bug#35254: 27.0.50; cc-mode/electric-pair-mode/electric-layout-mode: bad trailing whitespace behavior in cc-mode

[Alan Mackenzie <acm@muc.de>]

Hello, Stefan.

On Mon, May 13, 2019 at 19:32:49 -0400, Stefan Monnier wrote:
> >> Electric indent mode's post-self-insert hook entry has 3 effects:

> >> 1. Indent the previous line.
> >> 2. Remove trailing whitespace from the previous line.
> >> 3. Indent the current line (when at beginning of line).

> Note that `newline` itself already does some subset of 2 (before running
> electric-indent's post-self-insert hook).

> > I interpret the problem a little differently.
> > electric-indent-post-self-insert-function, when electric-indent-inhibit
> > is set, is inhibiting actions which are not really part of electric
> > indentation, in particular action 2 (above).  This is the heart of the
> > bug.  The following patch fixes the bug.  It would need tidying up before
> > being committed:

> I haven't followed enough of the discussion to understand why that might
> cause a bug.

The bug is, type lots of <CR>s in a row; the indentation WS isn't
getting removed from the blank lines.  Currently electric-indent-inhibit
is inhibiting this removal.

> > diff --git a/lisp/electric.el b/lisp/electric.el
> > index 07da2f1d9e..15a42930c1 100644
> > --- a/lisp/electric.el
> > +++ b/lisp/electric.el
> > @@ -282,9 +282,15 @@ electric-indent-post-self-insert-function
> >                    (condition-case-unless-debug ()
> >                        (indent-according-to-mode)
> >                      (error (throw 'indent-error nil)))
> > -                  ;; The goal here will be to remove the trailing
> > -                  ;; whitespace after reindentation of the previous line
> > -                  ;; because that may have (re)introduced it.
> > +                  )
> > +                (unless (memq indent-line-function
> > +                              electric-indent-functions-without-reindent)
> > +                  ;; The goal here will be to remove the indentation
> > +                  ;; whitespace from an otherwise blank line after
> > +                  ;; typing <CR> twice in succession.  Also to remove
> > +                  ;; trailing whitespace after reindentation of the
> > +                  ;; previous line because that may have
> > +                  ;; (re)introduced it.
> >                    (goto-char before)
> >                    ;; We were at EOL in marker `before' before the call
> >                    ;; to `indent-according-to-mode' but after we may

> I don't understand why you distinguish

>     electric-indent-inhibit

> from

>     (memq indent-line-function
>           electric-indent-functions-without-reindent)

It was quite late when I worked out the patch.  I just did it
mechanically, to get the discussion moving.

> When I introduced these, electric-indent-functions-without-reindent was
> only meant to paper over those pre-existing cases that don't set
> electric-indent-inhibit.

> So, I'd suggest an even simpler patch which just closes the `unless`
> earlier.  Would that work?

Probably.  Maybe João should check this, once he's fully back with us.

>         Stefan


> diff --git a/lisp/electric.el b/lisp/electric.el
> index 07da2f1d9e..beb3348755 100644
> --- a/lisp/electric.el
> +++ b/lisp/electric.el
> @@ -281,7 +281,7 @@ electric-indent-post-self-insert-function
>                    (goto-char before)
>                    (condition-case-unless-debug ()
>                        (indent-according-to-mode)
> -                    (error (throw 'indent-error nil)))
> +                    (error (throw 'indent-error nil))))
>                    ;; The goal here will be to remove the trailing
>                    ;; whitespace after reindentation of the previous line
>                    ;; because that may have (re)introduced it.
> @@ -290,7 +290,7 @@ electric-indent-post-self-insert-function
>                    ;; to `indent-according-to-mode' but after we may
>                    ;; not be (Bug#15767).
>                    (when (and (eolp))
> -                    (delete-horizontal-space t))))))
> +                    (delete-horizontal-space t)))))
>            (unless (and electric-indent-inhibit
>                         (not at-newline))
>              (condition-case-unless-debug ()

-- 
Alan Mackenzie (Nuremberg, Germany).