Fix zombifier require to return loaded flag

* Ruby 2.3 uses Kernel#require to expand autoloads, and autload constant
  propagation only is done on #require returning true.
* The zombifier used to return incorrect falsy/truthy values.
* This would never have happened on a static language

config/flay.yml

@@ -1,3 +1,3 @@
 ---
 threshold: 18
-total_score: 1171
+total_score: 1167

lib/mutant/zombifier.rb

@@ -57,13 +57,15 @@ module Mutant
     #
     # @param [#to_s] logical_name
     #
-    # @return [undefined]
+    # @return [Bool]
+    #   true if successful and false if feature already loaded
     def require(logical_name)
       logical_name = logical_name.to_s
-      @original.call(logical_name)
-      return unless include?(logical_name)
+      loaded = @original.call(logical_name)
+      return loaded unless include?(logical_name)
       @zombified << logical_name
       zombify(find(logical_name))
+      true
     end
 
     # Find file by logical path

spec/support/ruby_vm.rb

@@ -3,7 +3,7 @@ module MutantSpec
   # require semantics Zombifier relies on in a way we can avoid having to
   # mock around everywhere to test every detail.
   class RubyVM
-    include Concord.new(:expected_events)
+    include Concord::Public.new(:expected_events)
 
     # An event being observed by the VM handlers
     class EventObservation
@@ -14,7 +14,8 @@ module MutantSpec
     class EventExpectation
       include AbstractType, Anima.new(
         :expected_payload,
-        :trigger_requires
+        :trigger_requires,
+        :return_value
       )
 
       DEFAULTS = IceNine.deep_freeze(trigger_requires: [])
@@ -29,12 +30,12 @@ module MutantSpec
         end
 
         trigger_requires.each(&vm.method(:require))
+
+        self
       end
 
     private
 
-      abstract_method :advance_vm
-
       def match?(observation)
         observation.type.eql?(self.class) && observation.payload.eql?(expected_payload)
       end
@@ -51,7 +52,6 @@ module MutantSpec
     # A fake implementation of Kernel#require
     def require(logical_name)
       handle_event(EventObservation.new(EventExpectation::Require, logical_name: logical_name))
-      self
     end
 
     # A fake implementation of Kernel#eval
@@ -64,7 +64,6 @@ module MutantSpec
           source_location: location
         )
       )
-      self
     end
 
     # Test if VM events where fully processed
@@ -77,7 +76,7 @@ module MutantSpec
     def handle_event(observation)
       fail "Unexpected event: #{observation.type} / #{observation.payload}" if expected_events.empty?
 
-      expected_events.slice!(0).handle(self, observation)
+      expected_events.slice!(0).handle(self, observation).return_value
     end
   end
 end # MutantSpec

spec/unit/mutant/zombifier_spec.rb

@@ -5,7 +5,10 @@ RSpec.describe Mutant::Zombifier do
   let(:require_highjack) do
     lambda do |block|
       original = ruby_vm.method(:require)
-      allow(ruby_vm).to receive(:require, &block)
+      allow(ruby_vm).to receive(:require) do |argument|
+        return_value = ruby_vm.expected_events.first.return_value
+        expect(block.call(argument)).to be(return_value)
+      end
       original
     end
   end
@@ -28,7 +31,8 @@ RSpec.describe Mutant::Zombifier do
         MutantSpec::RubyVM::EventExpectation::Require.new(
           expected_payload: {
             logical_name: 'project'
-          }
+          },
+          return_value: true
         ),
         MutantSpec::RubyVM::EventExpectation::Eval.new(
           expected_payload: {
@@ -36,18 +40,21 @@ RSpec.describe Mutant::Zombifier do
             source:          "module Zombie\n  module Project\n  end\nend",
             source_location: 'a/project.rb'
           },
-          trigger_requires: %w[foo bar]
+          trigger_requires: %w[foo bar],
+          return_value: nil
         ),
         MutantSpec::RubyVM::EventExpectation::Require.new(
           expected_payload: {
             logical_name: 'foo'
           },
-          trigger_requires: %w[bar]
+          trigger_requires: %w[bar],
+          return_value: true
         ),
         MutantSpec::RubyVM::EventExpectation::Require.new(
           expected_payload: {
             logical_name: 'bar'
-          }
+          },
+          return_value: true
         ),
         MutantSpec::RubyVM::EventExpectation::Eval.new(
           expected_payload: {
@@ -55,23 +62,19 @@ RSpec.describe Mutant::Zombifier do
             source:          "module Zombie\n  module Bar\n  end\nend",
             source_location: 'b/bar.rb'
           },
-          trigger_requires: %w[]
+          trigger_requires: %w[],
+          return_value: nil
         ),
         MutantSpec::RubyVM::EventExpectation::Require.new(
           expected_payload: {
             logical_name: 'bar'
-          }
+          },
+          return_value: false
         )
       ]
     )
   end
 
-  let(:require_effects) do
-    {
-      'project' => { requires: [] }
-    }
-  end
-
   let(:file_entries) do
     {
       'a/project.rb' => { file: true, contents: 'module Project; end' },
@@ -100,7 +103,7 @@ RSpec.describe Mutant::Zombifier do
       expect(apply).to be(described_class)
     end
 
-    it 'consumes walks the VM through expected steps' do
+    it 'walks the VM through expected steps' do
       expect { apply }.to change(ruby_vm, :done?).from(false).to(true)
     end