read-cache: fix reading the shared index for other repos

read_index_from() takes a path argument for the location of the index
file.  For reading the shared index in split index mode however it just
ignores that path argument, and reads it from the gitdir of the current
repository.

This works as long as an index in the_repository is read.  Once that
changes, such as when we read the index of a submodule, or of a
different working tree than the current one, the gitdir of
the_repository will no longer contain the appropriate shared index,
and git will fail to read it.

For example t3007-ls-files-recurse-submodules.sh was broken with
GIT_TEST_SPLIT_INDEX set in 188dce131f ("ls-files: use repository
object", 2017-06-22), and t7814-grep-recurse-submodules.sh was also
broken in a similar manner, probably by introducing struct repository
there, although I didn't track down the exact commit for that.

be489d02d2 ("revision.c: --indexed-objects add objects from all
worktrees", 2017-08-23) breaks with split index mode in a similar
manner, not erroring out when it can't read the index, but instead
carrying on with pruning, without taking the index of the worktree into
account.

Fix this by passing an additional gitdir parameter to read_index_from,
to indicate where it should look for and read the shared index from.

read_cache_from() defaults to using the gitdir of the_repository.  As it
is mostly a convenience macro, having to pass get_git_dir() for every
call seems overkill, and if necessary users can have more control by
using read_index_from().

Helped-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 13 insertions, 10 deletions

diff --git a/read-cache.c b/read-cache.c
index 65f4fe8..1248a09 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1568,7 +1568,7 @@ int hold_locked_index(struct lock_file *lk, int lock_flags)
 
 int read_index(struct index_state *istate)
 {
-	return read_index_from(istate, get_index_file());
+	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
 static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
@@ -1824,20 +1824,19 @@ unmap:
  * This way, shared index can be removed if they have not been used
  * for some time.
  */
-static void freshen_shared_index(char *base_sha1_hex, int warn)
+static void freshen_shared_index(const char *shared_index, int warn)
 {
-	char *shared_index = git_pathdup("sharedindex.%s", base_sha1_hex);
 	if (!check_and_freshen_file(shared_index, 1) && warn)
 		warning("could not freshen shared index '%s'", shared_index);
-	free(shared_index);
 }
 
-int read_index_from(struct index_state *istate, const char *path)
+int read_index_from(struct index_state *istate, const char *path,
+		    const char *gitdir)
 {
 	struct split_index *split_index;
 	int ret;
 	char *base_sha1_hex;
-	const char *base_path;
+	char *base_path;
 
 	/* istate->initialized covers both .git/index and .git/sharedindex.xxx */
 	if (istate->initialized)
@@ -1857,16 +1856,17 @@ int read_index_from(struct index_state *istate, const char *path)
 		split_index->base = xcalloc(1, sizeof(*split_index->base));
 
 	base_sha1_hex = sha1_to_hex(split_index->base_sha1);
-	base_path = git_path("sharedindex.%s", base_sha1_hex);
+	base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_sha1_hex);
 	ret = do_read_index(split_index->base, base_path, 1);
 	if (hashcmp(split_index->base_sha1, split_index->base->sha1))
 		die("broken index, expect %s in %s, got %s",
 		    base_sha1_hex, base_path,
 		    sha1_to_hex(split_index->base->sha1));
 
-	freshen_shared_index(base_sha1_hex, 0);
+	freshen_shared_index(base_path, 0);
 	merge_base_index(istate);
 	post_read_index_from(istate);
+	free(base_path);
 	return ret;
 }
 
@@ -2521,8 +2521,11 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 	ret = write_split_index(istate, lock, flags);
 
 	/* Freshen the shared index only if the split-index was written */
-	if (!ret && !new_shared_index)
-		freshen_shared_index(sha1_to_hex(si->base_sha1), 1);
+	if (!ret && !new_shared_index) {
+		const char *shared_index = git_path("sharedindex.%s",
+						    sha1_to_hex(si->base_sha1));
+		freshen_shared_index(shared_index, 1);
+	}
 
 	return ret;
 }