Layout multiple inheritance works with operators

The case of using relative operators and multiple inheritance is handled now.

Fixes #244

docs/layouts.rst

@@ -169,7 +169,8 @@ If you want to extend multiple parents, it looks like this::
     extends:
       - socrates
       - plato
-    x: += 50    # evaluates to 250 from plato
+    x: += 50    # evaluates to 150 from socrates
+    # y is going to be 200 too from Plato
 
 If multiple keys override the same keys in a parent, the later ("younger") child in the ``extends`` list takes precedent. Like this::
 

lib/squib/layout_parser.rb

@@ -49,6 +49,24 @@ module Squib
       h = {}
       parent_keys.each do |parent_key|
         from_extends = yml[key].merge(recurse_extends(yml, parent_key, visited)) do |key, child_val, parent_val|
+          handle_relative_operators(parent_val, child_val)
+        end
+        h = h.merge(from_extends) do |key, older_sibling, younger_sibling|
+          # In general, go with the younger sibling.
+          # UNLESS that younger sibling had a relative operator, in which use the
+          # (already computed) relative operator applied, which lands in older_sibling
+          # See bug 244.
+          sibling = younger_sibling
+          %w(+= -= *= /=).each do |op|
+            sibling = older_sibling if younger_sibling.to_s.strip.start_with? op
+          end
+          sibling
+        end
+      end
+      return h
+    end
+
+    def handle_relative_operators(parent_val, child_val)
       if child_val.to_s.strip.start_with?('+=')
         add_parent_child(parent_val, child_val)
       elsif child_val.to_s.strip.start_with?('-=')
@@ -61,12 +79,6 @@ module Squib
         child_val # child overrides parent when merging, no +=
       end
     end
-        h = h.merge(from_extends) do |key, older_sibling, younger_sibling|
-          younger_sibling # when two siblings have the same entry, the "younger" (lower one) overrides
-        end
-      end
-      return h
-    end
 
     def add_parent_child(parent, child)
       parent_pixels = Args::UnitConversion.parse(parent, @dpi).to_f

spec/data/layouts/multi-extends-operators-complex.yml

@@ -0,0 +1,12 @@
+# Here's a complex test case inspired by bug 244
+socrates:
+  x: 100
+  y: 1000
+plato:
+  y: 2000
+aristotle:
+  extends:
+    - socrates
+    - plato
+  x: += 0.1in    # 0.1in -> 30.0, so 100 + 30 = 130.0
+  y: += 18       # From Plato, 2000 + 18

spec/data/layouts/multi-extends-operators-same.yml

@@ -0,0 +1,9 @@
+socrates:
+  x: 100
+plato:
+  x: 200
+aristotle:
+  extends:
+    - socrates
+    - plato
+  x: += 50    # evaluates to 250 from plato

spec/data/layouts/multi-extends-operators.yml

@@ -0,0 +1,9 @@
+socrates:
+  x: 100
+plato:
+  y: 200
+aristotle:
+  extends:
+    - socrates
+    - plato
+  x: += 50    # evaluates to 150 from socrates

spec/layout_parser_spec.rb

@@ -92,6 +92,57 @@ describe Squib::LayoutParser do
         )
   end
 
+  it 'applies multiple extends with relative operators' do
+    layout = subject.load_layout(layout_file('multi-extends-operators.yml'))
+    expect(layout).to eq({
+      'socrates' => {
+        'x' => 100,
+      },
+      'plato' => {
+        'y' => 200,
+      },
+      'aristotle' => {
+        'extends' => ['socrates', 'plato'],
+        'x' => 150.0, # do the += 50 on socrates
+        'y' => 200,
+      },
+    })
+  end
+
+  it 'applies multiple extends with relative operators on same key' do
+    layout = subject.load_layout(layout_file('multi-extends-operators-same.yml'))
+    expect(layout).to eq({
+      'socrates' => {
+        'x' => 100,
+      },
+      'plato' => {
+        'x' => 200,
+      },
+      'aristotle' => {
+        'extends' => ['socrates', 'plato'],
+        'x' => 250, # do the += 50 from plato, NOT socrates
+      },
+    })
+  end
+
+  it 'applies multiple extends with relative operators with ' do
+    layout = subject.load_layout(layout_file('multi-extends-operators-complex.yml'))
+    expect(layout).to eq({
+      'socrates' => {
+        'x' => 100,
+        'y' => 1000,
+      },
+      'plato' => {
+        'y' => 2000,
+      },
+      'aristotle' => {
+        'extends' => ['socrates', 'plato'],
+        'x' => 130.0, # 0.1in -> 30.0, so 100 + 30 = 130.0
+        'y' => 2018.0, # From Plato, 2000 + 18
+      },
+    })
+  end
+
   it 'applies multi-level extends' do
     layout = subject.load_layout(layout_file('multi-level-extends.yml'))
     expect(layout).to eq({ 'frame' => {

spec/spec_helper.rb

@@ -1,6 +1,6 @@
 require 'simplecov'
 require 'coveralls'
-# require 'byebug'
+require 'byebug'
 
 SimpleCov.formatter = SimpleCov::Formatter::MultiFormatter.new([
   SimpleCov::Formatter::HTMLFormatter,