fix source patching perf with no patches

CHANGELOG.md

@@ -8,6 +8,7 @@
 - The create_adapter_plugin.py script creates a version 2 dbt_project.yml file ([#2451](https://github.com/fishtown-analytics/dbt/issues/2451), [#2455](https://github.com/fishtown-analytics/dbt/pull/2455))
 - Fixed dbt crashing with an AttributeError on duplicate sources ([#2463](https://github.com/fishtown-analytics/dbt/issues/2463), [#2464](https://github.com/fishtown-analytics/dbt/pull/2464))
 - Fixed DBT Docker entrypoint ([#2470](https://github.com/fishtown-analytics/dbt/issues/2470), [#2475](https://github.com/fishtown-analytics/dbt/pull/2475))
+- Fixed a performance regression that occurred even when a user was not using the relevant feature ([#2474](https://github.com/fishtown-analytics/dbt/issues/2474), [#2478](https://github.com/fishtown-analytics/dbt/pull/2478))
 
 Contributors:
 - [@dmateusp](https://github.com/dmateusp) ([#2475](https://github.com/fishtown-analytics/dbt/pull/2475))

core/dbt/contracts/graph/model_config.py

@@ -267,8 +267,9 @@ def update_from(
         return self.from_dict(dct, validate=validate)
 
     def finalize_and_validate(self: T) -> T:
-        self.to_dict(validate=True)
-        return self.replace()
+        # from_dict will validate for us
+        dct = self.to_dict(omit_none=False, validate=False)
+        return self.from_dict(dct)
 
 
 @dataclass

core/dbt/parser/sources.py

@@ -46,6 +46,8 @@ def patch_source(
         unpatched: UnpatchedSourceDefinition,
         patch: Optional[SourcePatch],
     ) -> UnpatchedSourceDefinition:
+        if patch is None:
+            return unpatched
 
         source_dct = unpatched.source.to_dict()
         table_dct = unpatched.table.to_dict()