As announced in #1148038, new upstream releases of WebKitGTK no longer
support big-endian architectures.

swt4-gtk currently builds an Architecture: any package,
libswt-webkit-gtk-4-jni, which Depends on WebKitGTK libraries. Please
limit building of this package to little-endian architectures, so that
we can remove its old s390x binaries without them coming back (and being
uninstallable) in the next upload.

One way to do this would be something like (untested)

 Package: libswt-webkit-gtk-4-jni
-Architecture: any
+Architecture: amd64 arm64 armhf i386 loong64 ppc64el riscv64
 Depends: libswt-gtk-4-jni (= ${binary:Version}), libwebkit2gtk-4.1-0, ${shlibs:Depends}, ${misc:Depends}

Or the package could be disabled on big-endian architectures by
something like this in debian/rules (again untested)

ifneq ($(DEB_HOST_ARCH_ENDIAN),little)
dh_options += -Nlibswt-webkit-gtk-4-jni
endif

and then passing $(dh_options) to all dh invocations.

This will make two packages (biglybt and davmail) uninstallable on
s390x, but that seems harmless.

    smcv

The other way this could be handled, if not by disabling this one binary
package, would be to remove src:swt4-gtk and everything that depends on
it from s390x.

I believe that would mean removing binaries from these source packages
from s390x:

libjogl2-java
openjfx
scilab
swt4-gtk

resulting in these Architecture: all packages becoming unbuildable on s390x:

biglybt
controlsfx
eclipse-equinox
eclipse-jdt-debug
eclipse-jdt-ui
eclipse-linuxtools
eclipse-platform
eclipse-platform-ui
eclipse-remote
eclipse-swtchart
eclipse-wtp
equinox-p2
freecol
insubstantial
ipscan
jftp
king
libiscwt-java
libmiglayout-java
mediathekview
nattable
pdfsam
piccolo
stegosuite
swtchart
triplea
tuxguitar

That's a somewhat larger impact on the software available on s390x, but
has the advantage of not requiring packaging changes in src:swt4-gtk.

The latest webkit2gtk security advisory lists around 200 CVEs, so I
think continuing to hold it back to 2.52.x for the benefit of an
architecture where GUIs aren't normally run would be doing a disservice
to our users, and it might be time to start removing these packages from
s390x? They can always come back later if the swt4-gtk packaging is
updated.

Thanks,
     smcv