odb: only provide the empty tree

Only provide the empty tree internally, which matches git's behavior.
If we provide the empty blob then any users trying to write it with
libgit2 would omit it from actually landing in the odb, which appear
to git proper as a broken repository (missing that object).

src/odb.c

@@ -803,19 +803,12 @@ int git_odb__read_header_or_object(
 	return 0;
 }
 
-static git_oid empty_blob = {{ 0xe6, 0x9d, 0xe2, 0x9b, 0xb2, 0xd1, 0xd6, 0x43, 0x4b, 0x8b,
-			       0x29, 0xae, 0x77, 0x5a, 0xd8, 0xc2, 0xe4, 0x8c, 0x53, 0x91 }};
 static git_oid empty_tree = {{ 0x4b, 0x82, 0x5d, 0xc6, 0x42, 0xcb, 0x6e, 0xb9, 0xa0, 0x60,
 			       0xe5, 0x4b, 0xf8, 0xd6, 0x92, 0x88, 0xfb, 0xee, 0x49, 0x04 }};
 
 static int hardcoded_objects(git_rawobj *raw, const git_oid *id)
 {
-	if (!git_oid_cmp(id, &empty_blob)) {
-		raw->type = GIT_OBJ_BLOB;
-		raw->len = 0;
-		raw->data = git__calloc(1, sizeof(uint8_t));
-		return 0;
-	} else if (!git_oid_cmp(id, &empty_tree)) {
+	if (!git_oid_cmp(id, &empty_tree)) {
 		raw->type = GIT_OBJ_TREE;
 		raw->len = 0;
 		raw->data = git__calloc(1, sizeof(uint8_t));

tests/odb/emptyobjects.c

@@ -2,29 +2,33 @@
 #include "odb.h"
 #include "filebuf.h"
 
+#define TEST_REPO_PATH "redundant.git"
+
 git_repository *g_repo;
+git_odb *g_odb;
 
 void test_odb_emptyobjects__initialize(void)
 {
-	cl_git_pass(git_repository_open(&g_repo, cl_fixture("testrepo.git")));
+	g_repo = cl_git_sandbox_init(TEST_REPO_PATH);
+	cl_git_pass(git_repository_odb(&g_odb, g_repo));
 }
+
 void test_odb_emptyobjects__cleanup(void)
 {
-	git_repository_free(g_repo);
+	git_odb_free(g_odb);
+	cl_git_sandbox_cleanup();
 }
 
-void test_odb_emptyobjects__read(void)
+void test_odb_emptyobjects__blob_notfound(void)
 {
-	git_oid id;
+	git_oid id, written_id;
 	git_blob *blob;
 
 	cl_git_pass(git_oid_fromstr(&id, "e69de29bb2d1d6434b8b29ae775ad8c2e48c5391"));
-	cl_git_pass(git_blob_lookup(&blob, g_repo, &id));
-	cl_assert_equal_i(GIT_OBJ_BLOB, git_object_type((git_object *) blob));
-	cl_assert(git_blob_rawcontent(blob));
-	cl_assert_equal_s("", git_blob_rawcontent(blob));
-	cl_assert_equal_i(0, git_blob_rawsize(blob));
-	git_blob_free(blob);
+	cl_git_fail_with(GIT_ENOTFOUND, git_blob_lookup(&blob, g_repo, &id));
+
+	cl_git_pass(git_odb_write(&written_id, g_odb, "", 0, GIT_OBJ_BLOB));
+	cl_assert(git_path_exists(TEST_REPO_PATH "/objects/e6/9de29bb2d1d6434b8b29ae775ad8c2e48c5391"));
 }
 
 void test_odb_emptyobjects__read_tree(void)
@@ -43,15 +47,12 @@ void test_odb_emptyobjects__read_tree(void)
 void test_odb_emptyobjects__read_tree_odb(void)
 {
 	git_oid id;
-	git_odb *odb;
 	git_odb_object *tree_odb;
 
 	cl_git_pass(git_oid_fromstr(&id, "4b825dc642cb6eb9a060e54bf8d69288fbee4904"));
-	cl_git_pass(git_repository_odb(&odb, g_repo));
-	cl_git_pass(git_odb_read(&tree_odb, odb, &id));
+	cl_git_pass(git_odb_read(&tree_odb, g_odb, &id));
 	cl_assert(git_odb_object_data(tree_odb));
 	cl_assert_equal_s("", git_odb_object_data(tree_odb));
 	cl_assert_equal_i(0, git_odb_object_size(tree_odb));
 	git_odb_object_free(tree_odb);
-	git_odb_free(odb);
 }