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New rule: warning accidental garbage collection of asyncio.create_task #2809

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Glyphack opened this issue Feb 12, 2023 · 5 comments · Fixed by #2935
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New rule: warning accidental garbage collection of asyncio.create_task #2809

Glyphack opened this issue Feb 12, 2023 · 5 comments · Fixed by #2935
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rule Implementing or modifying a lint rule

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@Glyphack
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I wanted to purpose a new lint rule. The asyncio.create_task function has a caveat, which is when you create a task in order to make sure it finishes you need to take a reference to it.
image

I first read about this in this post. Which also sites a lot of projects that are doing this wrong.

Is this something that ruff wants to support? I could give it a try to implement it in that case.
@edgarrmondragon
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This was requested in flake8-async: Zac-HD/flake8-async-archive#5

@charliermarsh
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We could implement it as part of RUF for now. I'd support it!

@charliermarsh charliermarsh added the rule Implementing or modifying a lint rule label Feb 12, 2023
@samuelcolvin
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amazing!

@charliermarsh
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Lol, I can do this today, I didn't realize there were so many upvotes on it.

@Lunarmagpie
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I didn't know I needed this lol

@charliermarsh charliermarsh mentioned this issue Feb 15, 2023
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charliermarsh added a commit that referenced this issue Feb 15, 2023
@charliermarsh
Implement asyncio-dangling-task to track asyncio.create_task calls (
f8d46d0 
#2935)

This rule guards against `asyncio.create_task` usages of the form:

```py
asyncio.create_task(coordinator.ws_connect())  # Error
```

...which can lead to unexpected bugs due to the lack of a strong reference to the created task. See Will McGugan's blog post for reference: https://textual.textualize.io/blog/2023/02/11/the-heisenbug-lurking-in-your-async-code/.

Note that we can't detect issues like:

```py
def f():
    # Stored as `task`, but never used...
    task = asyncio.create_task(coordinator.ws_connect())
```

So that would be a false negative. But this catches the common case of failing to assign the task in any way.

Closes #2809.
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Implement asyncio-dangling-task to track asyncio.create_task calls astral-sh/ruff
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@charliermarsh @samuelcolvin @edgarrmondragon @Glyphack @Lunarmagpie