hash: provide per-algorithm null OIDs

Up until recently, object IDs did not have an algorithm member, only a
hash.  Consequently, it was possible to share one null (all-zeros)
object ID among all hash algorithms.  Now that we're going to be
handling objects from multiple hash algorithms, it's important to make
sure that all object IDs have a correct algorithm field.

Introduce a per-algorithm null OID, and add it to struct hash_algo.
Introduce a wrapper function as well, and use it everywhere we used to
use the null_oid constant.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

archive.c

@@ -275,9 +275,11 @@ int write_archive_entries(struct archiver_args *args,
 	int err;
 	struct strbuf path_in_archive = STRBUF_INIT;
 	struct strbuf content = STRBUF_INIT;
-	struct object_id fake_oid = null_oid;
+	struct object_id fake_oid;
 	int i;
 
+	oidcpy(&fake_oid, null_oid());
+
 	if (args->baselen > 0 && args->base[args->baselen - 1] == '/') {
 		size_t len = args->baselen;
 

blame.c

@@ -242,7 +242,7 @@ static struct commit *fake_working_tree_commit(struct repository *r,
 		switch (st.st_mode & S_IFMT) {
 		case S_IFREG:
 			if (opt->flags.allow_textconv &&
-			    textconv_object(r, read_from, mode, &null_oid, 0, &buf_ptr, &buf_len))
+			    textconv_object(r, read_from, mode, null_oid(), 0, &buf_ptr, &buf_len))
 				strbuf_attach(&buf, buf_ptr, buf_len, buf_len + 1);
 			else if (strbuf_read_file(&buf, read_from, st.st_size) != st.st_size)
 				die_errno("cannot open or read '%s'", read_from);

branch.c

@@ -322,7 +322,7 @@ void create_branch(struct repository *r,
 		transaction = ref_transaction_begin(&err);
 		if (!transaction ||
 		    ref_transaction_update(transaction, ref.buf,
-					   &oid, forcing ? NULL : &null_oid,
+					   &oid, forcing ? NULL : null_oid(),
 					   0, msg, &err) ||
 		    ref_transaction_commit(transaction, &err))
 			die("%s", err.buf);

builtin/checkout.c

@@ -106,8 +106,8 @@ static int post_checkout_hook(struct commit *old_commit, struct commit *new_comm
 			      int changed)
 {
 	return run_hook_le(NULL, "post-checkout",
-			   oid_to_hex(old_commit ? &old_commit->object.oid : &null_oid),
-			   oid_to_hex(new_commit ? &new_commit->object.oid : &null_oid),
+			   oid_to_hex(old_commit ? &old_commit->object.oid : null_oid()),
+			   oid_to_hex(new_commit ? &new_commit->object.oid : null_oid()),
 			   changed ? "1" : "0", NULL);
 	/* "new_commit" can be NULL when checking out from the index before
 	   a commit exists. */
@@ -638,7 +638,7 @@ static int reset_tree(struct tree *tree, const struct checkout_opts *o,
 	opts.src_index = &the_index;
 	opts.dst_index = &the_index;
 	init_checkout_metadata(&opts.meta, info->refname,
-			       info->commit ? &info->commit->object.oid : &null_oid,
+			       info->commit ? &info->commit->object.oid : null_oid(),
 			       NULL);
 	parse_tree(tree);
 	init_tree_desc(&tree_desc, tree->buffer, tree->size);

builtin/clone.c

@@ -820,7 +820,7 @@ static int checkout(int submodule_progress)
 	if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
 		die(_("unable to write new index file"));
 
-	err |= run_hook_le(NULL, "post-checkout", oid_to_hex(&null_oid),
+	err |= run_hook_le(NULL, "post-checkout", oid_to_hex(null_oid()),
 			   oid_to_hex(&oid), "1", NULL);
 
 	if (!err && (option_recurse_submodules.nr > 0)) {

builtin/describe.c

@@ -502,7 +502,7 @@ static void describe_blob(struct object_id oid, struct strbuf *dst)
 {
 	struct rev_info revs;
 	struct strvec args = STRVEC_INIT;
-	struct process_commit_data pcd = { null_oid, oid, dst, &revs};
+	struct process_commit_data pcd = { *null_oid(), oid, dst, &revs};
 
 	strvec_pushl(&args, "internal: The first arg is not parsed",
 		     "--objects", "--in-commit-order", "--reverse", "HEAD",

builtin/diff.c

@@ -98,7 +98,7 @@ static int builtin_diff_b_f(struct rev_info *revs,
 
 	stuff_change(&revs->diffopt,
 		     blob[0]->mode, canon_mode(st.st_mode),
-		     &blob[0]->item->oid, &null_oid,
+		     &blob[0]->item->oid, null_oid(),
 		     1, 0,
 		     blob[0]->path ? blob[0]->path : path,
 		     path);

builtin/fast-export.c

@@ -870,7 +870,7 @@ static void handle_tag(const char *name, struct tag *tag)
 				p = rewrite_commit((struct commit *)tagged);
 				if (!p) {
 					printf("reset %s\nfrom %s\n\n",
-					       name, oid_to_hex(&null_oid));
+					       name, oid_to_hex(null_oid()));
 					free(buf);
 					return;
 				}
@@ -884,7 +884,7 @@ static void handle_tag(const char *name, struct tag *tag)
 
 	if (tagged->type == OBJ_TAG) {
 		printf("reset %s\nfrom %s\n\n",
-		       name, oid_to_hex(&null_oid));
+		       name, oid_to_hex(null_oid()));
 	}
 	skip_prefix(name, "refs/tags/", &name);
 	printf("tag %s\n", name);
@@ -1016,7 +1016,7 @@ static void handle_tags_and_duplicates(struct string_list *extras)
 				 * it.
 				 */
 				printf("reset %s\nfrom %s\n\n",
-				       name, oid_to_hex(&null_oid));
+				       name, oid_to_hex(null_oid()));
 				continue;
 			}
 
@@ -1035,7 +1035,7 @@ static void handle_tags_and_duplicates(struct string_list *extras)
 				if (!reference_excluded_commits) {
 					/* delete the ref */
 					printf("reset %s\nfrom %s\n\n",
-					       name, oid_to_hex(&null_oid));
+					       name, oid_to_hex(null_oid()));
 					continue;
 				}
 				/* set ref to commit using oid, not mark */
@@ -1146,7 +1146,7 @@ static void handle_deletes(void)
 			continue;
 
 		printf("reset %s\nfrom %s\n\n",
-				refspec->dst, oid_to_hex(&null_oid));
+				refspec->dst, oid_to_hex(null_oid()));
 	}
 }
 

builtin/grep.c

@@ -421,7 +421,7 @@ static int grep_submodule(struct grep_opt *opt,
 	struct grep_opt subopt;
 	int hit;
 
-	sub = submodule_from_path(superproject, &null_oid, path);
+	sub = submodule_from_path(superproject, null_oid(), path);
 
 	if (!is_submodule_active(superproject, path))
 		return 0;

builtin/ls-files.c

@@ -210,7 +210,7 @@ static void show_submodule(struct repository *superproject,
 {
 	struct repository subrepo;
 	const struct submodule *sub = submodule_from_path(superproject,
-							  &null_oid, path);
+							  null_oid(), path);
 
 	if (repo_submodule_init(&subrepo, superproject, sub))
 		return;

builtin/rebase.c

@@ -485,7 +485,7 @@ static const char * const builtin_rebase_interactive_usage[] = {
 int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 {
 	struct rebase_options opts = REBASE_OPTIONS_INIT;
-	struct object_id squash_onto = null_oid;
+	struct object_id squash_onto = *null_oid();
 	enum action command = ACTION_NONE;
 	struct option options[] = {
 		OPT_NEGBIT(0, "ff", &opts.flags, N_("allow fast-forward"),
@@ -1139,7 +1139,7 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
 
 	merge_bases = get_merge_bases(onto, head);
 	if (!merge_bases || merge_bases->next) {
-		oidcpy(merge_base, &null_oid);
+		oidcpy(merge_base, null_oid());
 		goto done;
 	}
 

builtin/receive-pack.c

@@ -329,7 +329,7 @@ static void write_head_info(void)
 	for_each_alternate_ref(show_one_alternate_ref, &seen);
 	oidset_clear(&seen);
 	if (!sent_capabilities)
-		show_ref("capabilities^{}", &null_oid);
+		show_ref("capabilities^{}", null_oid());
 
 	advertise_shallow_grafts(1);
 

builtin/submodule--helper.c

@@ -426,7 +426,8 @@ static int module_list(int argc, const char **argv, const char *prefix)
 		const struct cache_entry *ce = list.entries[i];
 
 		if (ce_stage(ce))
-			printf("%06o %s U\t", ce->ce_mode, oid_to_hex(&null_oid));
+			printf("%06o %s U\t", ce->ce_mode,
+			       oid_to_hex(null_oid()));
 		else
 			printf("%06o %s %d\t", ce->ce_mode,
 			       oid_to_hex(&ce->oid), ce_stage(ce));
@@ -466,7 +467,7 @@ static void runcommand_in_submodule_cb(const struct cache_entry *list_item,
 
 	displaypath = get_submodule_displaypath(path, info->prefix);
 
-	sub = submodule_from_path(the_repository, &null_oid, path);
+	sub = submodule_from_path(the_repository, null_oid(), path);
 
 	if (!sub)
 		die(_("No url found for submodule path '%s' in .gitmodules"),
@@ -623,7 +624,7 @@ static void init_submodule(const char *path, const char *prefix,
 
 	displaypath = get_submodule_displaypath(path, prefix);
 
-	sub = submodule_from_path(the_repository, &null_oid, path);
+	sub = submodule_from_path(the_repository, null_oid(), path);
 
 	if (!sub)
 		die(_("No url found for submodule path '%s' in .gitmodules"),
@@ -783,14 +784,14 @@ static void status_submodule(const char *path, const struct object_id *ce_oid,
 	struct strbuf buf = STRBUF_INIT;
 	const char *git_dir;
 
-	if (!submodule_from_path(the_repository, &null_oid, path))
+	if (!submodule_from_path(the_repository, null_oid(), path))
 		die(_("no submodule mapping found in .gitmodules for path '%s'"),
 		      path);
 
 	displaypath = get_submodule_displaypath(path, prefix);
 
 	if ((CE_STAGEMASK & ce_flags) >> CE_STAGESHIFT) {
-		print_status(flags, 'U', path, &null_oid, displaypath);
+		print_status(flags, 'U', path, null_oid(), displaypath);
 		goto cleanup;
 	}
 
@@ -916,7 +917,7 @@ static int module_name(int argc, const char **argv, const char *prefix)
 	if (argc != 2)
 		usage(_("git submodule--helper name <path>"));
 
-	sub = submodule_from_path(the_repository, &null_oid, argv[1]);
+	sub = submodule_from_path(the_repository, null_oid(), argv[1]);
 
 	if (!sub)
 		die(_("no submodule mapping found in .gitmodules for path '%s'"),
@@ -1040,7 +1041,7 @@ static void generate_submodule_summary(struct summary_cb *info,
 	char *errmsg = NULL;
 	int total_commits = -1;
 
-	if (!info->cached && oideq(&p->oid_dst, &null_oid)) {
+	if (!info->cached && oideq(&p->oid_dst, null_oid())) {
 		if (S_ISGITLINK(p->mod_dst)) {
 			struct ref_store *refs = get_submodule_ref_store(p->sm_path);
 			if (refs)
@@ -1177,7 +1178,7 @@ static void prepare_submodule_summary(struct summary_cb *info,
 
 		if (info->for_status && p->status != 'A' &&
 		    (sub = submodule_from_path(the_repository,
-					       &null_oid, p->sm_path))) {
+					       null_oid(), p->sm_path))) {
 			char *config_key = NULL;
 			const char *value;
 			int ignore_all = 0;
@@ -1373,7 +1374,7 @@ static void sync_submodule(const char *path, const char *prefix,
 	if (!is_submodule_active(the_repository, path))
 		return;
 
-	sub = submodule_from_path(the_repository, &null_oid, path);
+	sub = submodule_from_path(the_repository, null_oid(), path);
 
 	if (sub && sub->url) {
 		if (starts_with_dot_dot_slash(sub->url) ||
@@ -1525,7 +1526,7 @@ static void deinit_submodule(const char *path, const char *prefix,
 	struct strbuf sb_config = STRBUF_INIT;
 	char *sub_git_dir = xstrfmt("%s/.git", path);
 
-	sub = submodule_from_path(the_repository, &null_oid, path);
+	sub = submodule_from_path(the_repository, null_oid(), path);
 
 	if (!sub || !sub->name)
 		goto cleanup;
@@ -1925,7 +1926,7 @@ static void determine_submodule_update_strategy(struct repository *r,
 						const char *update,
 						struct submodule_update_strategy *out)
 {
-	const struct submodule *sub = submodule_from_path(r, &null_oid, path);
+	const struct submodule *sub = submodule_from_path(r, null_oid(), path);
 	char *key;
 	const char *val;
 
@@ -2077,7 +2078,7 @@ static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
 		goto cleanup;
 	}
 
-	sub = submodule_from_path(the_repository, &null_oid, ce->name);
+	sub = submodule_from_path(the_repository, null_oid(), ce->name);
 
 	if (suc->recursive_prefix)
 		displaypath = relative_path(suc->recursive_prefix,
@@ -2395,7 +2396,7 @@ static const char *remote_submodule_branch(const char *path)
 	const char *branch = NULL;
 	char *key;
 
-	sub = submodule_from_path(the_repository, &null_oid, path);
+	sub = submodule_from_path(the_repository, null_oid(), path);
 	if (!sub)
 		return NULL;
 
@@ -2533,7 +2534,7 @@ static int ensure_core_worktree(int argc, const char **argv, const char *prefix)
 
 	path = argv[1];
 
-	sub = submodule_from_path(the_repository, &null_oid, path);
+	sub = submodule_from_path(the_repository, null_oid(), path);
 	if (!sub)
 		BUG("We could get the submodule handle before?");
 

builtin/unpack-objects.c

@@ -421,7 +421,8 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
 			 * has not been resolved yet.
 			 */
 			oidclr(&obj_list[nr].oid);
-			add_delta_to_list(nr, &null_oid, base_offset, delta_data, delta_size);
+			add_delta_to_list(nr, null_oid(), base_offset,
+					  delta_data, delta_size);
 			return;
 		}
 	}

builtin/worktree.c

@@ -331,7 +331,7 @@ static int add_worktree(const char *path, const char *refname,
 	 */
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/HEAD", sb_repo.buf);
-	write_file(sb.buf, "%s", oid_to_hex(&null_oid));
+	write_file(sb.buf, "%s", oid_to_hex(null_oid()));
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/commondir", sb_repo.buf);
 	write_file(sb.buf, "../..");
@@ -394,7 +394,7 @@ static int add_worktree(const char *path, const char *refname,
 			cp.argv = NULL;
 			cp.trace2_hook_name = "post-checkout";
 			strvec_pushl(&cp.args, absolute_path(hook),
-				     oid_to_hex(&null_oid),
+				     oid_to_hex(null_oid()),
 				     oid_to_hex(&commit->object.oid),
 				     "1", NULL);
 			ret = run_command(&cp);

combine-diff.c

@@ -1068,7 +1068,7 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 						   &result_size, NULL, NULL);
 		} else if (textconv) {
 			struct diff_filespec *df = alloc_filespec(elem->path);
-			fill_filespec(df, &null_oid, 0, st.st_mode);
+			fill_filespec(df, null_oid(), 0, st.st_mode);
 			result_size = fill_textconv(opt->repo, textconv, df, &result);
 			free_filespec(df);
 		} else if (0 <= (fd = open(elem->path, O_RDONLY))) {

connect.c

@@ -254,7 +254,7 @@ static int process_dummy_ref(const struct packet_reader *reader)
 		return 0;
 	name++;
 
-	return oideq(&null_oid, &oid) && !strcmp(name, "capabilities^{}");
+	return oideq(null_oid(), &oid) && !strcmp(name, "capabilities^{}");
 }
 
 static void check_no_capabilities(const char *line, int len)

diff-lib.c

@@ -232,7 +232,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 				   ce_intent_to_add(ce)) {
 				newmode = ce_mode_from_stat(ce, st.st_mode);
 				diff_addremove(&revs->diffopt, '+', newmode,
-					       &null_oid, 0, ce->name, 0);
+					       null_oid(), 0, ce->name, 0);
 				continue;
 			}
 
@@ -249,7 +249,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 		}
 		oldmode = ce->ce_mode;
 		old_oid = &ce->oid;
-		new_oid = changed ? &null_oid : &ce->oid;
+		new_oid = changed ? null_oid() : &ce->oid;
 		diff_change(&revs->diffopt, oldmode, newmode,
 			    old_oid, new_oid,
 			    !is_null_oid(old_oid),
@@ -307,7 +307,7 @@ static int get_stat_data(const struct index_state *istate,
 						    0, dirty_submodule);
 		if (changed) {
 			mode = ce_mode_from_stat(ce, st.st_mode);
-			oid = &null_oid;
+			oid = null_oid();
 		}
 	}
 

diff-no-index.c

@@ -83,7 +83,7 @@ static struct diff_filespec *noindex_filespec(const char *name, int mode)
 	if (!name)
 		name = "/dev/null";
 	s = alloc_filespec(name);
-	fill_filespec(s, &null_oid, 0, mode);
+	fill_filespec(s, null_oid(), 0, mode);
 	if (name == file_from_standard_input)
 		populate_from_stdin(s);
 	return s;

diff.c

@@ -4190,7 +4190,7 @@ static struct diff_tempfile *prepare_temp_file(struct repository *r,
 				die_errno("readlink(%s)", name);
 			prep_temp_blob(r->index, name, temp, sb.buf, sb.len,
 				       (one->oid_valid ?
-					&one->oid : &null_oid),
+					&one->oid : null_oid()),
 				       (one->oid_valid ?
 					one->mode : S_IFLNK));
 			strbuf_release(&sb);
@@ -4199,7 +4199,7 @@ static struct diff_tempfile *prepare_temp_file(struct repository *r,
 			/* we can borrow from the file in the work tree */
 			temp->name = name;
 			if (!one->oid_valid)
-				oid_to_hex_r(temp->hex, &null_oid);
+				oid_to_hex_r(temp->hex, null_oid());
 			else
 				oid_to_hex_r(temp->hex, &one->oid);
 			/* Even though we may sometimes borrow the