[flake8-simplify] Omit select context managers from SIM117

crates/ruff_linter/resources/test/fixtures/flake8_simplify/SIM117.py

@@ -134,3 +134,32 @@ def method1(self) -> T:
         f" something { my_dict["key"] } something else "
 
         f"foo {f"bar {x}"} baz"
+
+# Allow cascading for some statements.
+import anyio
+import asyncio
+import trio
+
+async with asyncio.timeout(1):
+    async with A() as a:
+        pass
+
+async with A():
+    async with asyncio.timeout(1):
+        pass
+
+async with asyncio.timeout(1):
+    async with asyncio.timeout_at(1):
+        async with anyio.CancelScope():
+            async with anyio.fail_after(1):
+                async with anyio.move_on_after(1):
+                    async with trio.fail_after(1):
+                        async with trio.fail_at(1):
+                            async with trio.move_on_after(1):
+                                async with trio.move_on_at(1):
+                                    pass
+
+# Do not supress combination, if a context manager is already combined with another.
+async with asyncio.timeout(1), A():
+    async with B():
+        pass

crates/ruff_linter/src/rules/flake8_simplify/rules/ast_with.rs

@@ -1,3 +1,4 @@
+use ast::Expr;
 use log::error;
 
 use ruff_diagnostics::{Diagnostic, Fix};
@@ -24,6 +25,13 @@ use super::fix_with;
 /// will minimize the indentation depth of the code, making it more
 /// readable.
 ///
+/// The following context managers are exempt when used as standalone
+/// statements:
+///
+///  - `anyio`.{`CancelScope`, `fail_after`, `move_on_after`}
+///  - `asyncio`.{`timeout`, `timeout_at`}
+///  - `trio`.{`fail_after`, `fail_at`, `move_on_after`, `move_on_at`}
+///
 /// ## Example
 /// ```python
 /// with A() as a:
@@ -73,6 +81,38 @@ fn next_with(body: &[Stmt]) -> Option<(bool, &[WithItem], &[Stmt])> {
     Some((*is_async, items, body))
 }
 
+/// Check if `with_items` contains a single item which should not necessarily be
+/// grouped with other items.
+///
+/// For example:
+/// ```python
+/// async with asyncio.timeout(1):
+///     with resource1(), resource2():
+///         ...
+/// ```
+fn explicit_with_items(checker: &mut Checker, with_items: &[WithItem]) -> bool {
+    let [with_item] = with_items else {
+        return false;
+    };
+    let Expr::Call(expr_call) = &with_item.context_expr else {
+        return false;
+    };
+    checker
+        .semantic()
+        .resolve_call_path(&expr_call.func)
+        .is_some_and(|call_path| {
+            matches!(
+                call_path.as_slice(),
+                ["asyncio", "timeout" | "timeout_at"]
+                    | ["anyio", "CancelScope" | "fail_after" | "move_on_after"]
+                    | [
+                        "trio",
+                        "fail_after" | "fail_at" | "move_on_after" | "move_on_at"
+                    ]
+            )
+        })
+}
+
 /// SIM117
 pub(crate) fn multiple_with_statements(
     checker: &mut Checker,
@@ -111,6 +151,10 @@ pub(crate) fn multiple_with_statements(
             return;
         }
 
+        if explicit_with_items(checker, &with_stmt.items) || explicit_with_items(checker, items) {
+            return;
+        }
+
         let Some(colon) = items.last().and_then(|item| {
             SimpleTokenizer::starts_at(item.end(), checker.locator().contents())
                 .skip_trivia()

crates/ruff_linter/src/rules/flake8_simplify/snapshots/ruff_linter__rules__flake8_simplify__tests__SIM117_SIM117.py.snap

@@ -316,5 +316,28 @@ SIM117.py:126:1: SIM117 [*] Use a single `with` statement with multiple contexts
 135 134 | 
 136     |-        f"foo {f"bar {x}"} baz"
     135 |+    f"foo {f"bar {x}"} baz"
+137 136 | 
+138 137 | # Allow cascading for some statements.
+139 138 | import anyio
+
+SIM117.py:163:1: SIM117 [*] Use a single `with` statement with multiple contexts instead of nested `with` statements
+    |
+162 |   # Do not supress combination, if a context manager is already combined with another.
+163 | / async with asyncio.timeout(1), A():
+164 | |     async with B():
+    | |___________________^ SIM117
+165 |           pass
+    |
+    = help: Combine `with` statements
+
+ℹ Unsafe fix
+160 160 |                                     pass
+161 161 | 
+162 162 | # Do not supress combination, if a context manager is already combined with another.
+163     |-async with asyncio.timeout(1), A():
+164     |-    async with B():
+165     |-        pass
+    163 |+async with asyncio.timeout(1), A(), B():
+    164 |+    pass