[Fix #11485] Fix a false positive for Lint/UselessAssignment

changelog/fix_a_false_positive_for_lint_useless_assignment.md

@@ -0,0 +1 @@
+* [#11485](https://github.com/rubocop/rubocop/issues/11485): Fix a false positive for `Lint/UselessAssignment` when using numbered block parameter. ([@koic][])

lib/rubocop/cop/variable_force/variable_table.rb

@@ -97,8 +97,10 @@ def find_variable(name)
           scope_stack.reverse_each do |scope|
             variable = scope.variables[name]
             return variable if variable
+
             # Only block scope allows referencing outer scope variables.
-            return nil unless scope.node.block_type?
+            node = scope.node
+            return nil unless node.block_type? || node.numblock_type?
           end
 
           nil

spec/rubocop/cop/lint/useless_assignment_spec.rb

@@ -1318,6 +1318,16 @@ def some_method(name: value, **)
     end
   end
 
+  context 'using numbered block parameter', :ruby27 do
+    it 'does not register an offense when the variable is used' do
+      expect_no_offenses(<<~RUBY)
+        var = 42
+
+        do_something { _1 == var }
+      RUBY
+    end
+  end
+
   # regression test, from problem in Locatable
   context 'when a variable is assigned in 2 identical if branches' do
     it "doesn't think 1 of the 2 assignments is useless" do