From 054eaf8493cbcf35ad386675fcaa0cc38d6b63e7 Mon Sep 17 00:00:00 2001
From: Olivia Kinnear <git@superatomic.dev>
Date: Thu, 11 Dec 2025 12:58:40 -0600
Subject: [PATCH] feat(lsp): warn about unknown filetype #36910

---
 runtime/lua/vim/lsp/health.lua | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/runtime/lua/vim/lsp/health.lua b/runtime/lua/vim/lsp/health.lua
index 34a6dd59ab..17f2a81139 100644
--- a/runtime/lua/vim/lsp/health.lua
+++ b/runtime/lua/vim/lsp/health.lua
@@ -215,6 +215,8 @@ 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[]
@@ -242,6 +244,16 @@ 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