Add `UselessAssign#exclude_type_declarations`

spec/ameba/rule/lint/useless_assign_spec.cr

@@ -3,6 +3,7 @@ require "../../../spec_helper"
 module Ameba::Rule::Lint
   describe UselessAssign do
     subject = UselessAssign.new
+      .tap(&.exclude_type_declarations = false)
 
     it "does not report used assignments" do
       expect_no_issues subject, <<-CRYSTAL
@@ -1007,6 +1008,27 @@ module Ameba::Rule::Lint
       end
     end
 
+    context "#properties" do
+      context "#exclude_type_declarations" do
+        it "doesn't report type declarations if enabled" do
+          rule = UselessAssign.new
+          rule.exclude_type_declarations = true
+
+          expect_no_issues rule, <<-CRYSTAL
+            a : String?
+
+            class Foo
+              b : String?
+            end
+
+            def foo
+              c : String?
+            end
+            CRYSTAL
+        end
+      end
+    end
+
     context "uninitialized" do
       it "reports if uninitialized assignment is not referenced at a top level" do
         expect_issue subject, <<-CRYSTAL

src/ameba/rule/lint/useless_assign.cr

@@ -24,10 +24,12 @@ module Ameba::Rule::Lint
   # ```
   # Lint/UselessAssign:
   #   Enabled: true
+  #   ExcludeTypeDeclarations: false
   # ```
   class UselessAssign < Base
     properties do
       description "Disallows useless variable assignments"
+      exclude_type_declarations false
     end
 
     MSG = "Useless assignment to variable `%s`"
@@ -39,6 +41,7 @@ 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 exclude_type_declarations? && scope.assigns_type_dec?(var.name)
 
         var.assignments.each do |assign|
           next if assign.referenced?