Problem:
Users of the Roslyn (C#) LSP have encountered significant delays when
retrieving pull diagnostics in large documents while using Neovim. For
instance, diagnostics in a 2000-line .cs file can take over 20 seconds
to display after edits in Neovim, whereas in VS Code, diagnostics for
the same file are displayed almost instantly.
As [mparq noted](https://github.com/seblj/roslyn.nvim/issues/93#issuecomment-2508940330)
in https://github.com/seblj/roslyn.nvim/issues/93, VS Code leverages
additional parameters specified in the [LSP documentation for
textDocument/diagnostic](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#documentDiagnosticParams),
specifically:
- previousResultId
- identifier
Solution:
When requesting diagnostics, Neovim should include the
`previousResultId` and `identifier` parameters as part of the request.
These parameters enable the server to utilize caching and return
incremental results.
Support for maintaining state is already present in the
[textDocument/semanticTokens implementation](8f84167c30/runtime/lua/vim/lsp/semantic_tokens.lua (L289)).
A similar mechanism can be implemented in `textDocument/diagnostic` handler.
f486f1742e