Top hitting IntelliSense parsing crash on Mac, probably Linux too (also repros on Windows, but less frequently). Might just be able to add a null check.
With 0.21.0-insiders, the top of the crashing thread call stack looks like:
Microsoft.VSCode.CPP.IntelliSense.Msvc.darwin
0 scan_function_body + 4240
1 function_definition + 4642
2 scan_nonmember_declaration + 16702
3 declaration + 212
On Windows, process_vla_parameters is at the top of the stack due to differences in inlining.
UPDATE: We'll have a fix for December's release, but we're not 100% sure it'll solve the issue.