lsp-server: handle_shutdown crashing on response

Hello,

We are using your crate lsp-server in our project, and we face an issue when exiting the server.
There is a method that handle the shutdown Request from the client:
https://github.com/rust-lang/rust-analyzer/blob/3c2aca1e5e9fbabb4e05fc4baa62e807aadc476a/lib/lsp-server/src/lib.rs#L348

This method receive the shutdown request, then send the response and wait for the exit notification, sending an error if another message arrives.
But according to the lsp specification (https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#shutdown) , it is normal in my understanding that the client do not send any new Request after sending the shutdown request, but he could still send Responses to previous requests. ("If a server receives requests after a shutdown request those requests should error with InvalidRequest")
If that's the case, handle_shutdown is erroring, and we lose the responses we are still waiting.
We use the vscode client to develop our server, so I guess that receive Responses after the shutdown request is valid regarding the specifications.
We are thinking about modifying the line https://github.com/rust-lang/rust-analyzer/blob/3c2aca1e5e9fbabb4e05fc4baa62e807aadc476a/lib/lsp-server/src/lib.rs#L356C13-L356C25 , but we wanted to share this feedback with you and know what you think about that

Have a nice day

Start with handle_shutdown in lib/lsp-server/src/lib.rs around lines 348 and 356, then compare its message handling with the LSP 3.17 shutdown specification. Verify how responses to earlier requests are treated after shutdown, and define completion by preserving valid responses while handling later requests according to the specification.