Add optarg arity mutation

- Adds mutation from `def foo(a = true); end`
  to `def foo(a = true); a = true; end`
- closes #310

Changelog.md

@@ -1,6 +1,7 @@
 # v0.8.3 2015-08-xx
 
 * Remove invalid mutation `super(...)` to `super`
+* Add mutation from `def foo(a = true); end` to `def foo(a = true); a = true; end` #419
 
 # v0.8.2 2015-08-11
 

config/flay.yml

@@ -1,3 +1,3 @@
 ---
 threshold: 18
-total_score: 1189
+total_score: 1200

lib/mutant/ast/meta.rb

@@ -10,6 +10,24 @@ module Mutant
         children :captures, :assignment, :body
       end # Resbody
 
+      # Metadata for optional argument nodes
+      class Optarg
+        include NamedChildren, Concord.new(:node)
+
+        UNDERSCORE = '_'.freeze
+
+        children :name, :default_value
+
+        # Test if optarg definition intends to be used
+        #
+        # @return [Boolean]
+        #
+        # @api private
+        def used?
+          !name.to_s.start_with?(UNDERSCORE)
+        end
+      end # Optarg
+
       # Metadata for send nodes
       class Send
         include NamedChildren, Concord.new(:node)

lib/mutant/mutator/node/define.rb

@@ -13,11 +13,40 @@ module Mutant
         # @api private
         def dispatch
           emit_arguments_mutations
+          emit_optarg_body_assignments
           emit_body(N_RAISE)
           emit_body(nil)
           emit_body_mutations if body
         end
 
+        # Emit mutations with optional arguments as assignments in method
+        #
+        # @return [undefined]
+        #
+        # @api private
+        def emit_optarg_body_assignments
+          arguments.children.each do |argument|
+            next unless n_optarg?(argument) && AST::Meta::Optarg.new(argument).used?
+
+            emit_body_prepend(s(:lvasgn, *argument))
+          end
+        end
+
+        # Emit valid body ASTs depending on instance body
+        #
+        # @param node [Parser::AST::Node]
+        #
+        # @return [undefined]
+        #
+        # @api private
+        def emit_body_prepend(node)
+          if body
+            emit_body(s(:begin, node, body))
+          else
+            emit_body(node)
+          end
+        end
+
         # Mutator for instance method defines
         class Instance < self
 

meta/def.rb

@@ -80,6 +80,22 @@ Mutant::Meta::Example.add do
   mutation 'def foo(a, b); raise; end'
 end
 
+Mutant::Meta::Example.add do
+  source 'def foo(a, b = nil); true; end'
+
+  mutation 'def foo(_a, b = nil); true; end'
+  mutation 'def foo(a, b = nil); end'
+  mutation 'def foo; true; end'
+  mutation 'def foo(a, b = nil); raise; end'
+  mutation 'def foo(a, b = nil); nil; end'
+  mutation 'def foo(a, b = nil); false; end'
+  mutation 'def foo(a); true; end'
+  mutation 'def foo(a, b = nil); b = nil; true; end'
+  mutation 'def foo(b = nil); true; end'
+  mutation 'def foo(a, _b = nil); true; end'
+  mutation 'def foo(a, b); true; end'
+end
+
 Mutant::Meta::Example.add do
   source 'def foo(_unused); end'
 
@@ -113,6 +129,8 @@ Mutant::Meta::Example.add do
   mutation 'def foo(b = 0); end'
   mutation 'def foo(a, b = 0); end'
   mutation 'def foo; end'
+  mutation 'def foo(a = 0, b = 0); a = 0; end'
+  mutation 'def foo(a = 0, b = 0); b = 0; end'
   mutation 'def foo(a = 0, b = 0); raise; end'
 end
 
@@ -125,6 +143,7 @@ Mutant::Meta::Example.add do
   mutation 'def foo(a = nil); end'
   mutation 'def foo(_a = true); end'
   mutation 'def foo(a = true); raise; end'
+  mutation 'def foo(a = true); a = true; end'
 end
 
 Mutant::Meta::Example.add do

spec/unit/mutant/ast/meta/optarg_spec.rb

@@ -0,0 +1,22 @@
+RSpec.describe Mutant::AST::Meta::Optarg do
+  subject(:object) { described_class.new(node) }
+
+  let(:node)  { s(:optarg, name, value) }
+  let(:name)  { :foo                    }
+  let(:value) { s(:sym, :bar)           }
+
+  its(:name) { should be(:foo) }
+  its(:default_value) { should eql(s(:sym, :bar)) }
+
+  describe '#used?' do
+    subject { object.used? }
+
+    it { should be true }
+
+    context 'when name is prefixed with an underscore' do
+      let(:name) { :_foo }
+      it { should be false }
+    end
+  end
+
+end