fix(lsp): reuse client if configs match and no root dir

Problem:
An LSP configuration that creates client with no root_dir or
workspace_folders can result in vim.lsp.enable attaching to it multiple
times.

Solution:
When checking existing clients, reuse a client if it wasn't initially
configured have any workspace_folders. This more closely matches the
behaviour we had prior to d9235ef

runtime/lua/vim/lsp.lua

@@ -201,23 +201,28 @@ local function reuse_client_default(client, config)
   end
 
   local config_folders = lsp._get_workspace_folders(config.workspace_folders or config.root_dir)
-    or {}
-  local config_folders_included = 0
 
-  if not next(config_folders) then
-    return false
+  if not config_folders or not next(config_folders) then
+    -- Reuse if the client was configured with no workspace folders
+    local client_config_folders =
+      lsp._get_workspace_folders(client.config.workspace_folders or client.config.root_dir)
+    return not client_config_folders or not next(client_config_folders)
   end
 
   for _, config_folder in ipairs(config_folders) do
+    local found = false
     for _, client_folder in ipairs(client.workspace_folders) do
       if config_folder.uri == client_folder.uri then
-        config_folders_included = config_folders_included + 1
+        found = true
         break
       end
     end
+    if not found then
+      return false
+    end
   end
 
-  return config_folders_included == #config_folders
+  return true
 end
 
 --- Reset defaults set by `set_defaults`.

test/functional/plugin/lsp/completion_spec.lua

@@ -731,9 +731,10 @@ describe('vim.lsp.completion: item conversion', function()
   )
 end)
 
+--- @param name string
 --- @param completion_result lsp.CompletionList
 --- @return integer
-local function create_server(completion_result)
+local function create_server(name, completion_result)
   return exec_lua(function()
     local server = _G._create_server({
       capabilities = {
@@ -751,7 +752,7 @@ local function create_server(completion_result)
     local bufnr = vim.api.nvim_get_current_buf()
     vim.api.nvim_win_set_buf(0, bufnr)
     return vim.lsp.start({
-      name = 'dummy',
+      name = name,
       cmd = server.cmd,
       on_attach = function(client, bufnr0)
         vim.lsp.completion.enable(true, client.id, bufnr0, {
@@ -800,7 +801,7 @@ describe('vim.lsp.completion: protocol', function()
   end
 
   it('fetches completions and shows them using complete on trigger', function()
-    create_server({
+    create_server('dummy', {
       isIncomplete = false,
       items = {
         {
@@ -892,7 +893,7 @@ describe('vim.lsp.completion: protocol', function()
   end)
 
   it('merges results from multiple clients', function()
-    create_server({
+    create_server('dummy1', {
       isIncomplete = false,
       items = {
         {
@@ -900,7 +901,7 @@ describe('vim.lsp.completion: protocol', function()
         },
       },
     })
-    create_server({
+    create_server('dummy2', {
       isIncomplete = false,
       items = {
         {
@@ -933,7 +934,7 @@ describe('vim.lsp.completion: protocol', function()
         },
       },
     }
-    local client_id = create_server(completion_list)
+    local client_id = create_server('dummy', completion_list)
 
     exec_lua(function()
       _G.called = false
@@ -970,7 +971,7 @@ describe('vim.lsp.completion: protocol', function()
   end)
 
   it('enable(…,{convert=fn}) custom word/abbr format', function()
-    create_server({
+    create_server('dummy', {
       isIncomplete = false,
       items = {
         {
@@ -1012,7 +1013,7 @@ describe('vim.lsp.completion: integration', function()
     exec_lua(function()
       vim.o.completeopt = 'menuone,noselect'
     end)
-    create_server(completion_list)
+    create_server('dummy', completion_list)
     feed('i world<esc>0ih<c-x><c-o>')
     retry(nil, nil, function()
       eq(

test/functional/plugin/lsp_spec.lua

@@ -5184,8 +5184,8 @@ describe('LSP', function()
         local win = vim.api.nvim_get_current_win()
         vim.api.nvim_buf_set_lines(bufnr, 0, -1, true, { 'local x = 10', '', 'print(x)' })
         vim.api.nvim_win_set_cursor(win, { 3, 6 })
-        local client_id1 = assert(vim.lsp.start({ name = 'dummy', cmd = server1.cmd }))
-        local client_id2 = assert(vim.lsp.start({ name = 'dummy', cmd = server2.cmd }))
+        local client_id1 = assert(vim.lsp.start({ name = 'dummy1', cmd = server1.cmd }))
+        local client_id2 = assert(vim.lsp.start({ name = 'dummy2', cmd = server2.cmd }))
         local response
         vim.lsp.buf.definition({
           on_list = function(r)
@@ -6203,5 +6203,33 @@ describe('LSP', function()
         end)
       )
     end)
+
+    it('does not attach to buffers more than once if no root_dir', function()
+      exec_lua(create_server_definition)
+
+      local tmp1 = t.tmpname(true)
+
+      eq(
+        1,
+        exec_lua(function()
+          local server = _G._create_server({
+            handlers = {
+              initialize = function(_, _, callback)
+                callback(nil, { capabilities = {} })
+              end,
+            },
+          })
+
+          vim.lsp.config('foo', { cmd = server.cmd, filetypes = { 'foo' } })
+          vim.lsp.enable('foo')
+
+          vim.cmd.edit(assert(tmp1))
+          vim.bo.filetype = 'foo'
+          vim.bo.filetype = 'foo'
+
+          return #vim.lsp.get_clients({ bufnr = vim.api.nvim_get_current_buf() })
+        end)
+      )
+    end)
   end)
 end)