How can I make Vim autosave files when it loses focus?

Question

I'm used to my editors autosaving files when they lose focus. I recently switched to MacVim, and I can't recreate that behavior. I tried this:

autocmd BufLeave,FocusLost * wall 

but if a buffer is unnamed when the window or MacVim loses focus, I get an error like the following:

Error detected while processing BufLeave Auto commands for "*": E141: No file name for buffer 1 

I'm confused, because :wall's documentation says:

Write all changed buffers.  Buffers without a file name or which are readonly are not written. 

so I'd expect it to skip unnamed buffers. Is there a better way to do this?

Edit:

I'm pretty sure that the better way to do what I intended by using BufLeave -- saving buffers when I switch between them, so I don't get "No write since last change" -- is to set 'autowriteall'. The question still stands for when MacVim loses focus to other applications (FocusLost).

Answer 1

You don’t care about errors in those circumstances since there is nothing you can reasonably do about them anyway – especially when losing focus. So just swallow them:

autocmd BufLeave,FocusLost * silent! wall 

Much simpler than an elaborate dance to figure out where there would be an error in order to avoid it.