Created attachment 164889 [details]
debug log from kate, with lsp logs

SUMMARY
***
NOTE: If you are reporting a crash, please try to attach a backtrace with debug symbols.
See https://community.kde.org/Guidelines_and_HOWTOs/Debugging/How_to_create_useful_crash_reports
***

Given the following document of Nix code:

let x = 5;
in 1

When the formatting button is pressed using the nixd language server, the following becomes the buffer content:

in 1
let x = 5;
in 1

This is essentially pasting the content of the file a second time, which is a bug. This does not happen in neovim with coc, and I strongly suspect this is a bug in kate's LSP client.

This is what the language server responds to the format request with:

"{\"id\":4,\"jsonrpc\":\"2.0\",\"result\":[{\"newText\":\"let x = 5;\\nin 1\\n\",\"range\":{\"end\":{\"character\":2147483647,\"line\":2147483647},\"start\":{\"character\":0,\"line\":0}}}]}"

This message is intending to overwrite the entire contents of the file with the provided text. However, kate seems to do something different with it.

I have attached a full debug log of the LSP interaction.

I ran kate with the following:

LSPCLIENT_DEBUG=1 QT_FORCE_STDERR_LOGGING=1 QT_LOGGING_RULES='katelspclientplugin=true;default.debug=true' kate --startanon -b bad.nix

STEPS TO REPRODUCE
0. Acquire nixd and nixpkgs-fmt from nixpkgs. If you have nix, this can be done with `nix-shell -p nixd nixpkgs-fmt`, then running kate from the resulting shell.
1. Configure kate with nixd like so:
{
    "servers": {
        "nix": {
            "command": ["nixd"],
            "highlightingModeRegex": "^Nix$"
        }
    }
}

2.  Write this into bad.nix:
let x = 5;
in 1

3. Press the LSP format button
4. Get mangled text

OBSERVED RESULT

Text is mangled.

EXPECTED RESULT

Text should be replaced with the new text from the language server.

SOFTWARE/OS VERSIONS
Operating System: NixOS 24.05
KDE Plasma Version: 5.27.10
KDE Frameworks Version: 5.112.0
Qt Version: 5.15.11
Kernel Version: 6.1.69 (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-7700HQ CPU @ 2.80GHz
Memory: 31.2 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 630

ADDITIONAL INFORMATION