Cannot use fail_silently on non-optional or non-list field

Description

This error is thrown when a permission extension is configured to use silent permissions on a field that is required and not a list:

import strawberry
from strawberry.permission import PermissionExtension


@strawberry.type
class Query:
    @strawberry.field(
        extensions=[PermissionExtension([IsAuthorized()], fail_silently=True)]
    )
    def name(
        self,
    ) -> str:  # This is a required field, the schema type will be NonNull (String!)
        return "ABC"


schema = strawberry.Schema(query=Query)  

This happens because fail_silently is suppsed to hide the field from a user without an error in case of no permissions. However, non-nullable fields always raise an error when they are set to null. The only exception to that is a list, because an empty list can be returned.

How to fix this error

You can fix this error by making this field an optional field. For example, the following code will fix this error in the above example:

import strawberry
from strawberry.permission import PermissionExtension


@strawberry.type
class Query:
    @strawberry.field(
        extensions=[PermissionExtension([IsAuthorized()], fail_silently=True)]
    )
    def name(self) -> str | None:  # This is now a nullable field
        return "ABC"


schema = strawberry.Schema(query=Query)  

Alternatively, not using fail_silently might be a good design choice as well.