10: add trio[301], don't await trio.sleep inside loop

CHANGELOG.md

@@ -3,6 +3,7 @@
 
 ## Future
 - 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`

README.md

@@ -32,3 +32,4 @@ pip install flake8-trio
 - **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`.
 - **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`.

flake8_trio.py

@@ -154,6 +154,7 @@ def visit_AsyncWith(self, node: ast.AsyncWith):
     def visit_FunctionDef(self, node: Union[ast.FunctionDef, ast.AsyncFunctionDef]):
         outer = self.get_state()
         self._yield_is_error = False
+        self._inside_loop = False
 
         # check for @<context_manager_name> and @<library>.<context_manager_name>
         if has_decorator(node.decorator_list, *context_manager_names):
@@ -198,6 +199,19 @@ def check_109(self, args: ast.arguments):
             if arg.arg == "timeout":
                 self.error(TRIO109, arg.lineno, arg.col_offset)
 
+    def visit_While(self, node: ast.While):
+        self.check_for_110(node)
+        self.generic_visit(node)
+
+    def check_for_110(self, node: ast.While):
+        if (
+            len(node.body) == 1
+            and isinstance(node.body[0], ast.Expr)
+            and isinstance(node.body[0].value, ast.Await)
+            and get_trio_scope(node.body[0].value.value, "sleep", "sleep_until")
+        ):
+            self.error(TRIO110, node.lineno, node.col_offset)
+
 
 def critical_except(node: ast.ExceptHandler) -> Optional[Tuple[int, int, str]]:
     def has_exception(node: Optional[ast.expr]) -> str:
@@ -639,3 +653,4 @@ def run(self) -> Iterable[Error]:
 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."
 TRIO109 = "TRIO109: Async function definition with a `timeout` parameter - use `trio.[fail/move_on]_[after/at]` instead"
+TRIO110 = "TRIO110: `while <condition>: await trio.sleep()` should be replaced by a `trio.Event`."

tests/trio110.py

@@ -0,0 +1,70 @@
+import trio
+import trio as noerror
+
+
+async def foo():
+    # only trigger on while loop with body being exactly one sleep[_until] statement
+    while ...:  # error: 4
+        await trio.sleep()
+
+    while ...:  # error: 4
+        await trio.sleep_until()
+
+    # nested
+
+    while ...:  # safe
+        while ...:  # error: 8
+            await trio.sleep()
+        await trio.sleep()
+
+    while ...:  # safe
+        while ...:  # error: 8
+            await trio.sleep()
+
+    ### the rest are all safe
+
+    # don't trigger on bodies with more than one statement
+    while ...:
+        await trio.sleep()
+        await trio.sleep()
+
+    while ...:  # safe
+        ...
+        await trio.sleep()
+
+    while ...:
+        await trio.sleep()
+        await trio.sleep_until()
+
+    # check library name
+    while ...:
+        await noerror.sleep()
+
+    async def sleep():
+        ...
+
+    while ...:
+        await sleep()
+
+    # check function name
+    while ...:
+        await trio.sleepies()
+
+    # don't trigger on [async] for
+    for _ in "":
+        await trio.sleep()
+
+    async for _ in trio.blah:
+        await trio.sleep()
+
+    while ...:
+
+        async def blah():
+            await trio.sleep()
+
+    while ...:
+        if ...:
+            await trio.sleep()
+
+    while await trio.sleep():
+        ...