[PATCH v3 5/9] repository: add repo reference to index_state

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

It will be helpful to add behavior to index operations that might
trigger an object lookup. Since each index belongs to a specific
repository, add a 'repo' pointer to struct index_state that allows
access to this repository.

Add a BUG() statement if the repo already has an index, and the index
already has a repo, but somehow the index points to a different repo.

This will prevent future changes from needing to pass an additional
'struct repository *repo' parameter and instead rely only on the 'struct
index_state *istate' parameter.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 cache.h      | 1 +
 repository.c | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/cache.h b/cache.h
index 71097657489..f9c7a603841 100644
--- a/cache.h
+++ b/cache.h
@@ -328,6 +328,7 @@ struct index_state {
 	struct ewah_bitmap *fsmonitor_dirty;
 	struct mem_pool *ce_mem_pool;
 	struct progress *progress;
+	struct repository *repo;
 };
 
 /* Name hashing */
diff --git a/repository.c b/repository.c
index a4174ddb062..c98298acd01 100644
--- a/repository.c
+++ b/repository.c
@@ -264,6 +264,12 @@ int repo_read_index(struct repository *repo)
 	if (!repo->index)
 		repo->index = xcalloc(1, sizeof(*repo->index));
 
+	/* Complete the double-reference */
+	if (!repo->index->repo)
+		repo->index->repo = repo;
+	else if (repo->index->repo != repo)
+		BUG("repo's index should point back at itself");
+
 	return read_index_from(repo->index, repo->index_file, repo->gitdir);
 }
 
-- 
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