treewide: always have a valid "index_state.repo" member

When the "repo" member was added to "the_index" in [1] the
repo_read_index() was made to populate it, but the unpopulated
"the_index" variable didn't get the same treatment.

Let's do that in initialize_the_repository() when we set it up, and
likewise for all of the current callers initialized an empty "struct
index_state".

This simplifies code that needs to deal with "the_index" or a custom
"struct index_state", we no longer need to second-guess this part of
the "index_state" deep in the stack. A recent example of such
second-guessing is the "istate->repo ? istate->repo : the_repository"
code in [2]. We can now simply use "istate->repo".

We're doing this by making use of the INDEX_STATE_INIT() macro (and
corresponding function) added in [3], which now have mandatory "repo"
arguments.

Because we now call index_state_init() in repository.c's
initialize_the_repository() we don't need to handle the case where we
have a "repo->index" whose "repo" member doesn't match the "repo"
we're setting up, i.e. the "Complete the double-reference" code in
repo_read_index() being altered here. That logic was originally added
in [1], and was working around the lack of what we now have in
initialize_the_repository().

For "fsmonitor-settings.c" we can remove the initialization of a NULL
"r" argument to "the_repository". This was added back in [4], and was
needed at the time for callers that would pass us the "r" from an
"istate->repo". Before this change such a change to
"fsmonitor-settings.c" would segfault all over the test suite (e.g. in
t0002-gitfile.sh).

This change has wider eventual implications for
"fsmonitor-settings.c". The reason the other lazy loading behavior in
it is required (starting with "if (!r->settings.fsmonitor) ..." is
because of the previously passed "r" being "NULL".

I have other local changes on top of this which move its configuration
reading to "prepare_repo_settings()" in "repo-settings.c", as we could
now start to rely on it being called for our "r". But let's leave all
of that for now, and narrowly remove this particular part of the
lazy-loading.

1. 1fd9ae517c4 (repository: add repo reference to index_state,
   2021-01-23)
2. ee1f0c242ef (read-cache: add index.skipHash config option,
   2023-01-06)
3. 2f6b1eb794e (cache API: add a "INDEX_STATE_INIT" macro/function,
   add release_index(), 2023-01-12)
4. 1e0ea5c4316 (fsmonitor: config settings are repository-specific,
   2022-03-25)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Acked-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 7 deletions

diff --git a/repository.c b/repository.c
index a5805fa33b..937fa974b3 100644
--- a/repository.c
+++ b/repository.c
@@ -28,6 +28,8 @@ void initialize_the_repository(void)
 	the_repo.remote_state = remote_state_new();
 	the_repo.parsed_objects = parsed_object_pool_new();
 
+	index_state_init(&the_index, the_repository);
+
 	repo_set_hash_algo(&the_repo, GIT_HASH_SHA1);
 }
 
@@ -302,16 +304,13 @@ int repo_read_index(struct repository *repo)
 {
 	int res;
 
+	/* Complete the double-reference */
 	if (!repo->index) {
 		ALLOC_ARRAY(repo->index, 1);
-		index_state_init(repo->index);
-	}
-
-	/* Complete the double-reference */
-	if (!repo->index->repo)
-		repo->index->repo = repo;
-	else if (repo->index->repo != repo)
+		index_state_init(repo->index, repo);
+	} else if (repo->index->repo != repo) {
 		BUG("repo's index should point back at itself");
+	}
 
 	res = read_index_from(repo->index, repo->index_file, repo->gitdir);