Make failure to close a stream an error, as it would be by default.

snowfakery/api.py

@@ -224,16 +224,9 @@ def configure_output_stream(
         try:
             yield output_stream
         finally:
-            try:
-                messages = output_stream.close()
-            except Exception as e:
-                messages = None
-                parent_application.echo(
-                    f"Could not close {output_stream}: {str(e)}", err=True
-                )
-            if messages:
-                for message in messages:
-                    parent_application.echo(message)
+            messages = output_stream.close() or []
+            for message in messages:
+                parent_application.echo(message)
 
 
 @contextmanager

snowfakery/output_streams.py

@@ -125,7 +125,7 @@ def close(self) -> Optional[Sequence[str]]:
 
         Return a list of messages to print out.
         """
-        return super().close()
+        raise NotImplementedError()
 
     def __enter__(self, *args):
         return self
@@ -578,8 +578,20 @@ def write_row(self, tablename: str, row_with_references: Dict) -> None:
             stream.write_row(tablename, row_with_references)
 
     def close(self) -> Optional[Sequence[str]]:
+        all_messages = []
+        closing_errors = []
         for stream in self.outputstreams:
-            stream.close()
+            try:
+                messages = stream.close() or []
+                all_messages.extend(messages)
+            except Exception as e:
+                closing_errors.append(e)
+
+        if len(closing_errors) == 1:
+            raise closing_errors[1]
+        elif closing_errors:
+            raise IOError(f"Could not close streams: {closing_errors}")
+        return all_messages
 
     def write_single_row(self, tablename: str, row: Dict) -> None:
         return super().write_single_row(tablename, row)

tests/test_embedding.py

@@ -63,7 +63,7 @@ def test_continuation_as_open_file(self):
             with mapping_file.open() as f:
                 assert yaml.safe_load(f)
 
-    def test_parent_application__echo(self):
+    def test_parent_application__exception_raised(self):
         called = False
 
         class MyEmbedder(SnowfakeryApplication):
@@ -74,10 +74,10 @@ def echo(self, *args, **kwargs):
         meth = "snowfakery.output_streams.DebugOutputStream.close"
         with mock.patch(meth) as close:
             close.side_effect = AssertionError
-            generate_data(
-                yaml_file="examples/company.yml", parent_application=MyEmbedder()
-            )
-            assert called
+            with pytest.raises(AssertionError):
+                generate_data(
+                    yaml_file="examples/company.yml", parent_application=MyEmbedder()
+                )
 
     def test_parent_application__early_finish(self, generated_rows):
         class MyEmbedder(SnowfakeryApplication):
@@ -89,14 +89,9 @@ def check_if_finished(self, idmanager):
                 assert self.__class__.count < 100, "Runaway recipe!"
                 return idmanager["Employee"] >= 10
 
-        meth = "snowfakery.output_streams.DebugOutputStream.close"
-        with mock.patch(meth) as close:
-            close.side_effect = AssertionError
-            generate_data(
-                yaml_file="examples/company.yml", parent_application=MyEmbedder()
-            )
-            # called 5 times, after generating 2 employees each
-            assert MyEmbedder.count == 5
+        generate_data(yaml_file="examples/company.yml", parent_application=MyEmbedder())
+        # called 5 times, after generating 2 employees each
+        assert MyEmbedder.count == 5
 
     def test_embedding__cannot_infer_output_format(self):
         with pytest.raises(exc.DataGenError, match="No format"):