Bug#1070706: gtk4 udeb has unsatisfiable dependencies

[Simon McVittie]

Control: tags -1 + d-i
Control: found -1 4.12.5+ds-3
Control: retitle -1 gtk4 udeb has unsatisfiable dependencies
Control: clone -1 -2
Control: retitle -2 libvte-2.91-0-udeb depends on both GTK 3 and GTK 4
Control: reassign -2 src:vte2.91 0.75.92-1

On Tue, 07 May 2024 at 15:44:02 +0100, Peter Michael Green wrote:
> According to britney, gtk4's udebs are uninstallable.

gtk4 is not yet used by debian-installer (which is still on GTK 2)
so the udeb is not actually necessary, and one workaround would be to
disable it entirely (but then we'd have to put GTK 4 through NEW again
if we are ever able to upgrade d-i to it).

The version in testing, 4.12.5+ds-3, has the same dependencies, so this
is not a regression. Is this requirement newly enforced by britney?

I think a large part of the problem is that when GTK 4 support was added
to src:vte2.91, both the GTK 3 and GTK 4 versions were put into the same
udeb package, libvte-2.91-0-udeb, instead of giving the GTK 4 version
its own udeb. However, I'm unsure how that change got into testing -
if britney is enforcing installability of udebs, I would have expected
that the updated libvte-2.91-0-udeb would have been newly-uninstallable,
preventing its migration?

It seems most realistic that d-i in Debian 13 will depend on GTK 3 if
someone finds the time to do the necessary porting and testing, or stay
on GTK 2 if not, so libvte-2.91-0-udeb should become a udeb version of
only libvte-2.91-0 (i.e. GTK 3 only) as it was in Debian 12, and drop
its GTK 4 parts. That would mean that GTK 4 would no longer be regressing
the installability of libvte-2.91-0-udeb.

If there is a serious attempt to get d-i using GTK *4*, then that would
require a new libvte-2.91-gtk4-0-udeb. However, GTK 4's threading model
is definitely incompatible with the current design of cdebconf-gtk (it
calls into GTK from more than one thread, which is discouraged in GTK
3 and not allowed at all in GTK 4), so a prerequisite for that would
be to move all of cdebconf-gtk's GTK interactions onto one thread,
with message-passing between that thread and the cdebconf thread.

I'm also unsure how GTK 4 can possibly have caused libvte-2.91-0-udeb's
installability to regress anyway, because libvte-2.91-0-udeb in testing
depends on liblz4-1, which does not have a corresponding udeb. That
will need fixing (by adding a liblz4-1-udeb, or linking it statically,
or allowing .deb libraries to satisfy udebs' dependencies) if we ever
want a GTK 3 or later installer.

Making the GTK 4 udeb installable looks like a significant task. It depends
on:

OK - fontconfig-udeb (>= 2.15.0),
OK - libc6-udeb (>= 2.37),
!! - libcairo-script-interpreter2 (>= 1.18.0),
OK - libcairo2-udeb (>= 1.18.0),
OK - libepoxy0-udeb (>= 1.5.4),
OK - libfribidi0-udeb (>= 1.0.13),
OK - libgdk-pixbuf-2.0-0-udeb (>= 2.42.10+dfsg),
OK - libglib2.0-udeb (>= 2.78.4),
!! - libgraphene-1.0-0 (>= 1.10.8),
OK - libharfbuzz0-udeb (>= 8.3.0),
!! - libjpeg62-turbo (>= 1:2.1.5),
OK - libpango1.0-udeb (>= 1.52.1+ds),
OK - libpng16-16t64-udeb (>= 1.6.2),
!! - libtiff6 (>= 4.5.1+git230720),
OK - libx11-6-udeb (>= 2:1.6.0),
OK - libxcursor1-udeb (>> 1.1.2),
!! - libxdamage1 (>= 1:1.1),
OK - libxext6-udeb (>= 2:1.3.0),
OK - libxfixes3-udeb (>= 1:5.0),
OK - libxi6-udeb (>= 2:1.6.99.1),
OK - libxinerama1-udeb (>= 2:1.1.4),
OK - libxrandr2-udeb (>= 2:1.5)

cairo has a udeb, but it doesn't include the equivalent of
libcairo-script-interpreter2. It might be possible to disable the GTK
features that rely on that library? Or it might be possible to add the
script interpreter to the udeb?

graphene does not have udebs at all, and I think it's a mandatory
dependency for GTK 4, so if we ever want a GTK-4-based d-i, there is
no avoiding adding a graphene udeb.

libjpeg-turbo, tiff and libxdamage are in the same situation as graphene
(these were optional in GTK 3 but are required in GTK 4). Unlike graphene,
these are not maintained by the GNOME team, so we cannot unilaterally
add udebs to them.

    smcv