feat(LspconfigServerLifeCycle): start/stop servers when gaining or lo…

…sing focus

Start/stop servers when nvim session looses focus and restart them on demand.
This features is motivated by the fact that some servers may gain serious
memory footprint and may incur performance issues.

plugin/lspconfig.lua

@@ -61,7 +61,7 @@ end
 -- Called from plugin/lspconfig.vim because it requires knowing that the last
 -- script in scriptnames to be executed is lspconfig.
 api.nvim_create_user_command('LspInfo', function()
-  require 'lspconfig.ui.lspinfo'()
+  require 'lspconfig.ui.lspinfo' ()
 end, {
   desc = 'Displays attached, active, and configured language servers',
 })
@@ -150,3 +150,54 @@ api.nvim_create_user_command('LspLog', function()
 end, {
   desc = 'Opens the Nvim LSP client log.',
 })
+
+--- Start/stop servers when nvim session looses focus and restart them on demand.
+-- This features is motivated by the fact that some servers may gain serious
+-- memory footprint and may incur performance issues. Added on May 12, 2023
+vim.api.nvim_create_augroup('LspconfigServerLifeCycle', { clear = true })
+vim.api.nvim_create_autocmd({
+  'FocusGained',
+}, {
+  pattern = '*',
+  group = 'LspconfigServerLifeCycle',
+  desc = 'Lspconfig: restart halted lsp servers for given',
+  callback = function()
+    if _G.nvimLspconfigTimer then
+      _G.nvimLspconfigTimer:stop()
+      _G.nvimLspconfigTimer:close()
+      _G.nvimLspconfigTimer = nil
+    end
+    if #vim.lsp.get_active_clients() <= 1 then
+      vim.cmd 'LspStart'
+    end
+  end,
+})
+
+vim.api.nvim_create_autocmd({
+  'FocusLost',
+}, {
+  pattern = '*',
+  group = 'LspconfigServerLifeCycle',
+  desc = 'Lspconfig: halt lsp servers when focus is lost',
+  callback = function()
+    if not _G.nvimLspconfigTimer and #vim.lsp.get_active_clients() > 0 then
+      local timeout = 1000 * 60 * 5 -- 5 minutes
+      _G.nvimLspconfigTimer = vim.loop.new_timer()
+      _G.nvimLspconfigTimer:start(
+        timeout,
+        0,
+        vim.schedule_wrap(function()
+          local activeServers = #vim.lsp.get_active_clients()
+          vim.cmd 'LspStop'
+          vim.notify(
+            ('[lspconfig]: nvim has lost focus, stop current language servers. Number of servers left: %s'):format(
+              activeServers
+            ),
+            vim.log.levels.INFO
+          )
+          _G.nvimLspconfigTimer = nil
+        end)
+      )
+    end
+  end,
+})