Warn on non-existing layout

Fix #99 and refactor args_loader a bit

lib/squib/args/arg_loader.rb

@@ -52,16 +52,17 @@ module Squib
       #
       def defaultify(p, args, layout)
         return args[p] if args.key? p # arg was specified, no defaults used
-        dsl_method_defaults = @dsl_method_defaults || {}
+        defaults = self.class.parameters.merge(@dsl_method_defaults || {})
         args[:layout].map do |layout_arg|
-          if layout_arg.nil?
-            self.class.parameters.merge(dsl_method_defaults)[p]  # no layout specified, use default
-          else
-            if layout[layout_arg.to_s].key? p.to_s
+          return defaults[p] if layout_arg.nil?  # no layout specified, use default
+          unless layout.key? layout_arg.to_s     # specified a layout, but it doesn't exist in layout. Oops!
+            Squib.logger.warn("Layout \"#{layout_arg.to_s}\" does not exist in layout file - using default instead")
+            return defaults[p]
+          end
+          if layout[layout_arg.to_s].key?(p.to_s)
             layout[layout_arg.to_s][p.to_s]     # param specified in layout
           else
-              self.class.parameters.merge(dsl_method_defaults)[p]  # layout specified, but not this param
-            end
+            defaults[p]                         # layout specified, but not this param
           end
         end
       end

spec/args/box_spec.rb

@@ -79,6 +79,16 @@ describe Squib::Args::Box do
          y: [0, 0],    # Box default
         )
     end
+
+    it 'warns on non-existent layouts' do
+      args = { layout: :heal}
+      expect(Squib.logger).to receive(:warn).with('Layout "heal" does not exist in layout file - using default instead').at_least(:once)
+      box.load!(args, expand_by: 2, layout: layout)
+      expect(box).to have_attributes(
+         x: [0, 0], # Box default
+         y: [0, 0], # Box default
+        )
+    end
   end
 
   context 'unit conversion' do