Apply lsp client filtering before filter callback

templates/nvim/lua/lsp.lua.j2

@@ -176,7 +176,7 @@ vim.diagnostic.config {
   },
 }
 
-local enable_formatting = os.getenv("ENABLE_FORMATTING", False)
+local enable_formatting = os.getenv("ENABLE_FORMATTING")
 
 -- format buffers before saving for specific LSPs
 if (enable_formatting) then
@@ -188,10 +188,29 @@ if (enable_formatting) then
       vim.api.nvim_create_autocmd('BufWritePre', {
         buffer = args.buf,
         callback = function()
+          local formatting_clients = vim.lsp.get_clients {
+            bufnr = args.buf,
+            method = 'textDocument/formatting'
+          }
+
+          local filtered_clients = {}
+
+          for _, client in pairs(formatting_clients) do
+            if vim.list_contains(excluded_clients, client.name) then
+              goto skip
+            end
+
+            table.insert(filtered_clients, client.name)
+            ::skip::
+          end
+
+          if #filtered_clients == 0 then
+            return
+          end
+
           vim.lsp.buf.format {
             filter = function(client)
-              if not client.supports_method('textDocument/formatting') then return end
-              return not vim.list_contains(excluded_clients, client.name)
+              return vim.list_contains(filtered_clients, client.name)
             end,
             async = false,
             id = args.data.client_id