# flake8-trio
A highly opinionated flake8 plugin for Trio-related problems.
This can include anything from outright bugs, to pointless/dead code,
to likely performance issues, to minor points of idiom that might signal
a misunderstanding.
It may well be too noisy for anyone with different opinions, that's OK.
Pairs well with flake8-async and flake8-bugbear.
## Installation
```console
pip install flake8-trio
```
## List of warnings
- **TRIO100**: a `with trio.fail_after(...):` or `with trio.move_on_after(...):`
context does not contain any `await` statements. This makes it pointless, as
the timeout can only be triggered by a checkpoint.
- **TRIO101**: `yield` inside a nursery or cancel scope is only safe when implementing a context manager - otherwise, it breaks exception handling.
- **TRIO102**: it's unsafe to await inside `finally:` or `except BaseException/trio.Cancelled` unless you use a shielded
cancel scope with a timeout.
- **TRIO103**: `except BaseException` and `except trio.Cancelled` with a code path that doesn't re-raise.
- **TRIO104**: `Cancelled` and `BaseException` must be re-raised - when a user tries to `return` or `raise` a different exception.
- **TRIO105**: Calling a trio async function without immediately `await`ing it.
- **TRIO106**: trio must be imported with `import trio` for the linter to work.
- **TRIO107**: exit or `return` from async function with no guaranteed checkpoint or exception since function definition.
- **TRIO108**: exit, yield or return from async iterable with no guaranteed checkpoint since possible function entry (yield or function definition)
Checkpoints are `await`, `async for`, and `async with` (on one of enter/exit).
- **TRIO109**: Async function definition with a `timeout` parameter - use `trio.[fail/move_on]_[after/at]` instead
- **TRIO110**: `while <condition>: await trio.sleep()` should be replaced by a `trio.Event`.
- **TRIO111**: Variable, from context manager opened inside nursery, passed to `start[_soon]` might be invalidly accesed while in use, due to context manager closing before the nursery. This is usually a bug, and nurseries should generally be the inner-most context manager.
- **TRIO112**: nursery body with only a call to `nursery.start[_soon]` and not passing itself as a parameter can be replaced with a regular function call.
# Changelog
*[CalVer, YY.month.patch](https://calver.org/)*
## 22.8.7
- TRIO107+108 now ignores `asynccontextmanager`s, since both `__aenter__` and `__aexit__` should checkpoint. `async with` is also treated as checkpointing on both enter and exit.
- TRIO107 now completely ignores any function whose body consists solely of ellipsis, pass, or string constants.
- TRIO103, 107 and 108 now inspects `while` conditions and `for` iterables to avoid false alarms on a couple cases where the loop body is guaranteed to run at least once.
## 22.8.6
- TRIO103 now correctly handles raises in loops, i.e. `raise` in else is guaranteed to run unless there's a `break` in the body.
## 22.8.5
- Add TRIO111: Variable, from context manager opened inside nursery, passed to `start[_soon]` might be invalidly accesed while in use, due to context manager closing before the nursery. This is usually a bug, and nurseries should generally be the inner-most context manager.
- Add TRIO112: this single-task nursery could be replaced by awaiting the function call directly.
## 22.8.4
- Fix TRIO108 raising errors on yields in some sync code.
- TRIO109 now skips all decorated functions to avoid false alarms
## 22.8.3
- TRIO108 now gives multiple error messages; one for each path lacking a guaranteed checkpoint
## 22.8.2
- Merged TRIO108 into TRIO107
- TRIO108 now handles checkpointing in async iterators
## 22.8.1
- Added TRIO109: Async definitions should not have a `timeout` parameter. Use `trio.[fail/move_on]_[at/after]`
- Added TRIO110: `while <condition>: await trio.sleep()` should be replaced by a `trio.Event`.
## 22.7.6
- Extend TRIO102 to also check inside `except BaseException` and `except trio.Cancelled`
- Extend TRIO104 to also check for `yield`
- Update error messages on TRIO102 and TRIO103
## 22.7.5
- Add TRIO103: `except BaseException` or `except trio.Cancelled` with a code path that doesn't re-raise
- Add TRIO104: "Cancelled and BaseException must be re-raised" if user tries to return or raise a different exception.
- Added TRIO107: Async functions must have at least one checkpoint on every code path, unless an exception is raised
- Added TRIO108: Early return from async function must have at least one checkpoint on every code path before it.
## 22.7.4
- Added TRIO105 check for not immediately `await`ing async trio functions.
- Added TRIO106 check that trio is imported in a form that the plugin can easily parse.
## 22.7.3
- Added TRIO102 check for unsafe checkpoints inside `finally:` blocks
## 22.7.2
- Avoid `TRIO100` false-alarms on cancel scopes containing `async for` or `async with`.
## 22.7.1
- Initial release with TRIO100 and TRIO101
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