make job_name param on PartitionArgs and PartitionNames args optional

python_modules/dagster/dagster/_grpc/types.py

@@ -408,10 +408,10 @@ class PartitionArgs(
         "_PartitionArgs",
         [
             ("repository_origin", RemoteRepositoryOrigin),
-            ("job_name", str),
             # This is here for backcompat. it's expected to always be f"{job_name}_partition_set".
             ("partition_set_name", str),
             ("partition_name", str),
+            ("job_name", Optional[str]),
             ("instance_ref", Optional[InstanceRef]),
             # This is introduced in the same release that we're making it possible for an asset job
             # to target assets with different PartitionsDefinitions. Prior user code versions can
@@ -424,9 +424,9 @@ class PartitionArgs(
     def __new__(
         cls,
         repository_origin: RemoteRepositoryOrigin,
-        job_name: str,
         partition_set_name: str,
         partition_name: str,
+        job_name: Optional[str] = None,
         instance_ref: Optional[InstanceRef] = None,
         selected_asset_keys: Optional[AbstractSet[AssetKey]] = None,
     ):
@@ -438,7 +438,7 @@ def __new__(
                 RemoteRepositoryOrigin,
             ),
             partition_set_name=check.str_param(partition_set_name, "partition_set_name"),
-            job_name=check.str_param(job_name, "job_name"),
+            job_name=check.opt_str_param(job_name, "job_name"),
             partition_name=check.str_param(partition_name, "partition_name"),
             instance_ref=check.opt_inst_param(instance_ref, "instance_ref", InstanceRef),
             selected_asset_keys=check.opt_nullable_set_param(
@@ -459,30 +459,30 @@ class PartitionNamesArgs(
         "_PartitionNamesArgs",
         [
             ("repository_origin", RemoteRepositoryOrigin),
-            ("job_name", str),
             # This is here for backcompat. it's expected to always be f"{job_name}_partition_set".
             ("partition_set_name", str),
             # This is introduced in the same release that we're making it possible for an asset job
             # to target assets with different PartitionsDefinitions. Prior user code versions can
             # (and do) safely ignore this parameter, because, in those versions, the job name on its
             # own is enough to specify which PartitionsDefinition to use.
+            ("job_name", Optional[str]),
             ("selected_asset_keys", Optional[AbstractSet[AssetKey]]),
         ],
     )
 ):
     def __new__(
         cls,
         repository_origin: RemoteRepositoryOrigin,
-        job_name: str,
         partition_set_name: str,
+        job_name: Optional[str] = None,
         selected_asset_keys: Optional[AbstractSet[AssetKey]] = None,
     ):
         return super(PartitionNamesArgs, cls).__new__(
             cls,
             repository_origin=check.inst_param(
                 repository_origin, "repository_origin", RemoteRepositoryOrigin
             ),
-            job_name=check.str_param(job_name, "job_name"),
+            job_name=check.opt_str_param(job_name, "job_name"),
             partition_set_name=check.str_param(partition_set_name, "partition_set_name"),
             selected_asset_keys=check.opt_nullable_set_param(
                 selected_asset_keys, "selected_asset_keys", of_type=AssetKey

python_modules/dagster/dagster_tests/api_tests/test_api_snapshot_partition.py

@@ -340,3 +340,25 @@ def test_dynamic_partition_set_grpc(instance: DagsterInstance):
         )
         assert isinstance(data, ExternalPartitionSetExecutionParamData)
         assert data.partition_data == []
+
+
+def test_external_partition_tags_grpc_backcompat_no_job_name(instance: DagsterInstance):
+    with get_bar_repo_code_location(instance) as code_location:
+        repository_handle = code_location.get_repository("bar_repo").handle
+
+        api_client = code_location.client
+
+        result = deserialize_value(
+            api_client.external_partition_tags(
+                partition_args=PartitionArgs(
+                    repository_origin=repository_handle.get_external_origin(),
+                    partition_set_name="baz_partition_set",
+                    partition_name="c",
+                    instance_ref=instance.get_ref(),
+                )
+            )
+        )
+
+        assert isinstance(result, ExternalPartitionTagsData)
+        assert result.tags
+        assert result.tags["foo"] == "bar"