Do not report if variable is assigned and referenced in MacroFor/MacroIf/MacroExpression

closes #194

spec/ameba/rule/lint/useless_assign_spec.cr

@@ -944,6 +944,66 @@ module Ameba::Rule::Lint
         )
         subject.catch(s).should be_valid
       end
+
+      it "doesn't report if assignment is referenced in a macro expression as string" do
+        s = Source.new %(
+          foo = 1
+          puts {{ "foo".id }}
+        )
+        subject.catch(s).should be_valid
+      end
+
+      it "doesn't report if assignement is referenced in for macro in exp" do
+        s = Source.new %(
+          foo = 22
+
+          {% for x in %w(foo) %}
+            add({{x.id}})
+          {% end %}
+        )
+        subject.catch(s).should be_valid
+      end
+
+      it "doesn't report if assignement is referenced in for macro in body" do
+        s = Source.new %(
+          foo = 22
+
+          {% for x in %w(bar) %}
+            puts {{ "foo".id }}
+          {% end %}
+        )
+        subject.catch(s).should be_valid
+      end
+
+      it "doesn't report if assignement is referenced in if macro in cond" do
+        s = Source.new %(
+          foo = 22
+          {% if "foo".id %}
+          {% end %}
+        )
+        subject.catch(s).should be_valid
+      end
+
+      it "doesn't report if assignement is referenced in if macro in then" do
+        s = Source.new %(
+          foo = 22
+          {% if true %}
+             puts {{ "foo".id }}
+          {% end %}
+        )
+        subject.catch(s).should be_valid
+      end
+
+      it "doesn't report if assignement is referenced in if macro in else" do
+        s = Source.new %(
+          foo = 22
+          {% if true %}
+          {% else %}
+             puts {{ "foo".id }}
+          {% end %}
+        )
+        subject.catch(s).should be_valid
+      end
     end
 
     context "uninitialized" do

src/ameba/ast/variabling/variable.cr

@@ -120,12 +120,13 @@ module Ameba::AST
       false
     end
 
-    # Returns true if current variable potentially referenced in a macro literal,
+    # Returns true if current variable potentially referenced in a macro,
     # false if not.
     def used_in_macro?(scope = @scope)
       scope.inner_scopes.each do |inner_scope|
-        return true if MacroLiteralFinder.new(inner_scope.node).references? node
+        return true if MacroReferenceFinder.new(inner_scope.node, node.name).references
       end
+      return true if MacroReferenceFinder.new(scope.node, node.name).references
       return true if (outer_scope = scope.outer_scope) && used_in_macro?(outer_scope)
       false
     end
@@ -167,23 +168,35 @@ module Ameba::AST
           var_location.column_number < node_location.column_number)
     end
 
-    private class MacroLiteralFinder < Crystal::Visitor
-      @macro_literals = [] of Crystal::MacroLiteral
+    private class MacroReferenceFinder < Crystal::Visitor
+      property references = false
 
-      def initialize(node)
+      def initialize(node, @reference : String = reference)
         node.accept self
       end
 
-      def references?(node : Crystal::Var)
-        @macro_literals.any? { |literal| literal.value.includes? node.name }
-      end
-
       def visit(node : Crystal::ASTNode)
         true
       end
 
       def visit(node : Crystal::MacroLiteral)
-        @macro_literals << node
+        !(self.references ||= node.value.includes?(@reference))
+      end
+
+      def visit(node : Crystal::MacroExpression)
+        !(self.references ||= node.exp.to_s.includes?(@reference))
+      end
+
+      def visit(node : Crystal::MacroFor)
+        exp, body = node.exp, node.body
+        !(self.references ||= exp.to_s.includes?(@reference) ||
+                              body.to_s.includes?(@reference))
+      end
+
+      def visit(node : Crystal::MacroIf)
+        !(self.references ||= node.cond.to_s.includes?(@reference) ||
+                              node.then.to_s.includes?(@reference) ||
+                              node.else.to_s.includes?(@reference))
       end
     end