Since Ubuntu's sddm is hardcoded to use the Breeze theme, add postinst and prerm scripts which install the Lubuntu SDDM theme as the Breeze theme. Conflict against sddm-theme-breeze accordingly.

debian/changelog

@@ -1,6 +1,9 @@
 lubuntu-artwork (1.4) UNRELEASED; urgency=medium
 
   * Rename sddm-theme-lubuntu-chooser to sddm-theme-lubuntu.
+  * Since Ubuntu's sddm is hardcoded to use the Breeze theme, add postinst and
+    prerm scripts which install the Lubuntu SDDM theme as the Breeze theme.
+    Conflict against sddm-theme-breeze accordingly.
 
  -- Simon Quigley <tsimonq2@ubuntu.com>  Sat, 07 Jul 2018 16:09:18 -0500
 

debian/control

@@ -48,7 +48,7 @@ Package: sddm-theme-lubuntu
 Architecture: all
 Depends: ${misc:Depends}
 Recommends: sddm
-Conflicts: sddm-theme-lubuntu-chooser (<< 1.4)
+Conflicts: sddm-theme-lubuntu-chooser (<< 1.4), sddm-theme-breeze
 Replaces: sddm-theme-lubuntu-chooser (<< 1.4)
 Provides: sddm-theme
 Description: 'Lubuntu chooser' theme for SDDM X11 display manager

debian/sddm-theme-lubuntu.postinst

@@ -0,0 +1,12 @@
+#!/bin/sh
+set -e
+
+if [ "$1" = "configure" ] || [ "$1" = "abort-upgrade" ] || [ "$1" = "abort-remove" ]; then
+    update-alternatives --install \
+        /usr/share/sddm/themes/breeze \
+        breeze \
+        /usr/share/sddm/themes/lubuntu 20
+fi
+
+# Tag to allow some debhelper commands to inject relevant code
+#DEBHELPER#

debian/sddm-theme-lubuntu.prerm

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -e
+
+if [ "$1" = "remove" ] || [ "$1" = "deconfigure" ]; then
+    update-alternatives --remove \
+        breeze \
+        /usr/share/sddm/themes/lubuntu
+fi
+
+# Tag to allow some debhelper commands to inject relevant code
+#DEBHELPER#