Merge remote-tracking branch 'toabctl/focal-backport-optional-allow-core-snaps' into ubuntu/focal

* toabctl/focal-backport-optional-allow-core-snaps:
  Update debian/changelog
  Allow to install core snap optionally

debian/changelog

@@ -1,8 +1,14 @@
 livecd-rootfs (2.664.41) UNRELEASED; urgency=medium
 
-  * Split UEFI image out of `disk-image` series file into `disk-image-uefi` (LP: #1961760) 
+  [ Ivan Kapelyukhin ]
+  * Split UEFI image out of `disk-image` series file into
+    `disk-image-uefi`. (LP: #1961760)
 
- -- Ivan Kapelyukhin <ivan.kapelyukhin@canonical.com>  Thu, 03 Mar 2022 15:57:13 +0100
+  [ Thomas Bechtold ]
+  * Optionally (when ALLOW_CORE_SNAP env var is set) allow to install
+    core snap. Still needed by some CPC projects. (LP: #1964303)
+
+ -- Thomas Bechtold <thomas.bechtold@canonical.com>  Fri, 04 Mar 2022 14:00:16 +0100
 
 livecd-rootfs (2.664.40) focal; urgency=medium
 

live-build/functions

@@ -562,8 +562,13 @@ _snap_preseed() {
                 # If snap info does not list a base the default is 'core'
                 # which is now an error to use.
                 if [ -z "$core_snap" ]; then
-                    echo "Legacy snap with no base declaration found, refusing to install 'core' snap"
-                    exit 1
+		    if [ -z "$ALLOW_CORE_SNAP" ]; then
+			echo "Legacy snap with no base declaration found, refusing to install 'core' snap"
+			exit 1
+		    else
+			echo "Legacy snap with no base declaration found, but \$ALLOW_CORE_SNAP set. continue (but FIX YOUR SNAPS!)"
+			core_snap=${core_snap:-core}
+		    fi
                 fi
 
                 _snap_preseed $CHROOT_ROOT $core_snap stable