Do not look for a base snap on snaps of type base, because recursive dependencies are not allowed for snaps. LP: #1957123.

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (2.750) UNRELEASED; urgency=medium
+
+  * Do not look for a base snap on snaps of type base, because recursive
+    dependencies are not allowed for snaps.  LP: #1957123.
+
+ -- Steve Langasek <steve.langasek@ubuntu.com>  Tue, 11 Jan 2022 15:38:05 -0800
+
 livecd-rootfs (2.749) jammy; urgency=medium
 
   [ Heinrich Schuchardt ]

live-build/functions

@@ -592,12 +592,16 @@ _snap_preseed() {
                 exit 1
             fi
 
-            local core_snap=$(echo "$snap_info" | grep '^base:' | awk '{print $2}')
+            local snap_type=$(echo "$snap_info" | awk '/^type:/ { print $2 }')
 
-            # If snap info does not list a base use 'core'
-            core_snap=${core_snap:-core}
+            if [ "$snap_type" != base ]; then
+                local core_snap=$(echo "$snap_info" | grep '^base:' | awk '{print $2}')
 
-            _snap_preseed $CHROOT_ROOT $core_snap stable
+                # If snap info does not list a base use 'core'
+                core_snap=${core_snap:-core}
+
+                _snap_preseed $CHROOT_ROOT $core_snap stable
+            fi
             ;;
     esac