Add methods to build eraseable component

app/models/ci/build.rb

@@ -35,6 +35,9 @@
 
 module Ci
   class Build < CommitStatus
+    include Compoundable
+    component :eraseable, Gitlab::Ci::Build::Eraseable
+
     include Gitlab::Application.routes.url_helpers
     LAZY_ATTRIBUTES = ['trace']
 

app/models/concerns/compoundable.rb

+module Compoundable
+  extend ActiveSupport::Concern
+
+  class_methods do
+    private
+
+    def component(name, klass)
+      define_method(name) do
+        component_object = instance_variable_get("@#{name}")
+        return component_object if component_object
+        instance_variable_set("@#{name}", klass.new(self))
+      end
+
+      klass.instance_methods(false).each do |method|
+        delegate method, to: name
+      end
+    end
+  end
+end

lib/gitlab/ci/build/eraseable.rb

+module Gitlab
+  module Ci
+    module Build
+      class Eraseable
+        def initialize(build)
+          @build = build
+        end
+
+        def erase!
+          raise NotImplementedError
+        end
+
+        def erased?
+          @build.artifacts_file.exists? && @build.artifacts_metadata.exists?
+        end
+
+        private
+
+        def trace_file
+          raise NotImplementedError
+        end
+      end
+    end
+  end
+end