chore: no warning if array.target_shard_size_bytes is set with shards="auto"

changes/3883.misc.md

@@ -0,0 +1 @@
+Do not warn with `shards="auto"` when `zarr.config.array.target_shard_size_bytes` is set.

src/zarr/core/chunk_grids.py

@@ -756,13 +756,15 @@ def _auto_partition(
             _chunks_out = chunk_shape
 
         if shard_shape == "auto":
-            warnings.warn(
-                "Automatic shard shape inference is experimental and may change without notice.",
-                ZarrUserWarning,
-                stacklevel=2,
-            )
             _shards_out = ()
             target_shard_size_bytes = zarr.config.get("array.target_shard_size_bytes", None)
+            if target_shard_size_bytes is None:
+                warnings.warn(
+                    "Automatic shard shape inference is experimental and may change without notice."
+                    "To set a target uncompressed shard size, use zarr.config.array.target_shard_size_bytes.",
+                    ZarrUserWarning,
+                    stacklevel=2,
+                )
             num_chunks_per_shard_axis = (
                 _guess_num_chunks_per_axis_shard(
                     chunk_shape=_chunks_out,

tests/test_array.py

@@ -6,6 +6,7 @@
 import pickle
 import re
 import sys
+from contextlib import nullcontext
 from itertools import accumulate, starmap
 from typing import TYPE_CHECKING, Any, Literal
 from unittest import mock
@@ -1073,9 +1074,13 @@ def test_auto_partition_auto_shards(
     where there are 8 or more chunks.
     """
     dtype = np.dtype("uint8")
-    with pytest.warns(
-        ZarrUserWarning,
-        match="Automatic shard shape inference is experimental and may change without notice.",
+    with (
+        pytest.warns(
+            ZarrUserWarning,
+            match="Automatic shard shape inference is experimental and may change without notice.",
+        )
+        if target_shard_size_bytes is None
+        else nullcontext()
     ):
         with zarr.config.set({"array.target_shard_size_bytes": target_shard_size_bytes}):
             auto_shards, _ = _auto_partition(
@@ -1091,17 +1096,13 @@ def test_auto_partition_auto_shards_with_auto_chunks_should_be_close_to_1MiB() -
     """
     Test that automatically picking a shard size and a chunk size gives roughly 1MiB chunks.
     """
-    with pytest.warns(
-        ZarrUserWarning,
-        match="Automatic shard shape inference is experimental and may change without notice.",
-    ):
-        with zarr.config.set({"array.target_shard_size_bytes": 10_000_000}):
-            _, chunk_shape = _auto_partition(
-                array_shape=(10_000_000,),
-                chunk_shape="auto",
-                shard_shape="auto",
-                item_size=1,
-            )
+    with zarr.config.set({"array.target_shard_size_bytes": 10_000_000}):
+        _, chunk_shape = _auto_partition(
+            array_shape=(10_000_000,),
+            chunk_shape="auto",
+            shard_shape="auto",
+            item_size=1,
+        )
     assert chunk_shape == (625000,)