ASYNC912: timeout/cancelscope with only conditional checkpoints

flake8_async/visitors/helpers.py

@@ -320,6 +320,8 @@ class AttributeCall(NamedTuple):
 def with_has_call(
     node: cst.With, *names: str, base: Iterable[str] = ("trio", "anyio")
 ) -> list[AttributeCall]:
+    if isinstance(base, str):
+        base = (base,)
     res_list: list[AttributeCall] = []
     for item in node.items:
         if res := m.extract(

flake8_async/visitors/visitor91x.py

@@ -18,11 +18,13 @@
 from ..base import Statement
 from .flake8asyncvisitor import Flake8AsyncVisitor_cst
 from .helpers import (
+    cancel_scope_names,
     disabled_by_default,
     error_class_cst,
     fnmatch_qualified_name_cst,
     func_has_decorator,
     iter_guaranteed_once_cst,
+    with_has_call,
 )
 
 if TYPE_CHECKING:
@@ -243,6 +245,10 @@ class Visitor91X(Flake8AsyncVisitor_cst, CommonVisitors):
             "{0} from async iterable with no guaranteed checkpoint since {1.name} "
             "on line {1.lineno}."
         ),
+        "ASYNC912": (
+            "CancelScope with no guaranteed checkpoint. This makes it potentially "
+            "impossible to cancel."
+        ),
     }
 
     def __init__(self, *args: Any, **kwargs: Any):
@@ -420,8 +426,26 @@ def leave_Await(
     def visit_With_body(self, node: cst.With):
         if getattr(node, "asynchronous", None):
             self.uncheckpointed_statements = set()
+        if with_has_call(node, *cancel_scope_names) or with_has_call(
+            node, "timeout", "timeout_at", base="asyncio"
+        ):
+            pos = self.get_metadata(PositionProvider, node).start  # pyright: ignore
+            line: int = pos.line  # pyright: ignore
+            column: int = pos.column  # pyright: ignore
+            self.uncheckpointed_statements.add(Statement("with", line, column))
+            # self.uncheckpointed_statements.add(res[0])
+
+    def leave_With_body(self, node: cst.With):
+        pos = self.get_metadata(PositionProvider, node).start  # pyright: ignore
+        line: int = pos.line  # pyright: ignore
+        column: int = pos.column  # pyright: ignore
+        s = Statement("with", line, column)
+        if s in self.uncheckpointed_statements:
+            self.error(node, error_code="ASYNC912")
+            self.uncheckpointed_statements.remove(s)
 
-    leave_With_body = visit_With_body
+        if getattr(node, "asynchronous", None):
+            self.uncheckpointed_statements = set()
 
     # error if no checkpoint since earlier yield or function entry
     def leave_Yield(

tests/autofix_files/async91x_autofix.py

@@ -9,6 +9,7 @@
 # ARG --enable=ASYNC910,ASYNC911
 
 from typing import Any
+
 import trio
 
 
@@ -124,3 +125,19 @@ async def async_func(): ...
         break
     [... for i in range(5)]
     return
+
+
+# TODO: issue 240
+async def livelocks():
+    while True:
+        ...
+
+
+# this will autofix 910 by adding a checkpoint outside the loop
+async def no_checkpoint():  # ASYNC910: 0, "exit", Statement("function definition", lineno)
+    while bar():
+        try:
+            await trio.sleep("1")  # type: ignore[arg-type]
+        except ValueError:
+            ...
+    await trio.lowlevel.checkpoint()

tests/autofix_files/async91x_autofix.py.diff

@@ -1,13 +1,5 @@
 ---
 +++
-@@ x,6 x,7 @@
- # ARG --enable=ASYNC910,ASYNC911
-
- from typing import Any
-+import trio
-
-
- def bar() -> Any: ...
 @@ x,30 x,38 @@
 
  async def foo1():  # ASYNC910: 0, "exit", Statement("function definition", lineno)
@@ -78,3 +70,8 @@
          yield  # ASYNC911: 8, "yield", Statement("function definition", lineno-2) # ASYNC911: 8, "yield", Statement("yield", lineno)
 
          async def bar():
+@@ x,3 x,4 @@
+             await trio.sleep("1")  # type: ignore[arg-type]
+         except ValueError:
+             ...
++    await trio.lowlevel.checkpoint()

tests/eval_files/async912.py

@@ -0,0 +1,108 @@
+# ASYNCIO_NO_ERROR
+import trio
+
+
+async def foo():
+    with trio.move_on_after(0.1):  # error: 4
+        ...
+    with trio.move_on_at(0.1):  # error: 4
+        ...
+    with trio.fail_after(0.1):  # error: 4
+        ...
+    with trio.fail_at(0.1):  # error: 4
+        ...
+    with trio.CancelScope(0.1):  # error: 4
+        ...
+
+    with open(""):
+        ...
+
+    with trio.move_on_after(0.1):
+        await trio.lowlevel.checkpoint()
+
+    with trio.move_on_after(0.1):  # error: 4
+        with trio.move_on_after(0.1):  # error: 8
+            ...
+
+    with trio.move_on_after(0.1):  # TODO: should probably raise an error?
+        with trio.move_on_after(0.1):
+            await trio.lowlevel.checkpoint()
+
+    with trio.move_on_after(0.1):
+        await trio.lowlevel.checkpoint()
+        with trio.move_on_after(0.1):
+            await trio.lowlevel.checkpoint()
+
+    with trio.move_on_after(0.1):
+        with trio.move_on_after(0.1):
+            await trio.lowlevel.checkpoint()
+        await trio.lowlevel.checkpoint()
+
+    # TODO: should probably raise the error at the call, rather than at the with statement
+    # fmt: off
+    with (  # error: 4
+            # a
+            # b
+            trio.move_on_after(0.1)
+            # c
+            ):
+        ...
+
+    with (  # error: 4
+            open(""),
+            trio.move_on_at(5),
+            open(""),
+            ):
+        ...
+    # fmt: on
+
+    # TODO: only raises one error currently, can make it raise 2(?)
+    with (  # error: 4
+        trio.move_on_after(0.1),
+        trio.fail_at(5),
+    ):
+        ...
+
+
+# TODO: issue #240
+async def livelocks():
+    with trio.move_on_after(0.1):  # should error
+        while True:
+            try:
+                await trio.sleep("1")  # type: ignore
+            except TypeError:
+                pass
+
+
+def condition() -> bool:
+    return True
+
+
+async def livelocks_2():
+    with trio.move_on_after(0.1):  # error: 4
+        while condition():
+            try:
+                await trio.sleep("1")  # type: ignore
+            except TypeError:
+                pass
+
+
+# TODO: add --async912-context-managers=
+async def livelocks_3():
+    import contextlib
+
+    with trio.move_on_after(0.1):  # should error
+        while True:
+            with contextlib.suppress(TypeError):
+                await trio.sleep("1")  # type: ignore
+
+
+# raises an error...?
+with trio.move_on_after(10):  # error: 0
+    ...
+
+
+# completely sync function ... is this something we care about?
+def sync_func():
+    with trio.move_on_after(10):
+        ...

tests/eval_files/async912_asyncio.py

@@ -0,0 +1,19 @@
+# BASE_LIBRARY asyncio
+# ANYIO_NO_ERROR
+# TRIO_NO_ERROR
+
+# timeout[_at] added in py3.11
+# mypy: disable-error-code=attr-defined
+
+import asyncio
+
+
+async def foo():
+    async with asyncio.timeout(10):  # error: 4
+        ...
+    async with asyncio.timeout(10):
+        await foo()
+    async with asyncio.timeout_at(10):  # error: 4
+        ...
+    async with asyncio.timeout_at(10):
+        await foo()

tests/eval_files/async91x_autofix.py

@@ -10,6 +10,8 @@
 
 from typing import Any
 
+import trio
+
 
 def bar() -> Any: ...
 
@@ -109,3 +111,18 @@ async def async_func(): ...
         break
     [... for i in range(5)]
     return
+
+
+# TODO: issue 240
+async def livelocks():
+    while True:
+        ...
+
+
+# this will autofix 910 by adding a checkpoint outside the loop
+async def no_checkpoint():  # ASYNC910: 0, "exit", Statement("function definition", lineno)
+    while bar():
+        try:
+            await trio.sleep("1")  # type: ignore[arg-type]
+        except ValueError:
+            ...

tests/test_flake8_async.py

@@ -452,6 +452,7 @@ def _parse_eval_file(
     "ASYNC116",
     "ASYNC117",
     "ASYNC118",
+    "ASYNC912",
 }
 
 
@@ -479,7 +480,7 @@ def visit_AsyncFor(self, node: ast.AsyncFor):
         return self.replace_async(node, ast.For, node.target, node.iter)
 
 
-@pytest.mark.parametrize(("test", "path"), test_files)
+@pytest.mark.parametrize(("test", "path"), test_files, ids=[f[0] for f in test_files])
 def test_noerror_on_sync_code(test: str, path: Path):
     if any(e in test for e in error_codes_ignored_when_checking_transformed_sync_code):
         return