha1(head_sha1))
-		fsck_handle_ref("HEAD", head_sha1, 0, NULL);
+	if (head_points_at && !is_null_oid(&head_oid))
+		fsck_handle_ref("HEAD", &head_oid, 0, NULL);
 	for_each_rawref(fsck_handle_ref, NULL);
 	if (include_reflogs)
 		for_each_reflog(fsck_handle_reflog, NULL);
@@ -556,7 +558,7 @@ static int fsck_head_link(void)
 	if (verbose)
 		fprintf(stderr, "Checking HEAD link\n");
 
-	head_points_at = resolve_ref_unsafe("HEAD", 0, head_sha1, &flag);
+	head_points_at = resolve_ref_unsafe("HEAD", 0, head_oid.hash, &flag);
 	if (!head_points_at)
 		return error("Invalid HEAD");
 	if (!strcmp(head_points_at, "HEAD"))
@@ -565,7 +567,7 @@ static int fsck_head_link(void)
 	else if (!starts_with(head_points_at, "refs/heads/"))
 		return error("HEAD points to something strange (%s)",
 			     head_points_at);
-	if (is_null_sha1(head_sha1)) {
+	if (is_null_oid(&head_oid)) {
 		if (null_is_error)
 			return error("HEAD: detached HEAD points at nothing");
 		fprintf(stderr, "notice: HEAD points to an unborn branch (%s)\n",
diff --git a/builtin/name-rev.c b/builtin/name-rev.c
index 9736d4452f..248a3eb260 100644
--- a/builtin/name-rev.c
+++ b/builtin/name-rev.c
@@ -138,9 +138,9 @@ static int tipcmp(const void *a_, const void *b_)
 	return hashcmp(a->sha1, b->sha1);
 }
 
-static int name_ref(const char *path, const unsigned char *sha1, int flags, void *cb_data)
+static int name_ref(const char *path, const struct object_id *oid, int flags, void *cb_data)
 {
-	struct object *o = parse_object(sha1);
+	struct object *o = parse_object(oid->hash);
 	struct name_ref_data *data = cb_data;
 	int can_abbreviate_output = data->tags_only && data->name_only;
 	int deref = 0;
@@ -160,7 +160,7 @@ static int name_ref(const char *path, const unsigned char *sha1, int flags, void
 		}
 	}
 
-	add_to_tip_table(sha1, path, can_abbreviate_output);
+	add_to_tip_table(oid->hash, path, can_abbreviate_output);
 
 	while (o && o->type == OBJ_TAG) {
 		struct tag *t = (struct tag *) o;
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index c067107a6a..80fe8c7dc1 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -540,11 +540,11 @@ static enum write_one_status write_one(struct sha1file *f,
 	return WRITE_ONE_WRITTEN;
 }
 
-static int mark_tagged(const char *path, const unsigned char *sha1, int flag,
+static int mark_tagged(const char *path, const struct object_id *oid, int flag,
 		       void *cb_data)
 {
 	unsigned char peeled[20];
-	struct object_entry *entry = packlist_find(&to_pack, sha1, NULL);
+	struct object_entry *entry = packlist_find(&to_pack, oid->hash, NULL);
 
 	if (entry)
 		entry->tagged = 1;
@@ -2097,14 +2097,14 @@ static void ll_find_deltas(struct object_entry **list, unsigned list_size,
 #define ll_find_deltas(l, s, w, d, p)	find_deltas(l, &s, w, d, p)
 #endif
 
-static int add_ref_tag(const char *path, const unsigned char *sha1, int flag, void *cb_data)
+static int add_ref_tag(const char *path, const struct object_id *oid, int flag, void *cb_data)
 {
-	unsigned char peeled[20];
+	struct object_id peeled;
 
 	if (starts_with(path, "refs/tags/") && /* is a tag? */
-	    !peel_ref(path, peeled)        && /* peelable? */
-	    packlist_find(&to_pack, peeled, NULL))      /* object packed? */
-		add_object_entry(sha1, OBJ_TAG, NULL, 0);
+	    !peel_ref(path, peeled.hash)    && /* peelable? */
+	    packlist_find(&to_pack, peeled.hash, NULL))      /* object packed? */
+		add_object_entry(oid->hash, OBJ_TAG, NULL, 0);
 	return 0;
 }
 
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index d2ec52bca9..94d0571776 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -197,7 +197,7 @@ static void show_ref(const char *path, const unsigned char *sha1)
 	}
 }
 
-static int show_ref_cb(const char *path, const unsigned char *sha1, int flag, void *unused)
+static int show_ref_cb(const char *path, const struct object_id *oid, int flag, void *unused)
 {
 	path = strip_namespace(path);
 	/*
@@ -210,7 +210,7 @@ static int show_ref_cb(const char *path, const unsigned char *sha1, int flag, vo
 	 */
 	if (!path)
 		path = ".have";
-	show_ref(path, sha1);
+	show_ref(path, oid->hash);
 	return 0;
 }
 
@@ -228,6 +228,7 @@ static void collect_one_alternate_ref(const struct ref *ref, void *data)
 static void write_head_info(void)
 {
 	struct sha1_array sa = SHA1_ARRAY_INIT;
+
 	for_each_alternate_ref(collect_one_alternate_ref, &sa);
 	sha1_array_for_each_unique(&sa, show_one_alternate_sha1, NULL);
 	sha1_array_clear(&sa);
diff --git a/builtin/reflog.c b/builtin/reflog.c
index 8182b648b9..c2eb8ff840 100644
--- a/builtin/reflog.c
+++ b/builtin/reflog.c
@@ -313,14 +313,14 @@ static int should_expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
 	return 0;
 }
 
-static int push_tip_to_list(const char *refname, const unsigned char *sha1,
+static int push_tip_to_list(const char *refname, const struct object_id *oid,
 			    int flags, void *cb_data)
 {
 	struct commit_list **list = cb_data;
 	struct commit *tip_commit;
 	if (flags & REF_ISSYMREF)
 		return 0;
-	tip_commit = lookup_commit_reference_gently(sha1, 1);
+	tip_commit = lookup_commit_reference_gently(oid->hash, 1);
 	if (!tip_commit)
 		return 0;
 	commit_list_insert(tip_commit, list);
@@ -352,6 +352,7 @@ static void reflog_expiry_prepare(const char *refname,
 	if (cb->unreachable_expire_kind != UE_ALWAYS) {
 		if (cb->unreachable_expire_kind == UE_HEAD) {
 			struct commit_list *elem;
+
 			for_each_ref(push_tip_to_list, &cb->tips);
 			for (elem = cb->tips; elem; elem = elem->next)
 				commit_list_insert(elem->item, &cb->mark_list);
@@ -379,14 +380,14 @@ static void reflog_expiry_cleanup(void *cb_data)
 	}
 }
 
-static int collect_reflog(const char *ref, const unsigned char *sha1, int unused, void *cb_data)
+static int collect_reflog(const char *ref, const struct object_id *oid, int unused, void *cb_data)
 {
 	struct collected_reflog *e;
 	struct collect_reflog_cb *cb = cb_data;
 	size_t namelen = strlen(ref);
 
 	e = xmalloc(sizeof(*e) + namelen + 1);
-	hashcpy(e->sha1, sha1);
+	hashcpy(e->sha1, oid->hash);
 	memcpy(e->reflog, ref, namelen + 1);
 	ALLOC_GROW(cb->e, cb->nr + 1, cb->alloc);
 	cb->e[cb->nr++] = e;
diff --git a/builtin/remote.c b/builtin/remote.c
index ad57fc984e..f4a6ec9f13 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -509,11 +509,10 @@ struct branches_for_remote {
 };
 
 static int add_branch_for_removal(const char *refname,
-	const unsigned char *sha1, int flags, void *cb_data)
+	const struct object_id *oid, int flags, void *cb_data)
 {
 	struct branches_for_remote *branches = cb_data;
 	struct refspec refspec;
-	struct string_list_item *item;
 	struct known_remote *kr;
 
 	memset(&refspec, 0, sizeof(refspec));
@@ -543,9 +542,7 @@ static int add_branch_for_removal(const char *refname,
 	if (flags & REF_ISSYMREF)
 		return unlink(git_path("%s", refname));
 
-	item = string_list_append(branches->branches, refname);
-	item->util = xmalloc(20);
-	hashcpy(item->util, sha1);
+	string_list_append(branches->branches, refname);
 
 	return 0;
 }
@@ -557,20 +554,20 @@ struct rename_info {
 };
 
 static int read_remote_branches(const char *refname,
-	const unsigned char *sha1, int flags, void *cb_data)
+	const struct object_id *oid, int flags, void *cb_data)
 {
 	struct rename_info *rename = cb_data;
 	struct strbuf buf = STRBUF_INIT;
 	struct string_list_item *item;
 	int flag;
-	unsigned char orig_sha1[20];
+	struct object_id orig_oid;
 	const char *symref;
 
 	strbuf_addf(&buf, "refs/remotes/%s/", rename->old);
 	if (starts_with(refname, buf.buf)) {
 		item = string_list_append(rename->remote_branches, xstrdup(refname));
 		symref = resolve_ref_unsafe(refname, RESOLVE_REF_READING,
-					    orig_sha1, &flag);
+					    orig_oid.hash, &flag);
 		if (flag & REF_ISSYMREF)
 			item->util = xstrdup(symref);
 		else
@@ -704,9 +701,9 @@ static int mv(int argc, const char **argv)
 	for (i = 0; i < remote_branches.nr; i++) {
 		struct string_list_item *item = remote_branches.items + i;
 		int flag = 0;
-		unsigned char sha1[20];
+		struct object_id oid;
 
-		read_ref_full(item->string, RESOLVE_REF_READING, sha1, &flag);
+		read_ref_full(item->string, RESOLVE_REF_READING, oid.hash, &flag);
 		if (!(flag & REF_ISSYMREF))
 			continue;
 		if (delete_ref(item->string, NULL, REF_NODEREF))
@@ -826,7 +823,7 @@ static int rm(int argc, const char **argv)
 
 	if (!result)
 		result = remove_branches(&branches);
-	string_list_clear(&branches, 1);
+	string_list_clear(&branches, 0);
 
 	if (skipped.nr) {
 		fprintf_ln(stderr,
@@ -867,7 +864,7 @@ static void free_remote_ref_states(struct ref_states *states)
 }
 
 static int append_ref_to_tracked_list(const char *refname,
-	const unsigned char *sha1, int flags, void *cb_data)
+	const struct object_id *oid, int flags, void *cb_data)
 {
 	struct ref_states *states = cb_data;
 	struct refspec refspec;
diff --git a/builtin/replace.c b/builtin/replace.c
index 54bf01acb4..0d52e7fa1d 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -35,7 +35,7 @@ struct show_data {
 	enum replace_format format;
 };
 
-static int show_reference(const char *refname, const unsigned char *sha1,
+static int show_reference(const char *refname, const struct object_id *oid,
 			  int flag, void *cb_data)
 {
 	struct show_data *data = cb_data;
@@ -44,19 +44,19 @@ static int show_reference(const char *refname, const unsigned char *sha1,
 		if (data->format == REPLACE_FORMAT_SHORT)
 			printf("%s\n", refname);
 		else if (data->format == REPLACE_FORMAT_MEDIUM)
-			printf("%s -> %s\n", refname, sha1_to_hex(sha1));
+			printf("%s -> %s\n", refname, oid_to_hex(oid));
 		else { /* data->format == REPLACE_FORMAT_LONG */
-			unsigned char object[20];
+			struct object_id object;
 			enum object_type obj_type, repl_type;
 
-			if (get_sha1(refname, object))
+			if (get_sha1(refname, object.hash))
 				return error("Failed to resolve '%s' as a valid ref.", refname);
 
-			obj_type = sha1_object_info(object, NULL);
-			repl_type = sha1_object_info(sha1, NULL);
+			obj_type = sha1_object_info(object.hash, NULL);
+			repl_type = sha1_object_info(oid->hash, NULL);
 
 			printf("%s (%s) -> %s (%s)\n", refname, typename(obj_type),
-			       sha1_to_hex(sha1), typename(repl_type));
+			       oid_to_hex(oid), typename(repl_type));
 		}
 	}
 
@@ -82,7 +82,7 @@ static int list_replace_refs(const char *pattern, const char *format)
 		    "valid formats are 'short', 'medium' and 'long'\n",
 		    format);
 
-	for_each_replace_ref(show_reference, (void *) &data);
+	for_each_replace_ref(show_reference, (void *)&data);
 
 	return 0;
 }
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 4d10dd9545..b6232390a6 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -190,17 +190,17 @@ static int show_default(void)
 	return 0;
 }
 
-static int show_reference(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int show_reference(const char *refname, const struct object_id *oid, int flag, void *cb_data)
 {
 	if (ref_excluded(ref_excludes, refname))
 		return 0;
-	show_rev(NORMAL, sha1, refname);
+	show_rev(NORMAL, oid->hash, refname);
 	return 0;
 }
 
-static int anti_reference(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int anti_reference(const char *refname, const struct object_id *oid, int flag, void *cb_data)
 {
-	show_rev(REVERSED, sha1, refname);
+	show_rev(REVERSED, oid->hash, refname);
 	return 0;
 }
 
diff --git a/builtin/show-branch.c b/builtin/show-branch.c
index e69fb7c489..323f857463 100644
--- a/builtin/show-branch.c
+++ b/builtin/show-branch.c
@@ -369,10 +369,10 @@ static void sort_ref_range(int bottom, int top)
 	      compare_ref_name);
 }
 
-static int append_ref(const char *refname, const unsigned char *sha1,
+static int append_ref(const char *refname, const struct object_id *oid,
 		      int allow_dups)
 {
-	struct commit *commit = lookup_commit_reference_gently(sha1, 1);
+	struct commit *commit = lookup_commit_reference_gently(oid->hash, 1);
 	int i;
 
 	if (!commit)
@@ -394,39 +394,42 @@ static int append_ref(const char *refname, const unsigned char *sha1,
 	return 0;
 }
 
-static int append_head_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int append_head_ref(const char *refname, const struct object_id *oid,
+			   int flag, void *cb_data)
 {
-	unsigned char tmp[20];
+	struct object_id tmp;
 	int ofs = 11;
 	if (!starts_with(refname, "refs/heads/"))
 		return 0;
 	/* If both heads/foo and tags/foo exists, get_sha1 would
 	 * get confused.
 	 */
-	if (get_sha1(refname + ofs, tmp) || hashcmp(tmp, sha1))
+	if (get_sha1(refname + ofs, tmp.hash) || oidcmp(&tmp, oid))
 		ofs = 5;
-	return append_ref(refname + ofs, sha1, 0);
+	return append_ref(refname + ofs, oid, 0);
 }
 
-static int append_remote_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int append_remote_ref(const char *refname, const struct object_id *oid,
+			     int flag, void *cb_data)
 {
-	unsigned char tmp[20];
+	struct object_id tmp;
 	int ofs = 13;
 	if (!starts_with(refname, "refs/remotes/"))
 		return 0;
 	/* If both heads/foo and tags/foo exists, get_sha1 would
 	 * get confused.
 	 */
-	if (get_sha1(refname + ofs, tmp) || hashcmp(tmp, sha1))
+	if (get_sha1(refname + ofs, tmp.hash) || oidcmp(&tmp, oid))
 		ofs = 5;
-	return append_ref(refname + ofs, sha1, 0);
+	return append_ref(refname + ofs, oid, 0);
 }
 
-static int append_tag_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int append_tag_ref(const char *refname, const struct object_id *oid,
+			  int flag, void *cb_data)
 {
 	if (!starts_with(refname, "refs/tags/"))
 		return 0;
-	return append_ref(refname + 5, sha1, 0);
+	return append_ref(refname + 5, oid, 0);
 }
 
 static const char *match_ref_pattern = NULL;
@@ -440,7 +443,8 @@ static int count_slash(const char *s)
 	return cnt;
 }
 
-static int append_matching_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int append_matching_ref(const char *refname, const struct object_id *oid,
+			       int flag, void *cb_data)
 {
 	/* we want to allow pattern hold/<asterisk> to show all
 	 * branches under refs/heads/hold/, and v0.99.9? to show
@@ -456,21 +460,23 @@ static int append_matching_ref(const char *refname, const unsigned char *sha1, i
 	if (wildmatch(match_ref_pattern, tail, 0, NULL))
 		return 0;
 	if (starts_with(refname, "refs/heads/"))
-		return append_head_ref(refname, sha1, flag, cb_data);
+		return append_head_ref(refname, oid, flag, cb_data);
 	if (starts_with(refname, "refs/tags/"))
-		return append_tag_ref(refname, sha1, flag, cb_data);
-	return append_ref(refname, sha1, 0);
+		return append_tag_ref(refname, oid, flag, cb_data);
+	return append_ref(refname, oid, 0);
 }
 
 static void snarf_refs(int head, int remotes)
 {
 	if (head) {
 		int orig_cnt = ref_name_cnt;
+
 		for_each_ref(append_head_ref, NULL);
 		sort_ref_range(orig_cnt, ref_name_cnt);
 	}
 	if (remotes) {
 		int orig_cnt = ref_name_cnt;
+
 		for_each_ref(append_remote_ref, NULL);
 		sort_ref_range(orig_cnt, ref_name_cnt);
 	}
@@ -530,14 +536,15 @@ static int show_independent(struct commit **rev,
 
 static void append_one_rev(const char *av)
 {
-	unsigned char revkey[20];
-	if (!get_sha1(av, revkey)) {
-		append_ref(av, revkey, 0);
+	struct object_id revkey;
+	if (!get_sha1(av, revkey.hash)) {
+		append_ref(av, &revkey, 0);
 		return;
 	}
 	if (strchr(av, '*') || strchr(av, '?') || strchr(av, '[')) {
 		/* glob style match */
 		int saved_matches = ref_name_cnt;
+
 		match_ref_pattern = av;
 		match_ref_slash = count_slash(av);
 		for_each_ref(append_matching_ref, NULL);
@@ -636,7 +643,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 	char head[128];
 	const char *head_p;
 	int head_len;
-	unsigned char head_sha1[20];
+	struct object_id head_oid;
 	int merge_base = 0;
 	int independent = 0;
 	int no_name = 0;
@@ -722,7 +729,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 		all_heads = 1;
 
 	if (reflog) {
-		unsigned char sha1[20];
+		struct object_id oid;
 		char nth_desc[256];
 		char *ref;
 		int base = 0;
@@ -733,7 +740,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 
 			fake_av[0] = resolve_refdup("HEAD",
 						    RESOLVE_REF_READING,
-						    sha1, NULL);
+						    oid.hash, NULL);
 			fake_av[1] = NULL;
 			av = fake_av;
 			ac = 1;
@@ -744,7 +751,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 		if (MAX_REVS < reflog)
 			die("Only %d entries can be shown at one time.",
 			    MAX_REVS);
-		if (!dwim_ref(*av, strlen(*av), sha1, &ref))
+		if (!dwim_ref(*av, strlen(*av), oid.hash, &ref))
 			die("No such ref %s", *av);
 
 		/* Has the base been specified? */
@@ -755,7 +762,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 				/* Ah, that is a date spec... */
 				unsigned long at;
 				at = approxidate(reflog_base);
-				read_ref_at(ref, flags, at, -1, sha1, NULL,
+				read_ref_at(ref, flags, at, -1, oid.hash, NULL,
 					    NULL, NULL, &base);
 			}
 		}
@@ -766,7 +773,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 			unsigned long timestamp;
 			int tz;
 
-			if (read_ref_at(ref, flags, 0, base+i, sha1, &logmsg,
+			if (read_ref_at(ref, flags, 0, base+i, oid.hash, &logmsg,
 					&timestamp, &tz, NULL)) {
 				reflog = i;
 				break;
@@ -781,7 +788,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 						msg);
 			free(logmsg);
 			sprintf(nth_desc, "%s@{%d}", *av, base+i);
-			append_ref(nth_desc, sha1, 1);
+			append_ref(nth_desc, &oid, 1);
 		}
 		free(ref);
 	}
@@ -795,7 +802,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 	}
 
 	head_p = resolve_ref_unsafe("HEAD", RESOLVE_REF_READING,
-				    head_sha1, NULL);
+				    head_oid.hash, NULL);
 	if (head_p) {
 		head_len = strlen(head_p);
 		memcpy(head, head_p, head_len + 1);
@@ -814,7 +821,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 			if (rev_is_head(head,
 					head_len,
 					ref_name[i],
-					head_sha1, NULL))
+					head_oid.hash, NULL))
 				has_head++;
 		}
 		if (!has_head) {
@@ -829,17 +836,17 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 	}
 
 	for (num_rev = 0; ref_name[num_rev]; num_rev++) {
-		unsigned char revkey[20];
+		struct object_id revkey;
 		unsigned int flag = 1u << (num_rev + REV_SHIFT);
 
 		if (MAX_REVS <= num_rev)
 			die("cannot handle more than %d revs.", MAX_REVS);
-		if (get_sha1(ref_name[num_rev], revkey))
+		if (get_sha1(ref_name[num_rev], revkey.hash))
 			die("'%s' is not a valid ref.", ref_name[num_rev]);
-		commit = lookup_commit_reference(revkey);
+		commit = lookup_commit_reference(revkey.hash);
 		if (!commit)
 			die("cannot find commit %s (%s)",
-			    ref_name[num_rev], revkey);
+			    ref_name[num_rev], oid_to_hex(&revkey));
 		parse_commit(commit);
 		mark_seen(commit, &seen);
 
@@ -873,7 +880,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 			int is_head = rev_is_head(head,
 						  head_len,
 						  ref_name[i],
-						  head_sha1,
+						  head_oid.hash,
 						  rev[i]->object.sha1);
 			if (extra < 0)
 				printf("%c [%s] ",
diff --git a/builtin/show-ref.c b/builtin/show-ref.c
index afb10309d6..dfbc314ac2 100644
--- a/builtin/show-ref.c
+++ b/builtin/show-ref.c
@@ -17,19 +17,20 @@ static int deref_tags, show_head, tags_only, heads_only, found_match, verify,
 static const char **pattern;
 static const char *exclude_existing_arg;
 
-static void show_one(const char *refname, const unsigned char *sha1)
+static void show_one(const char *refname, const struct object_id *oid)
 {
-	const char *hex = find_unique_abbrev(sha1, abbrev);
+	const char *hex = find_unique_abbrev(oid->hash, abbrev);
 	if (hash_only)
 		printf("%s\n", hex);
 	else
 		printf("%s %s\n", hex, refname);
 }
 
-static int show_ref(const char *refname, const unsigned char *sha1, int flag, void *cbdata)
+static int show_ref(const char *refname, const struct object_id *oid,
+		    int flag, void *cbdata)
 {
 	const char *hex;
-	unsigned char peeled[20];
+	struct object_id peeled;
 
 	if (show_head && !strcmp(refname, "HEAD"))
 		goto match;
@@ -69,26 +70,27 @@ match:
 	 * detect and return error if the repository is corrupt and
 	 * ref points at a nonexistent object.
 	 */
-	if (!has_sha1_file(sha1))
+	if (!has_sha1_file(oid->hash))
 		die("git show-ref: bad ref %s (%s)", refname,
-		    sha1_to_hex(sha1));
+		    oid_to_hex(oid));
 
 	if (quiet)
 		return 0;
 
-	show_one(refname, sha1);
+	show_one(refname, oid);
 
 	if (!deref_tags)
 		return 0;
 
-	if (!peel_ref(refname, peeled)) {
-		hex = find_unique_abbrev(peeled, abbrev);
+	if (!peel_ref(refname, peeled.hash)) {
+		hex = find_unique_abbrev(peeled.hash, abbrev);
 		printf("%s %s^{}\n", hex, refname);
 	}
 	return 0;
 }
 
-static int add_existing(const char *refname, const unsigned char *sha1, int flag, void *cbdata)
+static int add_existing(const char *refname, const struct object_id *oid,
+			int flag, void *cbdata)
 {
 	struct string_list *list = (struct string_list *)cbdata;
 	string_list_insert(list, refname);
@@ -208,12 +210,12 @@ int cmd_show_ref(int argc, const char **argv, const char *prefix)
 		if (!pattern)
 			die("--verify requires a reference");
 		while (*pattern) {
-			unsigned char sha1[20];
+			struct object_id oid;
 
 			if (starts_with(*pattern, "refs/") &&
-			    !read_ref(*pattern, sha1)) {
+			    !read_ref(*pattern, oid.hash)) {
 				if (!quiet)
-					show_one(*pattern, sha1);
+					show_one(*pattern, &oid);
 			}
 			else if (!quiet)
 				die("'%s' - not a valid ref", *pattern);
diff --git a/builtin/tag.c b/builtin/tag.c
index 6f07ac6b93..5f6cdc5a03 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -176,7 +176,7 @@ static enum contains_result contains(struct commit *candidate,
 	return contains_test(candidate, want);
 }
 
-static void show_tag_lines(const unsigned char *sha1, int lines)
+static void show_tag_lines(const struct object_id *oid, int lines)
 {
 	int i;
 	unsigned long size;
@@ -184,14 +184,14 @@ static void show_tag_lines(const unsigned char *sha1, int lines)
 	char *buf, *sp, *eol;
 	size_t len;
 
-	buf = read_sha1_file(sha1, &type, &size);
+	buf = read_sha1_file(oid->hash, &type, &size);
 	if (!buf)
-		die_errno("unable to read object %s", sha1_to_hex(sha1));
+		die_errno("unable to read object %s", oid_to_hex(oid));
 	if (type != OBJ_COMMIT && type != OBJ_TAG)
 		goto free_return;
 	if (!size)
 		die("an empty %s object %s?",
-		    typename(type), sha1_to_hex(sha1));
+		    typename(type), oid_to_hex(oid));
 
 	/* skip header */
 	sp = strstr(buf, "\n\n");
@@ -215,7 +215,7 @@ free_return:
 	free(buf);
 }
 
-static int show_reference(const char *refname, const unsigned char *sha1,
+static int show_reference(const char *refname, const struct object_id *oid,
 			  int flag, void *cb_data)
 {
 	struct tag_filter *filter = cb_data;
@@ -224,14 +224,14 @@ static int show_reference(const char *refname, const unsigned char *sha1,
 		if (filter->with_commit) {
 			struct commit *commit;
 
-			commit = lookup_commit_reference_gently(sha1, 1);
+			commit = lookup_commit_reference_gently(oid->hash, 1);
 			if (!commit)
 				return 0;
 			if (!contains(commit, filter->with_commit))
 				return 0;
 		}
 
-		if (points_at.nr && !match_points_at(refname, sha1))
+		if (points_at.nr && !match_points_at(refname, oid->hash))
 			return 0;
 
 		if (!filter->lines) {
@@ -242,7 +242,7 @@ static int show_reference(const char *refname, const unsigned char *sha1,
 			return 0;
 		}
 		printf("%-15s ", refname);
-		show_tag_lines(sha1, filter->lines);
+		show_tag_lines(oid, filter->lines);
 		putchar('\n');
 	}
 
@@ -268,7 +268,7 @@ static int list_tags(const char **patterns, int lines,
 	memset(&filter.tags, 0, sizeof(filter.tags));
 	filter.tags.strdup_strings = 1;
 
-	for_each_tag_ref(show_reference, (void *) &filter);
+	for_each_tag_ref(show_reference, (void *)&filter);
 	if (sort) {
 		int i;
 		if ((sort & SORT_MASK) == VERCMP_SORT)
diff --git a/fetch-pack.c b/fetch-pack.c
index ff8a13b8c4..a912935a63 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -65,7 +65,7 @@ static void rev_list_push(struct commit *commit, int mark)
 	}
 }
 
-static int rev_list_insert_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int rev_list_insert_ref(const char *refname, const unsigned char *sha1)
 {
 	struct object *o = deref_tag(parse_object(sha1), refname, 0);
 
@@ -75,9 +75,16 @@ static int rev_list_insert_ref(const char *refname, const unsigned char *sha1, i
 	return 0;
 }
 
-static int clear_marks(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int rev_list_insert_ref_oid(const char *refname, const struct object_id *oid,
+				   int flag, void *cb_data)
 {
-	struct object *o = deref_tag(parse_object(sha1), refname, 0);
+	return rev_list_insert_ref(refname, oid->hash);
+}
+
+static int clear_marks(const char *refname, const struct object_id *oid,
+		       int flag, void *cb_data)
+{
+	struct object *o = deref_tag(parse_object(oid->hash), refname, 0);
 
 	if (o && o->type == OBJ_COMMIT)
 		clear_commit_marks((struct commit *)o,
@@ -231,7 +238,7 @@ static void send_request(struct fetch_pack_args *args,
 
 static void insert_one_alternate_ref(const struct ref *ref, void *unused)
 {
-	rev_list_insert_ref(NULL, ref->old_sha1, 0, NULL);
+	rev_list_insert_ref(NULL, ref->old_sha1);
 }
 
 #define INITIAL_FLUSH 16
@@ -268,7 +275,7 @@ static int find_common(struct fetch_pack_args *args,
 		for_each_ref(clear_marks, NULL);
 	marked = 1;
 
-	for_each_ref(rev_list_insert_ref, NULL);
+	for_each_ref(rev_list_insert_ref_oid, NULL);
 	for_each_alternate_ref(insert_one_alternate_ref, NULL);
 
 	fetching = 0;
@@ -471,7 +478,7 @@ done:
 
 static struct commit_list *complete;
 
-static int mark_complete(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int mark_complete(const unsigned char *sha1)
 {
 	struct object *o = parse_object(sha1);
 
@@ -492,6 +499,12 @@ static int mark_complete(const char *refname, const unsigned char *sha1, int fla
 	return 0;
 }
 
+static int mark_complete_oid(const char *refname, const struct object_id *oid,
+			     int flag, void *cb_data)
+{
+	return mark_complete(oid->hash);
+}
+
 static void mark_recent_complete_commits(struct fetch_pack_args *args,
 					 unsigned long cutoff)
 {
@@ -570,7 +583,7 @@ static void filter_refs(struct fetch_pack_args *args,
 
 static void mark_alternate_complete(const struct ref *ref, void *unused)
 {
-	mark_complete(NULL, ref->old_sha1, 0, NULL);
+	mark_complete(ref->old_sha1);
 }
 
 static int everything_local(struct fetch_pack_args *args,
@@ -605,7 +618,7 @@ static int everything_local(struct fetch_pack_args *args,
 	}
 
 	if (!args->depth) {
-		for_each_ref(mark_complete, NULL);
+		for_each_ref(mark_complete_oid, NULL);
 		for_each_alternate_ref(mark_alternate_complete, NULL);
 		commit_list_sort_by_date(&complete);
 		if (cutoff)
diff --git a/help.c b/help.c
index 8f72051ae0..80ca8ee68d 100644
--- a/help.c
+++ b/help.c
@@ -429,7 +429,7 @@ struct similar_ref_cb {
 	struct string_list *similar_refs;
 };
 
-static int append_similar_ref(const char *refname, const unsigned char *sha1,
+static int append_similar_ref(const char *refname, const struct object_id *oid,
 			      int flags, void *cb_data)
 {
 	struct similar_ref_cb *cb = (struct similar_ref_cb *)(cb_data);
diff --git a/http-backend.c b/http-backend.c
index 6bf139b768..501bf797c0 100644
--- a/http-backend.c
+++ b/http-backend.c
@@ -421,16 +421,16 @@ static void run_service(const char **argv, int buffer_input)
 		exit(1);
 }
 
-static int show_text_ref(const char *name, const unsigned char *sha1,
-	int flag, void *cb_data)
+static int show_text_ref(const char *name, const struct object_id *oid,
+			 int flag, void *cb_data)
 {
 	const char *name_nons = strip_namespace(name);
 	struct strbuf *buf = cb_data;
-	struct object *o = parse_object(sha1);
+	struct object *o = parse_object(oid->hash);
 	if (!o)
 		return 0;
 
-	strbuf_addf(buf, "%s\t%s\n", sha1_to_hex(sha1), name_nons);
+	strbuf_addf(buf, "%s\t%s\n", oid_to_hex(oid), name_nons);
 	if (o->type == OBJ_TAG) {
 		o = deref_tag(o, name, 0);
 		if (!o)
@@ -473,21 +473,21 @@ static void get_info_refs(char *arg)
 	strbuf_release(&buf);
 }
 
-static int show_head_ref(const char *refname, const unsigned char *sha1,
-	int flag, void *cb_data)
+static int show_head_ref(const char *refname, const struct object_id *oid,
+			 int flag, void *cb_data)
 {
 	struct strbuf *buf = cb_data;
 
 	if (flag & REF_ISSYMREF) {
-		unsigned char unused[20];
+		struct object_id unused;
 		const char *target = resolve_ref_unsafe(refname,
 							RESOLVE_REF_READING,
-							unused, NULL);
+							unused.hash, NULL);
 		const char *target_nons = strip_namespace(target);
 
 		strbuf_addf(buf, "ref: %s\n", target_nons);
 	} else {
-		strbuf_addf(buf, "%s\n", sha1_to_hex(sha1));
+		strbuf_addf(buf, "%s\n", oid_to_hex(oid));
 	}
 
 	return 0;
diff --git a/log-tree.c b/log-tree.c
index 8dba7be92e..01beb11f65 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -89,7 +89,8 @@ const struct name_decoration *get_name_decoration(const struct object *obj)
 	return lookup_decoration(&name_decoration, obj);
 }
 
-static int add_ref_decoration(const char *refname, const unsigned char *sha1, int flags, void *cb_data)
+static int add_ref_decoration(const char *refname, const struct object_id *oid,
+			      int flags, void *cb_data)
 {
 	struct object *obj;
 	enum decoration_type type = DECORATION_NONE;
@@ -97,20 +98,20 @@ static int add_ref_decoration(const char *refname, const unsigned char *sha1, in
 	assert(cb_data == NULL);
 
 	if (starts_with(refname, "refs/replace/")) {
-		unsigned char original_sha1[20];
+		struct object_id original_oid;
 		if (!check_replace_refs)
 			return 0;
-		if (get_sha1_hex(refname + 13, original_sha1)) {
+		if (get_oid_hex(refname + 13, &original_oid)) {
 			warning("invalid replace ref %s", refname);
 			return 0;
 		}
-		obj = parse_object(original_sha1);
+		obj = parse_object(original_oid.hash);
 		if (obj)
 			add_name_decoration(DECORATION_GRAFTED, "replaced", obj);
 		return 0;
 	}
 
-	obj = parse_object(sha1);
+	obj = parse_object(oid->hash);
 	if (!obj)
 		return 0;
 
@@ -149,6 +150,7 @@ static int add_graft_decoration(const struct commit_graft *graft, void *cb_data)
 void load_ref_decorations(int flags)
 {
 	if (!decoration_loaded) {
+
 		decoration_loaded = 1;
 		decoration_flags = flags;
 		for_each_ref(add_ref_decoration, NULL);
diff --git a/notes.c b/notes.c
index 2be4d7f3fd..df08209dee 100644
--- a/notes.c
+++ b/notes.c
@@ -918,7 +918,7 @@ out:
 	return ret;
 }
 
-static int string_list_add_one_ref(const char *refname, const unsigned char *sha1,
+static int string_list_add_one_ref(const char *refname, const struct object_id *oid,
 				   int flag, void *cb)
 {
 	struct string_list *refs = cb;
diff --git a/reachable.c b/reachable.c
index 69fa6851da..9cff25b490 100644
--- a/reachable.c
+++ b/reachable.c
@@ -22,9 +22,10 @@ static void update_progress(struct connectivity_progress *cp)
 		display_progress(cp->progress, cp->count);
 }
 
-static int add_one_ref(const char *path, const unsigned char *sha1, int flag, void *cb_data)
+static int add_one_ref(const char *path, const struct object_id *oid,
+		       int flag, void *cb_data)
 {
-	struct object *object = parse_object_or_die(sha1, path);
+	struct object *object = parse_object_or_die(oid->hash, path);
 	struct rev_info *revs = (struct rev_info *)cb_data;
 
 	add_pending_object(revs, object, "");
diff --git a/refs.c b/refs.c
index 8480d8dbf5..a742d7925d 100644
--- a/refs.c
+++ b/refs.c
@@ -10,7 +10,7 @@ struct ref_lock {
 	char *ref_name;
 	char *orig_ref_name;
 	struct lock_file *lk;
-	unsigned char old_sha1[20];
+	struct object_id old_oid;
 };
 
 /*
@@ -161,7 +161,7 @@ struct ref_value {
 	 * null.  If REF_ISSYMREF, then this is the name of the object
 	 * referred to by the last reference in the symlink chain.
 	 */
-	unsigned char sha1[20];
+	struct object_id oid;
 
 	/*
 	 * If REF_KNOWS_PEELED, then this field holds the peeled value
@@ -169,7 +169,7 @@ struct ref_value {
 	 * be peelable.  See the documentation for peel_ref() for an
 	 * exact definition of "peelable".
 	 */
-	unsigned char peeled[20];
+	struct object_id peeled;
 };
 
 struct ref_cache;
@@ -351,8 +351,8 @@ static struct ref_entry *create_ref_entry(const char *refname,
 		die("Reference has invalid format: '%s'", refname);
 	len = strlen(refname) + 1;
 	ref = xmalloc(sizeof(struct ref_entry) + len);
-	hashcpy(ref->u.value.sha1, sha1);
-	hashclr(ref->u.value.peeled);
+	hashcpy(ref->u.value.oid.hash, sha1);
+	oidclr(&ref->u.value.peeled);
 	memcpy(ref->name, refname, len);
 	ref->flag = flag;
 	return ref;
@@ -626,7 +626,7 @@ static int is_dup_ref(const struct ref_entry *ref1, const struct ref_entry *ref2
 		/* This is impossible by construction */
 		die("Reference directory conflict: %s", ref1->name);
 
-	if (hashcmp(ref1->u.value.sha1, ref2->u.value.sha1))
+	if (oidcmp(&ref1->u.value.oid, &ref2->u.value.oid))
 		die("Duplicated ref, and SHA1s don't match: %s", ref1->name);
 
 	warning("Duplicated ref: %s", ref1->name);
@@ -674,7 +674,7 @@ static int ref_resolves_to_object(struct ref_entry *entry)
 {
 	if (entry->flag & REF_ISBROKEN)
 		return 0;
-	if (!has_sha1_file(entry->u.value.sha1)) {
+	if (!has_sha1_file(entry->u.value.oid.hash)) {
 		error("%s does not point to a valid object!", entry->name);
 		return 0;
 	}
@@ -722,7 +722,7 @@ static int do_one_ref(struct ref_entry *entry, void *cb_data)
 	/* Store the old value, in case this is a recursive call: */
 	old_current_ref = current_ref;
 	current_ref = entry;
-	retval = data->fn(entry->name + data->trim, entry->u.value.sha1,
+	retval = data->fn(entry->name + data->trim, &entry->u.value.oid,
 			  entry->flag, data->cb_data);
 	current_ref = old_current_ref;
 	return retval;
@@ -1258,7 +1258,7 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
 		    line.len == PEELED_LINE_LENGTH &&
 		    line.buf[PEELED_LINE_LENGTH - 1] == '\n' &&
 		    !get_sha1_hex(line.buf + 1, sha1)) {
-			hashcpy(last->u.value.peeled, sha1);
+			hashcpy(last->u.value.peeled.hash, sha1);
 			/*
 			 * Regardless of what the file header said,
 			 * we definitely know the value of *this*
@@ -1439,7 +1439,7 @@ static int resolve_gitlink_packed_ref(struct ref_cache *refs,
 	if (ref == NULL)
 		return -1;
 
-	hashcpy(sha1, ref->u.value.sha1);
+	hashcpy(sha1, ref->u.value.oid.hash);
 	return 0;
 }
 
@@ -1526,7 +1526,7 @@ static int resolve_missing_loose_ref(const char *refname,
 	 */
 	entry = get_packed_ref(refname);
 	if (entry) {
-		hashcpy(sha1, entry->u.value.sha1);
+		hashcpy(sha1, entry->u.value.oid.hash);
 		if (flags)
 			*flags |= REF_ISPACKED;
 		return 0;
@@ -1756,13 +1756,14 @@ int ref_exists(const char *refname)
 	return !!resolve_ref_unsafe(refname, RESOLVE_REF_READING, sha1, NULL);
 }
 
-static int filter_refs(const char *refname, const unsigned char *sha1, int flags,
-		       void *data)
+static int filter_refs(const char *refname, const struct object_id *oid,
+			   int flags, void *data)
 {
 	struct ref_filter *filter = (struct ref_filter *)data;
+
 	if (wildmatch(filter->pattern, refname, 0, NULL))
 		return 0;
-	return filter->fn(refname, sha1, flags, filter->cb_data);
+	return filter->fn(refname, oid, flags, filter->cb_data);
 }
 
 enum peel_status {
@@ -1836,9 +1837,9 @@ static enum peel_status peel_entry(struct ref_entry *entry, int repeel)
 	if (entry->flag & REF_KNOWS_PEELED) {
 		if (repeel) {
 			entry->flag &= ~REF_KNOWS_PEELED;
-			hashclr(entry->u.value.peeled);
+			oidclr(&entry->u.value.peeled);
 		} else {
-			return is_null_sha1(entry->u.value.peeled) ?
+			return is_null_oid(&entry->u.value.peeled) ?
 				PEEL_NON_TAG : PEEL_PEELED;
 		}
 	}
@@ -1847,7 +1848,7 @@ static enum peel_status peel_entry(struct ref_entry *entry, int repeel)
 	if (entry->flag & REF_ISSYMREF)
 		return PEEL_IS_SYMREF;
 
-	status = peel_object(entry->u.value.sha1, entry->u.value.peeled);
+	status = peel_object(entry->u.value.oid.hash, entry->u.value.peeled.hash);
 	if (status == PEEL_PEELED || status == PEEL_NON_TAG)
 		entry->flag |= REF_KNOWS_PEELED;
 	return status;
@@ -1862,7 +1863,7 @@ int peel_ref(const char *refname, unsigned char *sha1)
 			    || !strcmp(current_ref->name, refname))) {
 		if (peel_entry(current_ref, 0))
 			return -1;
-		hashcpy(sha1, current_ref->u.value.peeled);
+		hashcpy(sha1, current_ref->u.value.peeled.hash);
 		return 0;
 	}
 
@@ -1882,7 +1883,7 @@ int peel_ref(const char *refname, unsigned char *sha1)
 		if (r) {
 			if (peel_entry(r, 0))
 				return -1;
-			hashcpy(sha1, r->u.value.peeled);
+			hashcpy(sha1, r->u.value.peeled.hash);
 			return 0;
 		}
 	}
@@ -1897,17 +1898,17 @@ struct warn_if_dangling_data {
 	const char *msg_fmt;
 };
 
-static int warn_if_dangling_symref(const char *refname, const unsigned char *sha1,
+static int warn_if_dangling_symref(const char *refname, const struct object_id *oid,
 				   int flags, void *cb_data)
 {
 	struct warn_if_dangling_data *d = cb_data;
 	const char *resolves_to;
-	unsigned char junk[20];
+	struct object_id junk;
 
 	if (!(flags & REF_ISSYMREF))
 		return 0;
 
-	resolves_to = resolve_ref_unsafe(refname, 0, junk, NULL);
+	resolves_to = resolve_ref_unsafe(refname, 0, junk.hash, NULL);
 	if (!resolves_to
 	    || (d->refname
 		? strcmp(resolves_to, d->refname)
@@ -2027,18 +2028,18 @@ static int do_for_each_ref(struct ref_cache *refs, const char *base,
 
 static int do_head_ref(const char *submodule, each_ref_fn fn, void *cb_data)
 {
-	unsigned char sha1[20];
+	struct object_id oid;
 	int flag;
 
 	if (submodule) {
-		if (resolve_gitlink_ref(submodule, "HEAD", sha1) == 0)
-			return fn("HEAD", sha1, 0, cb_data);
+		if (resolve_gitlink_ref(submodule, "HEAD", oid.hash) == 0)
+			return fn("HEAD", &oid, 0, cb_data);
 
 		return 0;
 	}
 
-	if (!read_ref_full("HEAD", RESOLVE_REF_READING, sha1, &flag))
-		return fn("HEAD", sha1, flag, cb_data);
+	if (!read_ref_full("HEAD", RESOLVE_REF_READING, oid.hash, &flag))
+		return fn("HEAD", &oid, flag, cb_data);
 
 	return 0;
 }
@@ -2113,12 +2114,12 @@ int head_ref_namespaced(each_ref_fn fn, void *cb_data)
 {
 	struct strbuf buf = STRBUF_INIT;
 	int ret = 0;
-	unsigned char sha1[20];
+	struct object_id oid;
 	int flag;
 
 	strbuf_addf(&buf, "%sHEAD", get_git_namespace());
-	if (!read_ref_full(buf.buf, RESOLVE_REF_READING, sha1, &flag))
-		ret = fn(buf.buf, sha1, flag, cb_data);
+	if (!read_ref_full(buf.buf, RESOLVE_REF_READING, oid.hash, &flag))
+		ret = fn(buf.buf, &oid, flag, cb_data);
 	strbuf_release(&buf);
 
 	return ret;
@@ -2224,16 +2225,16 @@ static struct ref_lock *verify_lock(struct ref_lock *lock,
 {
 	if (read_ref_full(lock->ref_name,
 			  mustexist ? RESOLVE_REF_READING : 0,
-			  lock->old_sha1, NULL)) {
+			  lock->old_oid.hash, NULL)) {
 		int save_errno = errno;
 		error("Can't verify ref %s", lock->ref_name);
 		unlock_ref(lock);
 		errno = save_errno;
 		return NULL;
 	}
-	if (hashcmp(lock->old_sha1, old_sha1)) {
+	if (hashcmp(lock->old_oid.hash, old_sha1)) {
 		error("Ref %s is at %s but expected %s", lock->ref_name,
-			sha1_to_hex(lock->old_sha1), sha1_to_hex(old_sha1));
+			oid_to_hex(&lock->old_oid), sha1_to_hex(old_sha1));
 		unlock_ref(lock);
 		errno = EBUSY;
 		return NULL;
@@ -2381,7 +2382,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 	}
 
 	refname = resolve_ref_unsafe(refname, resolve_flags,
-				     lock->old_sha1, &type);
+				     lock->old_oid.hash, &type);
 	if (!refname && errno == EISDIR) {
 		/* we are trying to lock foo but we used to
 		 * have foo/bar which now does not exist;
@@ -2400,7 +2401,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 			goto error_return;
 		}
 		refname = resolve_ref_unsafe(orig_refname, resolve_flags,
-					     lock->old_sha1, &type);
+					     lock->old_oid.hash, &type);
 	}
 	if (type_p)
 	    *type_p = type;
@@ -2420,7 +2421,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 	 * refname, nor a packed ref whose name is a proper prefix of
 	 * our refname.
 	 */
-	if (is_null_sha1(lock->old_sha1) &&
+	if (is_null_oid(&lock->old_oid) &&
 	    verify_refname_available(refname, extras, skip,
 				     get_packed_refs(&ref_cache), err)) {
 		last_errno = ENOTDIR;
@@ -2496,9 +2497,9 @@ static int write_packed_entry_fn(struct ref_entry *entry, void *cb_data)
 	if (peel_status != PEEL_PEELED && peel_status != PEEL_NON_TAG)
 		error("internal error: %s is not a valid packed reference!",
 		      entry->name);
-	write_packed_entry(cb_data, entry->name, entry->u.value.sha1,
+	write_packed_entry(cb_data, entry->name, entry->u.value.oid.hash,
 			   peel_status == PEEL_PEELED ?
-			   entry->u.value.peeled : NULL);
+			   entry->u.value.peeled.hash : NULL);
 	return 0;
 }
 
@@ -2615,24 +2616,24 @@ static int pack_if_possible_fn(struct ref_entry *entry, void *cb_data)
 	peel_status = peel_entry(entry, 1);
 	if (peel_status != PEEL_PEELED && peel_status != PEEL_NON_TAG)
 		die("internal error peeling reference %s (%s)",
-		    entry->name, sha1_to_hex(entry->u.value.sha1));
+		    entry->name, oid_to_hex(&entry->u.value.oid));
 	packed_entry = find_ref(cb->packed_refs, entry->name);
 	if (packed_entry) {
 		/* Overwrite existing packed entry with info from loose entry */
 		packed_entry->flag = REF_ISPACKED | REF_KNOWS_PEELED;
-		hashcpy(packed_entry->u.value.sha1, entry->u.value.sha1);
+		oidcpy(&packed_entry->u.value.oid, &entry->u.value.oid);
 	} else {
-		packed_entry = create_ref_entry(entry->name, entry->u.value.sha1,
+		packed_entry = create_ref_entry(entry->name, entry->u.value.oid.hash,
 						REF_ISPACKED | REF_KNOWS_PEELED, 0);
 		add_ref(cb->packed_refs, packed_entry);
 	}
-	hashcpy(packed_entry->u.value.peeled, entry->u.value.peeled);
+	oidcpy(&packed_entry->u.value.peeled, &entry->u.value.peeled);
 
 	/* Schedule the loose reference for pruning if requested. */
 	if ((cb->flags & PACK_REFS_PRUNE)) {
 		int namelen = strlen(entry->name) + 1;
 		struct ref_to_prune *n = xcalloc(1, sizeof(*n) + namelen);
-		hashcpy(n->sha1, entry->u.value.sha1);
+		hashcpy(n->sha1, entry->u.value.oid.hash);
 		strcpy(n->name, entry->name);
 		n->next = cb->ref_to_prune;
 		cb->ref_to_prune = n;
@@ -2943,7 +2944,7 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
 		strbuf_release(&err);
 		goto rollback;
 	}
-	hashcpy(lock->old_sha1, orig_sha1);
+	hashcpy(lock->old_oid.hash, orig_sha1);
 
 	if (write_ref_to_lockfile(lock, orig_sha1) ||
 	    commit_ref_update(lock, orig_sha1, logmsg)) {
@@ -3198,9 +3199,9 @@ static int commit_ref_update(struct ref_lock *lock,
 			     const unsigned char *sha1, const char *logmsg)
 {
 	clear_loose_ref_cache(&ref_cache);
-	if (log_ref_write(lock->ref_name, lock->old_sha1, sha1, logmsg) < 0 ||
+	if (log_ref_write(lock->ref_name, lock->old_oid.hash, sha1, logmsg) < 0 ||
 	    (strcmp(lock->ref_name, lock->orig_ref_name) &&
-	     log_ref_write(lock->orig_ref_name, lock->old_sha1, sha1, logmsg) < 0)) {
+	     log_ref_write(lock->orig_ref_name, lock->old_oid.hash, sha1, logmsg) < 0)) {
 		unlock_ref(lock);
 		return -1;
 	}
@@ -3224,7 +3225,7 @@ static int commit_ref_update(struct ref_lock *lock,
 					      head_sha1, &head_flag);
 		if (head_ref && (head_flag & REF_ISSYMREF) &&
 		    !strcmp(head_ref, lock->ref_name))
-			log_ref_write("HEAD", lock->old_sha1, sha1, logmsg);
+			log_ref_write("HEAD", lock->old_oid.hash, sha1, logmsg);
 	}
 	if (commit_ref(lock)) {
 		error("Couldn't set %s", lock->ref_name);
@@ -3616,11 +3617,12 @@ static int do_for_each_reflog(struct strbuf *name, each_ref_fn fn, void *cb_data
 				strbuf_addch(name, '/');
 				retval = do_for_each_reflog(name, fn, cb_data);
 			} else {
-				unsigned char sha1[20];
-				if (read_ref_full(name->buf, 0, sha1, NULL))
+				struct object_id oid;
+
+				if (read_ref_full(name->buf, 0, oid.hash, NULL))
 					retval = error("bad ref for %s", name->buf);
 				else
-					retval = fn(name->buf, sha1, 0, cb_data);
+					retval = fn(name->buf, &oid, 0, cb_data);
 			}
 			if (retval)
 				break;
@@ -3921,7 +3923,7 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 						  (update->flags & REF_NODEREF));
 
 			if (!overwriting_symref &&
-			    !hashcmp(update->lock->old_sha1, update->new_sha1)) {
+			    !hashcmp(update->lock->old_oid.hash, update->new_sha1)) {
 				/*
 				 * The reference already has the desired
 				 * value, so we don't need to write it.
diff --git a/refs.h b/refs.h
index 6d7d9b40f3..8c3d433a8a 100644
--- a/refs.h
+++ b/refs.h
@@ -67,7 +67,7 @@ struct ref_transaction;
  * single callback invocation.
  */
 typedef int each_ref_fn(const char *refname,
-			const unsigned char *sha1, int flags, void *cb_data);
+			const struct object_id *oid, int flags, void *cb_data);
 
 /*
  * The following functions invoke the specified callback function for
diff --git a/remote.c b/remote.c
index a467d4ff07..26504b7447 100644
--- a/remote.c
+++ b/remote.c
@@ -2168,7 +2168,8 @@ int format_tracking_info(struct branch *branch, struct strbuf *sb)
 	return 1;
 }
 
-static int one_local_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int one_local_ref(const char *refname, const struct object_id *oid,
+			 int flag, void *cb_data)
 {
 	struct ref ***local_tail = cb_data;
 	struct ref *ref;
@@ -2180,7 +2181,7 @@ static int one_local_ref(const char *refname, const unsigned char *sha1, int fla
 
 	len = strlen(refname) + 1;
 	ref = xcalloc(1, sizeof(*ref) + len);
-	hashcpy(ref->new_sha1, sha1);
+	hashcpy(ref->new_sha1, oid->hash);
 	memcpy(ref->name, refname, len);
 	**local_tail = ref;
 	*local_tail = &ref->next;
@@ -2190,6 +2191,7 @@ static int one_local_ref(const char *refname, const unsigned char *sha1, int fla
 struct ref *get_local_heads(void)
 {
 	struct ref *local_refs = NULL, **local_tail = &local_refs;
+
 	for_each_ref(one_local_ref, &local_tail);
 	return local_refs;
 }
@@ -2242,8 +2244,8 @@ struct stale_heads_info {
 	int ref_count;
 };
 
-static int get_stale_heads_cb(const char *refname,
-	const unsigned char *sha1, int flags, void *cb_data)
+static int get_stale_heads_cb(const char *refname, const struct object_id *oid,
+			      int flags, void *cb_data)
 {
 	struct stale_heads_info *info = cb_data;
 	struct string_list matches = STRING_LIST_INIT_DUP;
@@ -2272,7 +2274,7 @@ static int get_stale_heads_cb(const char *refname,
 
 	if (stale) {
 		struct ref *ref = make_linked_ref(refname, &info->stale_refs_tail);
-		hashcpy(ref->new_sha1, sha1);
+		hashcpy(ref->new_sha1, oid->hash);
 	}
 
 clean_exit:
@@ -2285,6 +2287,7 @@ struct ref *get_stale_heads(struct refspec *refs, int ref_count, struct ref *fet
 	struct ref *ref, *stale_refs = NULL;
 	struct string_list ref_names = STRING_LIST_INIT_NODUP;
 	struct stale_heads_info info;
+
 	info.ref_names = &ref_names;
 	info.stale_refs_tail = &stale_refs;
 	info.refs = refs;
diff --git a/replace_object.c b/replace_object.c
index 0ab2dc1374..f0b39f06d5 100644
--- a/replace_object.c
+++ b/replace_object.c
@@ -53,7 +53,7 @@ static int register_replace_object(struct replace_object *replace,
 }
 
 static int register_replace_ref(const char *refname,
-				const unsigned char *sha1,
+				const struct object_id *oid,
 				int flag, void *cb_data)
 {
 	/* Get sha1 from refname */
@@ -68,7 +68,7 @@ static int register_replace_ref(const char *refname,
 	}
 
 	/* Copy sha1 from the read ref */
-	hashcpy(repl_obj->replacement, sha1);
+	hashcpy(repl_obj->replacement, oid->hash);
 
 	/* Register new object */
 	if (register_replace_object(repl_obj, 1))
diff --git a/revision.c b/revision.c
index 7ddbaa083e..1d903cf311 100644
--- a/revision.c
+++ b/revision.c
@@ -1218,7 +1218,8 @@ int ref_excluded(struct string_list *ref_excludes, const char *path)
 	return 0;
 }
 
-static int handle_one_ref(const char *path, const unsigned char *sha1, int flag, void *cb_data)
+static int handle_one_ref(const char *path, const struct object_id *oid,
+			  int flag, void *cb_data)
 {
 	struct all_refs_cb *cb = cb_data;
 	struct object *object;
@@ -1226,9 +1227,9 @@ static int handle_one_ref(const char *path, const unsigned char *sha1, int flag,
 	if (ref_excluded(cb->all_revs->ref_excludes, path))
 	    return 0;
 
-	object = get_reference(cb->all_revs, path, sha1, cb->all_flags);
+	object = get_reference(cb->all_revs, path, oid->hash, cb->all_flags);
 	add_rev_cmdline(cb->all_revs, object, path, REV_CMD_REF, cb->all_flags);
-	add_pending_sha1(cb->all_revs, path, sha1, cb->all_flags);
+	add_pending_sha1(cb->all_revs, path, oid->hash, cb->all_flags);
 	return 0;
 }
 
@@ -1292,7 +1293,8 @@ static int handle_one_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
 	return 0;
 }
 
-static int handle_one_reflog(const char *path, const unsigned char *sha1, int flag, void *cb_data)
+static int handle_one_reflog(const char *path, const struct object_id *oid,
+			     int flag, void *cb_data)
 {
 	struct all_refs_cb *cb = cb_data;
 	cb->warned_bad_reflog = 0;
@@ -1304,6 +1306,7 @@ static int handle_one_reflog(const char *path, const unsigned char *sha1, int fl
 void add_reflogs_to_pending(struct rev_info *revs, unsigned flags)
 {
 	struct all_refs_cb cb;
+
 	cb.all_revs = revs;
 	cb.all_flags = flags;
 	for_each_reflog(handle_one_reflog, &cb);
diff --git a/server-info.c b/server-info.c
index 34b0253177..c82e9ee396 100644
--- a/server-info.c
+++ b/server-info.c
@@ -47,14 +47,15 @@ out:
 	return ret;
 }
 
-static int add_info_ref(const char *path, const unsigned char *sha1, int flag, void *cb_data)
+static int add_info_ref(const char *path, const struct object_id *oid,
+			int flag, void *cb_data)
 {
 	FILE *fp = cb_data;
-	struct object *o = parse_object(sha1);
+	struct object *o = parse_object(oid->hash);
 	if (!o)
 		return -1;
 
-	if (fprintf(fp, "%s	%s\n", sha1_to_hex(sha1), path) < 0)
+	if (fprintf(fp, "%s	%s\n", oid_to_hex(oid), path) < 0)
 		return -1;
 
 	if (o->type == OBJ_TAG) {
diff --git a/sha1_name.c b/sha1_name.c
index 4f3c142c7a..e57513e610 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -845,11 +845,11 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1, unsigned l
 /* Remember to update object flag allocation in object.h */
 #define ONELINE_SEEN (1u<<20)
 
-static int handle_one_ref(const char *path,
-		const unsigned char *sha1, int flag, void *cb_data)
+static int handle_one_ref(const char *path, const struct object_id *oid,
+			  int flag, void *cb_data)
 {
 	struct commit_list **list = cb_data;
-	struct object *object = parse_object(sha1);
+	struct object *object = parse_object(oid->hash);
 	if (!object)
 		return 0;
 	if (object->type == OBJ_TAG) {
@@ -1379,6 +1379,7 @@ static int get_sha1_with_context_1(const char *name,
 		int pos;
 		if (!only_to_die && namelen > 2 && name[1] == '/') {
 			struct commit_list *list = NULL;
+
 			for_each_ref(handle_one_ref, &list);
 			commit_list_sort_by_date(&list);
 			return get_sha1_oneline(name + 2, sha1, list);
diff --git a/shallow.c b/shallow.c
index d08d264dd2..257d8115c7 100644
--- a/shallow.c
+++ b/shallow.c
@@ -475,11 +475,10 @@ static void paint_down(struct paint_info *info, const unsigned char *sha1,
 	free(tmp);
 }
 
-static int mark_uninteresting(const char *refname,
-			      const unsigned char *sha1,
+static int mark_uninteresting(const char *refname, const struct object_id *oid,
 			      int flags, void *cb_data)
 {
-	struct commit *commit = lookup_commit_reference_gently(sha1, 1);
+	struct commit *commit = lookup_commit_reference_gently(oid->hash, 1);
 	if (!commit)
 		return 0;
 	commit->object.flags |= UNINTERESTING;
@@ -584,12 +583,12 @@ struct commit_array {
 	int nr, alloc;
 };
 
-static int add_ref(const char *refname,
-		   const unsigned char *sha1, int flags, void *cb_data)
+static int add_ref(const char *refname, const struct object_id *oid,
+		   int flags, void *cb_data)
 {
 	struct commit_array *ca = cb_data;
 	ALLOC_GROW(ca->commits, ca->nr + 1, ca->alloc);
-	ca->commits[ca->nr] = lookup_commit_reference_gently(sha1, 1);
+	ca->commits[ca->nr] = lookup_commit_reference_gently(oid->hash, 1);
 	if (ca->commits[ca->nr])
 		ca->nr++;
 	return 0;
@@ -674,6 +673,7 @@ int delayed_reachability_test(struct shallow_info *si, int c)
 
 		if (!si->commits) {
 			struct commit_array ca;
+
 			memset(&ca, 0, sizeof(ca));
 			head_ref(add_ref, &ca);
 			for_each_ref(add_ref, &ca);
diff --git a/submodule.c b/submodule.c
index b8747f5c26..15e90d1c10 100644
--- a/submodule.c
+++ b/submodule.c
@@ -422,7 +422,8 @@ void set_config_fetch_recurse_submodules(int value)
 	config_fetch_recurse_submodules = value;
 }
 
-static int has_remote(const char *refname, const unsigned char *sha1, int flags, void *cb_data)
+static int has_remote(const char *refname, const struct object_id *oid,
+		      int flags, void *cb_data)
 {
 	return 1;
 }
@@ -616,10 +617,10 @@ static void submodule_collect_changed_cb(struct diff_queue_struct *q,
 	}
 }
 
-static int add_sha1_to_array(const char *ref, const unsigned char *sha1,
+static int add_sha1_to_array(const char *ref, const struct object_id *oid,
 			     int flags, void *data)
 {
-	sha1_array_append(data, sha1);
+	sha1_array_append(data, oid->hash);
 	return 0;
 }
 
diff --git a/transport.c b/transport.c
index f080e93dcd..40692f8ae8 100644
--- a/transport.c
+++ b/transport.c
@@ -278,8 +278,8 @@ static int fetch_objs_via_rsync(struct transport *transport,
 	return run_command(&rsync);
 }
 
-static int write_one_ref(const char *name, const unsigned char *sha1,
-		int flags, void *data)
+static int write_one_ref(const char *name, const struct object_id *oid,
+			 int flags, void *data)
 {
 	struct strbuf *buf = data;
 	int len = buf->len;
@@ -291,7 +291,7 @@ static int write_one_ref(const char *name, const unsigned char *sha1,
 
 	strbuf_addstr(buf, name);
 	if (safe_create_leading_directories(buf->buf) ||
-	    write_file(buf->buf, 0, "%s\n", sha1_to_hex(sha1)))
+	    write_file(buf->buf, 0, "%s\n", oid_to_hex(oid)))
 		return error("problems writing temporary file %s: %s",
 			     buf->buf, strerror(errno));
 	strbuf_setlen(buf, len);
@@ -299,18 +299,18 @@ static int write_one_ref(const char *name, const unsigned char *sha1,
 }
 
 static int write_refs_to_temp_dir(struct strbuf *temp_dir,
-		int refspec_nr, const char **refspec)
+				  int refspec_nr, const char **refspec)
 {
 	int i;
 
 	for (i = 0; i < refspec_nr; i++) {
-		unsigned char sha1[20];
+		struct object_id oid;
 		char *ref;
 
-		if (dwim_ref(refspec[i], strlen(refspec[i]), sha1, &ref) != 1)
+		if (dwim_ref(refspec[i], strlen(refspec[i]), oid.hash, &ref) != 1)
 			return error("Could not get ref %s", refspec[i]);
 
-		if (write_one_ref(ref, sha1, 0, temp_dir)) {
+		if (write_one_ref(ref, &oid, 0, temp_dir)) {
 			free(ref);
 			return -1;
 		}
diff --git a/upload-pack.c b/upload-pack.c
index 640eae1bbe..89e832b64a 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -690,9 +690,9 @@ static void receive_needs(void)
 }
 
 /* return non-zero if the ref is hidden, otherwise 0 */
-static int mark_our_ref(const char *refname, const unsigned char *sha1)
+static int mark_our_ref(const char *refname, const struct object_id *oid)
 {
-	struct object *o = lookup_unknown_object(sha1);
+	struct object *o = lookup_unknown_object(oid->hash);
 
 	if (ref_is_hidden(refname)) {
 		o->flags |= HIDDEN_REF;
@@ -702,9 +702,10 @@ static int mark_our_ref(const char *refname, const unsigned char *sha1)
 	return 0;
 }
 
-static int check_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int check_ref(const char *refname, const struct object_id *oid,
+		     int flag, void *cb_data)
 {
-	mark_our_ref(refname, sha1);
+	mark_our_ref(refname, oid);
 	return 0;
 }
 
@@ -718,15 +719,16 @@ static void format_symref_info(struct strbuf *buf, struct string_list *symref)
 		strbuf_addf(buf, " symref=%s:%s", item->string, (char *)item->util);
 }
 
-static int send_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
+static int send_ref(const char *refname, const struct object_id *oid,
+		    int flag, void *cb_data)
 {
 	static const char *capabilities = "multi_ack thin-pack side-band"
 		" side-band-64k ofs-delta shallow no-progress"
 		" include-tag multi_ack_detailed";
 	const char *refname_nons = strip_namespace(refname);
-	unsigned char peeled[20];
+	struct object_id peeled;
 
-	if (mark_our_ref(refname, sha1))
+	if (mark_our_ref(refname, oid))
 		return 0;
 
 	if (capabilities) {
@@ -734,7 +736,7 @@ static int send_ref(const char *refname, const unsigned char *sha1, int flag, vo
 
 		format_symref_info(&symref_info, cb_data);
 		packet_write(1, "%s %s%c%s%s%s%s%s agent=%s\n",
-			     sha1_to_hex(sha1), refname_nons,
+			     oid_to_hex(oid), refname_nons,
 			     0, capabilities,
 			     (allow_unadvertised_object_request & ALLOW_TIP_SHA1) ?
 				     " allow-tip-sha1-in-want" : "",
@@ -745,24 +747,24 @@ static int send_ref(const char *refname, const unsigned char *sha1, int flag, vo
 			     git_user_agent_sanitized());
 		strbuf_release(&symref_info);
 	} else {
-		packet_write(1, "%s %s\n", sha1_to_hex(sha1), refname_nons);
+		packet_write(1, "%s %s\n", oid_to_hex(oid), refname_nons);
 	}
 	capabilities = NULL;
-	if (!peel_ref(refname, peeled))
-		packet_write(1, "%s %s^{}\n", sha1_to_hex(peeled), refname_nons);
+	if (!peel_ref(refname, peeled.hash))
+		packet_write(1, "%s %s^{}\n", oid_to_hex(&peeled), refname_nons);
 	return 0;
 }
 
-static int find_symref(const char *refname, const unsigned char *sha1, int flag,
-		       void *cb_data)
+static int find_symref(const char *refname, const struct object_id *oid,
+		       int flag, void *cb_data)
 {
 	const char *symref_target;
 	struct string_list_item *item;
-	unsigned char unused[20];
+	struct object_id unused;
 
 	if ((flag & REF_ISSYMREF) == 0)
 		return 0;
-	symref_target = resolve_ref_unsafe(refname, 0, unused, &flag);
+	symref_target = resolve_ref_unsafe(refname, 0, unused.hash, &flag);
 	if (!symref_target || (flag & REF_ISSYMREF) == 0)
 		die("'%s' is a symref but it is not?", refname);
 	item = string_list_append(cb_data, refname);
diff --git a/walker.c b/walker.c
index 58ffeca264..44a936c1cf 100644
--- a/walker.c
+++ b/walker.c
@@ -200,9 +200,11 @@ static int interpret_target(struct walker *walker, char *target, unsigned char *
 	return -1;
 }
 
-static int mark_complete(const char *path, const unsigned char *sha1, int flag, void *cb_data)
+static int mark_complete(const char *path, const struct object_id *oid,
+			 int flag, void *cb_data)
 {
-	struct commit *commit = lookup_commit_reference_gently(sha1, 1);
+	struct commit *commit = lookup_commit_reference_gently(oid->hash, 1);
+
 	if (commit) {
 		commit->object.flags |= COMPLETE;
 		commit_list_insert(commit, &complete);