[PATCH 25/27] fsmonitor: disable if index is sparse

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

From: Derrick Stolee <dstolee@microsoft.com>

The FS Monitor feature uses a bitmap over the index entries. This
currently interacts poorly with a sparse index. We will revisit this
interaction in the future, but for now protect the index by refusing to
use the FS Monitor extension at all if the index is sparse.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 fsmonitor.c                              | 21 ++++++++++++++-------
 read-cache.c                             |  3 ++-
 t/t1092-sparse-checkout-compatibility.sh |  8 ++++----
 3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/fsmonitor.c b/fsmonitor.c
index 7b8cd3975b9..99b26576baa 100644
--- a/fsmonitor.c
+++ b/fsmonitor.c
@@ -58,6 +58,9 @@ int read_fsmonitor_extension(struct index_state *istate, const void *data,
 	uint64_t timestamp;
 	struct strbuf last_update = STRBUF_INIT;
 
+	if (istate->sparse_index)
+		return 0;
+
 	if (sz < sizeof(uint32_t) + 1 + sizeof(uint32_t))
 		return error("corrupt fsmonitor extension (too short)");
 
@@ -98,7 +101,8 @@ void fill_fsmonitor_bitmap(struct index_state *istate)
 {
 	unsigned int i, skipped = 0;
 
-	ensure_full_index(istate);
+	if (istate->sparse_index)
+		return;
 
 	istate->fsmonitor_dirty = ewah_new();
 	for (i = 0; i < istate->cache_nr; i++) {
@@ -161,11 +165,7 @@ static int query_fsmonitor(int version, const char *last_update, struct strbuf *
 
 static void fsmonitor_refresh_callback(struct index_state *istate, const char *name)
 {
-	int pos;
-
-	ensure_full_index(istate);
-
-	pos = index_name_pos(istate, name, strlen(name));
+	int pos = index_name_pos(istate, name, strlen(name));
 
 	if (pos >= 0) {
 		struct cache_entry *ce = istate->cache[pos];
@@ -190,7 +190,8 @@ void refresh_fsmonitor(struct index_state *istate)
 	char *buf;
 	unsigned int i;
 
-	if (!core_fsmonitor || istate->fsmonitor_has_run_once)
+	if (!core_fsmonitor || istate->fsmonitor_has_run_once ||
+	    istate->sparse_index)
 		return;
 
 	hook_version = fsmonitor_hook_version();
@@ -300,6 +301,9 @@ void add_fsmonitor(struct index_state *istate)
 	unsigned int i;
 	struct strbuf last_update = STRBUF_INIT;
 
+	if (istate->sparse_index)
+		return;
+
 	if (!istate->fsmonitor_last_update) {
 		trace_printf_key(&trace_fsmonitor, "add fsmonitor");
 		istate->cache_changed |= FSMONITOR_CHANGED;
@@ -335,6 +339,9 @@ void tweak_fsmonitor(struct index_state *istate)
 	unsigned int i;
 	int fsmonitor_enabled = git_config_get_fsmonitor();
 
+	if (istate->sparse_index)
+		fsmonitor_enabled = 0;
+
 	if (istate->fsmonitor_dirty) {
 		if (fsmonitor_enabled) {
 			ensure_full_index(istate);
diff --git a/read-cache.c b/read-cache.c
index 8c974829497..96d9b95128a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -3017,7 +3017,8 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 		if (err)
 			return -1;
 	}
-	if (!strip_extensions && istate->fsmonitor_last_update) {
+	if (!strip_extensions && istate->fsmonitor_last_update &&
+	    !istate->sparse_index) {
 		struct strbuf sb = STRBUF_INIT;
 
 		write_fsmonitor_extension(&sb, istate);
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 2e8efe6ab37..1cdf33a4025 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -388,7 +388,7 @@ test_expect_success 'sparse-index is expanded and converted back' '
 	init_repos &&
 
 	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
-		git -C sparse-index -c core.fsmonitor="" reset --hard &&
+		git -C sparse-index reset --hard &&
 	test_region index convert_to_sparse trace2.txt &&
 	test_region index ensure_full_index trace2.txt
 '
@@ -398,19 +398,19 @@ test_expect_success 'sparse-index is not expanded' '
 
 	rm -f trace2.txt &&
 	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
-		git -C sparse-index -c core.fsmonitor="" status -uno &&
+		git -C sparse-index status -uno &&
 	test_region ! index ensure_full_index trace2.txt &&
 
 	rm trace2.txt &&
 	echo >>sparse-index/README.md &&
 	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
-		git -C sparse-index -c core.fsmonitor="" add -A &&
+		git -C sparse-index add -A &&
 	test_region ! index ensure_full_index trace2.txt &&
 
 	rm trace2.txt &&
 	echo >>sparse-index/extra.txt &&
 	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
-		git -C sparse-index -c core.fsmonitor="" add extra.txt &&
+		git -C sparse-index add extra.txt &&
 	test_region ! index ensure_full_index trace2.txt
 '
 
-- 
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