Add custom NodeVisitor subclass for Style/VariableNames

spec/ameba/rule/style/variable_names_spec.cr

@@ -38,7 +38,6 @@ module Ameba
         class Greeting
           def initialize(@badNamed = nil)
                        # ^ error: Var name should be underscore-cased: @bad_named, not @badNamed
-                       # ^ error: Var name should be underscore-cased: bad_named, not badNamed
           end
         end
         CRYSTAL

src/ameba/rule/style/variable_names.cr

@@ -35,17 +35,9 @@ module Ameba::Rule::Style
       issue_for node, MSG % {expected, node.name}
     end
 
-    # TODO: Handle special case where instance variable is method parameter.
+    def test(source : Source)
-    #       For example, this:
+      VarVisitor.new self, source
-    #
+    end
-    #         def initialize(@foo)
-    #         end
-    #
-    #       is represented in the AST as:
-    #
-    #         def initialize(foo)
-    #           @foo = foo
-    #         end
 
     def test(source, node : Crystal::Var)
       check_node source, node
@@ -58,5 +50,20 @@ module Ameba::Rule::Style
     def test(source, node : Crystal::ClassVar)
       check_node source, node
     end
+
+    private class VarVisitor < AST::NodeVisitor
+      private getter var_locations = [] of Crystal::Location
+
+      def visit(node : Crystal::Var)
+        !var_locations.includes?(node.location) && super
+      end
+
+      def visit(node : Crystal::InstanceVar | Crystal::ClassVar)
+        if (location = node.location)
+          var_locations << location
+        end
+        super
+      end
+    end
   end
 end