Fixes meta#4632 When accessing an attribute on a class instance where the attribute does not exist statically, Pyrefly falls back to __getattr__ / __getattribute__. When __getattr__ has a protocol-annotated self parameter (e.g. def __getattr__(self: Awaitable, name: str): ...), Pyrefly validates receiver compatibility via structural protocol subtyping (C <: Awaitable). During structural protocol subtyping, Pyrefly checks whether C provides each member of Awaitable (such as __await__). Because C does not statically define __await__, looking up __await__ on C falls back to C.__getattr__ again, triggering another receiver self validation against Awaitable. Because each fallback invocation initiates a new subset query across query boundaries, local cycle detection in Subset alone does not observe the outer in-progress protocol-member check. This leads to unbounded recursion and a stack overflow abort. To address this: - Added protocol_member_guard_stack: RefCell<FxHashSet<(Type, ClassType, Name)>> and coinductive_assumptions_used: Cell<bool> to ThreadState in answers_solver.rs. - Key the guard on (got_type, protocol_class_type, attr_name), preserving type arguments (e.g. P[int] vs P[str]). - Scoped the coinductive guard strictly to the dynamic Attribute::GetAttr fallback in attr.rs so that standard attribute lookups incur zero overhead. - When recursion is detected, mark coinductive_assumptions_used = true so speculative results depending on coinductive hypotheses are not persisted in protocol_cache. - Updated test_getattr_self_awaitable_recursion signature and added test_getattr_self_protocol_generic_cache_order.

Commits

Commits on Aug 25, 2026

Guard against recursive protocol member checking in __getattr__ self validation

Guard against recursive protocol member checking in getattr self validation