unpack_all*()/await promise can loop forever on cyclic Promise resolution

[coderabbitai]

Summary

Both full-unpack paths in promising/promise.py follow nested Promise results without tracking previously seen promises. If a promise resolves to itself or back to an earlier promise in the chain, unpack_all_sync() and await promise/unpack_all() will spin forever or recurse until they blow up instead of raising a PromisingError.

Affected code

• Promise.unpack_all_sync() — lines ~260-297
• _AwaitablePromiseUnpacker.__await__() (the loop used by await promise/unpack_all()) — lines ~668-689

Suggested fix

Add a seen set guard in both unpack-all loops:

# unpack_all_sync
def unpack_all_sync(self, *, timeout: float | None = None) -> T_co:
    deadline = None if timeout is None else time.monotonic() + timeout
    result = self.as_concurrent_future().result(timeout=timeout)
    seen: set[int] = {id(self)}

    while isinstance(result, Promise):
        if id(result) in seen:
            raise PromisingError("Cyclic promise resolution detected")
        seen.add(id(result))

        remaining = None if deadline is None else deadline - time.monotonic()
        if remaining is not None:
            remaining = max(remaining, 0)

        result = result.as_concurrent_future().result(timeout=remaining)

    return result

# _AwaitablePromiseUnpacker.__await__
def __await__(self) -> Generator[Any, None, T_co | Promise[T_co]]:
    seen: set[int] = {id(self._promise)}
    ...
    if self._unpack_all:
        while isinstance(result, Promise):
            if id(result) in seen:
                raise PromisingError("Cyclic promise resolution detected")
            seen.add(id(result))
            result = yield from result.__await__()

    return result

Origin

Flagged as an outside-diff-range comment in PR #93 (review run 5f7583e4-f8cc-417e-b8e8-81118bf59de3, commit d00143025be5aa65f9ebb18b02de0b1bfe8783b2).

PR: #93
Requested by: @teremterem