Wrap multiple context managers in parentheses when targeting Python 3.9+

[yilei]

Description

Fixes #3486.

This also fixes the target version detection logic for parenthesized context managers (3.9) and match statements (3.10). But as far as I can tell, this didn't have user visible impact (until this PR).

I added a dedicated test data folder preview_context_managers, because this relies on the version detection logic when --target-version is not explicitly specified.

Checklist - did you ...

• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

[github-actions]

diff-shades reports zero changes comparing this PR (95bca0f) to main (18fb884).

---

What is this? | Workflow run | diff-shades documentation

[yilei]

I manually ran diff-shades analyze base.json --work-dir projects-cache --force-preview-style -- --target-version=py39 forcing to target 3.9. The attached diffs look good.

cm.diff.zip

First example:

╭──────────────────────── Summary ─────────────────────────╮
│ 12 projects & 29 files changed / 608 changes [+347/-261] │
│                                                          │
│ ... out of 2 384 528 lines, 11 521 files & 23 projects   │
╰──────────────────────────────────────────────────────────╯

[aioexabgp - https://github.com/cooperlees/aioexabgp.git]
╰─> revision fc83c5c705e3c818934ce0cdd04d6169a6977996
--- a/aioexabgp:aioexabgp/tests/fibs_tests.py
+++ b/aioexabgp:aioexabgp/tests/fibs_tests.py
@@ -190,31 +190,37 @@
                 )
             )

     def test_del_all_routes(self) -> None:
         # Test delete all with a nexthop
-        with patch(
-            f"{BASE_MODULE}.LinuxFib.get_route_table",
-            fibs_tests_fixtures.mocked_get_route_table,
-        ), patch(
-            f"{BASE_MODULE}.LinuxFib.del_route", return_value=True
-        ) as mock_del_route:
+        with (
+            patch(
+                f"{BASE_MODULE}.LinuxFib.get_route_table",
+                fibs_tests_fixtures.mocked_get_route_table,
+            ),
+            patch(
+                f"{BASE_MODULE}.LinuxFib.del_route", return_value=True
+            ) as mock_del_route,
+        ):
             self.assertTrue(
                 self.loop.run_until_complete(
                     self.lfib.del_all_routes(ip_address("fd00::4"))
                 )
             )
             # 1 prefix/route from v4 and 1 from v6 table
             self.assertEqual(2, mock_del_route.call_count)

         # Test no next hope and ensure we delete them all
-        with patch(
-            f"{BASE_MODULE}.LinuxFib.get_route_table",
-            fibs_tests_fixtures.mocked_get_route_table,
-        ), patch(
-            f"{BASE_MODULE}.LinuxFib.del_route", return_value=True
-        ) as mock_del_route:
+        with (
+            patch(
+                f"{BASE_MODULE}.LinuxFib.get_route_table",
+                fibs_tests_fixtures.mocked_get_route_table,
+            ),
+            patch(
+                f"{BASE_MODULE}.LinuxFib.del_route", return_value=True
+            ) as mock_del_route,
+        ):
             self.assertTrue(
                 self.loop.run_until_complete(self.lfib.del_all_routes(None))
             )
             # 2 prefix/route from v4 and 1 from v6 table
             self.assertEqual(3, mock_del_route.call_count)

[JelleZijlstra]

Thank you as always!