feat(lsp): workspace_required #31824

Problem:
Some language servers do not work properly without a workspace folder.

Solution:
Add `workspace_required`, which skips starting the lsp client if no
workspace folder is found.

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

runtime/lua/vim/lsp.lua

@@ -615,6 +615,17 @@ function lsp.start(config, opts)
     config.root_dir = vim.fs.root(bufnr, opts._root_markers)
   end
 
+  if
+    not config.root_dir
+    and (not config.workspace_folders or #config.workspace_folders == 0)
+    and config.workspace_required
+  then
+    log.info(
+      ('skipping config "%s": workspace_required=true, no workspace found'):format(config.name)
+    )
+    return
+  end
+
   for _, client in pairs(all_clients) do
     if reuse_client(client, config) then
       if opts.attach == false then

runtime/lua/vim/lsp/client.lua

@@ -63,6 +63,9 @@ local validate = vim.validate
 --- folder in this list. See `workspaceFolders` in the LSP spec.
 --- @field workspace_folders? lsp.WorkspaceFolder[]
 ---
+--- (default false) Server requires a workspace (no "single file" support).
+--- @field workspace_required? boolean
+---
 --- Map overriding the default capabilities defined by |vim.lsp.protocol.make_client_capabilities()|,
 --- passed to the language server on initialization. Hint: use make_client_capabilities() and modify
 --- its result.