feat(mbyte): support extended grapheme clusters including more emoji

Use the grapheme break algorithm from utf8proc to support grapheme
clusters from recent unicode versions.

Handle variant selector VS16 turning some codepoints into double-width
emoji. This means we need to use ptr2cells rather than char2cells when
possible.

1 files changed, 22 insertions, 0 deletions

diff --git a/test/functional/api/vim_spec.lua b/test/functional/api/vim_spec.lua
index 4210b7ecf0..074d3ac0a3 100644
--- a/test/functional/api/vim_spec.lua
+++ b/test/functional/api/vim_spec.lua
@@ -1435,6 +1435,28 @@ describe('API', function()
     it('cannot handle NULs', function()
       eq(0, api.nvim_strwidth('\0abc'))
     end)
+
+    it('can handle emoji with variant selectors and ZWJ', function()
+      local selector = '❤️'
+      eq(2, fn.strchars(selector))
+      eq(1, fn.strcharlen(selector))
+      eq(2, api.nvim_strwidth(selector))
+
+      local no_selector = '❤'
+      eq(1, fn.strchars(no_selector))
+      eq(1, fn.strcharlen(no_selector))
+      eq(1, api.nvim_strwidth(no_selector))
+
+      local selector_zwj_selector = '🏳️‍⚧️'
+      eq(5, fn.strchars(selector_zwj_selector))
+      eq(1, fn.strcharlen(selector_zwj_selector))
+      eq(2, api.nvim_strwidth(selector_zwj_selector))
+
+      local emoji_zwj_emoji = '🧑‍🌾'
+      eq(3, fn.strchars(emoji_zwj_emoji))
+      eq(1, fn.strcharlen(emoji_zwj_emoji))
+      eq(2, api.nvim_strwidth(emoji_zwj_emoji))
+    end)
   end)
 
   describe('nvim_get_current_line, nvim_set_current_line', function()