Add rule "no-empty-chunks"

CHANGES.md

@@ -3,10 +3,11 @@
 ## Version 0.3.0 (in development)
 
 - Added more rules
-  - core rule "flags"
-  - core rule "lon-coordinate"
-  - core rule "lat-coordinate"
-  - core rule "time-coordinate"  (#15)
+  - core/CF rule "flags"
+  - core/CF rule "lon-coordinate"
+  - core/CF rule "lat-coordinate"
+  - core/CF rule "time-coordinate"  (#15)
+  - core rule "no-empty-chunks"
   - xcube rule "time-naming"  (#15)
 
 - Fixed problem where referring to values in modules via 

docs/rule-ref.md

@@ -22,7 +22,7 @@ Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-alert:
 Validate attributes 'flag_values', 'flag_masks' and 'flag_meanings' that make variables that contain flag values self describing. 
 [:material-information-variant:](https://cfconventions.org/cf-conventions/cf-conventions.html#flags)
 
-Contained in:  `all`-:material-lightning-bolt:
+Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-lightning-bolt:
 
 ### :material-bug: `grid-mappings`
 
@@ -33,27 +33,34 @@ Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-lightning
 ### :material-bug: `lat-coordinate`
 
 Latitude coordinate should have standard units and standard names.
-[More information.](https://cfconventions.org/cf-conventions/cf-conventions.html#latitude-coordinate)
+[:material-information-variant:](https://cfconventions.org/cf-conventions/cf-conventions.html#latitude-coordinate)
 
-Contained in:  `all`-:material-lightning-bolt:
+Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-lightning-bolt:
 
 ### :material-bug: `lon-coordinate`
 
 Longitude coordinate should have standard units and standard names.
-[More information.](https://cfconventions.org/cf-conventions/cf-conventions.html#longitude-coordinate)
+[:material-information-variant:](https://cfconventions.org/cf-conventions/cf-conventions.html#longitude-coordinate)
 
-Contained in:  `all`-:material-lightning-bolt:
+Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-lightning-bolt:
 
 ### :material-lightbulb: `no-empty-attrs`
 
 Every dataset element should have metadata that describes it.
 
 Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-alert:
 
+### :material-lightbulb: `no-empty-chunks`
+
+Empty chunks should not be encoded and written. The rule currently applies to Zarr format only.
+[:material-information-variant:](https://docs.xarray.dev/en/stable/generated/xarray.Dataset.to_zarr.html#xarray-dataset-to-zarr)
+
+Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-alert:
+
 ### :material-bug: `time-coordinate`
 
 Time coordinate (standard_name='time') should have unambiguous time units encoding.
-[More information.](https://cfconventions.org/cf-conventions/cf-conventions.html#time-coordinate)
+[:material-information-variant:](https://cfconventions.org/cf-conventions/cf-conventions.html#time-coordinate)
 
 Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-lightning-bolt:
 
@@ -117,7 +124,7 @@ Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-lightning
 ### :material-bug: `time-naming`
 
 Time coordinate and dimension should be called 'time'.
-[More information.](https://xcube.readthedocs.io/en/latest/cubespec.html#temporal-reference)
+[:material-information-variant:](https://xcube.readthedocs.io/en/latest/cubespec.html#temporal-reference)
 
 Contained in:  `all`-:material-lightning-bolt: `recommended`-:material-lightning-bolt:
 

notebooks/mkdataset.py

@@ -13,18 +13,22 @@ def make_dataset() -> xr.Dataset:
         attrs=dict(title="SST-Climatology Subset"),
         coords={
             "x": xr.DataArray(
-                np.linspace(-180, 180, nx), dims="x", attrs={
+                np.linspace(-180, 180, nx),
+                dims="x",
+                attrs={
                     "standard_name": "longitude",
                     "long_name": "longitude",
-                    "units": "degrees_east"
-                }
+                    "units": "degrees_east",
+                },
             ),
             "y": xr.DataArray(
-                np.linspace(-90, 90, ny), dims="y", attrs={
+                np.linspace(-90, 90, ny),
+                dims="y",
+                attrs={
                     "standard_name": "latitude",
                     "long_name": "latitude",
-                    "units": "degrees_north"
-                }
+                    "units": "degrees_north",
+                },
             ),
             "time": xr.DataArray(
                 [365 * i for i in range(nt)],

tests/plugins/core/rules/test_no_empty_chunks.py

@@ -0,0 +1,41 @@
+import xarray as xr
+
+from xrlint.plugins.core.rules.no_empty_chunks import NoEmptyChunks
+from xrlint.testing import RuleTest, RuleTester
+
+# valid, because it does not write empty chunks
+valid_dataset_0 = xr.Dataset(attrs=dict(title="OC-Climatology"))
+valid_dataset_0.encoding["source"] = "test.zarr"
+valid_dataset_0["sst"] = xr.DataArray([273, 274, 272], dims="time")
+valid_dataset_0["sst"].encoding["_FillValue"] = 0
+valid_dataset_0["sst"].encoding["chunks"] = [
+    1,
+]
+valid_dataset_0["sst"].encoding["write_empty_chunks"] = False
+# valid, because it does not apply
+valid_dataset_1 = valid_dataset_0.copy()
+del valid_dataset_1.encoding["source"]
+# valid, because it does not apply
+valid_dataset_2 = valid_dataset_0.copy()
+valid_dataset_2.encoding["source"] = "test.nc"
+# valid, because it does not apply
+valid_dataset_3 = valid_dataset_0.copy()
+valid_dataset_3.sst.encoding["write_empty_chunks"] = True
+
+# valid, because it does not apply
+invalid_dataset_0 = valid_dataset_0.copy()
+del invalid_dataset_0.sst.encoding["write_empty_chunks"]
+
+NoEmptyChunksTest = RuleTester.define_test(
+    "no-empty-chunks",
+    NoEmptyChunks,
+    valid=[
+        RuleTest(dataset=valid_dataset_0),
+        RuleTest(dataset=valid_dataset_1),
+        RuleTest(dataset=valid_dataset_2),
+        RuleTest(dataset=valid_dataset_3),
+    ],
+    invalid=[
+        RuleTest(dataset=invalid_dataset_0),
+    ],
+)

tests/plugins/core/test_plugin.py

@@ -16,6 +16,7 @@ def test_rules_complete(self):
                 "lon-coordinate",
                 "no-empty-attrs",
                 "time-coordinate",
+                "no-empty-chunks",
                 "var-units-attr",
             },
             set(plugin.rules.keys()),

tests/plugins/xcube/test_plugin.py

@@ -4,7 +4,6 @@
 
 
 class ExportPluginTest(TestCase):
-
     def test_rules_complete(self):
         plugin = export_plugin()
         self.assertEqual(

xrlint/plugins/core/__init__.py

@@ -19,6 +19,7 @@ def export_plugin() -> Plugin:
                 "lat-coordinate": "error",
                 "lon-coordinate": "error",
                 "no-empty-attrs": "warn",
+                "no-empty-chunks": "warn",
                 "time-coordinate": "error",
                 "var-units-attr": "warn",
             },

xrlint/plugins/core/rules/flags.py

@@ -70,8 +70,7 @@ def _validate_flag_values(
 ) -> int | None:
     if not has_meanings:
         ctx.report(
-            f"Missing attribute {FLAG_MEANINGS!r} to explain"
-            f" attribute {FLAG_VALUES!r}"
+            f"Missing attribute {FLAG_MEANINGS!r} to explain attribute {FLAG_VALUES!r}"
         )
     type_ok, flag_count = _check_values(flag_values)
     if not type_ok or flag_count is None:
@@ -87,8 +86,7 @@ def _validate_flag_masks(
 ) -> int | None:
     if not has_meanings:
         ctx.report(
-            f"Missing attribute {FLAG_MEANINGS!r} to explain"
-            f" attribute {FLAG_MASKS!r}"
+            f"Missing attribute {FLAG_MEANINGS!r} to explain attribute {FLAG_MASKS!r}"
         )
     type_ok, flag_masks_count = _check_values(flag_masks)
     if not type_ok or flag_masks_count is None:

xrlint/plugins/core/rules/no_empty_chunks.py

@@ -0,0 +1,33 @@
+from xrlint.node import DataArrayNode
+from xrlint.plugins.core.rules import plugin
+from xrlint.rule import RuleContext, RuleExit, RuleOp
+
+
+@plugin.define_rule(
+    "no-empty-chunks",
+    version="1.0.0",
+    type="suggestion",
+    description=(
+        "Empty chunks should not be encoded and written."
+        " The rule currently applies to Zarr format only."
+    ),
+    docs_url=(
+        "https://docs.xarray.dev/en/stable/generated/xarray.Dataset.to_zarr.html"
+        "#xarray-dataset-to-zarr"
+    ),
+)
+class NoEmptyChunks(RuleOp):
+    def dataset(self, ctx: RuleContext, node: DataArrayNode):
+        source = ctx.dataset.encoding.get("source")
+        is_zarr = isinstance(source, str) and source.endswith(".zarr")
+        if not is_zarr:
+            # if not a Zarr, no need to check further
+            raise RuleExit
+
+    def data_array(self, ctx: RuleContext, node: DataArrayNode):
+        if (
+            "write_empty_chunks" not in node.data_array.encoding
+            and "chunks" in node.data_array.encoding
+            and "_FillValue" in node.data_array.encoding
+        ):
+            ctx.report("Consider writing the dataset using 'write_empty_chunks=True`.")

xrlint/plugins/core/rules/time_coordinate.py

@@ -15,13 +15,11 @@
         " unambiguous time units encoding."
     ),
     docs_url=(
-        "https://cfconventions.org/cf-conventions/cf-conventions.html"
-        "#time-coordinate"
+        "https://cfconventions.org/cf-conventions/cf-conventions.html#time-coordinate"
     ),
 )
 class TimeCoordinate(RuleOp):
     def data_array(self, ctx: RuleContext, node: DataArrayNode):
-
         array = node.data_array
         attrs = array.attrs
         encoding = array.encoding