Add test for diffs with submodules and bug fixes

The adds a test for the submodule diff capabilities and then
fixes a few bugs with how the output is generated.  It improves
the accuracy of OIDs in the diff delta object and makes the
submodule output more closely mirror the OIDs that will be used
by core git.

1 files changed, 30 insertions, 7 deletions

diff --git a/src/diff.c b/src/diff.c
index 8718e5ada..8ab8af3a1 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -224,7 +224,10 @@ static int diff_delta__from_one(
 	}
 
 	delta->old_file.flags |= GIT_DIFF_FILE_VALID_OID;
-	delta->new_file.flags |= GIT_DIFF_FILE_VALID_OID;
+
+	if (delta->status == GIT_DELTA_DELETED ||
+		!git_oid_iszero(&delta->new_file.oid))
+		delta->new_file.flags |= GIT_DIFF_FILE_VALID_OID;
 
 	if (git_vector_insert(&diff->deltas, delta) < 0) {
 		git__free(delta);
@@ -441,17 +444,28 @@ static int oid_for_workdir_item(
 	const git_index_entry *item,
 	git_oid *oid)
 {
-	int result;
+	int result = 0;
 	git_buf full_path = GIT_BUF_INIT;
 
-	if (git_buf_joinpath(&full_path, git_repository_workdir(repo), item->path) < 0)
+	if (git_buf_joinpath(
+		&full_path, git_repository_workdir(repo), item->path) < 0)
 		return -1;
 
-	/* calculate OID for file if possible*/
+	/* calculate OID for file if possible */
 	if (S_ISGITLINK(item->mode)) {
-		/* Don't bother to figure out an oid for a submodule. We won't use it anyway. */
-		memset(oid, 0, sizeof(*oid));
-		result = 0;
+		git_submodule *sm;
+		const git_oid *sm_oid;
+
+		if (!git_submodule_lookup(&sm, repo, item->path) &&
+			(sm_oid = git_submodule_wd_oid(sm)) != NULL)
+			git_oid_cpy(oid, sm_oid);
+		else {
+			/* if submodule lookup failed probably just in an intermediate
+			 * state where some init hasn't happened, so ignore the error
+			 */
+			giterr_clear();
+			memset(oid, 0, sizeof(*oid));
+		}
 	} else if (S_ISLNK(item->mode))
 		result = git_odb__hashlink(oid, full_path.ptr);
 	else if (!git__is_sizet(item->file_size)) {
@@ -570,6 +584,15 @@ static int maybe_modified(
 					return -1;
 				status = GIT_SUBMODULE_STATUS_IS_UNMODIFIED(sm_status)
 						 ? GIT_DELTA_UNMODIFIED : GIT_DELTA_MODIFIED;
+
+				/* grab OID while we are here */
+				if (git_oid_iszero(&nitem->oid)) {
+					const git_oid *sm_oid = git_submodule_wd_oid(sub);
+					if (sub != NULL) {
+						git_oid_cpy(&noid, sm_oid);
+						use_noid = &noid;
+					}
+				}
 			}
 		}
 	}