first pass: flags.allow_materialization_overrides

core/dbt/contracts/graph/manifest.py

@@ -906,14 +906,29 @@ def _materialization_candidates_for(
         adapter_type: str,
         specificity: int,
     ) -> CandidateList:
+
+        # Do not include imported macros in materialization macro candidates
+        def filter(candidate: MacroCandidate) -> bool:
+            flags = get_flags()
+            # legacy behaviour - allow materialization overrides from packages
+            if flags.allow_materialization_overrides is None:
+                # TODO: fire deprecation event
+                return True
+            else:
+                return (
+                    candidate.macro.package_name in flags.allow_materialization_overrides
+                    if candidate.locality == Locality.Imported
+                    else True
+                )
+
         full_name = dbt_common.utils.get_materialization_macro_name(
             materialization_name=materialization_name,
             adapter_type=adapter_type,
             with_prefix=False,
         )
         return CandidateList(
             MaterializationCandidate.from_macro(m, specificity)
-            for m in self._find_macros_by_name(full_name, project_name)
+            for m in self._find_macros_by_name(full_name, project_name, filter=filter)
         )
 
     def find_materialization_macro_by_name(

core/dbt/contracts/project.py

@@ -297,6 +297,10 @@ def validate(cls, data):
 @dataclass
 class ProjectFlags(ExtensibleDbtClassMixin):
     allow_spaces_in_model_names: Optional[bool] = True
+    # None => default, allow from all (default behaviour)
+    # ["dbt_utils"] => only allow from these packages
+    # [] => allow from none, will be new default behaviour
+    allow_materialization_overrides: Optional[List[str]] = None
     cache_selected_only: Optional[bool] = None
     debug: Optional[bool] = None
     fail_fast: Optional[bool] = None
@@ -324,6 +328,7 @@ def project_only_flags(self) -> Dict[str, Any]:
         return {
             "source_freshness_run_project_hooks": self.source_freshness_run_project_hooks,
             "allow_spaces_in_model_names": self.allow_spaces_in_model_names,
+            "allow_materialization_overrides": self.allow_materialization_overrides,
         }