Struct setter's parameters == `[:req, :_]`

fix [Bug #18405]

Note that the parameter name `_` is not a spec, so we shouldn't
rely on this behavior.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/ruby/test_struct.rb b/test/ruby/test_struct.rb
index 0301612395..b0e6bae9e3 100644
--- a/test/ruby/test_struct.rb
+++ b/test/ruby/test_struct.rb
@@ -497,6 +497,21 @@ module TestStruct
     assert_equal(42, x.public_send("a"))
   end
 
+  def test_parameters
+    klass = @Struct.new(:a)
+    assert_equal [], klass.instance_method(:a).parameters
+    # NOTE: :_ may not be a spec.
+    assert_equal [[:req, :_]], klass.instance_method(:a=).parameters
+
+    klass.module_eval do
+      define_method(:b=, &klass.new.method(:a=).to_proc)
+      alias c= a=
+    end
+
+    assert_equal [[:req, :_]], klass.instance_method(:b=).parameters
+    assert_equal [[:req, :_]], klass.instance_method(:c=).parameters
+  end
+
   class TopStruct < Test::Unit::TestCase
     include TestStruct