Cleanup (#1161)

* Move logic for directly linkable metrics to _get_joined_elements

* Get more specific about avoiding cycle creation

* Update documentation

metricflow-semantics/metricflow_semantics/model/semantics/linkable_spec_resolver.py

@@ -223,9 +223,12 @@ def get_joinable_metrics_for_semantic_model(
         """Get the set of linkable metrics that can be joined to this semantic model."""
         properties = frozenset({LinkableElementProperty.METRIC, LinkableElementProperty.JOINED})
         if using_join_path:
-            assert (
-                semantic_model.reference == using_join_path.last_semantic_model_reference
-            ), "Last join path element should match semantic model when building LinkableMetrics."
+            assert semantic_model.reference == using_join_path.last_semantic_model_reference, (
+                "Last join path element should match semantic model when building LinkableMetrics. "
+                f"Got semantic model: {semantic_model.reference.semantic_model_name}; "
+                f"last join path element: {using_join_path.last_semantic_model_reference.semantic_model_name}",
+            )
+            # TODO: confirm that this is what we internally consider multi-hop
             properties = properties.union(frozenset({LinkableElementProperty.MULTI_HOP}))
 
         path_key_to_linkable_metrics: Dict[ElementPathKey, Tuple[LinkableMetric, ...]] = {}
@@ -253,6 +256,7 @@ def _get_elements_in_semantic_model(self, semantic_model: SemanticModel) -> Link
         """Gets the elements in the semantic model, without requiring any joins.
 
         Elements related to metric_time are handled separately in _get_metric_time_elements().
+        Linkable metrics are not considered local to the semantic model since they always require a join.
         """
         linkable_dimensions = []
         linkable_entities = []
@@ -446,6 +450,8 @@ def _get_metric_time_elements(self, measure_reference: Optional[MeasureReference
 
     def _get_joined_elements(self, measure_semantic_model: SemanticModel) -> LinkableElementSet:
         """Get the elements that can be generated by joining other models to the given model."""
+        directly_linkable_metrics = self.get_joinable_metrics_for_semantic_model(semantic_model=measure_semantic_model)
+
         # Create single-hop elements
         join_paths = []
         for entity in measure_semantic_model.entities:
@@ -490,7 +496,9 @@ def _get_joined_elements(self, measure_semantic_model: SemanticModel) -> Linkabl
             )
             join_paths = new_join_paths
 
-        return LinkableElementSet.merge_by_path_key((single_hop_elements, multi_hop_elements))
+        return LinkableElementSet.merge_by_path_key(
+            (directly_linkable_metrics, single_hop_elements, multi_hop_elements)
+        )
 
     def _get_linkable_element_set_for_measure(
         self,
@@ -502,17 +510,11 @@ def _get_linkable_element_set_for_measure(
         measure_semantic_model = self._get_semantic_model_for_measure(measure_reference)
 
         elements_in_semantic_model = self._get_elements_in_semantic_model(measure_semantic_model)
-        metrics_linked_to_semantic_model = self.get_joinable_metrics_for_semantic_model(measure_semantic_model)
         metric_time_elements = self._get_metric_time_elements(measure_reference)
         joined_elements = self._get_joined_elements(measure_semantic_model)
 
         return LinkableElementSet.merge_by_path_key(
-            (
-                elements_in_semantic_model,
-                metrics_linked_to_semantic_model,
-                metric_time_elements,
-                joined_elements,
-            )
+            (elements_in_semantic_model, metric_time_elements, joined_elements)
         ).filter(
             with_any_of=with_any_of,
             without_any_of=without_any_of,
@@ -655,8 +657,8 @@ def create_linkable_element_set_from_join_path(
                 raise RuntimeError(f"Unhandled type: {dimension_type}")
 
         for entity in semantic_model.entities:
-            # Avoid creating "booking_id__booking_id"
-            if entity.reference != join_path.last_entity_link:
+            # Avoid creating an entity cycle
+            if entity.reference not in join_path.entity_links:
                 linkable_entities.append(
                     LinkableEntity(
                         semantic_model_origin=semantic_model.reference,