fix: Set DatabricksConnectionConfig to only use a shared_connection with U2M OAuth

sqlmesh/core/config/connection.py

@@ -13,8 +13,8 @@
 from sys import version_info
 
 import pydantic
+from pydantic import Field, computed_field
 from packaging import version
-from pydantic import Field
 from pydantic_core import from_json
 from sqlglot import exp
 from sqlglot.errors import ParseError
@@ -110,7 +110,14 @@ class ConnectionConfig(abc.ABC, BaseConfig):
     catalog_type_overrides: t.Optional[t.Dict[str, str]] = None
 
     # Whether to share a  single connection across threads or create a new connection per thread.
-    shared_connection: t.ClassVar[bool] = False
+    #
+    # MyPy throws a "Decorators on top of @property are not supported" error despite this being a
+    # valid decoration, and Pydantic recommend disabling the MyPy hint for this reason - see:
+    # https://pydantic.dev/docs/validation/2.0/usage/computed_fields/
+    @computed_field  # type: ignore[prop-decorator]
+    @property
+    def shared_connection(self) -> bool:
+        return False
 
     @property
     @abc.abstractmethod
@@ -311,7 +318,10 @@ class BaseDuckDBConnectionConfig(ConnectionConfig):
 
     token: t.Optional[str] = None
 
-    shared_connection: t.ClassVar[bool] = True
+    @computed_field  # type: ignore[prop-decorator]
+    @property
+    def shared_connection(self) -> bool:
+        return True
 
     _data_file_to_adapter: t.ClassVar[t.Dict[str, EngineAdapter]] = {}
 
@@ -820,11 +830,15 @@ class DatabricksConnectionConfig(ConnectionConfig):
     DISPLAY_NAME: t.ClassVar[t.Literal["Databricks"]] = "Databricks"
     DISPLAY_ORDER: t.ClassVar[t.Literal[3]] = 3
 
-    shared_connection: t.ClassVar[bool] = True
-
     _concurrent_tasks_validator = concurrent_tasks_validator
     _http_headers_validator = http_headers_validator
 
+    @computed_field  # type: ignore[prop-decorator]
+    @property
+    def shared_connection(self) -> bool:
+        """The connection should only be shared if U2M OAuth is being used"""
+        return self.auth_type is not None and self.oauth_client_id is None
+
     @model_validator(mode="before")
     def _databricks_connect_validator(cls, data: t.Any) -> t.Any:
         # SQLQueryContextLogger will output any error SQL queries even if they are in a try/except block.