Comment 6 for bug 1844158

Failure appears to be vala-related:

make[2]: Entering directory '/builddir/build/BUILD/libunity-7.1.4/src'
/usr/bin/valac -C -H unity.h -d . --gir=Unity-7.0.gir --library unity --internal-vapi=unity-internal.vapi --internal-header=unity-internal.h --target-glib=2.32 --thread --use-header --vapidir ../vapi --vapidir ../protocol --vapidir . --pkg unity-protocol --pkg config --pkg unity-trace --pkg glib-2.0 --pkg gmodule-2.0 --pkg gobject-2.0 --pkg gio-2.0 --pkg gio-unix-2.0 --pkg dee-1.0 --pkg Dbusmenu-0.4 unity-appinfo-manager.vala unity-icon.vala unity-inspector.vala unity-io.vala unity-launcher.vala unity-category.vala unity-filters.vala unity-preferences-manager.vala unity-merge-strategy.vala unity-models.vala unity-search.vala unity-synchronizer.vala unity-previews.vala unity-result-activation.vala unity-scope-interface.vala unity-scope-dbus-connector.vala unity-scope-dbus-impl.vala unity-scope-channel.vala unity-deprecated-scope.vala unity-deprecated-scope-impl.vala unity-aggregator-scope.vala unity-aggregator-scope-private.vala unity-master-scope.vala unity-simple-scope.vala unity-scope-loader.vala unity-scope-tracker.vala unity-sound-menu.vala unity-sound-menu-mpris.vala unity-utils.vala
Command-line option `--thread` is deprecated and will be ignored
Compilation failed: 2 error(s), 0 warning(s)
BUILDSTDERR: unity-deprecated-scope.vala:64.3-64.28: error: Creation method of abstract class cannot be public.
BUILDSTDERR: public DeprecatedScopeBase (string dbus_path_, string id_)
BUILDSTDERR: ^^^^^^^^^^^^^^^^^^^^^^^^^^
BUILDSTDERR: unity-aggregator-scope.vala:54.3-54.24: error: Creation method of abstract class cannot be public.
BUILDSTDERR: public AggregatorScope (string dbus_path_, string id_, MergeMode merge_mode = AggregatorScope.MergeMode.OWNER_SCOPE, bool proxy_filter_hints = false)
BUILDSTDERR: ^^^^^^^^^^^^^^^^^^^^^^
BUILDSTDERR: make[2]: *** [Makefile:1389: libunity_la_vala.stamp] Error 1
make[2]: Leaving directory '/builddir/build/BUILD/libunity-7.1.4/src'
BUILDSTDERR: make[1]: *** [Makefile:571: all-recursive] Error 1