fix(formatting): show message when it fails

Shows error messages for well defined errors, but we don't receive
any signal that it failed for a plugin being missing, unfortunately.

Closes #463

lib/next_ls.ex

@@ -559,8 +559,16 @@ defmodule NextLS do
 
                 {:reply, nil, lsp}
 
-              _ ->
-                NextLS.Logger.warning(lsp.assigns.logger, "Failed to format the file: #{uri}")
+              e ->
+                case e do
+                  {:ok, {:badrpc, {:EXIT, {%{description: description, file: file}, _stacktrace}}}} ->
+                    NextLS.Logger.show_message(lsp.assigns.logger, :error, "Failed to format #{file}: #{description}")
+                    NextLS.Logger.warning(lsp.assigns.logger, "Failed to format #{file}: #{description}")
+
+                  _ ->
+                    NextLS.Logger.show_message(lsp.assigns.logger, :error, "Failed to format #{uri}")
+                    NextLS.Logger.warning(lsp.assigns.logger, "Failed to format #{uri}")
+                end
 
                 {:reply, nil, lsp}
             end

test/next_ls_test.exs

@@ -186,6 +186,12 @@ defmodule NextLSTest do
     }
 
     assert_result 2, nil
+
+    assert_notification "window/showMessage", %{
+      "message" =>
+        "Failed to format /home/mitchell/src/next-ls/tmp/NextLSTest/test-formatting-gracefully-handles-files-with-syntax-errors-375a6619/my_proj/lib/foo/bar.ex: missing terminator: end",
+      "type" => 1
+    }
   end
 
   test "workspace symbols", %{client: client, cwd: cwd} = context do