Fix emit of invalid block body promotions

lib/mutant/mutator/node/block.rb

@@ -32,12 +32,21 @@ module Mutant
           emit_body(N_RAISE)
 
           return unless body
-          emit(body)
+          emit(body) unless body_has_control?
           emit_body_mutations
 
           mutate_body_receiver
         end
 
+        # Test if body has control structures
+        #
+        # @return [Boolean]
+        def body_has_control?
+          AST.find_last_path(body) do |node|
+            n_break?(node) || n_next?(node)
+          end.any?
+        end
+
         # Mutate method send in body scope of `send`
         #
         # @return [undefined]

meta/block.rb

@@ -121,3 +121,61 @@ Mutant::Meta::Example.add :block do
   mutation 'foo { }'
   mutation 'foo'
 end
+
+Mutant::Meta::Example.add :block do
+  source 'foo { next if true }'
+
+  singleton_mutations
+  mutation 'foo'
+  mutation 'foo { }'
+  mutation 'foo { self }'
+  mutation 'foo { nil }'
+  mutation 'foo { raise }'
+  mutation 'foo { self if true }'
+  mutation 'foo { nil if true }'
+  mutation 'foo { break if true }'
+  mutation 'foo { next if !true }'
+  mutation 'foo { next if false }'
+  mutation 'foo { next if nil }'
+  mutation 'foo { next }'
+end
+
+Mutant::Meta::Example.add :block do
+  source 'foo { next }'
+
+  singleton_mutations
+  mutation 'foo { nil }'
+  mutation 'foo { raise }'
+  mutation 'foo { self }'
+  mutation 'foo { break }'
+  mutation 'foo { }'
+  mutation 'foo'
+end
+
+Mutant::Meta::Example.add :block do
+  source 'foo { break if true }'
+
+  singleton_mutations
+  mutation 'foo'
+  mutation 'foo { }'
+  mutation 'foo { self }'
+  mutation 'foo { nil }'
+  mutation 'foo { raise }'
+  mutation 'foo { self if true }'
+  mutation 'foo { nil if true }'
+  mutation 'foo { break if !true }'
+  mutation 'foo { break if false }'
+  mutation 'foo { break if nil }'
+  mutation 'foo { break }'
+end
+
+Mutant::Meta::Example.add :block do
+  source 'foo { break }'
+
+  singleton_mutations
+  mutation 'foo { nil }'
+  mutation 'foo { raise }'
+  mutation 'foo { self }'
+  mutation 'foo { }'
+  mutation 'foo'
+end