bug#31676: 27.0.50; More helpful error message for unescaped character literals

[Philipp Stephani <p.stephani2@gmail.com>]

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Eli Zaretskii <eliz@gnu.org> schrieb am Fr., 8. Juni 2018 um 16:51 Uhr:

> > Date: Sat, 2 Jun 2018 12:00:26 +0200
> > Cc: 31676@debbugs.gnu.org
> >
> > Sounds reasonable, here's a patch.
> >
> > From 4bd8348753980be95dc4bcba47e52f7f79255fb6 Mon Sep 17 00:00:00 2001
> > From: Philipp Stephani <phst@google.com>
> > Date: Sat, 2 Jun 2018 11:59:02 +0200
> > Subject: [PATCH] Make warning about unescaped character literals more
> helpful.
> >
> > See Bug#31676.
> >
> > * src/lread.c (Flread_unescaped_character_literals_warning): New
> > defun.
> > (load_warn_unescaped_character_literals): Use it.
> > (syms_of_lread): Define new defun.  Unintern internal
> > variable, which is not used any more outside of lread.c
> >
> > * lisp/emacs-lisp/bytecomp.el (byte-compile-from-buffer): Use new
> > defun.
> >
> > * test/src/lread-tests.el (lread-tests--unescaped-char-literals):
> > test/lisp/emacs-lisp/bytecomp-tests.el
> > (bytecomp-tests--unescaped-char-literals): Adapt unit tests.
>
> Sounds okay, but can you tell why you implemented
> lread--unescaped-character-literals in C?  If that's because you need
> to call it from load_warn_unescaped_character_literals, then C
> functions can call Lisp functions with no problems, we have several
> examples of that in the sources.  AFAICT, the C implementation is just
> a "transliteration" of straightforward Lisp code, so it reads strange.
>

The function uses an uninterned variable, so it has to be in C. I think
that's slightly better than interning the variable and having some Lisp
function access it (the latter would have one additional internal symbol).

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