Extending a non-existent parent yells at you now

Fixes #24

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 * Added `showcase` feature to create a fancy-looking 3D reflection to showcase your cards. Documented, tested, and added a sample for it.
 * Added a basic Rakefile, documented in README.
-* Some internal refactoring and better testing around layouts
+* Some internal refactoring, better testing, and more documentation with layouts
 
 ## v0.1.0
 * Added `save_sheet` command that saves a range into PNG sheets, complete with trim, gap, margin, columns, and sometimes automagically computed rows. See samples/saves.rb.

README.md

@@ -209,6 +209,20 @@ yang:
   x: += 50
 ```
 
+Furthermore, if you want to extend multiple parents, it looks like this:
+
+```yaml
+socrates:
+  x: 100
+aristotle:
+  y: 200
+aristotle:
+  extends:
+    - socrates
+    - plato
+  x: += 50
+```
+
 ### Multiple layout files
 
 Squib also supports the combination of multiple layout files. As shown in the above example, if you provide an `Array` of files then Squib will merge them sequentially. Colliding keys will be completely re-defined by the later file. Extends is processed after _each file_. YAML merge keys are NOT supported across multiple files - use extends instead. Here's a demonstrative example:

lib/squib/layout_parser.rb

@@ -34,6 +34,7 @@ module Squib
     def self.recurse_extends(yml, key, visited )
       assert_not_visited(key, visited)
       return yml[key] unless has_extends?(yml, key)
+      return yml[key] unless parents_exist?(yml, key)
       visited[key] = key
       parent_keys = [yml[key]['extends']].flatten
       h = {}
@@ -62,6 +63,19 @@ module Squib
       !!yml[key] && yml[key].key?('extends')
     end
 
+    # Checks if we have any absentee parents
+    # @api private
+    def self.parents_exist?(yml, key)
+      exists = true
+      Array(yml[key]['extends']).each do |parent|
+        unless yml.key?(parent)
+          exists = false unless
+          Squib.logger.error "Processing layout: '#{key}' attempts to extend a missing '#{yml[key]['extends']}'"
+        end
+      end
+      return exists
+    end
+
     # Safeguard against malformed circular extends
     # :nodoc:
     # @api private

spec/data/layouts/extends-nonexists.yml

@@ -0,0 +1,3 @@
+verbal:
+  extends: kaisersoze
+  font_size: 25

spec/layout_parser_spec.rb

@@ -173,4 +173,17 @@ describe Squib::LayoutParser do
     Squib::LayoutParser.load_layout('yeti')
   end
 
+  it 'freaks out if you extend something doesn\'t exist' do
+    expect(Squib.logger)
+      .to receive(:error)
+      .with("Processing layout: 'verbal' attempts to extend a missing 'kaisersoze'")
+    layout = Squib::LayoutParser.load_layout(layout_file('extends-nonexists.yml'))
+    expect(layout).to eq({
+      'verbal'  => {
+          'font_size' => 25,
+          'extends' => 'kaisersoze'
+        }
+      })
+  end
+
 end