Handle attribute assignments to self correctly

* Closes mbj#149

lib/mutant/mutator/node/send.rb

@@ -18,7 +18,7 @@ class Send < self
 
         INDEX_REFERENCE = :[]
         INDEX_ASSIGN    = :[]=
-        ASSIGN_SUFFIX   = :'='
+        ASSIGN_SUFFIX   = '='.freeze
 
         # Base mutator for index operations
         class Index < self
@@ -81,11 +81,12 @@ def dispatch
         # @api private
         #
         def non_index_dispatch
-          if binary_operator?
+          case
+          when binary_operator?
             run(Binary)
-            return
+          else
+            normal_dispatch
           end
-          normal_dispatch
         end
 
         # Return arguments
@@ -149,6 +150,19 @@ def binary_operator?
           arguments.one? && BINARY_METHOD_OPERATORS.include?(selector)
         end
 
+        # Test for attribute assignment
+        #
+        # @return [true]
+        #   if node represetns and attribute assignment
+        #
+        # @return [false]
+        #
+        # @api private
+        #
+        def attribute_assignment?
+          !BINARY_OPERATORS.include?(selector) && !UNARY_OPERATORS.include?(selector) && assignment? && !mlhs?
+        end
+
         # Mutate arguments
         #
         # @return [undefined]
@@ -196,11 +210,55 @@ def mutate_receiver
         # @api private
         #
         def emit_implicit_self
-          if receiver.type == :self and !KEYWORDS.include?(selector)
+          if receiver.type == :self && !KEYWORDS.include?(selector) && !attribute_assignment?
             emit_receiver(nil)
           end
         end
 
+        # Test for assignment
+        #
+        # FIXME: This also returns true for <= operator!
+        #
+        # @return [true]
+        #   if node represents attribute / element assignment
+        #
+        # @return [false]
+        #   otherwise
+        #
+        # @api private
+        #
+        def assignment?
+          selector.to_s[-1] == ASSIGN_SUFFIX
+        end
+
+        # Test for mlhs
+        #
+        # @return [true]
+        #   if node is within an mlhs
+        #
+        # @return [false]
+        #   otherwise
+        #
+        # @api private
+        #
+        def mlhs?
+          assignment? && !arguments?
+        end
+
+        # Test for empty arguments
+        #
+        # @return [true]
+        #   if arguments are empty
+        #
+        # @return [false]
+        #   otherwise
+        #
+        # @api private
+        #
+        def arguments?
+          arguments.any?
+        end
+
       end # Send
     end # Node
   end # Mutator

spec/unit/mutant/mutator/node/send_spec.rb

@@ -56,20 +56,40 @@
   end
 
   context 'attribute assign' do
-    let(:source) { 'foo.bar=baz' }
 
-    let(:mutations) do
-      mutations = []
-      mutations << 'foo'
-      mutations << 'nil'
-      mutations << 'foo.bar=nil'
-      mutations << 'foo.bar'
-      mutations << 'baz'
-      # This one could probably be removed
-      mutations << 'nil.bar=baz'
+    context 'to self' do
+      let(:source) { 'self.bar=baz' }
+
+      let(:mutations) do
+        mutations = []
+        mutations << 'nil'
+        mutations << 'self.bar=nil'
+        mutations << 'self'
+        mutations << 'self.bar'
+        mutations << 'baz'
+        # This one could probably be removed
+        mutations << 'nil.bar=baz'
+      end
+
+      it_should_behave_like 'a mutator'
     end
 
-    it_should_behave_like 'a mutator'
+    context 'to other object' do
+      let(:source) { 'foo.bar=baz' }
+
+      let(:mutations) do
+        mutations = []
+        mutations << 'foo'
+        mutations << 'nil'
+        mutations << 'foo.bar=nil'
+        mutations << 'foo.bar'
+        mutations << 'baz'
+        # This one could probably be removed
+        mutations << 'nil.bar=baz'
+      end
+
+      it_should_behave_like 'a mutator'
+    end
   end
 
   context 'index assign' do