[PATCH v3 1/2] list-objects-filter: only parse sparse OID when 'have_git_dir'

[Jon Simons <jon@jonsimons.org>]

Fix a bug in partial cloning with sparse filters by ensuring to check
for 'have_git_dir' before attempting to resolve the sparse filter OID.

Otherwise the client will trigger:

    BUG: refs.c:1851: attempting to get main_ref_store outside of repository

when attempting to git clone with a sparse filter.

Note that this fix is the minimal one which avoids the BUG and allows
for the clone to complete successfully:

There is an open question as to whether there should be any attempt
to resolve the OID provided by the client in this context, as a filter
for the clone to be used on the remote side.  For cases where local
and remote OID resolutions differ, resolving on the client side could
be considered a bug.  For now, the minimal approach here is used to
unblock further testing for partial clones with sparse filters, while
a more invasive fix could make sense to pursue as a future direction.

t5616 is updated to demonstrate the change.

Signed-off-by: Jon Simons <jon@jonsimons.org>
---
 list-objects-filter-options.c |  3 ++-
 t/t5616-partial-clone.sh      | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/list-objects-filter-options.c b/list-objects-filter-options.c
index 1cb20c659c..aaba312edb 100644
--- a/list-objects-filter-options.c
+++ b/list-objects-filter-options.c
@@ -71,7 +71,8 @@ static int gently_parse_list_objects_filter(
 		 * command, but DO NOT complain if we don't have the blob or
 		 * ref locally.
 		 */
-		if (!get_oid_with_context(the_repository, v0, GET_OID_BLOB,
+		if (have_git_dir() &&
+		    !get_oid_with_context(the_repository, v0, GET_OID_BLOB,
 					  &sparse_oid, &oc))
 			filter_options->sparse_oid_value = oiddup(&sparse_oid);
 		filter_options->choice = LOFC_SPARSE_OID;
diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index 565254558f..5c68431d10 100755
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -241,6 +241,27 @@ test_expect_success 'fetch what is specified on CLI even if already promised' '
 	! grep "?$(cat blob)" missing_after
 '
 
+test_expect_success 'setup src repo for sparse filter' '
+	git init sparse-src &&
+	git -C sparse-src config --local uploadpack.allowfilter 1 &&
+	git -C sparse-src config --local uploadpack.allowanysha1inwant 1 &&
+	for n in 1 2 3 4
+	do
+		test_commit -C sparse-src "this-is-file-$n" file.$n.txt || return 1
+	done &&
+	test_write_lines /file1.txt /file3.txt >sparse-src/odd-files &&
+	test_write_lines /file2.txt /file4.txt >sparse-src/even-files &&
+	echo "/*" >sparse-src/all-files &&
+	git -C sparse-src add odd-files even-files all-files &&
+	git -C sparse-src commit -m "some sparse checkout files"
+'
+
+test_expect_success 'partial clone with sparse filter succeeds' '
+	git clone --no-local --no-checkout --filter=sparse:oid=master:all-files sparse-src pc-all &&
+	git clone --no-local --no-checkout --filter=sparse:oid=master:even-files sparse-src pc-even &&
+	git clone --no-local --no-checkout --filter=sparse:oid=master:odd-files sparse-src pc-odd
+'
+
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd
 
-- 
2.23.0.37.g745f681289.dirty