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

[Dima Kogan]

Hi.

I'm seeing a regression introduced in 2019/01 by an update meant to make
electric-pair-mode and electric-layout-mode play nicely:

  
http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=fd943124439b7644392919bca8bc2a77e6316d92

Recipe:

1. 'emacs -Q' with any emacs more recent than that patch

2. Open up tst.c that contains this:

int main(int argc, char* argv[])
{
    return 0;
}


3. Move the point to the beginning of the line containing "return 0"

4. RET RET RET RET RET

Now there're a bunch of new lines between the { and the "return 0", as
expected. But these lines aren't empty: they contain the initial
indentation whitespace. This whitespace shouldn't be there; and it
wasn't there prior to this patch.

Thanks for working on emacs!