fix: handle PermissionError in version check cache write

aider/versioncheck.py

@@ -91,8 +91,11 @@ def check_version(io, just_check=False, verbose=False):
         io.tool_error(f"Error checking pypi for new version: {err}")
         return False
     finally:
-        VERSION_CHECK_FNAME.parent.mkdir(parents=True, exist_ok=True)
-        VERSION_CHECK_FNAME.touch()
+        try:
+            VERSION_CHECK_FNAME.parent.mkdir(parents=True, exist_ok=True)
+            VERSION_CHECK_FNAME.touch()
+        except OSError:
+            pass
 
     ###
     # is_update_available = True

tests/basic/test_versioncheck.py

@@ -0,0 +1,86 @@
+from unittest.mock import MagicMock, patch
+
+from aider.versioncheck import check_version
+
+
+class TestCheckVersion:
+    @patch("aider.versioncheck.VERSION_CHECK_FNAME")
+    @patch("aider.versioncheck.requests", create=True)
+    def test_permission_error_on_touch_does_not_crash(self, mock_requests, mock_fname):
+        """Regression test for issue #4958.
+
+        When the version cache file cannot be written (e.g. read-only filesystem,
+        permission denied), check_version should handle the error gracefully
+        instead of raising an uncaught PermissionError.
+        """
+        mock_fname.exists.return_value = False
+        mock_fname.parent.mkdir.return_value = None
+        mock_fname.touch.side_effect = PermissionError(
+            "[Errno 13] Permission denied: '/root/.aider/caches/versioncheck'"
+        )
+
+        mock_response = MagicMock()
+        mock_response.json.return_value = {"info": {"version": "0.86.2"}}
+        mock_requests.get.return_value = mock_response
+
+        io = MagicMock()
+
+        # Should not raise
+        check_version(io)
+
+    @patch("aider.versioncheck.VERSION_CHECK_FNAME")
+    @patch("aider.versioncheck.requests", create=True)
+    def test_permission_error_on_mkdir_does_not_crash(self, mock_requests, mock_fname):
+        """When even the parent directory cannot be created, check_version
+        should still not crash."""
+        mock_fname.exists.return_value = False
+        mock_fname.parent.mkdir.side_effect = PermissionError(
+            "[Errno 13] Permission denied: '/root/.aider/caches'"
+        )
+
+        mock_response = MagicMock()
+        mock_response.json.return_value = {"info": {"version": "0.86.2"}}
+        mock_requests.get.return_value = mock_response
+
+        io = MagicMock()
+
+        # Should not raise
+        check_version(io)
+
+    @patch("aider.versioncheck.VERSION_CHECK_FNAME")
+    @patch("aider.versioncheck.requests", create=True)
+    def test_oserror_on_touch_does_not_crash(self, mock_requests, mock_fname):
+        """Other OSError variants (read-only filesystem, disk full) should
+        also be handled gracefully."""
+        mock_fname.exists.return_value = False
+        mock_fname.parent.mkdir.return_value = None
+        mock_fname.touch.side_effect = OSError("[Errno 30] Read-only file system")
+
+        mock_response = MagicMock()
+        mock_response.json.return_value = {"info": {"version": "0.86.2"}}
+        mock_requests.get.return_value = mock_response
+
+        io = MagicMock()
+
+        # Should not raise
+        check_version(io)
+
+    @patch("aider.versioncheck.VERSION_CHECK_FNAME")
+    @patch("aider.versioncheck.requests", create=True)
+    @patch("aider.versioncheck.aider")
+    def test_normal_version_check_still_works(self, mock_aider, mock_requests, mock_fname):
+        """Ensure the fix doesn't break normal version checking behavior."""
+        mock_fname.exists.return_value = False
+        mock_fname.parent.mkdir.return_value = None
+        mock_fname.touch.return_value = None
+        mock_aider.__version__ = "0.1.0"
+
+        mock_response = MagicMock()
+        mock_response.json.return_value = {"info": {"version": "99.0.0"}}
+        mock_requests.get.return_value = mock_response
+
+        io = MagicMock()
+
+        result = check_version(io, just_check=True)
+        assert result is True
+        mock_fname.touch.assert_called_once()