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

[Basil L. Contovounesios]

Alan Mackenzie <acm@muc.de> writes:

> On Sun, May 12, 2019 at 22:45:09 +0100, Basil L. Contovounesios wrote:
>> Alan Mackenzie <acm@muc.de> writes:
>
>> > On Sat, May 11, 2019 at 20:34:51 +0100, Basil L. Contovounesios wrote:
>
>> >> Sorry if my question is completely naive or irrelevant (I haven't read
>> >> the discussion very carefully), but how does the command
>> >> c-context-line-break, which is described under "Making the <RET> key
>> >> indent the new line" in (info "(ccmode) Getting Started") relate to this
>> >> issue, if at all?
>
>> > c-context-line-break doesn't really have much to say in the matter.  The
>> > function is mainly about how to indent the _new_ line, and inserting
>> > various continuation markers.
>
>> > This bug is about trailing space in the _old_ line not getting removed
>> > on typing <CR>, about which c-context-line-break has nothing to say.
>
>> AFAICS c-context-line-break removes trailing space on the old line:
>
>> 0. emacs -Q
>> 1. C-x h C-w
>> 2. M-x c-mode RET
>> 3. int main() {
>> 4. RET RET
>
>> Line 2 now contains two trailing spaces.
>
>> 5. M-x c-context-line-break RET
>
>> Line 3 is now empty (has no trailing space).
>
>> Have I misunderstood something?
>
> Er, no.  You're right, c-context-line-break does indeed remove the
> trailing WS, at least on normal code lines.  Sorry about the mistake.
>
> But I don't think I've really understood how this observation fits in
> with the bug scenario.  The bug is about the current master's default
> binding of <CR> (namely newline) not removing the trailing whitespace
> from the line it's typed in.
>
> I think you might be suggesting binding c-context-line-break to <CR> in
> CC Mode as a workaround for the problem; or possibly using its ideas to
> code up a CC Mode version of newline.

(Or pointing users in its direction should they wish to configure this
behaviour themselves.)

> I still think the bug should be fixed in the Emacs core, so that other
> modes which want the old line to have trailing spaces removed, yet don't
> use electric-indent-mode, will just work.

Indeed, that would be nice.

Thanks,

-- 
Basil