Add support for nix command

README.md

@@ -107,7 +107,7 @@ If this is not what you want, you can give a try to the [curated configuration](
 
 ## How it works
 
-`lazy-lsp` registers all available configurations from lspconfig to start LSP servers by wrapping the commands in a [nix-shell](https://nixos.org/manual/nix/unstable/command-ref/nix-shell.html) environment. The nix-shell prepares the environment by pulling all specified dependencies regardless of what is installed on the host system and avoids packages clashes. The first time a server is run there is a delay until dependencies are downloaded, but on subsequent runs the time to prepare the shell environment is negligible.
+`lazy-lsp` registers all available configurations from lspconfig to start LSP servers by wrapping the commands in a [`nix shell`](https://nix.dev/manual/nix/latest/command-ref/new-cli/nix3-env-shell) or an older [nix-shell](https://nixos.org/manual/nix/unstable/command-ref/nix-shell.html) environment. The nix shell prepares the environment by pulling all specified dependencies regardless of what is installed on the host system and avoids packages clashes. The first time a server is run there is a delay until dependencies are downloaded, but on subsequent runs the time to prepare the shell environment is negligible.
 
 ## Versions
 

lua/lazy-lsp/helpers.lua

@@ -16,11 +16,55 @@ local function escape_shell_args(args)
   return table.concat(escaped, " ")
 end
 
+local cache_nix_command_available = nil
+-- Check whether both `nix` command and `nixpkgs` flake are available
+---@return boolean?
+local function nix_command_available()
+  if cache_nix_command_available ~= nil then
+    return cache_nix_command_available
+  end
+  cache_nix_command_available = false
+
+  local registry = vim.fn.system({ "nix", "--flake-registry", "", "registry", "list" })
+  if vim.v.shell_error == 0 then
+    for flake in vim.gsplit(registry, "\n") do
+      local flake_url = string.match(flake, "^%S+ flake:nixpkgs (.*)")
+      if flake_url then
+        -- And we won't accidentally fetch `nixpkgs-unstable` as it used to be.
+        -- Only since NixOS 24.05, system has its nixpkgs flake in the registry by default
+        if string.match(flake_url, "^path:") then
+          cache_nix_command_available = true
+        end
+        break
+      end
+    end
+  end
+  return cache_nix_command_available
+end
+
+---@param nix_pkgs string[]
+---@param cmd string[]
+---@return string[]
 local function in_shell(nix_pkgs, cmd)
-  local nix_cmd = { "nix-shell", "-p" }
-  vim.list_extend(nix_cmd, nix_pkgs)
-  table.insert(nix_cmd, "--run")
-  table.insert(nix_cmd, escape_shell_args(cmd))
+  if #nix_pkgs == 0 then
+    error("No nix pkg provided")
+    return {}
+  end
+
+  local nix_cmd = {}
+  if nix_command_available() then
+    nix_cmd = { "nix", "--flake-registry", "", "shell" }
+    for _, nix_pkg in ipairs(nix_pkgs) do
+      table.insert(nix_cmd, "nixpkgs#" .. nix_pkg)
+    end
+    table.insert(nix_cmd, "--command")
+    vim.list_extend(nix_cmd, cmd)
+  else
+    nix_cmd = { "nix-shell", "-p" }
+    vim.list_extend(nix_cmd, nix_pkgs)
+    table.insert(nix_cmd, "--run")
+    table.insert(nix_cmd, escape_shell_args(cmd))
+  end
   return nix_cmd
 end
 
@@ -48,8 +92,8 @@ local function process_config(
 
     config.on_new_config = function(new_config, root_path)
       pcall(original_on_new_config, new_config, root_path)
-      -- Don't wrap with nix-shell if user callback already wrapped it
-      if new_config.cmd[1] ~= "nix-shell" then
+      -- Don't wrap with nix shell if user callback already wrapped it
+      if not vim.list_contains({ "nix", "nix-shell" }, new_config.cmd[1]) then
         if prefer_local == false or vim.fn.executable(new_config.cmd[1]) == 0 then
           local nix_pkgs = type(nix_pkg) == "string" and { nix_pkg } or nix_pkg
           new_config.cmd = in_shell(nix_pkgs, new_config.cmd)

tests/helpers_spec.lua

@@ -5,7 +5,52 @@ local function make_config(config)
   return config
 end
 
+local nix_conf_var = "NIX_CONFIG"
+local nix_conf_dir_var = "NIX_CONF_DIR"
+vim.uv.os_unsetenv(nix_conf_var)
+vim.uv.os_setenv(nix_conf_dir_var, "/dev/null")
+
 describe("lazy-lsp", function()
+  it("in_shell with `nix shell` command", function()
+    local nix_dir = vim.fs.joinpath(vim.uv.cwd(), ".tests", "nix")
+    vim.uv.os_setenv(nix_conf_dir_var, nix_dir)
+    vim.uv.os_setenv(nix_conf_var, "extra-experimental-features = nix-command flakes")
+
+    assert(vim.fn.system({
+      "nix",
+      "registry",
+      "add",
+      "--registry",
+      vim.fs.joinpath(nix_dir, "registry.json"),
+      "nixpkgs",
+      "path:/nix/store/smth",
+    }))
+
+    package.loaded["lazy-lsp.helpers"] = nil
+    helpers = require("lazy-lsp.helpers")
+
+    assert.same(
+      { "nix", "--flake-registry", "", "shell", "nixpkgs#nix_pkg_a", "--command", "cmd_a" },
+      helpers.in_shell({ "nix_pkg_a" }, { "cmd_a" })
+    )
+
+    assert.same(
+      { "nix", "--flake-registry", "", "shell", "nixpkgs#nix_pkg_a", "--command", "cmd_a", "arg_a" },
+      helpers.in_shell({ "nix_pkg_a" }, { "cmd_a", "arg_a" })
+    )
+
+    assert.same(
+      { "nix", "--flake-registry", "", "shell", "nixpkgs#nix_pkg_a", "nixpkgs#nix_pkg_b", "--command", "cmd_a" },
+      helpers.in_shell({ "nix_pkg_a", "nix_pkg_b" }, { "cmd_a" })
+    )
+
+    vim.uv.os_setenv(nix_conf_dir_var, "/dev/null")
+    vim.uv.os_unsetenv(nix_conf_var)
+
+    package.loaded["lazy-lsp.helpers"] = nil
+    helpers = require("lazy-lsp.helpers")
+  end)
+
   it("escape_shell_arg", function()
     assert.same("'hello world'", helpers.escape_shell_arg("hello world"))
     assert.same("'h\"i'", helpers.escape_shell_arg('h"i'))