Set Emacs to smart auto-line after a parentheses pair?

Question

I have electric-pair-mode on (which isn't really particularly relevant, as this could apply to any auto-pairing mode or even manual parens), but in a nutshell, I'd like it so that in the case I have:

function foo() {|}

(where | is the mark)

If I press enter, I would like to have it automatically go to

function foo() {
|
}

It would also mean that

function foo(|) {}

would become

function foo(
|
){}

I already have things to take care of the indentation, but I'm not sure how to say "if I'm inside any empty pair of matched parenthesis, when I press return, actually insert two new lines and put me at the first one".

Thanks!

Answer 1

Here is what I have in my init file, I got this from Magnar Sveen's .emacs.d

(defun new-line-dwim ()
  (interactive)
  (let ((break-open-pair (or (and (looking-back "{") (looking-at "}"))
                             (and (looking-back ">") (looking-at "<"))
                             (and (looking-back "(") (looking-at ")"))
                             (and (looking-back "\\[") (looking-at "\\]")))))
    (newline)
    (when break-open-pair
      (save-excursion
        (newline)
        (indent-for-tab-command)))
    (indent-for-tab-command)))

You can bind it to a key of your choice. I have bound it to M-RET but if you want, you can bind it to RET. The lines

(or (and (looking-back "{") (looking-at "}"))
    (and (looking-back ">") (looking-at "<"))
    (and (looking-back "(") (looking-at ")"))
    (and (looking-back "\\[") (looking-at "\\]")))

check if cursor is at {|}, [|], (|) or >|< (html).

Answer 2

You may also want to look into smartparens. Specifically, see the page on insertion hooks.

Here's the config I personally use:

(with-eval-after-load 'smartparens
  (sp-with-modes
      '(c++-mode objc-mode c-mode)
    (sp-local-pair "{" nil :post-handlers '(:add ("||\n[i]" "RET")))))

This has the added benefit of indenting the current line automatically as well. This can easily be generalized to more modes (using sp-pair for global pairs) and paren types (just duplicate the code), if you please.