string-width for emojis

[Evgeny Zajcev]

I'm experiencing a bin unexpected behaviour with "string-width".

If I evaluate

  (insert "ABCDEF\n"
          "\x2734\xfe0f -> "
          (format "%d" (string-width "\x2734\xfe0f")))

directly in the scratch buffer, I'll get

  ABCDEF
  ✴️ -> 2

as output.  However, if I evaluate

  (with-current-buffer (get-buffer-create "*help2*")
    (erase-buffer)
    (insert "ABCDEF\n"
            "\x2734\xfe0f -> "
            (format "%d" (string-width "\x2734\xfe0f")))
    (display-buffer (current-buffer)))

I'll get

  ABCDEF
  ✴️ -> 1

as output.

Documentation states, that "Width is measured by how many columns it occupies on the screen."  I see visually that ✴️ occupies approximately 2 columns (see screenshot at http://lgarc.narod.ru/pics/emacs-string-width.png)

What is the correct use of `string-width` to always get 2 as width for the "\x2734\xfe0f" ?

Thanks

--

lg