Fix UnboundMethod#== for methods from included/extended modules

Method#unbind clones the method entry, preserving its defined_class.
For methods mixed in via include/extend, defined_class is an ICLASS,
causing UnboundMethod#== to return false when comparing against the
same method obtained via Module#instance_method.

Resolve ICLASS defined_class in method_eq.

Fixes [Bug #21873]

2 files changed, 16 insertions, 0 deletions

diff --git a/proc.c b/proc.c
index f0cdcae7b1..67963a1b01 100644
--- a/proc.c
+++ b/proc.c
@@ -2006,6 +2006,8 @@ method_eq(VALUE method, VALUE other)
 
     klass1 = method_entry_defined_class(m1->me);
     klass2 = method_entry_defined_class(m2->me);
+    if (RB_TYPE_P(klass1, T_ICLASS)) klass1 = RBASIC_CLASS(klass1);
+    if (RB_TYPE_P(klass2, T_ICLASS)) klass2 = RBASIC_CLASS(klass2);
 
     if (!rb_method_entry_eq(m1->me, m2->me) ||
         klass1 != klass2 ||
diff --git a/test/ruby/test_method.rb b/test/ruby/test_method.rb
index 8561f841a8..c3819cdebf 100644
--- a/test/ruby/test_method.rb
+++ b/test/ruby/test_method.rb
@@ -111,6 +111,20 @@ class TestMethod < Test::Unit::TestCase
     end
   end
 
+  def test_unbound_method_equality_with_extended_module
+    m = Module.new { def hello; "hello"; end }
+    base = Class.new { extend m }
+    sub = Class.new(base)
+
+    from_module = m.instance_method(:hello)
+    from_base   = base.method(:hello).unbind
+    from_sub    = sub.method(:hello).unbind
+
+    assert_equal(from_module, from_base)
+    assert_equal(from_module, from_sub)
+    assert_equal(from_base, from_sub)
+  end
+
   def test_callee
     assert_equal(:test_callee, __method__)
     assert_equal(:m, Class.new {def m; __method__; end}.new.m)