diff --git a/lua/rustaceanvim/cargo.lua b/lua/rustaceanvim/cargo.lua
index 487e128d..6207378c 100644
--- a/lua/rustaceanvim/cargo.lua
+++ b/lua/rustaceanvim/cargo.lua
@@ -29,92 +29,98 @@ end
 ---client root is found, returns the result of evaluating `config.root_dir`.
 ---@param config rustaceanvim.lsp.ClientConfig
 ---@param file_name string
----@return string | nil root_dir
-function cargo.get_config_root_dir(config, file_name)
+---@param callback fun(root_dir: string?)
+function cargo.get_config_root_dir(config, file_name, callback)
   local reuse_active = get_mb_active_client_root(file_name)
   if reuse_active then
-    return reuse_active
+    return callback(reuse_active)
   end
 
   local config_root_dir = config.root_dir
   if type(config_root_dir) == 'function' then
-    return config_root_dir(file_name, cargo.get_root_dir)
+    config_root_dir(file_name, callback, function(file_name_)
+      cargo.get_root_dir(file_name_, callback)
+    end)
   else
-    return config_root_dir
+    callback(config_root_dir)
   end
 end
 
 ---@param path string The directory to search upward from
----@return string? cargo_crate_dir
----@return table? cargo_metadata
-local function get_cargo_metadata(path)
+---@param callback fun(cargo_crate_dir: string?, cargo_metadata: table?)
+local function get_cargo_metadata(path, callback)
   ---@diagnostic disable-next-line: missing-fields
   local cargo_crate_dir = vim.fs.dirname(vim.fs.find({ 'Cargo.toml' }, {
     upward = true,
     path = path,
   })[1])
   if vim.fn.executable('cargo') ~= 1 then
-    return cargo_crate_dir
+    return callback(cargo_crate_dir)
   end
   local cmd = { 'cargo', 'metadata', '--no-deps', '--format-version', '1' }
   if cargo_crate_dir ~= nil then
     cmd[#cmd + 1] = '--manifest-path'
     cmd[#cmd + 1] = vim.fs.joinpath(cargo_crate_dir, 'Cargo.toml')
   end
-  local sc = vim
-    .system(cmd, {
-      cwd = vim.uv.fs_stat(path) and path or cargo_crate_dir or vim.fn.getcwd(),
-    })
-    :wait()
-  if sc.code ~= 0 then
-    return cargo_crate_dir
-  end
-  local ok, cargo_metadata_json = pcall(vim.fn.json_decode, sc.stdout)
-  if ok and cargo_metadata_json then
-    return cargo_crate_dir, cargo_metadata_json
-  end
-  return cargo_crate_dir
+  vim.uv.fs_stat(path, function(_, stat)
+    vim.system(cmd, {
+      cwd = stat and path or cargo_crate_dir or vim.fn.getcwd(),
+    }, function(sc)
+      if sc.code ~= 0 then
+        return callback(cargo_crate_dir)
+      end
+      local ok, cargo_metadata_json = pcall(vim.fn.json_decode, sc.stdout)
+      if ok and cargo_metadata_json then
+        return callback(cargo_crate_dir, cargo_metadata_json)
+      end
+      return callback(cargo_crate_dir)
+    end)
+  end)
 end
 
 ---@param buf_name? string
----@return string edition
-function cargo.get_rustc_edition(buf_name)
+---@param callback fun(edition: string)
+function cargo.get_rustc_edition(buf_name, callback)
   local config = require('rustaceanvim.config.internal')
   ---@diagnostic disable-next-line: undefined-field
   if config.tools.rustc.edition then
     vim.deprecate('vim.g.rustaceanvim.config.tools.edition', 'default_edition', '6.0.0', 'rustaceanvim')
     ---@diagnostic disable-next-line: undefined-field
-    return config.tools.rustc.edition
+    callback(config.tools.rustc.edition)
   end
   buf_name = buf_name or vim.api.nvim_buf_get_name(0)
   local path = vim.fs.dirname(buf_name)
-  local _, cargo_metadata = get_cargo_metadata(path)
-  local default_edition = config.tools.rustc.default_edition
-  if not cargo_metadata then
-    return default_edition
-  end
-  local package = vim.iter(cargo_metadata.packages or {}):find(function(pkg)
-    return type(pkg.edition) == 'string'
+  get_cargo_metadata(path, function(_, cargo_metadata)
+    local default_edition = config.tools.rustc.default_edition
+    if not cargo_metadata then
+      return callback(default_edition)
+    end
+    local package = vim.iter(cargo_metadata.packages or {}):find(function(pkg)
+      return type(pkg.edition) == 'string'
+    end)
+    callback(package and package.edition or default_edition)
   end)
-  return package and package.edition or default_edition
 end
 
 ---The default implementation used for `vim.g.rustaceanvim.server.root_dir`
 ---@param file_name string
----@return string | nil root_dir
-function cargo.get_root_dir(file_name)
+---@param callback fun(root_dir: string | nil)
+function cargo.get_root_dir(file_name, callback)
   local path = file_name:find('%.rs$') and vim.fs.dirname(file_name) or file_name
   if not path then
     return nil
   end
-  local cargo_crate_dir, cargo_metadata = get_cargo_metadata(path)
-  return cargo_metadata and cargo_metadata.workspace_root
-    or cargo_crate_dir
-    ---@diagnostic disable-next-line: missing-fields
-    or vim.fs.dirname(vim.fs.find({ 'rust-project.json' }, {
-      upward = true,
-      path = path,
-    })[1])
+  get_cargo_metadata(path, function(cargo_crate_dir, cargo_metadata)
+    callback(
+      cargo_metadata and cargo_metadata.workspace_root
+        or cargo_crate_dir
+        ---@diagnostic disable-next-line: missing-fields
+        or vim.fs.dirname(vim.fs.find({ 'rust-project.json' }, {
+          upward = true,
+          path = path,
+        })[1])
+    )
+  end)
 end
 
 return cargo
diff --git a/lua/rustaceanvim/commands/rustc_unpretty.lua b/lua/rustaceanvim/commands/rustc_unpretty.lua
index 73b51c9e..90da2ea1 100644
--- a/lua/rustaceanvim/commands/rustc_unpretty.lua
+++ b/lua/rustaceanvim/commands/rustc_unpretty.lua
@@ -135,18 +135,20 @@ function M.rustc_unpretty(level)
   end
   text = table.concat(b, '\n')
 
-  vim.system({
-    rustc,
-    '--crate-type',
-    'lib',
-    '--edition',
-    cargo.get_rustc_edition(),
-    '-Z',
-    'unstable-options',
-    '-Z',
-    'unpretty=' .. level,
-    '-',
-  }, { stdin = text }, vim.schedule_wrap(handler))
+  cargo.get_rustc_edition(nil, function(edition)
+    vim.system({
+      rustc,
+      '--crate-type',
+      'lib',
+      '--edition',
+      edition,
+      '-Z',
+      'unstable-options',
+      '-Z',
+      'unpretty=' .. level,
+      '-',
+    }, { stdin = text }, vim.schedule_wrap(handler))
+  end)
 end
 
 return M
diff --git a/lua/rustaceanvim/config/internal.lua b/lua/rustaceanvim/config/internal.lua
index fdb96cdf..af6e4096 100644
--- a/lua/rustaceanvim/config/internal.lua
+++ b/lua/rustaceanvim/config/internal.lua
@@ -286,7 +286,7 @@ local RustaceanDefaultConfig = {
       return { 'rust-analyzer', '--log-file', RustaceanConfig.server.logfile }
     end,
 
-    ---@type string | fun(filename: string, default: fun(filename: string):string|nil):string|nil
+    ---@type string | fun(filename: string, callback: fun(root_dir: string|nil), default: fun(filename: string):string|nil)
     root_dir = cargo.get_root_dir,
 
     ra_multiplex = {
diff --git a/lua/rustaceanvim/lsp/init.lua b/lua/rustaceanvim/lsp/init.lua
index 7b6e8ace..75dea951 100644
--- a/lua/rustaceanvim/lsp/init.lua
+++ b/lua/rustaceanvim/lsp/init.lua
@@ -158,156 +158,162 @@ end
 
 --- Start or attach the LSP client
 ---@param bufnr? number The buffer number (optional), defaults to the current buffer
----@return integer|nil client_id The LSP client ID
-M.start = function(bufnr)
+---@param callback? fun(client_id: integer?)
+M.start = function(bufnr, callback)
   bufnr = bufnr or vim.api.nvim_get_current_buf()
+  callback = callback or function() end
   local bufname = vim.api.nvim_buf_get_name(bufnr)
   local client_config = config.server
   ---@type rustaceanvim.lsp.StartConfig
   local lsp_start_config = vim.tbl_deep_extend('force', {}, client_config)
-  local root_dir = cargo.get_config_root_dir(client_config, bufname)
-  if not root_dir then
-    vim.notify(
-      [[
+  cargo.get_config_root_dir(
+    client_config,
+    bufname,
+    vim.schedule_wrap(function(root_dir)
+      if not root_dir then
+        vim.notify(
+          [[
 rustaceanvim:
 No project root found.
 Starting rust-analyzer client in detached/standalone mode (with reduced functionality).
 ]],
-      vim.log.levels.INFO
-    )
-    root_dir = vim.fs.dirname(bufname)
-    lsp_start_config.init_options = { detachedFiles = { bufname } }
-  end
-  root_dir = os.normalize_path_on_windows(root_dir)
-  lsp_start_config.root_dir = root_dir
-
-  lsp_start_config.settings = get_start_settings(bufname, root_dir, client_config)
-  configure_file_watcher(lsp_start_config)
-
-  -- Check if a client is already running and add the workspace folder if necessary.
-  for _, client in pairs(rust_analyzer.get_active_rustaceanvim_clients()) do
-    if root_dir and not is_in_workspace(client, root_dir) then
-      local workspace_folder = { uri = vim.uri_from_fname(root_dir), name = root_dir }
-      local params = {
-        event = {
-          added = { workspace_folder },
-          removed = {},
-        },
-      }
-      compat.client_notify(client, 'workspace/didChangeWorkspaceFolders', params)
-      if not client.workspace_folders then
-        client.workspace_folders = {}
+          vim.log.levels.INFO
+        )
+        root_dir = vim.fs.dirname(bufname)
+        lsp_start_config.init_options = { detachedFiles = { bufname } }
+      end
+      root_dir = os.normalize_path_on_windows(root_dir)
+      lsp_start_config.root_dir = root_dir
+
+      lsp_start_config.settings = get_start_settings(bufname, root_dir, client_config)
+      configure_file_watcher(lsp_start_config)
+
+      -- Check if a client is already running and add the workspace folder if necessary.
+      for _, client in pairs(rust_analyzer.get_active_rustaceanvim_clients()) do
+        if root_dir and not is_in_workspace(client, root_dir) then
+          local workspace_folder = { uri = vim.uri_from_fname(root_dir), name = root_dir }
+          local params = {
+            event = {
+              added = { workspace_folder },
+              removed = {},
+            },
+          }
+          compat.client_notify(client, 'workspace/didChangeWorkspaceFolders', params)
+          if not client.workspace_folders then
+            client.workspace_folders = {}
+          end
+          table.insert(client.workspace_folders, workspace_folder)
+          vim.lsp.buf_attach_client(bufnr, client.id)
+          return callback()
+        end
       end
-      table.insert(client.workspace_folders, workspace_folder)
-      vim.lsp.buf_attach_client(bufnr, client.id)
-      return
-    end
-  end
 
-  local rust_analyzer_cmd = types.evaluate(client_config.cmd)
+      local rust_analyzer_cmd = types.evaluate(client_config.cmd)
 
-  local ra_multiplex = lsp_start_config.ra_multiplex
-  if ra_multiplex.enable then
-    local ok, running_ra_multiplex = pcall(function()
-      local result = vim.system({ 'pgrep', 'ra-multiplex' }):wait().code
-      return result == 0
-    end)
-    if ok and running_ra_multiplex then
-      rust_analyzer_cmd = vim.lsp.rpc.connect(ra_multiplex.host, ra_multiplex.port)
-      local ra_settings = lsp_start_config.settings['rust-analyzer'] or {}
-      ra_settings.lspMux = ra_settings.lspMux
-        or {
-          version = '1',
-          method = 'connect',
-          server = 'rust-analyzer',
-        }
-      lsp_start_config.settings['rust-analyzer'] = ra_settings
-    end
-  end
+      local ra_multiplex = lsp_start_config.ra_multiplex
+      if ra_multiplex.enable then
+        local ok, running_ra_multiplex = pcall(function()
+          local result = vim.system({ 'pgrep', 'ra-multiplex' }):wait().code
+          return result == 0
+        end)
+        if ok and running_ra_multiplex then
+          rust_analyzer_cmd = vim.lsp.rpc.connect(ra_multiplex.host, ra_multiplex.port)
+          local ra_settings = lsp_start_config.settings['rust-analyzer'] or {}
+          ra_settings.lspMux = ra_settings.lspMux
+            or {
+              version = '1',
+              method = 'connect',
+              server = 'rust-analyzer',
+            }
+          lsp_start_config.settings['rust-analyzer'] = ra_settings
+        end
+      end
 
-  -- special case: rust-analyzer has a `rust-analyzer.server.path` config option
-  -- that allows you to override the path via .vscode/settings.json
-  local server_path = vim.tbl_get(lsp_start_config.settings, 'rust-analyzer', 'server', 'path')
-  if type(server_path) == 'string' then
-    if type(rust_analyzer_cmd) == 'table' then
-      rust_analyzer_cmd[1] = server_path
-    else
-      rust_analyzer_cmd = { server_path }
-    end
-    --
-  end
-  if type(rust_analyzer_cmd) == 'table' then
-    if #rust_analyzer_cmd == 0 then
-      vim.schedule(function()
-        vim.notify('rust-analyzer command is not set!', vim.log.levels.ERROR)
-      end)
-      return
-    end
-    if vim.fn.executable(rust_analyzer_cmd[1]) ~= 1 then
-      vim.schedule(function()
-        vim.notify(('%s is not executable'):format(rust_analyzer_cmd[1]), vim.log.levels.ERROR)
-      end)
-      return
-    end
-  end
-  ---@cast rust_analyzer_cmd string[]
-  lsp_start_config.cmd = rust_analyzer_cmd
-  lsp_start_config.name = 'rust-analyzer'
-  lsp_start_config.filetypes = { 'rust' }
+      -- special case: rust-analyzer has a `rust-analyzer.server.path` config option
+      -- that allows you to override the path via .vscode/settings.json
+      local server_path = vim.tbl_get(lsp_start_config.settings, 'rust-analyzer', 'server', 'path')
+      if type(server_path) == 'string' then
+        if type(rust_analyzer_cmd) == 'table' then
+          rust_analyzer_cmd[1] = server_path
+        else
+          rust_analyzer_cmd = { server_path }
+        end
+        --
+      end
+      if type(rust_analyzer_cmd) == 'table' then
+        if #rust_analyzer_cmd == 0 then
+          vim.schedule(function()
+            vim.notify('rust-analyzer command is not set!', vim.log.levels.ERROR)
+          end)
+          return callback()
+        end
+        if vim.fn.executable(rust_analyzer_cmd[1]) ~= 1 then
+          vim.schedule(function()
+            vim.notify(('%s is not executable'):format(rust_analyzer_cmd[1]), vim.log.levels.ERROR)
+          end)
+          return callback()
+        end
+      end
+      ---@cast rust_analyzer_cmd string[]
+      lsp_start_config.cmd = rust_analyzer_cmd
+      lsp_start_config.name = 'rust-analyzer'
+      lsp_start_config.filetypes = { 'rust' }
 
-  local custom_handlers = {}
-  custom_handlers['experimental/serverStatus'] = server_status.handler
+      local custom_handlers = {}
+      custom_handlers['experimental/serverStatus'] = server_status.handler
 
-  if config.tools.hover_actions.replace_builtin_hover then
-    custom_handlers['textDocument/hover'] = require('rustaceanvim.hover_actions').handler
-  end
+      if config.tools.hover_actions.replace_builtin_hover then
+        custom_handlers['textDocument/hover'] = require('rustaceanvim.hover_actions').handler
+      end
 
-  lsp_start_config.handlers = vim.tbl_deep_extend('force', custom_handlers, lsp_start_config.handlers or {})
+      lsp_start_config.handlers = vim.tbl_deep_extend('force', custom_handlers, lsp_start_config.handlers or {})
 
-  local commands = require('rustaceanvim.commands')
-  local old_on_init = lsp_start_config.on_init
-  lsp_start_config.on_init = function(...)
-    override_apply_text_edits()
-    commands.create_rust_lsp_command()
-    if type(old_on_init) == 'function' then
-      old_on_init(...)
-    end
-  end
+      local commands = require('rustaceanvim.commands')
+      local old_on_init = lsp_start_config.on_init
+      lsp_start_config.on_init = function(...)
+        override_apply_text_edits()
+        commands.create_rust_lsp_command()
+        if type(old_on_init) == 'function' then
+          old_on_init(...)
+        end
+      end
 
-  local old_on_attach = lsp_start_config.on_attach
-  lsp_start_config.on_attach = function(...)
-    if type(old_on_attach) == 'function' then
-      old_on_attach(...)
-    end
-    if config.dap.autoload_configurations then
-      -- When switching projects, there might be new debuggables (#466)
-      require('rustaceanvim.commands.debuggables').add_dap_debuggables()
-    end
-  end
+      local old_on_attach = lsp_start_config.on_attach
+      lsp_start_config.on_attach = function(...)
+        if type(old_on_attach) == 'function' then
+          old_on_attach(...)
+        end
+        if config.dap.autoload_configurations then
+          -- When switching projects, there might be new debuggables (#466)
+          require('rustaceanvim.commands.debuggables').add_dap_debuggables()
+        end
+      end
 
-  local old_on_exit = lsp_start_config.on_exit
-  lsp_start_config.on_exit = function(...)
-    override_apply_text_edits()
-    -- on_exit runs in_fast_event
-    vim.schedule(function()
-      commands.delete_rust_lsp_command()
-    end)
-    if type(old_on_exit) == 'function' then
-      old_on_exit(...)
-    end
-  end
+      local old_on_exit = lsp_start_config.on_exit
+      lsp_start_config.on_exit = function(...)
+        override_apply_text_edits()
+        -- on_exit runs in_fast_event
+        vim.schedule(function()
+          commands.delete_rust_lsp_command()
+        end)
+        if type(old_on_exit) == 'function' then
+          old_on_exit(...)
+        end
+      end
 
-  -- rust-analyzer treats settings in initializationOptions specially -- in particular, workspace_discoverConfig
-  -- so copy them to init_options (the vim name)
-  -- so they end up in initializationOptions (the LSP name)
-  -- ... and initialization_options (the rust name) in rust-analyzer's main.rs
-  lsp_start_config.init_options = vim.tbl_deep_extend(
-    'force',
-    lsp_start_config.init_options or {},
-    vim.tbl_get(lsp_start_config.settings, 'rust-analyzer')
+      -- rust-analyzer treats settings in initializationOptions specially -- in particular, workspace_discoverConfig
+      -- so copy them to init_options (the vim name)
+      -- so they end up in initializationOptions (the LSP name)
+      -- ... and initialization_options (the rust name) in rust-analyzer's main.rs
+      lsp_start_config.init_options = vim.tbl_deep_extend(
+        'force',
+        lsp_start_config.init_options or {},
+        vim.tbl_get(lsp_start_config.settings, 'rust-analyzer')
+      )
+
+      callback(vim.lsp.start(lsp_start_config))
+    end)
   )
-
-  return vim.lsp.start(lsp_start_config)
 end
 
 ---Stop the LSP client.