WebKit-GTK dependency in some GNOME applications: why not Gjs?

[Émeric MASCHINO <emeric maschino gmail com>]

[Please CC me, I'm not (yet?) subscribed to this list]

Hi,

If I understand correctly, Gjs or Seed provide JS implementation for
the GNOME project [1]. It seems that Seed is dead [2] and that many
GNOME components have adopted Gjs, including GNOME 3's most central
one: GNOME Shell.

I'm not familiar enough with the GNOME project, nor JS development
(I'm a C++ guy), so I'm probably missing the point, but how is it that
some GNOME applications have dependencies neither on Gjs, nor Seed,
but directly on WebKit-GTK? Namely, Sushi, Yelp, Evolution, Shotwell,
Empathy, GNOME-Online-Accounts (G-O-A) and Epiphany directly require
WebKit-GTK and GNOME-Contacts and Evolution-Data-Server indirectly
require WebKit-GTK if G-O-A is enabled [3].

I'm asking this because, although WebKit-GTK never worked on the ia64
arch (whereas Spidermonky do), WebKit-GTK >= 2.8 simply can't be built
on ia64 nowadays. This is blocking for GNOME >= 3.16 because of the
above-listed GNOME applications that now require an WebKit-GTK >= 2.8.
However, even if WebKit-GTK >= 2.8 could be built successfully on
ia64, GNOME applications based on WebKit-GTK would badly crash in the
end. I've summarized the situation in this Gentoo's BR [3], Gentoo
being the last (to my knowledge) Linux distribution supporting ia64.

So, questions are: is the WebKit-GTK dependency in some GNOME
applications expected? Why not depend on Gjs, as it seems that Gjs is
GNOME's default JS implementation?

Thanks,

     Émeric


[1] https://wiki.gnome.org/JavaScript
[2] https://mail.gnome.org/archives/javascript-list/2015-March/msg00002.html
[3] https://bugs.gentoo.org/show_bug.cgi?id=555504