ShadowedVolHelper works if all subvols are deleted

src/lib/storage/shadowed_vol_helper.rb

@@ -134,9 +134,11 @@ def restore_aborted_subvols(target_part)
         name = subvol["name"]
         log.info "Restore subvol #{name}?"
         log.debug "subvol: #{subvol}"
-        existing_subvol = target_part["subvol"].detect { |s| s["name"] == name}
+        subvols = target_part["subvol"] || []
+        existing_subvol = subvols.detect { |s| s["name"] == name}
         if existing_subvol.nil?
           log.info "Restoring subvol"
+          target_part["subvol"] ||= []
           target_part["subvol"] << subvol
         elsif existing_subvol["delete"]
           log.info "Rejecting subvol deletion"

test/lib/storage_shadowed_vol_helper_test.rb

@@ -84,6 +84,29 @@ def update_partition(target_map, path, new_part, clean_deleted: false)
             subvol = find_subvol(second_root, "@/boot/grub2/i386-pc")
             expect(subvol).to be_nil
           end
+
+          # See bsc#1008740
+          context "if all the other subvolumes have been deleted" do
+            before do
+              # If all the subvolumes are deleted (not the same that 'marked for
+              # deletion'), the value for 'subvol' becomes nil (not empty)
+              root = find_partition(target_map, "/")
+              root.delete("subvol")
+            end
+
+            it "does not raise an exception" do
+              expect { helper.root_partition(target_map: target_map) }
+                .to_not raise_error
+            end
+
+            it "restores only the corresponding subvolumes" do
+              second_root = helper.root_partition(target_map: target_map)
+              subvolumes = second_root["subvol"].reject { |s| s["delete"] }
+              expect(subvolumes.map { |s| s["name"] }).to contain_exactly(
+                "@/boot/grub2/i386-pc", "@/boot/grub2/x86_64-efi"
+              )
+            end
+          end
         end
 
         context "before committing the changes" do