fix(lsp): check if client is stopping before reuse #33796

Problem:
Stopping a language server and then calling vim.lsp.start() with the same name/root will return the old language server that's in the middle of shutting down. vim.lsp.start() won't return a new server until the old process has terminated.

Solution:
Introducing a client._is_stopping field that tracks the shutdown phase, preventing the client from being reused.

runtime/lua/vim/lsp.lua

@@ -148,7 +148,7 @@ end
 --- @param config vim.lsp.ClientConfig
 --- @return boolean
 local function reuse_client_default(client, config)
-  if client.name ~= config.name then
+  if client.name ~= config.name or client:is_stopped() then
     return false
   end
 

runtime/lua/vim/lsp/client.lua

@@ -387,6 +387,7 @@ function Client.create(config)
     capabilities = config.capabilities,
     workspace_folders = lsp._get_workspace_folders(config.workspace_folders or config.root_dir),
     root_dir = config.root_dir,
+    _is_stopping = false,
     _before_init_cb = config.before_init,
     _on_init_cbs = vim._ensure_list(config.on_init),
     _on_exit_cbs = vim._ensure_list(config.on_exit),
@@ -804,12 +805,13 @@ end
 ---
 --- @param force? boolean
 function Client:stop(force)
-  local rpc = self.rpc
-
-  if rpc.is_closing() then
+  if self:is_stopped() then
     return
   end
 
+  self._is_stopping = true
+  local rpc = self.rpc
+
   vim.lsp._watchfiles.cancel(self.id)
 
   if force or not self.initialized or self._graceful_shutdown_failed then
@@ -936,7 +938,7 @@ end
 --- @return boolean # true if client is stopped or in the process of being
 --- stopped; false otherwise
 function Client:is_stopped()
-  return self.rpc.is_closing()
+  return self.rpc.is_closing() or self._is_stopping
 end
 
 --- Execute a lsp command, either via client command function (if available)

test/functional/plugin/lsp_spec.lua

@@ -218,6 +218,25 @@ describe('LSP', function()
         )
       end)
     end)
+
+    it('does not reuse an already-stopping client #33616', function()
+      -- we immediately try to start a second client with the same name/root
+      -- before the first one has finished shutting down; we must get a new id.
+      local clients = exec_lua([[
+        local client1 = vim.lsp.start({
+          name = 'dup-test',
+          cmd = { vim.v.progpath, '-l', fake_lsp_code, 'basic_init' },
+        }, { attach = false })
+        vim.lsp.get_client_by_id(client1):stop()
+        local client2 = vim.lsp.start({
+          name = 'dup-test',
+          cmd = { vim.v.progpath, '-l', fake_lsp_code, 'basic_init' },
+        }, { attach = false })
+        return { client1, client2 }
+        ]])
+      local c1, c2 = clients[1], clients[2]
+      eq(false, c1 == c2, 'Expected a fresh client while the old one is stopping')
+    end)
   end)
 
   describe('basic_init test', function()