Add some type tests for defaulted typevar classes

src/trio/_tests/type_tests/raisesgroup.py

@@ -37,6 +37,14 @@ def check_inheritance_and_assignments() -> None:
     assert a
 
 
+def check_matcher_typevar_default(e: Matcher) -> object:
+    assert e.exception_type is not None
+    exc: type[BaseException] = e.exception_type
+    # this would previously pass, as the type would be `Any`
+    e.exception_type().blah()  # type: ignore
+    return exc  # Silence Pyright unused var warning
+
+
 def check_basic_contextmanager() -> None:
     # One level of Group is correctly translated - except it's a BaseExceptionGroup
     # instead of an ExceptionGroup.

src/trio/_tests/type_tests/task_status.py

@@ -0,0 +1,29 @@
+"""Check that started() can only be called for TaskStatus[None]."""
+
+from trio import TaskStatus
+from typing_extensions import assert_type
+
+
+async def check_status(
+    none_status_explicit: TaskStatus[None],
+    none_status_implicit: TaskStatus,
+    int_status: TaskStatus[int],
+) -> None:
+    assert_type(none_status_explicit, TaskStatus[None])
+    assert_type(none_status_implicit, TaskStatus[None])  # Default typevar
+    assert_type(int_status, TaskStatus[int])
+
+    # Omitting the parameter is only allowed for None.
+    none_status_explicit.started()
+    none_status_implicit.started()
+    int_status.started()  # type: ignore
+
+    # Explicit None is allowed.
+    none_status_explicit.started(None)
+    none_status_implicit.started(None)
+    int_status.started(None)  # type: ignore
+
+    none_status_explicit.started(42)  # type: ignore
+    none_status_implicit.started(42)  # type: ignore
+    int_status.started(42)
+    int_status.started(True)