Disallow writing empty Manifest files (apache#876)

* Disallow writing empty Avro files/blocks

Raising an exception when doing this might look extreme, but
there is no real good reason to allow this.

* Relax the constaints a bit

Author: Fokko

pyiceberg/manifest.py

@@ -685,6 +685,10 @@ def __exit__(
         traceback: Optional[TracebackType],
     ) -> None:
         """Close the writer."""
+        if (self._added_files + self._existing_files + self._deleted_files) == 0:
+            # This is just a guard to ensure that we don't write empty manifest files
+            raise ValueError("An empty manifest file has been written")
+
         self.closed = True
         self._writer.__exit__(exc_type, exc_value, traceback)
 
@@ -757,6 +761,8 @@ def add_entry(self, entry: ManifestEntry) -> ManifestWriter:
         elif entry.status == ManifestEntryStatus.DELETED:
             self._deleted_files += 1
             self._deleted_rows += entry.data_file.record_count
+        else:
+            raise ValueError(f"Unknown entry: {entry.status}")
 
         self._partitions.append(entry.data_file.partition)
 

tests/utils/test_manifest.py

@@ -35,7 +35,7 @@
     write_manifest,
     write_manifest_list,
 )
-from pyiceberg.partitioning import PartitionField, PartitionSpec
+from pyiceberg.partitioning import UNPARTITIONED_PARTITION_SPEC, PartitionField, PartitionSpec
 from pyiceberg.schema import Schema
 from pyiceberg.table.snapshots import Operation, Snapshot, Summary
 from pyiceberg.transforms import IdentityTransform
@@ -306,6 +306,23 @@ def test_read_manifest_v2(generated_manifest_file_file_v2: str) -> None:
     assert entry.status == ManifestEntryStatus.ADDED
 
 
+def test_write_empty_manifest() -> None:
+    io = load_file_io()
+    test_schema = Schema(NestedField(1, "foo", IntegerType(), False))
+    with TemporaryDirectory() as tmpdir:
+        tmp_avro_file = tmpdir + "/test_write_manifest.avro"
+
+        with pytest.raises(ValueError, match="An empty manifest file has been written"):
+            with write_manifest(
+                format_version=1,
+                spec=UNPARTITIONED_PARTITION_SPEC,
+                schema=test_schema,
+                output_file=io.new_output(tmp_avro_file),
+                snapshot_id=8744736658442914487,
+            ) as _:
+                pass
+
+
 @pytest.mark.parametrize("format_version", [1, 2])
 def test_write_manifest(
     generated_manifest_file_file_v1: str, generated_manifest_file_file_v2: str, format_version: TableVersion