Is it possible to auto-save a file when focus is switch to another tab?

Question

I am not sure that this possible but I have I two splitted panes while using tmux inside iTerm2 and I am using emacs daemon. I am using iTerm's keybinding to switch between tabs.

One one of them emacs is open and on the another one shell is open.

---------------
|file  |$     |
|      |      |
|      |      |
---------------

I usually make a change on the file and switch to other tab (that is on shell) to run the test.

• During this whenever I switch to other tab is it possible for emacs to save the file automatically triggered by the iTerm's keybinding to switch between tabs without using C-x C-s?

• If not from the shell can I force emacs save all its open files right before running its tests?

Answer 1

The short answer is that Emacs running in a terminal cannot observe GUI events such as switching to another tab. If you want Emacs to observe GUI events, run a GUI Emacs.

(This may be possible using a companion program, but even so this would depend to some extent on the goodwill of iTerm2. If it's at all possible, it's not easy and may have side effects in conditions that you may or may not care about such as attaching Emacs windows to terminals provided by different terminal emulators.)

On the other hand, it's pretty easy to remotely ask Emacs to save. This assumes that you're running the Emacs server: either start Emacs with emacs --daemon or run (server-start) from your init file. To remotely ask Emacs to save all buffers, run the shell command

emacsclient -e '(save-some-buffers t)'

Answer 2

Take a look at after-focus-change-function. You can advise this function with an :before function to save all buffers. That's easily accomplished by using an anonymous function like:

(lambda () (save-some-buffers t))

like @alper suggested. You can use the advice-add function or the define-advice macro like so

(advice-add 'after-focus-change-function :before #'(lambda () (save-some-buffers t)))

or

(define-advice after-focus-change-function (:before ())
  (save-some-buffers t))

Answer 3

super-save-mode to saves the buffer automatically when focus moves away from it.

I do not use emacs in terminals, so I do not know if this works out of the box there, but I am pretty sure it can be configured to do what you want.