commit: Do not raise error when listing tree entries for nonexistent ref

The GetTreeEntries RPC has weird calling semantics: when the caller
requests entries for a nonexisteng revision or path, then it won't error
but instead just returns an empty set. While the rewrite for recursive
listings introduced via 08507b227 (commit: Convert GetTreeEntries to use
git-ls-tree(1), 2021-11-08) correctly honors the case when trying to
list entries for an object which is not a treeish, it fails to do the
same when using an invalid revision. As a result, the new code returns
errors where we previously just silently failed.

Fix this by swallowing `lstree.ErrNotExist` errors.

Changelog: fixed

2 files changed, 12 insertions, 0 deletions

diff --git a/internal/gitaly/service/commit/tree_entries.go b/internal/gitaly/service/commit/tree_entries.go
index 98eb0b7f9..897d93f05 100644
--- a/internal/gitaly/service/commit/tree_entries.go
+++ b/internal/gitaly/service/commit/tree_entries.go
@@ -108,6 +108,11 @@ func (s *server) sendTreeEntries(
 				return nil
 			}
 
+			// Same if we try to list tree entries of a revision which doesn't exist.
+			if errors.Is(err, lstree.ErrNotExist) {
+				return nil
+			}
+
 			return fmt.Errorf("listing tree entries: %w", err)
 		}
 
diff --git a/internal/gitaly/service/commit/tree_entries_test.go b/internal/gitaly/service/commit/tree_entries_test.go
index a1ca7b750..b5371dbeb 100644
--- a/internal/gitaly/service/commit/tree_entries_test.go
+++ b/internal/gitaly/service/commit/tree_entries_test.go
@@ -378,6 +378,13 @@ func testGetTreeEntriesSuccessful(t *testing.T, ctx context.Context) {
 			entries:     nil,
 		},
 		{
+			description: "with a non-existing path",
+			revision:    []byte(commitID),
+			path:        []byte("i-dont/exist"),
+			recursive:   true,
+			entries:     nil,
+		},
+		{
 			description: "with root path and sorted by trees first",
 			revision:    []byte(commitID),
 			path:        []byte("."),