[BUG] jdtls does not specify a command to run the language server by default

[s1idewhist1e]

Plugin

jdtls

Nixpkgs Release

unstable

Home Manager Release

unstable

I have read the FAQ

• I have read the FAQ and my bug is not listed there.

Description

By default, plugins.jdtls.enable does not populate plugins.jdtls.settings.cmd field. When this is not populated, an assertion fails because the plugin expects to have the command to start the language server in this field. Expected behavior is that it would populate this with the plugins.jdtls.jdtLanguageServerPackage field so it works without needing further configuration which is not clearly documented.

Minimal, Reproducible Example (MRE)

programs.nixvim = {
    plugins.jdtls.enable = true;
};

[MattSturgeon]

Is the assertion an eval-time Nixvim assertion or a runtime Neovim assertion?

Actually adding the default cmd should be done upstream in nvim-lspconfig, not here in Nixvim.

We install the configured packages onto the PATH, so that they should usually work with default nvim-lspconfig configs.

[s1idewhist1e]

The issue is a Neovim assertion in the jdtls plugin. It expects start_or_attach to have the field cmd, which is not filled by default. The full runtime error:

Error detected while processing BufReadPost Autocommands for "*":                                                                     
Error executing lua callback: ...-neovim-unwrapped-0.11.5/share/nvim/runtime/filetype.lua:36: BufReadPost Autocommands for "*"..FileTy
pe Autocommands for "java": Vim(append):Error executing lua callback: ...ck/myNeovimPackages/start/nvim-jdtls/lua/jdtls/setup.lua:298:
 Config must have a `cmd` property and that must be a table. Got: nil                                                                 
stack traceback:                                                                                                                      
        [C]: in function 'assert'                                                                                                     
        ...ck/myNeovimPackages/start/nvim-jdtls/lua/jdtls/setup.lua:298: in function 'start_or_attach'                                
        /home/sekibanki/.config/nvim/init.lua:184: in function </home/sekibanki/.config/nvim/init.lua:183>                            
        [C]: in function 'nvim_cmd'                                                                                                   
        ...-neovim-unwrapped-0.11.5/share/nvim/runtime/filetype.lua:36: in function <...-neovim-unwrapped-0.11.5/share/nvim/runtime/fi
letype.lua:35>                                                                                                                        
        [C]: in function 'pcall'                                                                                                      
        vim/shared.lua: in function <vim/shared.lua:0>                                                                                
        [C]: in function '_with'                                                                                                      
        ...-neovim-unwrapped-0.11.5/share/nvim/runtime/filetype.lua:35: in function <...-neovim-unwrapped-0.11.5/share/nvim/runtime/fi
letype.lua:10>                                                                                                                        
stack traceback:                                                                                                                      
        [C]: in function '_with'                                                                                                      
        ...-neovim-unwrapped-0.11.5/share/nvim/runtime/filetype.lua:35: in function <...-neovim-unwrapped-0.11.5/share/nvim/runtime/fi
letype.lua:10>                                      

As to whether or not this is a nixvim issue, my understanding is that nixvim itself explicitly puts this in init.lua:

        {
            callback = function()
                require("jdtls").start_or_attach({})
            end,
            event = "FileType",
            pattern = "java",
        },
 -- ...

This occurs regardless of whether or not lsp.servers.jdtls.enable is true

The simplest workaround is simply to specify jdtls.settings.cmd = [ "jdtls" ].

[shimeoki]

as said above, nixvim puts a FileType callback for a start_or_attach call, where the table is the jdtls.settings attribute set. it is blank by default, so jdtls received a blank table and threw an error. it is located here.

the transition to nvim 0.11 is a bit foggy for me, but as i understand, start_or_attach method of using the plugin is "legacy". nvim-jdtls just attaches itself to the native lsp, so using it explicitly is needed only in edge-cases.

i mention nvim 0.11 here, because as i remember, usage of lspconfig to launch language servers was almost necessary, because you needed to launch the language server manually and the start_or_attach function was made for that.

in the readme the first recommended method is just enabling jdtls via nvim api, and the configuration is also retrieved from the native lsp config, as well as the filetypes.

both lspconfig and nvim-jdtls provide default lsp configurations, so "overriding" default configuration from the plugin via explicit call of empty table to start_or_attach is really not needed and even harmful.

because of this, i "installed the plugin" in my configuration like this:

programs.nixvim = {
    extraPlugins = [
        pkgs.vimPlugins.nvim-jdtls
    ];

    lsp.servers = {
        jdtls.enable = true;
    };
};
# and i provided configuration in extraFiles at after/lsp/jdtls.lua

so the whole thing with the autoCmd can be removed from nixvim for nvim 0.11+.