Do not report type declarations within lib definitions

spec/ameba/ast/scope_spec.cr

@@ -180,6 +180,28 @@ module Ameba::AST
     end
   end
 
+  describe "#def?" do
+    context "when check_outer_scopes: true" do
+      it "returns true if outer scope is Crystal::Def" do
+        nodes = as_nodes("def foo; 3.times {}; end")
+        outer_scope = Scope.new nodes.def_nodes.first
+        scope = Scope.new nodes.block_nodes.first, outer_scope
+        scope.def?(check_outer_scopes: true).should be_true
+      end
+    end
+
+    it "returns true if Crystal::Def" do
+      nodes = as_nodes("def foo; end")
+      scope = Scope.new nodes.def_nodes.first
+      scope.def?.should be_true
+    end
+
+    it "returns false otherwise" do
+      scope = Scope.new as_node("a = 1")
+      scope.def?.should be_false
+    end
+  end
+
   describe "#in_macro?" do
     it "returns true if Crystal::Macro" do
       nodes = as_nodes <<-CRYSTAL

spec/ameba/rule/lint/useless_assign_spec.cr

@@ -998,6 +998,16 @@ module Ameba::Rule::Lint
           CRYSTAL
       end
 
+      it "doesn't report if it's referenced in a lib" do
+        expect_no_issues subject, <<-CRYSTAL
+          lib LibFoo
+            struct Foo
+              a : Int32
+            end
+          end
+          CRYSTAL
+      end
+
       it "doesn't report if it's referenced" do
         expect_no_issues subject, <<-CRYSTAL
           def foo

src/ameba/ast/scope.cr

@@ -180,20 +180,15 @@ module Ameba::AST
       @visibility || outer_scope.try(&.visibility)
     end
 
-    # Returns `true` if current scope is a def, `false` otherwise.
-    def def?
-      node.is_a?(Crystal::Def)
-    end
-
-    # Returns `true` if current scope is a class, `false` otherwise.
-    def class_def?
-      node.is_a?(Crystal::ClassDef)
-    end
-
-    # Returns `true` if current scope is a module, `false` otherwise.
-    def module_def?
-      node.is_a?(Crystal::ModuleDef)
-    end
+    {% for type in %w[Def ClassDef ModuleDef EnumDef LibDef FunDef].map(&.id) %}
+      {% method_name = type.underscore %}
+      # Returns `true` if current scope is a {{ method_name[0..-5] }} def, `false` otherwise.
+      def {{ method_name }}?(*, check_outer_scopes = false)
+        node.is_a?(Crystal::{{ type }}) ||
+          !!(check_outer_scopes &&
+            outer_scope.try(&.{{ method_name }}?(check_outer_scopes: true)))
+      end
+    {% end %}
 
     # Returns `true` if this scope is a top level scope, `false` otherwise.
     def top_level?

src/ameba/rule/lint/useless_assign.cr

@@ -39,6 +39,8 @@ module Ameba::Rule::Lint
     end
 
     def test(source, node, scope : AST::Scope)
+      return if scope.lib_def?(check_outer_scopes: true)
+
       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)