feat(lsp): warn about unknown filetype #36910

(cherry picked from commit 054eaf8493)

runtime/lua/vim/lsp/health.lua

@@ -183,6 +183,8 @@ end
 local function check_enabled_configs()
   vim.health.start('vim.lsp: Enabled Configurations')
 
+  local valid_filetypes = vim.fn.getcompletion('', 'filetype')
+
   for name in vim.spairs(vim.lsp._enabled_configs) do
     local config = vim.lsp.config[name]
     local text = {} --- @type string[]
@@ -210,6 +212,16 @@ local function check_enabled_configs()
           report_warn(("'%s' is not executable. Configuration will not be used."):format(v[1]))
         end
 
+        if k == 'filetypes' and type(v) == 'table' then
+          for _, filetype in
+            ipairs(v --[[@as string[] ]])
+          do
+            if not vim.list_contains(valid_filetypes, filetype) then
+              report_warn(("Unknown filetype '%s'."):format(filetype))
+            end
+          end
+        end
+
         if v_str then
           text[#text + 1] = ('- %s: %s'):format(k, v_str)
         end