Fix interfaces with duplicate directives

RELEASE.md

@@ -0,0 +1,5 @@
+Release type: patch
+
+This release addresses a bug where directives were being added multiple times when defined in an interface which multiple objects inherits from.
+
+The fix involves deduplicating directives when applying extensions/permissions to a field, ensuring that each directive is only added once.

strawberry/permission.py

@@ -156,11 +156,19 @@ def __init__(
         self.use_directives = use_directives
 
     def apply(self, field: StrawberryField) -> None:
-        """Applies all of the permission directives to the schema and sets up silent permissions."""
+        """Applies all of the permission directives (deduped) to the schema and sets up silent permissions."""
         if self.use_directives:
-            field.directives.extend(
-                p.schema_directive for p in self.permissions if p.schema_directive
-            )
+            permission_directives = [
+                perm.schema_directive
+                for perm in self.permissions
+                if perm.schema_directive
+            ]
+            # Iteration, because we want to keep order
+            for perm_directive in permission_directives:
+                # Dedupe multiple directives
+                if perm_directive in field.directives:
+                    continue
+                field.directives.append(perm_directive)
         # We can only fail silently if the field is optional or a list
         if self.fail_silently:
             if isinstance(field.type, StrawberryOptional):

tests/test_printer/test_schema_directives.py

@@ -1,9 +1,11 @@
 import textwrap
 from enum import Enum
-from typing import List, Optional, Union
+from typing import Any, List, Optional, Union
 from typing_extensions import Annotated
 
 import strawberry
+from strawberry import BasePermission, Info
+from strawberry.permission import PermissionExtension
 from strawberry.printer import print_schema
 from strawberry.schema.config import StrawberryConfig
 from strawberry.schema_directive import Location
@@ -532,6 +534,71 @@ class Query:
     assert print_schema(schema) == textwrap.dedent(expected_output).strip()
 
 
+def test_dedupe_multiple_equal_directives():
+    class MemberRoleRequired(BasePermission):
+        message = "Keine Rechte"
+
+        def has_permission(self, source, info: Info, **kwargs: Any) -> bool:
+            return True
+
+    @strawberry.interface
+    class MyInterface:
+        id: strawberry.ID
+
+        @strawberry.field(
+            extensions=[PermissionExtension(permissions=[MemberRoleRequired()])]
+        )
+        def hello(self, info: Info) -> str:
+            return "world"
+
+    @strawberry.type
+    class MyType1(MyInterface):
+        name: str
+
+    @strawberry.type
+    class MyType2(MyInterface):
+        age: int
+
+    @strawberry.type
+    class Query:
+        @strawberry.field
+        def my_type(self, info: Info) -> MyInterface:
+            return MyType1(id=strawberry.ID("1"), name="Hello")
+
+    expected_output = """
+    directive @memberRoleRequired on FIELD_DEFINITION
+
+    interface MyInterface {
+      id: ID!
+      hello: String! @memberRoleRequired
+    }
+
+    type MyType1 implements MyInterface {
+      id: ID!
+      hello: String! @memberRoleRequired
+      name: String!
+    }
+
+    type MyType2 implements MyInterface {
+      id: ID!
+      hello: String! @memberRoleRequired
+      age: Int!
+    }
+
+    type Query {
+      myType: MyInterface!
+    }
+    """
+
+    schema = strawberry.Schema(Query, types=[MyType1, MyType2])
+
+    assert print_schema(schema) == textwrap.dedent(expected_output).strip()
+
+    retval = schema.execute_sync("{ myType { id hello } }")
+    assert retval.errors is None
+    assert retval.data == {"myType": {"id": "1", "hello": "world"}}
+
+
 def test_print_directive_on_union():
     @strawberry.type
     class A: