Enable formatting on save

Requires `ENABLE_FORMATTING` to be set

templates/nvim/lua/lsp.lua.j2

@@ -156,3 +156,28 @@ vim.diagnostic.config({
     border = border
   },
 })
+
+local enable_formatting = os.getenv("ENABLE_FORMATTING", False)
+
+-- format buffers before saving for specific LSPs
+if (enable_formatting) then
+  local excluded_clients = { 'pyright' }
+
+  vim.api.nvim_create_autocmd('LspAttach', {
+    group = vim.api.nvim_create_augroup('lsp', { clear = true }),
+    callback = function(args)
+      vim.api.nvim_create_autocmd('BufWritePre', {
+        buffer = args.buf,
+        callback = function()
+          vim.lsp.buf.format {
+            filter = function(client)
+              return not vim.list_contains(excluded_clients, client.name)
+            end,
+            async = false,
+            id = args.data.client_id
+          }
+        end,
+      })
+    end
+  })
+end