Shutdown request fails with "invalid type: map, expected unit" when params is empty object

The rust-analyzer language server rejects LSP shutdown requests when the params field contains an empty JSON object {}, causing the server to crash instead of shutting down gracefully. Emacs eglot recently changed to send {} instead of null to accommodate other language servers (like ocamllsp) that have strict validation requirements. This appears to be an issue with the lsp-server or lsp-types crates used by rust-analyzer. The deserialization logic expects unit (no params or null) but rejects an empty object {}, which is technically valid per the JSON-RPC spec.

Steps to Reproduce

1. Start rust-analyzer via M-x eglot
2. Send a shutdown request with M-x eglot-shutdown
3. Server crashes with the following error

[eglot] Asking EGLOT (downloads/(rust-ts-mode rust-mode)) politely to terminate
[jsonrpc] (warning) Sentinel for EGLOT (downloads/(rust-ts-mode rust-mode)) still hasn't run, deleting it!
[jsonrpc] Server exited with status 9
jsonrpc-request: jsonrpc-error: "request id=6 failed:", (jsonrpc-error-code . -32602), 
  (jsonrpc-error-message . "Failed to deserialize shutdown: invalid type: map, expected unit; {}")

Expected Behavior

According to the JSON-RPC 2.0 specification, section 4.2:

If present, parameters for the rpc call MUST be provided as a Structured value. Either by-position through an Array or by-name through an Object.

An empty object {} is a valid structured value and should be accepted. The LSP specification inherits this from JSON-RPC.

Related Issues

• Emacs bug report: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=66144
• Similar issue reported for ty language server: https://github.com/astral-sh/ty/issues/1330
• Helix editor issue with ocamllsp: https://github.com/helix-editor/helix/issues/5400

rust-analyzer version: rust-analyzer 2025-08-25

rustc version: rustc 1.89.0 (29483883e 2025-08-04)

editor or extension: GNU Emacs 31.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.49, cairo version 1.18.4)

Inspect the shutdown-parameter deserialization logic in the lsp-server or lsp-types crates, starting from the error reported for the shutdown request. Reproduce the request with an empty params object through Emacs eglot, then verify that rust-analyzer accepts {} and shuts down gracefully without the deserialization error.