Fields with resolvers raise Type Errors when using Generic Subclasses

[invokermain]

Describe the Bug

Following on from: https://github.com/strawberry-graphql/strawberry/pull/1891

The case where a field's resolver has a subclassed generic return type still raises a Type Error. The isinstance check is too weak.

See this gist for examples: https://gist.github.com/invokermain/31c783c76dd26e1da862cbe5218d2500

System Information

• Strawberry version (if applicable): 0.111.2

Additional Context

There is a wider discussion about resolver return type hint behaviour here: https://github.com/strawberry-graphql/strawberry/issues/1896

[invokermain]

Behavior table:

Let T = TypeVar("T") ... the extended table might like:

field type	resolver return type	current behaviour	expected behaviour	current type	expected type
int	T	no error	no error [1]	int	int
int	GenericClass[T]	runtime error	no errors, no warnings	int	int
int	Optional[T]	runtime error	no errors, no warnings	int	int

[1] recently fixed here: https://github.com/strawberry-graphql/strawberry/pull/1891