Update UselessAssign rule to report unreferenced type declarations

spec/ameba/rule/lint/useless_assign_spec.cr

@@ -492,8 +492,8 @@ module Ameba::Rule::Lint
         subject.catch(s).should be_valid
       end
 
-      it "doesn't report if type declaration assigned inside class" do
-        s = Source.new %(
+      it "reports if type declaration assigned inside class" do
+        s = Source.new path: "source.cr", code: %(
           class A
             foo : String? = "foo"
 
@@ -502,7 +502,11 @@ module Ameba::Rule::Lint
             end
           end
         )
-        subject.catch(s).should be_valid
+        subject.catch(s).should_not be_valid
+
+        issue = s.issues.first
+        issue.location.to_s.should eq "source.cr:2:3"
+        issue.message.should eq "Useless assignment to variable `foo`"
       end
     end
 
@@ -1068,6 +1072,43 @@ module Ameba::Rule::Lint
       subject.catch(s).should be_valid
     end
 
+    context "type declaration" do
+      it "reports if it's not referenced at a top level" do
+        s = Source.new %(
+          a : String?
+        )
+        subject.catch(s).should_not be_valid
+      end
+
+      it "reports if it's not referenced in a method" do
+        s = Source.new %(
+          def foo
+            a : String?
+          end
+        )
+        subject.catch(s).should_not be_valid
+      end
+
+      it "reports if it's not referenced in a class" do
+        s = Source.new %(
+          class Foo
+            a : String?
+          end
+        )
+        subject.catch(s).should_not be_valid
+      end
+
+      it "doesn't report if it's referenced" do
+        s = Source.new %(
+          def foo
+            a : String?
+            a
+          end
+        )
+        subject.catch(s).should be_valid
+      end
+    end
+
     context "uninitialized" do
       it "reports if uninitialized assignment is not referenced at a top level" do
         s = Source.new %(

src/ameba/rule/lint/useless_assign.cr

@@ -39,7 +39,11 @@ module Ameba::Rule::Lint
     def test(source, node, scope : AST::Scope)
       scope.variables.each do |var|
         next if var.ignored? || var.used_in_macro? || var.captured_by_block?
-        next if scope.assigns_type_dec?(var.name)
+
+        if scope.assigns_type_dec?(var.name) && var.assignments.empty?
+          issue_for var.node, MSG % var.name
+          return
+        end
 
         var.assignments.each do |assign|
           next if assign.referenced?