Support null coalescing properties for metric nodes (#8700)

* Include 'join_to_timespine` and `fill_nulls_with` in metric fixture

* Support `join_to_timespine` and `fill_nulls_with` properties on measure inputs to metrics

* Assert new `fill_nulls_with` and `join_to_timespine` properties don't break associated DSI protocol

* Add doc for metric null coalescing improvements

* Fix unit test for unparsed metric objects

The `assert_symmetric` function asserts that dictionaries are mostly
equivalent. I say mostly equivalent because it drops keys that are
`None`. The issue is that that `join_to_timespine` gets defaulted
to `False`, so we have to specify it in the `get_ok_dict` so that
they match.

.changes/unreleased/Features-20230922-150754.yaml

@@ -0,0 +1,6 @@
+kind: Features
+body: Support `fill_nulls_with` and `join_to_timespine` for metric nodes
+time: 2023-09-22T15:07:54.981752-07:00
+custom:
+  Author: QMalcolm
+  Issue: "8593"

core/dbt/contracts/graph/nodes.py

@@ -1411,6 +1411,8 @@ class MetricInputMeasure(dbtClassMixin):
     name: str
     filter: Optional[WhereFilter] = None
     alias: Optional[str] = None
+    join_to_timespine: bool = False
+    fill_nulls_with: Optional[int] = None
 
     def measure_reference(self) -> MeasureReference:
         return MeasureReference(element_name=self.name)

core/dbt/contracts/graph/unparsed.py

@@ -584,6 +584,8 @@ class UnparsedMetricInputMeasure(dbtClassMixin):
     name: str
     filter: Optional[str] = None
     alias: Optional[str] = None
+    join_to_timespine: bool = False
+    fill_nulls_with: Optional[int] = None
 
 
 @dataclass

core/dbt/parser/schema_yaml_readers.py

@@ -178,6 +178,8 @@ def _get_input_measure(
                 name=unparsed_input_measure.name,
                 filter=filter,
                 alias=unparsed_input_measure.alias,
+                join_to_timespine=unparsed_input_measure.join_to_timespine,
+                fill_nulls_with=unparsed_input_measure.fill_nulls_with,
             )
 
     def _get_optional_input_measure(

tests/functional/metrics/fixtures.py

@@ -116,6 +116,8 @@
       measure:
         name: years_tenure
         filter: "{{ Dimension('id__loves_dbt') }} is true"
+        join_to_timespine: true
+        fill_nulls_with: 0
 
   - name: collective_window
     label: "Collective window"

tests/unit/test_contracts_graph_unparsed.py

@@ -858,6 +858,7 @@ def get_ok_dict(self):
                 "measure": {
                     "name": "customers",
                     "filter": "is_new = true",
+                    "join_to_timespine": False,
                 },
             },
             "config": {},

tests/unit/test_semantic_layer_nodes_satisfy_protocols.py

@@ -216,7 +216,11 @@ def simple_metric_input_measure() -> MetricInputMeasure:
 @pytest.fixture(scope="session")
 def complex_metric_input_measure(where_filter) -> MetricInputMeasure:
     return MetricInputMeasure(
-        name="test_complex_metric_input_measure", filter=where_filter, alias="complex_alias"
+        name="test_complex_metric_input_measure",
+        filter=where_filter,
+        alias="complex_alias",
+        join_to_timespine=True,
+        fill_nulls_with=0,
     )