Re: Change of Lisp syntax for "fancy" quotes in Emacs 27?

[Noam Postavsky <npostavs@users.sourceforge.net>]

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On Sun, Feb 4, 2018 at 12:37 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
>> Date: Sun, 4 Feb 2018 10:36:49 -0500
>>
>> > The middle line would require Emacs to do a fuzzy search for similar
>> > symbols, which may be too much.
>>
>> OCaml does this (but at compile time).  Do we have a way to delay the fuzzy search to the point when the error message is displayed?  Otherwise we'll pay the price of the search even if the error is then swallowed by a condition-case.
>
> Isn't this premature optimization?

I think the check fits nicely into command-error-default-function
though. Attaching a quick proof-of-concept (handles only a single
curved quote at the beginning of symbol name). We would want something
also for the byte-compiler.

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From c9d1e761cea56e94d9ad3d783c8ed7fcf448b082 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Sun, 4 Feb 2018 16:20:32 -0500
Subject: [PATCH v1] [sketch] Catch strange quotes on error time

* src/keyboard.c (Fcommand_error_default_function): Check for RIGHT
SINGLE QUOTATION MARK and give a more detailed message.  TODO: check
for other confusables.
* src/lread.c (read1): Don't signal error on strange quotes.
* src/eval.c (Fsetq): Pass full arglist in error data.  TODO: the same
for all the other Qwrong_number_of_arguments cases.
---
 src/eval.c     |  3 ++-
 src/keyboard.c | 20 ++++++++++++++++++++
 src/lread.c    |  7 -------
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/src/eval.c b/src/eval.c
index 7db4dbcf18..db61c0421f 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -507,7 +507,8 @@ DEFUN ("setq", Fsetq, Ssetq, 0, UNEVALLED, 0,
       Lisp_Object sym = XCAR (tail), lex_binding;
       tail = XCDR (tail);
       if (!CONSP (tail))
-	xsignal2 (Qwrong_number_of_arguments, Qsetq, make_number (nargs + 1));
+        xsignal3 (Qwrong_number_of_arguments, Qsetq,
+                  make_number (nargs + 1), args);
       Lisp_Object arg = XCAR (tail);
       tail = XCDR (tail);
       val = eval_sub (arg);
diff --git a/src/keyboard.c b/src/keyboard.c
index 4324991da4..24c5f66934 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -1047,6 +1047,26 @@ DEFUN ("command-error-default-function", Fcommand_error_default_function,
       bitch_at_user ();
 
       print_error_message (data, Qt, SSDATA (context), signal);
+
+      Lisp_Object errname = Fcar (data);
+      /* TODO: Add arglist to Qwrong_number_of_arguments errors, and
+         check those too.  */
+      if (EQ (errname, Qvoid_variable))
+        {
+          Lisp_Object void_symname = Fsymbol_name (Fnth (make_number (1), data));
+          if (SCHARS (void_symname) > 0 &&
+              /* TODO: check all confusables.  */
+              EQ (Faref (void_symname, make_number (0)), make_number (0x2019)))
+            {
+              Lisp_Object msg = CALLN
+                (Fformat_message,
+                 build_string ("\nSymbol has with `%c' (%s) at character 0,"
+                               " did you mean `%c' (%s)"),
+                 make_number (0x2019), build_string ("RIGHT SINGLE QUOTATION MARK"),
+                 make_number ('\''), build_string ("APOSTROPHE"));
+              Fprinc (msg, Qt);
+            }
+        }
     }
   return Qnil;
 }
diff --git a/src/lread.c b/src/lread.c
index 3b0a17c90b..ee08902f81 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -3470,13 +3470,6 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
 	    if (! NILP (result))
 	      return unbind_to (count, result);
 	  }
-        if (!quoted && multibyte)
-          {
-            int ch = STRING_CHAR ((unsigned char *) read_buffer);
-            if (confusable_symbol_character_p (ch))
-              xsignal2 (Qinvalid_read_syntax, build_string ("strange quote"),
-                        CALLN (Fstring, make_number (ch)));
-          }
 	{
 	  Lisp_Object result;
 	  ptrdiff_t nbytes = p - read_buffer;
-- 
2.11.0