bug#63731: [PATCH] Support Emoji Variation Sequence 16 (FE0F) where appropriate

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Fri, 26 May 2023 15:06:40 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Robert Pluim <rpluim@gmail.com>
    >> 
    >> Composition is done for 1f44d+fe0f, but I suspect that with the current
    >> setup, composition is called again for FE0F, which results in the box
    >> glyph. With the second patch we will only do backwards looking composition
    >> for FE0F

    Eli> OK, then I think we should install this on the emacs-29 branch.

    >> Youʼre right, thereʼs no forward looking regexp, only a backwards one
    >> and a no-regexp. But itʼs undeniable that:
    >> 
    >> [nil 0 compose-gstring-for-graphic]
    >> 
    >> causes the issue. Iʼve never been clear on the semantics of that.

    Eli> It has special support in compose-gstring-for-graphic, see there.  The
    Eli> doc string also says a few words about that.  We use this, e.g., in
    Eli> describe-char display, where we sometimes need to show a single
    Eli> combining character with no base character to combine it with.  I
    Eli> think this is only relevant for accents and other such combining
    Eli> characters, not for VS-n.

OK

    Eli> What does this issue mean for the other VS-n characters, though?
    Eli> Should we perhaps install something similar for them as well?

For VS-15 maybe? The following gets me text-presentation composition
with CHAR+FE0E and emoji-presentation with CHAR+FE0F

diff --git a/lisp/composite.el b/lisp/composite.el
index fb8b76114f4..ada35010146 100644
--- a/lisp/composite.el
+++ b/lisp/composite.el
@@ -762,6 +762,11 @@ compose-gstring-for-dotted-circle
 	 (if (memq val '(Mn Mc Me))
 	     (set-char-table-range composition-function-table key elt)))
      unicode-category-table))
+  ;; for Emoji presentation selector
+  (set-char-table-range
+   composition-function-table
+   '(#xFE0E . #xFE0F)
+    `([,(purecopy "\\c.[\ufe0f\ufe0e]") 1 compose-gstring-for-graphic]))
   ;; for dotted-circle
   (aset composition-function-table #x25CC
 	`([,(purecopy ".\\c^") 0 compose-gstring-for-dotted-circle]))
@@ -861,7 +866,7 @@ compose-gstring-for-variation-glyph
 ;; handled in font_range, we end up choosing the Emoji presentation
 ;; rather than the Text presentation.
 (let ((elt '([".." 1 compose-gstring-for-variation-glyph])))
-  (set-char-table-range composition-function-table '(#xFE00 . #xFE0E) elt)
+  (set-char-table-range composition-function-table '(#xFE00 . #xFE0D) elt)
   (set-char-table-range composition-function-table '(#xE0100 . #xE01EF) elt))
 
 (defun auto-compose-chars (func from to font-object string direction)

although perhaps we could have both `compose-gstring-for-graphic' and
`compose-gstring-for-variation-glyph' for FE0E

Robert
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