Change emit_nil to not emit on the left node of an assignment

* Add emit_nil to other nodes so that they can be replaced
  with nil, effectively removing them from the code.

lib/mutant/mutator/node.rb

@@ -181,7 +181,7 @@ module Mutant
       # @api private
       #
       def emit_nil
-        emit(N_NIL)
+        emit(N_NIL) unless agsn_left?
       end
 
       # Return new self typed child
@@ -222,6 +222,17 @@ module Mutant
         parent && parent.node.type
       end
 
+      # Test if the node is the left of an or_asgn or op_asgn
+      #
+      # @return [Boolean]
+      #
+      # @api private
+      #
+      def agsn_left?
+        [:or_asgn, :op_asgn, :and_asgn].include?(parent_type) &&
+        parent.left.equal?(node)
+      end
+
     end # Node
   end # Mutator
 end # Mutant

lib/mutant/mutator/node/block.rb

@@ -26,6 +26,7 @@ module Mutant
           end
           emit_body(nil)
           emit_body(RAISE)
+          emit_nil
         end
 
       end # Block

lib/mutant/mutator/node/case.rb

@@ -23,6 +23,7 @@ module Mutant
           emit_condition_mutations
           emit_when_mutations
           emit_else_mutations
+          emit_nil
         end
 
         # Emit when mutations

lib/mutant/mutator/node/dstr.rb

@@ -9,6 +9,19 @@ module Mutant
 
         handle(:dstr)
 
+      private
+
+        # Emit mutations
+        #
+        # @return [undefined]
+        #
+        # @api private
+        #
+        def dispatch
+          super
+          emit_nil
+        end
+
       end # Dstr
     end # Node
   end # Mutator

lib/mutant/mutator/node/if.rb

@@ -22,6 +22,7 @@ module Mutant
           mutate_condition
           mutate_if_branch
           mutate_else_branch
+          emit_nil
         end
 
         # Emit conditon mutations

lib/mutant/mutator/node/masgn.rb

@@ -20,7 +20,7 @@ module Mutant
         # @api private
         #
         def dispatch
-          # noop, for now
+          emit_nil
         end
 
       end # MultipleAssignment

lib/mutant/mutator/node/named_value/variable_assignment.rb

@@ -30,6 +30,7 @@ module Mutant
           def dispatch
             mutate_name
             emit_value_mutations if value # mlhs!
+            emit_nil
           end
 
           # Emit name mutations

lib/mutant/mutator/node/return.rb

@@ -22,9 +22,8 @@ module Mutant
           if value
             emit(value)
             emit_value_mutations
-          else
-            emit_nil
           end
+          emit_nil
         end
 
       end # Return

lib/mutant/mutator/node/send.rb

@@ -71,6 +71,7 @@ module Mutant
           else
             non_index_dispatch
           end
+          emit_nil
         end
 
         # Perform non index dispatch

lib/mutant/mutator/node/super.rb

@@ -27,6 +27,7 @@ module Mutant
             mutate_child(index)
             delete_child(index)
           end
+          emit_nil
         end
 
       end # Super

lib/mutant/mutator/node/while.rb

@@ -23,6 +23,7 @@ module Mutant
           emit_condition_mutations
           emit_body_mutations
           emit_body(nil)
+          emit_nil
         end
 
       end # While

spec/unit/mutant/mutator/node/block/mutation_spec.rb

@@ -12,7 +12,10 @@ describe Mutant::Mutator, 'block' do
       mutations << 'foo { b }'
       mutations << 'foo {}'
       mutations << 'foo { raise }'
+      mutations << 'foo { a; nil }'
+      mutations << 'foo { nil; b }'
       mutations << 'foo'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -35,6 +38,7 @@ describe Mutant::Mutator, 'block' do
       mutations << 'foo { |a| }'
       mutations << 'foo { |b| }'
       mutations << 'foo { || }'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -61,6 +65,7 @@ describe Mutant::Mutator, 'block' do
       mutations << 'foo { |(a, srandom), c| }'
       mutations << 'foo { |(a, b), srandom| }'
       mutations << 'foo'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/block_pass/mutation_spec.rb

@@ -8,6 +8,7 @@ describe Mutant::Mutator::Node::NamedValue::Access, 'block_pass' do
   let(:mutations) do
     mutants = []
     mutants << 'foo'
+    mutants << 'nil'
   end
 
   it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/case/mutation_spec.rb

@@ -217,6 +217,8 @@ describe Mutant::Mutator::Node::Case do
           :else
         end
       RUBY
+
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -314,6 +316,8 @@ describe Mutant::Mutator::Node::Case do
           :else
         end
       RUBY
+
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/defined_predicate/mutation_spec.rb

@@ -4,7 +4,11 @@ require 'spec_helper'
 
 describe Mutant::Mutator::Node::Generic, 'defined?' do
   let(:source) { 'defined?(foo)' }
-  let(:mutations) { []              }
+
+  let(:mutations) do
+    mutations = []
+    mutations << 'defined?(nil)'
+  end
 
   it_should_behave_like 'a mutator'
 end

spec/unit/mutant/mutator/node/dstr/mutation_spec.rb

@@ -15,6 +15,8 @@ describe Mutant::Mutator::Node::Dstr, 'dstr' do
     mutations << '"#{nil}#{bar}baz"'
     mutations << '"foo#{bar}random"'
     mutations << '"foo#{bar}#{nil}"'
+    mutations << '"foo#{nil}baz"'
+    mutations << 'nil'
   end
 
   it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/dsym/mutation_spec.rb

@@ -15,6 +15,7 @@ describe Mutant::Mutator::Node::Generic, 'dsum' do
     mutations << ':"#{nil}#{bar}baz"'
     mutations << ':"foo#{bar}random"'
     mutations << ':"foo#{bar}#{nil}"'
+    mutations << ':"foo#{nil}baz"'
   end
 
   it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/if/mutation_spec.rb

@@ -36,6 +36,8 @@ describe Mutant::Mutator, 'if' do
       # mutations of else body
       mutants << 'if :condition; true;  else true;  end'
       mutants << 'if :condition; true;  else nil;   end'
+
+      mutants << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -51,6 +53,8 @@ describe Mutant::Mutator, 'if' do
       mutants << 'if condition;  nil;   end'
       mutants << 'if true;       true;  end'
       mutants << 'if false;      true;  end'
+      mutants << 'if nil;        true;  end'
+      mutants << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -69,6 +73,7 @@ describe Mutant::Mutator, 'if' do
       mutants << 'unless true;        true;  end'
       mutants << 'unless false;       true;  end'
       mutants << 'if     :condition;  true;  end'
+      mutants << 'nil'
     end
 
     it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/literal/regex_spec.rb

@@ -9,9 +9,9 @@ describe Mutant::Mutator::Node::Literal, 'regex' do
 
     let(:mutations) do
       mutations = []
-      mutations << 'nil'
       mutations << '//' # match all
       mutations << '/a\A/' # match nothing
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -22,10 +22,12 @@ describe Mutant::Mutator::Node::Literal, 'regex' do
 
     let(:mutations) do
       mutations = []
-      mutations << 'nil'
       mutations << '//' # match all
       mutations << '/#{foo}n/' # match all
       mutations << '/a\A/' # match nothing
+      mutations << '/#{nil.bar}n/'
+      mutations << '/#{nil}n/'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/masgn/mutation_spec.rb

@@ -4,7 +4,11 @@ require 'spec_helper'
 
 describe Mutant::Mutator, 'masgn' do
   let(:source) { 'a, b = c, d' }
-  let(:mutations) { []            }
+
+  let(:mutations) do
+    mutations = []
+    mutations << 'nil'
+  end
 
   it_should_behave_like 'a mutator'
 end

spec/unit/mutant/mutator/node/match_current_line/mutation_spec.rb

@@ -14,6 +14,7 @@ describe Mutant::Mutator::Node::Generic, 'match_current_line' do
     mutations << 'true if nil'
     mutations << 'true if !//'
     mutations << 'true if /a\A/'
+    mutations << 'nil'
   end
 
   it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/named_value/access/mutation_spec.rb

@@ -17,6 +17,7 @@ describe Mutant::Mutator::Node::NamedValue::Access, 'mutations' do
       mutants << '$a'
       mutants << '$a = ::Object.new; $a'
       mutants << '$srandom = nil; $a'
+      mutants << 'nil; $a'
     end
 
     it_should_behave_like 'a mutator'
@@ -32,6 +33,7 @@ describe Mutant::Mutator::Node::NamedValue::Access, 'mutations' do
       mutants << '@@a'
       mutants << '@@a = ::Object.new; @@a'
       mutants << '@@srandom = nil; @@a'
+      mutants << 'nil; @@a'
     end
   end
 
@@ -45,6 +47,7 @@ describe Mutant::Mutator::Node::NamedValue::Access, 'mutations' do
       mutants << '@a'
       mutants << '@a = ::Object.new; @a'
       mutants << '@srandom = nil; @a'
+      mutants << 'nil; @a'
     end
 
     it_should_behave_like 'a mutator'
@@ -60,6 +63,7 @@ describe Mutant::Mutator::Node::NamedValue::Access, 'mutations' do
       mutants << 'a'
       mutants << 'a = ::Object.new; a'
       mutants << 'srandom = nil; a'
+      mutants << 'nil; a'
     end
 
     it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/named_value/variable_assignment/mutation_spec.rb

@@ -15,6 +15,7 @@ describe Mutant::Mutator::Node::NamedValue::VariableAssignment, 'mutations' do
       mutations << '$srandom = true'
       mutations << '$a = false'
       mutations << '$a = nil'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -25,10 +26,10 @@ describe Mutant::Mutator::Node::NamedValue::VariableAssignment, 'mutations' do
 
     let(:mutations) do
       mutations = []
-
       mutations << '@@srandom = true'
       mutations << '@@a = false'
       mutations << '@@a = nil'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -39,10 +40,10 @@ describe Mutant::Mutator::Node::NamedValue::VariableAssignment, 'mutations' do
 
     let(:mutations) do
       mutations = []
-
       mutations << '@srandom = true'
       mutations << '@a = false'
       mutations << '@a = nil'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -53,10 +54,10 @@ describe Mutant::Mutator::Node::NamedValue::VariableAssignment, 'mutations' do
 
     let(:mutations) do
       mutations = []
-
       mutations << 'srandom = true'
       mutations << 'a = false'
       mutations << 'a = nil'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/restarg/mutation_spec.rb

@@ -10,6 +10,8 @@ describe Mutant::Mutator::Node::Generic, 'restarg' do
     mutants << 'foo'
     mutants << 'foo(nil)'
     mutants << 'foo(bar)'
+    mutants << 'foo(*nil)'
+    mutants << 'nil'
   end
 
   it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/return/mutation_spec.rb

@@ -7,18 +7,22 @@ describe Mutant::Mutator, 'return' do
   context 'return without value' do
     let(:source) { 'return' }
 
-    let(:mutations) { ['nil'] }
+    let(:mutations) do
+      mutations = []
+      mutations << 'nil'
+    end
 
     it_should_behave_like 'a mutator'
   end
 
   context 'return with value' do
-    let(:source) { 'return nil' }
+    let(:source) { 'return foo' }
 
     let(:mutations) do
       mutations = []
+      mutations << 'foo'
+      mutations << 'return nil'
       mutations << 'nil'
-      mutations << 'return ::Object.new'
     end
 
     it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/send/mutation_spec.rb

@@ -15,6 +15,10 @@ describe Mutant::Mutator, 'send' do
       mutations << 'foo.gsub(b)'
       mutations << 'foo.gsub'
       mutations << 'foo.sub(a, b)'
+      mutations << 'foo.gsub(a, nil)'
+      mutations << 'foo.gsub(nil, b)'
+      mutations << 'nil.gsub(a, b)'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -29,6 +33,9 @@ describe Mutant::Mutator, 'send' do
       mutations << 'foo.public_send(bar)'
       mutations << 'bar'
       mutations << 'foo'
+      mutations << 'foo.send(nil)'
+      mutations << 'nil.send(bar)'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -40,6 +47,7 @@ describe Mutant::Mutator, 'send' do
     let(:mutations) do
       mutations = []
       mutations << 'foo ||= expression'
+      mutations << 'self.foo ||= nil'
       mutations << 'nil.foo ||= expression'
       mutations << 'nil'
     end
@@ -53,6 +61,7 @@ describe Mutant::Mutator, 'send' do
     let(:mutations) do
       mutations = []
       mutations << 'foo'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -66,6 +75,8 @@ describe Mutant::Mutator, 'send' do
       mutations << 'foo'
       mutations << 'foo(nil)'
       mutations << 'foo(bar)'
+      mutations << 'foo(*nil)'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -77,6 +88,7 @@ describe Mutant::Mutator, 'send' do
     let(:mutations) do
       mutations = []
       mutations << 'foo'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -88,6 +100,7 @@ describe Mutant::Mutator, 'send' do
     let(:mutations) do
       mutations = []
       mutations << 'foo'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -97,7 +110,12 @@ describe Mutant::Mutator, 'send' do
     context 'implicit' do
       let(:source) { 'foo' }
 
-      it_should_behave_like 'a noop mutator'
+      let(:mutations) do
+        mutations = []
+        mutations << 'nil'
+      end
+
+      it_should_behave_like 'a mutator'
     end
 
     context 'explict receiver' do
@@ -108,6 +126,7 @@ describe Mutant::Mutator, 'send' do
         mutations << 'foo'
         mutations << 'self'
         mutations << 'nil.foo'
+        mutations << 'nil'
       end
 
       it_should_behave_like 'a mutator'
@@ -133,6 +152,8 @@ describe Mutant::Mutator, 'send' do
       let(:mutations) do
         mutations = []
         mutations << 'foo'
+        mutations << 'nil.bar'
+        mutations << 'nil'
       end
 
       it_should_behave_like 'a mutator'
@@ -146,6 +167,8 @@ describe Mutant::Mutator, 'send' do
         mutations << 'self.class'
         mutations << 'self.foo'
         mutations << 'nil.class.foo'
+        mutations << 'nil.foo'
+        mutations << 'nil'
       end
 
       it_should_behave_like 'a mutator'
@@ -192,8 +215,9 @@ describe Mutant::Mutator, 'send' do
             mutations = []
             mutations << "foo.#{keyword}"
             mutations << 'foo'
-            mutations << 'nil'
             mutations << "foo.#{keyword}(::Object.new)"
+            mutations << "nil.#{keyword}(nil)"
+            mutations << 'nil'
           end
 
           it_should_behave_like 'a mutator'
@@ -210,6 +234,7 @@ describe Mutant::Mutator, 'send' do
         mutations << 'foo(nil)'
         mutations << 'foo(::Object.new, nil)'
         mutations << 'foo(nil, ::Object.new)'
+        mutations << 'nil'
       end
 
       it_should_behave_like 'a mutator'
@@ -225,6 +250,11 @@ describe Mutant::Mutator, 'send' do
           mutations << '(left - right)'
           mutations << 'left / foo'
           mutations << 'right / foo'
+          mutations << '(left - right) / nil'
+          mutations << '(left - nil) / foo'
+          mutations << '(nil - right) / foo'
+          mutations << 'nil / foo'
+          mutations << 'nil'
         end
 
         it_should_behave_like 'a mutator'
@@ -242,6 +272,7 @@ describe Mutant::Mutator, 'send' do
             mutations << "true  #{operator} nil"
             mutations << 'true'
             mutations << 'false'
+            mutations << 'nil'
           end
 
           it_should_behave_like 'a mutator'
@@ -253,6 +284,9 @@ describe Mutant::Mutator, 'send' do
             mutations = []
             mutations << 'left'
             mutations << 'right'
+            mutations << "left #{operator} nil"
+            mutations << "nil #{operator} right"
+            mutations << 'nil'
           end
 
           it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/super/mutation_spec.rb

@@ -21,6 +21,7 @@ describe Mutant::Mutator, 'super' do
     let(:mutations) do
       mutations = []
       mutations << 'super'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'
@@ -35,6 +36,9 @@ describe Mutant::Mutator, 'super' do
       mutations << 'super()'
       mutations << 'super(foo)'
       mutations << 'super(bar)'
+      mutations << 'super(foo, nil)'
+      mutations << 'super(nil, bar)'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/while/mutation_spec.rb

@@ -14,6 +14,9 @@ describe Mutant::Mutator::Node::While do
       mutations << 'while true; end'
       mutations << 'while false; foo; bar; end'
       mutations << 'while nil;   foo; bar; end'
+      mutations << 'while true;  foo; nil; end'
+      mutations << 'while true;  nil; bar; end'
+      mutations << 'nil'
     end
 
     it_should_behave_like 'a mutator'