hash: stop depending on `the_repository` in `null_oid()`

The `null_oid()` function returns the object ID that only consists of
zeroes. Naturally, this ID also depends on the hash algorithm used, as
the number of zeroes is different between SHA1 and SHA256. Consequently,
the function returns the hash-algorithm-specific null object ID.

This is currently done by depending on `the_hash_algo`, which implicitly
makes us depend on `the_repository`. Refactor the function to instead
pass in the hash algorithm for which we want to retrieve the null object
ID. Adapt callsites accordingly by passing in `the_repository`, thus
bubbling up the dependency on that global variable by one layer.

There are a couple of trivial exceptions for subsystems that already got
rid of `the_repository`. These subsystems instead use the repository
that is available via the calling context:

  - "builtin/grep.c"
  - "grep.c"
  - "refs/debug.c"

There are also two non-trivial exceptions:

  - "diff-no-index.c": Here we know that we may not have a repository
    initialized at all, so we cannot rely on `the_repository`. Instead,
    we adapt `diff_no_index()` to get a `struct git_hash_algo` as
    parameter. The only caller is located in "builtin/diff.c", where we
    know to call `repo_set_hash_algo()` in case we're running outside of
    a Git repository. Consequently, it is fine to continue passing
    `the_repository->hash_algo` even in this case.

  - "builtin/ls-files.c": There is an in-flight patch series that drops
    `USE_THE_REPOSITORY_VARIABLE` in this file, which causes a semantic
    conflict because we use `null_oid()` in `show_submodule()`. The
    value is passed to `repo_submodule_init()`, which may use the object
    ID to resolve a tree-ish in the superproject from which we want to
    read the submodule config. As such, the object ID should refer to an
    object in the superproject, and consequently we need to use its hash
    algorithm.

    This means that we could in theory just not bother about this edge
    case at all and just use `the_repository` in "diff-no-index.c". But
    doing so would feel misdesigned.

Remove the `USE_THE_REPOSITORY_VARIABLE` preprocessor define in
"hash.c".

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

14 files changed, 40 insertions, 38 deletions

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 01ea9ff8b2..2e7486cf65 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -130,8 +130,8 @@ static int post_checkout_hook(struct commit *old_commit, struct commit *new_comm
 			      int changed)
 {
 	return run_hooks_l(the_repository, "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(the_hash_algo)),
+			   oid_to_hex(new_commit ? &new_commit->object.oid : null_oid(the_hash_algo)),
 			   changed ? "1" : "0", NULL);
 	/* "new_commit" can be NULL when checking out from the index before
 	   a commit exists. */
@@ -710,7 +710,7 @@ static int reset_tree(struct tree *tree, const struct checkout_opts *o,
 	opts.src_index = the_repository->index;
 	opts.dst_index = the_repository->index;
 	init_checkout_metadata(&opts.meta, info->refname,
-			       info->commit ? &info->commit->object.oid : null_oid(),
+			       info->commit ? &info->commit->object.oid : null_oid(the_hash_algo),
 			       NULL);
 	if (parse_tree(tree) < 0)
 		return 128;
diff --git a/builtin/clone.c b/builtin/clone.c
index f14229abf4..36aba65e06 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -690,7 +690,7 @@ static int checkout(int submodule_progress, int filter_submodules,
 	if (write_locked_index(the_repository->index, &lock_file, COMMIT_LOCK))
 		die(_("unable to write new index file"));
 
-	err |= run_hooks_l(the_repository, "post-checkout", oid_to_hex(null_oid()),
+	err |= run_hooks_l(the_repository, "post-checkout", oid_to_hex(null_oid(the_hash_algo)),
 			   oid_to_hex(&oid), "1", NULL);
 
 	if (!err && (option_recurse_submodules.nr > 0)) {
diff --git a/builtin/describe.c b/builtin/describe.c
index e2e73f3d75..23df333fd0 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -518,7 +518,7 @@ 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(the_hash_algo), oid, dst, &revs};
 
 	strvec_pushl(&args, "internal: The first arg is not parsed",
 		     "--objects", "--in-commit-order", "--reverse", "HEAD",
diff --git a/builtin/diff.c b/builtin/diff.c
index a4fffee42c..fa963808c3 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -104,7 +104,7 @@ static void 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(the_hash_algo),
 		     1, 0,
 		     blob[0]->path ? blob[0]->path : path,
 		     path);
@@ -498,7 +498,8 @@ int cmd_diff(int argc,
 
 	/* If this is a no-index diff, just run it and exit there. */
 	if (no_index)
-		exit(diff_no_index(&rev, no_index == DIFF_NO_INDEX_IMPLICIT,
+		exit(diff_no_index(&rev, the_repository->hash_algo,
+				   no_index == DIFF_NO_INDEX_IMPLICIT,
 				   argc, argv));
 
 
diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index a5c82eef1d..7a5c2925cd 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -869,7 +869,7 @@ 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(the_hash_algo)));
 					free(buf);
 					return;
 				}
@@ -883,7 +883,7 @@ 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(the_hash_algo)));
 	}
 	skip_prefix(name, "refs/tags/", &name);
 	printf("tag %s\n", name);
@@ -1023,7 +1023,7 @@ 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(the_hash_algo)));
 				continue;
 			}
 
@@ -1042,7 +1042,7 @@ 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(the_hash_algo)));
 					continue;
 				}
 				/* set ref to commit using oid, not mark */
@@ -1153,7 +1153,7 @@ 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(the_hash_algo)));
 	}
 }
 
diff --git a/builtin/fsck.c b/builtin/fsck.c
index 62c7494bbd..f86ecd8eaa 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -625,7 +625,7 @@ static int fsck_loose(const struct object_id *oid, const char *path, void *data)
 	void *contents = NULL;
 	int eaten;
 	struct object_info oi = OBJECT_INFO_INIT;
-	struct object_id real_oid = *null_oid();
+	struct object_id real_oid = *null_oid(the_hash_algo);
 	int err = 0;
 
 	strbuf_reset(&cb_data->obj_type);
diff --git a/builtin/grep.c b/builtin/grep.c
index cbbf6f2643..283d64cab8 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -453,7 +453,7 @@ static int grep_submodule(struct grep_opt *opt,
 		return 0;
 
 	subrepo = xmalloc(sizeof(*subrepo));
-	if (repo_submodule_init(subrepo, superproject, path, null_oid())) {
+	if (repo_submodule_init(subrepo, superproject, path, null_oid(opt->repo->hash_algo))) {
 		free(subrepo);
 		return 0;
 	}
diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index a4431429b7..7bc418be5d 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -234,7 +234,8 @@ static void show_submodule(struct repository *superproject,
 {
 	struct repository subrepo;
 
-	if (repo_submodule_init(&subrepo, superproject, path, null_oid()))
+	if (repo_submodule_init(&subrepo, superproject, path,
+				null_oid(superproject->hash_algo)))
 		return;
 
 	if (repo_read_index(&subrepo) < 0)
diff --git a/builtin/rebase.c b/builtin/rebase.c
index d4715ed35d..1cd802dd92 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -925,7 +925,7 @@ static void fill_branch_base(struct rebase_options *options,
 				 options->orig_head, &merge_bases) < 0)
 		exit(128);
 	if (!merge_bases || merge_bases->next)
-		oidcpy(branch_base, null_oid());
+		oidcpy(branch_base, null_oid(the_hash_algo));
 	else
 		oidcpy(branch_base, &merge_bases->item->object.oid);
 
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 7b28fc9df6..b3e2a9d0c6 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -363,7 +363,7 @@ static void write_head_info(void)
 	strvec_clear(&excludes_vector);
 
 	if (!sent_capabilities)
-		show_ref("capabilities^{}", null_oid());
+		show_ref("capabilities^{}", null_oid(the_hash_algo));
 
 	advertise_shallow_grafts(1);
 
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index c1a8029714..570226ea16 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -78,7 +78,7 @@ static int get_default_remote_submodule(const char *module_path, char **default_
 	int ret;
 
 	if (repo_submodule_init(&subrepo, the_repository, module_path,
-				null_oid()) < 0)
+				null_oid(the_hash_algo)) < 0)
 		return die_message(_("could not get a repository handle for submodule '%s'"),
 				   module_path);
 	ret = repo_get_default_remote(&subrepo, default_remote);
@@ -308,7 +308,7 @@ static void runcommand_in_submodule_cb(const struct cache_entry *list_item,
 	displaypath = get_submodule_displaypath(path, info->prefix,
 						info->super_prefix);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub)
 		die(_("No url found for submodule path '%s' in .gitmodules"),
@@ -468,7 +468,7 @@ static void init_submodule(const char *path, const char *prefix,
 
 	displaypath = get_submodule_displaypath(path, prefix, super_prefix);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub)
 		die(_("No url found for submodule path '%s' in .gitmodules"),
@@ -645,14 +645,14 @@ static void status_submodule(const char *path, const struct object_id *ce_oid,
 	if (validate_submodule_path(path) < 0)
 		exit(128);
 
-	if (!submodule_from_path(the_repository, null_oid(), path))
+	if (!submodule_from_path(the_repository, null_oid(the_hash_algo), path))
 		die(_("no submodule mapping found in .gitmodules for path '%s'"),
 		      path);
 
 	displaypath = get_submodule_displaypath(path, prefix, super_prefix);
 
 	if ((CE_STAGEMASK & ce_flags) >> CE_STAGESHIFT) {
-		print_status(flags, 'U', path, null_oid(), displaypath);
+		print_status(flags, 'U', path, null_oid(the_hash_algo), displaypath);
 		goto cleanup;
 	}
 
@@ -912,7 +912,7 @@ static void generate_submodule_summary(struct summary_cb *info,
 	struct strbuf errmsg = STRBUF_INIT;
 	int total_commits = -1;
 
-	if (!info->cached && oideq(&p->oid_dst, null_oid())) {
+	if (!info->cached && oideq(&p->oid_dst, null_oid(the_hash_algo))) {
 		if (S_ISGITLINK(p->mod_dst)) {
 			struct ref_store *refs = repo_get_submodule_ref_store(the_repository,
 									      p->sm_path);
@@ -1051,7 +1051,7 @@ 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(the_hash_algo), p->sm_path))) {
 			char *config_key = NULL;
 			const char *value;
 			int ignore_all = 0;
@@ -1259,7 +1259,7 @@ static void sync_submodule(const char *path, const char *prefix,
 	if (validate_submodule_path(path) < 0)
 		exit(128);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (sub && sub->url) {
 		if (starts_with_dot_dot_slash(sub->url) ||
@@ -1404,7 +1404,7 @@ static void deinit_submodule(const char *path, const char *prefix,
 	if (validate_submodule_path(path) < 0)
 		exit(128);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub || !sub->name)
 		goto cleanup;
@@ -1929,7 +1929,7 @@ static int determine_submodule_update_strategy(struct repository *r,
 					       enum submodule_update_type 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(the_hash_algo), path);
 	char *key;
 	const char *val;
 	int ret;
@@ -2089,7 +2089,7 @@ 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(the_hash_algo), ce->name);
 
 	if (!sub) {
 		next_submodule_warn_missing(suc, out, displaypath);
@@ -2485,7 +2485,7 @@ static int remote_submodule_branch(const char *path, const char **branch)
 	char *key;
 	*branch = NULL;
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 	if (!sub)
 		return die_message(_("could not initialize submodule at path '%s'"),
 				   path);
@@ -2531,7 +2531,7 @@ static int ensure_core_worktree(const char *path)
 	const char *cw;
 	struct repository subrepo;
 
-	if (repo_submodule_init(&subrepo, the_repository, path, null_oid()))
+	if (repo_submodule_init(&subrepo, the_repository, path, null_oid(the_hash_algo)))
 		return die_message(_("could not get a repository handle for submodule '%s'"),
 				   path);
 
@@ -2644,7 +2644,7 @@ static int update_submodule(struct update_data *update_data)
 		return ret;
 
 	if (update_data->just_cloned)
-		oidcpy(&update_data->suboid, null_oid());
+		oidcpy(&update_data->suboid, null_oid(the_hash_algo));
 	else if (repo_resolve_gitlink_ref(the_repository, update_data->sm_path,
 					  "HEAD", &update_data->suboid))
 		return die_message(_("Unable to find current revision in submodule path '%s'"),
@@ -2697,8 +2697,8 @@ static int update_submodule(struct update_data *update_data)
 		struct update_data next = *update_data;
 
 		next.prefix = NULL;
-		oidcpy(&next.oid, null_oid());
-		oidcpy(&next.suboid, null_oid());
+		oidcpy(&next.oid, null_oid(the_hash_algo));
+		oidcpy(&next.suboid, null_oid(the_hash_algo));
 
 		cp.dir = update_data->sm_path;
 		cp.git_cmd = 1;
@@ -3057,7 +3057,7 @@ static int module_set_url(int argc, const char **argv, const char *prefix,
 	if (argc != 2 || !(path = argv[0]) || !(newurl = argv[1]))
 		usage_with_options(usage, options);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub)
 		die(_("no submodule mapping found in .gitmodules for path '%s'"),
@@ -3113,7 +3113,7 @@ static int module_set_branch(int argc, const char **argv, const char *prefix,
 	if (argc != 1 || !(path = argv[0]))
 		usage_with_options(usage, options);
 
-	sub = submodule_from_path(the_repository, null_oid(), path);
+	sub = submodule_from_path(the_repository, null_oid(the_hash_algo), path);
 
 	if (!sub)
 		die(_("no submodule mapping found in .gitmodules for path '%s'"),
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index e20c120913..73d431a0dd 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -505,7 +505,7 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
 			 * has not been resolved yet.
 			 */
 			oidclr(&obj_list[nr].oid, the_repository->hash_algo);
-			add_delta_to_list(nr, null_oid(), base_offset,
+			add_delta_to_list(nr, null_oid(the_hash_algo), base_offset,
 					  delta_data, delta_size);
 			return;
 		}
diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 4d35bdc4b4..3796b9844d 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -500,7 +500,7 @@ static void parse_cmd_symref_verify(struct ref_transaction *transaction,
 	 */
 	old_target = parse_next_refname(&next);
 	if (!old_target)
-		oidcpy(&old_oid, null_oid());
+		oidcpy(&old_oid, null_oid(the_hash_algo));
 
 	if (*next != line_termination)
 		die("symref-verify %s: extra input: %s", refname, next);
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 48448a8355..87ccd47794 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -578,7 +578,7 @@ done:
 
 		strvec_pushl(&opt.env, "GIT_DIR", "GIT_WORK_TREE", NULL);
 		strvec_pushl(&opt.args,
-			     oid_to_hex(null_oid()),
+			     oid_to_hex(null_oid(the_hash_algo)),
 			     oid_to_hex(&commit->object.oid),
 			     "1",
 			     NULL);