Add trio[300], async functions should not have a timeout parameter

Author: jakkdl

CHANGELOG.md

@@ -1,6 +1,9 @@
 # Changelog
 *[CalVer, YY.month.patch](https://calver.org/)*
 
+## Future
+- Added TRIO300: Async definitions should not have a `timeout` parameter. Use `trio.[fail/move_on]_[at/after]`
+
 ## 22.7.6
 - Extend TRIO102 to also check inside `except BaseException` and `except trio.Cancelled`
 - Extend TRIO104 to also check for `yield`

README.md

@@ -31,3 +31,4 @@ pip install flake8-trio
 - **TRIO107**: Async functions must have at least one checkpoint on every code path, unless an exception is raised.
 - **TRIO108**: Early return from async function must have at least one checkpoint on every code path before it, unless an exception is raised.
   Checkpoints are `await`, `async with` `async for`.
+- **TRIO300**: Async function definition with a `timeout` parameter - use `trio.[fail/move_on]_[after/at]` instead"

flake8_trio.py

@@ -157,6 +157,7 @@ def visit_FunctionDef(self, node: Union[ast.FunctionDef, ast.AsyncFunctionDef]):
         self._safe_decorator, self._yield_is_error = outer
 
     def visit_AsyncFunctionDef(self, node: ast.AsyncFunctionDef):
+        self.check_300(node.args)
         self.visit_FunctionDef(node)
 
     def visit_Yield(self, node: ast.Yield):
@@ -187,6 +188,11 @@ def visit_Import(self, node: ast.Import):
             if name.name == "trio" and name.asname is not None:
                 self.problems.append(make_error(TRIO106, node.lineno, node.col_offset))
 
+    def check_300(self, args: ast.arguments):
+        for arg in (*args.posonlyargs, *args.args, *args.kwonlyargs):
+            if arg.arg == "timeout":
+                self.error(TRIO300, arg.lineno, arg.col_offset)
+
 
 def critical_except(node: ast.ExceptHandler) -> Optional[Tuple[int, int, str]]:
     def has_exception(node: Optional[ast.expr]) -> str:
@@ -629,3 +635,4 @@ def run(self) -> Generator[Tuple[int, int, str, Type[Any]], None, None]:
 TRIO106 = "TRIO106: trio must be imported with `import trio` for the linter to work"
 TRIO107 = "TRIO107: Async functions must have at least one checkpoint on every code path, unless an exception is raised"
 TRIO108 = "TRIO108: Early return from async function must have at least one checkpoint on every code path before it."
+TRIO300 = "TRIO300: Async function definition with a `timeout` parameter - use `trio.[fail/move_on]_[after/at]` instead"

tests/trio300.py

@@ -0,0 +1,65 @@
+timeout = 10
+
+
+async def foo():
+    return
+
+
+# args
+async def foo_1(timeout):  # error: 16
+    return
+
+
+# arg in args wih default & annotation
+async def foo_2(timeout: int = 3):  # error: 16
+    return
+
+
+# vararg
+async def foo_3(*timeout):  # ??
+    return
+
+
+# kwarg
+async def foo_4(**timeout):  # ??
+    return
+
+
+# correct line/col
+async def foo_5(
+    bar,
+    timeouts,
+    my_timeout,
+    timeout_,
+    timeout,  # error: 4
+):
+    return
+
+
+# posonlyargs
+async def foo_6(
+    timeout,  # error: 4
+    /,
+    bar,
+):
+    return
+
+
+# kwonlyargs
+async def foo_7(
+    *,
+    timeout,  # error: 4
+):
+    return
+
+
+# kwonlyargs (and kw_defaults)
+async def foo_8(
+    *,
+    timeout=5,  # error: 4
+):
+    return
+
+
+async def foo_9(k=timeout):
+    return