Enable warning support explicitly

Author: JonRowe

features/command_line/warnings_option.feature

@@ -15,6 +15,23 @@ Feature: `--warnings` option (run with warnings enabled)
     When I run `rspec --warnings example_spec.rb`
     Then the output should contain "warning"
 
+  @ruby-2-7
+  Scenario:
+    Given a file named "example_spec.rb" with:
+      """ruby
+      def foo(**kwargs)
+        kwargs
+      end
+
+      RSpec.describe do
+       it "should warn about keyword arguments with 'rspec -w'" do
+         expect(foo({a: 1})).to eq({a: 1})
+        end
+      end
+      """
+    When I run `rspec -w example_spec.rb`
+    Then the output should contain "warning"
+
   @unsupported-on-rbx
   Scenario:
     Given a file named "example_spec.rb" with:

lib/rspec/core/option_parser.rb

@@ -184,6 +184,9 @@ def parser(options)
         end
 
         parser.on('-w', '--warnings', 'Enable ruby warnings') do
+          if Object.const_defined?(:Warning) and Warning.respond_to?(:[]=)
+            Warning[:deprecated] = true
+          end
           $VERBOSE = true
         end