Slow LSP syntax highlighting with simple config

[emsknock]

Syntax highlighting has a noticeable lag when using a language server. See below for an MRE.

flake.nix

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
    nvf.url = "github:notashelf/nvf";
  };

  outputs =
    inputs:
    let
      system = "x86_64-linux";
    in
    {
      packages."${system}" = inputs.nvf.lib.neovimConfiguration {
        pkgs = inputs.nixpkgs.legacyPackages."${system}";
        modules = [
          {
            vim = {
              lsp = {
                enable = true;
                formatOnSave = true;
              };
              languages.nix.enable = true;
            };
          }
        ];
      };
    };
}

flake.lock

{
  "nodes": {
    "flake-compat": {
      "flake": false,
      "locked": {
        "lastModified": 1751685974,
        "narHash": "sha256-NKw96t+BgHIYzHUjkTK95FqYRVKB8DHpVhefWSz/kTw=",
        "ref": "refs/heads/main",
        "rev": "549f2762aebeff29a2e5ece7a7dc0f955281a1d1",
        "revCount": 92,
        "type": "git",
        "url": "https://git.lix.systems/lix-project/flake-compat.git"
      },
      "original": {
        "type": "git",
        "url": "https://git.lix.systems/lix-project/flake-compat.git"
      }
    },
    "flake-parts": {
      "inputs": {
        "nixpkgs-lib": [
          "nvf",
          "nixpkgs"
        ]
      },
      "locked": {
        "lastModified": 1756770412,
        "narHash": "sha256-+uWLQZccFHwqpGqr2Yt5VsW/PbeJVTn9Dk6SHWhNRPw=",
        "owner": "hercules-ci",
        "repo": "flake-parts",
        "rev": "4524271976b625a4a605beefd893f270620fd751",
        "type": "github"
      },
      "original": {
        "owner": "hercules-ci",
        "repo": "flake-parts",
        "type": "github"
      }
    },
    "mnw": {
      "locked": {
        "lastModified": 1756659871,
        "narHash": "sha256-v6Rh4aQ6RKjM2N02kK9Usn0Ix7+OY66vNpeklc1MnGE=",
        "owner": "Gerg-L",
        "repo": "mnw",
        "rev": "ed6cc3e48557ba18266e598a5ebb6602499ada16",
        "type": "github"
      },
      "original": {
        "owner": "Gerg-L",
        "repo": "mnw",
        "type": "github"
      }
    },
    "nixpkgs": {
      "locked": {
        "lastModified": 1758690382,
        "narHash": "sha256-NY3kSorgqE5LMm1LqNwGne3ZLMF2/ILgLpFr1fS4X3o=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "e643668fd71b949c53f8626614b21ff71a07379d",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixos-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "nixpkgs_2": {
      "locked": {
        "lastModified": 1756696532,
        "narHash": "sha256-6FWagzm0b7I/IGigOv9pr6LL7NQ86mextfE8g8Q6HBg=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "58dcbf1ec551914c3756c267b8b9c8c86baa1b2f",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixpkgs-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "nvf": {
      "inputs": {
        "flake-compat": "flake-compat",
        "flake-parts": "flake-parts",
        "mnw": "mnw",
        "nixpkgs": "nixpkgs_2",
        "systems": "systems"
      },
      "locked": {
        "lastModified": 1758271661,
        "narHash": "sha256-ENqd2/33uP5vB44ClDjjAV+J78oF8q1er4QUZuT8Z7g=",
        "owner": "notashelf",
        "repo": "nvf",
        "rev": "b7571df4d6e9ac08506a738ddceeec0b141751b0",
        "type": "github"
      },
      "original": {
        "owner": "notashelf",
        "repo": "nvf",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "nixpkgs": "nixpkgs",
        "nvf": "nvf"
      }
    },
    "systems": {
      "locked": {
        "lastModified": 1681028828,
        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
        "owner": "nix-systems",
        "repo": "default",
        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
        "type": "github"
      },
      "original": {
        "owner": "nix-systems",
        "repo": "default",
        "type": "github"
      }
    }
  },
  "root": "root",
  "version": 7
}

When I e.g. comment out a line from flake.nix, the line stays highlighted for a bit (less than a second, but still slowly enough for it to feel laggy) before turning grey. The same delay happens when uncommenting.

I'm coming from Helix where highlighting is instant even with language servers configured (including nil, which – to my understanding – is running in this example).

---

If I add vim.treesitter.enable = true and set lsp.enable = false, the lag disappears completely and highlighting feels instant. From what I understand, there's a (neo)vim option to somehow prioritise TS highlighting over LS highlighting but I'm not familiar enough with (neo)vim to apply that here. I grepped the nvf options for "highlight" and "prio" but couldn't spot anything related.

How can I run treesitter and a language server without highlighting having this lag?

[horriblename]

I vaguely recall seeing nil or nixd having slow semantic highlighting, which is proabbly the cause

disabling semantic tokena should fix that, but I forgot how, I'll check again tomorrow

[emsknock]

This's sounding like something that could be an option in languages.* – should I open an issue instead?

[horriblename]

in v0.8 you should be able to disable it per-LSP with:

vim.lsp.servers.nil.capabilities.semanticTokensProvider = lib.generators.mkLuaInline "vim.NIL";

unfortunately there's no quick way to disable it in 0.7 (asides from setting up nil-ls yourself)

This's sounding like something that could be an option in languages.* – should I open an issue instead?

I don't think it needs its own option

[emsknock]

I tried it out with the following (with my work MacBook – I can check with a linux box later if that's relevant for some reason):

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
    nvf.url = "github:notashelf/nvf?ref=v0.8";
  };

  outputs =
    inputs:
    let
      system = "aarch64-darwin";
      pkgs = inputs.nixpkgs.legacyPackages."${system}";
    in
    {
      packages."${system}" = inputs.nvf.lib.neovimConfiguration {
        inherit pkgs;
        modules = [
          {
            vim = {
              lsp = {
                enable = true;
                formatOnSave = true;
                servers.nil.capabilities.semanticTokensProvider = pkgs.lib.generators.mkLuaInline "vim.NIL";
              };
              treesitter.enable = true;
              languages.nix.enable = true;
            };
          }
        ];
      };
    };
}

flake.lock

{
  "nodes": {
    "flake-compat": {
      "flake": false,
      "locked": {
        "lastModified": 1751685974,
        "narHash": "sha256-NKw96t+BgHIYzHUjkTK95FqYRVKB8DHpVhefWSz/kTw=",
        "ref": "refs/heads/main",
        "rev": "549f2762aebeff29a2e5ece7a7dc0f955281a1d1",
        "revCount": 92,
        "type": "git",
        "url": "https://git.lix.systems/lix-project/flake-compat.git"
      },
      "original": {
        "type": "git",
        "url": "https://git.lix.systems/lix-project/flake-compat.git"
      }
    },
    "flake-parts": {
      "inputs": {
        "nixpkgs-lib": [
          "nvf",
          "nixpkgs"
        ]
      },
      "locked": {
        "lastModified": 1759362264,
        "narHash": "sha256-wfG0S7pltlYyZTM+qqlhJ7GMw2fTF4mLKCIVhLii/4M=",
        "owner": "hercules-ci",
        "repo": "flake-parts",
        "rev": "758cf7296bee11f1706a574c77d072b8a7baa881",
        "type": "github"
      },
      "original": {
        "owner": "hercules-ci",
        "repo": "flake-parts",
        "type": "github"
      }
    },
    "mnw": {
      "locked": {
        "lastModified": 1758834834,
        "narHash": "sha256-Y7IvY4F8vajZyp3WGf+KaiIVwondEkMFkt92Cr9NZmg=",
        "owner": "Gerg-L",
        "repo": "mnw",
        "rev": "cfbc7d1cc832e318d0863a5fc91d940a96034001",
        "type": "github"
      },
      "original": {
        "owner": "Gerg-L",
        "repo": "mnw",
        "type": "github"
      }
    },
    "nixpkgs": {
      "locked": {
        "lastModified": 1760878510,
        "narHash": "sha256-K5Osef2qexezUfs0alLvZ7nQFTGS9DL2oTVsIXsqLgs=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "5e2a59a5b1a82f89f2c7e598302a9cacebb72a67",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixos-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "nixpkgs_2": {
      "locked": {
        "lastModified": 1759386674,
        "narHash": "sha256-wg1Lz/1FC5Q13R+mM5a2oTV9TA9L/CHHTm3/PiLayfA=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "625ad6366178f03acd79f9e3822606dd7985b657",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixpkgs-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "nvf": {
      "inputs": {
        "flake-compat": "flake-compat",
        "flake-parts": "flake-parts",
        "mnw": "mnw",
        "nixpkgs": "nixpkgs_2",
        "systems": "systems"
      },
      "locked": {
        "lastModified": 1760781693,
        "narHash": "sha256-kNLWWt/FXqDpPZdmNYCTeeUBYZM0RV0UL7+Cg3CvQMI=",
        "owner": "notashelf",
        "repo": "nvf",
        "rev": "ea3ee477fa1814352b30d114f31bf4895eed053e",
        "type": "github"
      },
      "original": {
        "owner": "notashelf",
        "ref": "v0.8",
        "repo": "nvf",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "nixpkgs": "nixpkgs",
        "nvf": "nvf"
      }
    },
    "systems": {
      "locked": {
        "lastModified": 1681028828,
        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
        "owner": "nix-systems",
        "repo": "default",
        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
        "type": "github"
      },
      "original": {
        "owner": "nix-systems",
        "repo": "default",
        "type": "github"
      }
    }
  },
  "root": "root",
  "version": 7
}

But the same lag persists. I've a vague feeling I'm being stupid and done it wrong somehow but can't spot anything… I'll blame insomnia messing with my brain if that's the case though 😅

[horriblename]

apparently there is a distinction between client and server capabilities. The above code was supposed to be set on server capabilities. I'm not really sure what the new code is but this is what people used to do:

vim.api.nvim_create_autocmd("LspAttach", { 
  callback = function(args)
     local client = vim.lsp.get_client_by_id(args.data.client_id)
     client.server_capabilities.semanticTokensProvider = nil
 end, });

you can probably translate this code to into something vim.lsp.servers.nil.on_attach accepts.

I think get_client_by_id might be deprecated so if you get a warning follow it i guess

[emsknock]

Alright! Thank you for your time with this 🙏🏼

[emsknock]

Coming back to this, just to document how exactly to get it working in case someone else stumbles on this, it's looking like the following works:

vim.lsp.servers.nil.on_attach = lib.generators.mkLuaInline ''
  function(client, _)
    client.server_capabilities.semanticTokensProvider = nil
  end
'';