"""
Minimal reproduction for ty type checker exponential slowdown.

Run with:
    TY_MAX_PARALLELISM=1 ty check slow_ty_repro.py

Timings:
    4 types: <1s
    5 types: <1s
    6 types: ~8s
    7 types: >60s (hits my timeout)

Example debug logs:
2025-12-17 01:33:38.681798202 DEBUG left implies right left=(M6 ≤ U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements) right=(U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements)
2025-12-17 01:33:38.682086278 DEBUG left and right overlap left=(M6 ≤ U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements) right=(U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements) intersection=(M6 ≤ U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements)
2025-12-17 01:33:38.683285882 DEBUG left implies right left=(M3 ≤ U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements) right=(U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements)
2025-12-17 01:33:38.683605638 DEBUG left and right overlap left=(M3 ≤ U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements) right=(U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements) intersection=(M3 ≤ U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements)
2025-12-17 01:33:38.683894444 DEBUG left implies right left=(M3 ≤ U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements) right=(M3 ≤ U_co@apply)
2025-12-17 01:33:38.683919264 DEBUG left and right overlap left=(M3 ≤ U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements) right=(M3 ≤ U_co@apply) intersection=(M3 ≤ U_co@apply ≤ M1 | M2 | M3 | ... omitted 4 union elements)

"""

from __future__ import annotations

from typing import Callable
from typing import Generic
from typing import TypeVar
from typing import Union


class M1: pass
class M2: pass
class M3: pass
class M4: pass
class M5: pass
class M6: pass
class M7: pass

Msg = Union[M1, M2, M3, M4, M5, M6, M7]

T = TypeVar("T")
U_co = TypeVar("U_co", covariant=True)


class Stream(Generic[T]):
    def apply(self, func: Callable[["Stream[T]"], "Stream[U_co]"]) -> "Stream[U_co]":
        return func(self)


TMsg = TypeVar("TMsg", bound=Msg)


class Builder(Generic[TMsg]):
    def build(self) -> Stream[TMsg]:
        stream: Stream[TMsg] = Stream()
        stream = stream.apply(self._handler) # i think here is where the issue triggers?
        return stream

    def _handler(self, stream: Stream[Msg]) -> Stream[Msg]:
        return stream