[ty] Add tests for protocols with generic method members (#20316)

Author: AlexWaygood

crates/ty_python_semantic/resources/mdtest/protocols.md

@@ -1801,6 +1801,136 @@ static_assert(is_assignable_to(str, SupportsLessThan))
 static_assert(is_assignable_to(int, Invertable))
 ```
 
+## Subtyping of protocols with generic method members
+
+Protocol method members can be generic. They can have generic contexts scoped to the class:
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+from typing_extensions import TypeVar, Self, Protocol
+from ty_extensions import is_equivalent_to, static_assert, is_assignable_to, is_subtype_of
+
+class NewStyleClassScoped[T](Protocol):
+    def method(self, input: T) -> None: ...
+
+S = TypeVar("S")
+
+class LegacyClassScoped(Protocol[S]):
+    def method(self, input: S) -> None: ...
+
+static_assert(is_equivalent_to(NewStyleClassScoped, LegacyClassScoped))
+static_assert(is_equivalent_to(NewStyleClassScoped[int], LegacyClassScoped[int]))
+
+class NominalGeneric[T]:
+    def method(self, input: T) -> None: ...
+
+def _[T](x: T) -> T:
+    static_assert(is_equivalent_to(NewStyleClassScoped[T], LegacyClassScoped[T]))
+    static_assert(is_subtype_of(NominalGeneric[T], NewStyleClassScoped[T]))
+    static_assert(is_subtype_of(NominalGeneric[T], LegacyClassScoped[T]))
+    return x
+
+class NominalConcrete:
+    def method(self, input: int) -> None: ...
+
+static_assert(is_assignable_to(NominalConcrete, NewStyleClassScoped))
+static_assert(is_assignable_to(NominalConcrete, LegacyClassScoped))
+static_assert(is_assignable_to(NominalGeneric[int], NewStyleClassScoped))
+static_assert(is_assignable_to(NominalGeneric[int], LegacyClassScoped))
+static_assert(is_assignable_to(NominalGeneric, NewStyleClassScoped[int]))
+static_assert(is_assignable_to(NominalGeneric, LegacyClassScoped[int]))
+
+# `NewStyleClassScoped` is implicitly `NewStyleClassScoped[Unknown]`,
+# and there exist fully static materializations of `NewStyleClassScoped[Unknown]`
+# where `Nominal` would not be a subtype of the given materialization,
+# hence there is no subtyping relation:
+#
+# TODO: these should pass
+static_assert(not is_subtype_of(NominalConcrete, NewStyleClassScoped))  # error: [static-assert-error]
+static_assert(not is_subtype_of(NominalConcrete, LegacyClassScoped))  # error: [static-assert-error]
+
+# Similarly, `NominalGeneric` is implicitly `NominalGeneric[Unknown`]
+#
+# TODO: these should pass
+static_assert(not is_subtype_of(NominalGeneric, NewStyleClassScoped[int]))  # error: [static-assert-error]
+static_assert(not is_subtype_of(NominalGeneric, LegacyClassScoped[int]))  # error: [static-assert-error]
+
+static_assert(is_subtype_of(NominalConcrete, NewStyleClassScoped[int]))
+static_assert(is_subtype_of(NominalConcrete, LegacyClassScoped[int]))
+static_assert(is_subtype_of(NominalGeneric[int], NewStyleClassScoped[int]))
+static_assert(is_subtype_of(NominalGeneric[int], LegacyClassScoped[int]))
+
+# TODO: these should pass
+static_assert(not is_assignable_to(NominalConcrete, NewStyleClassScoped[str]))  # error: [static-assert-error]
+static_assert(not is_assignable_to(NominalConcrete, LegacyClassScoped[str]))  # error: [static-assert-error]
+static_assert(not is_subtype_of(NominalGeneric[int], NewStyleClassScoped[str]))  # error: [static-assert-error]
+static_assert(not is_subtype_of(NominalGeneric[int], LegacyClassScoped[str]))  # error: [static-assert-error]
+```
+
+And they can also have generic contexts scoped to the method:
+
+```py
+class NewStyleFunctionScoped(Protocol):
+    def f[T](self, input: T) -> T: ...
+
+S = TypeVar("S")
+
+class LegacyFunctionScoped(Protocol):
+    def f(self, input: S) -> S: ...
+
+class UsesSelf(Protocol):
+    def g(self: Self) -> Self: ...
+
+class NominalNewStyle:
+    def f[T](self, input: T) -> T:
+        return input
+
+class NominalLegacy:
+    def f(self, input: S) -> S:
+        return input
+
+class NominalWithSelf:
+    def g(self: Self) -> Self:
+        return self
+
+class NominalNotGeneric:
+    def f(self, input: int) -> int:
+        return input
+
+class NominalReturningSelfNotGeneric:
+    def g(self) -> "NominalReturningSelfNotGeneric":
+        return self
+
+# TODO: should pass
+static_assert(is_equivalent_to(LegacyFunctionScoped, NewStyleFunctionScoped))  # error: [static-assert-error]
+
+static_assert(is_subtype_of(NominalNewStyle, NewStyleFunctionScoped))
+static_assert(is_subtype_of(NominalNewStyle, LegacyFunctionScoped))
+static_assert(not is_assignable_to(NominalNewStyle, UsesSelf))
+
+static_assert(is_subtype_of(NominalLegacy, NewStyleFunctionScoped))
+static_assert(is_subtype_of(NominalLegacy, LegacyFunctionScoped))
+static_assert(not is_assignable_to(NominalLegacy, UsesSelf))
+
+static_assert(not is_assignable_to(NominalWithSelf, NewStyleFunctionScoped))
+static_assert(not is_assignable_to(NominalWithSelf, LegacyFunctionScoped))
+static_assert(is_subtype_of(NominalWithSelf, UsesSelf))
+
+# TODO: these should pass
+static_assert(not is_assignable_to(NominalNotGeneric, NewStyleFunctionScoped))  # error: [static-assert-error]
+static_assert(not is_assignable_to(NominalNotGeneric, LegacyFunctionScoped))  # error: [static-assert-error]
+static_assert(not is_assignable_to(NominalNotGeneric, UsesSelf))
+
+static_assert(not is_assignable_to(NominalReturningSelfNotGeneric, NewStyleFunctionScoped))
+static_assert(not is_assignable_to(NominalReturningSelfNotGeneric, LegacyFunctionScoped))
+# TODO: should pass
+static_assert(not is_assignable_to(NominalReturningSelfNotGeneric, UsesSelf))  # error: [static-assert-error]
+```
+
 ## Equivalence of protocols with method or property members
 
 Two protocols `P1` and `P2`, both with a method member `x`, are considered equivalent if the
@@ -1919,7 +2049,7 @@ def f(arg1: type, arg2: type):
         reveal_type(arg2)  # revealed: type & ~type[OnlyMethodMembers]
 ```
 
-## Truthiness of protocol instance
+## Truthiness of protocol instances
 
 An instance of a protocol type generally has ambiguous truthiness:
 
@@ -2520,7 +2650,6 @@ Add tests for:
 - `super()` on nominal subtypes (explicit and implicit) of protocol classes
 - [Recursive protocols][recursive_protocols_spec]
 - Generic protocols
-- Non-generic protocols with function-scoped generic methods
 - Protocols with instance attributes annotated with `Callable` (can a nominal type with a method
     satisfy that protocol, and if so in what cases?)
 - Protocols decorated with `@final`