bug#33913: 26.1; Optionally not font-lock newline char when `comment-end' = ""

[Alan Mackenzie]

Hello, Drew.

In article <mailman.6534.1546123809.1284.bug-gnu-emacs@gnu.org> you wrote:
> See https://emacs.stackexchange.com/q/46808/105.

> Please consider letting users easily (e.g. user option) not highlight a
> newline character when it ends a comment, such as in Lisp.

OK, let's consider it.  The comment delimiters in Emacs are considered
part of the comment, and fontified with it.  In fact, I believe they get
font-lock-comment-delimiter-face.

It is open to the user to customize f-l-comment-delimiter-face not to
inherit from f-l-comment-face, but instead to have a neutral effect.

> The effect should be to highlight only the chars of the line, starting
> with `comment-start', up to but not including the newline char.

So the starting and stopping delimiters of a comment should get different
faces.  Hmmm.  Why?

One way to get this would be to introduce
font-lock-comment-terminator-face, inheriting by default from one of the
two existing comment faces.

> (I never would have noticed how annoying the default behavior is if I
> hadn't tried putting a background color on comments, as the OP did.  I
> don't even think it should be the default behavior to highlight the
> newline char.)

If the OP doesn't want the terminators fontified, why does he want the
comment openers fontified?  This seems a bit inconsistent.  I mean, if a
string's being fontified, you'd want either both of the "s (as Emacs
does) or neither of them (XEmacs) to get string face.  Why are comments
different?

> In GNU Emacs 26.1 (build 1, x86_64-w64-mingw32)
>  of 2018-05-30
> Repository revision: 07f8f9bc5a51f5aa94eb099f3e15fbe0c20ea1ea
> Windowing system distributor `Microsoft Corp.', version 10.0.16299
> Configured using:
>  `configure --without-dbus --host=x86_64-w64-mingw32
>  --without-compress-install 'CFLAGS=-O2 -static -g3''

-- 
Alan Mackenzie (Nuremberg, Germany).