Subject: Re: bug#33794: 26.1; electric-pair-mode breaks auto-newline minor mode of cc-mode

From: Beatrix Klebe <[email-masked]>
Date: Fri, 21 Dec 2018 14:06:34 -0500

Here's the link, I believe it was Stefan that answered it:
https://emacs.stackexchange.com/questions/2837/automatically-formatting-brackets/2853#2853

I have tried this with emacs -Q and it does not fix the issue, which
is as follows.

Ordinarily in cc-mode when you have auto-newline-mode activated, and
as far as I can tell, a cc-mode configuration that supports it, (which
csharp-mode contains), the following happens when opening a block
(pipe is the cursor):

void Main() {| // opening bracket is typed

becomes

void Main
{
    |

when c-toggle-auto-newline is activated. However, if you also want
your braces automatically paired, with electric-pair-mode, instead the
following occurs:

void Main() {| // opening bracket is typed

void Main() {|} // electric-pair-mode closes the open bracket, but
auto-newline-mode does not appear to do anything.

void Main() {
    |
} // user hits return, inserting the cursor at the correct indent
level, but leaving the opening brace where it is.

The ideal/desired behavior is:

void Main() {| // opening bracket is typed

void Main()
{
    |
} // user hits return key, electric-pair-mode pairs up the brackets,
and auto-newline-mode formats the braces correctly

It would also probably suffice to format with the newline before
hitting enter as well, although I think I prefer hitting enter to open
the block. I'm quite curious as to the internals of these formatting
systems and would be happy to help with a fix/feature if that would be
desired, I am mostly an OCaml programmer but C# is my day job and I've
just recently gotten deeper into Emacs Lisp.

On Fri, Dec 21, 2018 at 1:49 PM João Távora <[email-masked]> wrote:
>
> Beatrix Klebe <[email-masked]> writes:
>
> > I believe I saw your Stack Overflow answer about this while searching
> > for the solution. electric-layout-mode works with some quirks, such as
> > that if you put a space after parens in a function definition, the
> > space gets carried on to the newline with that method, which is a bit
> > annoying. What would be ideal, and what I'm looking for, is to get
> > auto-pairing of brackets with braces being placed where they should be
> > automatically and the insertion point getting put in between them at
> > the correct indent level, such as what happens with Visual Studio, or
> > Visual Studio Code, or several other editors with this functionality.
> > Perhaps it is not emacslike to have such behavior be totally
> > automated, but I am used to it and finds it decreases my ordinary
> > levels of frustration when working with verbose and imperative
> > languages. I am currently trying to write some insert specifiers for
> > smartparens to do this, but it is proving more difficult to find an
> > elegant solution than I had expected.
>
> It is quite emacslike (though maybe not activated by default): you just
> have to report the bugs to the Emacs developers as efficiently as
> possible.
>
> 1. Though Alan possibly has already, I still cannot understand the
>    original problem.  Can you start by describing what the buffer looked
>    like before, what you did, what it looked like afterwards, and what
>    you expected it to look like?  If possible start with a clean Emacs
>    -Q recpe.
>
> 2. I have experimented with nicer-playing like alternatives like
>    electric-layout-mode.  I came across a few quirks myself (though I'm
>    not sure if they are the same as yours). So I prepared a patch (in
>    branch scratch/fix-33794-extend-electric-layout-mode) and attached
>    it after the sig.
>
> After loading this patch, in a simple Emacs -Q the configuration:
>
>    (electric-pair-mode)
>    (electric-layout-mode)
>
>    (add-hook 'c-mode-hook
>           (lambda ()
>             (setq-local electric-layout-rules
>                         '((?\{ . after)
>                           (?\{ . after-stay)))))
>
> And, when visiting a C file, if I press `{' I get the expected
> pair+layout+indent behaviour.  Sor example opening a brace after
> int main () gives me:
>
>     int main () {
>         <cursor here>
>     }
>
> I, like Stefan, think cc-mode could/should set electric-layout-rules
> buffer-locally to reflect whatever c-style the user has selected.
>
> Thanks,
> João
>
> PS: Also, can you link to the the relevant to the stack overflow answer you
> mentioned?
>
> commit ab036bdedbb49ecc96d550b5e883e43bb03eaccc
> Author: JoÃ£o TÃ¡vora <[email-masked]>
> Date:   Fri Dec 21 18:00:08 2018 +0000
>
>     Extend electric-layout-mode to handle more complex layouts
>
>     Also, have it play nice with electric-pair-mode.
>
>     Multiple matching entries in `electric-layout-rules' are executed in
>     order of appearance.  When inserting a newline in the 'after-stay
>     rule, ensure electric-pair-open-newline-between-pairs is nil.
>
>     Arguably the logic behind electric-pair-open-newline-between-pairs
>     should be moved to electric-layout-mode, but the current rule-matching
>     engine doesn't allow for it.  The current solution seems to be good
>     enough for the situations reported in bug#33794.
>
>     * lisp/electric.el (electric-layout-rules): Adjust docstring.
>     (electric-layout-post-self-insert-function): Loop through rules.  Bind
>     electric-pair-open-newline-between-pairs to nil when handling
>     after-stay.
>
> diff --git a/lisp/electric.el b/lisp/electric.el
> index 6dbf46b80c..6a307a49b9 100644
> --- a/lisp/electric.el
> +++ b/lisp/electric.el
> @@ -370,38 +370,43 @@ electric-layout-rules
>
>  The symbols specify where in relation to CHAR the newline
>  character(s) should be inserted. `after-stay' means insert a
> -newline after CHAR but stay in the same place.")
> +newline after CHAR but stay in the same place.
> +
> +If multiple rules match, they are all executed in order of
> +appearance.")
>
>  (defun electric-layout-post-self-insert-function ()
> -  (let* ((rule (cdr (assq last-command-event electric-layout-rules)))
> -         pos)
> -    (when (and rule
> -               (setq pos (electric--after-char-pos))
> +  (let (pos)
> +    (when (and (setq pos (electric--after-char-pos))
>                 ;; Not in a string or comment.
>                 (not (nth 8 (save-excursion (syntax-ppss pos)))))
> -      (let ((end (point-marker))
> -            (sym (if (functionp rule) (funcall rule) rule)))
> -        (set-marker-insertion-type end (not (eq sym 'after-stay)))
> -        (goto-char pos)
> -        (pcase sym
> -          ;; FIXME: we used `newline' down here which called
> -          ;; self-insert-command and ran post-self-insert-hook recursively.
> -          ;; It happened to make electric-indent-mode work automatically with
> -          ;; electric-layout-mode (at the cost of re-indenting lines
> -          ;; multiple times), but I'm not sure it's what we want.
> -          ;;
> -          ;; FIXME: check eolp before inserting \n?
> -          ('before (goto-char (1- pos)) (skip-chars-backward " \t")
> -                   (unless (bolp) (insert "\n")))
> -          ('after  (insert "\n"))
> -          ('after-stay (save-excursion
> -                         (let ((electric-layout-rules nil))
> -                           (newline 1 t))))
> -          ('around (save-excursion
> -                     (goto-char (1- pos)) (skip-chars-backward " \t")
> -                     (unless (bolp) (insert "\n")))
> -                   (insert "\n")))      ; FIXME: check eolp before inserting \n?
> -        (goto-char end)))))
> +      (goto-char pos)
> +      (dolist (rule electric-layout-rules)
> +        (when (eq last-command-event (car rule))
> +          (let* ((end (point-marker))
> +                 (rule (cdr rule))
> +                 (sym (if (functionp rule) (funcall rule) rule)))
> +            (set-marker-insertion-type end (not (eq sym 'after-stay)))
> +            (pcase sym
> +              ;; FIXME: we used `newline' down here which called
> +              ;; self-insert-command and ran post-self-insert-hook recursively.
> +              ;; It happened to make electric-indent-mode work automatically with
> +              ;; electric-layout-mode (at the cost of re-indenting lines
> +              ;; multiple times), but I'm not sure it's what we want.
> +              ;;
> +              ;; FIXME: check eolp before inserting \n?
> +              ('before (goto-char (1- pos)) (skip-chars-backward " \t")
> +                       (unless (bolp) (insert "\n")))
> +              ('after  (insert "\n"))
> +              ('after-stay (save-excursion
> +                             (let ((electric-layout-rules nil)
> +                                   (electric-pair-open-newline-between-pairs nil))
> +                               (newline 1 t))))
> +              ('around (save-excursion
> +                         (goto-char (1- pos)) (skip-chars-backward " \t")
> +                         (unless (bolp) (insert "\n")))
> +                       (insert "\n")))      ; FIXME: check eolp before inserting \n?
> +            (goto-char end)))))))
>
>  (put 'electric-layout-post-self-insert-function 'priority  40)
>