feat(lsp): vim.lsp.get_configs() #37237

Problem:
No way to iterate configs. Users need to reach
for `vim.lsp.config._configs`, an internal interface.

Solution:
Provide vim.lsp.get_configs().
Also indirectly improves :lsp enable/disable completion
by discarding invalid configs from completion.

runtime/lua/vim/lsp.lua

@@ -387,6 +387,76 @@ lsp.config = setmetatable({ _configs = {} }, {
   end,
 })
 
+--- @return string[]
+local function get_config_names()
+  local config_names = vim
+    .iter(api.nvim_get_runtime_file('lsp/*.lua', true))
+    --- @param path string
+    :map(function(path)
+      local file_name = path:match('[^/]*.lua$')
+      return file_name:sub(0, #file_name - 4)
+    end)
+    :totable()
+
+  vim.list_extend(config_names, vim.tbl_keys(lsp.config._configs))
+
+  return vim
+    .iter(config_names)
+    :unique()
+    --- @param name string
+    :filter(function(name)
+      return name ~= '*'
+    end)
+    :totable()
+end
+
+--- Key-value pairs used to filter the returned configs.
+--- @class vim.lsp.get_configs.Filter
+--- @inlinedoc
+---
+--- If true, only return enabled configs. If false, only return configs that
+--- aren't enabled.
+--- @field enabled? boolean
+---
+--- Only return configs which attach to the given filetype.
+--- @field filetype? string
+
+--- Get LSP configs.
+---
+--- Note: Will eagerly evaluate config files in `'runtimepath'` if necessary.
+--- @param filter? vim.lsp.get_configs.Filter
+--- @return vim.lsp.Config[]: List of |vim.lsp.Config| objects
+function lsp.get_configs(filter)
+  validate('filter', filter, 'table', true)
+
+  filter = filter or {}
+
+  local configs = {} --- @type vim.lsp.Config[]
+
+  local config_names --- @type string[]
+  if not filter.enabled then
+    config_names = get_config_names()
+  else
+    -- Shortcut filtering enabled configs by directly getting enabled configs
+    config_names = vim.tbl_keys(lsp._enabled_configs)
+  end
+
+  for _, config_name in ipairs(config_names) do
+    local config = lsp.config[config_name]
+    if
+      config
+      and (filter.enabled ~= false or not lsp.is_enabled(config_name))
+      and (
+        filter.filetype == nil
+        or (config.filetypes ~= nil and vim.list_contains(config.filetypes, filter.filetype))
+      )
+    then
+      configs[#configs + 1] = config
+    end
+  end
+  return configs
+end
+
 local lsp_enable_autocmd_id --- @type integer?
 
 local function validate_cmd(v)