feat: add single file mode (#1385)

* This adds a "single file mode" option for each language server
* Currently, if a root is not detected, a new language server is started
  for each file opened.
* Root directory is set to `nil` in start_client. Some servers will
  refuse to start, or otherwise panic. This is opt-in per server.
* Some servers, such as rust-analyzer, explicitly have a "single file
  mode", we will not support that until it is officially part of the LSP
  specification

Co-authored-by: Peter Lithammer <peter.lithammer@gmail.com>

42 files changed, 160 insertions, 134 deletions

diff --git a/lua/lspconfig/bashls.lua b/lua/lspconfig/bashls.lua
index c42f4c74..9fe3f397 100644
--- a/lua/lspconfig/bashls.lua
+++ b/lua/lspconfig/bashls.lua
@@ -14,9 +14,8 @@ configs[server_name] = {
       GLOB_PATTERN = vim.env.GLOB_PATTERN or '*@(.sh|.inc|.bash|.command)',
     },
     filetypes = { 'sh' },
-    root_dir = function(fname)
-      return util.root_pattern '.git'(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern '.git',
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/beancount.lua b/lua/lspconfig/beancount.lua
index 2aa92479..f5e69114 100644
--- a/lua/lspconfig/beancount.lua
+++ b/lua/lspconfig/beancount.lua
@@ -8,9 +8,8 @@ configs[server_name] = {
   default_config = {
     cmd = { bin_name },
     filetypes = { 'beancount' },
-    root_dir = function(fname)
-      return util.find_git_ancestor(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.find_git_ancestor,
+    single_file_support = true,
     init_options = {
       -- this is the path to the beancout journal file
       journalFile = '',
diff --git a/lua/lspconfig/ccls.lua b/lua/lspconfig/ccls.lua
index d7170662..ac5949e8 100644
--- a/lua/lspconfig/ccls.lua
+++ b/lua/lspconfig/ccls.lua
@@ -5,10 +5,8 @@ configs.ccls = {
   default_config = {
     cmd = { 'ccls' },
     filetypes = { 'c', 'cpp', 'objc', 'objcpp' },
-    root_dir = function(fname)
-      return util.root_pattern('compile_commands.json', '.ccls', 'compile_flags.txt', '.git')(fname)
-        or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern('compile_commands.json', '.ccls', 'compile_flags.txt', '.git'),
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/clangd.lua b/lua/lspconfig/clangd.lua
index d2a1000d..7fe9ada1 100644
--- a/lua/lspconfig/clangd.lua
+++ b/lua/lspconfig/clangd.lua
@@ -43,8 +43,9 @@ configs.clangd = {
     filetypes = { 'c', 'cpp', 'objc', 'objcpp' },
     root_dir = function(fname)
       local filename = util.path.is_absolute(fname) and fname or util.path.join(vim.loop.cwd(), fname)
-      return root_pattern(filename) or util.path.dirname(filename)
+      return root_pattern(filename)
     end,
+    single_file_support = true,
     capabilities = default_capabilities,
   },
   commands = {
diff --git a/lua/lspconfig/cmake.lua b/lua/lspconfig/cmake.lua
index a648c444..9592dec2 100644
--- a/lua/lspconfig/cmake.lua
+++ b/lua/lspconfig/cmake.lua
@@ -5,9 +5,8 @@ configs.cmake = {
   default_config = {
     cmd = { 'cmake-language-server' },
     filetypes = { 'cmake' },
-    root_dir = function(fname)
-      return util.root_pattern('.git', 'compile_commands.json', 'build')(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern('.git', 'compile_commands.json', 'build'),
+    single_file_support = true,
     init_options = {
       buildDirectory = 'build',
     },
diff --git a/lua/lspconfig/codeqlls.lua b/lua/lspconfig/codeqlls.lua
index 5bb13a48..e80070e7 100644
--- a/lua/lspconfig/codeqlls.lua
+++ b/lua/lspconfig/codeqlls.lua
@@ -3,15 +3,12 @@ local util = require 'lspconfig/util'
 
 local server_name = 'codeqlls'
 
-local root_pattern = util.root_pattern 'qlpack.yml'
-
 configs[server_name] = {
   default_config = {
     cmd = { 'codeql', 'execute', 'language-server', '--check-errors', 'ON_CHANGE', '-q' },
     filetypes = { 'ql' },
-    root_dir = function(fname)
-      return root_pattern(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern 'qlpack.yml',
+    single_file_support = true,
     log_level = vim.lsp.protocol.MessageType.Warning,
     before_init = function(initialize_params)
       initialize_params['workspaceFolders'] = {
diff --git a/lua/lspconfig/configs.lua b/lua/lspconfig/configs.lua
index 2f4cd0d7..f69e2673 100644
--- a/lua/lspconfig/configs.lua
+++ b/lua/lspconfig/configs.lua
@@ -78,22 +78,29 @@ function configs.__newindex(t, config_name, config_def)
 
     function M.launch()
       local root_dir = get_root_dir(api.nvim_buf_get_name(0), api.nvim_get_current_buf())
-      if not root_dir then
-        vim.notify(string.format('Launching %s failed: matching root directory not detected.', config_name))
-        return
-      end
-      api.nvim_command(
-        string.format(
-          "autocmd %s unsilent lua require'lspconfig'[%q].manager.try_add_wrapper()",
-          'BufReadPost ' .. root_dir .. '/*',
-          config.name
+      if root_dir then
+        api.nvim_command(
+          string.format(
+            "autocmd %s unsilent lua require'lspconfig'[%q].manager.try_add_wrapper()",
+            'BufReadPost ' .. root_dir .. '/*',
+            config.name
+          )
         )
-      )
-      for _, bufnr in ipairs(vim.api.nvim_list_bufs()) do
-        local buf_dir = api.nvim_buf_get_name(bufnr)
-        if buf_dir:sub(1, root_dir:len()) == root_dir then
-          M.manager.try_add_wrapper(bufnr)
+        for _, bufnr in ipairs(vim.api.nvim_list_bufs()) do
+          local buf_dir = api.nvim_buf_get_name(bufnr)
+          if buf_dir:sub(1, root_dir:len()) == root_dir then
+            M.manager.try_add_wrapper(bufnr)
+          end
         end
+      elseif config.single_file_support then
+        -- This allows on_new_config to use the parent directory of the file
+        -- Effectively this is the root from lspconfig's perspective, as we use
+        -- this to attach additional files in the same parent folder to the same server.
+        -- We just no longer send rootDirectory or workspaceFolders during initialization.
+        local pseudo_root = util.path.dirname(api.nvim_buf_get_name(0))
+        M.manager.add(pseudo_root, true)
+      else
+        vim.notify(string.format('Autostart for %s failed: matching root directory not detected.', config_name))
       end
     end
 
@@ -182,11 +189,23 @@ function configs.__newindex(t, config_name, config_def)
 
     function manager.try_add(bufnr)
       bufnr = bufnr or api.nvim_get_current_buf()
+
       if vim.api.nvim_buf_get_option(bufnr, 'buftype') == 'nofile' then
         return
       end
+
+      local id
       local root_dir = get_root_dir(api.nvim_buf_get_name(bufnr), bufnr)
-      local id = manager.add(root_dir)
+
+      if root_dir then
+        id = manager.add(root_dir, false)
+      elseif config.single_file_support then
+        local pseudo_root = util.path.dirname(api.nvim_buf_get_name(0))
+        id = manager.add(pseudo_root, true)
+      else
+        vim.notify(string.format('Autostart for %s failed: matching root directory not detected.', config_name))
+      end
+
       if id then
         lsp.buf_attach_client(bufnr, id)
       end
diff --git a/lua/lspconfig/crystalline.lua b/lua/lspconfig/crystalline.lua
index 8943937d..3bd4e390 100644
--- a/lua/lspconfig/crystalline.lua
+++ b/lua/lspconfig/crystalline.lua
@@ -5,9 +5,8 @@ configs.crystalline = {
   default_config = {
     cmd = { 'crystalline' },
     filetypes = { 'crystal' },
-    root_dir = function(fname)
-      return util.root_pattern 'shard.yml'(fname) or util.find_git_ancestor(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern 'shard.yml' or util.find_git_ancestor,
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/cssls.lua b/lua/lspconfig/cssls.lua
index 3a2fe3c7..07cc608f 100644
--- a/lua/lspconfig/cssls.lua
+++ b/lua/lspconfig/cssls.lua
@@ -8,9 +8,8 @@ configs[server_name] = {
   default_config = {
     cmd = { bin_name, '--stdio' },
     filetypes = { 'css', 'scss', 'less' },
-    root_dir = function(fname)
-      return util.root_pattern('package.json', '.git')(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern('package.json', '.git'),
+    single_file_support = true,
     settings = {
       css = { validate = true },
       scss = { validate = true },
diff --git a/lua/lspconfig/dhall_lsp_server.lua b/lua/lspconfig/dhall_lsp_server.lua
index ae08b928..9378ed62 100644
--- a/lua/lspconfig/dhall_lsp_server.lua
+++ b/lua/lspconfig/dhall_lsp_server.lua
@@ -5,9 +5,8 @@ configs.dhall_lsp_server = {
   default_config = {
     cmd = { 'dhall-lsp-server' },
     filetypes = { 'dhall' },
-    root_dir = function(fname)
-      return util.root_pattern '.git'(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.find_git_ancestor,
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/diagnosticls.lua b/lua/lspconfig/diagnosticls.lua
index 3c61e156..ccfd76bd 100644
--- a/lua/lspconfig/diagnosticls.lua
+++ b/lua/lspconfig/diagnosticls.lua
@@ -10,8 +10,9 @@ end
 configs[server_name] = {
   default_config = {
     cmd = { bin_name, '--stdio' },
+    root_dir = util.find_git_ancestor,
+    single_file_support = true,
     filetypes = {},
-    root_dir = util.path.dirname,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/dotls.lua b/lua/lspconfig/dotls.lua
index 7d660295..be1e86f3 100644
--- a/lua/lspconfig/dotls.lua
+++ b/lua/lspconfig/dotls.lua
@@ -12,9 +12,8 @@ configs[server_name] = {
   default_config = {
     cmd = { bin_name, '--stdio' },
     filetypes = { 'dot' },
-    root_dir = function(fname)
-      return util.root_pattern(unpack(root_files))(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern(unpack(root_files)),
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/efm.lua b/lua/lspconfig/efm.lua
index 0f2779d4..445dc6da 100644
--- a/lua/lspconfig/efm.lua
+++ b/lua/lspconfig/efm.lua
@@ -7,9 +7,8 @@ local bin_name = 'efm-langserver'
 configs[server_name] = {
   default_config = {
     cmd = { bin_name },
-    root_dir = function(fname)
-      return util.root_pattern '.git'(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.find_git_ancestor,
+    single_file_support = true,
   },
 
   docs = {
@@ -31,7 +30,7 @@ require('lspconfig')['efm'].setup{
 
 ]],
     default_config = {
-      root_dir = [[util.root_pattern(".git")(fname) or util.path.dirname(fname)]],
+      root_dir = [[util.root_pattern(".git")]],
     },
   },
 }
diff --git a/lua/lspconfig/erlangls.lua b/lua/lspconfig/erlangls.lua
index a161a194..adaf9b35 100644
--- a/lua/lspconfig/erlangls.lua
+++ b/lua/lspconfig/erlangls.lua
@@ -5,9 +5,8 @@ configs.erlangls = {
   default_config = {
     cmd = { 'erlang_ls' },
     filetypes = { 'erlang' },
-    root_dir = function(fname)
-      return util.root_pattern('rebar.config', 'erlang.mk', '.git')(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern('rebar.config', 'erlang.mk', '.git'),
+    single_file_support = true,
   },
   docs = {
     description = [[
@@ -25,7 +24,7 @@ Installation requirements:
     - [rebar3 3.9.1+](https://github.com/erlang/rebar3)
 ]],
     default_config = {
-      root_dir = [[root_pattern('rebar.config', 'erlang.mk', '.git') or util.path.dirname(fname)]],
+      root_dir = [[root_pattern('rebar.config', 'erlang.mk', '.git')]],
     },
   },
 }
diff --git a/lua/lspconfig/html.lua b/lua/lspconfig/html.lua
index 01a7dcc0..c2ac4f36 100644
--- a/lua/lspconfig/html.lua
+++ b/lua/lspconfig/html.lua
@@ -8,9 +8,8 @@ configs[server_name] = {
   default_config = {
     cmd = { bin_name, '--stdio' },
     filetypes = { 'html' },
-    root_dir = function(fname)
-      return util.root_pattern('package.json', '.git')(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern('package.json', '.git'),
+    single_file_support = true,
     settings = {},
     init_options = {
       embeddedLanguages = { css = true, javascript = true },
diff --git a/lua/lspconfig/jdtls.lua b/lua/lspconfig/jdtls.lua
index d48272db..ad448448 100644
--- a/lua/lspconfig/jdtls.lua
+++ b/lua/lspconfig/jdtls.lua
@@ -134,8 +134,8 @@ configs[server_name] = {
           return root
         end
       end
-      return vim.fn.getcwd()
     end,
+    single_file_mode = true,
     init_options = {
       workspace = get_workspace_dir(),
       jvm_args = {},
diff --git a/lua/lspconfig/jedi_language_server.lua b/lua/lspconfig/jedi_language_server.lua
index 714814af..4de08799 100644
--- a/lua/lspconfig/jedi_language_server.lua
+++ b/lua/lspconfig/jedi_language_server.lua
@@ -1,12 +1,20 @@
 local configs = require 'lspconfig/configs'
+local util = require 'lspconfig/util'
+
+local root_files = {
+  'pyproject.toml',
+  'setup.py',
+  'setup.cfg',
+  'requirements.txt',
+  'Pipfile',
+}
 
 configs.jedi_language_server = {
   default_config = {
     cmd = { 'jedi-language-server' },
     filetypes = { 'python' },
-    root_dir = function(fname)
-      return vim.fn.getcwd()
-    end,
+    root_dir = util.root_pattern(unpack(root_files)),
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/jsonls.lua b/lua/lspconfig/jsonls.lua
index 4349d401..6b391950 100644
--- a/lua/lspconfig/jsonls.lua
+++ b/lua/lspconfig/jsonls.lua
@@ -11,9 +11,8 @@ configs[server_name] = {
     init_options = {
       provideFormatter = true,
     },
-    root_dir = function(fname)
-      return util.root_pattern '.git'(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern '.git',
+    single_file_support = true,
   },
   docs = {
     -- this language server config is in VSCode built-in package.json
diff --git a/lua/lspconfig/julials.lua b/lua/lspconfig/julials.lua
index e67e788b..75acf07f 100644
--- a/lua/lspconfig/julials.lua
+++ b/lua/lspconfig/julials.lua
@@ -48,9 +48,8 @@ configs.julials = {
       new_config.cmd_cwd = root_dir
     end,
     filetypes = { 'julia' },
-    root_dir = function(fname)
-      return util.find_git_ancestor(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.find_git_ancestor,
+    single_file_support = true,
   },
   docs = {
     package_json = 'https://raw.githubusercontent.com/julia-vscode/julia-vscode/master/package.json',
diff --git a/lua/lspconfig/lean3ls.lua b/lua/lspconfig/lean3ls.lua
index 0ac7cf54..65dc815b 100644
--- a/lua/lspconfig/lean3ls.lua
+++ b/lua/lspconfig/lean3ls.lua
@@ -19,8 +19,8 @@ configs.lean3ls = {
         or util.root_pattern 'leanpkg.path'(fname)
         or stdlib_dir
         or util.find_git_ancestor(fname)
-        or util.path.dirname(fname)
     end,
+    single_file_support = true,
     on_new_config = function(config, root)
       if not config.cmd_cwd then
         config.cmd_cwd = root
diff --git a/lua/lspconfig/leanls.lua b/lua/lspconfig/leanls.lua
index 328da43e..cfefb808 100644
--- a/lua/lspconfig/leanls.lua
+++ b/lua/lspconfig/leanls.lua
@@ -15,11 +15,9 @@ configs.leanls = {
         end
       end
 
-      return util.root_pattern 'leanpkg.toml'(fname)
-        or stdlib_dir
-        or util.find_git_ancestor(fname)
-        or util.path.dirname(fname)
+      return util.root_pattern 'leanpkg.toml'(fname) or stdlib_dir or util.find_git_ancestor(fname)
     end,
+    single_file_support = true,
     on_new_config = function(config, root)
       if not config.cmd_cwd then
         config.cmd_cwd = root
diff --git a/lua/lspconfig/lemminx.lua b/lua/lspconfig/lemminx.lua
index ecb0b444..31f4df23 100644
--- a/lua/lspconfig/lemminx.lua
+++ b/lua/lspconfig/lemminx.lua
@@ -5,9 +5,8 @@ local server_name = 'lemminx'
 configs[server_name] = {
   default_config = {
     filetypes = { 'xml', 'xsd', 'svg' },
-    root_dir = function(filename)
-      return util.root_pattern '.git'(filename) or util.path.dirname(filename)
-    end,
+    root_dir = util.root_pattern '.git',
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/mint.lua b/lua/lspconfig/mint.lua
index 3d213d08..670d26d8 100644
--- a/lua/lspconfig/mint.lua
+++ b/lua/lspconfig/mint.lua
@@ -6,8 +6,9 @@ configs.mint = {
     cmd = { 'mint', 'ls' },
     filetypes = { 'mint' },
     root_dir = function(fname)
-      return util.root_pattern 'mint.json'(fname) or util.find_git_ancestor(fname) or util.path.dirname(fname)
+      return util.root_pattern 'mint.json'(fname) or util.find_git_ancestor(fname)
     end,
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/nimls.lua b/lua/lspconfig/nimls.lua
index 3f537f7c..d74dcc99 100644
--- a/lua/lspconfig/nimls.lua
+++ b/lua/lspconfig/nimls.lua
@@ -6,8 +6,9 @@ configs.nimls = {
     cmd = { 'nimlsp' },
     filetypes = { 'nim' },
     root_dir = function(fname)
-      return util.root_pattern '*.nimble'(fname) or util.find_git_ancestor(fname) or util.path.dirname(fname)
+      return util.root_pattern '*.nimble'(fname) or util.find_git_ancestor(fname)
     end,
+    single_file_support = true,
   },
   docs = {
     package_json = 'https://raw.githubusercontent.com/pragmagic/vscode-nim/master/package.json',
diff --git a/lua/lspconfig/pasls.lua b/lua/lspconfig/pasls.lua
index 4cceb13f..e818300c 100644
--- a/lua/lspconfig/pasls.lua
+++ b/lua/lspconfig/pasls.lua
@@ -5,9 +5,8 @@ configs.pasls = {
   default_config = {
     cmd = { 'pasls' },
     filetypes = { 'pascal' },
-    root_dir = function(fname)
-      return util.find_git_ancestor(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.find_git_ancestor,
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/perlls.lua b/lua/lspconfig/perlls.lua
index 4ef81596..61275267 100644
--- a/lua/lspconfig/perlls.lua
+++ b/lua/lspconfig/perlls.lua
@@ -22,9 +22,8 @@ configs.perlls = {
       },
     },
     filetypes = { 'perl' },
-    root_dir = function(fname)
-      return util.root_pattern '.git'(fname) or vim.fn.getcwd()
-    end,
+    root_dir = util.find_git_ancestor,
+    single_file_mode = true,
   },
   docs = {
     package_json = 'https://raw.githubusercontent.com/richterger/Perl-LanguageServer/master/clients/vscode/perl/package.json',
diff --git a/lua/lspconfig/perlpls.lua b/lua/lspconfig/perlpls.lua
index af0b51e4..81ea7ad6 100644
--- a/lua/lspconfig/perlpls.lua
+++ b/lua/lspconfig/perlpls.lua
@@ -10,9 +10,8 @@ configs.perlpls = {
       },
     },
     filetypes = { 'perl' },
-    root_dir = function(fname)
-      return util.root_pattern '.git'(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern '.git',
+    single_file_support = true,
   },
   docs = {
     package_json = 'https://raw.githubusercontent.com/FractalBoy/perl-language-server/master/client/package.json',
diff --git a/lua/lspconfig/powershell_es.lua b/lua/lspconfig/powershell_es.lua
index 528b8cf3..e2fd86ef 100644
--- a/lua/lspconfig/powershell_es.lua
+++ b/lua/lspconfig/powershell_es.lua
@@ -20,9 +20,8 @@ configs[server_name] = {
       new_config.cmd = make_cmd(bundle_path)
     end,
     filetypes = { 'ps1' },
-    root_dir = function(fname)
-      return util.find_git_ancestor(fname) or vim.fn.getcwd()
-    end,
+    root_dir = util.find_git_ancestor,
+    single_file_mode = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/puppet.lua b/lua/lspconfig/puppet.lua
index abdbfc5a..3882823d 100644
--- a/lua/lspconfig/puppet.lua
+++ b/lua/lspconfig/puppet.lua
@@ -15,9 +15,8 @@ configs[server_name] = {
   default_config = {
     cmd = { bin_name, '--stdio' },
     filetypes = { 'puppet' },
-    root_dir = function(fname)
-      return util.root_pattern(unpack(root_files))(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern(unpack(root_files)),
+    single_file_support = true,
   },
   docs = {
     package_json = 'https://raw.githubusercontent.com/puppetlabs/puppet-vscode/main/package.json',
diff --git a/lua/lspconfig/pylsp.lua b/lua/lspconfig/pylsp.lua
index 66756da5..42a87150 100644
--- a/lua/lspconfig/pylsp.lua
+++ b/lua/lspconfig/pylsp.lua
@@ -13,8 +13,9 @@ configs.pylsp = {
         'requirements.txt',
         'Pipfile',
       }
-      return util.root_pattern(unpack(root_files))(fname) or util.find_git_ancestor(fname) or util.path.dirname(fname)
+      return util.root_pattern(unpack(root_files))(fname) or util.find_git_ancestor(fname)
     end,
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/pyright.lua b/lua/lspconfig/pyright.lua
index f9fe56d6..d17aac5e 100644
--- a/lua/lspconfig/pyright.lua
+++ b/lua/lspconfig/pyright.lua
@@ -7,6 +7,15 @@ if vim.fn.has 'win32' == 1 then
   bin_name = bin_name .. '.cmd'
 end
 
+local root_files = {
+  'pyproject.toml',
+  'setup.py',
+  'setup.cfg',
+  'requirements.txt',
+  'Pipfile',
+  'pyrightconfig.json',
+}
+
 local function organize_imports()
   local params = {
     command = 'pyright.organizeimports',
@@ -19,17 +28,8 @@ configs[server_name] = {
   default_config = {
     cmd = { bin_name, '--stdio' },
     filetypes = { 'python' },
-    root_dir = function(fname)
-      local root_files = {
-        'pyproject.toml',
-        'setup.py',
-        'setup.cfg',
-        'requirements.txt',
-        'Pipfile',
-        'pyrightconfig.json',
-      }
-      return util.root_pattern(unpack(root_files))(fname) or util.find_git_ancestor(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern(unpack(root_files)),
+    single_file_support = true,
     settings = {
       python = {
         analysis = {
diff --git a/lua/lspconfig/racket_langserver.lua b/lua/lspconfig/racket_langserver.lua
index 7a31562b..71c95636 100644
--- a/lua/lspconfig/racket_langserver.lua
+++ b/lua/lspconfig/racket_langserver.lua
@@ -9,9 +9,8 @@ configs.racket_langserver = {
   default_config = {
     cmd = { 'racket', '--lib', 'racket-langserver' },
     filetypes = { 'racket', 'scheme' },
-    root_dir = function(fname)
-      return util.root_pattern(unpack(root_files))(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern(unpack(root_files)),
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/rome.lua b/lua/lspconfig/rome.lua
index a54b0168..242fa2c2 100644
--- a/lua/lspconfig/rome.lua
+++ b/lua/lspconfig/rome.lua
@@ -16,8 +16,8 @@ configs.rome = {
       return util.find_package_json_ancestor(fname)
         or util.find_node_modules_ancestor(fname)
         or util.find_git_ancestor(fname)
-        or util.path.dirname(fname)
     end,
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/scry.lua b/lua/lspconfig/scry.lua
index 0d8c5b25..3d57d801 100644
--- a/lua/lspconfig/scry.lua
+++ b/lua/lspconfig/scry.lua
@@ -6,8 +6,9 @@ configs.scry = {
     cmd = { 'scry' },
     filetypes = { 'crystal' },
     root_dir = function(fname)
-      return util.root_pattern 'shard.yml'(fname) or util.find_git_ancestor(fname) or util.path.dirname(fname)
+      return util.root_pattern 'shard.yml'(fname) or util.find_git_ancestor(fname)
     end,
+    single_file_support = true,
   },
   docs = {
     description = [[
diff --git a/lua/lspconfig/sqls.lua b/lua/lspconfig/sqls.lua
index 6eeb8f83..307f204f 100644
--- a/lua/lspconfig/sqls.lua
+++ b/lua/lspconfig/sqls.lua
@@ -5,9 +5,8 @@ configs.sqls = {
   default_config = {
     cmd = { 'sqls' },
     filetypes = { 'sql', 'mysql' },
-    root_dir = function(fname)
-      return util.root_pattern 'config.yml'(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern 'config.yml',
+    single_file_support = true,
     settings = {},
   },
   docs = {
diff --git a/lua/lspconfig/sumneko_lua.lua b/lua/lspconfig/sumneko_lua.lua
index da95db88..36df08ed 100644
--- a/lua/lspconfig/sumneko_lua.lua
+++ b/lua/lspconfig/sumneko_lua.lua
@@ -6,9 +6,8 @@ local name = 'sumneko_lua'
 configs[name] = {
   default_config = {
     filetypes = { 'lua' },
-    root_dir = function(fname)
-      return util.find_git_ancestor(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.find_git_ancestor,
+    single_file_support = true,
     log_level = vim.lsp.protocol.MessageType.Warning,
     settings = { Lua = { telemetry = { enable = false } } },
   },
diff --git a/lua/lspconfig/taplo.lua b/lua/lspconfig/taplo.lua
index f9a14631..5c64adc3 100644
--- a/lua/lspconfig/taplo.lua
+++ b/lua/lspconfig/taplo.lua
@@ -6,8 +6,9 @@ configs.taplo = {
     cmd = { 'taplo-lsp', 'run' },
     filetypes = { 'toml' },
     root_dir = function(fname)
-      return util.root_pattern '*.toml'(fname) or util.find_git_ancestor(fname) or util.path.dirname(fname)
+      return util.root_pattern '*.toml'(fname) or util.find_git_ancestor(fname)
     end,
+    single_file_support = true,
   },
   docs = {
     description = [[
@@ -21,7 +22,7 @@ cargo install taplo-lsp
 ```
     ]],
     default_config = {
-      root_dir = [[root_pattern("*.toml", ".git") or dirname]],
+      root_dir = [[root_pattern("*.toml", ".git")]],
     },
   },
 }
diff --git a/lua/lspconfig/texlab.lua b/lua/lspconfig/texlab.lua
index 232773bc..c1612255 100644
--- a/lua/lspconfig/texlab.lua
+++ b/lua/lspconfig/texlab.lua
@@ -69,7 +69,8 @@ configs.texlab = {
   default_config = {
     cmd = { 'texlab' },
     filetypes = { 'tex', 'bib' },
-    root_dir = util.path.dirname,
+    root_dir = util.find_git_ancestor,
+    single_file_support = true,
     settings = {
       texlab = {
         rootDirectory = nil,
diff --git a/lua/lspconfig/ui/lspinfo.lua b/lua/lspconfig/ui/lspinfo.lua
index 5178939d..6aaa6196 100644
--- a/lua/lspconfig/ui/lspinfo.lua
+++ b/lua/lspconfig/ui/lspinfo.lua
@@ -73,7 +73,11 @@ local function make_client_info(client)
   local client_info = {}
 
   client_info.cmd = remove_newlines(client.config.cmd)
-  client_info.root_dir = client.workspaceFolders[1].name
+  if client.workspaceFolders then
+    client_info.root_dir = client.workspaceFolders[1].name
+  else
+    client_info.root_dir = 'Running in single file mode.'
+  end
   client_info.filetypes = table.concat(client.config.filetypes or {}, ', ')
   client_info.autostart = (client.config.autostart and 'true') or 'false'
   client_info.attached_buffers_list = table.concat(vim.lsp.get_buffers_by_client_id(client.id), ', ')
diff --git a/lua/lspconfig/util.lua b/lua/lspconfig/util.lua
index 3691da68..dbac70fd 100644
--- a/lua/lspconfig/util.lua
+++ b/lua/lspconfig/util.lua
@@ -233,18 +233,24 @@ end)()
 -- seen before, will call make_config(root_dir) and start a new client.
 function M.server_per_root_dir_manager(_make_config)
   local clients = {}
+  local single_file_clients = {}
   local manager = {}
 
-  function manager.add(root_dir)
-    if not root_dir then
-      return
-    end
-    if not M.path.is_dir(root_dir) then
-      return
+  function manager.add(root_dir, single_file_mode)
+    local client_id
+    if single_file_mode then
+      client_id = single_file_clients[root_dir]
+    else
+      if not root_dir then
+        return
+      end
+      if not M.path.is_dir(root_dir) then
+        return
+      end
+      client_id = clients[root_dir]
     end
 
     -- Check if we have a client already or start and store it.
-    local client_id = clients[root_dir]
     if not client_id then
       local new_config = _make_config(root_dir)
       -- do nothing if the client is not enabled
@@ -265,9 +271,20 @@ function M.server_per_root_dir_manager(_make_config)
       end
       new_config.on_exit = M.add_hook_before(new_config.on_exit, function()
         clients[root_dir] = nil
+        single_file_clients[root_dir] = nil
       end)
+      -- Sending rootDirectory and workspaceFolders as null is not explicitly
+      -- codified in the spec. Certain servers crash if initialized with a NULL
+      -- root directory.
+      if single_file_mode then
+        new_config.root_dir = nil
+      end
       client_id = lsp.start_client(new_config)
-      clients[root_dir] = client_id
+      if single_file_mode then
+        single_file_clients[root_dir] = client_id
+      else
+        clients[root_dir] = client_id
+      end
     end
     return client_id
   end
diff --git a/lua/lspconfig/yamlls.lua b/lua/lspconfig/yamlls.lua
index 3154556d..bb432c70 100644
--- a/lua/lspconfig/yamlls.lua
+++ b/lua/lspconfig/yamlls.lua
@@ -8,9 +8,8 @@ configs[server_name] = {
   default_config = {
     cmd = { bin_name, '--stdio' },
     filetypes = { 'yaml' },
-    root_dir = function(fname)
-      return util.root_pattern '.git'(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern '.git',
+    single_file_support = true,
     settings = {
       -- https://github.com/redhat-developer/vscode-redhat-telemetry#how-to-disable-telemetry-reporting
       redhat = { telemetry = { enabled = false } },
diff --git a/lua/lspconfig/zls.lua b/lua/lspconfig/zls.lua
index 311be3f5..a156f029 100644
--- a/lua/lspconfig/zls.lua
+++ b/lua/lspconfig/zls.lua
@@ -5,9 +5,8 @@ configs.zls = {
   default_config = {
     cmd = { 'zls' },
     filetypes = { 'zig', 'zir' },
-    root_dir = function(fname)
-      return util.root_pattern('zls.json', '.git')(fname) or util.path.dirname(fname)
-    end,
+    root_dir = util.root_pattern('zls.json', '.git'),
+    single_file_support = true,
   },
   docs = {
     description = [[