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Fixes #21824 Fixes #19920 Closes #19921 Note that ilevkivskyi has a suggestion to change overload inference here: #19920 (comment) While that is right, it is a little separate, and I think it is okay to remove the crash given that it now affects numpy and has been reported in other contexts too. We just keep the originally inferred tuple

The `env_class` object associated with a mypyc coroutine is not immediately cleared when the coroutine completes. This can significantly increase memory usage, since the env class may hold references to captured locals and values spilled across suspension points. The objects are eventually collectible by the GC but the collection might be delayed in cases where a nested coroutine is awaited, eg. ```python async def allocate(size: int) -> None: payload = bytearray(size) async def nested() -> int: return payload[-1] assert await nested() == 0 ``` With nesting mypyc creates env classes for both `allocate` and `nested` that may reference each other and form a cycle. To fix this, clear the `env_class` immediately after the coroutine completes. This matches behavior of cpython, which clears frames of completed coroutines immediately in the eval loop.

Closes mypyc/mypyc#1204, a `mypyc` issue. The issue likely unblocks `isort` from being compiled with `mypyc`, which is why I took an interest it. Full disclosure is that I used AI to write this, it provided this test and code just from the linked issue but it looks sensible to me. I did not use additional prompting. Like I said, fix looks sensible: we now call `dataclass_type` for each entry in the MRO, instead of once. I am aware the contributing guidelines say new contributors are not encourage to use LLMs but I hope the size of the PR and my track record as open source maintainer gives some flexibility here. I'm very aware that reviewing AI written PRs creates maintainer burden, but I'm committed to getting this over the finish line. To that end I: Tested locally with `pytest mypyc/test/test_run.py ` and that looked okay. Also tested that without the changes the added test would fail on `master`. Also tried to run CI on my local fork (DanielNoord#1), which succeeded. Feel free to push changes to the branch or cherry pick this into another branch. I am not necessarily interested in getting credits for the fix/PR, I'd just like to continue with my attempt to get `isort` compiled and for that I need this in a `mypy` release :)

Closes mypyc/mypyc#1210 This fixes another issue I ran into while trying to use `mypyc` for `isort`. I am aware the contributing guidelines say new contributors are not encouraged to use LLMs but I hope this can get the same handling as #21785. I have tried to ensure this patch works as much as I can by: Testing locally with `pytest mypyc/test/test_run.py `. Tested that the test fails on `master` without the changes. Also tried to run CI on my local fork (DanielNoord#2), which succeeded. As with the previous PR, feel free to push changes to the branch or cherry pick this into another branch. I just want to unblock `isort` :)

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Commits on Aug 15, 2026

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