how to evaluate the "emoji support level" in given font?

[suzuki toshiya]

Hi,

Recently, fontconfig developers are discussing how to evaluate
"is this font supporting 'emoji' set sufficiently?". Is it possible
to design a subset of emoji to serve common use of emoji?

For detail about the discussion of fontconfig developers, please
refer the thread from:
https://lists.freedesktop.org/archives/fontconfig/2016-September/005830.html

* about fontconfig
fontconfig is a library which is widely used by Unix-like operating
systems to locate a (pathname of) font file, by the query with a few
typographic category (serif/sans-serif/monospace etc), script, and
language. fontconfig crawls the font files on the systems, and make
a database to respond such query. To guess the supported script and
language, basically fontconfig checks the coverage of the codepoints
with relevant glyph data. The coverage is compared with the orthography
database: for the case of CJK script, the coverage is compared with
GB 2312, Big5, HKSCS, JIS X 0208, KS X 1001 etc.

* emoji and fontconfig
At present, fontconfig developers are wondering how they can list the
codepoints to evaluate the query "this font support emoji?". The stable
subset of emoji would be the repertoire used by Japanese legacy cellular
phones, but (personally) I don't think it is still respected to design
some emoji fonts, as far as the developer is careful about the legacy
cellular phone users.

Is it possible to design a subset of emoji to serve common use of emoji?
Or, if such attempt (evaluate the support level of emoji by checking
some codepoints) is wrong, is there any good method to evaluate the
support level of emoji in given font?

Regards,
mpsuzuki