I tried to trigger this in the corpus tests and the LSP server, but didn't manage to do so, so reporting as a playground problem for now:

Start with https://play.ty.dev/089aad00-e47d-4076-bc45-c9c9f4293f81 and then type if after the 1 in the match case:

match 0:
    case 1:  # try to add ` if …` after the `1` here
        pass

This crashes with "entered unreachable code: If we have at least one declaration, the scope-start should not be definitely visible".

This seems to be triggered by auto-completions. When starting with https://play.ty.dev/e0c377ca-5e64-4478-86a2-8c6f11f31ee8

match 0:
    case 1 i:
        pass

there is no crash. But when I explicitly trigger the autocompletions using ctrl-space after the i, I get the same crash.