python-trio
diff --git a/‎CHANGELOG.md
Lines changed: 3 additions & 0 deletions b/‎CHANGELOG.md
Lines changed: 3 additions & 0 deletions
diff --git a/‎README.md
Lines changed: 1 addition & 0 deletions b/‎README.md
Lines changed: 1 addition & 0 deletions
diff --git a/‎flake8_trio.py
Lines changed: 22 additions & 4 deletions b/‎flake8_trio.py
Lines changed: 22 additions & 4 deletions
diff --git a/‎tests/trio302.py
Lines changed: 56 additions & 0 deletions b/‎tests/trio302.py
Lines changed: 56 additions & 0 deletions
@@ -1,6 +1,9 @@
 # Changelog
 *[CalVer, YY.month.patch](https://calver.org/)*
 
+## Future
+- Added TRIO302: async context manager inside nursery. Nurseries should be outermost.
+
 ## 22.7.6
 - Extend TRIO102 to also check inside `except BaseException` and `except trio.Cancelled`
 - Extend TRIO104 to also check for `yield`
 
@@ -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`.
+- **TRIO302**: async context manager inside nursery. Nurseries should be outermost.
@@ -98,9 +98,8 @@ def get_trio_scope(node: ast.AST, *names: str) -> Optional[TrioScope]:
         and isinstance(node.func, ast.Attribute)
         and isinstance(node.func.value, ast.Name)
         and node.func.value.id == "trio"
-        and node.func.attr in names
+        and (node.func.attr in names or not names)
     ):
-        # return "trio." + node.func.attr
         return TrioScope(node, node.func.attr, node.func.value.id)
     return None
 
@@ -120,6 +119,7 @@ def __init__(self):
         super().__init__()
         self._yield_is_error = False
         self._safe_decorator = False
+        self._inside_nursery: Optional[int] = None
 
     def visit_With(self, node: Union[ast.With, ast.AsyncWith]):
         self.check_for_trio100(node)
@@ -142,19 +142,23 @@ def visit_With(self, node: Union[ast.With, ast.AsyncWith]):
         self._yield_is_error = outer_yie
 
     def visit_AsyncWith(self, node: ast.AsyncWith):
+        outer = self._inside_nursery
+        self.check_for_trio302(node.items)
         self.visit_With(node)
+        self._inside_nursery = outer
 
     def visit_FunctionDef(self, node: Union[ast.FunctionDef, ast.AsyncFunctionDef]):
-        outer = self._safe_decorator, self._yield_is_error
+        outer = self._safe_decorator, self._yield_is_error, self._inside_nursery
         self._yield_is_error = False
+        self._inside_nursery = None
 
         # check for @<context_manager_name> and @<library>.<context_manager_name>
         if has_decorator(node.decorator_list, *context_manager_names):
             self._safe_decorator = True
 
         self.generic_visit(node)
 
-        self._safe_decorator, self._yield_is_error = outer
+        self._safe_decorator, self._yield_is_error, self._inside_nursery = outer
 
     def visit_AsyncFunctionDef(self, node: ast.AsyncFunctionDef):
         self.visit_FunctionDef(node)
@@ -187,6 +191,19 @@ 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_for_trio302(self, withitems: List[ast.withitem]):
+        calls = [w.context_expr for w in withitems]
+        for call in calls:
+            ss = get_trio_scope(call)
+            if not ss:
+                continue
+            if ss.funcname == "open_nursery":
+                self._inside_nursery = ss.node.lineno
+            elif self._inside_nursery is not None:
+                self.error(
+                    TRIO302, ss.node.lineno, ss.node.col_offset, self._inside_nursery
+                )
+
 
 def critical_except(node: ast.ExceptHandler) -> Optional[Tuple[int, int, str]]:
     def has_exception(node: Optional[ast.expr]) -> str:
@@ -629,3 +646,4 @@ 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."
+TRIO302 = "TRIO302: async context manager inside nursery opened on line {}. Nurseries should be outermost."
@@ -0,0 +1,56 @@
+import trio
+import trio as noterror
+
+
+async def foo():
+    async with trio.open_nursery():
+        async with trio.open_process():  # error: 19, 6
+            ...
+
+    async with trio.open_process():
+        async with trio.open_nursery():
+            ...
+
+    async with trio.open_nursery():
+
+        async def bar():
+            async with trio.open_process():  # safe
+                ...
+
+    async with trio.open_nursery():
+        with trio.anything():  # safe (not async)
+            ...
+
+    async with trio.open_nursery():
+        async with noterror.booboo():  # safe
+            ...
+
+    async with trio.open_nursery():
+        async with trio.anything.anything.anything():  # ??? - currently safe
+            ...
+
+    async with trio.open_nursery():
+        async with trio.open_nursery():  # safe
+            ...
+        async with trio.anything():  # error: 19, 32
+            ...
+
+    async with trio.anything():
+        async with trio.open_nursery():  # safe
+            async with trio.open_nursery():  # safe
+                async with trio.anything():  # error: 27, 40
+                    async with trio.anything():  # error: 31, 40
+                        ...
+
+    async with noterror.booboo(), trio.open_nursery():
+        async with noterror.booboo(), trio.anything():  # error: 38, 45
+            ...
+
+    async with trio.open_nursery(), trio.anything(): # error: 36, 49
+        ...
+
+    async with trio.anything(), trio.open_nursery(): # safe
+        ...
+
+    async with trio.open_nursery(), trio.anything(), trio.open_nursery(): # error: 36, 55
+        ...