Subject: char-syntax differs in interpreter and bytecode

From: Mattias Engdegård <[email-masked]>
Date: Fri, 14 Jan 2022 17:43:00 +0100

Fchar_syntax and the bytecode Bchar_syntax differ:

Fchar_syntax calls SETUP_BUFFER_SYNTAX_TABLE. Bchar_syntax does not.
Bchar_syntax converts arguments to multibyte. Fchar_syntax does not.

The last property can be used to get different behaviour:

(let ((cs (byte-compile (lambda (x) (char-syntax x)))))
  (with-temp-buffer
    (let ((st (make-syntax-table)))
      (set-buffer-multibyte nil)
      (modify-syntax-entry 128 "_" st)
      (set-syntax-table st)
      (list (funcall cs 128) (char-syntax 128)))))
-> (119 95)

Not sure how to expose the presence or absence of SETUP_BUFFER_SYNTAX_TABLE. Suggestions?

And, most importantly, what would be the correct code?

(I suppose char-syntax is rare enough that we could call Fchar_syntax from Bchar_syntax and thus avoid any future divergence.)