refactor(lsp): resolve the config-client entanglement

Previously the LSP-Client object contained some fields that are also
in the client config, but for a lot of other fields, the config was used
directly making the two objects vaguely entangled with either not having
a clear role.

Now the config object is treated purely as config (read-only) from the
client, and any fields the client needs from the config are now copied
in as additional fields.

This means:
- the config object is no longet normalised and is left as the user
  provided it.
- the client only reads the config on creation of the client and all
  other implementations now read the clients version of the fields.

In addition, internal support for multiple callbacks has been added to
the client so the client tracking logic (done in lua.lsp) can be done
more robustly instead of wrapping the user callbacks which may error.

11 files changed, 241 insertions, 168 deletions

diff --git a/runtime/doc/lsp.txt b/runtime/doc/lsp.txt
index fc4c164ea0..56d7b98a3c 100644
--- a/runtime/doc/lsp.txt
+++ b/runtime/doc/lsp.txt
@@ -763,6 +763,10 @@ client()                                                      *vim.lsp.client*
         before text is sent to the server.
       • {handlers} (table): The handlers used by the client as described in
         |lsp-handler|.
+      • {commands} (table): Table of command name to function which is called
+        if any LSP action (code action, code lenses, ...) triggers the
+        command. Client commands take precedence over the global command
+        registry.
       • {requests} (table): The current pending requests in flight to the
         server. Entries are key-value pairs with the key being the request ID
         while the value is a table with `type`, `bufnr`, and `method`
@@ -770,12 +774,16 @@ client()                                                      *vim.lsp.client*
         "cancel" for a cancel request. It will be "complete" ephemerally while
         executing |LspRequest| autocmds when replies are received from the
         server.
-      • {config} (table): copy of the table that was passed by the user to
-        |vim.lsp.start_client()|.
+      • {config} (table): Reference of the table that was passed by the user
+        to |vim.lsp.start_client()|.
       • {server_capabilities} (table): Response from the server sent on
         `initialize` describing the server's capabilities.
       • {progress} A ring buffer (|vim.ringbuf()|) containing progress
         messages sent by the server.
+      • {settings} Map with language server specific settings. See {config} in
+        |vim.lsp.start_client()|
+      • {flags} A table with flags for the client. See {config} in
+        |vim.lsp.start_client()|
 
 client_is_stopped({client_id})                   *vim.lsp.client_is_stopped()*
     Checks whether a client is stopped.
diff --git a/runtime/lua/vim/_meta.lua b/runtime/lua/vim/_meta.lua
index 4c50627fe4..731dd5b923 100644
--- a/runtime/lua/vim/_meta.lua
+++ b/runtime/lua/vim/_meta.lua
@@ -1,5 +1,7 @@
 --- @meta
 
+--- @alias elem_or_list<T> T|T[]
+
 ---@type uv
 vim.uv = ...
 
diff --git a/runtime/lua/vim/lsp.lua b/runtime/lua/vim/lsp.lua
index 13f2c92cc2..8608bdfa57 100644
--- a/runtime/lua/vim/lsp.lua
+++ b/runtime/lua/vim/lsp.lua
@@ -143,6 +143,14 @@ local function for_each_buffer_client(bufnr, fn, restrict_client_ids)
   end
 end
 
+local client_errors_base = table.maxn(lsp.rpc.client_errors)
+local client_errors_offset = 0
+
+local function new_error_index()
+  client_errors_offset = client_errors_offset + 1
+  return client_errors_base + client_errors_offset
+end
+
 --- Error codes to be used with `on_error` from |vim.lsp.start_client|.
 --- Can be used to look up the string from a the number or the number
 --- from the string.
@@ -151,9 +159,10 @@ lsp.client_errors = tbl_extend(
   'error',
   lsp.rpc.client_errors,
   vim.tbl_add_reverse_lookup({
-    BEFORE_INIT_CALLBACK_ERROR = table.maxn(lsp.rpc.client_errors) + 1,
-    ON_INIT_CALLBACK_ERROR = table.maxn(lsp.rpc.client_errors) + 2,
-    ON_ATTACH_ERROR = table.maxn(lsp.rpc.client_errors) + 3,
+    BEFORE_INIT_CALLBACK_ERROR = new_error_index(),
+    ON_INIT_CALLBACK_ERROR = new_error_index(),
+    ON_ATTACH_ERROR = new_error_index(),
+    ON_EXIT_CALLBACK_ERROR = new_error_index(),
   })
 )
 
@@ -262,6 +271,10 @@ end
 ---
 ---  - {handlers} (table): The handlers used by the client as described in |lsp-handler|.
 ---
+---  - {commands} (table): Table of command name to function which is called if
+---    any LSP action (code action, code lenses, ...) triggers the command.
+---    Client commands take precedence over the global command registry.
+---
 ---  - {requests} (table): The current pending requests in flight
 ---    to the server. Entries are key-value pairs with the key
 ---    being the request ID while the value is a table with `type`,
@@ -270,7 +283,7 @@ end
 ---    be "complete" ephemerally while executing |LspRequest| autocmds
 ---    when replies are received from the server.
 ---
----  - {config} (table): copy of the table that was passed by the user
+---  - {config} (table): Reference of the table that was passed by the user
 ---    to |vim.lsp.start_client()|.
 ---
 ---  - {server_capabilities} (table): Response from the server sent on
@@ -278,6 +291,11 @@ end
 ---
 ---  - {progress} A ring buffer (|vim.ringbuf()|) containing progress messages
 ---    sent by the server.
+---
+---  - {settings} Map with language server specific settings.
+---    See {config} in |vim.lsp.start_client()|
+---
+---  - {flags} A table with flags for the client. See {config} in |vim.lsp.start_client()|
 function lsp.client()
   error()
 end
@@ -337,7 +355,7 @@ function lsp.start(config, opts)
   opts = opts or {}
   local reuse_client = opts.reuse_client
     or function(client, conf)
-      return client.config.root_dir == conf.root_dir and client.name == conf.name
+      return client.root_dir == conf.root_dir and client.name == conf.name
     end
 
   local bufnr = resolve_bufnr(opts.bufnr)
@@ -537,20 +555,6 @@ local function on_client_exit(code, signal, client_id)
   end)
 end
 
---- @generic F: function
---- @param ... F
---- @return F
-local function join_cbs(...)
-  local funcs = vim.F.pack_len(...)
-  return function(...)
-    for i = 1, funcs.n do
-      if funcs[i] ~= nil then
-        funcs[i](...)
-      end
-    end
-  end
-end
-
 -- FIXME: DOC: Currently all methods on the `vim.lsp.client` object are
 -- documented twice: Here, and on the methods themselves (e.g.
 -- `client.request()`). This is a workaround for the vimdoc generator script
@@ -671,21 +675,22 @@ end
 --- fully initialized. Use `on_init` to do any actions once
 --- the client has been initialized.
 function lsp.start_client(config)
-  config = vim.deepcopy(config, false)
-  config.on_init = join_cbs(config.on_init, on_client_init)
-  config.on_exit = join_cbs(config.on_exit, on_client_exit)
-
-  local client = require('vim.lsp.client').start(config)
+  local client = require('vim.lsp.client').create(config)
 
   if not client then
     return
   end
 
+  --- @diagnostic disable-next-line: invisible
+  table.insert(client._on_init_cbs, on_client_init)
+  --- @diagnostic disable-next-line: invisible
+  table.insert(client._on_exit_cbs, on_client_exit)
+
   -- Store the uninitialized_clients for cleanup in case we exit before initialize finishes.
-  -- TODO(lewis6991): do this on before_init(). Requires API change to before_init() so it
-  -- can access the client_id.
   uninitialized_clients[client.id] = client
 
+  client:initialize()
+
   return client.id
 end
 
@@ -732,7 +737,7 @@ local function text_document_did_save_handler(bufnr)
         textDocument = {
           version = 0,
           uri = uri,
-          languageId = client.config.get_language_id(bufnr, vim.bo[bufnr].filetype),
+          languageId = client.get_language_id(bufnr, vim.bo[bufnr].filetype),
           text = lsp._buf_get_full_text(bufnr),
         },
       })
@@ -1034,7 +1039,7 @@ api.nvim_create_autocmd('VimLeavePre', {
     local send_kill = false
 
     for client_id, client in pairs(active_clients) do
-      local timeout = if_nil(client.config.flags.exit_timeout, false)
+      local timeout = if_nil(client.flags.exit_timeout, false)
       if timeout then
         send_kill = true
         timeouts[client_id] = timeout
diff --git a/runtime/lua/vim/lsp/_changetracking.lua b/runtime/lua/vim/lsp/_changetracking.lua
index 8b624cd5ea..3ecdec1659 100644
--- a/runtime/lua/vim/lsp/_changetracking.lua
+++ b/runtime/lua/vim/lsp/_changetracking.lua
@@ -64,7 +64,7 @@ local state_by_group = setmetatable({}, {
 ---@param client lsp.Client
 ---@return vim.lsp.CTGroup
 local function get_group(client)
-  local allow_inc_sync = vim.F.if_nil(client.config.flags.allow_incremental_sync, true) --- @type boolean
+  local allow_inc_sync = vim.F.if_nil(client.flags.allow_incremental_sync, true) --- @type boolean
   local change_capability = vim.tbl_get(client.server_capabilities, 'textDocumentSync', 'change')
   local sync_kind = change_capability or protocol.TextDocumentSyncKind.None
   if not allow_inc_sync and change_capability == protocol.TextDocumentSyncKind.Incremental then
@@ -134,12 +134,12 @@ function M.init(client, bufnr)
   local group = get_group(client)
   local state = state_by_group[group]
   if state then
-    state.debounce = math.min(state.debounce, client.config.flags.debounce_text_changes or 150)
+    state.debounce = math.min(state.debounce, client.flags.debounce_text_changes or 150)
     state.clients[client.id] = client
   else
     state = {
       buffers = {},
-      debounce = client.config.flags.debounce_text_changes or 150,
+      debounce = client.flags.debounce_text_changes or 150,
       clients = {
         [client.id] = client,
       },
diff --git a/runtime/lua/vim/lsp/_dynamic.lua b/runtime/lua/vim/lsp/_dynamic.lua
index b6c335bb13..9c2af979fa 100644
--- a/runtime/lua/vim/lsp/_dynamic.lua
+++ b/runtime/lua/vim/lsp/_dynamic.lua
@@ -19,7 +19,7 @@ function M:supports_registration(method)
   if not client then
     return false
   end
-  local capability = vim.tbl_get(client.config.capabilities, unpack(vim.split(method, '/')))
+  local capability = vim.tbl_get(client.capabilities, unpack(vim.split(method, '/')))
   return type(capability) == 'table' and capability.dynamicRegistration
 end
 
@@ -91,7 +91,7 @@ function M:match(bufnr, documentSelector)
   if not client then
     return false
   end
-  local language = client.config.get_language_id(bufnr, vim.bo[bufnr].filetype)
+  local language = client.get_language_id(bufnr, vim.bo[bufnr].filetype)
   local uri = vim.uri_from_bufnr(bufnr)
   local fname = vim.uri_to_fname(uri)
   for _, filter in ipairs(documentSelector) do
diff --git a/runtime/lua/vim/lsp/_watchfiles.lua b/runtime/lua/vim/lsp/_watchfiles.lua
index 59b8c38166..6ca60b78cd 100644
--- a/runtime/lua/vim/lsp/_watchfiles.lua
+++ b/runtime/lua/vim/lsp/_watchfiles.lua
@@ -44,12 +44,8 @@ function M.register(reg, ctx)
   local client = assert(vim.lsp.get_client_by_id(client_id), 'Client must be running')
   -- Ill-behaved servers may not honor the client capability and try to register
   -- anyway, so ignore requests when the user has opted out of the feature.
-  local has_capability = vim.tbl_get(
-    client.config.capabilities or {},
-    'workspace',
-    'didChangeWatchedFiles',
-    'dynamicRegistration'
-  )
+  local has_capability =
+    vim.tbl_get(client.capabilities, 'workspace', 'didChangeWatchedFiles', 'dynamicRegistration')
   if not has_capability or not client.workspace_folders then
     return
   end
diff --git a/runtime/lua/vim/lsp/client.lua b/runtime/lua/vim/lsp/client.lua
index a279be55e9..a460d95cc6 100644
--- a/runtime/lua/vim/lsp/client.lua
+++ b/runtime/lua/vim/lsp/client.lua
@@ -6,28 +6,33 @@ local ms = lsp.protocol.Methods
 local changetracking = lsp._changetracking
 local validate = vim.validate
 
+--- @alias vim.lsp.client.on_init_cb fun(client: lsp.Client, initialize_result: lsp.InitializeResult)
+--- @alias vim.lsp.client.on_attach_cb fun(client: lsp.Client, bufnr: integer)
+--- @alias vim.lsp.client.on_exit_cb fun(code: integer, signal: integer, client_id: integer)
+--- @alias vim.lsp.client.before_init_cb fun(params: lsp.InitializeParams, config: lsp.ClientConfig)
+
 --- @class lsp.ClientConfig
---- @field cmd (string[]|fun(dispatchers: table):table)
---- @field cmd_cwd string
---- @field cmd_env (table)
---- @field detached boolean
---- @field workspace_folders (table)
---- @field capabilities lsp.ClientCapabilities
---- @field handlers table<string,function>
---- @field settings table
---- @field commands table
+--- @field cmd string[]|fun(dispatchers: vim.lsp.rpc.Dispatchers): vim.lsp.rpc.PublicClient?
+--- @field cmd_cwd? string
+--- @field cmd_env? table
+--- @field detached? boolean
+--- @field workspace_folders? lsp.WorkspaceFolder[]
+--- @field capabilities? lsp.ClientCapabilities
+--- @field handlers? table<string,function>
+--- @field settings? table
+--- @field commands? table<string,fun(command: lsp.Command, ctx: table)>
 --- @field init_options table
 --- @field name? string
---- @field get_language_id fun(bufnr: integer, filetype: string): string
---- @field offset_encoding string
---- @field on_error fun(code: integer)
---- @field before_init fun(params: lsp.InitializeParams, config: lsp.ClientConfig)
---- @field on_init fun(client: lsp.Client, initialize_result: lsp.InitializeResult)
---- @field on_exit fun(code: integer, signal: integer, client_id: integer)
---- @field on_attach fun(client: lsp.Client, bufnr: integer)
---- @field trace 'off'|'messages'|'verbose'|nil
---- @field flags table
---- @field root_dir string
+--- @field get_language_id? fun(bufnr: integer, filetype: string): string
+--- @field offset_encoding? string
+--- @field on_error? fun(code: integer, err: string)
+--- @field before_init? vim.lsp.client.before_init_cb
+--- @field on_init? elem_or_list<vim.lsp.client.on_init_cb>
+--- @field on_exit? elem_or_list<vim.lsp.client.on_exit_cb>
+--- @field on_attach? elem_or_list<vim.lsp.client.on_attach_cb>
+--- @field trace? 'off'|'messages'|'verbose'
+--- @field flags? table
+--- @field root_dir? string
 
 --- @class lsp.Client.Progress: vim.Ringbuf<{token: integer|string, value: any}>
 --- @field pending table<lsp.ProgressToken,lsp.LSPAny>
@@ -66,21 +71,43 @@ local validate = vim.validate
 ---
 --- Response from the server sent on
 --- initialize` describing the server's capabilities.
---- @field server_capabilities lsp.ServerCapabilities
+--- @field server_capabilities lsp.ServerCapabilities?
 ---
 --- A ring buffer (|vim.ringbuf()|) containing progress messages
 --- sent by the server.
 --- @field progress lsp.Client.Progress
 ---
 --- @field initialized true?
+---
+--- The workspace folders configured in the client when the server starts.
+--- This property is only available if the client supports workspace folders.
+--- It can be `null` if the client supports workspace folders but none are
+--- configured.
 --- @field workspace_folders lsp.WorkspaceFolder[]?
+--- @field root_dir string
+---
 --- @field attached_buffers table<integer,true>
 --- @field private _log_prefix string
+---
 --- Track this so that we can escalate automatically if we've already tried a
 --- graceful shutdown
 --- @field private _graceful_shutdown_failed true?
---- @field private commands table
 ---
+--- The initial trace setting. If omitted trace is disabled ("off").
+--- trace = "off" | "messages" | "verbose";
+--- @field private _trace 'off'|'messages'|'verbose'
+---
+--- Table of command name to function which is called if any LSP action
+--- (code action, code lenses, ...) triggers the command.
+--- Client commands take precedence over the global command registry.
+--- @field commands table<string,fun(command: lsp.Command, ctx: table)>
+---
+--- @field settings table
+--- @field flags table
+--- @field get_language_id fun(bufnr: integer, filetype: string): string
+---
+--- The capabilities provided by the client (editor or tool)
+--- @field capabilities lsp.ClientCapabilities
 --- @field dynamic_capabilities lsp.DynamicCapabilities
 ---
 --- Sends a request to the server.
@@ -122,6 +149,12 @@ local validate = vim.validate
 --- Useful for buffer-local setup.
 --- @field on_attach fun(bufnr: integer)
 ---
+--- @field private _before_init_cb? vim.lsp.client.before_init_cb
+--- @field private _on_attach_cbs vim.lsp.client.on_attach_cb[]
+--- @field private _on_init_cbs vim.lsp.client.on_init_cb[]
+--- @field private _on_exit_cbs vim.lsp.client.on_exit_cb[]
+--- @field private _on_error_cb? fun(code: integer, err: string)
+---
 --- Checks if a client supports a given method.
 --- Always returns true for unknown off-spec methods.
 --- [opts] is a optional `{bufnr?: integer}` table.
@@ -196,9 +229,18 @@ local function optional_validator(fn)
   end
 end
 
+--- By default, get_language_id just returns the exact filetype it is passed.
+--- It is possible to pass in something that will calculate a different filetype,
+--- to be sent by the client.
+--- @param _bufnr integer
+--- @param filetype string
+local function default_get_language_id(_bufnr, filetype)
+  return filetype
+end
+
 --- Validates a client configuration as given to |vim.lsp.start_client()|.
 --- @param config lsp.ClientConfig
-local function process_client_config(config)
+local function validate_config(config)
   validate({
     config = { config, 't' },
   })
@@ -210,15 +252,17 @@ local function process_client_config(config)
     detached = { config.detached, 'b', true },
     name = { config.name, 's', true },
     on_error = { config.on_error, 'f', true },
-    on_exit = { config.on_exit, 'f', true },
-    on_init = { config.on_init, 'f', true },
+    on_exit = { config.on_exit, { 'f', 't' }, true },
+    on_init = { config.on_init, { 'f', 't' }, true },
+    on_attach = { config.on_attach, { 'f', 't' }, true },
     settings = { config.settings, 't', true },
     commands = { config.commands, 't', true },
-    before_init = { config.before_init, 'f', true },
+    before_init = { config.before_init, { 'f', 't' }, true },
     offset_encoding = { config.offset_encoding, 's', true },
     flags = { config.flags, 't', true },
     get_language_id = { config.get_language_id, 'f', true },
   })
+
   assert(
     (
       not config.flags
@@ -227,51 +271,98 @@ local function process_client_config(config)
     ),
     'flags.debounce_text_changes must be a number with the debounce time in milliseconds'
   )
+end
+
+--- @param trace string
+--- @return 'off'|'messages'|'verbose'
+local function get_trace(trace)
+  local valid_traces = {
+    off = 'off',
+    messages = 'messages',
+    verbose = 'verbose',
+  }
+  return trace and valid_traces[trace] or 'off'
+end
 
-  if not config.name and type(config.cmd) == 'table' then
-    config.name = config.cmd[1] and vim.fs.basename(config.cmd[1]) or nil
+--- @param id integer
+--- @param config lsp.ClientConfig
+--- @return string
+local function get_name(id, config)
+  local name = config.name
+  if name then
+    return name
   end
 
-  config.offset_encoding = validate_encoding(config.offset_encoding)
-  config.flags = config.flags or {}
-  config.settings = config.settings or {}
-  config.handlers = config.handlers or {}
+  if type(config.cmd) == 'table' and config.cmd[1] then
+    return assert(vim.fs.basename(config.cmd[1]))
+  end
 
-  -- By default, get_language_id just returns the exact filetype it is passed.
-  --    It is possible to pass in something that will calculate a different filetype,
-  --    to be sent by the client.
-  config.get_language_id = config.get_language_id or function(_, filetype)
-    return filetype
+  return tostring(id)
+end
+
+--- @param workspace_folders lsp.WorkspaceFolder[]?
+--- @param root_dir string?
+--- @return lsp.WorkspaceFolder[]?
+local function get_workspace_folders(workspace_folders, root_dir)
+  if workspace_folders then
+    return workspace_folders
   end
+  if root_dir then
+    return {
+      {
+        uri = vim.uri_from_fname(root_dir),
+        name = string.format('%s', root_dir),
+      },
+    }
+  end
+end
 
-  config.capabilities = config.capabilities or lsp.protocol.make_client_capabilities()
-  config.commands = config.commands or {}
+--- @generic T
+--- @param x elem_or_list<T>?
+--- @return T[]
+local function ensure_list(x)
+  if type(x) == 'table' then
+    return x
+  end
+  return { x }
 end
 
 --- @package
 --- @param config lsp.ClientConfig
 --- @return lsp.Client?
-function Client.start(config)
-  process_client_config(config)
+function Client.create(config)
+  validate_config(config)
 
   client_index = client_index + 1
   local id = client_index
-
-  local name = config.name or tostring(id)
+  local name = get_name(id, config)
 
   --- @class lsp.Client
   local self = {
     id = id,
     config = config,
-    handlers = config.handlers,
-    offset_encoding = config.offset_encoding,
+    handlers = config.handlers or {},
+    offset_encoding = validate_encoding(config.offset_encoding),
     name = name,
     _log_prefix = string.format('LSP[%s]', name),
     requests = {},
     attached_buffers = {},
     server_capabilities = {},
-    dynamic_capabilities = vim.lsp._dynamic.new(id),
-    commands = config.commands, -- Remove in Nvim 0.11
+    dynamic_capabilities = lsp._dynamic.new(id),
+    commands = config.commands or {},
+    settings = config.settings or {},
+    flags = config.flags or {},
+    get_language_id = config.get_language_id or default_get_language_id,
+    capabilities = config.capabilities or lsp.protocol.make_client_capabilities(),
+    workspace_folders = get_workspace_folders(config.workspace_folders, config.root_dir),
+    root_dir = config.root_dir,
+    _before_init_cb = config.before_init,
+    _on_init_cbs = ensure_list(config.on_init),
+    _on_exit_cbs = ensure_list(config.on_exit),
+    _on_attach_cbs = ensure_list(config.on_attach),
+    _on_error_cb = config.on_error,
+    _root_dir = config.root_dir,
+    _trace = get_trace(config.trace),
 
     --- Contains $/progress report messages.
     --- They have the format {token: integer|string, value: any}
@@ -327,41 +418,31 @@ function Client.start(config)
 
   setmetatable(self, Client)
 
-  self:initialize()
-
   return self
 end
 
---- @private
-function Client:initialize()
-  local valid_traces = {
-    off = 'off',
-    messages = 'messages',
-    verbose = 'verbose',
-  }
+--- @param cbs function[]
+--- @param error_id integer
+--- @param ... any
+function Client:_run_callbacks(cbs, error_id, ...)
+  for _, cb in pairs(cbs) do
+    --- @type boolean, string?
+    local status, err = pcall(cb, ...)
+    if not status then
+      self:write_error(error_id, err)
+    end
+  end
+end
 
+--- @package
+function Client:initialize()
   local config = self.config
 
-  local workspace_folders --- @type lsp.WorkspaceFolder[]?
   local root_uri --- @type string?
   local root_path --- @type string?
-  if config.workspace_folders or config.root_dir then
-    if config.root_dir and not config.workspace_folders then
-      workspace_folders = {
-        {
-          uri = vim.uri_from_fname(config.root_dir),
-          name = string.format('%s', config.root_dir),
-        },
-      }
-    else
-      workspace_folders = config.workspace_folders
-    end
-    root_uri = workspace_folders[1].uri
+  if self.workspace_folders then
+    root_uri = self.workspace_folders[1].uri
     root_path = vim.uri_to_fname(root_uri)
-  else
-    workspace_folders = nil
-    root_uri = nil
-    root_path = nil
   end
 
   local initialize_params = {
@@ -383,26 +464,19 @@ function Client:initialize()
     -- The rootUri of the workspace. Is null if no folder is open. If both
     -- `rootPath` and `rootUri` are set `rootUri` wins.
     rootUri = root_uri or vim.NIL,
-    -- The workspace folders configured in the client when the server starts.
-    -- This property is only available if the client supports workspace folders.
-    -- It can be `null` if the client supports workspace folders but none are
-    -- configured.
-    workspaceFolders = workspace_folders or vim.NIL,
+    workspaceFolders = self.workspace_folders or vim.NIL,
     -- User provided initialization options.
     initializationOptions = config.init_options,
-    -- The capabilities provided by the client (editor or tool)
-    capabilities = config.capabilities,
-    -- The initial trace setting. If omitted trace is disabled ("off").
-    -- trace = "off" | "messages" | "verbose";
-    trace = valid_traces[config.trace] or 'off',
+    capabilities = self.capabilities,
+    trace = self._trace,
   }
-  if config.before_init then
-    --- @type boolean, string?
-    local status, err = pcall(config.before_init, initialize_params, config)
-    if not status then
-      self:write_error(lsp.client_errors.BEFORE_INIT_CALLBACK_ERROR, err)
-    end
-  end
+
+  self:_run_callbacks(
+    { self._before_init_cb },
+    lsp.client_errors.BEFORE_INIT_CALLBACK_ERROR,
+    initialize_params,
+    config
+  )
 
   log.trace(self._log_prefix, 'initialize_params', initialize_params)
 
@@ -413,7 +487,6 @@ function Client:initialize()
     assert(result, 'server sent empty result')
     rpc.notify('initialized', vim.empty_dict())
     self.initialized = true
-    self.workspace_folders = workspace_folders
 
     -- These are the cleaned up capabilities we use for dynamically deciding
     -- when to send certain events to clients.
@@ -425,17 +498,11 @@ function Client:initialize()
       self.offset_encoding = self.server_capabilities.positionEncoding
     end
 
-    if next(config.settings) then
-      self:_notify(ms.workspace_didChangeConfiguration, { settings = config.settings })
+    if next(self.settings) then
+      self:_notify(ms.workspace_didChangeConfiguration, { settings = self.settings })
     end
 
-    if config.on_init then
-      --- @type boolean, string?
-      local status, err = pcall(config.on_init, self, result)
-      if not status then
-        self:write_error(lsp.client_errors.ON_INIT_CALLBACK_ERROR, err)
-      end
-    end
+    self:_run_callbacks(self._on_init_cbs, lsp.client_errors.ON_INIT_CALLBACK_ERROR, self, result)
 
     log.info(
       self._log_prefix,
@@ -672,7 +739,7 @@ function Client:_is_stopped()
   return self.rpc.is_closing()
 end
 
---- @private
+--- @package
 --- Execute a lsp command, either via client command function (if available)
 --- or via workspace/executeCommand (if supported by the server)
 ---
@@ -684,7 +751,7 @@ function Client:_exec_cmd(command, context, handler)
   context.bufnr = context.bufnr or api.nvim_get_current_buf()
   context.client_id = self.id
   local cmdname = command.command
-  local fn = self.config.commands[cmdname] or lsp.commands[cmdname]
+  local fn = self.commands[cmdname] or lsp.commands[cmdname]
   if fn then
     fn(command, context)
     return
@@ -730,7 +797,7 @@ function Client:_text_document_did_open_handler(bufnr)
     textDocument = {
       version = 0,
       uri = vim.uri_from_bufnr(bufnr),
-      languageId = self.config.get_language_id(bufnr, filetype),
+      languageId = self.get_language_id(bufnr, filetype),
       text = lsp._buf_get_full_text(bufnr),
     },
   }
@@ -742,13 +809,13 @@ function Client:_text_document_did_open_handler(bufnr)
     -- Protect against a race where the buffer disappears
     -- between `did_open_handler` and the scheduled function firing.
     if api.nvim_buf_is_valid(bufnr) then
-      local namespace = vim.lsp.diagnostic.get_namespace(self.id)
+      local namespace = lsp.diagnostic.get_namespace(self.id)
       vim.diagnostic.show(namespace, bufnr)
     end
   end)
 end
 
---- @private
+--- @package
 --- Runs the on_attach function from the client's config if it was defined.
 --- @param bufnr integer Buffer number
 function Client:_on_attach(bufnr)
@@ -762,13 +829,7 @@ function Client:_on_attach(bufnr)
     data = { client_id = self.id },
   })
 
-  if self.config.on_attach then
-    --- @type boolean, string?
-    local status, err = pcall(self.config.on_attach, self, bufnr)
-    if not status then
-      self:write_error(lsp.client_errors.ON_ATTACH_ERROR, err)
-    end
-  end
+  self:_run_callbacks(self._on_attach_cbs, lsp.client_errors.ON_ATTACH_ERROR, self, bufnr)
 
   -- schedule the initialization of semantic tokens to give the above
   -- on_attach and LspAttach callbacks the ability to schedule wrap the
@@ -795,7 +856,6 @@ end
 --- @param method string
 --- @param opts? {bufnr: integer?}
 function Client:_supports_method(method, opts)
-  opts = opts or {}
   local required_capability = lsp._request_name_to_capability[method]
   -- if we don't know about the method, assume that the client supports it.
   if not required_capability then
@@ -803,12 +863,11 @@ function Client:_supports_method(method, opts)
   end
   if vim.tbl_get(self.server_capabilities, unpack(required_capability)) then
     return true
-  else
-    if self.dynamic_capabilities:supports_registration(method) then
-      return self.dynamic_capabilities:supports(method, opts)
-    end
-    return false
   end
+  if self.dynamic_capabilities:supports_registration(method) then
+    return self.dynamic_capabilities:supports(method, opts)
+  end
+  return false
 end
 
 --- @private
@@ -853,9 +912,9 @@ end
 --- `vim.lsp.rpc.client_errors[code]` to get a human-friendly name.
 function Client:_on_error(code, err)
   self:write_error(code, err)
-  if self.config.on_error then
+  if self._on_error_cb then
     --- @type boolean, string
-    local status, usererr = pcall(self.config.on_error, code, err)
+    local status, usererr = pcall(self._on_error_cb, code, err)
     if not status then
       log.error(self._log_prefix, 'user on_error failed', { err = usererr })
       err_message(self._log_prefix, ' user on_error failed: ', tostring(usererr))
@@ -869,9 +928,13 @@ end
 --- @param code integer) exit code of the process
 --- @param signal integer the signal used to terminate (if any)
 function Client:_on_exit(code, signal)
-  if self.config.on_exit then
-    pcall(self.config.on_exit, code, signal, self.id)
-  end
+  self:_run_callbacks(
+    self._on_exit_cbs,
+    lsp.client_errors.ON_EXIT_CALLBACK_ERROR,
+    code,
+    signal,
+    self.id
+  )
 end
 
 return Client
diff --git a/runtime/lua/vim/lsp/codelens.lua b/runtime/lua/vim/lsp/codelens.lua
index ab49e03c52..966c7f4d03 100644
--- a/runtime/lua/vim/lsp/codelens.lua
+++ b/runtime/lua/vim/lsp/codelens.lua
@@ -48,7 +48,6 @@ local function execute_lens(lens, bufnr, client_id)
 
   local client = vim.lsp.get_client_by_id(client_id)
   assert(client, 'Client is required to execute lens, client_id=' .. client_id)
-  ---@diagnostic disable-next-line: invisible
   client:_exec_cmd(lens.command, { bufnr = bufnr }, function(...)
     vim.lsp.handlers[ms.workspace_executeCommand](...)
     M.refresh()
diff --git a/runtime/lua/vim/lsp/handlers.lua b/runtime/lua/vim/lsp/handlers.lua
index 4bb14e5a09..a9da812231 100644
--- a/runtime/lua/vim/lsp/handlers.lua
+++ b/runtime/lua/vim/lsp/handlers.lua
@@ -197,10 +197,10 @@ M[ms.workspace_configuration] = function(_, result, ctx)
   local response = {}
   for _, item in ipairs(result.items) do
     if item.section then
-      local value = lookup_section(client.config.settings, item.section)
+      local value = lookup_section(client.settings, item.section)
       -- For empty sections with no explicit '' key, return settings as is
       if value == nil and item.section == '' then
-        value = client.config.settings
+        value = client.settings
       end
       if value == nil then
         value = vim.NIL
diff --git a/runtime/lua/vim/lsp/health.lua b/runtime/lua/vim/lsp/health.lua
index d770735895..15e4555b55 100644
--- a/runtime/lua/vim/lsp/health.lua
+++ b/runtime/lua/vim/lsp/health.lua
@@ -38,7 +38,7 @@ function M.check()
           '%s (id=%s, root_dir=%s, attached_to=[%s])',
           client.name,
           client.id,
-          vim.fn.fnamemodify(client.config.root_dir, ':~'),
+          vim.fn.fnamemodify(client.root_dir, ':~'),
           attached_to
         )
       )
diff --git a/test/functional/plugin/lsp_spec.lua b/test/functional/plugin/lsp_spec.lua
index fb153b83ca..341ad014a6 100644
--- a/test/functional/plugin/lsp_spec.lua
+++ b/test/functional/plugin/lsp_spec.lua
@@ -523,7 +523,7 @@ describe('LSP', function()
           if ctx.method == 'start' then
             exec_lua([=[
               local client = vim.lsp.get_client_by_id(TEST_RPC_CLIENT_ID)
-              client.config.settings = {
+              client.settings = {
                 testSetting1 = true;
                 testSetting2 = false;
                 test = {Setting3 = 'nested' };