Fix json indent

src/zarr/core/metadata/v3.py

@@ -135,8 +135,8 @@ def parse_storage_transformers(data: object) -> tuple[dict[str, JSON], ...]:
 
 class V3JsonEncoder(json.JSONEncoder):
     def __init__(self, *args: Any, **kwargs: Any) -> None:
-        self.indent = kwargs.pop("indent", config.get("json_indent"))
         super().__init__(*args, **kwargs)
+        self.indent = config.get("json_indent")
 
     def default(self, o: object) -> Any:
         if isinstance(o, np.dtype):

tests/test_metadata/test_v3.py

@@ -10,7 +10,8 @@
 from zarr.codecs.bytes import BytesCodec
 from zarr.core.buffer import default_buffer_prototype
 from zarr.core.chunk_key_encodings import DefaultChunkKeyEncoding, V2ChunkKeyEncoding
-from zarr.core.group import parse_node_type
+from zarr.core.config import config
+from zarr.core.group import GroupMetadata, parse_node_type
 from zarr.core.metadata.v3 import (
     ArrayV3Metadata,
     DataType,
@@ -304,6 +305,26 @@ def test_metadata_to_dict(
     assert observed == expected
 
 
+@pytest.mark.parametrize("indent", [2, 4, None])
+def test_json_indent(indent: int):
+    with config.set({"json_indent": indent}):
+        m = GroupMetadata()
+        d = m.to_buffer_dict(default_buffer_prototype())["zarr.json"].to_bytes()
+
+        class TestIndentEncoder(json.JSONEncoder):
+            def __init__(self, *args: Any, **kwargs: Any) -> None:
+                super().__init__(*args, **kwargs)
+                self.indent = indent
+
+        # using json.JSONEncoder adds an extra ' ' on each line
+        # compared with json.dumps(json.loads(d), indent=2)...
+        expected = json.dumps(json.loads(d), cls=TestIndentEncoder).encode()
+        assert d == expected
+        # ...but we can check that None really removes indent.
+        if indent is None:
+            assert d == json.dumps(json.loads(d), indent=indent).encode()
+
+
 # @pytest.mark.parametrize("fill_value", [-1, 0, 1, 2932897])
 # @pytest.mark.parametrize("precision", ["ns", "D"])
 # async def test_datetime_metadata(fill_value: int, precision: str) -> None: