One thing I’ve missed since switching to fish is a multi-line prompt. If your prompt has newlines in it, they’re stripped out when the prompt is rendered on-screen.

First things first: here’s the patch.

  for( i=0; i<al_get_count( &prompt_list); i++ )
  {
    sb_append( &data->prompt_buff, (wchar_t *)al_get( &prompt_list, i ) );
+     if (i + 1 < al_get_count( &prompt_list))
+     {
+       sb_append( &data->prompt_buff, L"\n" );
+     }
  }

  al_foreach( &prompt_list, &free );

The reason the newlines are removed arises from the way fish runs subcommands. Rendering the prompt is a call to the fish_prompt function, which in turn runs other subcommands like whoami, pwd and git ls-files, depending what you have in your prompt.

When fish receives fish_prompt’s output, it splits on \n and stores each line in an array, specifically an array_list_t. When the output is reassembled by exec_prompt() for output to the terminal, however, it joins the lines in the array (that’s prompt_list in the patch above) back together without any join token, so the line separation is gone.

My patch adds a \n after every line but the last, so that the newlines in the original un-split output from fish_prompt are re-inserted for rendering.