chore: remove warning on fixed length utf32 (zarr-developers#3979)

Author: d-v-b

changes/3979.misc.md

@@ -0,0 +1 @@
+Remove the `UnstableSpecificationWarning` emitted when serializing a `FixedLengthUTF32` data type instance, as a spec for this data type has been published to zarr-extensions.

src/zarr/core/dtype/npy/string.py

@@ -26,7 +26,6 @@
     HasLength,
     HasObjectCodec,
     check_dtype_spec_v2,
-    v3_unstable_dtype_warning,
 )
 from zarr.core.dtype.npy.common import (
     check_json_str,
@@ -115,6 +114,9 @@ class FixedLengthUTF32(
     Wraps the ``np.dtypes.StrDType`` data type. Scalars for this data type are instances of
     ``np.str_``.
 
+    The Zarr V3 specification for this data type is defined at
+    https://github.com/zarr-developers/zarr-extensions/tree/main/data-types/fixed_length_utf32.
+
     Attributes
     ----------
     dtype_cls : Type[np.dtypes.StrDType]
@@ -247,7 +249,6 @@ def to_json(
         if zarr_format == 2:
             return {"name": self.to_native_dtype().str, "object_codec_id": None}
         elif zarr_format == 3:
-            v3_unstable_dtype_warning(self)
             return {
                 "name": self._zarr_v3_name,
                 "configuration": {"length_bytes": self.length * self.code_point_bytes},

tests/test_dtype/test_npy/test_string.py

@@ -6,7 +6,6 @@
 from tests.test_dtype.test_wrapper import BaseTestZDType
 from zarr.core.dtype import FixedLengthUTF32
 from zarr.core.dtype.npy.string import _NUMPY_SUPPORTS_VLEN_STRING, VariableLengthUTF8
-from zarr.errors import UnstableSpecificationWarning
 
 if _NUMPY_SUPPORTS_VLEN_STRING:
 
@@ -125,21 +124,6 @@ class TestFixedLengthUTF32(BaseTestZDType):
     invalid_scalar_params = (None,)
 
 
-@pytest.mark.parametrize(
-    "zdtype",
-    [
-        FixedLengthUTF32(length=10),
-    ],
-)
-def test_unstable_dtype_warning(zdtype: FixedLengthUTF32 | VariableLengthUTF8) -> None:
-    """
-    Test that we get a warning when serializing a dtype without a zarr v3 spec to json
-    when zarr_format is 3
-    """
-    with pytest.warns(UnstableSpecificationWarning):
-        zdtype.to_json(zarr_format=3)
-
-
 def test_invalid_size() -> None:
     """
     Test that it's impossible to create a data type that has no length