backport: feat(lsp): pass resolved config to cmd() #34560

Problem:
In LSP configs, the function form of `cmd()` cannot easily get the
resolved root dir (workspace). One of the main use-cases of a dynamic
`cmd()` is to be able to start a new server  whose binary may be located
*in the workspace* ([example](https://github.com/neovim/nvim-lspconfig/pull/3912)).

Compare `reuse_client()`, which also receives the resolved config.

Solution:
Pass the resolved config to `cmd()`.


(cherry picked from commit 32f30c4874)

Co-authored-by: Julian Visser <12615757+justmejulian@users.noreply.github.com>

runtime/doc/lsp.txt

@@ -1309,16 +1309,16 @@ Lua module: vim.lsp.client                                        *lsp-client*
                                • Note: To send an empty dictionary use
                                  |vim.empty_dict()|, else it will be encoded
                                  as an array.
-      • {cmd}                  (`string[]|fun(dispatchers: vim.lsp.rpc.Dispatchers): vim.lsp.rpc.PublicClient`)
+      • {cmd}                  (`string[]|fun(dispatchers: vim.lsp.rpc.Dispatchers, config: vim.lsp.ClientConfig): vim.lsp.rpc.PublicClient`)
                                Command `string[]` that launches the language
                                server (treated as in |jobstart()|, must be
                                absolute or on `$PATH`, shell constructs like
                                "~" are not expanded), or function that creates
                                an RPC client. Function receives a
-                               `dispatchers` table and returns a table with
+                               `dispatchers` table and the resolved `config`,
-                               member functions `request`, `notify`,
+                               and must return a table with member functions
-                               `is_closing` and `terminate`. See
+                               `request`, `notify`, `is_closing` and
-                               |vim.lsp.rpc.request()|,
+                               `terminate`. See |vim.lsp.rpc.request()|,
                                |vim.lsp.rpc.notify()|. For TCP there is a
                                builtin RPC client factory:
                                |vim.lsp.rpc.connect()|

runtime/doc/news.txt

@@ -283,6 +283,8 @@ LSP
   its parameters.
 • |vim.lsp.Config| gained `workspace_required`.
 • `root_markers` in |vim.lsp.Config| can now be ordered by priority.
+• The function form of `cmd` in a vim.lsp.Config or vim.lsp.ClientConfig
+  receives the resolved config as the second arg: `cmd(dispatchers, config)`.
 
 LUA
 

runtime/lua/vim/lsp/client.lua

@@ -45,11 +45,11 @@ local validate = vim.validate
 ---
 --- Command `string[]` that launches the language server (treated as in |jobstart()|, must be
 --- absolute or on `$PATH`, shell constructs like "~" are not expanded), or function that creates an
---- RPC client. Function receives a `dispatchers` table and returns a table with member functions
+--- RPC client. Function receives a `dispatchers` table and the resolved `config`, and must return
---- `request`, `notify`, `is_closing` and `terminate`.
+--- a table with member functions `request`, `notify`, `is_closing` and `terminate`.
 --- See |vim.lsp.rpc.request()|, |vim.lsp.rpc.notify()|.
 --- For TCP there is a builtin RPC client factory: |vim.lsp.rpc.connect()|
---- @field cmd string[]|fun(dispatchers: vim.lsp.rpc.Dispatchers): vim.lsp.rpc.PublicClient
+--- @field cmd string[]|fun(dispatchers: vim.lsp.rpc.Dispatchers, config: vim.lsp.ClientConfig): vim.lsp.rpc.PublicClient
 ---
 --- Directory to launch the `cmd` process. Not related to `root_dir`.
 --- (default: cwd)
@@ -455,7 +455,7 @@ function Client.create(config)
   -- Start the RPC client.
   local config_cmd = config.cmd
   if type(config_cmd) == 'function' then
-    self.rpc = config_cmd(dispatchers)
+    self.rpc = config_cmd(dispatchers, config)
   else
     self.rpc = lsp.rpc.start(config_cmd, dispatchers, {
       cwd = config.cmd_cwd,

test/functional/plugin/lsp/testutil.lua

@@ -54,7 +54,7 @@ M.create_server_definition = function()
     local server = {}
     server.messages = {}
 
-    function server.cmd(dispatchers)
+    function server.cmd(dispatchers, _config)
       local closing = false
       local handlers = opts.handlers or {}
       local srv = {}

test/functional/plugin/lsp_spec.lua

@@ -6490,7 +6490,7 @@ describe('LSP', function()
       )
     end)
 
-    it('supports async function for root_dir', function()
+    it('async root_dir, cmd(…,config) gets resolved config', function()
       exec_lua(create_server_definition)
 
       local tmp1 = t.tmpname(true)
@@ -6504,7 +6504,10 @@ describe('LSP', function()
         })
 
         vim.lsp.config('foo', {
-          cmd = server.cmd,
+          cmd = function(dispatchers, config)
+            _G.test_resolved_root = config.root_dir --[[@type string]]
+            return server.cmd(dispatchers, config)
+          end,
           filetypes = { 'foo' },
           root_dir = function(bufnr, cb)
             assert(tmp1 == vim.api.nvim_buf_get_name(bufnr))
@@ -6527,6 +6530,12 @@ describe('LSP', function()
           end)
         )
       end)
+      eq(
+        'some_dir',
+        exec_lua(function()
+          return _G.test_resolved_root
+        end)
+      )
     end)
 
     it('starts correct LSP and stops incorrect LSP when filetype changes', function()
@@ -6784,10 +6793,8 @@ describe('LSP', function()
       markers_resolve_to({ 'marker_a', { 'marker_b', 'marker_d' } }, tmp_root)
       markers_resolve_to({ 'foo', { 'bar', 'baz' }, 'marker_d' }, dir_b)
     end)
-  end)
 
-  describe('vim.lsp.is_enabled()', function()
+    it('vim.lsp.is_enabled()', function()
-    it('works', function()
       exec_lua(function()
         vim.lsp.config('foo', {
           cmd = { 'foo' },