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

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

Am Sa., 9. Juni 2018 um 19:12 Uhr schrieb 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:
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>> > 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.
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> 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).

However, your point about the C function being strange is valid. I've
reimplemented it in Lisp now and pushed commit 0b4b380ce4 to master.