diff conflicts: don't include incorrect ID

Since a diff entry only concerns a single entry, zero the information
for the index side of a conflict.  (The index entry would otherwise
erroneously include the lowest-stage index entry - generally the
ancestor of a conflict.)

Test that during status, the index side of the conflict is empty.

2 files changed, 67 insertions, 16 deletions

diff --git a/src/diff.c b/src/diff.c
index c061a903b..abe0de0d4 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -149,9 +149,10 @@ static int diff_delta__from_two(
 	uint32_t old_mode,
 	const git_index_entry *new_entry,
 	uint32_t new_mode,
-	git_oid *new_oid,
+	const git_oid *new_id,
 	const char *matched_pathspec)
 {
+	const git_oid *old_id = &old_entry->id;
 	git_diff_delta *delta;
 	const char *canonical_path = old_entry->path;
 
@@ -159,38 +160,42 @@ static int diff_delta__from_two(
 		DIFF_FLAG_ISNT_SET(diff, GIT_DIFF_INCLUDE_UNMODIFIED))
 		return 0;
 
+	if (!new_id)
+		new_id = &new_entry->id;
+
 	if (DIFF_FLAG_IS_SET(diff, GIT_DIFF_REVERSE)) {
 		uint32_t temp_mode = old_mode;
 		const git_index_entry *temp_entry = old_entry;
+		const git_oid *temp_id = old_id;
+
 		old_entry = new_entry;
 		new_entry = temp_entry;
 		old_mode = new_mode;
 		new_mode = temp_mode;
+		old_id = new_id;
+		new_id = temp_id;
 	}
 
 	delta = diff_delta__alloc(diff, status, canonical_path);
 	GITERR_CHECK_ALLOC(delta);
 	delta->nfiles = 2;
 
-	git_oid_cpy(&delta->old_file.id, &old_entry->id);
-	delta->old_file.size = old_entry->file_size;
-	delta->old_file.mode = old_mode;
-	delta->old_file.flags |= GIT_DIFF_FLAG_VALID_ID;
+	if (!git_index_entry_stage(old_entry)) {
+		delta->old_file.size = old_entry->file_size;
+		delta->old_file.mode = old_mode;
+		git_oid_cpy(&delta->old_file.id, old_id);
+		delta->old_file.flags |= GIT_DIFF_FLAG_VALID_ID;
+	}
 
-	git_oid_cpy(&delta->new_file.id, &new_entry->id);
-	delta->new_file.size = new_entry->file_size;
-	delta->new_file.mode = new_mode;
+	if (!git_index_entry_stage(new_entry)) {
+		git_oid_cpy(&delta->new_file.id, new_id);
+		delta->new_file.size = new_entry->file_size;
+		delta->new_file.mode = new_mode;
 
-	if (new_oid) {
-		if (DIFF_FLAG_IS_SET(diff, GIT_DIFF_REVERSE))
-			git_oid_cpy(&delta->old_file.id, new_oid);
-		else
-			git_oid_cpy(&delta->new_file.id, new_oid);
+		if (!git_oid_iszero(&new_entry->id))
+			delta->new_file.flags |= GIT_DIFF_FLAG_VALID_ID;
 	}
 
-	if (new_oid || !git_oid_iszero(&new_entry->id))
-		delta->new_file.flags |= GIT_DIFF_FLAG_VALID_ID;
-
 	return diff_insert_delta(diff, delta, matched_pathspec);
 }
 
diff --git a/tests/status/worktree.c b/tests/status/worktree.c
index 9be0a4172..e272c0a10 100644
--- a/tests/status/worktree.c
+++ b/tests/status/worktree.c
@@ -645,6 +645,52 @@ void test_status_worktree__conflicted_item(void)
 	git_index_free(index);
 }
 
+void test_status_worktree__conflict_has_no_oid(void)
+{
+	git_repository *repo = cl_git_sandbox_init("status");
+	git_index *index;
+	git_index_entry entry = {0};
+	git_status_list *statuslist;
+	const git_status_entry *status;
+	git_oid zero_id = {0};
+
+	entry.mode = 0100644;
+	entry.path = "modified_file";
+	git_oid_fromstr(&entry.id, "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef");
+
+	cl_git_pass(git_repository_index(&index, repo));
+	cl_git_pass(git_index_conflict_add(index, &entry, &entry, &entry));
+
+	git_status_list_new(&statuslist, repo, NULL);
+
+	cl_assert_equal_i(16, git_status_list_entrycount(statuslist));
+
+	status = git_status_byindex(statuslist, 2);
+
+	cl_assert_equal_i(GIT_STATUS_CONFLICTED, status->status);
+	cl_assert_equal_s("modified_file", status->head_to_index->old_file.path);
+	cl_assert(!git_oid_equal(&zero_id, &status->head_to_index->old_file.id));
+	cl_assert(0 != status->head_to_index->old_file.mode);
+	cl_assert_equal_s("modified_file", status->head_to_index->new_file.path);
+	cl_assert_equal_oid(&zero_id, &status->head_to_index->new_file.id);
+	cl_assert_equal_i(0, status->head_to_index->new_file.mode);
+	cl_assert_equal_i(0, status->head_to_index->new_file.size);
+
+	cl_assert_equal_s("modified_file", status->index_to_workdir->old_file.path);
+	cl_assert_equal_oid(&zero_id, &status->index_to_workdir->old_file.id);
+	cl_assert_equal_i(0, status->index_to_workdir->old_file.mode);
+	cl_assert_equal_i(0, status->index_to_workdir->old_file.size);
+	cl_assert_equal_s("modified_file", status->index_to_workdir->new_file.path);
+	cl_assert(
+		!git_oid_equal(&zero_id, &status->index_to_workdir->new_file.id) ||
+		!(status->index_to_workdir->new_file.flags & GIT_DIFF_FLAG_VALID_ID));
+	cl_assert(0 != status->index_to_workdir->new_file.mode);
+	cl_assert(0 != status->index_to_workdir->new_file.size);
+
+	git_index_free(index);
+	git_status_list_free(statuslist);
+}
+
 static void stage_and_commit(git_repository *repo, const char *path)
 {
 	git_index *index;